Broadview affected PSCAD Study - oatioasis.com · PNM / Broadview affected PSCAD Study iii E00017437A-R00 • For sensitivity studies with Blackwater online at 15 MW E-W, the following

Public Service of New Mexico Broadview Affected PSCAD Study

Final Report Report No.E00017437A-R00 12 December 2016

LEGAL NOTICE This document, prepared by ABB Inc, is an account of work sponsored by Public Service Company of New Mexico (PNM). Neither PNM nor ABB Inc. nor any person or persons acting on behalf of either party: (i) makes any warranty or representation, expressed or implied, with respect to the use of any information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights, or (ii) assumes any liabilities with respect to the use of or for damages resulting from the use of any information, apparatus, method, or process disclosed in this document. Prepared for: Public Service of New Mexico (PNM) Report No.: E00017437A-R00 Date: November 30, 2016 Revised: December 12, 2016

ABB Inc. Power Systems Division Grid Systems Consulting 901 Main Campus Drive, Suite 300 Raleigh, NC27606

Power Systems Consulting Technical Report

ABB Inc. 2016- E000174370A-1.0.R00

Public Service Company of New Mexico Broadview PSCAD Study

Dept.

Consulting Date

November 30, 2016

Pages 712

Executive Summary:

PNM requested consulting services from ABB to perform electromagnetic transient simulation studies in PSCAD to (1) evaluate whether there is sufficient synchronizing voltage strength (short-circuit capacity) for various combinations of power injections along the BA-Blackwater 345 kV line, (2) provide recommendations for coordinating the voltage control devices along the line and (3) if voltage performance or short circuit capacity is unacceptable, identify system improvements needed to accommodate the power injections that use the full 1000 MW capacity of the BA-Blackwater 345 kV line (full buildout scenario) as shown below.

PNM’s 216 mile 345 kV transmission line from BA 345 kV Station (north of Albuquerque) to PNM’s Blackwater 345 kV Station (in the Clovis-Portales area of eastern New Mexico), known as the “BB line” is located in proximity to areas of New Mexico with very large wind

Guadalupe 345 Taiban Mesa345 kV

Clines C

orners 345 kV

54 Miles

70 Miles

BA

345 kV

svc

Black W

ater 345 kV

Rio P

uerco 345 kV

To 115 kVSystem

To Four Corners

To San Juan

To West M

esa6 Miles

62 Miles

Blackwater Converter

Norton 345 kV bus

+250/-100 MVAR

31 Miles

Aragonne Mesa 90 MW

Tiaban Mesa 200 MW

20.38 miles

BA

2 345 kV B

us

34.5kV/345 kV transformer

El Cabo 34.5 kV Bus

El Cabo 345 kV Bus 2

Broadview 345 kV Bus

Broadview 297 MW El Cabo 213 MW

DSTATCOM

Aragonne 138 kV Bus 3

Aragonne 138/345 kV transformer

Aragonne 34.5kV/138 kV transformer

Aragonne 34.5 kV Bus 2


Grady 200 MW

33 Miles

ii

ABB Power Systems Consulting

PNM / Broadview affected PSCAD Study E00017437A-R00

generation potential.

A radial transmission line of this length will often have low short-circuit conditions that present challenges for control and operation of power electronic systems for the high-voltage direct current convertor and wind farms located at or near the Blackwater 345 kV station (Blackwater station). Previous studies [1-4] performed by ABB identified the need for a synchronous condenser at Blackwater station to maintain acceptable system performance due to the low short circuit MVA available at Blackwater station.

The goal of this study was to focus on (1) determining preliminary sizing requirements for the synchronous condenser and (2) establishing whether the short circuit MVA strength with the synchronous condenser is sufficient to achieve stable post-fault recoveries after disturbances on or near the BB line, including three-phase and single-phase faults, equipment trips, and single-phase trip and reclose (SPTR) sequences with the increased wind generation levels resulting in a total of 497 MW of wind generation being injected at Blackwater station and 213 MW of wind generation being injected at Clines Corners 345 kV station, for conditions with Blackwater HVDC converter offline. A limited sensitivity study with the Blackwater converter online at minimum power is included.

From the studies in this report, the following observations and conclusions are reached:

• A preliminary strategy (detailed in Section 7) for control of voltage along the BB line, with coordination of the various voltage controlling devices (Statcom, SVC, and windfarms) has been developed based on the PSLF study. The controls of the existing systems (Aragonne Mesa and Taiban Mesa windfarms) are left unchanged.

• Sustained oscillation in post-contingency recovery period can be observed along the entire BB line, in 11 out of 17 cases. The typical oscillation frequency varies from 1.8 to 1.9 Hz. These oscillations have been observed previously and are related to the Broadview wind farm. Per information from Siemens, the oscillations a known artifact of the aggregate modeling method, which tends to enhance drive train oscillations to a greater degree than would be expected in the actual system. The oscillations observed in this study are, however, more pronounced than in prior studies, and this should be reviewed by Siemens.

• The following strategies are needed to reduce the likelihood of El Cabo tripping on 1.2 pu overvoltage during post-fault recoveries:

• No capacitor banks connected at El Cabo; • Modified Undervoltage (UV) Strategy in Guadalupe SVC controls; • Blackwater Synchronous Condenser.

• Part of Broadview windfarm tripped in 6 out of 17 cases. Tripping of Broadview wind farm was however also noted as an issue in previous studies as reported in Reference [3].

• Part of the Taiban Mesa windfarm tripped in 3 out of 17 cases. This issue has also been observed in previous studies.


iii PNM / Broadview affected PSCAD Study E00017437A-R00

• For sensitivity studies with Blackwater online at 15 MW E-W, the following results are noted:

• For the full buildout case with Blackwater HVDC at 15 MW E-W and Broadview at 482 MW, the results are similar to the cases without Blackwater HVDC. One exception is in Case 6, where it was found that Broadview wind farm tripping did not occur but sustained drive train oscillations and repetitive commutation failures in the HVDC are observed.

• Drive train oscillations were reduced for conditions where El Cabo windfarm and Blackwater condenser were offline and the total power transfers are thus lower than in the full buildout case.

• For conditions with El Cabo and the condenser taken offline and Broadview power successively reduced, improvement is seen when the Broadview power is reduced to 172 MW. At this level, tripping of the Broadview wind farm is avoided in two of the three studied cases. Above this level, however, the Broadview wind farm trips during the simulations.

• For conditions with the full buildout and Blackwater HVDC online at 200 MW W-E, the low-order resonance frequency falls just below 3rd harmonic. This implies that as capacitance is removed from the system, for example by switching an ac filter off at Blackwater, the resonance frequency will shift up to 3rd harmonic. Resonance near 3rd harmonic can be problematic for an HVDC converter in rectifier operation.

Overall recommendations are listed below:

• Install a synchronous condenser at Blackwater 345 kV station that provides 830 MVA of short circuit capacity.

• To mitigate sustained low frequency (power swing frequency) oscillations during the post-contingency recovery period the following strategies should be investigated:

• adding oscillation damping capability to the Broadview wind turbine controls; • Implementing a power oscillation damping controller (POD) in the Guadalupe

SVC; • Implementing power oscillation damping or PSS control in the Blackwater

synchronous condenser.

Additional recommendations are listed below:

• The El Cabo windfarm model should be further revised to resolve issues with tripping during initialization and issues with snapshot functionality.

• Sensitivity to overvoltage tripping of El Cabo wind farm, due to El Cabo capacitor banks should be investigated. Tripping of El Cabo was minimized with no capacitor banks connected, but conditions with varying numbers of connected banks should be studied to quantify the sensitivity further.

• The undervoltage strategy in the Guadalupe SVC should be further reviewed during

iv



the SVC Dynamic Performance Study (DPS) to confirm acceptable dynamic performance.

• The fault ride-through capability of Broadview windfarm needs to be improved to achieve robust post-fault recovery for SPTR events. This was also noted in Reference [3].

• It should be confirmed that 3rd harmonic voltage distortion is within acceptable limits for the full buildout scenario with Blackwater in W-E operation. It should also be confirmed that ac filter stresses under such conditions are within the equipment ratings.

Rev # Revision Date Author Reviewed Approved DISTRIBUTION Public Service Company of New Mexico


v PNM / Broadview affected PSCAD Study E00017437A-R00

Contents 1 Introduction .......................................................................................................................... 8

2 Original PSCAD Model .......................................................................................................11

3 Modified full Buildout PSCAD Model ...................................................................................14

4 Broadview Windfarm Models ..............................................................................................16

4.1 WINDFARM MODEL .........................................................................................................16

4.2 PARALLEL SIMULATION ...................................................................................................17

5 El Cabo Windfarm Models ..................................................................................................18

5.1 WINDFARM MODEL .........................................................................................................18

5.2 PARALLEL SIMULATION ...................................................................................................19

5.3 RESOLUTION OF EL CABO WINDFARM MODEL ISSUES ......................................................19

5.4 MITIGATION OF EL CABO WINDFARM TRIPPING ................................................................20

6 Synchronous Condenser Sizing and Parameters................................................................23

6.1 CONDENSER SIZING REQUIREMENTS ..............................................................................23

6.2 EQUIVALENT SHORT CIRCUIT RATIO (ESCR) ...................................................................23

6.3 SHORT-CIRCUIT RATIO (SCR) ........................................................................................24

6.4 CONDITIONS CONSIDERED FOR CONDENSER SIZING ........................................................24

6.5 CALCULATED DRIVING-POINT IMPEDANCE .......................................................................25

6.6 ASSUMED MINIMUM SCR AND ESCR ..............................................................................26

6.7 CONDENSER SIZING CALCULATIONS................................................................................26

6.8 SYNCHRONOUS MACHINE PARAMETERS ..........................................................................30

6.8.1 GE 60 MVA Condenser .........................................................................................30

6.8.2 Siemens 200 MVA Condenser ...............................................................................30 7 Coordination of Voltage Controls ........................................................................................31

8 Dynamic Simulations and Analysis .....................................................................................36

8.1 DYNAMIC SIMULATION CASE LIST AND RESULTS ..............................................................36

8.2 DYNAMIC SIMULATION ANALYSIS .....................................................................................37

9 Maximum Dispatch with El Cabo Off-line ............................................................................38

9.1 DYNAMIC SIMULATION CASE LIST AND RESULTS ..............................................................38

9.2 DYNAMIC SIMULATION ANALYSIS .....................................................................................39

10 Blackwater Minimum Power Operation ...............................................................................41

11 Low-order Harmonic Resonance ........................................................................................45

6



12 Conclusions ........................................................................................................................47

13 References .........................................................................................................................50

Appendix A: Dynamic simulations for full buildout scenario Appendix B: Maximum Dispatch with 497 MW Broadview windfarm and El Cabo off-line Appendix C: Maximum Dispatch with 297 MW Broadview windfarm and El Cabo off-line Appendix D: Maximum Dispatch with 172 MW Broadview windfarm and El Cabo off-line Appendix E: Max Dispatch with 297 MW Broadview, one 60 MVA GE condenser, El Cabo off-line Appendix F: Max Dispatch with 297 MW Broadview, two 60 MVA condensers, El Cabo off-line Appendix G: Blackwater Minimum Power Operation


7 PNM / Broadview affected PSCAD Study E00017437A-R00

1 Introduction PNM has requested consulting services from ABB to perform electromagnetic transient simulation studies in PSCAD for a buildout scenario that uses the remaining capacity of the BA-Blackwater 345 kV line as per the full buildout scenario as shown in Figure 1-1. The goal of this study is to (1) evaluate whether there is sufficient synchronizing voltage strength (short-circuit capacity) for the existing and proposed windfarms to support the transmission service conditions listed below, (2) provide recommendations for coordinating the voltage control devices along the line and (3) if voltage performance or short circuit capacity is unacceptable, identify system improvements needed to accommodate the injections in the full buildout scenario.

Figure 1.1: Study Scenario Requested by PNM

PNM’s 216 mile 345 kV transmission line from BA 345 kV Station (north of Albuquerque) to PNM’s Blackwater 345 kV Station (in the Clovis-Portales area of eastern New Mexico), known as the “BB line” is located in proximity to areas of New Mexico with very large wind generation potential. Previous PSCAD studies [1] performed by ABB have indicated the need for a synchronous condenser at Blackwater station to maintain acceptable system performance due to the low short circuit levels available at the Blackwater station. These prior studies focused on scenarios involving up to 297 MW of wind generation at Blackwater 345 kV coordinated with up to 200 MW of east to west transfers through the Blackwater HVDC converter.

Guadalupe 345 Taiban Mesa345 kV

Clines C

orners 345 kV

54 Miles

70 Miles

BA

345 kV

svc

Black W

ater 345 kV

Rio P

uerco 345 kV

To 115 kVSystem

To Four Corners

To San Juan

To West M

esa

6 Miles

62 Miles

Blackwater Converter

Norton 345 kV bus

+250/-100 MVAR

31 Miles

Aragonne Mesa 90 MW

Tiaban Mesa 200 MW

20.38 miles

BA

2 345 kV B

us

34.5kV/345 kV transformer

El Cabo 34.5 kV Bus

El Cabo 345 kV Bus 2

Broadview 345 kV Bus

Broadview 297 MW El Cabo 213 MW

DSTATCOM


Aragonne 138/345 kV transformer

Aragonne 34.5kV/138 kV transformer

Aragonne 34.5 kV Bus 2


Grady 200 MW

33 Miles

8



A companion study has been performed that included PSLF steady-state and dynamic analysis of the full system buildout. The goal of the PSCAD study described in this report was to focus on establishing whether the short circuit capability is sufficient to achieve stable post-fault recoveries after disturbances on or near the BB line, including three-phase and single-phase faults, equipment trips, and single-phase trip and reclose (SPTR) sequences with the increased wind generation levels resulting in a total of 497 MW of wind generation being injected at Blackwater station and 213 MW of wind generation being injected at EI Cabo and with the Blackwater HVDC converter offline. A limited sensitivity study with the Blackwater converter online at minimum power is included. A summary of the power injections used for the main portion of the analysis is as follows:

• Broadview windfarm: 497 MW • Blackwater HVDC: off-line • Taiban Mesa: 200 MW • Aragonne Mesa: 90 MW • El Cabo: 213 MW

In this study, PNM requested ABB to perform the following:

1. Develop the preliminary main circuit parameters and control models, and preliminary tuning of the SVC model.

2. Modify the existing PSCAD model of the BB line, Blackwater HVDC converter, and Broadview windfarm.

3. Implement the El Cabo windfarm models. 4. Investigate the proper coordinated voltage controls along the BB line. 5. Perform dynamic studies in PSCAD to confirm adequate dynamic performance for fault

disturbance scenarios. 6. Investigate the maximum dispatch of Broadview with El Cabo off-line. 7. Perform a limited sensitivity study for the system condition shown in Figure 1-1, adding

the Blackwater HVDC converter at minimum transfer level of 15 MW east to west with Broadview generating 482 MW.

8. Investigate any potential low order harmonic resonance with the Blackwater HVDC converter operating at 200 MW west to east.

The studies requested by PNM have been performed by ABB and are described in this report, which is organized as follows. In Section 2, the original PSCAD model used as a starting point for the study is presented. Section 3 presents a preliminary model of the +250 MVAr (capacitive) to -100 MVAR (inductive) Guadalupe SVC. The incorporation of the Broadview and El carbo windfarms into the PSCAD model is described, with detailed parameters for the Siemens 2.3 MW Type 4 turbines used in the Broadview windfarm and Gamesa 2 MW Type 3 turbines used in El Cabo windfarm given in Sections 4 and Section 5, respectively. The synchronous condenser sizing and modeling aspects are described in Section 6. The overall



strategy developed for coordination of the various voltage controlling systems along the BB line is given in Section 7. The PSCAD dynamic simulation for the full buildout system, case lists, and results are given in Section 8. The investigation of the maximum dispatch of Broadview with El Cabo off-line is presented in Section 9, and conditions with Blackwater HVDC at minimum power are studied in Section 10. Low-order harmonic resonance conditions are evaluated in Section 11, and finally Conclusions from the study are given in Section 12.

10



2 Original PSCAD Model The PSCAD model in previous study that formed the basis for the studies described in this report is shown as Figure 2-1. The following PNM equipment is included in the model:

• B-A 345 kV (#10025) • B-A – Guadalupe 345 kV line • B-A 345/115 kV transformer (for application of faults at 115 kV) • Guadalupe 345 kV (#100116) • Shunt reactors at Guadalupe (44 and 65 Mvar) • Guadalupe – Taiban Mesa 345 kV line • Taiban Mesa 345 kV (#10999) • Taiban Mesa – Blackwater 345 kV line • Blackwater 345 kV (#13402)

The system west of B-A is represented as a simple Thevenin equivalent source at B-A. Weak and strong Thevenin equivalent sources are available. The weak Thevenin source represents conditions with one of the BA-Rio Puerco 345 kV lines out-of-service.

• Strong B-A Equivalent: o SCC (short circuit capacity) = 5422 MVA

• Z1 = 21.95 ohm, 83.37 deg • Z0 = 23.82 ohm, 78.59 deg

• Weak B-A Equivalent: o SCC = 3911 MVA

• Z1 = 30.43 ohm, 82.94 deg • Z0 = 30.79 ohm, 79.92 deg

The SPS ac system representation (eastern side of Blackwater HVDC 230 kV station) is a simple Thevenin equivalent source representing minimum short circuit conditions at the SPS 230 kV station as follows:

• SCC = 1900 MVA (minimum short circuit level) o Z1 = 27.84 ohm, 80.0 deg o Z0 = Z1

The values in the above system equivalents were established in consultation with PNM during PSCAD studies conducted in 2015. The PSCAD model is compatible with the following PSCAD version platform and compiler:

• PSCAD version 4.2.1 • Compaq Fortran 6.6



The PNM system model also includes black-box models of the Taiban Mesa, and Aragonne Mesa windfarms, and compatible with the above platform. The system model also includes components to represent single phase and 3 phase faults at various locations. A PSCAD model of the Guadalupe SVC was included, based on a similar model previously developed for the Rio Puerco SVC and with parameters modified for the Guadalupe installation. The Guadalupe SVC was first evaluated in studies described in Reference [1]. Previous PSCAD studies done by ABB as described in Reference [3] included a representation of the Broadview windfarm near Blackwater station. This windfarm is based on Siemens wind turbines, with the windfarm sized at 297 MW in the studies shown in [3]. The Broadview windfarm is represented using PSCAD 4.5, with an interface between the PSCAD 4.2.1 and PSCAD 4.5 platforms implemented using ETRAN Plus.

12



Figure 2.1: Original PSCAD Model (PNM System Shown)

BusNet1

60.0

PNM Equivalent sources:(more information inside)

4.85

7 [H

]

7.17

5 [H

]B

RK

_44

BR

K_6

5

V_10025V_10116V_10999V_13402

P = 557.9Q = -5.511V = 1.034

VA

P = 86.15Q = -3.313V = 1.021

VA

P = 614.1Q = -121.1V = 1.027

VA

Ph_10025Ph_10116Ph_10999Ph_13402

P = -546.7Q = 39.59

VA

P = 632.3Q = -36.97

VA

P = -366.5Q = -0.5565

VA

*

345.0

VP

h

345.

0 [k

V],

60.0

[Hz]

100.

0 [M

VA

]

P_10116LP_10116RP_10999LP_13402

P = -0.001786Q = -0.002178

VA

BRK_IS

N10999Taiban Mesa345 / 34.5 kV

system

P = 371.6Q = -20.01V = 1.042

VA

7.90

5 [H

]

4.82

8 [H

]

#1 #2

100.0 [MVA]115.0 [kV] / 345.0 [kV]

FLT_

L+

FLT_

R+

[Fault_Logic] FLT_loc8

FLT_

L+

FLT_

R+


FLT_

L+

FLT_

R+


FLT_

L+

FLT_

R+


FLT_type

FLT_type FLT_type

FLT_type

BRK_TM1

PNM SystemNew Mexico

AC_volt_TM

Ph_ang_TM

44 MVAr

1e6

[ohm

]

FLT_L +

FLT_R +


FLT_typeFLT_L +

FLT_R +


FLT_type

FLT_L +

FLT_R +


FLT_type

FLT_L +

FLT_R +


FLT_type

EQ_S

EQ_W

UAC_PNM

PH_PNM

FREQ_PNM

FREQ_PNMPH_PNMUAC_PNM

FREQ_PNMPH_PNMUAC_PNM

EQ_WEQ_S

PNM_EQ

0.01 [ohm]0.01 [ohm]

0.01 [ohm] 0.01 [ohm] 0.01 [ohm] 0.01 [ohm]

0.01 [ohm]

Uac_10025

GUAD_TMT

TM_BLWT

BA_GUADT

TM_345kV_P

TM_345kV_Q

P = 191.4Q = -6.07V = 1.032

VA

TM_345kV_abc

Aragonne Mesa345 / 138 / 34.5 kV

system

N10116

BA_10025

Guadalupe_10116

TaibanMesa_10999

Blackw ater_13402

N10116_PN10116_Q

P_AMQ_AM

V_10116

BRK_AM

Vabc_134021

RMS

BV_345kV_P

BV_345kV_Q

V = 1.022

VA

Uac_BA_115kVV_BA_115kV

65 MVAr

Uac_N10116

BV_345kV_abcBV_345kV_Vrms

Sync CondenserBRK_BW_Conds

P = 0Q = 0

VA

RL

V F Ph

RL

RL

V F Ph

RL

P_10025

Broadview345 kV

Wind Farm

N13402BV

BRK_BV_WF

P = 297Q = 1.302V = 1.042

VA

BV_345kV_PBV_345kV_Q

SVC_BRK

P = -0.248Q = -0.0005625

V = 1.021

VA

N10116 Guadalupe SVCSVC_BRK

5.951 [MVAR]-0.2479 [MW]

Iac_10025

*

345.0

VP

h

345.

0 [k

V],

60.0

[Hz]

100.

0 [M

VA

]

P = 0.0002109Q = -0.008161

VA

BRK_IS

AC_volt_BV

Ph_ang_BV

PNM AC ControlsPNM_EQ

0

EQ_S EQ_W

400

300

AC_volt_S1

359.5

kV

40

-40

Ph_ang_S1

15.5

deg



3 Modified full Buildout PSCAD Model The PSCAD model described in Section 2 was modified for this study as follows:

• The strong network equivalent at B-A was used. • Zero sequence susceptance on the BB line from BA 345 to Blackwater station was

updated. • El Cabo bus was created, and the BA- Guadalupe line was split into BA-El Cabo and El

Cabo – Guadalupe 345 kV lines. • The provided El Cabo windfarm model (298 MW) was downscaled to 213 MW, and the

collection system impedance was updated. • A preliminary Guadalupe SVC model was developed and connected to the Guadalupe

345 kV bus. • An additional 200 MW portion (Grady) of the Broadview windfarm is modeled which

increased the total Broadview wind generation from 297 MW (currently) to 497 MW represented as 100% Type 4, Siemens wind turbines. The parameters of the aggregated turbine model, the Turbine step-up transformer, collector system, shunt compensation, and windfarm step-up transformer were provided by PNM as described in the companion PSLF study [2]. A post-project one-line is shown as Figure 3-1.

Figure 3.1: Post-project generation connection at Blackwater 345 kV station

14



Table 3-1 provides the BB line impedance settings from BA 345 station to the Broadview POI 345 station.

Table 3-1: BB Line Impedance Settings in PSCAD

BA_El 60 mi

El_GUAD 30.1 mi

GUAD_TM 70.7 mi

TM_BLW 62.0 mi

BLW_BVS 0.001 km

BVS_BEJN 0.001 km

BVS_GR 0.001 km

R1 [pu/mile] 4.9834e-5 4.9834e-5 4.9078e-5 5.0645e-5 R1 [pu/m]

0.001422273 0.000267582 0.000380

X1[pu/mile] 4.8394e-4 4.8394e-4 4.7617e-4 4.9081e-4 X1[pu/m] 0.016505020 0.002631430 0.003527

B1[pu/mile] 8.7705e-3 8.7705e-3 8.6326e-3 8.8990e-3 B1[pu/m] 0.285590966 0.044819221 0.064800

R0[pu/mile] 4.2857e-4 4.2857e-4 4.2837e-4 4.3065e-4 R0 [pu/m]

0.012730183 0.002056694 0.0019

X0[pu/mile] 1.7907e-3 1.7907e-3 1.7872e-3 1.7903e-3 X0[pu/m] 0.043852468 0.006958294 0.010364

B0[pu/mile] 5.2923e-3 5.2923e-3 5.2091e-3 5.3699e-3 B0[pu/m] 0.165855386 0.026117656 0.0648

Setup of the Broadview windfarm for the full 497 MW buildout is described in Section 4. For the El Cabo wind farm, a Gamesa Type 3 wind turbine model was developed in PSCAD Version 4.5 using the Intel Fortran compiler was provided by DNV-GL PWR Solutions as input for this study. Setup of this model is described in Section 5.



4 Broadview Windfarm Models

4.1 Windfarm Model The Siemens Type 4 2.3 MVA wind turbine model provided for the studies was represented using PSCAD 4.5. The Siemens Variable Speed Wind Turbine (VSWT) model can be used either as a single wind turbine or as an aggregated setup where one wind turbine model represents many wind turbines lumped together. Previous PSCAD studies done by ABB included a representation of the Broadview windfarm at Blackwater station based on Rev 2 of the Siemens wind turbine model, with the windfarm sized as 297 MW. In this study, an additional 200 MW portion (Grady) of the Broadview windfarm consists of two sub-farms is implemented using the same Siemens VSWT, with settings in Table 4-1:

Table 4-1: Siemens 2.3 [MVA] wind turbine global variable values set [4]

Variables Values Comments

Sys S Base 2.3 [MVA] Wind turbine base power Rotor Length 82/93/101/108 [m] Rotor blade length Frequency 60 [Hz] System frequency Voltage MV 34.5 [kV] MV side voltage Voltage LV 0.69 [kV] LV side voltage Tx S Base 2.6 [MVA] Turbine Transformer MVA base

The new 200 MW portion of the Grady (Broadview) windfarm is modeled in a similar manner to the existing 297 MW portion, with detailed parameters shown below in Table 4-2. The windfarm collector system impedance and the windfarm transformer information are shown in Table 4-3 and Table 4-4, respectively.

Table 4-2. Broadview Windfarm Setup

Block Name # Turbines Rated Output [MW] Comments

BVGW1 44 101.2 44 turbines online to have the proposed BVGW1 100MW rating.

BVGW2 44 101.2 44 turbines online to have the proposed BVWG2 100MW rating.

16



Table 4-3: Broadview Windfarm GSU Transformers

Xfmr Name

Base MVA

Winding Voltage Vllrms [kV]

X1[%] Winding Type Saturation Saturation Winding

Saturation Knee voltage [pu]

Air Core Reactance [pu]

Magnetizing Current [%]

BVGW1 GSU

2.6 34.5/0.69 0.059[1] Delta/Y, Delta Lags Y

#1 1.225 0.12 0.462963

BVGW2 GSU

2.6 34.5/0.69 0.059 Delta/Y, Delta Lags Y

#1 1.225 0.12 0.462963

[1] Default value 0.06 pu shared by the parallel scaling transformer and the GSU.

Table 4-4: Broadview Windfarm Collector System Impedance

Block, |#wtgs Positive Sequence Zero Sequence

R1 (pu)

X1 (pu)

B1 (pu)

R0 (pu)

X0 (pu)

B0 (pu)

BVGW1, 44 0.008536 0.008759 0.055828 0.00256 0.0263 0.0279 BVGW2, 44 0.01314 0.01595 0.07558 0.0235 0.0230 0.0247

Note: Calculated with WECC Impedance Calculation Method

4.2 Parallel Simulation The ETRAN Plus parallel scaling transformer model can be used to connect electrical circuits built in different PSCAD versions. This approach was used in the previous studies described in [3], and the same approach was used in this study to interface the Grady portion of Broadview windfarm model with the original system.



5 El Cabo Windfarm Models

5.1 Windfarm Model The provided El Cabo windfarm model (298 MW) developed by Gamesa and DNV-GL PWR Solutions was based on the Gamesa G114 Type 3 2.0 MVA wind turbine and was downscaled to 213 MW from this study, with collection system impedance updated. A brief overview of the turbine model is as shown in Table 5-1:

Table 5-1: Gamesa G114 Type 3 2.0 [MVA] wind turbine global variable values [4]

Variables Values Comments

Sys S Base 2.0 [MVA] Wind turbine base power Rated Wind Speed 12 [m/s] Wind Speed Frequency 60 [Hz] System frequency Voltage MV 34.5 [kV] MV side voltage Voltage LV 0.69 [kV] LV side voltage

The El Cabo windfarm was modeled with two station transformers. An aggregated representation of the turbines, equivalent collection circuits and reactive compensation equipment was modeled behind each station transformer. The detailed parameters of the collection system and the station transformers were obtained from the companion PSLF study and are as shown in Table 5-2 and Table 5-3, respectively.

Table 5-2. El Cabo Windfarm Station Transformers PSCAD Model [5]

Xfmr Name

Base MVA

Winding Voltage Vllrms [kV]

X1 [%]

Winding Type

Saturation Saturation Winding

Saturation Knee [pu]

Air Core React. [pu]

Magnetizing Current [%]

Station 1 100 345/34.5 0.095 Y/Y #1 1.17 0.2 2 Station 2 100 345/34.5 0.095 Y/Y #1 1.17 0.2 2

Table 5-3: El Cabo Windfarm Collector System Impedance

Block Positive Sequence Zero Sequence

R1 (pu)

X1 (pu)

B1 (pu)

R0 (pu)

X0 (pu)

B0 (pu)

Collector 1 0.01078 0.06795 0.03693 0.079824 0.221377 0.03560 Collector 2 0.01073 0.06548 0.03428 0.079824 0.221377 0.03560 Gen-Tie 0.00101 0.01434 0.25784 0.017694 0.054472 0.1882

18



5.2 Parallel Simulation The El Cabo windfarm model was developed in PSAD/EMTDC Version 4.5 using the Intel Visual Fortran compiler. Using methods similar to those described for Broadview (Section 4.2), the ETRAN Plus parallel scaling transformer model was used to interface El Cabo windfarm model with the original system.

5.3 Resolution of El Cabo Windfarm Model Issues A number of issues were found with the El Cabo wind farm models that required investigation by DNV-GL PWR Solutions and Gamesa before studies of configurations could be undertaken: Model issues:

1. Premature termination of simulations before completion 2. Issues related to Intel compiler version 3. Issue with wind turbines tripping when capacitor banks were disconnected 4. Numerical solution difficulties (divergence) during simulations; sensitivity to weak

conditions 5. Model crashes when attempting to start from a snapshot 6. Inability to run cases in sequence using PSCAD multi-run feature 7. Wind farm tripping on overvoltage tripping during model initialization

System Issue: 8. Wind turbine tripping on overvoltage at fault clearing

Model Issues 1-4 were resolved after extensive model revisions by Gamesa and DNV-GL and testing by ABB in the PNM system. Issue 5 however, was not resolved and required all simulations to be run using flat start (zero network voltage conditions) and rampup, with steady state reached after approximately 20 seconds of simulation time after which the disturbance case could be applied. Issue 6 also required manual launching of individual cases. Taken together, issues 5 and 6 severely limited case production and extended the time required to run cases. Regarding Issue 7 above, the version of El Cabo windfarm model used for the final simulations in this study (Rev.03, dated 10-25-2016) has a known issue related to initialization during the early stage of the PSCAD simulation. If there’s no capacitor bank connected at El Cabo and the WTG protection system setting is enabled in the model parameter section, the initialization will fail. Further to Issue 7, according to the model description from Gamesa, the protection alarm signals from the WTG controller are always valid even if the WTG protection system setting is disabled in the model parameter section. To resolve this ABB used a workaround in this study which disables the protection system setting in the model parameter section and utilizes the



WTG protection alarm signals to directly control an external breaker for tripping WTG if overvoltage does occur. Issue 8 above is a system issue brought about by the weak network conditions on the BB line in combination with various capacitive impedances in the system (BB line charging, shunt capacitor banks, and SVC). This issue required extensive investigation to develop possible mitigation strategies as described in the following section.

5.4 Mitigation of El Cabo Windfarm Tripping Following resolution of the model issues described above to obtain a working El Cabo model, subsequent tests of the El Cabo windfarm model under dynamic disturbance conditions (faults and fault clearing) showed that the El Cabo windfarm would trip following a large number of contingencies. Investigations by ABB and Gamesa revealed the reason of tripping was because the phase-to-ground or phase-to-phase RMS voltages at the 690 V wind turbine bus were higher than the maximum limit of 1.2 pu in the post-contingency period. A maximum overvoltage limit of 1.2 pu is enforced by Gamesa in the model as a “hard limit” due to uncertainties regarding overvoltage capabilities of the wind turbine equipment. Since the short-circuit strength along the BB line is relatively weak, the system is prone to overvoltage of more than 1.2 pu if no mitigating actions are taken. ABB has developed and tested the following strategies, working together, to minimize the probability of tripping the El Cabo windfarm:

1. Revised Undervoltage (UV) Strategy for Guadalupe SVC 2. Installation of a Synchronous Condenser at Blackwater 3. Disconnection of capacitor banks at El Cabo

The purpose of the revised UV strategy is to respond to single line-to-ground (SLG) faults by blocking the SVC’s TSC and freezing the voltage regulator when the single-line-to-ground (SLG) fault is not yet fully cleared, in order to minimize the overvoltage that would otherwise occur at fault clearing. The revised UV strategy measures the negative sequence voltage at the Guadalupe 345-kV bus and blocks the SVC outputs (sets the susceptance reference Bref=0) if the negative sequence voltage is higher than 10%. When negative sequence voltage goes back below 10%, a 50-ms delay is assumed before SVC output is re-enabled. This will ensure the SVC output is low during the SLG fault and during the subsequent Single-Phase-Trip-and-Reclose (SPTR) sequence, with the SVC being restored to normal operation only after the SPTR sequence is fully completed. Note that the threshold for negative sequence voltage and time delay for restoring SVC output are preliminary and the values will need to be confirmed by ABB FACTS product group during the detailed DPS study for the Guadalupe SVC.

20



The installation of a synchronous condenser at Blackwater will increase the short-circuit strength along the BB line, which will also help to minimize the overvoltage at fault clearing. The details of the synchronous condenser are described in Section 6. One of the critical cases studied to develop the above strategy was Case #7 (1PhG, 100 ms at EI Cabo, SPTR on the line EI Cabo – BA). It was found that that synchronous condenser and modified UV strategies were needed in order to reduce the overvoltage and prevent El Cabo windfarm from tripping. It was also found that all capacitor banks at El Cabo needed to be disconnected to minimize the overvoltage. The power factor at the El Cabo POI was found to be 0.98 pu when the capacitor banks were disconnected, but PNM will need to review this finding with Avangrid. Figure 5-1 shows a comparison of voltage waveforms with various strategies. No capacitor banks were connected at the El Cabo windfarm in all waveform sets.

• Waveform Set 1: No mitigation strategies (no condenser or modified UV strategy) • Waveform Set 2: Modified UV Strategy at Guadalupe SVC only (no condenser) • Waveform Set 3: Synchronous Condenser at Blackwater only (no UV strategy) • Waveform Set 4: Modified UV Strategy at Guadalupe SVC and 200 MVA Synchronous

Condenser at Blackwater Tripping of the El Cabo windfarm is only avoided in Waveform Set 4 (the overvoltage protection signal “E-Vnet” remained inactive throughout the simulation for Waveform Set 4). Note that connection of capacitor bank(s) at El Cabo would result in tripping of the wind farm. In other words, all three strategies (synchronous condenser, modified UV strategies, and disconnection of capacitor banks) are needed to minimize the likelihood of El Cabo wind farm tripping. PNM and Avangrid may wish to investigate this further in future studies.



Figure 5.1: Comparison of Phase RMS Voltages at 690-V Wind Turbine Bus with Various Overvoltage

Mitigation Strategies

22



6 Synchronous Condenser Sizing and Parameters

6.1 Condenser Sizing Requirements Because of the interconnection to a very long radial 345 kV line, the short circuit conditions at Blackwater and Broadview are quite low. Low short circuit conditions present challenges for control and operation of power electronic systems such as those used in HVDC and wind turbines. At the time that the studies described in this report were undertaken, the need for a synchronous condenser had not been established, and estimates of appropriate synchronous condenser sizes were not available. The main uncertainty was with the minimum short circuit ratio (SCR) requirements for the wind turbines at Broadview, which were determined by Siemens in separate studies conducted in parallel with the studies described in this report. PNM also requested ABB to perform additional calculations of the anticipated short circuit levels and to develop a simplified method to determine preliminary sizing requirements for synchronous condensers. PNM further requested that the condensers be located at the Blackwater 345 kV station, and sized with consideration given to meeting minimum effective short circuit requirements (ESCR) for the Blackwater HVDC and the minimum SCR of the Broadview wind turbines.

6.2 Equivalent Short Circuit Ratio (ESCR)

The most fundamental consideration for design of conventional (line commutated) HVDC system is the short circuit level at the commutating bus. The minimum short circuit level drives a number of key considerations during the HVDC design process, including:

• AC voltage regulation and voltage stability • Voltage change on switching of reactive banks • Low-order ac harmonic resonance • AC filter design (performance, ratings) • Dynamic Overvoltage (DOV), Transient Overvoltage (TOV)

Line-commutated converters of the type used in conventional HVDC consume significant amounts of reactive power in the conversion process. For this reason, large shunt capacitor and ac filter banks are needed on the ac bus at the converter. The presence of large ac filter and shunt capacitor banks at the HVDC commutating bus has the effect of increasing the driving point impedance of the ac network at the fundamental frequency (i.e. 60 Hz). This effect is captured in a quantity called the Effective Short Circuit Ratio (ESCR) as follows:

HVDC

bankscapSC

MWMVARMVA

ESCR−

=



Higher ESCR values imply a strong ac network connection, giving good ac voltage regulation at the converter bus and good controllability of the converters. A conventional HVDC system is generally considered to have a high ESCR if the ESCR value is 3 or higher. ESCR of 2 to 3 is considered low, and ESCR less than 2 is considered very low. Generally, ESCR values less than 2 are considered marginal and possibly inadvisable for conventional HVDC.

6.3 Short-Circuit Ratio (SCR)

For applications involving power converters without large shunt capacitor banks nearby, a simplified expression, Short Circuit Ratio (SCR), is often used:

HVDC

SC

MWMVASCR =

Use of SCR rather than ESCR carries with it an assumption that the electrical network is primarily inductive throughout the lower harmonic frequency range; i.e. that the effects of shunt admittance from ac lines and shunt capacitor banks are relatively minor and can be neglected. This is generally true for lower voltage networks and networks that are relatively strong as compared to the rating of the power converters. In the present study, however, the conditions are very weak, dominated by a long radial 345 kV line. The effects of shunt admittance (line charging and SVC capacitance, in this case) should therefore be considered in the calculations. This has been done in the calculations presented later.

6.4 Conditions Considered for Condenser Sizing The PSCAD model as described earlier in Section 3 was the basis for the calculations. The conditions studied included the following:

• B-A: Strong and weak conditions as given in Section 3 • Guadalupe SVC: on (maximum capacitive output) and off • Taiban Mesa and Aragonne Mesa wind farms: disconnected

Conditions with the Guadalupe SVC “on” and “off” are included in order to evaluate the effect the SVC has on 60 Hz driving-point impedance as viewed from Broadview and Blackwater. Since the SVC has a capacitive shunt admittance, its effect at 60 Hz is to increase the 60 Hz impedance as compared to conditions with the SVC off.

From the point of view of short circuit levels, neglecting the contribution of induction wind turbines at Taiban Mesa and Aragonne Mesa is a conservative assumption. Wind turbines based on induction machine technology (singly-fed or doubly-fed) contribute a relatively low level of short circuit current at inception of an ac fault. However, this effect is brief and only lasts until the internal flux within the machine dies away. At fault clearing, the machine absorbs vars, since its rotor speed will have increased during the fault due to mechanical power from the turbine.

24



Since the contribution of induction-type wind turbines to short circuit levels is relatively minor, this effect is neglected in the simplified calculations. This also covers the possibility that the Taiban Mesa and/or Aragonne Mesa wind farms could be out of service at times.

6.5 Calculated Driving-Point Impedance The MVAsc values and corresponding driving-point impedance at Broadview and Blackwater 345 kV buses as calculated in PSCAD are given in Table 6-1 below. The conditions set up in PSCAD were:

• No synchronous condensers • No HVDC • Taiban Mesa and Argonne Mesa offline • Weak and strong conditions at B-A • Guadalupe SVC: on and off

Table 6-1. Driving point impedance and System Strength (MVAsc) without Condensers

System Conditions At Broadview

345 kV Bus At Blackwater 345 kV Bus

Guad SVC Off

Strong B-A 195.8 /83.2° Ω 176.1 /83.0° Ω

608.9 MVAsc 675.9 MVAsc Weak B-A 208.5 /82.9° Ω 188.8 /82.7° Ω

570.9 MVAsc 630.5 MVAsc Guad SVC On

Strong B-A 216.8 /82.2 ° Ω 197.1 /81.9° Ω

548.9 MVAsc 603.7 MVAsc Weak B-A 236.2 /81.7 ° Ω 216.5 /81.4° Ω

503.9 MVAsc 549.6 MVAsc The Broadview values above are based on 60 Hz impedance scans in PSCAD, which focused only on the conditions at Broadview 345 kV. The Blackwater values are derived from the Broadview values by backing out the series impedance of the Broadview-Blackwater 345 kV line. This gives a reasonable first approximation without running additional scans at Blackwater 345 kV.



6.6 Assumed Minimum SCR and ESCR Siemens initially provided a minimum SCR requirement of 1.75 for the Type 4 wind turbines to be installed at Broadview, and indicated that this value is expressed at the Broadview 345 kV bus. Neglecting the requirements of Blackwater HVDC and considering Broadview alone, this value translates to minimum short circuit levels at Broadview 345 kV bus of 520 MVA for the initial 297 MW phase of the project, increasing to 870 MVA for the final 497 MW buildout of the project. Later calculations by Siemens indicated that a minimum SCR requirement of 1.6 is applicable for the initial 297 MW portion of the project. Siemens has indicated that preliminary studies of the full buildout to 497 MW, without consideration of the Guadalupe SVC, indicated a minimum SCR requirement of 1.75. Blackwater HVDC also has minimum short circuit level requirements. The 1980s IEEE panel session paper describing Blackwater commissioning, Reference [9], states that the original design condition for Blackwater was with ESCR=2.1; SCR = 2.6. Allowing for 100 MVAR of ac filters, this means that the lowest short circuit level considered during the original design was 520 MVAsc. The following values thus form the basis for the condenser sizing calculations: Broadview: SCRmin = 1.6 to 1.75 at Broadview 345 kV (both values checked) Blackwater: ESCRmin = 2.1 at Blackwater 345 kV

6.7 Condenser Sizing Calculations With the above assumptions and data as background, the required short circuit MVA at Blackwater 345 kV is calculated by the following expression:

bankscapBWBWBVBWSCBVBVBWSC MVARPESCRMVAPSCRMVA +⋅+∆+⋅= −,,

Where

SCRBV is the minimum SCR at Broadview (=1.6 to 1.75) PBV is the wind generation power level at Broadview ΔMVASC, BW-BV is the reduction in short circuit MVA at Broadview as compared to Blackwater ESCRBW is the minimum ESCR at Blackwater (=2.1) PBW is the HVDC power level at Blackwater MVARcap banks is the amount of ac filtering connected at Blackwater

26



From the above expression, the resulting short circuit MVA at Broadview 345 kV is calculated directly as follows:

BVBWSCBWSCBVSC MVAMVAMVA −∆−= ,,,

The value ΔMVASC, BW-BV is an approximation of the difference between short circuit levels at Blackwater versus Broadview. This value depends somewhat on the system conditions, but from Table 6-1 it is observed that, for decisive conditions with weak system strength at B-A, the difference is approximately 60 MVA. In order to simplify the calculations, the value 60 MVA is adopted as the difference, but the value is parameterized in the calculations so that it can be varied if needed. With the value of MVAsc required by Broadview and Blackwater in hand, the MVAsc to be added at Blackwater 345 kV by condensers is then calculated by comparing the required MVAsc to the value calculated in PSCAD as given earlier in Table 6-1. From Table 6-1, it can be seen that the minimum effective MVAsc at Blackwater varies with conditions. The values with minimum short circuit levels at B-A, and with Guadalupe SVC on and off, are used in the calculations. Again, the values are parameterized so that variations can be studied if needed. Finally, the required MVA of condensers is calculated directly from the required additional MVAsc, with consideration of assumed subtransient reactance Xd” of the condenser and assumed leakage reactance Xl of the condenser step-up transformer. The results for a range of studied case conditions as requested by PNM are given in Table 6-2 (for minimum Broadview SCR requirement of 1.75) and Table 6-3 (for minimum Broadview SCR of 1.6). The calculations allowed for the possibility of investigating different MVA ratings of available condensers. In the tables, the condenser rating is set to 1 MVA in order to calculate the total MVA of condensers required. However, it is also possible to set the rating to values representative of available units. For example, setting the condenser rating to 60 MVA will result in a calculation of the minimum number of 60 MVA units that satisfy the minimum SCR and ESCR requirements. The “roundup” function in Excel was used for this. The results in Table 6-2 and Table 6-3 point to a need for a condenser in the 200-225 MVA range for conditions with Broadview Wind at 497 MW. Conditions with 297 MW at Broadview are marginal but indicate that operation at this power level may be possible without a condenser for the more relaxed SCR requirement of 1.6 for the Broadview wind turbines. Note however that all results in the tables need to be confirmed by PSCAD studies.

Table 6-2. Condenser Sizing Calculation Results (Broadview SCRmin=1.75)



Table 6-3. Condenser Sizing Calculation Results (Broadview SCRmin = 1.6)

Tabl

e 6-

2. C

onde

nser

Siz

ing

Calc

ulat

ion

Resu

lts (B

road

view

SCR

min

=1.7

5)

Win

d re

quire

men

tSC

R1.

75Bl

ackw

ater

filte

rs a

t min

pow

er53

HVDC

requ

irem

ent

ESCR

2.1

Blac

kwat

er fi

lters

at r

ated

pow

er10

6Sy

nchr

onou

s con

dens

er ra

ting

and

base

MVA

1M

in E

ffec

tive

Stre

ngth

at B

W w

ith G

uad

SVC

on55

0Sy

nchr

onou

s con

dens

er X

d", p

u on

mac

hine

bas

e M

VA0.

14M

in E

ffec

tive

Stre

ngth

at B

W w

ith G

uad

SVC

off

631

GSU

leak

age

reac

tanc

e ex

pres

sed

on m

achi

ne b

ase

MVA

0.10

MVA

sc d

iffer

ence

Bla

ckw

ater

ver

sus B

road

view

60

Stud

y Ca

ses

Case

1Ca

se 2

Case

3Ca

se 4

Case

5a

Case

5b

Case

6a

Case

6b

Case

7Ca

se 8

Broa

dvie

wM

W49

748

229

749

727

832

623

128

049

749

7HV

DC

MW

015

200

200

150

150

1520

0Gu

ad S

VCO

n/O

ffO

nO

nO

nO

nO

ffO

ffO

nO

nO

nO

n

Requ

ired

MVA

sc a

t Bla

ckw

ater

930

988

1106

1456

631

631

549

550

1014

1456

Resu

lting

MVA

sc a

t Bro

advi

ew87

092

810

4613

9657

157

148

949

095

413

96Ad

ditio

nal M

VAsc

nee

ded

at B

W38

043

855

690

60

-1-1

046

490

6N

umbe

r of c

onde

nser

s nee

ded,

at m

achi

ne ra

tings

abo

ve92

106

134

218

0-1

-10

112

218

Tota

l MVA

of n

eede

d co

nden

sers

at m

achi

ne ra

tings

abo

ve92

106

134

218

0-1

-10

112

218

28



Tabl

e 6-

3. C

onde

nser

Siz

ing

Calc

ulat

ion

Resu

lts (B

road

view

SCR

min

= 1

.6)

Win

d re

quire

men

tSC

R1.

6Bl

ackw

ater

filte

rs a

t min

pow

er53

HVDC

requ

irem

ent

ESCR

2.1

Blac

kwat

er fi

lters

at r

ated

pow

er10

6Sy

nchr

onou

s con

dens

er ra

ting

and

base

MVA

1M

in E

ffec

tive

Stre

ngth

at B

W w

ith G

uad

SVC

on55

0Sy

nchr

onou

s con

dens

er X

d", p

u on

mac

hine

bas

e M

VA0.

14M

in E

ffec

tive

Stre

ngth

at B

W w

ith G

uad

SVC

off

631

GSU

leak

age

reac

tanc

e ex

pres

sed

on m

achi

ne b

ase

MVA

0.10

MVA

sc d

iffer

ence

Bla

ckw

ater

ver

sus B

road

view

60

Stud

y Ca

ses

Case

1Ca

se 2

Case

3Ca

se 4

Case

5a

Case

5b

Case

6a

Case

6b

Case

7Ca

se 8

Broa

dvie

wM

W49

748

229

749

730

435

725

330

649

749

7HV

DC

MW

015

200

200

150

150

1520

0Gu

ad S

VCO

n/O

ffO

nO

nO

nO

nO

ffO

ffO

nO

nO

nO

n

Requ

ired

MVA

sc a

t Bla

ckw

ater

855

916

1061

1381

631

631

549

550

940

1381

Resu

lting

MVA

sc a

t Bro

advi

ew79

585

610

0113

2157

157

148

949

088

013

21Ad

ditio

nal M

VAsc

nee

ded

at B

W30

536

651

183

10

0-1

039

083

1N

umbe

r of c

onde

nser

s nee

ded,

at m

achi

ne ra

tings

abo

ve74

8812

320

00

0-1

094

200

Tota

l MVA

of n

eede

d co

nden

sers

at m

achi

ne ra

tings

abo

ve74

8812

320

00

0-1

094

200



Note that the calculations shown in Table 6-2 and Table 6-3 take into account SCR and ESCR requirements only, and this needs to be kept in mind when interpreting the results. For example, the SCR and ESCR calculations are not influenced by power direction, but there is a clear difference in loading of the BB line for Blackwater E-W operation versus W-E operation. This difference does not (and cannot) show up in the SCR and ESCR calculations. As confirmation of the results, Blackwater E-W and W-E conditions should therefore be studied separately in PSLF and PSCAD, as should all envisioned scenarios in Table 6-2 and Table 6-3 that have not been covered in the PSLF and PSCAD studies.

6.8 Synchronous Machine Parameters As mentioned earlier, the PSCAD studies described in this report were underway before the Broadview wind turbine SCR requirements were provided by Siemens. This means that the calculations above were not available during initial studies. For the initial PSCAD studies, synchronous condenser sizes in the 60 MVA range were tested using parameters established in prior studies as described in Reference [1]. After information on SCR requirements for the Broadview wind turbines were received later from Siemens, the condenser sizing calculations above were performed, resulting in an increase in the condenser size based on the more fully established requirements. The two condenser types tested in the PSCAD simulations are described in the following sections. 6.8.1 GE 60 MVA Condenser The parameters used for modeling of the GE 60 MVA condenser in PSCAD were supplied by PNM prior to start of the study. 6.8.2 Siemens 200 MVA Condenser The parameters of the Siemens 200 MVA synchronous condenser were provided by Siemens during the studies.

30



7 Coordination of Voltage Controls

For the 1000 MW buildout, a number of devices on the BB line will be tasked with control of voltage along the line including:

• The wind power plant at Taiban Mesa, which regulates the voltage at Taiban Mesa using the GE WindVAR system;

• The shunt reactors at Guadalupe; • The SVC at Guadalupe; • The STATCOM at Aragonne Mesa; • The Broadview wind generation including shunt compensation; • The El Cabo wind generation including shunt compensation.

A brief investigation of the PSLF steady-state voltage coordination was conducted based on the companion PSLF study described in Reference [2]. The purpose of the PSLF investigation presented here was to illustrate both transmission losses and the Blackwater-Taiban Mesa-Guadalupe 345 kV voltage profile for variations in the voltage schedules at Blackwater/Broadview and Taiban Mesa. The Broadview 345/34.5 kV plant transformer tap settings for various wind farms are set to 1.025 or 1.05 pu based on the study in reference [2]. The Broadview 34.5 shunt reactors are connected. Figure 7-1 and Figure 7-2 illustrate the BA-Blackwater transmission losses and voltage profile.



Figure 7.1: BA-Blackwater Transmission Losses for 497 MW and 1.025/1.05 pu Tap

Figure 7.2: BA-Blackwater Voltage Profile for 497 MW and 1.025/1.05 pu Tap

0

100

200

300

400

500

600

700

800

900

1.05 1.01 0.97 1.03 0.99 1.05 1.01 0.97 1.04 1 0.96 1.02 0.98 1.04 1 0.96 1.02 0.98 1.04 1 0.96 1.02 0.98

1.05 1.04 1.03 1.02 1.01 1 0.99 0.98 0.97

Loss

es (M

W/M

VAr)

Taiban Mesa/Broadview Scheduled Voltage (pu)

BA-Blackwater Transmission Losses Broadview 497 MW at 1.0 pf with 1.025/1.05 pu Plant Transformer Tap w/ Reactors

MW MVAr

0.9

0.92

0.94

0.96

0.98

1

1.02

1.04

1.06

1.05 1.02 0.99 0.96 1.03 1 0.97 1.04 1.01 0.98 0.95 1.03 1 0.97 1.04 1.01 0.98 1.05 1.02 0.99 0.96

1.05 1.04 1.03 1.02 1.01 1

345

kV V

olta

ge (p

u)

Taiban Mesa/Broadview Scheduled Voltage (pu)

BA-Blackwater 345 kV Voltage Profile Broadview 497 MW at 1.0 pf with 1.025/1.05 pu Plant Transformer Tap w/ Reactors

Blackwater Taiban Mesa Guadalupe

32



While real power losses are relatively unaffected by the Blackwater and Taiban Mesa voltage schedules and the transformer tap settings, the reactive power losses show a significant dependence on the Blackwater/Broadview voltage schedule, with a much lower level of dependence on the Taiban Mesa voltage schedule. Reactive losses range from 525 MVAr to 785 MVAr over the voltage range of 1.05 pu to 0.95 pu at Blackwater. Reactive losses increase at a much lower rate for decreases in the scheduled voltage at Taiban Mesa. The voltage profile plots illustrate a similar tendency, with the voltages across the BB transmission corridor decreasing more as a function of the Blackwater 345 kV voltage than for the Taiban Mesa voltage. The voltage setpoints and slopes of the various voltage regulators were investigated in the powerflow using the PSLF program. Other voltage regulators, for example at Taiban Mesa and Blackwater HVDC, were modeled using the existing PSLF models and power flow solution methods. Table 7-1 shows the BB line voltage profiles from the PSLF study. In the Siemens VSWT model, the turbine is controlling the GSU low side voltage. However, the Blackwater 345 kV bus voltage is indirectly affected by the Broadview windfarm main transformer tap setting. In addition, each Broadview sub-farm is equipped with a 10 MVAr shunt reactor and a 15 MVAr shunt capacitor at the 34.5 kV bus.

Table 7-1: BB Line full buildout Pre-Fault Steady State Voltage Profile from PSLF Study

Bus Config

BA 345 kV volt [pu]

El- Cabo 345 kV volt [pu]

Guad 345 kV volt [pu]

Taiban 345 kV volt [pu]

Blackwater 345 kV volt [pu]

Broadview POI 345 kV volt [pu]

Full Buildout

1.027 1.013 1.022 1.02 1.05 1.05

During the previous studies [3], protective tripping of the Broadview wind turbines was identified for cases involving load rejection overvoltage (for example as could occur at trip of e.g. Taiban Mesa windfarm). These cases pointed to a preference for the 1.05 or 1.025 pu tap setting for the Broadview main windfarm transformer. At that time, Broadview owner indicated a preference that the 1.05 pu tap not be used so that it can be reserved for future use. Broadview owners also indicated that Broadview windfarm is intended to operate with the reactors in service unless the Broadview high side voltage drops below 1.02 pu. For this condition, the reactors will be switched out and after a 5 minute delay the capacitors may be switched in if needed. In this study, the Broadview high side voltage is above 1.02 pu pre-contingency, and the studied period is short-term post-contingency (a few seconds). For these conditions, all



Broadview wind farm 34.5 kV bus reactors are connected and all capacitors are disconnected in PSCAD. Per the above considerations, the main windfarm transformer taps, the turbine AC voltage control reference and the Broadview wind farm shunt reactors/capacitors are set as in Table 7-2 below.

Table 7-2: Broadview Windfarm Configuration for PSCAD Study

Full Buildout Note

BVJN1 Park Tap [pu] 1.025 On 358.8 kV base BVJN2 Park Tap [pu] 1.025 On 358.8 kV base BVKW Park Tap [pu] 1.025 On 358.8 kV base BVGW1 Park Tap [pu] 1.025 On 358.8 kV base BVGW2 Park Tap [pu] 1.025 On 358.8 kV base BVJN1 GSU 690 Side Vref [pu] 1.0 BVJN2 GSU 690 Side Vref [pu] 1.0 BVKW GSU 690 Side Vref [pu] 1.0 BVJN1 GSU 690 Side Vref [pu] 1.0 BVJN2 GSU 690 Side Vref [pu] 1.0 BVJN1 MV bus 10MVAr Reactor/15MVAr Capacitor

Online/Off-line

BVJN2 MV bus 10MVAr Reactor/15MVAr Capacitor

Online/Off-line

BVKW MV bus 10MVAr Reactor/15MVAr Capacitor]

Online/Off-line

BVGW1 MV bus 10MVAr Reactor/15MVAr Capacitor

Online/Off-line

BVGW2 MV bus 10MVAr Reactor/15MVAr Capacitor

Online/Off-line

[1] Not applicable In the Gamesa Type 3 wind turbine, two reactive power control methods are integrated: reactive power control or power factor control. In the PSCAD model, the system west of the B-A 345 kV station is modeled using an equivalent source that can be either set to strong or weak network strength. In this study, the strong network strength is used. The voltage reference of the B-A equivalent source is set to 367 kV which approximates the value from the PSLF study (Table 7-1). The above conditions yields in PSCAD a BB line pre-fault voltage profile as given in Table 7-3.

34



Table 7-3: BB Line Pre-Fault Steady State Voltage Profile for PSCAD Study

Bus Config

BA 345 kV volt [pu]

El- Cabo 345 kV volt [pu]

Guad 345 kV volt [pu]

Taiban 345 kV volt [pu]

Blackwater 345 kV volt [pu]

Broadview POI 345 kV volt [pu]

Full Buildout

1.027 1.015 1.019 1.026 1.034 1.043



8 Dynamic Simulations and Analysis 8.1 Dynamic Simulation Case List and Results The PSCAD model of the full buildout system described in Sections 3 through 7 was set up as shown in Table E-1 (repeated here as Table 8-1).

Table 8-1: PSCAD Model Configurations Studied

Taiban Mesa Windfarm (MW)

Aragonne Mesa Windfarm (MW)

Broadview Windfarm (MW)

El Cabo windfarm (MW)

Blackwater HVDC E-W (MW)

Total BB Line (MW)

Guadalupe SVC (Mvar)

BA Equivalent Strength

Blackwater Condenser (Mvar)

Full Buildout 200 90 497 213 w/o Capacitors

0 1000 +250/-100 with UV Strategy

Strong 200

Dynamics cases were run in PSCAD to evaluate the behavior of the full buildout system configuration. The latest version (Rev.03) of the El Cabo windfarm model provided by Gamesa on October 25th 2016 was used. The contingency cases selected and the system performance are listed in Table 8-2.

Table 8-2: Dynamics Case List and Results (with El Cabo windfarm Rev.03)

Case 1 Conn./Disconn. 65 MVAr reactor at Guadalupe SO[2] Case 2 1PhG, 100 ms, Blackwater PNM side, 10% rem. volt. on converter bus SO Case 3 1PhG, 500 ms, Blackwater PNM side, 10% rem. volt. on converter bus SO,TMT[3] Case 4 1PhG, 500 ms, Blackwater PNM side, 10% rem. volt. on converter bus,

SPTR[1] on the line Blackwater – Taiban Mesa SO,BT[4]

Case 5 1PhG, 100 ms at Taiban Mesa, SPTR on the line Taiban - Guadalupe SO,BT Case 6 1PhG, 100 ms at Guadalupe, SPTR on the line Guadalupe - EI Cabo SO,BT,

TMT Case 7 1PhG, 100 ms at EI Cabo, SPTR on the line EI Cabo - BA DO[5],

BT,TMT Case 8 Trip part of the Broadview windfarm (200 MW) ELSR[6] Case 9 Trip full Broadview windfarm (497 MW) Pass Case 10 Trip of El Cabo windfarm (213 MW) SO Case 11 Trip of Taiban Mesa windfarms SO Case 12 Trip of Aragonne Mesa windfarm Pass Case 13 Trip of DSTATCOM at Aragonne Mesa Pass Case 14 Trip of SVC at Guadalupe Pass Case 15 3PhG, 100 ms, 10% rem. volt. at 115 kV bus at B-A SO,BT Case 16 1PhG, 100 ms, 10% rem. volt. at 345 kV bus at B-A SO Case 17 3PhG, 100 ms, 10% rem. volt. at 345 kV bus at B-A SO,BT

[1] SPTR = Single Phase Trip and Reclose [2] SO = Sustained Oscillation [3] TMT = Taiban Mesa Wind Farm Trip

36



[4] BT = Broadview Wind Farm Trip [5] DO = Damped Oscillation [6] ELSR = El Cabo Windfarm Slow Recovery

8.2 Dynamic Simulation Analysis Dynamic simulation results are presented in Appendix A: Broadview full buildout Windfarm with HVDC off-line. The analysis of results is as follows:

1. In most cases (11 out of 17), sustained oscillation can be observed on active/reactive powers and voltages output of Broadview Windfarm, El Cabo Windfarm, Taiban Mesa Windfarm, Aragonne Mesa Windfarm, Guadalupe SVC, and Blackwater Synchronous Condenser. In some cases such as Cases 2 and 3, the oscillation on reactive power output of Guadalupe SVC is slowly increasing. The typical oscillation frequency varies from 1.8 to 1.9 Hz. These oscillations require further investigation but possible mitigation methods may include the following possibilities:

• Investigation of the possibility of adding a damping controller to the Broadview wind turbine controls;

• Implementation of a power oscillation damping controller (POD) in the Guadalupe SVC (ABB has previous successful experience with this method)

• Implementation of a power system stabilizer (PSS) in the Blackwater condenser, if possible

The above possible strategies would need to be investigated in a future study.

2. El Cabo windfarm was able to ride through all simulated contingencies, provided that the three mitigating strategies are used (disconnection of El Cabo capacitors, installation of the condenser, and modified UV strategy in the Guadalupe SVC). However, as mentioned in Section 5.3, connection of capacitor bank(s) at El Cabo resulted in overvoltage on the 690V WTG exceeding the 1.2 pu threshold, resulting in windfarm tripping.

3. Part of the Broadview windfarm tripped in all 4 SPTR cases and other large disturbances

at B-A bus. Part of the Taiban Mesa windfarm also tripped in Cases 3, 6, and 7. Both of these findings have been reported previously, for example in Reference [3].



9 Maximum Dispatch with El Cabo Off-line

As a supplemental task, PNM requested ABB to perform an additional evaluation to determine the maximum dispatch at Broadview with the El Cabo windfarm offline and without adding condensers. This evaluation is described in the following sections. To provide additional information, conditions with and without condensers were evaluated.

9.1 Dynamic Simulation Case List and Results The dynamic cases described in Section 8 were investigated to determine the maximum dispatch of the Broadview windfarm (up to 497 MW) with the El Cabo windfarm off-line. The PSCAD model used is set up for the configurations shown in Table 9-1. Note the following:

• Configuration A was the full buildout system with synchronous condenser (Section 8 of this report)

• Configurations B through D are cases with different Broadview windfarm power levels without adding condensers. Configuration B has 497 MW wind generation in Broadview windfarm (BEJN 172 MW, BEKW 125 MW and Grady 200 MW), Configuration C has 297 MW wind generation including BEJN and BEKW windfarm, and Configuration D has 172 MW wind generation with only BEJN wind farm.

• Configurations E and F are the configuration studied for tests of a GE 60 MVA condenser.

Note that the cases described in this section were run prior to receipt of clarification from Siemens regarding the minimum SCR requirements of the Broadview wind turbines. Consequently, the calculations of condenser sizes based on SCR and ESCR conditions as shown in Section 6 were not available, and conditions with condensers as studied here were simply test cases based on GE 60 MVA condenser models as used in prior studies (Reference [1]) and as shown in Section 6.8.1.

Table 9-1: Reduced Dispatch Configurations Studied

Configuration






Total BB Line (MW)



Condenser

Conf. B 200 90 497 0 0 787 +250/-100 Strong none

Conf. C 200 90 297 0 0 587 +250/-100 Strong none

Conf. D 200 90 172 0 0 462 +250/-100 Strong none

Conf. E 200 90 297 0 0 587 +250/-100 Strong 1 GE 60MVA Sync Condenser

Conf. F 200 90 297 0 0 587 +250/-100 Strong 2 GE 60MVA Sync Condensers

38



9.2 Dynamic Simulation Analysis Dynamic cases were run in PSCAD to investigate the maximum Broadview windfarm power output level that can be dispatched. The studied dynamic cases with brief performance summaries are listed in Table 9-2. The detailed dynamic simulation plots are presented in the appendices as follows:

• Appendix B: 497 MW Broadview windfarm power with El Cabo windfarm offline, without synchronous condenser

• Appendix C: 297 MW Broadview windfarm power with El Cabo windfarm offline, without synchronous condenser

• Appendix D: 172 MW Broadview windfarm power with El Cabo windfarm offline, without synchronous condenser

• Appendix E: 297 MW Broadview windfarm power with El Cabo windfarm offline, with one GE 60 MVA synchronous condenser

• Appendix F: 297 MW Broadview windfarm power with El Cabo windfarm offline, with two GE 60 MVA synchronous condensers

Observations that need special attention are listed below: • It can been seen from Table 9-2 and Appendix B that for the maximum Broadview power

level (497 MW), stable post-fault recoveries were only achieved for the least severe cases (Case 1: Disconn./conn. 65 MVAr reactor at Guadalupe, Case 9: the trip of Broadview wind farm, Case 11: Trip of Aragonne Mesa wind farm, Case 12: Trip of DSTATCOM at Aragonne Mesa, and Case 13: Trip of Guadalupe SVC). For all other cases, Broadview wind farm was either tripped or showed sustained oscillatory behavior at roughly 1.85 Hz.

o The relatively low frequency oscillation observed is likely to be the rotor mechanical oscillation mode. The same problem was also observed in the previous study conducted in 2016 by ABB [3]. Given that the oscillation is not effectively dampened within the duration of the 5s run (very little reduction of the amplitude of the oscillation is shown), a damping controller or other mitigation may be needed for the Broadview windfarm.

• The Taiban Mesa windfarm was tripped from the system for Cases 3, 5, 6 and 7. Configurations C and D showed similar results. As noted in prior studies, the Taiban Mesa wind farm model is a black box model in PSCAD and the internal settings and signals are not accessible. The reason for the trip of the wind farm cannot be determined.

• Comparing Configuration B to Configuration C, some improvement in tripping behavior for Cases 15 and 17 is observed as the Broadview power level is reduced from 497 MW to 297 MW.



• Similar results occurred in Configurations C and D, indicating that further reduction of the Broadview power level below 297 MW does not offer significant improvement.

• Compared to Configuration C, improved damping of the above-described low frequency oscillations is observed in Configurations E (one 60MW GE condenser) and F (two 60MW GE condensers) in similar cases. The oscillations were however not fully damped at the end of the simulations.

• The comparison between Configurations C, E and F indicate that adding of condenser(s) can help to increase the strength of the BB line, improving the performance.

• As described previously (see Section 8), it is possible that investigation of adding a damping controller either to the Broadview wind turbines or the Guadalupe SVC may also help to mitigate the observed oscillations.

Table 9-2: Reduced Dispatch Cases; Dynamics Simulation Summary

Case

Conf

. B

Conf

. C

Conf

. D

Conf

. E

Conf

. F

Case 1 Pass Pass Pass Pass Pass Case 2 SO SO SO LFO LFO Case 3 TMT[1]&SO TMT&SO TMT&SO TMT&SO TMT&SO Case 4 BT BT BT PBT PBT Case 5 TMT&BT PTMT[2]&BT TMT&SO PTMT PTMT Case 6 TMT&BT TMT&BT TMT&BT PBT TMT Case 7 TMT&BT TMT&BT TMT&BT TMT&SO TMT&SO Case 8 PBT[3]&SO NA[4] NA NA NA Case 9 Pass Pass Pass Pass Pass Case 10 NA NA NA NA NA Case 11 SO SO SO Pass Pass Case 12 Pass Pass Pass Pass Pass Case 13 Pass Pass Pass Pass Pass Case 14 Pass Pass Pass Pass Pass Case 15 PBT&SO SO SO SO SO Case 16 SO SO SO SO SO Case 17 BT PBT BT PBT SO

[1] TMT = Taiban Mesa windfarm Trip [2] PTMT = Partial of Taiban Mesa windfarm Trip [3] PBT = Partial of Broadview windfarm Trip [4] NA = Dynamic simulation not performed for this configuration

40



10 Blackwater Minimum Power Operation

As an additional task, PNM requested a sensitivity study to evaluate the conditions shown in Figure 1-1 (full buildout), adding the Blackwater HVDC at a minimum transfer level of 15 MW east-to-west and performing a subset of the dynamics cases described in Section 8. The various PSCAD model configurations are shown in Table 10-1 below. Note the following:

• Configuration G1 is the full buildout system as in Table 8-1, adding the Blackwater HVDC a minimum transfer level of 15 MW east to west.

• Configurations G2 through G4 were modified from Configuration G1 by removing the El Cabo windfarm and the Blackwater condenser, with different Broadview windfarm output levels. The intent of these cases is to determine the maximum dispatch at Broadview with El Cabo wind farm offline and the Blackwater condenser also offline.

Table 10-1: PSCAD Model Configurations for Sensitivity Study






Total BB Line (MW)



Blackwater Condenser (Mvar)

Config. G1 200 90 482 213 w/o Capacitors

15 1000 +250/-100 with UV Strategy

Strong Siemens 175

Config. G2 200 90 497 Offline 15 802 +250/-100 with UV Strategy

Strong Offline


Strong Offline


Strong Offline

The case list and results of sensitivity study are shown in Table 10-2. As requested by PNM in the study agreement, the three most severe cases (4, 5, and 6) from Table 8-2 and two new cases (18, 19) involving SPS-side faults are included. The results of the four configurations shown in Table 10-1 and the five dynamics cases shown in Table 10-2 are given in Appendix G, with findings described below.



Table 10-2: Case List and Results of Sensitivity Study

Case # Description Config. G1

Config. G2 Config. G3

Config. G4

Case 4 1PhG, 500 ms, Blackwater PNM side, 10% rem. volt. on converter bus, SPTR on the line Blackwater – Taiban Mesa

SO[1],BT[2] BT BT

Case 5 1PhG, 100 ms at Taiban Mesa, SPTR on the line Taiban - Guadalupe

SO,BT BT BT,TMR BT,TMR

Case 6 1PhG, 100 ms at Guadalupe, SPTR on the line Guadalupe - EI Cabo

SO,TMR[3] BT,TMT[4] BT,TMR TMT

Case 18 1PhG, 100 ms, Blackwater SPS side, 10% rem. volt. on converter bus

SO Not Simulated

Not Simulated

Not Simulated

Case 19 1PhG, 300 ms, Blackwater SPS side, 10% rem. volt. on converter bus

SO Not Simulated

Not Simulated

Not Simulated

[1] SO = Sustained Oscillation [2] BT = Broadview Wind Farm Trip [3] TMR = Taiban Mesa Wind Farm Output Reduced [4] TMT = Taiban Mesa Wind Farm Trip

The observations are listed below: • Results of configuration G1 from cases 4-6 are similar to those in Table 8-2. Although

Broadview windfarm didn’t completely trip in case 6 as it did in Table 8-2 in the simulation timeframe, its performance was severely affected by sustained oscillations and will eventually likely trip, as shown in Figure 10.1.

42



Figure 10.1: BV Windfarm Performance in Config. G1, Case 6

• Further to the plots shown in Figure 10.1 and the above, it is noticed that the Blackwater HVDC is experiencing repetitive commutation failures during the voltage swings. This can be seen in Figure 10.2 below.

Figure 10.2. Config G1, Case 6: Repetitive Commutation Failures at Blackwater

20 20.5 21 21.5 22 22.5 23 23.5 24 24.5 25-20

0

20

40

60

P_S

1_W

[MW

]

Blackwater HVDC

20 20.5 21 21.5 22 22.5 23 23.5 24 24.5 25-100

-50

0

50

Q_S

1_W

[MV

Ar]

20 20.5 21 21.5 22 22.5 23 23.5 24 24.5 250

0.5

1

1.5

Uac

_345

kV_r

ms

[pu]

20 20.5 21 21.5 22 22.5 23 23.5 24 24.5 25-1.5

-1

-0.5

0

0.5

Udc

[pu]

20 20.5 21 21.5 22 22.5 23 23.5 24 24.5 25-0.5

0

0.5

1

1.5

Idc

[pu]

20 20.5 21 21.5 22 22.5 23 23.5 24 24.5 250

50

100

150

Time [s]

Gam

ma_

S1

[Deg

]



• Cases 18 and 19 involved faults at SPS side of Blackwater HVDC converter station. Results show the overall system performance is acceptable, except for small magnitude of sustain oscillation on SVC and condenser. Therefore, they were not the most severe cases and were not simulated in configurations G2 through G4.


• Comparing the results for cases G2 through G4 in Table 10-2, where El Cabo and the condenser are taken offline and the Broadview power is successively reduced, improvement is seen when the Broadview power is reduced to 172 MW (configuration G4). At this level, tripping of the Broadview wind farm is avoided in two of the three studied cases. Above this level, however, the Broadview wind farm trips during the simulations (configurations G2 and G3).

The detailed dynamic simulation plots are presented in Appendix G.

44



11 Low-order Harmonic Resonance The installed amount of ac filtering shunt capacitors at Blackwater HVDC is large relative to the short circuit capacity of the Blackwater station, and the installed shunt capacitors will be increased further by the addition of the Guadalupe SVC, and wind turbines at Broadview, Taiban Mesa and El Cabo. Thus, the possibility of parallel resonance at low-order harmonics between the capacitive shunt compensation and the ac network may be increased in the full buildout system. The damping effect that the power electronic control systems can introduce at harmonic frequencies also needs to be considered and this effect is not possible to capture using passive network equivalents. The amount of damping can be taken into account for active conditions (with power electronics at the wind farms and HVDC in operation) by injection of harmonic currents into the network during time simulations in PSCAD. The system response (harmonic voltage) is then extracted by Fourier analysis and the resulting driving point impedance at the injection frequencies is calculated. Low order harmonic resonance has been assessed by injection in PSCAD of harmonic currents at frequencies of 80Hz through 220 Hz during time-domain simulations. The Blackwater 345 kV bus (HVDC Bus) has been selected as the scan location and only the strong network condition at B-A has been studied. The following system configuration was used for the low order harmonic impedance scan:

• Blackwater HVDC 200 MW W-E (PNM side as rectifier), all ac filters connected • Siemens 200 MVA condenser • 213 MW El Cabo online • 90 MW Aragone Mesa and 200 MW Taiban Mesa online • SVC in operation (voltage regulation) • 497 MW Broadview online

Note that this case has Blackwater transferring 200 MW to the east (away from the BB line). This is because the lowest resonance frequency only occurs when all ac filters are connected, and this is only possible at 200 MW W-E (otherwise the total received power at B-A would be above 1000 MW). The resulting harmonic impedance scan is given as Figure 11.1 below,



Figure 11.1. Harmonic Impedance of Full Buildout Case with Blackwater at 200 MW W-E

From Figure 11.1, it is observed that the low-order resonance frequency falls just below 3rd harmonic. This implies that as capacitance is removed from the system, for example by switching an ac filter off at Blackwater, the resonance frequency will shift up to 3rd harmonic. Resonance near 3rd harmonic can be problematic for an HVDC converter in rectifier operation. This is because the converter itself is a source of 3rd harmonic current for conditions with unbalance between the phase voltages (negative sequence voltage). This converter-generated 3rd harmonic current will result in significant 3rd harmonic voltage distortion if the current meets a high impedance. It should be confirmed that the resulting 3rd harmonic voltage distortion is within acceptable limits. A more significant concern is during single line-to-ground ac faults, for which the converter can generate rather high levels of 3rd harmonic current. It should be confirmed that the ac filter stresses under such conditions are within the equipment ratings.

80 100 120 140 160 180 200 22050

100

150

200

250

Impe

danc

e (o

hm)

a

b

c

80 100 120 140 160 180 200 220

frequency (Hz)

0

20

40

60

80

Pha

se (d

eg)

a

b

c

46



12 Conclusions

This report has described electromagnetic transient simulation studies in PSCAD to (1) evaluate whether there is sufficient synchronizing voltage strength (short-circuit capacity) for various combinations of power injections along the BA-Blackwater 345 kV line, (2) provide recommendations for coordinating the voltage control devices along the line and (3) if voltage performance or short circuit capacity is unacceptable, identify system improvements needed to accommodate the power injections that use the full 1000 MW capacity of the BA-Blackwater 345 kV line (full buildout scenario)

From the studies in this report, the following observations and conclusions are reached:

• A preliminary strategy (detailed in Section 7) for control of voltage along the BB line, with coordination of the various voltage controlling devices (Statcom, SVC, and windfarms) has been developed based on the PSLF study. The controls of the existing systems (Aragonne Mesa and Taiban Mesa windfarms) are left unchanged.

• Sustained oscillation in post-contingency recovery period can be observed along the entire BB line, in 11 out of 17 cases. The typical oscillation frequency varies from 1.8 to 1.9 Hz. These oscillations have been observed previously and are related to the Broadview wind farm. These oscillations have been observed previously and are related to the Broadview wind farm. Per information from Siemens, the oscillations a known artifact of the aggregate modeling method, which tends to enhance drive train oscillations to a greater degree than would be expected in the actual system. The oscillations observed in this study are, however, more pronounced than in prior studies, and this should be reviewed by Siemens.

• The following strategies are needed to reduce the likelihood of El Cabo tripping on 1.2 pu overvoltage during post-fault recoveries:

• No capacitor banks connected at El Cabo; • Modified Undervoltage (UV) Strategy in Guadalupe SVC controls; • Blackwater Synchronous Condenser.

• Part of Broadview windfarm tripped in 6 out of 17 cases. Tripping of Broadview wind farm was however also noted as an issue in previous studies as reported in Reference [3].

• Part of the Taiban Mesa windfarm tripped in 3 out of 17 cases. This issue has also been observed in previous studies.

• For sensitivity studies with Blackwater online at 15 MW E-W, the following results are noted:

• For the full buildout case with Blackwater HVDC at 15 MW E-W and Broadview at 482 MW, the results are similar to the cases without Blackwater HVDC. One exception is in Case 6, where it was found that Broadview wind farm tripping did



not occur but sustained drive train oscillations and repetitive commutation failures in the HVDC are observed.


• For conditions with El Cabo and the condenser taken offline and Broadview power successively reduced, improvement is seen when the Broadview power is reduced to 172 MW. At this level, tripping of the Broadview wind farm is avoided in two of the three studied cases. Above this level, however, the Broadview wind farm trips during the simulations.

• For conditions with the full buildout and Blackwater HVDC online at 200 MW W-E, the low-order resonance frequency falls just below 3rd harmonic. This implies that as capacitance is removed from the system, for example by switching an ac filter off at Blackwater, the resonance frequency will shift up to 3rd harmonic. Resonance near 3rd harmonic can be problematic for an HVDC converter in rectifier operation.

Overall recommendations are listed below:

• Install a synchronous condenser at Blackwater 345 kV station that provides 830 MVA of short circuit capacity.

• To mitigate sustained low frequency (power swing frequency) oscillations during the post-contingency recovery period the following strategies should be investigated:

• adding oscillation damping capability to the Broadview wind turbine controls; • Implementing a power oscillation damping controller (POD) in the Guadalupe

SVC; • Implementing power oscillation damping or PSS control in the Blackwater

synchronous condenser.

Additional recommendations are listed below:

• The El Cabo windfarm model should be further revised to resolve issues with tripping during initialization and issues with snapshot functionality.

• Sensitivity to overvoltage tripping of El Cabo wind farm, due to El Cabo capacitor banks should be investigated. Tripping of El Cabo was minimized with no capacitor banks connected, but conditions with varying numbers of connected banks should be studied to quantify the sensitivity further.

• The undervoltage strategy in the Guadalupe SVC should be further reviewed during the SVC Dynamic Performance Study (DPS) to confirm acceptable dynamic performance.

• The fault ride-through capability of Broadview windfarm needs to be improved to achieve robust post-fault recovery for SPTR events. This was also noted in Reference [3].

48



• It should be confirmed that 3rd harmonic voltage distortion is within acceptable limits for the full buildout scenario with Blackwater in W-E operation. It should also be confirmed that ac filter stresses under such conditions are within the equipment ratings.



13 References [1] ABB Consulting Technical Report 2014-E00013367, “PNM Guadalupe SVC PSCAD Study”, 2014. [2] ABB Consulting Technical Report 2016-E00017437, “Broadview Affected PSLF Study”, 2016. [3] ABB Consulting Technical Report 2016-E00016010, “Broadview PSCAD study”, 2016. [4] ABB Consulting Technical Report 2016-E17436, “Preliminary Condenser Requirements”, 2016. [5] Siemens windfarm model user guide: UserGuide_PSCAD_Model_verCVT-02.pdf [6] BVS-ES-400.00 Rev E.PDF, received on Nov 24th, 2015 [7] Technical Data_100MVA_HICO.PDF and Technical Data_150MVA_HICO.PDF, received on Nov 24th, 2015 [8] ABB Technical Report 2015-E15783A-1.0.R00, December, 2015. [9] G. Wolf, A. Hammad, P. Daehler, “Commissioning and Operating Experience of Blackwater HVDC Scheme”, IEEE panel session paper.

50



Documents

Broadview affected PSCAD Study - oatioasis.com · PNM / Broadview affected PSCAD Study iii E00017437A-R00 • For sensitivity studies with Blackwater online at 15 MW E-W, the following