Copyright © SDG&E, Quanta Technology, and SEL 2016

Catching Falling Conductors in Midair –Detecting and Tripping Broken

Distribution Circuit Conductors at Protection Speeds

Kirsten PetersenSan Diego Gas & Electric

• 22,000 miles of lines• 60% underground and 40% overhead• Grounded three- and four-wire systems • Nominally 12kV and 4kV• High penetration of distribution PV requires new solutions

for monitoring, protection, and control

SDG&E Distribution System

• Driven by high penetration of distribution PV• Voltage profile monitoring and control • Selective load shedding and restoration• Power quality monitoring • Apparatus and system condition monitoring• Falling conductor protection (patent pending)

Advanced SCADA Project ApplicationsMore Than 60 Use Cases Defined

• Increased accuracy of voltage and current • Phase angles from across circuit• GPS time-stamped data• 30 synchrophasor sets per second for fast measurement• IEC 61850 GOOSE messaging for real-time control• Remote engineering access and event reports• Advanced security features

Advanced SCADA Features

SCADA System ArchitectureTraditional

SCADA System ArchitectureAdvanced

SCADA System ArchitectureTraditional and Advanced Overlay

SDG&E Typical Feeder

R1

N.O.

R2

PV

Five-Way Switch

Capacitor Bank

CB

Line Monitor

Capacitor Bank

Capacitor Bank

Substation

Advanced SCADA Locations

To Control Centervia WAN

P P

P

P

P

P

P

P

N.O.

P

P

P

Line Monitor

VR4

R1

P

VR1VR2

PV11 MW

PV21 MW

S

DVC

Feeder Relay

69 kV/12 kV

R3

VR6

VR3

R5 VR5

R4

C3

C2

C1

P

Substation

PDC and Controller Switchyard

Fiber

LEGEND

P IED With PMU and Ethernet

R Recloser

WAN Wide-Area NetworkN.O. Normally Open

PV Photovoltaic

DVC Dynamic VAR Compensator

VR Voltage Regulator

S Multiport Circuit Switch

0

5

10

15

20

25

30

0.00 0.25 0.50 0.75 1.00 1.25

Con

duct

or H

eigh

t (ft)

Time (s)

Falling Conductor Timeline

0.5 s, 4 ft

1 s, 16 ft

Conductor hits ground at 1.37 s

Detect Broken Conductor and Trip Circuit Before Line Hits the Ground?

2 2dg

1d gt t22(30)t32.2

time 1.37s

Sequence Components Analysis

c1 b2

a2a1

b1 c2

a0

b0

c0

c2 2 a2c1 a1

b1 2 a1a0 b0 c0 b2 a2

Open-Phase Analysis

jXTG

ZL

jXTHG HZ1GHX Y

I1G I1H

Z1S

E

N1

jXTG

ZL

jXTHG HZ1GHX Y

I2G I2H

Z2S

N2

jXTG

G HZ0GHX Y

I0G I0H

N0

jXTH

Open-Phase Analysis

• dV/dt (change detection) • V0 and V2 magnitude• V0 and V2 angle

Detection Methods

dV/dt MethoddV0/dt Supervision CheckConductor Break

Between PMU 1 and PMU2

Trip PMU1

and PMU2

PMU1dV/dt

PMU2dV/dt

PMU3dV/dt

OR

PMU1 PMU2 PMU3dV0/dt

Between PMU 2 and PMU3

OR

Trip PMU2

and PMU3

X = threshold

> 0

< 0

< 0 < 0

< –X

> X

< X > X

> 0 > 0 < –X

> X

< X < X > X

< –X

> X

> X

dV0/dtdV0/dt

V2 and V0 Magnitude MethodConductor Break

V2 and V0 Angle Method

PMU1 PMU2 PMU3 PMU4

2 3 4

1

PMU1 PMU2 PMU3 PMU4

3 4

1 2

FC

1 not aligned with the other PMUs

1 and 2 aligned with each other3 and 4 aligned with each other

Source 1 Source 2

Source 1 Source 2

FC

is V2 or V0 angle

RTDS Feeder Model

Example Lab Test ResultsPV Off, Loop Open

Load % FC1 FC2 FC3 FC4100 3 3 3 375 3 3 3 325 3 3 3 3

PV On, Loop OpenLoad % PV% FC1 FC2 FC3 FC4

100

100 3 3 3 375 3 3 4 450 3 3 3 325 3 3 3 3

25

100 3 3 3 375 3 3 3 350 3 3 3 325 3 3 3 3

0

10

20

0–99 100–199 200–299 300–399 400–499

Arc Speed = 5 m/s

FC1 FC2 FC3 FC4(ms)

Arc Speed and Results ComparisonNumber of Test Cases Versus dV/dt Pickup Times

0

10

20

0–99 100–199 200–299 300–399 400–499

Arc Speed = 0 m/s

FC1 FC2 FC3 FC4(ms)

• Capacitor bank switching• Voltage regulator tap unbalance Angle method for ≈ 4.5% voltage (6 taps)

V0 magnitude method for ≈ 10% voltage (15 taps)

• Largest single-phase load switching• PV operation• Internal / external faults

Security Testing

ResultsDetection Screen

• Conductor break between PMU1 and PMU2

• PV inverter source ON

Inverter Response

ResultsdV/dt and Magnitude Methods

• First system installation in January 2015• Falling Conductor Protection (FCP) in

monitoring mode• Simulation of conductor breaks with

disconnect switch opening on recloser• 100% correct operation• Ethernet radio tuning required

Field Installation and Testing

Breaking Arc – Field Versus Lab TestsField Result RTDS Model

Falling Conductor Zones

CIRCUITBREAKER

RECLOSERRECLOSER

LINE MONITOR

TRAYER SWITCH

PV

VzVyVyVz

Vv

N.O.

SUBSTATION

Zone 1 Zone 2Zone 3Zone 4

LEGEND

PMU

VOLTAGE REG

VOLTAGE REG

Synchrophasors show detailed circuit behavior Capacitive voltage sensor discoveries

11 kV

6.8 kV

2.8 kV/s

–1.7 kV/s

0

577 V/s

– 400 V/s

0

Pha

seA

Vol

t age

dVA

/ dt

dV0/

dt

Load Side

Source SideNominal

6.9 kV

Time

Time

Time

dVA /dt > 1000 V/s

dV0 /dt > 400 V/s

Zone 1 dV/dt Operation

• Field Event – 28th Feb 2016• FC detected by dV/dt between CB and R1

Zone 1 Current Spikes

• Current spikes observed at CB and VR1, but not at VR2

• Indicates temporary fault between VR1 and VR2

RTDS Simulation

CIRCUITBREAKER

RECLOSERRECLOSER

LINE MONITOR

TRAYER SWITCH

PV

VzVyVyVz

Vv

N.O.

SUBSTATION

Zone 1 Zone 2Zone 3Zone 4

LEGEND

PMU

VOLTAGE REG

VOLTAGE REG

Simulated Disturbance in RTDS - Phase C- SLG Fault (High Resistance)- 0.01 seconds duration- Speculated High Impedance Fault

• Threshold based on RTDS testing results• dI0/dt spikes at CB PMU used to block falling

conductor detection algorithms• Temporary faults can be blocked using this

supervision

dI0/dt Supervision

Lab Simulation – Before dI0/dt

• Zone-1 mis-operation confirmed in lab

• dI0/dt block not implemented

• Mis-operation similar to field event

Lab Simulation – After dI0/dt

• Zone-1 mis-operation simulated in lab

• dI0/dt blocks Falling Conductor scheme

• System abnormal alarm condition

System Protection is a Balancing Act

• SPEED• SENSITIVITY

• SELECTIVITY• SECURITY

FAST TO MINIMIZE DAMAGE

RELAY SEES FAULT

DO NOT TRIP FALSELY

REMOVE FAULTED ELEMENT ONLY

• SIMPLICITY SIMPLE CONTROL SCHEMES

FCP Compliments Existing Layers of Protection• FCP – Falling Conductor Protection detects break in conductor Fastest – trips before the fault Coordination – FCP should be first

• Overcurrent – Time and Instantaneous Simple implementation

• SGF – Sensitive Ground Fault detects high-impedance ground fault Slow – 3.5 to 5.5 seconds Could Trip on Load

• Advanced SGF - More sensitive than SGF using adaptive set point, spike counting, and/or harmonics Slower – > 5 seconds Coordination between devices is unlikely

• Does not detect wire down without break• Needs fast Ethernet path to circuit PMUs• Uses voltage from each protected circuit path end – a

journey of years for coverage • Learning features of new technology

FCP Limitations

Ease of Application

• Key requirement achieved – no circuit-dependent application settings

• FCP logic only needs topology of circuit and PMU IEDs

To Control Centervia WAN

P P

P

P

P

P

P

P

N.O.

P

P

P

Line Monitor

VR4

R1

P

VR1VR2

PV11 MW

PV21 MW

S

DVC

Feeder Relay

69 kV/12 kV

R3

VR6

VR3

R5 VR5

R4

C3

C2

C1

P

Substation

PDC and Controller Switchyard

Fiber

• Advanced SCADA has 60 use cases including FCP• FCP isolates broken conductors in 0.2 – 0.5 s (half the

distance to the ground) preventing the fault• FCP is dependable in lab test including high PV penetration• FCP mitigates HILP events – fire and hazard reduction • Confidence built from secure and reliable field performance• Compliments existing protection• Scalable design needs only circuit layout information

Summary

• FCP of first equipped circuit commissioned on 11/18/2016• Additional circuits equipped and commissioned in 2017• Pursuing ongoing work to reduce fire risk and enhance

public safety• Installing new IEDs with PMU capable devices with

moderate additional cost• SDG&E will be well positioned for future PV penetration

Next Steps

Questions?