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CASE STUDY – INDIAN BASIN UTILITY INTERCONNECTION
JAN. 2002
INDIAN BASIN GAS PLANT
Marathon Oil Co. Gas Processing Plant
Five Synchronous Generators Totaling 3.48MVA
Gas Turbine and Diesel Driven Equipment
No Export Agreement with Utility
INTERCONNECTION BENEFITS
Utility Provides a Source Instantaneous Energy when needed, Increasing Plant Electrical Reliability
Plant Operating Costs are Reduced by Using Fuels from Process
On-Site Generation can Maintain Critical Operations when Utility source is Unavailable, Creating Electrical Supply Redundancy
CASE STUDY CONTENT
Utility Interconnection and Interconnection Protection and Control
Directional Overcurrent Protection Improves Plant Protection Selectivity
Techniques used to Monitor Protection Quality
Logical Next Steps and Conclusions
PLANT ELECTRICAL SYSTEM LAYOUT
Load In - ZL IN
M
M 900 H P
800 H P
540 K W0.8 P F
540 K W0.8 P F
D IE S E L G E N E R A TIO N
C ritica l P lan t Loads
800 K W0.8 P F
800 K W0.8 P F
800 K W0.8 P F
G A S TU R B IN E G E N E R A TIO N
480 vac 4160 vac
12470 vac
#352
#552
M isc.Loads
Load O ut - ZLO U T
Forw ardR everse
1500kva480-4160vacD elta - D e lta
Z=3.6%
1000kva12470-480vac
G rounded W ye - D e ltaZ=2.5%
#252 #152 #452
#52U T
#52G 1 #52G 2
M AR ATH O N C O R P.IN D IAN BASIN G AS
PLAN TFigure N o. 1 - S im plified O neline
U tility D istribu tion S ystem
UTILITY SOURCE AND POINT OF COMMON COUPLING (PCC)
Load In - ZL IN
C ritica l P lan t Loads
800 K W0.8 P F
800 K W0.8 P F
G A S TU R B IN E G E N E R A TIO N
480 vac
12470 vac
#352
1000kva12470-480vac
G rounded W ye - D e ltaZ=2.5%
#252 #152 #452
U tility D istribu tion S ystem
• PCC resides at the low side of the 12470 – 480vac 1000 kva transformer • 1600 A, 480 V Circuit Breaker #352 Interconnect breaker• 480 V Plant Bus Feeds Critical Plant Loads
INTERCONNECTION EQUIPMENT
PCC resides at the low side of the 12470 – 480vac 1000 kva transformer
1600 A, 480 V Circuit Breaker #352 Interconnect breaker to Plant 480 V Bus
480 V Plant Bus Feeds Critical Plant Loads
GAS TURBINE GENERATIONAND CRITICAL PLANT LOADS
Three 800Kw 0.8 Power Factor Generators Feed the Plant 480 V Bus
Automatic Load and Var Controls
The Plant Electrical System is Predominantly High Resistance Grounded
480 V Plant Bus Feeds Critical Motor Control Centers, Process Loads and Building Loads
DIESEL GENERATION and 4160 V SYSTEM
M
M 900 H P
800 H P
540 K W0.8 P F
540 K W0.8 P F
D IE S E L G E N E R A TIO N
4160 vac#552
M isc.Loads
Forw ardR everse
1500kva480-4160vacD elta - D e lta
Z=3.6%
#52U T
#52G 1 #52G 2
DIESEL GENERATIONand 4160 V PLANT LOADS
Two 540Kw 0.8 Power Factor Generators Feed the Plant 4160 V System
Fixed Load and Voltage Regulations Controls
The 4160 V Plant Electrical System is Predominantly High Resistance Grounded
4160 V System Feeds Two Large Motors and Small Process Loads.
ELECTRICAL SYSTEM TIE EQUIPMENT
480 – 4160 V 1500 kva Transformer Connects the 480 V and 4160 V Systems
1600 A, 480 V Circuit Breaker #552 Tie breaker
4160 V Plant Bus Feeds Large Motor Loads
UTILITY SOURCE TRANSFORMER CONNECTION
Utility Advantages of the Ground Wye High Side Configuration Utility distribution system remains solidly
grounded even if plant generation feeds the distribution circuit
Utility Advantages of the Delta Low Side Configuration Zero Sequence Isolation, no ground fault
contribution from plant generation
UTILITY SOURCE TRANSFORMER CONNECTION
Plant Advantages of Grounded Wye High Side Configuration Plant generation does cause utility distribution
circuit arrestor damage during short periods of back feed
Plant Advantages of Delta Low Side Configuration Zero sequence isolation, plant can operate
with a High Resistance Grounded (HRG) system
DISTRIBUTION CIRCUIT ARRESTOR OVER VOLTAGE
P hase to G round Fau lt
A rrestors on fau lted phase are sub jected tovo ltage be low nom ina l ra ting
A rrestors on un fau lted phases o f system s w ithno ground re fe rence are sub jected to vo ltagesnear line to line m agn itudes, 138% of nom ina l.
U tility D istribution Transform er C onnections
M ain ta in ing the d istribu tion c ircu it g roundre ference a llow s d istribu ted resource to
m ain ta in a rrestor vo ltages w ith in nom ina lra tings.
If u tility d istribu tion c ircu it transform er h igh s ide is no t re fe renced to g round a t theneutra l po in t. A rrestor vo ltage above break over po in t fo rces the arrestor in toconduction w here susta ined curren t flow s can cause therm al dam age.
UTILITY INTERCONNECTION PROTECTION
The SEL-351 Multifunction Microprocessor Relay Protection and control
Event and sequential event reports
Programmable display messaging
Failsafe Alarm Contact Provides System Status
VOLTAGE PROTECTION ELEMENTS
Single Level Over Voltage and Under Voltage Protection Under voltage protection set at 94% of
nominal with 120 cycle delay Over voltage protection set at 132% of
nominal with 120 cycle delay
System Utilizes Open Delta Connected Potentials
FREQUENCY PROTECTION ELEMENTS
Single Level Definite Time Over and Under Frequency Protection Under frequency set at 59.25 Hz with
five cycle delay Over frequency set at 60.25 Hz with five
cycle delay
Under Voltage Frequency Disable Set at 40 V
ISLANDING PROTECTION ELEMENT
Load Encroachment Element Detects load flow to the utility via positive
sequence impedance calculations
Detects three-phase reverse power flow as small as 125 Kw
Reverse power time delay of four seconds allows plant generation control time to compensate after a load shed occurs
LOAD ENCROACHMENT ELEMENT
M in im um R everse Load de tected= 134.8 kva 3 phase
or 162.3 am ps / phase.Z1secondary = 128 ohm s ZLIN A sserted w hen
Z1- P ositive S equenceIm pedance P lo ts w ith th is
reg ion .
P LA R = 90 degrees
N LA R = 270 degrees
C TR = 300:1P TR = 4 :1
Load Encroachm ent Elem entU sed to de tect R everse P ow er F low via
P ositive S equence Im pedance characteris tic
X
R
RECOMMENDED ENHANCEMENTS
Inadvertent Energization of the Utility Distribution System Programmable close interlock contact to
prevent #352 interconnect breaker closing if distribution system is de-energized
Use SEL-351 check synch element as an additional layer for out of synch close protection
UTILITY VOLTAGE NORMAL
120
0
SV5N O T1O R 1
27AB
27BC
27C A
59AB
59BC
59C A
U tility Voltage N orm al (SV5T)
UTILTIY FREQUENCY NORMAL
0
SV4AN D 5AN D 6
N O T6
81D 1
N O T7
81D 2
SV5T
Frequency and U tility Voltage N orm al for 5 m inutes (SV4T)
CLOSE CIRCUIT CONTROL
O U T 103
AN D 7
SV4T
O R 2AN D 8
27S
SV5T
25A1
C lose C ircuit In terlock Logic
U tility F requency and Voltage have been norm al for 5 m inutes (SV4T)
U tility Energized and P lant Bus D e-energ ized or C heck Sync
C lose C ircuit In terlock contact
PROTECTION SYSTEM MONITORING
Utilize Loss of Potential Indication to Operate Protection System Abnormal Alarm Contact
Control Protection Element Operation with Loss of Potential Status if Interconnection is Critical
PLANT DISTRIBUTION 480-4160V TIE PROTECTION
SEL-351 Multi-Function Microprocessor Relay
Provide Fast Low Set Overcurrent Protection Not sensitive to loading Secure for disturbances on the utility feeder
Additional Overcurrent Protection for Balanced Fault Conditions Less sensitive and secure during motor starting
operations on the 4160 vac system
FAST LOW SET PROTECTION
Definite Time Directional Negative Sequence Element Operates for unbalance faults on the
4160V system
Two cycle definite time delay avoids tripping on negative sequence transients
BALANCED FAULT PROTECTION
Set Above Load and Motor Starting Inrush High set non-directional definite time
overcurrent
Non-directional extremely inverse time over current element
This Combination Operates During Balanced Fault Conditions and is Secure During Motor Starting Inrush
ADVANTAGES OF TIE PROTECTION SYSTEM
Closed Tie Continuity For unbalanced disturbances on the
utility distribution system For motor starting operations on the
4160V system
Fast Clearing of Unbalanced Faults on the 4160V System Minimizes Effects to the 480V Plant Bus
RECOMMENDED ENHANCEMENTS TO TIE PROTECTION
Use SEL-351 check synch element as an additional layer for out of synch close protection
Utilize Loss of Potential Indication to Operate Protection System Abnormal Alarm Contact
Control Protection Element Operation with Loss of Potential Status
PROTECTION QUALITY MEASUREMENTS
Sequential Event Reports Time tagged protection system element
status report
Unused levels of over current protection used for monitoring via sequential event reports
Unused levels of over current protection are not programmed for tripping
EVENT ANALYSIS
Event Reports Capture System Disturbances Provide greater detail with pre and post fault data Graphical representations of voltage and current
waveforms along with frequency magnitudes Protection system element status time
synchronized with voltage and current waveforms Phasor plots of voltage current and sequence
quantities
EVENT REPORT WAVEFROM GRAPHIICS
PHASOR PLOT GRAPHICS
DISPLAY MESSAGING
Protection System Display Messaging Add descriptive text into rotating display
based on protection element status
Enhances protection system targeting
Provides additional information to operating personnel
CONCLUSIONS
Multi-functional Microprocessor Relays are Well Suited for Interconnection Protection
Interconnection Protection Over and Under Frequency Elements Over and Under Voltage Elements Non-Islanding Protection Close Interlock Control
Monitor Protection System Performance