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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