Transcript Case Study: Indian Basin Utility Interconnection

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
Utility Distribution System
12470 vac
GAS TURBINE GENERATION
800 KW 800 KW 800 KW
0.8 PF 0.8 PF
0.8 PF
Load In - ZLIN
Load Out - ZLOUT
#352
#252
#152
#452
480 vac
Critical Plant
Loads
1000kva
12470-480vac
Grounded Wye - Delta
Z=2.5%
MARATHON CORP.
INDIAN BASIN GAS
PLANT
Figure No. 1 - Simplified Oneline
1500kva
480-4160vac
Delta - Delta
Z=3.6%
Reverse
#552
4160 vac
M
900 HP
M
800 HP
Forward
Misc.
Loads
#52UT
#52G1
540 KW
0.8 PF
#52G2
540 KW
0.8 PF
DIESEL GENERATION
UTILITY SOURCE AND POINT OF
COMMON COUPLING (PCC)
Utility Distribution System
12470 vac
GAS TURBINE GENERATION
800 KW 800 KW
0.8 PF 0.8 PF
Load In - ZLIN
#352
#252
#152
#452
480 vac
Critical Plant
Loads
1000kva
12470-480vac
Grounded Wye - Delta
Z=2.5%
• 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 GENERATION
AND 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
1500kva
480-4160vac
Delta - Delta
Z=3.6%
#552
Reverse
4160 vac
M
900 HP
M
800 HP
Forward
Misc.
Loads
#52UT
#52G1
540 KW
0.8 PF
#52G2
540 KW
0.8 PF
DIESEL GENERATION
DIESEL GENERATION
and 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
Utility Distribution Transformer Connections
If utility distribution circuit transformer high side is not referenced to ground at the
neutral point. Arrestor voltage above break over point forces the arrestor into
conduction where sustained current flows can cause thermal damage.
Arrestors on unfaulted phases of systems with
no ground reference are subjected to voltages
near line to line magnitudes, 138% of nominal.
Phase to Ground Fault
Arrestors on faulted phase are subjected to
voltage below nominal rating
Maintaining the distribution circuit ground
reference allows distributed resource to
maintain arrestor voltages within nominal
ratings.
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
X
Load Encroachment Element
Used to detect Reverse Power Flow via
Positive Sequence Impedance characteristic
PLAR = 90 degrees
Minimum Reverse Load detected
= 134.8 kva 3 phase
or 162.3 amps / phase.
Z1secondary = 128 ohms
CTR = 300:1
PTR = 4:1
ZLIN Asserted when
Z1- Positive Sequence
Impedance Plots with this
region.
NLAR = 270 degrees
R
RECOMMENDED ENHANCEMENTS

Inadvertent Energization of the Utility
Distribution System

Programmable close interlock contact to
prevent #352 interconnect breaker
closing if distribution system is deenergized

Use SEL-351 check synch element as
an additional layer for out of synch close
protection
UTILITY VOLTAGE NORMAL
Utility Voltage Normal (SV5T)
OR1
27AB
27BC
27CA
59AB
59BC
59CA
NOT1
SV5
120
0
UTILTIY FREQUENCY NORMAL
Frequency and Utility Voltage Normal for 5 minutes (SV4T)
NOT6
81D1
NOT7
81D2
SV5T
AND6
AND5
SV4
0
CLOSE CIRCUIT CONTROL
Close Circuit Interlock Logic
Utility Frequency and Voltage have been normal for 5 minutes (SV4T)
AND7
SV4T
OUT103
AND8
OR2
27S
SV5T
25A1
Utility Energized and Plant Bus De-energized or Check Sync
Close Circuit Interlock 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