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Power Distribution System Overview
• Overview of existing grid (transmission , generation, Distribution)• Distribution Transformer Station.• Distribution feeder and critical Equipment. • Important terms related DER , short-circuit capacity, thermal capacity,
islanding, anti islanding and temporary over voltages.
Traditional Power System This Photo by Unknown Author is licensed under CC BY
G
Volta
ge k
V
Transmission 400/230/115kV
Generation 12kVDistribution Voltage 27.6/25/4kV User level Voltages
120/240, 120/208, 600/347V
Step-Up transformerStep-Up transformer
Generator - 2Generator - 1
G2G1
Step-down Transformer
Distribution Transformer HV Fuse
Radial Distribution Feeder
Mesh Connected TX Lines
Circuit Breakers
GEN
ERAT
ION
TRAN
SMIS
SIO
N
DIST
RIBU
TIO
N
Distribution Transformer Station Typical Arrangement
115 kV Line # 1
115 kV Line # 2
T1 T2
F1
F3
F5 F6
F4
F2
Distribution feeders
115/27.6 kV Step-Down Transformers
NC – Normally CloseNO – Normally Open
NC NC
NC
NC
NC
NO
NO
NO
Remote OperableFeeder Tie 25M14 –MS-55M1Normally Open
Remote operableMid point Recloser25M25-RC1Normally close
Distribution feeder connectivity
Remote OperableFeeder Tie 25M14 –MS-55M1Normally Open(Close )Remote operable
Mid point Recloser25M25-RC1Normally close(Open)
Off Loading a Transformer Stations
Typical Feeder schematic Tr
ansf
orm
er S
tatio
n Bu
s (Normally Open)Remote Operable Switch
Normally closeMid point recloser
Load
Load Load
27.6 kV
G G
Load
FeederCircuitBreaker
Feeder Main trunk Conductor556 MCM
Load
Under Ground Switching Unit
Protective & Isolation Equipment in the Distribution feeder
34.5 kV, 1200 AFeeder Breaker
34.5 kV , 630 ARecloser
34.5 kV, 600 AMotorized Switch
27.6kV, 600AManual Switch
Dynamic behavior of the power system and Important terms related DER
• Frequency response to the load change
• Short circuit Capacity of a Transformer Station
• Thermal Capacity of a Transformer Station
• Islanding of a power system
• Remote trip requirement for Anti Islanding
• Temporary Over Voltage of distribution system
Generator – 2(Capacity - 100MW)
Generator – 1(Capacity - 100MW)
G2G1
Load100 MW
60.00 Hz
Generation = 50MW + Losses/2 Generation = 50MW + Losses/2
Syst
em F
requ
ency
Frequency response to the load change
Generator – 2(Capacity - 100MW)
Generator – 1(Capacity - 100MW)
G2G1
Load(100 + 15) MW
60.00 Hz
Generation = 50MW + Losses/2 Generation = 50MW + Losses/2Sy
stem
Fre
quen
cy
Load > Generation
Sudden Increase of 50MW Load
Frequency response to the load change
Generator – 2(Capacity - 100MW)
Generator – 1(Capacity - 100MW)
G2G1
Load(100 + 15) MW
60.00Hz
Generation = (50 + 7.5) MW + Losses/2 Generation = (50+ 7.5 )MW + Losses/2Sy
stem
Fre
quen
cy
Load = Generation
Sudden Increase of 15MW Load
Frequency response to the load change
Short circuit Capacity of a Transformer Station
115 kV Line # 1
115 kV Line # 2
T1 T2
F1
F3
F5 F6
F4
F2
Distribution feeders
115/27.6 kV Step-Down Transformers
NC – Normally CloseNO – Normally Open
NC NC
NC
NC
NC
NO
NO
NO
Supply Source
Distributed Generation
115 kV Line # 1
115 kV Line # 2
T1 T2
F1
F3
F5 F6
F4
F2
Distribution feeders
115/27.6 kV Step-Down Transformers
NC – Normally CloseNO – Normally Open
NC NC
NC
NC
NC
NO
NO
NO
Thermal Capacity of a Transformer Station
Islanding of a power systemTr
ansf
orm
er S
tatio
n Bu
s (Normally Open)Remote Operable Switch
Normally closeMid point recloser
Load 1
Load 4 Load 2
27.6 kV
G1 G2
Load 3
FeederCircuitBreaker
Feeder Main trunk Conductor556 MCM
Load 5
Under Ground Switching Unit
G1+G2 = Load 1 + Load 2 + Load 3 + Load 4 + Load 5
I = 0 Amp
Island Frequency is not equal to 60 Hz
Remote trip requirement for Anti Islanding Tr
ansf
orm
er S
tatio
n Bu
s (Normally Open)Remote Operable Switch
Normally closeMid point recloser
Load 1
Load 4 Load 2
27.6 kV
G1 G2
Load 3
FeederCircuitBreaker
Feeder Main trunk Conductor556 MCM
Load 5
Under Ground Switching Unit
Remote Trip Issued
Temporary Over Voltage of distribution systemTr
ansf
orm
er S
tatio
n Bu
s (Normally Open)Remote Operable Switch
Normally closeMid point recloser
Load
Load Load
27.6 kV
G G
Load
FeederCircuitBreaker
Load
Under Ground Switching Unit
Thank you
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