Utility System OperationPresented by
Scott Peele PE
Utility Power System
Utility System OverviewTransmission SystemDistribution System
How the System WorksTransmissionDistribution
Why It Works That WayDesign PhilosophyEvents & Causes
Transmission System OverviewHigh Voltage
500 kV230 kV115 kV
Purchased Right-of-WayWideClearedUtility Has Some Control
Few AttachmentsVery ReliableFew Disturbances
Distribution System Overview
Medium Voltage23 kV12 kV
Constructed Along Public Roads
Other Utility AttachmentsLess Clearance to TreesMore Public AccessMore Exposure
Most Customers Served This WayMore Disturbances
System Design Philosophy
Protect Transmission & Distribution Lines and EquipmentMinimize Number of Extended OutagesMinimize Number of Customers Out Due to a FaultTrade-off is More Short Duration Events Automatic Reclosing Feeder
Breakers at a T-D Substation
Protective Coordination Equipment
Automatic Reclosing Circuit Breakers
Transmission & Distribution
Automatic Line ReclosersDistribution System
Fuses - (Fused Cut-Outs)Mostly On Distribution
Grounding & BondingCritical for Safety & Protection
Lightning ArrestorsLimit Voltage, Divert Current
Automatic Three Phase Line Recloser
Single Phase Line Reclosers
Three Phase Dip Pole Fuse
Tap Line Fuse - Fused Cutout
Faults cause voltage sags, interruptions and outages
SagInterruptionOutage
SagInterruptionOutage
Magnitude and DurationMagnitude and Duration Duration
- 10% and <1 minute- 90% and < 1 minute> 1 minute
Simplified Transmission & Distribution System
Transmission @ 115 kV
Transformer
Distribution @ 23 kV
23 k
V Fe
eder
FeederBreaker
Transmission to DistributionSubstation
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
Customer Customer
Customer
Fuse Fuse
Fuse Fuse
Fuse
Fuse
FeederBreaker
Transformer
Customer Substation
Fault On Transmission System
Fault
Transmission @ 115 kV
Transformer
Distribution @ 23 kV
23 k
V Fe
eder
FeederBreaker
Transmission to DistributionSubstation
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
Customer Customer
Customer
Fuse Fuse
Fuse Fuse
Fuse
Fuse
FeederBreaker
Transformer
Customer Substation
Fault On Transmission SystemVo
ltage
All customers (transmission and distribution) served by the faulted transmission line will experience a short Voltage Sag.Customers served by other transmission lines which connect to the faulted transmission line may also experience a voltage sag.Depending on the configuration of the transmission line, some customers may experience a Momentary Interruption while a fault is clearing.
Fault On Transmission Line
480
Fault occurs here
0
Volta
ge
Time
Breaker opens here
Breaker recloses here
Fault cleared
0
4 cycles(~0.067 sec)
Four Cycle Voltage Sag
Causes of Faults on the System
Simplified Utility System
115 kV Substation
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
Customer Customer
Customer
Fuse Fuse
Fuse Fuse
Fuse
Fuse
FeederBreaker
Transmission @ 115 kV
Transformer
Distribution @ 23 kVRegulator
23 k
V Fe
eder
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
CustomerCustomer
Customer
FuseFuse
FuseFuse
Fuse
Fuse
FeederBreaker
23 k
V Fe
eder
Example
Simplified Utility System
115 kV Substation
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
Customer Customer
Customer
Fuse Fuse
Fuse Fuse
Fuse
Fuse
FeederBreaker
Transmission @ 115 kV
Transformer
Distribution @ 23 kVRegulator
23 k
V Fe
eder
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
CustomerCustomer
Customer
FuseFuse
FuseFuse
Fuse
Fuse
FeederBreaker
23 k
V Fe
eder
Outage
Momentary Interruption
Sag
Fault On Your Feeder
115 kV Substation
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
Customer Customer
Customer
Fuse Fuse
Fuse Fuse
Fuse
Fuse
FeederBreaker
Transmission @ 115 kV
Transformer
Distribution @ 23 kVRegulator
23 k
V Fe
eder
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
CustomerCustomer
Customer
FuseFuse
FuseFuse
Fuse
Fuse
FeederBreaker
23 k
V Fe
eder
Outage
Momentary Interruption
Fault On Your Feeder
480
Fault occurs here
0
Volta
ge
Time
Recloser opens here
recloses here
Fault cleared
0
7 cycles(~0.1 sec)
13 cycles(~0.2 sec)
~ 1/3 second
Voltage Sag & Momentary Interruption
Breaker Tripped
Squirrel Guard
Fault On Adjacent Feeder
Transformer480 V
Transformer480 V
115 kV Substation
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
Customer Customer
Customer
Fuse Fuse
Fuse Fuse
Fuse
Fuse
FeederBreaker
Transmission @ 115 kV
Transformer
Distribution @ 23 kVRegulator
23 k
V Fe
eder
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
CustomerCustomer
Customer
FuseFuse
FuseFuse
Fuse
Fuse
FeederBreaker
23 k
V Fe
eder
OutageSag
Fault on Adjacent Feeder
480
Fault occurs here
0
Volta
ge
Time
Breaker opens here
Breaker recloses here
Fault cleared
0
7 cycles(~0.117 sec)
Voltage Sag Due To Momentary Fault On Adjacent Feeder
Fuse Blow and Breaker Operation Due to Fault On Adjacent FeederTransmission @ 115 kV
Transformer
Distribution @ 23 kV
23 k
V Fe
eder
FeederBreaker
115 kV SubstationRegulator
23 k
V Fe
eder
Transformer480 V
Transformer480 V
Transformer480 V
Transformer480 V
Customer Customer
Customer
Fuse Fuse
Fuse Fuse
Fuse
Fuse
FeederBreaker
Fault
Customer
Fuse
Open or Blown Fused Cutout
Voltage Sag Due To Momentary Fault On Adjacent Feeder
480
Fault occurs here
0
Volta
ge
Time
Breaker opens here
Breaker recloses here
Fault clearedBy Fuse
0
7 cycles(~0.117 sec) .3 to 2 seconds
Fuse Blow and Breaker Operation Due to Fault On Adjacent Feeder
150.0V
75.0V
0.0V105.83 ms/div0sec 2.12sec
RMS Sag Disturbance PQPager/3100 PQNode
Silverline Plastics 10/26/97 06:44:49.00 PM
Three Phase Wye
2V
Permanent Fault On Distribution Feeder
Transmission @ 115 kV
Transformer
Distribution @ 23 kV
23 k
V Fe
eder
FeederBreaker
115 kV SubstationRegulator
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
Customer Customer
Customer
Fuse Fuse
Fuse Fuse
Fuse
Fuse
FeederBreaker
PermanentFault
Voltage During Permanent Fault
480
Fault occurs
0
Volta
ge
Time
open
lockout after3 tries
0
clos
e
open
clos
e
~ 1 minute
7 cycles
13 cycles 15 seconds 35 seconds
.3 - 2.0 seconds
10 seconds
clos
e
open
Ope
n
Fault On Adjacent Feeder
Transmission @ 115 kV
Transformer
Distribution @ 23 kV
23 k
V Fe
eder
FeederBreaker
115 kV SubstationRegulator
23 k
V Fe
eder
Transformer480 V
Customer
Transformer480 V
Transformer480 V
Transformer480 V
Customer Customer
Customer
Fuse Fuse
Fuse Fuse
Fuse
Fuse
FeederBreaker
PermanentFault
Voltage During Permanent Fault on an Adjacent Feeder
480
Fault occurs
0
Volta
ge
Time
lockout after3 tries
0
~ 1 minute
7 cycles
12 cycles
15 seconds35 seconds
.3 - 2.0 seconds
open
clos
e
open
clos
e
clos
e
open
Ope
n
10 seconds
Time
Quick Trip
6-12 cycles
.3 - 2.0 seconds
13 cycles 15 seconds 35 seconds
lockout
Load Current
FaultInitiated
FaultCurrent
13 cycles
13 cycles
6-12 cycles
6-12 cycles
15 seconds
15 seconds
35 seconds
35 seconds
.3 - 2.0 seconds
.3 - 2.0 seconds
Faulted Feeder
Adjacent Feeder
100%
0%
100%
0%
Voltage
Voltage
FeederBreakerOperation
Substation Voltages During a Feeder Fault
68% Cleared on FirstQuick trip
27% Cleared on Secondand Third Relay
5% Goes to Lock Out
Single Line of Substation
Utility Protection Coordination Schemes & Equipment
Fuse Save SchemeFuse Blow SchemeElectronic RecloserHydraulic RecloserUnderground NetworkElectronic Sectionalizer
Capacitor BanksElectrical utilities use capacitor banks for power factor correction and voltage support.Capacitors are used to meet the reactive power requirements of inductive loads such as motors.Switching capacitors can produce oscillatory transients which may cause tripping of adjustable speed drives.
Capacitor Bank Switching Transient
Line Capacitor Bank
Line Capacitor Bank
Utility’s Power SystemUtility System Overview
Transmission SystemDistribution System
How the System WorksTransmissionDistribution
Why It Works That WayDesign PhilosophyEvents & Causes
Questions?