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?