Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
Underground Transmission Capacity Increasesfrom Dynamic Rating Analysis
Erich Schoennagel, PECenterPoint Energy
Background
In 2000, CenterPoint Energy began an ampacity study of 138kV Polk to Garrott circuitAddition of new Midtown SubstationInvestigate methods to increase capacity
Circuit Detail
138kV UndergroundHPFF Cable8 inch pipe2500 Kcmil conductorOil Dielectric Rated 257 MVA Installed in 1966
Circuit Route
Downtown Houston12,300 feet
Approach
Evaluate dielectric fluid for evidence of agingEvaluate paper insulation agingInstall DTS fiber for temperature profileEvaluate impact of crossing pipe-type cable circuit
Testing
DGA test on oil performed by Detroit EdisonField Dissipation test performed on paper insulationResult showed cables virtually un-aged from initial installation
DTS Installation
Distributed Thermal Sensing (DTS)Installed in parallel ductMulti-mode fiber optic
DTS Midtown to Polk Hot SpotHot Spot
Ampacity Considerations
Association of Edison Illuminating Companies CS2 recommends reducing max conductor temperature from 85C to 75C when environmental conditions are unknownCenterPoint Energy followed AEIC and rated circuit at 75CStudy of circuit allowed 85C uprateTypically this would increase ampacity by 20%
Unfortunately, even with a 10C increase, the result was a 3.4% decrease in ampacity due to crossing circuit hot spot
DTCR Consideration
Polk to Garrott circuit has a cyclical load patternShort duration of high loadsThe long thermal time constant of underground HPFF circuits is approximately 130 hours
Load Pattern
DTCR Model
Modified to support a real time temperature interference from a measured sourceThis was used to model heating influence from a cable crossingRun in simulated mode using summer 2000 data
DTCR Result
Using summer 2000 data, DTCR showed an increase of almost 21% in dynamic rating over the conventional book rating
DTCR Components
ThermocouplesSCADASimple PC
DTCR Output
Calculated conductor temperatureReported AmperageAllowable AmperageInput parametersTime remaining to thermal overload
0
200
400
600
800
1000
1200
1400
1600
07/02
/07 00
:00:00
CDT
07/09
/07 02
:30:00
CDT
07/16
/07 05
:00:00
CDT
07/23
/07 07
:30:00
CDT
07/30
/07 10
:00:00
CDT
09/06
/07 04
:00:00
CDT
09/13
/07 06
:30:00
CDT
09/20
/07 09
:00:00
CDT
09/27
/07 11
:30:00
CDT
10/04
/07 05
:30:00
CDT
10/11
/07 08
:00:00
CDT
10/18
/07 10
:30:00
CDT
10/25
/07 13
:00:00
CDT
11/02
/07 07
:00:00
CDT
11/09
/07 08
:30:00
CST
11/16
/07 11
:00:00
CST
11/23
/07 13
:30:00
CST
11/30
/07 16
:00:00
CST
12/07
/07 11
:00:00
CST
12/14
/07 13
:30:00
CST
12/21
/07 16
:00:00
CST
01/05
/08 22
:50:00
CST
01/13
/08 01
:20:00
CST
01/20
/08 03
:50:00
CST
01/27
/08 06
:20:00
CST
02/02
/08 18
:00:00
CST
02/06
/08 21
:00:00
CST
02/11
/08 00
:00:00
CST
02/15
/08 03
:00:00
CST
Dynamic Normal Rating Static Normal RatingActual (amps) Static 300 hr Rating
Polk to Midtown Load History
Am
pere
s
Polk to Midtown Ratings (2/29/08)
Static Normal Rating = 1035 amperes300 hour Rating = 1180 amperesDynamic Normal Rating = 1311 amperesEmergency
Thermal Limit
What have we gained?
TimeEstablish a five part upgrade plan– Dynamic rating– Shuttle oil– Additional pipe for circulating
Design is ready
– Reconductor– Add a parallel circuit
DTCR Implementation
Ampacity increaseRTO tool during high circuit loadGrid operator predictive tool
Future Use of DTCR
XLPE Underground CablesOverhead circuits
Summary
Ampacity study of Polk to Garrott showed a decrease in book rating using steady state calculationsDTCR takes advantage of cyclical load pattern and thermal response of UG cable Dynamic rating uses real-time temperature and load inputPolk to Garrott ampacity increased almost 21%System operators have a better information toolMarket predictive tool
Project Team
EPRI - Cable system assessment- DTCR developmentPower Delivery Consultants, Inc.- DTCR development- Ampacity study and condition assessmentUlrich Associates, Inc.- Software development
Questions?
DTS Correlation
Utilities Using DTCR
Southern California Edison (XLPE cable)PECO Energy (pipe type cable)BC Hydro (submarine SCFF cable)United Illuminating Co. (pipe type cable)ComEd (XLPE cable)