1 Medium Voltage Reduced Voltage Autotransformer Starter Failures – Explaining The Unexplained – Medium Voltage Reduced Voltage Autotransformer Medium Voltage Reduced Voltage Autotransformer Starter Failures Starter Failures – Explaining The Unexplained Explaining The Unexplained – Larry Farr, Senior Member IEEE Principal Engineer Eaton Electrical Asheville NC Technical Advisor TC-17A IEC Chair of CANENA TC-17A SC-3 Arthur J. Smith III, Member IEEE Vice President Waldemar S. Nelson and Co. Inc. New Orleans, LA • Background Background Medium Voltage Reduced Voltage Autotransformer Starter Failures – Explaining The Unexplained – Medium Voltage Reduced Voltage Autotransformer Medium Voltage Reduced Voltage Autotransformer Starter Failures Starter Failures – Explaining The Unexplained Explaining The Unexplained – TODAY’S AGENDA TODAY TODAY’ S AGENDA S AGENDA • Investigation Investigation • Testing 1988 Testing 1988 • Findings Findings • Testing 2002 Testing 2002- 03 03 • Findings Findings • Solution Solution • Conclusions Conclusions
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Medium Voltage Reduced Voltage Autotransformer
Starter Failures– Explaining The Unexplained –
Medium Voltage Reduced Voltage AutotransformerMedium Voltage Reduced Voltage Autotransformer
Starter FailuresStarter Failures–– Explaining The Unexplained Explaining The Unexplained ––
Larry Farr, Senior Member IEEE Principal Engineer
Eaton ElectricalAsheville NC
Technical Advisor TC-17A IECChair of CANENA TC-17A SC-3
Arthur J. Smith III, Member IEEEVice President
Waldemar S. Nelson and Co. Inc.New Orleans, LA
•• BackgroundBackground
Medium Voltage Reduced Voltage Autotransformer
Starter Failures– Explaining The Unexplained –
Medium Voltage Reduced Voltage AutotransformerMedium Voltage Reduced Voltage Autotransformer
Starter FailuresStarter Failures–– Explaining The Unexplained Explaining The Unexplained ––
TODAY’S AGENDATODAYTODAY’’S AGENDAS AGENDA
•• InvestigationInvestigation
•• Testing 1988Testing 1988
•• FindingsFindings
••Testing 2002Testing 2002--0303
•• FindingsFindings
•• SolutionSolution•• ConclusionsConclusions
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• Background•• BackgroundBackground
Medium Voltage Reduced Voltage Autotransformer
Starter Failures– Explaining The Unexplained –
Medium Voltage Reduced Voltage AutotransformerMedium Voltage Reduced Voltage Autotransformer
Starter FailuresStarter Failures–– Explaining The Unexplained Explaining The Unexplained ––
•• For the past century the AutoFor the past century the Auto--transformer or transformer or ““KorndorferKorndorfer””Starter has been a standard in Starter has been a standard in the electrical industry.the electrical industry.
BackgroundBackground
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•• In the late 1970s, unexplained In the late 1970s, unexplained ““High Voltage StressHigh Voltage Stress”” failures failures started occurring.started occurring.
BackgroundBackground
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Failures Were Occurring WorldwideFailures Were Occurring WorldwideFailures Were Occurring Worldwide•• North Sea Platform 12kV starters failed multiple North Sea Platform 12kV starters failed multiple
times. Problems solved with single phase times. Problems solved with single phase autotransformers. autotransformers.
BackgroundBackground
•• 20,000 hp20,000 hp--15kV starter in British Columbia failed 15kV starter in British Columbia failed four times until surge arresters from the Zero tap to ground four times until surge arresters from the Zero tap to ground were installed.were installed.
•• South America 2400 volt failed multiple times.South America 2400 volt failed multiple times.
•• Gulf of Mexico Gulf of Mexico –– Multiple 5kV starter failuresMultiple 5kV starter failures
•• However, The Sample Rate Was However, The Sample Rate Was only 50,000 Samples Per Seconds only 50,000 Samples Per Seconds and I suspect some level of and I suspect some level of smoothing.smoothing.
•• Confirmed the Test Results From Confirmed the Test Results From 1988 on Three Coil Three Legged 1988 on Three Coil Three Legged TransformersTransformers
(February 2002 High Power Lab in Pennsylvania)(February 2002 High Power Lab in Pennsylvania)
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Dielectric WithstandDielectric WithstandTwo Layers of .005 Nomex 14kV rms for 60 Two Layers of .005 Nomex 14kV rms for 60 SecsSecs..
Medium Voltage Reduced Voltage AutotransformerMedium Voltage Reduced Voltage Autotransformer
Starter FailuresStarter Failures–– Explaining The Unexplained Explaining The Unexplained ––
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ConclusionsConclusions
•• When controllers are configured for When controllers are configured for transition on current sensing below 125% transition on current sensing below 125% FLA, high voltage potential is reduced but FLA, high voltage potential is reduced but not eliminated.not eliminated.
•• When autotransformer starters are forced When autotransformer starters are forced to transition before they reach near full to transition before they reach near full speed, high voltages are generated on the speed, high voltages are generated on the 0% taps0% taps
ConclusionsConclusions
•• Vacuum contactor autotransformer Vacuum contactor autotransformer starters and starter retrofits require starters and starter retrofits require surge arresters even if no problems surge arresters even if no problems were encountered with air break were encountered with air break contactorscontactors
•• When 6 kV distribution surge arresters are When 6 kV distribution surge arresters are installed on a 4,160 volt circuit from the 0% installed on a 4,160 volt circuit from the 0% tap to ground, the voltage is clamped to 13 tap to ground, the voltage is clamped to 13 kV without the resultant high kV without the resultant high dv/dtdv/dt across across the transformer coil regardless of transition the transformer coil regardless of transition currentcurrent
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ConclusionsConclusions
•• Care must be taken so the Metal Oxide Care must be taken so the Metal Oxide arrestors do not conduct near normal arrestors do not conduct near normal operating voltages.operating voltages.
•• The 15kV Autotransformer Starter in The 15kV Autotransformer Starter in British Columbia was set on the 55% British Columbia was set on the 55% tap. The starter used MV Circuit tap. The starter used MV Circuit Breakers. Therefore all Breakers. Therefore all autotransformer starters need surge autotransformer starters need surge arrestors zero tap to ground or across arrestors zero tap to ground or across the VI,s. the VI,s.