Loading Power Transformers Beyond Nameplate Ratings(1)
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Transcript of Loading Power Transformers Beyond Nameplate Ratings(1)
7/28/2019 Loading Power Transformers Beyond Nameplate Ratings(1)
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“Ratron”
Loading Transformers Beyond
Nameplate Rating
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Outline
• Background
• IEEE C57.91-1995• Calculations
• Benefits and Applications
• Conclusions
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• Background
– Most utilities limit their transformers to
nameplate ratings
– Emergency ratings do not exist
– Usually a rating philosophy is not in place
– Settings of overload relays is inaccurate
– Dispatchers reroute loads or load shed
costumers
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– IEEE Guide for Loading Mineral-Oil-Immerse
transformers (Std C57.91-1995)
• Transformers can be loaded beyond nameplate
ratings during critical conditions and peak hours• Offers a method to calculate continuous, long term
emergency and short term emergency ratings
• Offers a method to calculate the loss of life of the
transformer
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• Using the IEEE C57.91 standard to
calculate:
– Normal loading
– Long term emergency
– Short term emergency
– Loss of life
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• Normal Life expectancy loading
– This results when the transformer is operated
continuously at a hottest spot conductor
temperature of 110 deg C
– The standard allows a maximum temperature
of 120 deg C only if the transformer has
operated below 110 deg C for longer periodsof time
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• Planned Loading Beyond Nameplate
Rating
– Transformers that do not work at a continuous
temperature of 110 deg C, can be loaded to a
maximum temperature of 120-130 deg
– Loss of insulation life should be considered on
the length of time at this temperature
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• Long Term Emergency Loading
– During contingency conditions, transformers
hottest spot conductor temperature can reach
120-140 deg C
– Time will depend on loss of life
– It is expected that such occurrences happen
only 2-3 times during the life of thetransformer
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• Short Term Emergency Loadings
– During second or third contingency problems,
the transformer can be allowed to reach a
maximum hot-spot conductor temperature of
180 deg C
– Maximum time of 2-3 hours and an
occurrence of once or twice during the life of the transformer
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• Calculations with Ratron:
– Using the standard to calculate transformer
ratings can be time consuming and difficult
– Ratron makes it easier for the user to input
data he is familiar with and data that is
available to him
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• Data Required
– Top-Oil temperature rise above ambient (test
report)
– Winding average temperature above ambient
(nameplate 65 or 55deg C) (nameplate)
– Tank radiator oil capacity (nameplate)
– Tank and fittings weight (nameplate)
– Cooling mode (FOA,OA, FA) (nameplate)
– Load and no load losses (test report)
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Input Tab
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Results
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The Grid Tab
Here you can edit
load profile and
ambient temperature
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Graphical tab
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• Benefits and Applications
– Transmission Planning• Apply transformer emergency ratings for power
flow and contingency analysis – Real time operations
• Prepare dispatching centers with emergencyratings until they mitigate power failures
– Relay settings• Set overload relay settings based on the calculated
emergency ratings of the transformer
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• Benefits and Applications
– When two transformers are in parallel, emergency
ratings can help you know how much the other
transformer can be overloaded.• Rating Philosophies
– Ratron offers an easy way to create transformer rating
philosophies
• NERC compliance – Ratron allows you to back up your methodology and
gets you ready for NERC auditing
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Please visit our website for more informationwww.synchrogrid.com