When coordinating a feed with 3 primary 13.2kv, Delta/Wye 1500kva transformers conntected in a radial loop, how do you account for having all three transformers energize at once, what is the factor you multiply by to make sure your primary protective device (SEPAM 40 Relay) does not trip if this occurs?
Radial Feed With Three 1500KVA Transformers, Combined Inrush?
- Thread starter robgrant3
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mayanees
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- Westminster, MD
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- Electrical Engineer and Master Electrician
inrush...
inrush...
The inrush is actually the sum of the three devices, which is as high as (8-12X) * 3.
It won't be that high, but if I'm setting relays, that's what I calculate to.
The summation may dictate that the three never be energized together.
JM
inrush...
The inrush is actually the sum of the three devices, which is as high as (8-12X) * 3.
It won't be that high, but if I'm setting relays, that's what I calculate to.
The summation may dictate that the three never be energized together.
JM
ron
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Generally I try to step load, so that there is a delay between transformer inrush. If no delays, then in a similar fashion to JM's, I take the full load current and multiply it by the number of XFMRs then times 12. If that is higher than the inst settings on my relay, then I set it to the maximum value and cross my fingers.
mayanees
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- Westminster, MD
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- Electrical Engineer and Master Electrician
inrush comment
inrush comment
Agreed Ron, that it's a safer approach to energize the xfmrs separately.
I grew up in an industrial plant where there were two (2) 15kV breakers that fed three (3) transformers each.
The transformer primaries had 15kV, 600A manual fused switches.
The ideal way to bring the plant up would have been to energize each 15kV line with open disconnects on the xfmr primaries, then close each disconnect switch.
However, the real-world way, and the way that worked, was to never touch the switches - keeping them closed, and energize the each 15kV breaker picking up three (3) transformers at a time.
It was almost a necessity to do it that way because the switches were prone to cable misalignment which was evident during the biannual PMs, where the switches were exercised. On several occasions the switches broke during PM operation, and were left in the closed position until 2 years later when the appropriate parts were replaced.
JM
inrush comment
Agreed Ron, that it's a safer approach to energize the xfmrs separately.
I grew up in an industrial plant where there were two (2) 15kV breakers that fed three (3) transformers each.
The transformer primaries had 15kV, 600A manual fused switches.
The ideal way to bring the plant up would have been to energize each 15kV line with open disconnects on the xfmr primaries, then close each disconnect switch.
However, the real-world way, and the way that worked, was to never touch the switches - keeping them closed, and energize the each 15kV breaker picking up three (3) transformers at a time.
It was almost a necessity to do it that way because the switches were prone to cable misalignment which was evident during the biannual PMs, where the switches were exercised. On several occasions the switches broke during PM operation, and were left in the closed position until 2 years later when the appropriate parts were replaced.
JM
ron
Senior Member
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- New York, 40.7514,-73.9925
If I recall, the 12xFLA is found in the ANSI standards for transformers.
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