FEinTX
Electrical
- Jul 26, 2006
- 25
I need a transformer expert...
Recently, during commissioning of a new 230 MVA 345-34.5 KV transformer we came upon an interesting problem. The LTC controller (Beckwith) was wired to monitor the low-side voltage and thus regulate it to a pre-set value, even though the LTC is built on the high-side of the transformer. When the controller was set in Auto mode w/ the low-side voltage purposely outside the range (lower), the controller issued commands to change to raise the LTC one step, but the new voltage level actually went down.
After some thinking, this made sense. The 345 KV high-side is tied to directly to a very stout grid which is fixed at 345 KV--our relatively small power plant won't move this much. The Beckwith is wanting to raise the voltage at its input. Normally, this voltage is from the high side, so it will issue a command to raise the tap increasing the ratio between low and high side. We are inputting the low-side voltage, however, so now with a higher ratio and a high-side that is fixed at 345 KV, our low-side voltage goes down.
Now for questions:
(1) Someone suggested to us that we simply reverse the up and down outputs between the Beckwith controller and the LTC and our problem is solved. This sounded good until GE-Prolec (the transformer manufacturer) said not to do this. They cited problems w/ the design of the high-side coils saying flux densities would go beyond their design specs if we used the transformer this way. This makes no sense to me, but I'm not a transformer expert. Can anyone explain Prolec's concerns?
(2) Is there another way to make a transformer w/ a high-side LTC regulate the low-side? Basically, we want to keep the low-side set at 34.5 KV regardless of what is happening out on the grid.
Thanks for any help you can offer!
FEinTX
Recently, during commissioning of a new 230 MVA 345-34.5 KV transformer we came upon an interesting problem. The LTC controller (Beckwith) was wired to monitor the low-side voltage and thus regulate it to a pre-set value, even though the LTC is built on the high-side of the transformer. When the controller was set in Auto mode w/ the low-side voltage purposely outside the range (lower), the controller issued commands to change to raise the LTC one step, but the new voltage level actually went down.
After some thinking, this made sense. The 345 KV high-side is tied to directly to a very stout grid which is fixed at 345 KV--our relatively small power plant won't move this much. The Beckwith is wanting to raise the voltage at its input. Normally, this voltage is from the high side, so it will issue a command to raise the tap increasing the ratio between low and high side. We are inputting the low-side voltage, however, so now with a higher ratio and a high-side that is fixed at 345 KV, our low-side voltage goes down.
Now for questions:
(1) Someone suggested to us that we simply reverse the up and down outputs between the Beckwith controller and the LTC and our problem is solved. This sounded good until GE-Prolec (the transformer manufacturer) said not to do this. They cited problems w/ the design of the high-side coils saying flux densities would go beyond their design specs if we used the transformer this way. This makes no sense to me, but I'm not a transformer expert. Can anyone explain Prolec's concerns?
(2) Is there another way to make a transformer w/ a high-side LTC regulate the low-side? Basically, we want to keep the low-side set at 34.5 KV regardless of what is happening out on the grid.
Thanks for any help you can offer!
FEinTX