Howdy, I have a unique problem to propose to everyone. I would like some input, as I am looking for an explanation.
First a back round:
I work a power plant, that recently updated the entire electrical system. We have two generators that are configured in a very similar manner. The generator feeds 3 transformers from iso-phase (1 GSU and 2 AUX transformers). The axillary transformers are are all 3 winding transformers that are generator voltage on the primary, and 7200 and 4160 and the secondary and tertiary. For clarity each transformer has a letter identification A or B and feeds either 7200A, 7200B, 4160A, and 4160B. Large loads are split between the buses. All our major fans (4000HP+ are 7200V).
Second the problem (not so much a problem as an unexplained observation):
Lately we have been utilizing our new digital relays to observe voltage fluctuation during large fan starts. A clear pattern has started to develop. When we start a large fan (which would be on the 7200V bus) we actually see a voltage increase in the 4160 of the corresponding transformer. It happens on both units (despite one being 2 times the size of the other) irregardless to how heavily loaded the buses are (loading does slightly change the magnitude).
Little more information:
We are pretty sure the spikes are actually happening. We have testing using other PTs and it happens on both units (which are mostly independed of each other).
The spikes are approximately equal to the voltage dip in the 7200 times the turns ratio with the same time duration (typically 100V for 20 seconds).
The opposite aux transformer sees a very short voltage dip on both buses.
I have my thoughts on why it is happening, but I want to see what your independent thought is.
Thanks
First a back round:
I work a power plant, that recently updated the entire electrical system. We have two generators that are configured in a very similar manner. The generator feeds 3 transformers from iso-phase (1 GSU and 2 AUX transformers). The axillary transformers are are all 3 winding transformers that are generator voltage on the primary, and 7200 and 4160 and the secondary and tertiary. For clarity each transformer has a letter identification A or B and feeds either 7200A, 7200B, 4160A, and 4160B. Large loads are split between the buses. All our major fans (4000HP+ are 7200V).
Second the problem (not so much a problem as an unexplained observation):
Lately we have been utilizing our new digital relays to observe voltage fluctuation during large fan starts. A clear pattern has started to develop. When we start a large fan (which would be on the 7200V bus) we actually see a voltage increase in the 4160 of the corresponding transformer. It happens on both units (despite one being 2 times the size of the other) irregardless to how heavily loaded the buses are (loading does slightly change the magnitude).
Little more information:
We are pretty sure the spikes are actually happening. We have testing using other PTs and it happens on both units (which are mostly independed of each other).
The spikes are approximately equal to the voltage dip in the 7200 times the turns ratio with the same time duration (typically 100V for 20 seconds).
The opposite aux transformer sees a very short voltage dip on both buses.
I have my thoughts on why it is happening, but I want to see what your independent thought is.
Thanks