Normally different power generating units feed to the grid. But all transformers impedance levels may not be the same. How the circulating currents will suppress in the transformer.
Transformer parallel operation avoid such a way that to minimize the circulating currents between the transformers.
We have two Generator transformers (11/66KV) having separate 30MW 11KV Generators. %impedance and MVA rating of both of them are not same. One is having 20% impedance & 45MVA while other has 11% impedance & 37.5 MVA. We intend to connect them in parallel at 66KV side .Can we connect? I understand that Xmers can't be put in parallel on same source but in this case the source of the both Xmers are different. Please help me.
Ketan Shah... yes they probably can be paralleled! However following are several comments you must consider:
1. If they are to be paralleled on the 11kV side, then the increased short-circuit level produced by both generators must not exceed the capacity of the 11kV circuit-breakers and switchgear bus-bracing!
2. There is a similar concern if they are to be paralleled on the 66kV side of their xfmrs, but it is not nearly as severe!
3. Finally, once the above concerns are settled, then they can be paralleled by adjusting their tap-settings so that the resultant circulating-current does not materially increase transformer losses!
I suggest you search the Control.Com Archives for similar topics. If your search proves unsuccessful, then feel free to contact me.
when the %impedance are same, both the transformers that operate in parallel will share same amount of load. whereas it is possible to operate them even if %impedance are not equal but it results in flow of circulating currents in secondary and also in primary which results in unequal load sharing between the transformers.
I want to replace a 2MVA transformer...with all the technical parameters same.
What rest I will be needing to concentrate on.....any mechanical parameter?????
Let's say I have four paralleled transformers, all with equal X/R ratios. Is the net X/R ratio the same with all four in parallel, or do I have do divide by four?
Tim... your question can't be answered because you left out "stuff!" What about their capacities, impedances, and no-load voltages.
Capacity and Impedance influence their "sharing of load" capabilities, while no-load voltage differences affect circulating-current magnitude. X/R ratios have little effect, unless their differences are extreme.
> How do I calculate the circulating current for the following problem:
> I have 2 transformers in parallel. One 12/20 MVA 67/4.16kV, Z=7.29% and another 7.5/9.375MVA 70/4.360kV (because of how the taps are set) and Z=7.88%.
My problem is similar to the one posted by mani on 27 November, 2007. Need some guidance calculating circulating current.
Stacy... If I have properly interpreted your query, the problem is quite different!
Mani's case consisted of two Xfmrs having HV-side voltages that were reasonably close, i.e., 70kV and 67kV. In your case one HV-side is double that of the other.
Can you provide some detail about how their HV-sides eventually (perhaps via intermediate Xfmrs) connect to the same source? Or, contact me at [email protected]
Phil - I posted before I thought, which is why I'm having this "duh" moment. Of course there is another XFMR involved...
650MVA, 9.21%Z, 230/115kV
I've been in the Transmission utility business all my career, until recently taking a Distribution job. I'm used to calculating restrike voltage for a Transmission loop to determine if a switch can be used to break the loop, which is a calculation that requires conductor size and mileage for impedance. Is there a way to calculate a good educated guess at circulating current in the loop in my case without having the Transmission Line data (other than kV and XFMR MVA, Z, and ratio)?
I'm still a rookie at thinking from a Distribution point of view, but am convinced that tools can be developed for better choices in switching the system.
Stacy... you are correct about my screwing up the bus IDs.
Frankly, I don't believe you will have any appreciable circulating-current in the loop! The reason is that the existing xfmr-taps can be tweaked to reduce circulating-current to an acceptable minimum.
Do you still want to determine circulating-current within the 3-transformer loop arrangement using nominal Xfmr Capacities and Voltages?
If so, then the first step is to reduce the Xfmr-side of the loop to an equivalent Xfmr. Do you know the math?
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