Transformer inrush current problem at wind farm
Transformer inrush current problem at wind farm
(OP)
I am currently working within the wind farm sector (which is a new area for me and my company) can anyone help with the following problem;
Our companies normal arrangement for the connection of wind farm generators to a utilities network is via a daisy change set-up (ie Transformers 33/.690kV, 1.5MVA linked together with 33kv cables on one continuous circuit without 33kv RMU’s.). This form of connection has caused a problem at one site; when the transformers are energised the inrush current from the string of transformers causes a voltage dip on the utilities network that is outside their licence standard.
Is there any other solution to this problem other that fitting 33kv RMU’s at each transformer, along with a supervisory control scheme that allows each transformer to be energised individually? This would no doubt solve the problem but won’t help the bank balance.
Our companies normal arrangement for the connection of wind farm generators to a utilities network is via a daisy change set-up (ie Transformers 33/.690kV, 1.5MVA linked together with 33kv cables on one continuous circuit without 33kv RMU’s.). This form of connection has caused a problem at one site; when the transformers are energised the inrush current from the string of transformers causes a voltage dip on the utilities network that is outside their licence standard.
Is there any other solution to this problem other that fitting 33kv RMU’s at each transformer, along with a supervisory control scheme that allows each transformer to be energised individually? This would no doubt solve the problem but won’t help the bank balance.






RE: Transformer inrush current problem at wind farm
Could you replace the HV circuit breaker with one that has pre-insertion resistors or with a single phase operating mechanism and use a point-of-wave relay to initiate closing? Either method will limit the inrush current.
RE: Transformer inrush current problem at wind farm
RE: Transformer inrush current problem at wind farm
You could also consider US style deadfront padmounts with two loadbreak elbows per phase (in and out). This would not provide a switch for each transformer, but you could selectively connect portions of the transformers using the loadbreak elbows.
RE: Transformer inrush current problem at wind farm
Rcwilson,
‘pre-insertion resistors’ I managed to get some information on this, and I’m beginning to understand the concept. Within the information I have received it makes comment on ‘significant maintenance requirements’ have you any idea of what these requirements might be? As it doesn’t say within the documents I’ve received.
‘single phase operating mechanism’ I’ve had less success with this, can you explain what is meant by this? (Does the CB switch in one phase at a time?)
jghrist,
I’ve seen one wind farm site which has US style padmounted transformers with internal withdrawable fuses, I wasn’t aware that this type of transformer style can also come with integral oil switches. However, I’m not sure how this would help with the inrush current problem when energising a radial circuit. The idea behind the RMU CB set-up with supervisory control was so that each transformer could be switched in individually from one central point back at the main switch house.
‘US style deadfront padmounts with two loadbreak elbows’ I’m not sure what you mean here, can you explain? (Is this a MV cable ‘piggyback’ arrangement, which allows the MV cables to be disconnected from the transformer, but remain part of the ‘live’ circuit?)
Thanks again
RE: Transformer inrush current problem at wind farm
The load break elbows are Medium Voltage versions of an extension cord with a plug and receptacle. The cabel to the Xfmr HV bushing is terminated in an elbow that can be plugged and unplugged hot using a hot stick. It is a manual operation.
RE: Transformer inrush current problem at wind farm
For example you may find that you can energize half the transformers on a feeder at a time without causing a problem to the network. In that case you could install a switching device halfway down each feeder, so that only half the transformers on the feeder are energized simultaneously.
Although load break elbows are theoretically good for this purpose, I've not met any people on wind farms who like using them for this purpose in practice. I would prefer a proper switch like a RMU or a sectionalizer.
Windie
RE: Transformer inrush current problem at wind farm
http:
http://www.sandc.com/products/windenergy.asp
RE: Transformer inrush current problem at wind farm
Let's say you have 10 generators (on transformers numbered 1-10) daisy chained together and you figure you can only handle the inrush of two transformers. If you disconnect the the load side elbow of every other transformer, then energize transformers 1&2 - connect the elbow on transformer 2 to energize transformers 3&4 - connect the elbow on transformer 4 to energize transformers 5&6 - and so on until all 10 are energized two at a time. Maybe pretty time consuming, but you eliminate the need for any switches.
RE: Transformer inrush current problem at wind farm
RE: Transformer inrush current problem at wind farm
http:
Ken Smith
Dr K S Smith
Mott-MacDonald, Power Systems Division
Glasgow, Scotland.
RE: Transformer inrush current problem at wind farm
I agree with you on using the loadbreak elbows to switch 3Ø transformers. Better get the under oil 3Ø switches.
RE: Transformer inrush current problem at wind farm
Thanks for the link to your paper hvcad (very useful)