Fault Current & Instantaneous Protection setting

Would someone explain how the (impedance/Rating) of the generating system effects the way a bus can be connected(two transformers feeding two busses in parallel for redundancy of Primary supply)? I always assumed that the fault Current rating of the bus (being supplied by the feeder/transformer) as well as the impedance of the transformer was what decided the “Instantaneous Protection Setting “of the Transformer/Feeder. Also would you suggest a text books/Internet sites which give me some more info on the philosophy of Protection & Discrimination.

Effect of VVVF drives & PF Capacitors on Power Quality

Mark

I work for a large Iron Ore Company and we run a Bulk PFC/Power Monitoring system. The system is generally well designed and work well. It uses Genius Power Track blocks for monitoring/control of the Cap Banks(total of around 20MVARS). We have two banks which were installed during a recent upgrade and they cause problems. This area has quite a few VVVF drives and the problem was that they would cause the DC link fuses to blow when the banks switched in. The system has time delays for switching in as well as delays so as to ensure the demand has not reduced since the close request was initiated. Some testing was done and someone came up with an idea that the banks should be locked out when the VVVF Drives were in operation and so the PLC was edited to delay closing and opening during operation. This did not solve the problem. We engaged a consultant to do monitoring but when the job was done the current monitoring did not operate so we do not have a result from this option.

Would you be able to give me a step by step explanation of what happens when the banks switch in or out and also the effect of the VVVF Drives being either in operation or on satndby. We have a total of 5 X 15 MVA transformers(Auto tapchanging) fed off the grid and the area where these cap banks is fed from is fed from one of these five 15 MVA transformers. Our incoming voltage is 66 kv and we reticulate 11 kv. The Cap Banks are connected to the 11 kv network of which we run three separate networks(because of the auto tapchangers). The PFC is used to correct the incoming Power Factor and is sized to match the line area loads so we generally end up with near enough to a power factor of 1 in line areas. The two cap banks in question are1.67 and 2.5 MVARS other banks in the syatem are a max value of 4.175 mvar and a minimum of 2.5 mavr. Hopefully I have supplied enough info.

Thanks in advance,

Norm