Recent content by Borti

I agree with marmite, line to gnd fault on the 20 kv line is probably the biggest concern. I assume that the line would have some kind of effective grounding, and an ungrounded source is introduced by connecting a generator through a transformer with delta primary. Your line protection should...

You can check this site http://www.ipc-resistors.com/default.asp. They have complete solutions.

If you can rule out the transformer problem, try sectionalizing your load while monitoring the currents.

An open delta winding would cause similar problems. I would test transformers ratio and winding resistance.

You can add new curves or create new devices in EDSA. Their user manual explains the procedure. EDSA adds new devices but you have to send them the curves and manuals. I do not use EDSA anymore but I believe they have ITEKTOR trip units in their data base. Try search under ABB and Cutler-Hammer...

Hi Fuselink, No need to explain the through fault protection curve. Stevenal, dpc and DanDel have done it already. Ideally you should plot the breaker curve and then make a decision on the fuse rating but since you have an old oil dashpot trip unit, I believe that the lowest possible fuse...

FuseLink, What is the transformer winding arrangement? If it is delta-y with the neutral grounded you have to look at the ground fault on the secondary. The transformer curve has to be shifted by the factor of 0.58. Then you can look at the fuse curve. When selecting the fuse on the...

I agree that transfer trip is the safest way to isolate the faulted feeder on both ends but it is costly. I know instances where the distributed generation was installed without the transfer trip capabilities. Since your load does not exceed the generator rating it makes sense to use sensitive...

Humble2000, I do not know what you mean by "transformer short time curve". My assumption is that you were dealing with a transformer through-fault protection curve. The reason why your curves are the same is that 1000, 1500 and 2000 KVA transformers (3-phase) are category II transformers and the...

The first thing you should check is the short circuit rating of the low voltage switchgear. It is very likely that it is not high enough to allow for the paralleling of the two transformers.

The software packages I have worked with always asked for the ct ratio. The only time the ct ratio was not required was when you use LV breakers. Since you mentioned LTP and 750 kV transformer, it appears that you are dealing with small distribution transformers. You will have to enter breaker...

Try G&W Electric http://www.gwelec.com/product_current/hclimite.cfm

I suggest reading IEEE Std. 242 (Buff Book). There is a good chapter on transformer protection.

Max. and min. fault current is very important in feeder protection. Whether you use reclosers or just overcurrent relays, you should have one element covering the entire feeder and one for close faults. The minimum fault current you would consider is the one calculated for the fault at the end...

I would check the slope of the differential relay. That may take care of the CT saturation problems if you have any. The currents during the external fault should be in the restraining region. When it comes to 59N, neutral displacement relay, your time delay may be too short and you trip on the...