Search results for query: *

If 10 kA is largest possible calculated fault current (i.e. 3phase short circuit) the real fault current will be always smaller. So if you want to have the F50 element trip you could set it to a smaller threshold (i.e. 8 kA). Of course the situation can be more complicate (i.e. close to the...

I'm evaluating the overcurrent settings of an ABB REF 543 relay. I'm using the SKM software. The 51 element has been set with an extremely inverse characteristic and, looking at the time current diagram, at high currents it should be faster than the 50 element. The SKM software doesn't show that...

I apologize rbulsara but even if there is a load unbalance the vectorial sum of the phase currents is zero if no grnd fault is present. So under these ideal conditions the 51N element won't pickup. I think that in this case the phase CTs reacted differently during the fault transitory so the...

A core CT (toroidal CT enclosing all phases) or 3 CTs using Holmgreen connection (the CT current vectors are summed together) are not sensitive to unbalanced loading or to ph-ph faults not involving the ground. Indeed both configuration are measuring the 3I0 (zero sequence) current which is...

I mostly agree with Alehman; the other asynchronous motors should be quite big (big time constants, big inertia) to produce a so low decaying voltage for so many cycles. Other stuff: the relay is tripping in about a cycle. I wonder why the 51N element has been set with no delay. It seems that...

Yes, one phase current exceeding the threshold is usually enough to trip a 51 (or considering that we are protecting a generator a 51V ) element.

I think it depends on the manufacturer. Basically any relay has a low pass analog filter. Then simple over current relays are usually calculating the RMS value simply integrating in a discrete way (samples) the sinusoidal current wave. In that case the DC component and harmonics not cleared by...

I have basically no sales experience but 15 years of working experience in the protection art. I think that my role should be providing technical support both to the customers and to the sales people. However there are so few people here that probably my responsibility field won't be clearly...

I think it's related to the fuse minimum melt and to the fuse maximum clear characteristic. For every current value you have a minimum time at which the fuse starts melting and a maximum time at which the fuse cleared for sure the fault. Going to the vertical (first on the left) part of the...

I'm evaluating the possibility to join SEL. I'm based in Europe. What do you feel about the possibility to sell the SEL relays in the european market? I know their relays quite well from a technical point of view and I think they are impressive. I'm not sure about the commercial side here in...

A trip threshold equal to 2xIn = 616 A could make sense and is quite common in the practice. Please consider that the transformer damage characteristic is starting at about 2In.... In any case you can protect the transformer against overload with the relay at the secondary side set at about...

Did you try searching for "grading margin" too? You should find something useful (i.e. 2nd finding in the list)

It could be interesting to know the level of 2nd harmonic measured by the 7UT513 just before the trip. I know that for new transformers the generated 2nd harmonic level during the energization is lower so a typical value of about 10% should be used to inhibit the differential trip. Perhaps the...

Stason, please could you attach your PF .dz file with your project? I hope that your company policy could allow that. I have some experience with Power Factory and I would like to take a look. Moreover please consider that the PF differential relay models can include 2nd harmonic measurement and...

I think you should start asking: - earth fault current value - grounding system (low R, high R, Peterson coil) - CT connection (core CT or serial connection of the phase CTS) - CT data (ratio) - system configuration (voltage level, how many parallel branches, branches lengths) You could need an...

Perhaps I read too quickly but what about the negative sequence element of the generator protective relay? I think that for this size of machine it should be set about 8%In and it should disconnect the generator quite quickly. Otherwise we could have a quite dangerous overheating of the...

l5pl is saying that the E/F element is tripping in 300 ms. It means that the 51N element is tripping and that the I0x3 is more than 20 A but less than 30 A. The peak above 30 A is lasting less than 0.05 s, otherwise the 50N element would trip.... Anyway I agree with Slavag: as general rule the...

Ok Folks! Thanks you for all your answers and suggestions! I think I understood something more...now. I think that the solution will be overrating the CT. The choice should be a 500/1 CT.

Hi Slava, yes Rwire is taking care of 2 times the wire length. It's correct in my calculation , anyway thanks for pointing that out; it was not clear in what I wrote. By the way can somebody confirm that a IEC Class P CT can be approximately transfered into the IEC Class PX (BS Class X)...

Marmite, yes I took a look to this manual but I didn't find anything.... Perhaps I simply skipped the right page. Anyway I think that for a low impedance line differential as the P521 Kt is really 1. Some exotic values are available for the high impedance differential devices but nothing else...