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I am not sure we are talking about the same filter. I was talking about an analog low pass filter sitting behind the voltage transformers. I am simulating its behavior before the A/D converter. And from what I know the cutoff frequency = 1/(2*pi*R*C)

with the sampling rate of 1.25 ms that would lead to something like 63 Hz cutoff, which would cause a pretty strong reduction of the 50Hz when using the first-order low pass. But, the relay manual does not reveal the type of filter used. Thanks, pete, that's already something to start with.

Hello all, can anybody tell me what the cutoff frequency of the input low pass filter of a voltage / frequency protection relay, such as e.g. SEG MRN3, would be? The manual says the relay applies an analog filter to get rid of higher harmonics before it applies digital DFT filtering. I am...

dpc, According to wikipedia: # 50 - Instantaneous Overcurrent Relay # 51 - AC Inverse Time Overcurrent Relay so I asked if the definite time OC relay would also trip due to overcurrent at one phase only. BTW, does the Def.time OC relay have an ANSI number as well or does it share 51 with the...

Thank you! a 51 is an inverse time OC element. What about the definite time OC element and instantaneous one?

Hi guys, I am still new to protection system, so don't judge too hard. A 3-phase overcurrent relay at a generator normally monitors each phase and will pick up and subsequently trip the generator even if the current at ONE phase only exceeds the threshold, right? For example due to too high...

Thanks Bronzeado, going back to the 90s sounds good. ;) But I am graduating in 2 weeks, so I will get back at you in a couple of weeks. Best regards

Or maybe these two effects will exactly compensate each other so that the decay has the same rate?!

Hi Bronzeado, I have another thought about the sympathetic inrush. Maybe you could contribute to it?! If I have several (let's say 3) transformers in parallel and one of them is being energized driving the other two into sympathetic interaction, will the sympathetic inrush last longer because...

Thank you! Another question: are instantaneous pickup currents defined in Apeak or Arms? If an instantaneous current relay should operate with a 0,04 sec time delay, I suppose the corresponding curent pickup value is defined in Arms, since the relay has 2 whole periods (50 Hz) to measure the...

Hi guys, what current is usually measured by the overcurrent protective relays installed at synchronous generators below 10 MVA? Do they measure the true rms value (that is, all harmonics) or are some harmonics filtered out? How about the DC offset during a fault or transformer inrush? Is...

Hi folks, a kind of a different question: what is the flow path of the decaying DC offset component in the transformer current? It also appears at the generator. Does it only flow in the generator stator or also the rotor? And what is the return path to the transformer if the generator neutral...

Hi Bronzeado, thanks. I found a paper by you and Yacamini dating back to 1996 with the thorough explanation. I find it pretty good! Regards

Let me express it better: The inrush current of the transformer being energized is predominantly homopolar so that the voltage drop affects only one half-cycle. Let's say the fist half-cycle is positive, then the voltage drop makes this positive value to decrease. The waveform of the opposite...

A somewhat different question regarding sympathetic inrush of transformers connected in parallel or in series. Literature says the offset current of the already running transformer is of opposite polarity to that of the one being energized. Is that because the voltage drop across the system...

oh yes, a capacitor. That makes sense. Thank you!

thread238-222884 Hello, I have read in a certain thesis that the residual flux of a transformer which is de-energized but is left connected to a load will decay to zero. We are talking about immediate decay. I cannot explain to myself how would a passive load be able to do that. Does anyone...

The physical explanation for the DC offset would be the law of the flux linkages, which states that the flux just before the switching event and right after it has to be the same and can't change instantaneously, if that was the question, Bronzeado.

The fact that the inrush current can become negative while the flux stays above zero during the inrush means that each the flux and the current have their own DC offset magnitudes. That I just discovered from looking at some simulations.

Hi Mike, thank you for the input. I just looked up and discovered that the engines are actually kept pre-warmed all the time by district heat. But I don't know what that means in terms of temperature. My guess would be around 80 degrees C, that is 176F. So that should make it possible to ramp...