Uneven CT saturation might be the reason. Taka a disturbance recording of the three phase currents when the motor is started and calculate the residual current.
An old handbook states that a 5P CT at rated current and rated burden has less error than 1 % and 1 one degree. For a 10P CT the amplitude error is less than 3 % and angle error is not specified. I guess these are IEC specs. In practice the errors are smaller at least if the ratio is big and the...
I would like to know the english term used about an arc burning in an electric motor around the commutator.
"Circular arc fault at commutator" or how do you call this phenomena?
Here's an example of a rotor winding failure i.e. a total loss of excitation. This is from a real fault of an 18 MVA generator. Just the P, Q and f were recorded with 50 samples per second. There is no change in the active power at the moment the field diappears...
I'm trying to understand settings from an old SPAJ 3R5 motor protection relay by Stromberg (nowadays ABB). Where could I get a manual of this old relay? Google gives a hit on an ABB page, but it doesn't work.
From the unclear old setting sheet from the customer I read that CT is 800/5 and the...
Question:
If there is a short circuit fault inside the generator or a fault between the generator terminals and the circuit breaker, does it help to immediately switch off the excitation with the CB trip signal? Or is it enough just to start the shutdown procedure after some delay?
I found the same recursive pictures from CargoLaw
http://www.cargolaw.com/2005nightmare_catch-day.html#the-feature
and the last picture appears to be a FAKE.
The IEC 60255-8 thermal model is a simple single time constant model.
The two time constants are by no means for hot and cold but for "running" and "stopped" situations. For generators and cables there may not be any difference between the heating and the cooling time constants.
When the motor...
The secondary inductance will be more near 10 H than 1 mH. If the name plate contains S0, the idle apparent power, that can be used to calculate the winding inductances.
Anyway, I think dpc hit the nail on the head in his second comment:
Having three 700 uF capacitors in a Y-connection gives 350 uF for the line-to-line capacitance. There are two 700 uF capacitors in series: 700/2 = 350.
AMBMI said that with a non-zero fault resistance in an isolated network you get something less than 1.732 Un = sqrt(3) Un for the healthy phase-to-earth voltages. Yes, that is mostly true, but the relation of Uo and fault resistance is actually quite complex.
In fact with certain earth fault...
