We all know that in the power system, the shorter the fault process is, the better, the shorter the fault time is, the less the damage to the equipment is, and the more favorable it is to the safe and stable operation of the power grid. However, the shorter the fault process is, the more difficult it is for us to find it. We need to capture the fault process through fault recorder.
When we see the fault oscillogram, we first need to roughly judge what fault happened and how long the fault lasted through the knowledge learned by the composite sequence network of power system.
Secondly, the zero crossing point of a certain phase voltage or current is taken as the phase reference to check whether the current voltage phase relationship before fault is correct, whether it is positive phase sequence, and how many degrees the load angle is.
Then, the zero crossing point of the fault phase voltage or current is used as the phase reference to determine the phase relationship of the fault phase current and voltage. Draw a vector graph and analyze it.
According to the fault recording graph, the key points of two-phase short circuit fault are analyzed
The two-phase current increases and the two-phase voltage decreases; There is no zero sequence current or voltage.
When the current increases, the voltage decreases to the same two phases.
The two fault phase currents are basically reversed.
The fault phase voltage is about 80 degrees ahead of the fault phase current; The zero sequence current is about 110 degrees ahead of the zero sequence voltage.