Single-phase grounding protection of generator stator winding
Single-phase grounding protection of generator stator winding For safety reasons, the generator shell is therefore grounded. a certain phase winding of the generator stator is damaged. A short to the enclosure that occurs is a single phase ground. The risk of single-phase grounding mainly lies in the fact that the arc at the fault point burns the stator core, extends the damage to the winding insulation, and further develops it into a turn-to-turn short circuit. turn or a short circuit between phases. circuit, and even causes more serious damage to the generator.
Characteristics of single-phase grounding of the stator winding
Assume that single-phase grounding occurs at the stator winding. A phase away from the neutral point S, then the phase-to-voltage faulton earth UAD=0, this is not a fault. Phase voltage is line voltage. The zero sequence voltage at the fault point A is the phase voltage and the voltage is proportional to S, i.e. the further the fault point is from the neutral point B, the higher the zero sequence voltage. C In the past, it was thought that the generator stator winding was fully insulated and the operating voltage near the neutral point was low, making it difficult to establish a grounding point. Even if a grounding point occurs, grounding current occurs. is small and will not damage the iron core. Therefore, grounding is permitted to protect the neutral. There is a certain dead zone near the point. U Ground point voltage However, actual operation experience shows that even if the ground current is very small, if it is not discovered in time and the time ofcontinuous operation, it will cause serious damage to the iron core at the same time, water. -factory used cooled unit Considering that water leakage in the stator winding near the neutral point is very likely to cause insulation damage, zone-free stator winding grounding protection dead, i.e. a 100% protection zone, must be installed. Stator Grounding Protection: Generally, generators are equipped with two types of grounding protection. One is UB. In order to avoid the influence of higher harmonics such as the third harmonic, the relay is equipped with a low-pass filter to suppress harmonic voltage. , notably the influence of the third harmonic.
When near the neutral point of the generator stator winding, the zero sequence voltage is low. If the zero voltage is lower than the operating voltage of the voltage relay, the95% stator ground protection. does not work. Therefore, 100% earth protection of the stator with external power supply is ensured. The basic principle is to inject a generator grounding protection opening harmonic voltage filter 1/4 frequency voltage into the generator stator. During normal operation, between the stator and the grounding point, only the capacitor current flows between. them, and the feedback voltages at the neutral point of the generator and the ground point on the high voltage side of transformer A cancel each other out. When the insulation resistance is ∞, it displays 0; when directly grounded, it shows 100%. The set alarm value for 100% ground protection is 5%, the trigger value is 55%, and all switches are tripped.
Not less than 0.5 megohm. In the general linesrales at low voltage (400 V level and below), the insulation of newly laid lines should not be less than 0.5 megohm (between lines and lines and between lines and earth); the resistance should not be less than 1 megohm/kilovolt or 1 kohm/Volt.