The way of generator protection circuit
The phenomenon of reverse power is caused by the difference in speed (frequency) and voltage of the diesel generator set, that is, one diesel generator set has positive power, while the other unit has negative power. That is to say, the unit with negative power becomes a load at this time (the frequency of this unit is low and the speed is inconsistent). When the voltages are different, the unit with high voltage provides a reactive current and voltage to the unit with low voltage (the ammeter of this unit is positively indicating), which is equivalent to adding a phase-adjusting unit to the power supply system. The unit with low voltage becomes a large load at this time, and receives a large reactive current to maintain the voltage balance of the two units (the ammeter of this unit indicates the reverse direction). When monitoring, adjust the voltage of a certain unit to a higher level, or lower the voltage of another unit, causing a unit to have a reverse current, and its operating current is about 20% of the rated current. The reverse relay operates, trips, and alarms, but does not stop the machine.
The rated power of the current diesel generator set is certain, and its overload capacity is very low, basically about 5% of the rated power. The allowable load time is 15-30 minutes, and the maximum is no more than 60 minutes. Heat, wire insulation will be reduced, which reduces the service life. Therefore, if there is no special requirement when setting the over-current protection, the over-current protection can be set at 110% of the rated current. During the load test, the current is brought to 110% of the rated current, and the overcurrent relay operates. Trip, alarm, non-stop.
When diesel generator sets are used in parallel, the power supply system is most afraid of oscillation. Once the oscillation system voltage rises, it is easy to cause insulation breakdown of the electrical equipment and the power supply equipment, and the power supply equipment and the electrical equipment are paralyzed together. For this reason, the diesel generator sets used in parallel are all equipped with overvoltage protection, and its setting value is 105% of the rated voltage, which is the best. Short circuit the overvoltage relay, trip and stop, alarm action.