Today, we will briefly introduce the problem of what is the protection circuit of Cummins generator set.
Reverse power: The reverse power phenomenon is caused by the difference in the speed (frequency) and voltage of the Cummins generator set, that is, one Cummins generator set has positive power, while the other 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 rotational speed is inconsistent). When the voltages are not the same, the unit with high voltage will provide a reactive current and reactive voltage to the unit with low voltage (the ammeter of this unit indicates positive direction), which is equivalent to adding a phase control unit in 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 higher or lower the voltage of another unit, causing a unit to have a reverse power current, and its operating current is about 20% of the rated current. The reverse relay acts, trips, and alarms, but does not stop.
Overcurrent: The rated power of the current Cummins generator set is certain, and its overload capacity is very low, basically about 5% of the rated power, and the allowable load time is 15~30 minutes, up to 60 minutes, beyond this time, Cummins The generator set will heat up, and the wire insulation will be reduced, which will reduce the service life. Therefore, if there is no special requirement when setting the overcurrent protection, the overcurrent protection can be set at 110% of the rated current. During the on-load test, bring the current to 110% of the rated current, and the overcurrent relay will act. Trip, alarm, no shutdown.
Overvoltage: When using Cummins generator sets in parallel, the most fear is that the power supply system will oscillate. Once the voltage of the oscillating system rises, it is easy to cause the insulation breakdown of the electrical equipment and the power supply equipment, and the power supply equipment and the electrical equipment will be paralyzed together. For this reason, the Cummins generator sets used in parallel are equipped with overvoltage protection, and the setting value is 105% of the rated voltage is the best. Short-circuit over-voltage relay, trip and stop, alarm action.
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