How to protect the circuit of parallel diesel generator sets

In fact, the so-called parallel operation of diesel generators means that two or more generators with the same rated voltage and the same phase are merged into the same bus to supply active power and reactive power to the system. This is the parallel operation of the generators. Then we start one generator set first, and then send the generated voltage to the bus. After the other generator set is started, it will be paralleled with the previous generator set at this time. At the moment of closing,Generator setThere will be no abnormal inrush current, and the rotating shaft will not be subject to sudden impact. However, we should consider the overall current loop problem during parallel operation, so how should we protect the loop? Next, Haixing Power will give you a brief analysis.

1． reverse work

The phenomenon of reverse power is caused by the difference in rotation speed (frequency) and voltage of the generator set, that is, one generator set has positive power, while the other unit has negative power. That is to say, the unit with negative power becomes a load (the frequency of this unit is low and the speed is inconsistent). When the voltages are different, the unit with higher voltage provides a reactive current and reactive voltage to the unit with lower voltage (the ammeter of this unit indicates positive direction), which is equivalent to adding a camera unit to the power supply system. The unit with low voltage becomes a large load and receives a large reactive current to maintain the voltage balance of the two units (the ammeter of this unit indicates reverse direction). During monitoring, increase the voltage of a certain unit, or increase or decrease the voltage of another unit, causing a reverse current in one unit, and its operating current is about 20% of the rated current. The reverse relay operates, trips, and alarms, but does not stop the machine.

2． Overcurrent

Corresponding to the rated power of the current generator set, its overload capacity is very low, basically around 5% of the rated power. The allowed load time is 15 to 30 minutes, not more than 60 minutes. Beyond this time, the generator set will generate heat and the wires will The insulation will be reduced, which will also reduce the service life. Therefore, there are no other requirements when setting the overcurrent protection. The overcurrent protection can be set at 110% of the rated current. During the load test, bring the current to 110% of the rated current, and the overcurrent relay will operate. Trip, alarm, non-stop.

3． Overvoltage

When using generator sets in parallel, there is a fear that the power supply system will oscillate. Once the oscillation system voltage rises, it will easily cause insulation breakdown of the electrical equipment and the power supply equipment, causing the power supply equipment and the electrical equipment to be paralyzed together. For this purpose, the generator sets used in parallel are equipped with overvoltage protection, and its setting value is preferably 105% of the rated voltage. Short-circuit the over-voltage relay, trip and shutdown, and alarm action.