Parallel Operation Protection of Generator Sets

In fact, the so-called parallel operation of generator sets means integrating two or more generators with the same rated voltage and same phase into the same bus to supply active and reactive power to the system, which is the parallel operation of generator sets. Then we first run one generator and send the generated voltage to the bus. After another generator set is started, it should be paralleled with the previous generator set at this time. When closing, the generator set should have no abnormal inrush current and the shaft should not be subjected to sudden impact. However, during the parallel process, we should consider the problem of the entire current loop. So how to protect the loop?

1.Reverse Power Operation

The reverse power phenomenon is caused by different speeds (frequencies) and voltages of diesel generator sets, that is, one generator set has positive power and the other has negative power. When the voltages are different, the unit with high voltage will provide reactive current and reactive voltage to the unit with low voltage, which is equivalent to adding a camera unit system to the power supply. At this time, the low-voltage unit becomes a large load and receives a large reactive current to maintain the voltage balance of the two units. During monitoring, if the voltage of one unit increases or the voltage of the other unit increases, it will cause reverse current in one unit, and its operating current is about 20% of the rated current. The reverse relay acts, trips, alarms, but does not stop.

2.Overcurrent

The current rated power of Yuchai generator sets is fixed, and their overload capacity is very low, basically 5% of the rated power. The allowed loading time is 15-30 minutes, with a maximum of 60 minutes. After that, the generator set will heat up, and the wire insulation will decrease, thereby shortening the service life. Therefore, there are no special requirements when setting overcurrent protection, and the overcurrent protection can be set to 110% of the rated current. During the load test, when the current reaches 110% of the rated current, the overcurrent relay is activated, trips, alarms, and does not stop.

3.Overvoltage

When diesel generator sets are used in parallel, the power supply system is most afraid of oscillation. Once the voltage of the oscillation system rises, it is easy to cause insulation breakdown of power equipment and power supply equipment, and paralyze the power equipment and power equipment. For this reason, generator sets used in parallel are all equipped with overvoltage protection, and their setting value is 105% of the rated voltage. The overvoltage relay acts to short circuit, trip and stop, and alarm.

It can be seen that before preparing for the parallel operation of generator sets, the speeds (frequencies) of the two units must be adjusted to be the same. And when paralleling, you can adjust the speed of the first or standby unit according to the rotation speed of the synchroscope, so that the rotation direction of the synchroscope is clockwise or counterclockwise, and the slower the better, but the pointer of the synchroscope must be aligned. Finally, after paralleling, observe whether the current and power of the two units are balanced. If the difference is too large, the speed knob can be adjusted to make the power of the two units consistent to safely and reliably protect the circuit.

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