How to protect the circuit of the diesel generator set

In fact, the so-called parallel operation of diesel generator sets means that two or more generators have equal rated voltages and the same phases, and are incorporated into the same busbar at the same time to supply active and reactive power to the system. This is the parallel operation of the generator. Then we are running a generator set first and then sending the generated voltage to the busbar. After the other generator set is started, it is parallel to the previous generator set. At the moment of closing, the generator set will not experience abnormal impact current, and the shaft will not be hit suddenly. However, when we carry out parallel processing, we should consider the overall current loop problem. So how should we protect the loop? Let’s give you a brief analysis below.

1. The phenomenon of reverse power

and reverse power is caused by different speed (frequency) and voltage of the generator set, that is, one generator set has positive power, while the other unit has negative power. In other words, the unit with negative power becomes a load at this time (the unit has a low frequency and inconsistent speed). When the voltage is different, a unit with a high voltage provides a reactive current and reactive voltage to a unit with a low voltage (the positive indication of the ammeter of this unit), which is equivalent to adding a camera set to this power supply system. A unit with low voltage becomes a large load at this time, and receives a large reactive current to maintain the voltage balance between the two units (the ammeter inverse indication of this unit). During monitoring, the voltage of one unit is increased, or the voltage of another unit is high or low, causing a reverse power current to be produced by one unit, and its operating current is about 20%. The reverse relay operates, trips, and alarms, but does not stop.

2. The

current generator set has a corresponding rated power, and its overload capacity is very low, basically around 5% of the rated power. The allowable loading time is 15 to 30 minutes, not exceeding 60 minutes. After this time, the generator set will heat up, wire insulation will be reduced, which will reduce the service life. Therefore, if there are no other requirements when setting the overcurrent protection, the overcurrent protection can be set to 110% of the rated current. During load test, the current is brought to 110% of the rated current and the overcurrent relay operates. Trip, alarm, no shutdown.

3. When the overvoltage

is used in parallel, the power supply system is afraid of oscillation. Once the oscillation system voltage increases, it is easy to cause insulation breakdown of the power supply equipment and power supply equipment, causing the power supply equipment to be paralyzed together with the power supply equipment. The generator sets used side by side are all equipped with overvoltage protection, and the setting value is preferably 105% of the rated voltage. Short-circuit the overvoltage relay, trip and shut down, alarm operation.