What is Reverse Power Protection of Generator Set

As the owner and user of the generator set, the user should understand all aspects of the generator set, so as to master the operation and use methods of the generator set. Today Dingbo Power company share reverse power protection of generator set.

Generator set reverse power protection is also called power direction protection. Generally speaking, the power direction of generator should be from the generator to the bus. However, when the generator loses excitation or for some other reason, the generator may change to motor operation, that is, absorb active power from the system, which is reverse power. When the reverse power reaches a certain value, the protection of the generator acts, or acts to signal or trip.

The parallel operation of two diesel generator sets shall meet the conditions of the same phase of generator voltage, the same frequency of electric generator and the same phase sequence of generator set. In actual use, when two diesel generator sets are paralleled without load, there will be a problem of frequency difference and voltage difference. Sometimes the actual reverse power will be found with the monitoring instrument, which are the reverse power caused by unequal voltage. The other is the reverse work caused by inconsistent speed (frequency). In the face of this phenomenon, corresponding adjustments should be made.

1.Adjustment of reverse power caused by voltage difference.

When the power meter indication of both generating sets is zero and the ammeter still has current indication, the voltage adjustment knob of one diesel generator set can be adjusted according to the indication of ammeter and power factor.

2.Adjustment of reverse power caused by frequency.

If the frequencies of the two units are different and the difference is large, the current of the unit with high speed displays positive value and the power meter indicates positive power. On the contrary, the current indicates negative value and the power indicates negative value.

At this time, adjust the speed of one of the diesel generator sets and adjust the indication of the power meter to zero. However, when the ammeter still has indication, this is the reverse power phenomenon caused by voltage difference.

In most cases, the parallel connection of diesel generator sets will not produce reverse power. Only a few generators have low output voltage due to improper regulation when connected to the grid. We need to analyze the causes as soon as possible and take appropriate adjustment measures.

What is the function of generator reverse power protection?

When more than two diesel generator sets operate in parallel, if the diesel engine of one diesel generator set does not work normally or the paralleler between the diesel engine and the generator is damaged, the generator of the unit can not output active power, but absorb power from the power supply system, and the synchronous generator becomes a synchronous motor, that is, the synchronous generator operates in reverse power

If the synchronous generator operates in the reverse power state, it is unfavorable to the power supply system, resulting in overload tripping of other units participating in parallel operation and power supply interruption. Therefore, measures shall be taken for reverse power protection.

We can use transistor reverse power protection device.

Since the reverse power protection is an active power direction protection, its detection signal should take the signals of voltage and current and their phase relationship, and convert it into a DC voltage control signal reflecting the direction and size of active power.

The reverse power protection signal of the device is taken from the voltage and current of S phase of the generator for single-phase reverse power detection. In its voltage forming circuit, the primary sides of voltage converters M1 and M2 are connected into symmetrical stars, and the voltage Uso´ is taken out as the voltage signal. And make Uso´ in phase with the phase voltage USO output by the generator. Its current signal is obtained by S-phase current transformer and rectified by two single-phase bridge rectifier circuits VD1 and VD2. In the voltage U1 of resistor R3, the voltage U2 of resistor R4 and the power detection link, the absolute value comparison principle shall be used for detection. When R1 = R2, the DC control signal voltage UNM output by the power detection link is directly proportional to the active power P and reflects the direction of P. In reverse power, the DC control signal voltage UNM is negative, that is, the N-point potential is higher than the m-point potential. When the reverse power reaches 8% of the rated power of the generator, the triode VT1 is on and VT2 is off. The working power supply charges capacitor C through resistors R15 and R16, with a charging delay of about 5s. When the charging voltage of capacitor C reaches the breakdown voltage of voltage stabilizing tube W1, tube W1 is turned on, diode VD3 and triode VT3 are turned on, outlet relay D1 is powered on and acts, and the power supply switch trips automatically, so as to achieve the purpose of protection.

If you are interested in diesel generator set, contact Dingbo Power company by email dingbo@dieselgeneratortech.com.