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Automatic Control Circuit of Diesel Generator Set

Jan. 28, 2019

Once the external power supply is interrupted, the diesel generator should start the generator set and supply power to the low voltage busbar of the substation to ensure the continuity of the power supply. The starting diesel generator generally has manual starting mode and automatic starting mode. Generally, manual start is used for the substation with someone on duty, and automatic start is used for the unattended substation. However, the automatic starting device is often accompanied by manual starting function to facilitate its use.

Automatic Control Circuit of Diesel Generator Set.jpg


The starting of diesel engine can be divided into two kinds according to the starting power source: electric starting and pneumatic starting. The electric starting uses the DC motor (usually the series excited DC motor) as the power, drives the crankshaft to rotate through the transmission mechanism, when reaches the ignition speed, the fuel oil starts to burn, the work is done, the starting motor automatically withdraws from the work. The electric motor power supply uses the battery, its voltage is 24V or 12V. Pneumatic starting is to make the compressed air stored in the cylinder enter the cylinder of the diesel engine, use its pressure to push the piston, make the crankshaft rotate, when the ignition speed is reached, the fuel begins to burn, do the work, stop the air at the same time, when the start is successful, The diesel engine slowly entered the normal operation state.


Therefore, the starting solenoid valve of the starting circuit is either the contactor of the motor or the starting solenoid valve of the starting circuit. The automatic starting device should have three steps: receiving starting instruction, executing starting instruction and removing starting instruction. Some devices can start repeatedly usually three times, if the third start failure to give an alarm signal. For large capacity unit and warm cylinder operation program, it can prevent cylinder thermal stress overload caused by rough starting of diesel engine and affect the service life of diesel engine.


Automatic control circuit of diesel generator set


The diagram (above) is an automatic switching circuit between the backup power supply and the main power supply controlled by the relay contactor. U1 is the main power supply voltage, U2 is the backup power supply voltage, and when the external power supply is interrupted, U1 / 0, at this time, the circuit breaker QF1 undervoltage coil is cut off. QF1 off, cut off the main power supply. In the control circuit of the self-provided power supply, the normally closed contact of QF1 is closed, so the KV of the voltage relay will not operate because the standby unit has not been started, so the voltage relay KV will not operate either. Once the standby diesel generator set starts, the generator sends out the voltage, which makes the voltage relay KV action, which often open and close the contact point, connect K02, make the QF2 close and the standby power supply put into operation.



The figure (below) is an automatic starting device circuit. M is the starting motor, when the main power supply is interrupted, the QF1 tripping, its normally closed contact is closed, and the normal closed contact of the standby power circuit breaker QF2 is matched, the contactor KM4 is charged, the KM4's regular open contact is closed, so that the KM3 is electrified, and the KM3's regular open contact is closed. The starting motor M gets electricity and enters the automatic start. At the same time, the KM4 pair of regular open and close contacts are closed, so that the alarm bell HA is electrified, which indicates that the standby power supply is starting, and another pair of contacts are closed to make the time relay KT get electricity. The current limiting resistance R is serialized to prevent the KT coil of the time relay from passing through the large current for a long time. When the KT usually opens and contacts are closed, that is, when the electric driving time of diesel engine arrives, the KM5 gets electricity, which often opens and closes the contact, which makes the excitation winding of the generator electrify (the circuit is not drawn), and the generator establishes the voltage. KM5 often closed contact disconnected, KM3 power off, starting motor power loss, electric start end.


When the establishment voltage of the generator reaches the rated value, the KV action of the voltage relay is usually opened and closed, which makes the K02 power supply, the QF2 switch and the diesel generator power supply for the load. At the same time, the normal closing contact of QF2 is disconnected, the KM4 is cut off, the KM3 is cut off, the starting motor is separated from the starting power, the KT1,KM5 is restored, and the excitation of the generator is completed by the automatic constant voltage device (the circuit is not drawn).


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