Company News

News Categories

Conditions and working principle control of diesel generator parallel operation and grid connection

2025-12-05

1、 What are the conditions for parallel operation of Generator Sets?

The entire process of putting a generator set into parallel operation is called parallel operation. Start one generator set first and send voltage to the busbar, while the other generator set starts and is parallel to the previous generator set. At the moment of closing, the generator set should not have harmful surge current, and the shaft should not be subjected to sudden impact. After closing, the rotor should be able to be quickly pulled into synchronization. Therefore, the parallel connection of generator sets must meet the following conditions:

The effective value and waveform of the generator set voltage must be the same

2. The phase of the voltage of the two generators is the same

3. The frequencies of the two generator sets are the same

4. The phase sequence of the two generator sets is consistent

2、 What is the quasi synchronous parallel method for generator sets?

How to conduct parallel synchronization during the same period? Quasi synchronous refers to accurate cycles. Using the quasi synchronous method for parallel operation, the voltage, frequency, and phase of the generator set must be the same. This can be monitored by two voltage meters, two frequency meters, and synchronous and non synchronous indicator lights installed on the synchronous panel. The parallel operation steps are as follows:

Close the load switch of one of the Generator Units and send the voltage to the busbar, while the other unit is in a standby state. Close the start of the same period, adjust the speed of the generator set to be merged, so that it is equal to or close to the synchronous speed (within half a cycle of the frequency difference with the other generator set), adjust the voltage of the generator set to be merged, so that it is close to the voltage of the other generator set. When the frequency and voltage are both close, the rotation speed of the synchronization meter becomes slower and the synchronization indicator light is also on and off at times; When the phase of the unit to be merged is the same as that of another unit, the pointer of the synchronization meter indicates the upward middle position, and the synchronization light is dim. When the phase difference between the unit to be merged and the other unit is large, the synchronization meter points to the downward middle position, and the synchronization light is on. When the pointer of the synchronization meter rotates clockwise, it indicates that the frequency of the generator to be merged is higher than that of the other unit, and the speed of the generator to be merged should be reduced. Conversely, when the pointer of the synchronization meter rotates counterclockwise, the speed of the generator to be merged should be increased. When the synchronous meter pointer slowly rotates clockwise and approaches the synchronous point, immediately close the circuit breaker of the unit to be connected, so that the two generator units are parallel. Cut off the synchronous table switch and related synchronous switches after parallel connection.

3、 What should be noted when performing quasi synchronous parallel operation of generator sets?

Quasi synchronous parallel operation is a manual operation, and the smoothness of the operation is closely related to the experience of the operators. To prevent asynchronous parallel operation, the following three situations are not allowed to be closed.

When the pointer of the synchronous meter jumps, do not close it because there may be a jamming phenomenon inside the synchronous meter, which cannot reflect the correct parallel conditions.

When the synchronous meter rotates too fast, it indicates that the frequency difference between the generator set to be connected and another generator set is too large. Due to the difficulty in controlling the closing time of the circuit breaker, it often causes the circuit breaker to not close at the synchronous point, so it is not allowed to close at this time.

3. If the pointer of the synchronous meter stops at the synchronous point and does not move, it is not allowed to close the circuit breaker. This is because if the frequency of one of the generator sets suddenly changes during the closing process of the circuit breaker, it may cause the circuit breaker to close exactly at a non synchronous point.

4、 How to adjust the reverse power phenomenon of parallel units?

When two generator sets are parallel without load, there will be a frequency difference and voltage difference between the two units. And on the monitoring instruments of the two units (ammeter, power meter, power factor meter), the actual reverse power situation is reflected. One is the reverse power caused by inconsistent speed (frequency), and the other is the reverse power caused by unequal voltage. The adjustments are as follows:

1. Adjustment of reverse power phenomenon caused by frequency: If the frequencies of two units are not equal and there is a significant difference, the instrument (ammeter, power meter) will display that the current of the unit with higher speed is positive, and the power meter will indicate positive power. Conversely, if the current indicates negative value, the power indicator will indicate negative value. At this point, adjust the speed (frequency) of one of the units according to the indication on the power meter, and set the indication on the power meter to zero. Make the power indication of both units zero, so that the speed (frequency) of the two units is basically the same. However, when the ammeter still indicates, this is the reverse power phenomenon caused by voltage difference.

2. Adjustment of reverse power phenomenon caused by voltage difference: When the power meters of both units indicate zero, but the ammeter still has current indication (i.e. one reverse and one positive indication), the voltage adjustment knob of one of the generator units can be adjusted according to the indication of the ammeter and power factor. Eliminate the indication of the ammeter (i.e. adjust it to zero). After the ammeter shows no indication, adjust the power factor to lag by 0.5 or more based on the indication of the power factor meter Generally, it can be adjusted to around 0.8, which is the optimal state.

5、 Generator protection circuit

1. The phenomenon of reverse power is caused by differences in the speed (frequency) and voltage of the generator set, where one generator set carries positive power while the other carries negative power. That is to say, the unit with negative power becomes a load at this time (the phenomenon of low frequency and inconsistent speed of this unit). When the voltages are different, the unit with high voltage provides a reactive current and reactive voltage (indicated positively by the ammeter of this unit) to the unit with low voltage, which is equivalent to adding a phase-shifting camera group in this power supply system. The unit with low voltage becomes a large load, receiving a large reactive current to maintain voltage balance between the two units (the ammeter of this unit indicates in reverse). When monitoring, raising the voltage of one unit or raising the voltage of another unit can cause reverse current in one unit, with an operating current of about 20% of the rated current. Reverse relay action, tripping, alarm, but does not stop the machine.

2. Overcurrent: The rated power of current generator sets is constant, and their overload capacity is very low, basically around 5% of the rated power. The allowable load time is 15-30 minutes, and it may not exceed 60 minutes. After this time, the generator set will heat up, and the insulation of the wires will be reduced, which will also reduce the service life. So if there are no special requirements when setting overcurrent protection, the overcurrent protection should be set at 110% of the rated current. When conducting a load test, bring the current to 110% of the rated current and activate the overcurrent relay. Trip, alarm, and non-stop operation.

3. Overvoltage: When using generator sets in parallel, there is a risk of oscillation in the power supply system. Once the voltage of the oscillation system rises, it can easily cause insulation breakdown of the electrical equipment and power supply equipment, leading to the paralysis of both power supply and electrical equipment. The generator sets used in parallel for this purpose are all equipped with overvoltage protection, and the optimal setting value is 105% of the rated voltage. Short circuit the voltage relay, trip and stop the machine, and trigger an alarm.

6、 The opening and closing circuits are both connected to the mobile phone parallel, and the control circuit is automatically parallel

1. Manual opening and closing: Each unit can be used as the first machine or waiting for parallel opening and closing. During manual parallel operation or power supply, manual opening and closing can be used.

2. Automatic opening and closing: Each unit can be selected as the standby unit or the first unit; After the first unit starts up, the closing circuit automatically closes, and the synchronization is automatically activated and deactivated. After the same period, the waiting units will automatically close and operate in parallel.

3. Whether it is manual or automatic closing, once the unit experiences reverse power, low oil pressure, high water temperature, high water temperature, high oil temperature, or overvoltage, it will automatically open and disconnect from the load.

7、 Synchronous circuit

1. After the first machine is closed, the power is sent to the busbar. At this time, the busbar detects the synchronization circuit, which is connected to the synchronization circuit of the waiting machine. After receiving the signal, the synchronization detection relay is automatically closed. Send the bus voltage and the voltage to be parallel to the synchronous control module, which automatically detects the voltage and speed of the parallel units. If there is a difference in speed, the synchronization module automatically adjusts the speed of the parallel machine to reach the parallel condition. After finding the synchronization point, the synchronization module sends a closing instruction, and the merging unit executes the closing after receiving the instruction, that is, the two units run in parallel.

2. After the units are parallel, the synchronization circuit automatically exits the working state, but the automatic synchronization transfer switch must be manually turned off to prevent the units from receiving a parallel signal again when disconnecting after receiving power, and the synchronization device should be automatically put into operation to make the units parallel again.

8、 Load allocation

1.When running alone, the load distributor is not put into operation.

2. After the units are parallel, the load distributors of each unit are put into operation simultaneously, adjusting their own speed to evenly distribute the power of the two units. The working principle is to automatically adjust the speed of the Ding unit based on the output power (i.e. current) of the unit, so that its load is balanced

9、 Voltage regulation circuit

1.Before paralleling the units, the voltage of both units must be adjusted to the same value.

2. After no-load paralleling, adjust the voltage knob to eliminate the reverse power phenomenon and make its power factor lag around 0.8.

3. After parallel units are loaded, the voltage adjustment knob can be manually adjusted according to the load situation to ensure that the power factor is in the optimal position, and there is no need to adjust it again in the future.

10、 Speed adjustment circuit

Before parallel operation, the speed (frequency) of the two units must be adjusted to be consistent.

When parallel, the speed of the first machine or the unit to be parallel can be adjusted according to the rotation speed of the synchronous meter, so that the direction of rotation of the synchronous meter can be clockwise or counterclockwise. The slower the speed, the better, but the pointer of the synchronous meter must rotate in order to be parallel.

After parallel operation, observe whether the current and power of the two units are balanced. If the difference is not too large, adjust the speed knob to adjust the power of the two units

11、 Instrument detection circuit

1.Before operation, all relevant instruments must be adjusted to zero, but the power factor meter and frequency meter are not at zero.

2. During operation, observe the operating status of various instruments to ensure compliance with regulations (whether there is any phenomenon of instrument wiring being reversed).

3. The current and voltage should be checked with relevant instruments to see if the indicated values are normal.

12、 Start circuit

1.Before operation, it is necessary to first check whether the starting circuit is normal.

2. Whether the relevant components can work normally after startup.

3. Whether the combination of the starter and the host is normal and whether it can be exited.

13、 Shutdown circuit

1. Is the operation of the shutdown solenoid and solenoid valve reliable.

2. Does the unit automatically shut down in the event of a malfunction.

3. Is the manual shutdown circuit complete.

4. Whether to stop the machine when only tripping is required.