Conditions for parallel operation of diesel generators

As a power source, diesel generators are commonly used in weapon systems, defense works or ships. In order to meet the requirement of large load or uninterrupted power supply, it is necessary to start two or more units to supply power at the same time. In order to guarantee the reliability of the diesel generator set power supply, improve the quality of power supply (voltage and frequency), increase the flexibility of the running, do the economic operation, often need to diesel generator set in parallel operation.

However, the parallel operation of multiple units is not a simple matter, so what are the conditions for parallel operation of diesel generators? What are the methods of parallel operation of diesel generators? And how to adjust the load after parallel operation? These issues are discussed in detail below.

Conditions for parallel operation

Large shock current must be avoided during parallel operation to prevent synchronous generators from being damaged and the power grid from being disturbed. At this point, the generating set shall meet four basic conditions in electricity:

(1) the phase sequence of the output voltage of the unit to be merged must be consistent with that of the unit already in operation;

(2) the frequency of the output voltage of the unit to be merged is the same as that of the unit already in operation;

(3) the voltage of the voltage standby generating set is equal to that of the running generating set;

(4) the phase of the output voltage of the unit to be merged is the same as that of the unit to be operated.

If the above conditions do not satisfy any of them, the circulation will appear due to the instantaneous value difference. The same phase sequence must be strictly observed and the other three conditions allow for slight discrepancy. Generally speaking, phase sequence can satisfy, by the design and manufacture and installation of automatic for motor shows no shift and the phase sequence, phase sequence indicator can be used to determine, parallel to the main check the size of the frequency and voltage and phase.

In a power system, the process of adjustment and operation carried out in order to put into parallel is called synchronous process. Synchronization can be divided into self-synchronization and quasi-synchronization.

? Self synchronous mode

The operation of self-synchronous parallel operation is to raise the speed of the generator set without excitation current to near the rated speed. Then, the generator set is put into parallel, and the dc excitation is added immediately. At this point, the rotor can be automatically pulled into synchronization by relying on the electromagnetic torque formed between the magnetic fields of the stator and rotor. The advantage of self - synchronous method is that the input is rapid and no complicated device is needed.

? Quasi-synchronous mode

The quasi-synchronous mode is to adjust the prime motor speed by governor before the unit is put into the system, so that the generator speed is close to the synchronous speed. The excitation current of the generator set is adjusted by the excitation adjusting device so that the terminal voltage of the generator set is close to the system voltage. When the frequency difference and pressure difference in the synchronous condition meet the given value, the appropriate time before the zero phase Angle difference is selected to close the switch, and the generator set is quickly pulled into synchronous operation.

The advantage of quasi-synchronous parallel operation is that the power grid and the motor have little impact at the moment of input. According to the degree of automation, the quasi-synchronous mode can be divided into manual parallel operation and automatic parallel operation. Among them, manual parallel operation includes lighting out method (direct connection method), light rotation method (cross connection method), rough synchronization method, etc. Automatic parallel operation includes transistor automatic parallel operation, relay automatic parallel operation and MCU control automatic parallel operation. With the development of microcomputer control technology, the parallel operation technology of MCU automatic control has been widely used. The automatic parallel operation device controlled by single chip microcomputer has obvious advantages such as small size, low cost and flexible control.

Therefore, it is a trend to realize the control of MCU by automatic parallel operation. The principle is that, according to the conditions of the generator set in front of the grid, using single chip microcomputer detecting generator voltage difference, frequency difference and phase difference, and according to the size of the rate automatically adjust generating set, a cop value is very small, condition has been met, a closing pulse, synchronization operation. You can see from the above analysis, as long as the mastery of the diesel generator set parallel operation conditions, fully familiar with all kinds of parallel method, can according to the actual circumstances of the project, properly choose some parallel way. It is easy to operate, fast and reliable, and also can prevent the shock current and voltage fluctuation in parallel. However, after the synchronous operation of the generating set, there is still an important link, that is, power distribution of the generating set.