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Talk about some problems that may occur in parallel diesel generator sets
June 01, 2022
In the parallel operation of diesel generator sets, the phenomenon of uneven power distribution often occurs. Excessive uneven power distribution will seriously affect the safety and reliability of the operation of the power station system, and will cause serious harm to the generator set. This hazard is rooted in the circulation problem of the system. This is also a common difficult problem in parallel use.
Diesel generator sets can be used as common or backup power sources. In recent years, with the continuous development of society, the application scope of diesel generator sets has become more and more extensive. In order to meet the user's large load or uninterrupted power supply requirements, users often need to connect two Or multiple units run in parallel. In the parallel operation of diesel generator sets, the phenomenon of uneven power distribution often occurs. Tingbo Electric reminds you that excessive power distribution and uneven power distribution will seriously affect the safety and reliability of the operation of the power station system, and will cause serious harm to the generator set. This hazard is rooted in the circulation problem of the system. This is also a common difficult problem in parallel use.
Taking the modular parallel control system as an example, the parallel commissioning of generator sets generally first balances the circulating current of the parallel units with no-load parallel connection, makes it small enough and runs stably, and then adjusts and balances the active power through the load divider. Circulating current problem when the load is connected in parallel. Taking two units in parallel as an example, the common problems in no-load parallel connection are as follows:
1. The circulating current is too large, far exceeding 10% of the rated current of the parallel unit;
2. After parallel connection, the circulating current gradually increases with the running time until the reverse power alarm;
3. The circulation is unstable, and the randomness is large and small;
To solve the above problems, users should first understand the reasons for the circulation:
1. The root cause of circulating current is that the no-load voltages of the two units are not completely equal or the voltage regulation characteristics are different, resulting in unequal output voltages and circulating currents.
2. The no-load voltage and voltage regulation characteristics of the two units are equal, but the output currents of the two units are not equal, that is, the power distribution of the two units is uneven, and a circulating current will also occur.
3. There are many factors that affect the distribution of reactive power, such as the characteristics of the automatic voltage regulator, the stability of the voltage equalizing line, etc.
The dynamic balance analysis of power distribution takes the parallel connection of two equal-power generator sets as an example. GB/T12786-2006 General Technical Conditions for Automatic Internal Combustion Engine Power Plants stipulates that the difference in active power distribution between 20% and 80% of the calibration rating is ≤±10%, and the average distribution of active power between two parallel units mainly depends on the two units. This is done by balancing the chain between load dividers.
By adjusting the "load distribution" potentiometer of the load distributor, the power distribution parameters of the two load distributors can be adjusted to be equal. Assuming that the loads of the two units are absolutely equal, then this is an ideal state of complete balance.
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