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Why is The Three-phase Load of Diesel Generator Unbalanced

Jan. 28, 2021

Why is the three-phase load of diesel generator unbalanced? Today Dingbo Power answers for you.

Here are some reasons:

1.One phase of the generator and its circuit occurs phase loss, or one phase of its circuit breaker is in poor contact.

2.A power transmission sequence is in incomplete operation.

3.Single phase of the system is overloaded(if there is a single-phase load with large capacity).

4.The failure of stator ammeter and circuit of electric energy metering device also contribute to the indicative asymmetry of three phase ammeter.


Hazards of the unbalanced three-phase load of diesel generator.

1.It will undermine the operational output of the equipment. The design for capacity of the generator is fixed according to the three-phase load, so that the equipment takes the largest phase in it as the limit in consequence of the three-phase unbalance, and lead to the inefficient operation of the equipment.

2.When electricity goes through the neutral line, wastage of the low voltage line increases.

3.It will lead to the asymmetry of three-phase voltage and the displacement for electric potential of neutral point.

4.Excessive neutral current will rise the temperature of power transformer when it is in service, and will burn it out at worst.

5.It is able to undermine the output power of the generator, and rise the winding temperature.

6.It will make the voltage of some phases high and others low.

7.When the neutral line is overcurrent, the alien line might be burn out.


How to solve the problem of unbalanced three-phase load?

When the generator overruns under the three-phase imbalance load, you should immediately reduce the load of the generator set to make the unbalanced current lower than the allowed value and report to the system control. After the three-phase current becomes balanced, you can increase the load of the generator set according to the dispatching order. The current difference of the three phases must be lower than the 20% of rated current, and current of any phase must be of below rated value. The negative-sequence current goes through the generator must be less than 12% of the rated current.

 Yuchai genset

To better learn about the diesel generator and make a right decision in purchasing, the three-phase loads and single-phase load will be introduced here:

1.Three-phase load

Three-phase loads are defined as providing power source for the operation of power-driven equipment with three phases. The three-phase loads can fall into the balance of three-phase loads and the imbalance of three-phase loads.

The differences are as follow: the balance of three-phase loads sees similar values of current for the three phases; the imbalance of three-phase loads sees great different values of current for the three phases, and the phase with overcurrent is prone to cause a fire.


2.Single-phase load

Single-phase load is defined as the one or more impedances that are set in the two lines of the three-phase power source. It can also be deemed as a peculiar asymmetric three-phase loads. Electric locomotive is a classic example of it. In order to ensure the basic balance of three-phase loads, all the single-phase load will be evenly set in the three phases.


In a word, the single-phase means using a phase, which is commonly known as live wire, and a null line to provide power source for the operation of the electric appliance.


Therefore, when make a decision on the purchase for a diesel generator, whether the load of the generator is three-phase or single-phase should be confirmed. In doing so, imbalance in the load of a generator in service can be avoided, so as to make certain of the safe and stable operation of the generator set.


Being established in 1974, Guangxi Dingbo Power Equipment Manufacturing Co.,Ltd., is a manufacturer for diesel generator sets. We are committed to the production of high-quality diesel generator sets, providing products including Cummins, Perkins, Volvo, Deutz, Yuchai, SDEC, Weichai, Ricardo, MTU and the likes, with the power range from 20 KW to 3000 KW. For more information, please contact us by e-mail sales@dieselgeneratorech.com or telephone +86 13481024441.

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