What are the causes of three-phase imbalance in power systems?

There are numerous causes of three-phase voltage imbalance, including open conductor faults, single-phase grounding, system resonance, improper distribution of three-phase loads, and missing phase operation of loads. Operational management personnel must accurately distinguish these causes to enable prompt and correct response. Next, let us followNantongZhifeng Electric Technology Co., Ltd. to understand the causes of three-phase imbalance.

The causes of three-phase imbalance are as follows:

1. Open conductor fault

When the system experiences an open conductor fault without grounding, or when a circuit breaker or isolating switch phase is not closed, or when the voltage transformer fuse is blown, three-phase parameter imbalance occurs. The voltage of the faulted phase is zero, while the voltages of the non-faulted phases remain normal. Under these conditions, three-phase electrical equipment operates in a missing phase state.

2. Ground Fault

When an open conductor occurs and is grounded in a system where the neutral point is not directly grounded, it causes three-phase voltage imbalance; however, the line voltage values after grounding remain unchanged.

Single-phase grounding is classified into metallic grounding and non-metallic grounding. In the event of metallic grounding, the fault phase voltage is zero or near zero, the non-fault phase voltages increase to line voltage levels, and this condition persists. In the event of non-metallic grounding, an arc exists between the fault phase and ground; the voltage of the grounded phase is not zero but reduced to a certain value, while the voltages of the other two phases increase to less than √3 times; due to the presence of the arcing phenomenon, arc overvoltages occur.

3. System resonance

With the rapid development of industry, nonlinear power loads have increased significantly. Certain loads not only generate harmonics but also cause supply voltage fluctuations and flicker, which can even result in three-phase voltage imbalance.

4. Unbalanced distribution of three-phase loads

In most power systems in our country, transformers are shared by both power and lighting systems. Initial designs did not account for the balanced distribution of loads, nor was the three-phase usage evenly maintained as per design requirements during equipment startup, which largely contributes to three-phase load imbalance.

5. Single-phase operation of three-phase equipment

Due to faults, one phase of the three-phase load may cease operation or operate abnormally, resulting in three-phase current imbalance and abnormal equipment noise.

6. The reduction in monitoring intensity of distribution transformer loads.

In the management of distribution networks, issues related to the management of three-phase load distribution are frequently overlooked. In the inspection of distribution networks, the three-phase load of distribution transformers is not regularly inspected or adjusted. Furthermore, numerous other factors contribute to three-phase imbalance phenomena, such as line effects and unequal three-phase load matrices.