The transformer is S9-30/10. Phase A is equipped with a set of equipment. The measured long-term operating current is 15-17A. Phase B and C currents are small, and they will not exceed 2A. The transformer low voltage \? line is 25 square aluminum core wire, the neutral point is well grounded, and the grounding resistance is 3Ω.

1, 3 line voltage is basically balanced, all in 385-390.

2. The phase A voltage is low, between 198V and 208V.

3, B phase, C phase voltage is high, between 225V ~ 230.

4, A phase voltage and phase B phase voltage difference is basically no less than 20V, so I dare not use the method of increasing the voltage.

Phase A load is not adjustable because it is a complete set of equipment. What is the solution? As far as possible, increase the voltage of phase A and it can be more than 215V.

You did not provide the specifications of this transformer. I checked it and found the next table, which is about 30 KVA. Theoretically, the current should be about 60 amps at 220 V phase voltage, and your load current does not exceed the rated current. The grounding resistance of 3 ohms is also less than the required 4 ohms. Your customer's request can only be connected to one phase. Unbalanced loads can of course cause voltage imbalances.

One, probably analysis

Although the neutral point of the transformer is grounded, the potential of the neutral point is fixed, but the neutral voltage of the unbalanced transformer is not "dead fixed"! There are three reasons. One is that although the neutral point of the transformer is grounded, the grounding resistance is not zero. The standard requirement is less than 4 ohms. It is this 4 ohm. When the load is unbalanced, it will cause the three-phase voltage of the transformer to have Small offset.

The second is that although the resistance of the three-phase line is very small, due to the existence of single-phase load, the length, cross-section, and load size of the three-phase line are also inconsistent. Therefore, if the measurement is taken at the user, the neutral point must not be zero. The situation, that is, the three-phase voltage deviation. The third is that when the ground wire of the transformer is disconnected, the neutral point will be shifted due to unbalanced three-phase load, resulting in inconsistency of the three-phase voltage, and this inconsistency will, in turn, increase the unbalance of the three-phase load.

= (17-2) ÷ 17 × 100% = 88.24% In a three-phase four-wire transformer, the neutral current caused by the unbalanced current must not exceed 25% of the rated current of the low voltage winding, and you obviously exceed it, of course. To be solved.

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