Voltage Regulation Methods and Impacts of Distribution Transformers

Voltage qualification rate is one of the main indicators for measuring power quality. However, due to various reasons, the electricity consumption during peak and valley periods often differs significantly, causing the output voltage of distribution transformers to fluctuate. The fluctuation of voltage has varying degrees of impact on the performance of various electrical equipment, production efficiency, and product quality. Therefore, to ensure the qualification rate of supply voltage, timely adjustment of the tap changer position of distribution transformers is one of the solutions.

Generally, most distribution transformers are of the off-circuit tap-changing type, with three tap positions available for adjustment. By changing the position of the moving contact of the tap changer, the number of turns in the transformer winding is altered, thereby changing the output voltage. Common distribution transformers have a primary voltage of 10 kV and a secondary output voltage of 0.4 kV. The tap changer positions of distribution transformers are: position I at 10.5 kV, position II at 10 kV, and position III at 9.5 kV, and it should generally be at position II.

The specific steps for adjusting the tap changer are as follows:

1. First, cut off the power. After disconnecting the load on the low-voltage side of the distribution transformer, use an insulating rod to pull apart the high-voltage drop-out fuse, and then take necessary safety measures. Unscrew the protective cover of the tap changer on the transformer and place the positioning pin in the neutral position.

2. When adjusting the tap position, adjust the tap changer to the corresponding position based on the output voltage level. The basic principle for adjusting the tap changer is:

When the transformer output voltage is lower than the allowable value, adjust the tap changer position from position I to position II, or from position II to position III;

When the transformer output voltage is higher than the allowable value, adjust the tap changer position from position III to position II, or from position II to position I.

3. After adjusting the tap position, use a DC bridge to measure the DC resistance of each phase winding to check whether the DC resistance between windings is balanced. If the resistance difference between phases is greater than 2%, it must be readjusted; otherwise, after operation, the moving and static contacts may heat up or even discharge due to poor contact, damaging the transformer.