Voltage qualification rate is one of the main indicators to measure power quality. However, due to various reasons, the electricity consumption during peak and valley periods often differs greatly, 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, in order to ensure the qualification rate of supply voltage, timely adjustment of the tap changer position of the distribution transformer is one of the solutions.
Generally, most distribution transformers are of the no-load voltage regulation type, with three gear positions available for adjustment. By changing the position of the moving contact of the tap changer, the number of turns of the transformer winding is changed, thereby changing the output voltage. The primary voltage of common distribution transformers is 10 kV, and the secondary output voltage is 0.4 kV. The tap changer positions of the distribution transformer are: position I for 10.5 kV, position II for 10 kV, and position III for 9.5 kV. Generally, it should be at position II.
The specific steps for adjusting the tap changer are as follows:
1. First, cut off the power supply. After disconnecting the load on the low-voltage side of the distribution transformer, use an insulating rod to pull open the drop-out fuse on the high-voltage side, 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 gear position, the tap changer should be adjusted to the corresponding position according to the output voltage level. The basic principle for adjusting the tap changer is:
When the output voltage of the transformer 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 output voltage of the transformer 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 gear position, use a DC bridge to measure the DC resistance value of each phase winding to check whether the DC resistance among the windings is balanced. If the resistance difference among 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.
