Transformer voltage regulation can be achieved through on-load voltage regulation and off-load voltage regulation:
On-load voltage regulation refers to the capability of the transformer to adjust its tap position during operation, thereby changing the transformer turns ratio to achieve voltage regulation. There are two methods of on-load voltage regulation: line-end regulation and neutral point regulation. Line-end regulation involves adjusting the tap position on the high-voltage winding side, while neutral point regulation involves adjusting the tap position on the neutral point side of the high-voltage winding. Tap adjustment on the neutral point side can reduce the insulation level of tap changers, offering significant advantages, but it requires the neutral point of the transformer to be directly grounded during operation.
Off-load voltage regulation involves adjusting the tap position of the transformer during a power outage or maintenance to change the transformer turns ratio and achieve voltage regulation.
Tap changers of transformers are generally taken from the high-voltage side, mainly due to the following considerations:
The high-voltage winding of the transformer is usually located on the outer side, making the tap connection more convenient.
The current on the high-voltage side is smaller, resulting in smaller conductor cross-sections for tap connections and switchgear, making it easier to address issues related to poor contacts.
In principle, tap changers can be located on either side, but an economic and technical comparison is necessary. For example, in large-scale step-down transformers at 500 kV, tap changers are taken from the 220 kV side, while the 500 kV side remains fixed.