The transformer has impedance and will produce voltage drop during power transmission, which will change with the change of user side load. The fluctuation of system voltage plus the change of user side load will cause the great variation of voltage. On the premise of achieving local balance of reactive power, when the voltage changes beyond a fixed value, the on load transformer
will operate after a certain delay to adjust the voltage and keep the voltage stable.
The task of the power supply transformer is to supply power directly to the load center, and the primary side is directly connected to the main voltage network (220 kV and above) or to the regional power supply network (35 ~ 110 kV). Such transformers not only provide power to the load, but also often provide reactive power, and generally have a large short circuit impedance.
As the regional load changes, the supply busbar voltage will change if an on load transformer is not configured. Therefore, China's "technical guidelines for power systems (trial)" provisions "for 110 kV and below the transformer, it is appropriate to consider at least one level of voltage transformer with load regulation mode.
Therefore, on the premise of achieving the local balance of reactive power division, the on load transformers that directly supply power to the power supply center can be adjusted with the switching of shunt capacitors and low-voltage reactors of reactive power compensation equipment as the regional load increases and decreases, so as to ensure the quality of power supply voltage to users at any time.