By hvhipot 
1. Advantages of On Load Voltage Regulating Transformers
1.1 Maintain voltage stability. Transformers have impedance, which will cause voltage drops during power transmission and vary with changes in user side load. The fluctuation of system voltage combined with changes in user side load will cause significant voltage fluctuations. On the premise of achieving on-site balance of reactive power, when the voltage fluctuation exceeds the fixed value, the on load tap changer will operate after a certain delay to adjust the voltage and maintain its stability.
1.2 Ensuring Voltage Quality The task of a power supply transformer is to directly supply power to the load center, with the primary side connected directly to the main voltage grid (220 kV and above) or to the regional power grid (35-110 kV). This type of transformer not only provides active power to the load, but also often simultaneously provides reactive power, and generally has a high short-circuit impedance. As the regional load changes, if there is no on load tap changer configured, the voltage of the power supply bus will change accordingly. Therefore, China’s “Technical Guidelines for Power Systems (Trial)” stipulate that “for transformers of 110 kV and below, it is advisable to consider using load voltage regulation for transformers with at least one level of voltage”. Therefore, for on load tap changers that directly supply power to the power supply center, under the premise of achieving local balance of reactive power zoning, with the increase or decrease of regional load, the tap changer is adjusted in conjunction with the parallel switching of capacitors and low-voltage reactors of reactive power compensation equipment to ensure the quality of power supply voltage to users at any time.
2. Renovation of the main transformer
The on-site renovation of the main transformer for on load voltage regulation further ensures the quality of the distribution network voltage, laying a solid foundation for striving to become a first-class power supply enterprise. In addition, on load tap changers can maintain the operation of the power grid at a high voltage level, optimize reactive power, thereby reducing line losses and improving the economic benefits of the power grid.
3. Adopt corresponding technical measures
Although there are some shortcomings in on load tap changers, as long as we comprehensively consider them in power grid planning and schedule them reasonably when the system is disturbed, we can leverage their strengths and avoid their weaknesses, and play a positive role. Here are some suggestions from the author on the application of on load tap changers:
a) For power transformers, in order to improve the quality of power supply for users and reduce line losses, it is advisable to use on load voltage regulation..
b) When a major disturbance occurs in the system, causing a significant drop in voltage, the dispatcher should take timely measures to lock the on load voltage regulation, cut off some loads, eliminate active and reactive power shortages in the system, or set up voltage reduction automatic load reduction devices in the system to offset the negative impact of transformer control, act quickly, and limit local disturbances from developing into accidents in the entire or main network.
c) According to the “Technical Guidelines for Power Systems”, except for step-down transformers and interconnection transformers of 220 kV and above that may have significant changes in grid voltage (such as connected to power plants with large output changes or to busbars that are sometimes the sending end and sometimes the receiving end), load voltage regulation can be used
d) For high-voltage and large capacity transformers (including step-up transformers and interconnection transformers), in order to improve their reliability and prevent resonance overvoltage, tap changers should be avoided as much as possible. If necessary, only no-load voltage regulation methods with a small adjustment range should be used. Zinc oxide lightning arresters should be used inside the transformer to absorb overvoltage protection.
e) For two on load tap changers operating in parallel, it is allowed to perform tap changer operations when the rated load current of the transformer is 85% or below. For situations above 85%, tap changer operations should be locked. In addition, reliable out of step protection must be set up to ensure synchronous switching of the two transformers.
f) Strictly implement the “Regulations on Voltage and Reactive Power Management in Power Systems”. For transformer taps, they should be managed in a graded manner according to their voltage management range. Power dispatch departments at all levels should accurately issue commands to adjust the tap action of on load tap changers based on changes in load and power flow, in order to improve voltage quality. Under the changed tap voltage level, automatic switching of reactive power compensation is carried out to achieve comprehensive optimization management of system voltage and reactive power.
HV Hipot Electric Co., Ltd. is a high-tech enterprise specializing in the production of transformer on load switch testers and transformer no-load load load characteristic testers.