How to understand the reactive economic equivalent?

We know that reactive power will increase the loss of the system, but there is a new problem, that is, how much loss does reactive current increase?

According to the principle of reactive power balance, we already know that reactive current can be transmitted from load to generator, that is to say, reactive loss is distributed in the whole power grid, so it is impossible to measure the loss caused by accurate reactive current.

In order to solve this problem, the concept of economic equivalent of reactive power is proposed. The so-called reactive economic equivalent is to convert reactive current into active current, so that the loss caused by reactive current can be easily calculated. However, it is not necessarily convenient for us to calculate the reactive power equivalent based on the statistical data.

According to the national standard GB 12497 "three phase asynchronous motor economic operation" Regulations:

KQ is the economic equivalent of reactive power

When the motor is directly connected to the generator bus KQ = 0.02 ~ 0.04

KQ = 0.05-0.07 for secondary transformer

KQ = 0.08-0.10 for the third transformation;

This standard is applicable to asynchronous motor, of course, it can also refer to other reactive loads. The economic equivalent value of reactive power in the standard considers the loss of transformer, so when the load is directly connected to the generator bus, the economic equivalent value of reactive power is the minimum, and when the load is supplied after three times of voltage transformation, the economic equivalent value of reactive power is the maximum.

For example, we have installed a reactive power compensation device to reduce the reactive power of 100kvar, and the reactive power compensation device is 400V voltage level, then we can take KQ of three times transformation according to the standard of gb12497 = 0.09, then the energy saving effect of the reactive power compensation device can be calculated: 100 × 0.09 = 9kw

If the reactive power compensation device operates for 10 hours every day, we can say that the reactive power compensation device saves 90kw. H every day.