Selection of 10kV current transformer transformation ratio

In the process of 10kV power distribution design, the selection of 10kV current transformer transformation ratio is very important. If the selection is not appropriate, it is very likely that the relay protection function cannot be realized and the dynamic stability

The design staff should pay enough attention to problems such as failure to pass the check. 10kV current transformers can be divided into two types according to their use, one is for relay protection, the other is for measurement; they are set separately

In the incoming, metering, outgoing, and contact cabinets of the power distribution station. In design practice, the author found that in the design of distribution substations, the selection of current transformer ratio is not rare. example

For example, the author once found that: in a 630kVA station attached transformer (10kV side rated primary current is 36.4A) power supply circuit, the current transformer transformation ratio in the outlet cabinet of the distribution station is only 50/5 (using

GL type overcurrent relay, DC operation), this will cause a series of problems such as the current relay cannot be set.

For the selection of the transformation ratio of the 10kV current transformer for relay protection, at least the following conditions must be selected:

1. Calculate the ratio of the current to the current transformer-secondary rated current for the primary side;

2. In accordance with the requirements of relay protection;

Third, the calculation of the current transformer, the primary current multiple mjs is less than the saturation mb1 of the current transformer;

Fourth, it is stable by heat; and the fifth is stable by pressing. As for the selection of the 10kV current transformer for measurement, because it is used for the measurement of normal working conditions, there are no requirements for the above two and three; below

Take the common distribution transformer as an example, explain the influence of the above conditions on the selection of 10kV current transformer, and find out the main factors that affect the selection of current transformer ratio.