According to the requirements of the specification, in the current construction of the three-phase four-wire distribution line, two methods of zero sequence current protection and residual current protection are often installed.
But there are many electrician operators who are not very clear about the nature, protection characteristics, the difference between them and the installation location of these two types of protection. To this end, I will share with you the relevant knowledge:
Zero-sequence current protection and residual current transformer residual current protection have similarities (so many colleagues are easy to confuse them): both are used for line protection, and the current transformer is used to obtain the action signal, but both from the working principle and purpose There are fundamental differences.
Let's talk about zero-sequence current protection first: Alternative-sequence current protection is to detect three-phase unbalanced current. Its current transformer can only detect phase-line current or zero-line current, not both phase-line and zero-line current. The number of detection current levels is usually hundreds to thousands of amps.
The installation location is generally the beginning of the distribution line (or transmission line).
There are three commonly used installation wiring methods: three phase wires pass through a zero-sequence current transformer (CT), three phase wires each pass through a (CT), and one (CT) is installed on the N wire (CT is a zero-sequence current transformer) ) Looking at the residual current transformer residual current protection: residual current protection is to detect the leakage current on the line. Its current transformer is called residual current transformer and can only detect the leakage current. When the leakage value exceeds the setting value, the residual current circuit breaker (also called leakage switch, leakage circuit breaker, etc.) connected to it will act to cut off the power supply of the load and protect the load.
The number level of leakage current detection is generally from milliamps to hundreds of milliamps (line leakage is generally in this level).
The installation location can be used for any part of the distribution line, but it is mostly installed at the end of the line to protect the load.
There are also three installation wiring methods: when protecting a single-phase load, the phase wire and the N wire pass through the CT at the same time, and when protecting the three-phase load, the three phase wires pass through the CT at the same time, and there are single-phase load and three-phase load , Phase line and N line pass through CT at the same time (CT is the residual current transformer)