Residual current transformer function

- Jan 13, 2020-

What is a residual current transformer

Residual current transformer English name: residualcurrenttransformer Definition: One or three current transformers connected as a group to transform the residual current.

The residual current transformer is also called the leakage current transformer. Similar to the principle of zero-sequence current transformers, zero-sequence current transformers are generally suitable for TN grounding systems, and the setting current of the residual current transformer protection action can be from mA level to A level, which has a fairly high operating sensitivity, so the residual current protection The device is applicable to TT, IT, TN﹣STN﹣CS system grounding systems. During installation, the three-phase wires A, B, and C pass through a residual current transformer together with the N wire.

Principle of residual current transformer

Residual current transformers are often used in combination with residual current electrical fire monitoring detectors to detect leakage current (ie, residual current). It is a special transformer that consists of a coil and an iron core. The principle is based on Kirchhoff's current law: the algebraic sum of the complex currents flowing into any node in the circuit is equal to zero. When the line and electrical equipment are normal, the vector sum of the currents of the phases is equal to zero, and the secondary winding of the residual current transformer has no signal output; when the ground fault occurs, the vector sum of the currents of the phases is not zero. A magnetic flux is generated in the toroidal core of the residual current transformer, and the secondary winding will send a signal. When the electrical fire monitoring detector receives the signal, it will give an alarm.

Residual current transformer function

The setting current of the residual current transformer protection operation can be from mA level to A level, and the sensitivity is very high, so it can detect slight changes in leakage current in electrical circuits. It is used to extract the residual current signal of the monitored line, and it can continuously detect the leakage current to the ground system. It can convert the primary current with a larger value into a secondary current with a smaller value through a certain transformation ratio for protection and measurement. , And can simultaneously realize the power monitoring and other purposes of the three-phase system. When a leakage current occurs in the electrical circuit, the trip device will be driven to switch the power supply network to achieve the purpose of ground fault protection.

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