This section provides an overview for earth leakage relays as well as their applications and principles. Also, please take a look at the list of 10 earth leakage relay manufacturers and their company rankings.
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An earth leakage relay is a component used to detect current leakage caused by a short circuit between an electric circuit and the earth (ground) due to an insulation breakdown of a cable or circuit element. An earth leakage relay is also called ground fault relays (GR). Earth leakage relay can be either non-directional or directional.
Earth leakage relays are mainly used to detect earth leakage in circuits. Earth leakage relays can be classified into two main types, which should be selected according to the equipment used and the object to be detected. The following are examples of earth leakage relays applications.
Earth leakage relays consist of a zero-phase current transformer (ZCT) that detects earth leakage and a relay section that transmits signals. It differs from an RCD because it has only a leakage current detection function and does not have an interrupting function. There are two main types of earth leakage relays. One is the "non-directional" type, which is relatively simple to construct, and the other is the directional type, which is intended for high-voltage power transmission and the like. Both types of relays use a zero-phase current transformer to measure the zero-phase current to determine whether a leakage current exists and send a leakage current signal to the circuit.
Non-directional: The non-directional system detects the fault current in case of leakage current using a zero-phase current transformer, and is also called ground relay (GR). Currents in a three-phase AC circuit are divided into three types: positive-phase current flowing in the positive phase direction on each line, reverse-phase current flowing in the reverse phase direction, and zero-phase current flowing in the same phase. The zero-phase current is usually zero (i.e., it does not occur), and the measurement of the sum of current vectors by a zero-phase current transformer will also be zero. However, since zero-phase current flows during leakage current, the leakage current can be confirmed by observing the sum of vectors by a zero-phase current transformer.
Directional Ground Relay (DGR): Detects the fault current in case of leakage current by using a zero-phase current transformer and a zero-phase voltage detector (ZPD). A zero-phase voltage detector is a device to detect zero-phase voltage, specifically, zero-phase voltage is detected by a capacitor inside the device. Regarding the voltage in a three-phase AC circuit, the zero-phase voltage is normally zero (i.e., it does not occur), but in the case of a ground fault, the saturation state is broken and a voltage is generated. This voltage is divided by a series-connected square-phase capacitor and a detection capacitor, and the voltage across the detection capacitor is further reduced by a transformer to be detected. In 6kv distribution systems, which are widely used in power transmission and reception facilities, the detection of zero-phase voltage by a zero-phase voltage detector is used instead of detection by an overcurrent relay because it is difficult to distinguish fine ground currents from load currents.
*Including some distributors, etc.
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