Connection mode of current transformer
The current transformer is used in the AC circuit, and the direction of the current changes in the AC circuit. The polarity of a current transformer refers to the same polarity of one end of the primary side and one end of the secondary side at a certain time, i.e. both positive and negative. The polarity is called the same polarity end or the same name end, and is denoted by the symbols "*","-" or "." It can also be understood as the relationship between the primary current and the direction of the two current. According to the regulations, the primary coil of the current transformer is marked with L1 at the head and L2 at the tail; the secondary coil is marked with K1 at the head and K2 at the tail. In wiring, L1 and K1 are called the same polarity ends, L2 and K2 are also the same polarity ends. The three annotation methods are shown in Figure 1. The discrimination of the polarity ends of the current transformer is the same as that of the coupling coil. Simpler methods, such as connecting a primary coil with a 1.5V dry cell, and connecting a secondary coil with a high internal resistance large-range DC voltmeter. When the switch is closed, if the forward deflection of the voltmeter pointer is found, it can be judged that 1 and 2 are the same polar end, when the switch is closed, if the reverse deflection of the voltmeter pointer is found, it can be judged that 1 and 2 are not the same polar end.
One phase wiring
The current transformer with one-phase current protection is mainly used to measure one-phase current in three-phase equipment with symmetrical three-phase load or small phase load balance. The connection of the current transformer has little to do with the polarity, but it should be noted that the secondary side should be protected grounding to prevent the primary side from overcurrent, the current transformer is broken down, burning the secondary side of the instrument, relay equipment. But no grounding is strictly prohibited. A two point grounded two current will form a shunt in front of the relay, resulting in no action of the relay. Therefore, it is stipulated in the Technical Specification for Relay Protection that several groups of current transformers connected together should be grounded on the protection screen through the terminal row. For example, transformer differential protection, and several groups of current transformers after the combination of only a separate contact point.
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