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# Explain in detail the four connection methods of electromagnetic current transformers that are easy to understand -

by：Transmart     2023-01-06

Through the previous study, I have understood the basic principle structure, transformation ratio, capacity, accuracy level and precision of electromagnetic current transformers. This chapter will briefly introduce several common wiring methods of electromagnetic current transformers; 1. Single-phase Type wiring, as shown in the figure: This kind of wiring is only composed of a current transformer, the wiring is simple, and it is not commonly used in the power supply system. 2. Incomplete star connection, as shown in the incomplete star connection, is also called two-phase V-shaped connection form. According to the three-phase electric calculation formula IB=-(Ia+Ic), only the A-phase current and C-phase current need to be measured , the current flowing in their common return line is the B-phase current. (1ka shows A-phase current, 2ka shows B-phase current, 3ka shows V-phase current). Not commonly used in power supply system Incomplete star connection is often used in 6-10kV neutral point not directly grounded three-phase three-wire system 3. Two-phase current difference wiring, as shown in the two-phase current difference wiring, measure A phase and C respectively For phase current, connect S1 of phase A to S2 of phase C. In theory, when the circuit is faultless, Ia=Ic, and the current angle of phase C is minus 120 degrees, so Ka has no numerical display. ① When the AB phase is short-circuited, the CT of the A phase detects the fault current, and Ka has a fault current display. ② When the AC phase is short-circuited, the A and C phase CTs detect the fault current respectively, and Ka has a fault current display. ③ When the BC phase is short-circuited, the CT of the C phase detects the fault current, and Ka has a fault current display. The two-phase current difference wiring method can only be used in the small current grounding system in the power system. When a ground fault occurs in any phase, since it is a small current grounding system, it is allowed to operate with the ground point for 2 hours, so there is no need to trip. 4. Three-phase star connection, as shown in the figure three-phase star connection, this connection method is relatively common and widely used in the entire power system. It can measure the three-phase current of the circuit and monitor the load asymmetry of each phase.
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