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Will current transformer-resistance affect metering?

elecfans | 29/07/2021

It does not affect the measurement. The reason is that the secondary coil of the current transformer is used to collect current, and the collected current is used for measurement and measurement. Generally, it is equivalent to a resistance loop. The resistance of the current coil of the meter is smaller than yours. Therefore, the parallel resistance value does not affect the measurement. The resistance value of the coil on the two sides of the transformer is small, and then the voltage of the resistance is measured, and the current of the secondary side coil is converted through calculation. In fact, when the current transformer is working, the secondary side coil is basically equivalent to a short-circuit state.

Since the load connected to the secondary side of the current transformer is a current coil with relatively small impedance, its secondary measurement is working in a state close to a short circuit. According to the magnetomotive force balance agenda formula: I0N=1I1N1-I2N2, it can be seen that since most of I1N1 is offset by I2N2, the total magnetomotive force I0N1 is very small, that is, the exciting current I0 (ie no-load current) is very small, only once What percentage of the current I1. If the secondary side is open, then I2=0, I1N1=I0N1, that is, I1=I0, and I1 is the load current of the primary circuit, which does not change due to the change of the secondary load of the transformer. Therefore, at this time, the excitation current is I1, which greatly increases by several tens of times, and the excitation potential is greatly increased by several tens of times, which will produce:

1: Due to the large number of turns of the secondary winding, dangerous high voltages will be induced, endangering the safety of people and equipment.

2: The iron core is overheated and even the transformer is burnt. Therefore, please remember that the secondary side of the current transformer must not be open. The secondary side of the voltage transformer is not allowed to be short-circuited. Remember, one is not to open the circuit, and the other is not to be short-circuited. Finally, if you want the short-circuit current transformer to affect the measurement, it is not feasible. If the series resistance will affect the measurement, but this is Illegal oracle electricity.

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