11 Application Circuits of Current Transformer
This article lists the application circuits of 11 kinds of current transformers for electricians to refer to.Figure 3: it is a differential connection method. Two mutual inductors are used to connect the common circuit that can respond to symmetrical overload and three-phase short circuit. If it is used in motor protection circuit, the effect is poor, but the use of element equipment is at least. In order to trek the mobility, signals can be connected at the back to broaden the circuit and promote the operation of electronic circuits.Figure 4: in order to prevent high voltage protection in the application of electronic circuits, the simplest way is to clamp the voltage with diodes, and the clamping voltage is selected by the number of diodes in series. If voltage stabilizing tube and varistor are used, the effect will be very good.
Figure 5: this circuit can eliminate the phenomenon that the contactor coil f is not firmly pulled in due to the decrease of power supply voltage when the motor claims (the secondary voltage of the transformer will be superimposed with the power supply voltage of the control circuit, and pay attention to the polarity of the wiring).
Figure 6: the current transformer is used as a low impedance electrical component, which can be used for the test of current relay, thermal relay, etc. When manufacturing, the cross-sectional area of the penetrating conductor must be large and the length may be as short as possible. If the number of turns is added, the current will also increase. The transformer with large transformation ratio and large capacity is the best choice. For 150VA transformer, when the total resistance is 6 , the voltage can reach 30V. Caution: during the secondary boost process, the ammeter reading shall not exceed 5 a.
Figure 7: circuit for measuring volt ampere characteristics of current transformer. Step up the voltage step by step as shown in the figure. When the current is added and the reading of the voltmeter is no longer changed, the magnetic field is full. The volt ampere characteristic curve can be drawn by measuring the data corresponding to volt ampere.Figure 8: it is a control signal that reflects the current change taken out from the line by the transformer. If the number of turns of the primary winding is added, the signal can be enhanced.Figure 9: it is a motor open phase protection circuit of negative sequence current filter. When one phase is disconnected, the negative sequence current rises. If the secondary of the transformer is connected with a current filter combined with phase-shifting elements, the negative sequence current can be output. The transformer shall be made of magnetic ring with rectangular magnetic characteristics, and the secondary coil shall be generally distributed in hundreds of turns.
Figure 10: it is a third harmonic current and motor open phase protection circuit. Because the third harmonic is in phase, it is also called zero sequence current protection circuit. The current transformer is not linear, but flexible and full, so the iron core should be made of ferrite ring.Figure 11: using current transformer as transformer for single line telemetry. Transformer B can be replaced by output transformer, and the voltmeter scale in the control room shall be changed to the calibrated current scale. Voltage relay can be used as alarm signal or trip switch. Usually, the remote control interval can reach hundreds of meters.
