Application of PTC thermistor as overcurrent protection in single-phase multifunction watt hour meter
Nowadays, most power supply departments have to prevent the watt-hour meter from being damaged due to the wrong connection of the power grid, or to artificially use the over-voltage power supply method to destroy the watt-hour meter. The newly installed single-phase watt-hour meter is required to withstand high voltage (such as 380V) for a certain period of time (such as 4h) without damage. If the input circuit of the single-phase meter is not processed, the input high voltage will cause the meter to burn out in a short time. As long as a suitable PTC thermistor is connected in series with the input end of the transformer for overcurrent protection, and the external voltage is mainly applied to the PTC thermistor, the linear transformer can be prevented from being heated and damaged. In order to ensure that no malfunction occurs, the non-operating current of the thermistor should be selected with reference to the actual AC input current of the meter, leaving a 50% margin, and the Curie temperature should be ≥80 °C; At the maximum operating temperature, the meter cannot be protected during maximum load operation. At the lowest working temperature, when the input terminal is added with 380V AC, the PTC in the meter should be protected in a short time to ensure that the meter is not damaged.
The circuit diagram is shown in Figure 1.
The circuit diagram is shown in Figure 1.
