Current type anti-tamper circuit

When the load current of the circuit is greater than the rated current of the electric energy meter, the user's power supply is immediately cut off. After the excess load is subtracted, the power supply
can be restored after pressing the reset button . It is simple to make, convenient and feasible.     The circuit principle is shown in the figure. The AC relay K is controlled by the bidirectional thyristor VTH. The same terminals of TA1 and TA2 are connected. When the current through the BD section wire is equal to the current in the energy meter, the secondary side induced voltages of TA1 and TA2 are equal. There is no voltage between the "1" terminals of TA1 and TA2, and VTH is not conducting. K is released, and the normally closed contact of K supplies power to the user.     However, in the case of electricity theft, the current passing through the wire in the BD section is not equal to the current in the energy meter, and the voltage difference induced on the secondary side of TA] and TA2 causes VTH to trigger conduction. K pulls in, and its normally closed contact cuts off the user's power supply circuit; at the same time, K closes, keeping K in the pull-in state. After the power management personnel unpack and open the machine cover, and press the reset button SB, K will be released to restore power to the user . C in the VTH trigger circuit has an anti-interference effect and prevents the device from malfunctioning; R has the effect of limiting the trigger current to avoid damage to the VTH trigger junction.     Selection of components: Relay K can use AC 220V JQX-4 small high-power relay. Using several normal contacts in parallel can increase the load capacity. VTH can use 3CTSIB. 'rAl and TA2 parameters should be very consistent, otherwise malfunction will occur when the current is large. During production , it is better to use an annular core as the iron core. The power cord can pass through it as the primary side, and a suitable enameled wire can be wound with hundreds of turns as the secondary side.