ELECTRIC METER INTELLIGENT SWITCH, CARRIER MODULE CIRCUIT PROTECTION SOLUTION

The meter smart switch is an intelligent device that integrates multiple functions, mainly used to control  and monitor the switch status of the power system. Power line carrier module (PLC) is a device that uses power lines to transmit data signals. It is mainly  used in power systems, smart homes and remote meter reading. Its main working principle is to modulate  the data signal onto the power line, transmit it to the receiving end through the power line, and then  restore it to the original data signal through demodulation technology. Under normal circumstances, the  power line carrier signal will be converted into an RS232 or RS485 interface.

Instantaneous high voltage (surge) may occur in the power grid due to  lightning strikes, equipment start-up and stop (such as motors, transformers)  or line failures. The high voltage may break down the semiconductor devices  (such as MOSFET, relays) of the smart switch or the communication chip of  the PLC module. In addition, load short circuit, internal equipment failure or  wiring error may cause abnormal increase in current, resulting in heating of  the wire, burning of components, and even fire. Therefore, it is necessary to  protect it.

The PLC signal access point on the LN line needs to be behind the varistor (RV1), and the varistor  recommended is 20D821K.  Two differential mode inductors (L1/L2) need to be connected in series behind the PLC signal to  isolate it from the power supply of the whole machine, and the differential mode inductor value is recommended to be 50~100uH.

2.220VAC AC power supply protection circuit: 

Recommended components: 

Varistor: 14D561K, Gas discharge tube: 2R600L 

Solution advantages: Simple circuit, first-level protection, composite symmetrical circuit, common mode and differential mode full protection.

3.Recommended devices: 

Gas discharge tube GDT:  3R090L-5*7.6 3R090S-5*7.6 3R090L-8*10 3R090S-8*10 

Transient suppression diode TVS: SMBJ6.5CA SMBJ7.0CA 

Common mode filter: Common mode filter recommends CMZ4532A-501T or CML4532A-510T. You  can also connect a resistor (more than 2 ohms) or a magnetic bead to each line, or you can not use  it. 

Grounding design: Use an independent ground plane, and the TVS ground terminal is directly connected to the metal shell.

4.RS232 circuit protection 

Advantages and disadvantages of the solution: The lightning protection level is very high, TVS diodes  are used, the parasitic capacitance is high, and it has a certain impact on the rate.

5. Carrier coupling signal protection solution: 

Use semiconductor discharge tube P0300SC, which has the characteristics of ultra-fast response  speed, stable IH value, minimal signal attenuation, and strong continuous anti-interference ability,  ensuring sufficient surge capacity while ensuring signal integrity.