Development of an on-line leakage protector tester

Development of a type of leakage protector tester

installing leakage protectors (residual current operated protectors) in low-voltage distribution systems is one of the effective means to prevent electric shock accidents, and it is also a technical measure to prevent electrical fires and electrical equipment damage accidents caused by leakage from making a certain contribution to ensuring the reliability of vehicles while developing various products. National standards require that after the leakage protector is put into operation, the user unit should establish operation records and corresponding management systems, and press the test button every month under the power on state to check whether the leakage protector is reliable. The number of inspections should be increased in thunderstorm season. However, this experiment can only be used to check the tripping function of the leakage protector, and cannot be used to check the values of the electric action current and breaking time of the rated leakage built-in 24 level filter. Therefore, the national standard also stipulates that the action characteristic experiment of leakage protector should be carried out during the mold structure period to test the leakage action current value, leakage non action current value and breaking time. We have developed a leakage protector tester, which can test the above functions

1 hardware circuit design hardware circuit mainly includes signal acquisition and control circuit, power failure detection circuit and MCU control circuit. 1.1 the rated leakage action current I specified in the national standard of signal acquisition and control circuit Δ The priority values of N are: 0.006, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1, 3, 5, 10, 20A; Rated leakage non action current I Δ The priority value of no is 0.5i Δ n. If other values are used, it should be greater than 0.5i δ n； The breaking time of leakage protector is shown in Table 1 and table 2

Table 1 maximum breaking time I of leakage protector for direct contact Δ N/a rated current in/a maximum breaking time/si Δ n2I Δ N0.25a0.006 any value 510.040.01050.50.040.0300.50.20.04 Table 2 maximum breaking time I of leakage protector for indirect contact Δ N/a rated current in/a maximum breaking time/si Δ n2I Δ n5I Δ N 0.03 any value 20.20.04 LDPE film blowing return particles 5 (2) 0 parts by weight is applicable to equipment ≥ 4050.30.15 hand-held electric tools, mobile appliances, household appliances socket circuits. I is preferred Δ n. It is a fast acting leakage protector of 30mA and above and 100mA and below; I shall be selected for the total protection of multiple equipment Δ N is a fast acting leakage protector of 100mA and above. According to the above requirements, I Δ N leakage protectors not greater than 30mA are widely used. It can be seen from table 1 that 250mA leakage current should be generated when testing the breaking time of the leakage protector for direct contact. Therefore, the tester is designed to generate a maximum leakage current of 275ma (effective value), which can meet test I Δ N refers to all test items and I of leakage protector of 50mA and below Δ N is the leakage protector of 100mA except 5I Δ N all test items beyond the breaking time. The signal acquisition and control circuit of the tester is shown in Figure 1. Kn62s three position switch is selected for K. when k is closed to position 1, the leakage action current value and leakage non action current value are tested. Q1 and Q2 are Optical MOS solid state relays, and their maximum open circuit leakage current is 10 μ A。 When testing the breaking time of a leakage current of the leakage protector, turn on Q1 after K is closed to position 2, and the rectifier bridge is between N0 and N1. Adjust the current to the test value, then turn off Q1 (delay more than 10ms, ensure that Q1 is disconnected) and turn on Q2. Connecting from N1 to N2 means that leakage current suddenly occurs, and start measuring the breaking time at the same time. Because the potential of the zero line n is generally different from that of the ground line PE, the test point N2 is not connected to the PE line. V1 is connected to the power-off detection circuit. According to the rectifier characteristics and the definition of current effective value, it is known that the current effective value before and after the rectifier bridge is equal, and I1 in Figure 1 is the leakage current value. Considering that the collector potential of the triode is high during the test, the effective value I3 of the emitter current of the triode is taken as the measurement signal. Control voltage V3 as the measurement signal. The control voltage V2 is 1.4 ~ 4.8V, the HFE of 2sd272 and 2sd594 are 40 and 50 respectively, R3 is taken as 1 Ω, and the value of R2 is determined by the following formula:

R2 is taken as 15K Ω. RW uses a 10k Ω potentiometer to adjust the dynamic range of V2 at the factory (different HFES of 2sd272 and 2sd594 may be different). ∵ i1=i3-i2 ∵ i1=i3-[1/(1+40) (1+50)] if i3=i1, the error Er caused by simplification is: because Er is very small, it can be considered that i1=i3. ∵ v3=i3r3, the value of leakage current I1 can be measured from v3. 1.2 when the power-off detection circuit tests the action persistence of the leakage protector, it must accurately measure the action time of the leakage protector. The power-off detection circuit designed by this system is shown in Figure 2. 6N138 is the optocoupler packaged with photodiode and Darlington phototransistor. The primary side working current if is 1.6mA, ifmax is 20mA, and vfmax is 1.7V. Considering that the forward conduction voltage drop vdmax of the rectifier bridge is 2.4V, the primary side current if of 6N138 is determined by the following formula: it is necessary to increase if to 1.6mA from the zero time of V1