Insulation withstand voltage detector circuit

This insulation withstand voltage tester can test lamps.
Connect the lamp to be tested to terminals A and B, and press button SB1. The intermediate relay 1KA is energized and self-locking; then
adjust the voltage regulator VT (1: io, output o - 250V) to the voltage value to be measured.
If it needs be adjusted to 1500V, adjust VT to the voltmeter indication of 150V (same principle , when working with 2000V
withstand voltage. Adjust the voltmeter to indicate 200V). After the time relay KT is delayed,
the power supply is automatically cut off, as shown in Figure 5139.
    If the insulation of the object under test breaks down, the current will increase rapidly, and the current relay KA will act
. 2KA will be electrically activated and self-locking. 1KA will lose power. The moving and closing contacts of IKA will cut off
the main circuit power supply, and the buzzer HA will sound. Press After SB2 is turned off, all circuits
are turned off. When operating this instrument, special attention must be paid to personal safety. When the power is on during work,
it is forbidden to approach the high-voltage test area.