Thermal relay detector circuit

Thermal relays are prone to thermal aging during long-term energization, causing their operating characteristics to change. To maintain the consistency and stability of characteristics,
one of the most important measures is to conduct regular testing of thermal relays.
    The thermal relay detector is shown in Figure 5-40. It
is mainly composed of a regulator TV, a step-down transformer T, a slide
resistor R, a 410-type millisecond meter and other components.
    The three-phase bimetallic sheets (thermal relay FR) should
be connected in series and connected to the test circuit. Before testing, first check whether
the scale current of the thermal relay
matches the rated current (IN) of the motor. Then pass
1. 05A to the thermal relay (rated current, achieved by adjusting R
). Check the synchronicity, that is, whether the three-phase dual poles are
in contact at the same time. If they are out of sync, use flat-nose pliers to clamp
the spot welding between the bimetal piece and the bracket to adjust the synchronization. After the synchronization is adjusted, first do a starting test and pass
a current of 61N to the thermal relay FR. It should not act within 5s} Secondly, do an operation test to heat the thermal relay to a stable thermal state. After 30 minutes, slowly adjust R to
make FR act, and then rotate it a little further to make the FR contact open; then Increase the test current to L 21. , at this time it should take action within 20 minutes. In this
way, the setting verification of the thermal relay
ends.     The following two points should be noted when adjusting and testing: 1) It is not allowed to use pliers to bend the bimetal piece, so as not to affect the stability of the protection. 2) The detection connection
wire should have sufficient cross-sectional area to avoid affecting the action time.