Methods of monitoring the state of contact connections during operation of electrical networks

Contact heating is determined during the period of maximum loads. But contact metals are known to have significant heat capacity and thermal conductivity, and therefore it is difficult to determine a contact defect.

During operation, a more accurate assessment of the state of the contacts is possible not by heating, but by measuring the voltage drop in the section of the circuit containing the contact connection when the operating current flows through the contact or by measuring the value of the contact resistance using of millivoltmeter and ammeter (or microohmmeter).

Monitoring the condition of the contact connections using a dipstick with a millivoltmeter

In the first case, the measurement is carried out at operating voltage with a measuring rod with a millivoltmeter attached to it.The measurement method is based on comparing the voltage drop in the section with the contact connection with the voltage drop in the section of the entire conductor at a constant value of the load current.

Position of the arrow when measuring the voltage drop: a — on the wire contact; b — in the section of the conductor; 1 — insulating part of the measuring rod; 2 — millivoltmeter; 3 — head of the measuring rod; 4 — probes to which the millivoltmeter is connected

In the second case, with the section of the circuit disconnected and grounded (grounding does not affect the measurement result), the devices are connected according to the scheme shown in Figure 2. The device is powered by a source of direct current (batteries).

Monitoring of the state of contact connections using the ammeter-voltmeter method

During the repair of switches, disconnectors and separators, the direct current resistance of the contact system of these devices is measured. In this case, the resistance of the entire current-carrying circuit of each phase of the switch or disconnector is measured (output — output).

The ammeter and voltmeter (or microohmmeter) method has become widespread in practice for measuring the resistance of a contact system. However, more accurate results are obtained when measuring with a double bridge.

Scheme for measuring the resistance of a contact connection by the millivoltmeter and ammeter method