The State Grid Corporation has progressively standardized technical requirements for electricity meters, formulating relevant industry standards and technical specifications. This has presented certain technical challenges regarding the parameter testing of relays-specifically concerning aspects such as a relay's load switching capacity and switching characteristics. Consequently, there is an urgent need to develop a device capable of comprehensively testing relay performance parameters.
Based on the testing requirements for relay performance parameters, test items can be broadly categorized into two groups: (1) tests conducted without a load current-such as those for actuation values, contact resistance, and mechanical life; and (2) tests conducted with a load current-such as those for contact voltage drop, electrical life, and overload capacity.
The primary test items are briefly described below: (1) Actuation Value: The voltage value required to trigger the relay's operation. (2) Contact Resistance: The resistance value measured between the two contacts when the contacts are closed. (3) Mechanical Life: The number of times the relay can undergo repeated switching cycles without sustaining mechanical damage. (4) Contact Voltage Drop: The voltage value measured across the contacts when a specific load current is applied to the contact circuit while the contacts are closed. (5) Electrical Life: The number of reliable switching cycles the relay can perform when the rated voltage is applied across the drive coil and a rated resistive load is applied to the contact circuit, under conditions involving a cycling rate of less than 300 cycles per hour and a duty cycle of 1:4. (6) Overload Capacity: The number of reliable switching cycles the relay can perform when the rated voltage is applied across the drive coil and 1.5 times the rated load is applied to the contact circuit, at an operating frequency of (10 ± 1) cycles per minute.
① Measuring Contact Resistance: Use the resistance range of a multimeter to measure the resistance between the normally closed (NC) contact and the movable contact; this resistance value should be 0. Conversely, the resistance between the normally open (NO) contact and the movable contact should be infinite. This method allows one to distinguish which contact is the normally closed contact and which is the normally open contact.
② Measuring Coil Resistance: Use the R×10 range of a multimeter to measure the resistance value of the relay's drive coil; this allows for a determination of whether the coil suffers from an open-circuit fault.
③ Measuring Pull-in Voltage and Pull-in Current: Utilize an adjustable regulated power supply and an ammeter to apply a specific voltage to the relay, while connecting the ammeter in series within the power supply circuit to monitor the current flow. Gradually increase the power supply voltage; when you hear the click indicating the relay has actuated (pulled in), record the pickup voltage and pickup current. To ensure accuracy, you may repeat this process multiple times and calculate the average value.
④ Measuring the Release Voltage and Release Current: Connect the test setup as described above. Once the relay has actuated, gradually decrease the supply voltage. When you hear the click indicating the relay has released (dropped out), record the voltage and current at that moment. Again, you may repeat this process multiple times to obtain the average release voltage and release current. Typically, the release voltage of a relay falls within the range of 10% to 50% of its pickup voltage. If the release voltage is too low (specifically, less than one-tenth of the pickup voltage), the relay cannot be used reliably, as this poses a threat to the stability of the circuit and renders its operation unreliable.
