High-Precision Loop Resistance Tester Introduction:
Previously, in power systems, the conventional QJ44 double-arm DC bridge was commonly used to measure the DC resistance of transformer coils and the contact resistance of high-voltage circuit breakers. However, the test current of such bridges was only at the mA level, making it difficult to detect defects such as reduced cross-sectional area of the conductive loop in transformer coils. When measuring the contact resistance of high-voltage switch conductive loops, due to the influence of oil films and oxide layers between moving and static contacts, the measurement deviation was large, masking the true contact resistance value. Therefore, the Ministry of Power standard SD301-88 "AC 500KV Electrical Equipment Handover and Preventive Test Procedures" and the new edition of "Preventive Test Procedures for Electrical Equipment" stipulate that the measurement current for contact resistance of circuit breakers and disconnectors should not be less than DC 100A to ensure accuracy. Using micro-controller control and a user-friendly Chinese character interface display, it is a dedicated device for measuring contact resistance and loop resistance of switch control equipment; its test current adopts the 100A DC recommended by the national standard GB763, allowing direct measurement of loop resistance or contact resistance at 100A current, with LCD display of test current value and test resistance value, and print output. This instrument features accurate measurement, stable performance, and convenient operation. It is suitable for on-site high-voltage switch maintenance in power and power supply departments and for loop resistance testing requirements in high-voltage switch factories.
High-Precision Loop Resistance Tester Technical Specifications:
1. Measurement range: 1-1999.9µΩ Resolution: 0.1µΩ
2. Measurement current: DC 100A±2% (at power-on)
3. Measurement accuracy: 0.5%±5 digits
4. Display mode: Large-screen Chinese character LCD
5. Power supply: AC220V 50Hz
6. Maximum output voltage: DC 5V
7. Standard output current: DC 100A±2% (at power-on)
8. The voltage/current lines of this device have directions; do not connect arbitrarily.
9. Test time setting range: 10-30-60S
Measurement wiring diagram:
The wiring schematic during measurement is shown in the figure. The test clips equipped with this tester can simultaneously perform the dual functions of 100A current output and monitoring output voltage. The thick wire on the test lead is the current output line, which can provide 100A DC current to the test object; the thin wire on the test lead is the measurement input line, which sends the voltage across the test object to the measuring instrument, thereby converting it into a resistance value for display. Since micro resistance values are measured, to ensure accuracy, special attention must be paid: the position of the test clips must be as close as possible to the measurement points of the test object, and the test object should be clamped tightly, so that the measured value is reliable.
Measurement steps:
1. Connect the test leads to the instrument and clamp the test object properly.
2. Connect the ground wire (or clamp the grounding clip to the metal part of the case handle)!!!
3. Plug in the 220V power supply, turn on the power switch, and correctly input the test duration.
4. Correctly select the test current range.
5. If the measurement current cannot reach 100A, or is zero, check whether the connected loop is in good condition.
6. If a single measurement takes too long and the power supply overheats, automatic protection will activate. Turn off the power for a period (about 10-20 minutes) to allow the power supply to cool down before reuse.
7. After a measurement is completed, the machine displays the test result. At this time, press the save key to save, the print key to print, and the test key to retest.
8. The test current range must be selected before starting the test! (For models with current selection)
9. The interval between two tests should not be less than 30 seconds.
10. It is recommended to test three times and take the average (due to surface oil contamination or poor contact causing deviations in test values).
11. If the current line disconnects during testing, the instrument will automatically detect it, cut off the current output control, and prompt 'Please check the circuit'!!!
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