Importance of Surge Arrester Leakage Current Measurement
Measuring the leakage current of surge arresters is one of the most important routine preventive tests in power operation and maintenance. It is the most direct and effective method to judge whether the arrester is damp, whether the internal valve plates are aging, or whether the overall insulation performance has deteriorated. Whether it is 10kV distribution lines, substation high‑voltage equipment, or power distribution systems in industrial and mining enterprises, regular leakage current measurement must be carried out. This inspection can eliminate hidden dangers in advance and prevent equipment breakdown, line tripping and even grid accidents caused by arrester failure. Mastering standard measurement methods, operating procedures and judgment standards has become an essential professional skill for electrical maintenance personnel.
Mainstream Measurement Methods and Testing Principle
The measurement of arrester leakage current is mainly divided into two mainstream methods: DC power‑off measurement and AC live line measurement. DC testing is mostly used for handover acceptance and annual preventive tests, while AC live detection is commonly adopted in daily operation inspections. Among them, the DC measurement method is recognized as the standard detection method in the power industry. The testing principle is based on the nonlinear characteristics of zinc oxide valve plates. Under normal operating conditions, the arrester maintains a high‑resistance state, and the leakage current is only at the microampere level. Once the interior becomes damp, the valve plates age, or the insulation structure is damaged, the leakage current will increase significantly. The health status of the arrester can be accurately judged through data comparison.
Pre-test Preparation and Safety Requirements
Firstly,Adequate preparation must be completed before formal testing，disconnect all external connecting wires of the arrester, remove auxiliary components such as discharge counters and grounding leads, to avoid shunt current interfering with test data.
Secondly, prepare professional testing tools, including a DC high‑voltage generator, microammeter, insulated grounding wire, discharge rod and temperature and humidity recorder. All testing instruments must be within the valid calibration period. Meanwhile, strict on‑site safety protection measures should be implemented, high‑voltage warning areas should be marked, and at least two staff members are required for on‑site operation, one for operation and one for safety monitoring. Outdoor testing is prohibited in rainy, foggy and high‑humidity weather. The ambient humidity must be kept within a reasonable range to prevent surface creeping current from affecting the accuracy of test results.
Standard Operating Procedures for DC Power-off Measurement
Standard DC measurement follows strict operating steps. Connect the circuit reliably first: the output terminal of the high‑voltage generator is connected to the high‑voltage end of the arrester through a microammeter, and the equipment shell and arrester base must be firmly grounded. Recheck all wiring to ensure correctness before powering on. Before boosting pressure, turn the voltage regulating knob back to zero. After switching on the power supply, raise the voltage steadily and observe the microammeter reading in real time. Slow down the boosting speed when the current approaches 1mA, and accurately adjust the current to a stable value of 1mA. Record the voltage at this moment as the DC reference voltage U1mA. Then reduce the voltage to 75% of the reference value. After the data becomes stable, record the leakage current at this voltage point, which is the core basis for judging whether the arrester is damp or degraded.
Post-test Operation and Safety Specifications
Do not disconnect the wiring directly after the test. Operate strictly in the sequence of voltage reduction, power off and full discharge. Reset the voltage regulating knob to zero, turn off the DC generator, and use a discharge rod with current limiting resistance to fully release residual charge at the high‑voltage end and terminals of the arrester. Only after confirming no residual voltage can the test wires be removed in order, the original wiring of the arrester be restored, and on‑site tools be sorted out.
Data Judgment Criteria and Correction Notes
There are clear judgment criteria for measured data. For conventional zinc oxide arresters, the leakage current under 0.75 times U1mA should not exceed 50μA. Excessively high values usually indicate internal dampness or obvious performance degradation of valve plates. The deviation of the DC reference voltage compared with the factory initial value shall not exceed ±5%. A significant drop in reference voltage means aging and failure of the valve plates. In addition, the ambient temperature during the test should be recorded in detail, because temperature changes will affect the leakage current value. The reading will rise slightly under high temperature conditions, and reasonable correction should be made during evaluation to avoid misjudgment.
Overview of AC Live Line Measurement Method
In addition to power‑off DC testing, live AC measurement can be applied to arresters in operation. There is no need to cut off power or dismantle wires. Special live testers are used to collect total current and resistive current. The operating state is judged by comparing with historical data. If the resistive current increases by more than 30% compared with the initial value, or the total current fluctuates abnormally, power‑off re‑inspection shall be arranged in a timely manner to eliminate internal hidden troubles.
In summary, arrester leakage current measurement features rigorous procedures and strong professionalism. Operators must strictly abide by power test standards, complete pre‑test preparation, standardize wiring and pressure boosting, record readings accurately, and implement full discharge safety regulations. Regular detection can effectively discover latent faults such as internal dampness, aging and insulation damage of arresters, ensure the stable operation of high‑voltage lines and power distribution equipment, and is an indispensable key link in daily grid operation and maintenance.
