To determine whether the leakage current of a surge protector (SPD) exceeds the standard, a comprehensive judgment should be made based on standard requirements, measurement methods, and data comparison. Here are the specific steps and key points:
1、 Clarify the standard requirements for leakage current
The leakage current standards applicable to different types of surge protectors (such as pressure-sensitive, gap type, etc.) are different, and the product type and specifications need to be confirmed first:
Pressure sensitive SPD (with MOV as the core component)
Single MOV: initial measurement of leakage current ≤ manufacturer's nominal value; If there is no nominal value, ≤ 20 μ A.
Multiple MOVs in parallel: leakage current ≤ manufacturer's nominal value; If there is no nominal value, ≤ 20 μ A x MOV number (if the number of pieces is unknown, default is ≤ 20 μ A).
Subsequent measurement: Leakage current ≤ 2 times the initial measurement value (if the initial measurement is 10 μ A, subsequent measurements should be ≤ 20 μ A).
Special specifications: Small size low-voltage MOV (such as 5mm or less, varistor voltage<100V), at 0.85U ₀ Leakage current under voltage ≤ 30 μ A (U ₀) ₁ is the voltage at a current of 0.1mA.
Gap type SPD (such as gas discharge tube)
During normal operation, the leakage current is extremely small (close to 0 μ A), so there is generally no need to pay attention to the issue of excessive leakage current.
2、 Use professional instruments to measure leakage current
1. Measuring tools
Specialized SPD tester: such as the leakage current tester in lightning protection detection equipment, it can directly apply a specific voltage (such as 0.75U ₁ mA, the voltage sensitive voltage when U ₁ mA is 1mA current) and read the leakage current value.
High precision multimeter: requires an adjustable DC power supply to manually apply voltage and measure current (suitable for easy on-site testing).
2. Measurement steps
Disconnect the power supply: Ensure that the SPD is disconnected from the circuit to avoid interference from other components during measurement.
Apply test voltage:
For MOV type SPDs, a voltage of 0.75 times the U ₁ mA is usually applied (if U ₁ mA is 385V, a DC voltage of 288.75V is applied).
For small-sized MOVs, it may be necessary to apply 0.85 times the U ₀ according to the product standard ₁ Voltage.
Read leakage current value: Record the current value (unit: μ A) after stabilization.
3、 Compare standards to determine if they exceed the standard
1. First measurement of newly installed SPD
If the measured value is greater than the manufacturer's nominal maximum leakage current and exceeds the standard, it needs to be replaced or returned to the factory for testing.
If there is no nominal value, the measured value is greater than 20 μ A (single piece) or greater than 20 μ A multiplied by the number of pieces (multiple pieces) → exceeding the standard.
2. Regular testing of SPD during operation
Compared with the first measurement data, if the current leakage current is greater than twice the first value and exceeds the standard, it indicates that the MOV performance has deteriorated and needs to be replaced in a timely manner.
If the first measurement data is missing, it should be judged directly according to the "first measurement standard" (such as measurement value>20 μ A and no nominal value → exceeding the standard).
4、 Precautions and Exception Handling
environmental impact
An increase in temperature can lead to an increase in MOV leakage current (for example, for every 10 ℃ increase in temperature, the leakage current may double). When measuring, it is necessary to record the ambient temperature to avoid misjudgment.
Excessive humidity may cause surface leakage of SPD, and it is necessary to ensure that the equipment is dry and clean.
EXCEPTION
Slight leakage current exceeding the threshold: Check whether the SPD is aging, damp, or subjected to transient overvoltage impact, and conduct short-term monitoring and strengthen inspections.
Leakage current significantly exceeding the threshold: Immediately stop using SPD and replace with new equipment to avoid the risk of fire caused by MOV short circuit.
Record and Archive
Each measurement should record the leakage current value, measurement date, environmental conditions, and SPD status, and establish a file for tracking performance changes.
summarize
To determine whether the leakage current of surge protectors exceeds the standard, the principle of "standard first, professional measurement, and data comparison" should be followed, and regular testing should be conducted in conjunction with comprehensive analysis of environmental factors. For pressure-sensitive SPDs, excessive leakage current is usually a warning signal of component aging and needs to be promptly addressed to ensure lightning protection safety.
