Surge Arresters / MOA / Lightning Arresters
Surge arresters help prevent damage to apparatus due to transient overvoltages. The arrester provides a low-impedance path to ground for the current from a lightning strike or switching overvoltage and then restores to a normal operating condition. A surge arrester may be compared to a relief valve on a boiler or hot water heater. It releases high pressure until a normal operating condition is reached. When the pressure is returned to normal, the safety valve is ready for the next operation. When a high voltage (greater than the normal line voltage) exists on the line, the arrester immediately furnishes a path to ground and thus limits and drains off the excess voltage. The arrester must provide this relief and then prevent any further flow of current to ground. The arrester has two functions: it must provide a point in the circuit at which an overvoltage pulse can pass to ground, and it must prevent any follow-up current from flowing to ground.
TESTING SURGE ARRESTERS
Two of the most common tests to perform in the field on surge arresters are the electrical parameter test and infrared analysis. Some manufacturers state that no single test will indicate the complete operating characteristics of an arrester. Reference service advisories from some manufacturers recommend power factor testing and infrared as methods to detect possible problems caused by moisture ingress. Field testing of arresters by power factor, infrared or other methods is used as a reference.
Different models and makes of arresters will have different watts-loss readings. The tester is attempting to identify a variance in the past watts-loss readings. The arrester should have a visual inspection to detect cracks in the porcelain, abnormal rust staining and any abnormal physical condition of the arrester that is observed. Incorrect factory installation of arrester gaskets has been detected by visual inspection upon receipt of the arresters.
Few Advance equipment are available in market which can measure parameters such as Power factor , Watt Loss , Total Leakage Current , Total Resistive Current , Total Third Harmonic Current , Third Harmonic Resistive Current etc. Relationship of all these parameters helps us in deciding the health of LA Tester
Here is a format of comparison of various factors found after testing of Lightning Arresters .
For example the Angle shall be >80' , It is visible from below report that the LA with angle < 80' are under scanner , It is further observed that the P( Watt ) & Ir3 ( 3r harmonic resistive current ) of those arresters is also indicating health issue . All abnormal results are marked by red .
We can analyse the healthiness of the LA/MOA by analysing multiple factors . For broader perspective we should combine electrical as well as Infrared testing methods .