Surge Arresters ( Lightning Arresters ) are the protective devices for limiting the surge voltages on the equipments / power distribution system. These arresters help in discharging this surge current, thus protecting the system and equipment from dangerous overvoltages and also disturbances. These Lightning arresters, age out during its period of services due to,
• Moisture ingress, due to sealing problems.
• Ageing of Zinc Oxide Varistors.
• Dust particles on external surface.
• Cracks on porcelain surface.
As we are all aware, when Lightning Arrester fails it explodes with porcelain splinters and apart from creating a Short Circuit, it also mechanically damages the other surrounding equipments like CTs, PTs, Transformer Bushing etc, thus creating a total disruption of power circuit. In view of above, it is necessary to monitor the health of Lightning Arrester periodically, particularly, before stormy weather or monsoon. These lightning arresters can be tested online.
Online testing of Lightning Arrester is carried out by harmonic analysis of leakage current.
The 3rd Harmonic harmonic current analysis, Watt Loss, Total Resistive Current & Power angle measurement is used as a tool to diagnose the health / reliability of the Lightning Arresters.
1.0 Testing of surge arresters is carried out as follows,
1.1 Current cable is connected on the grounding strtip of the arrester across counter.
1.2 Voltage Signal is received by the device using any one of below methods -:
a) Wired method
b) Wireless method (using transmitter & receiver )
c) Electromagnetic (EM) Antenna
2.1 Following parameters are measured.
True rms value of total current, flowing through ground circuit.
Peak value of total current
True rms value of third harmonic leakage current.
Total Resistive Current
Total Power Loss
Power Angle
KPM LA100+ & KPM LA 103+ have all above features
An increase in the above interdependent parameters brings the arrester to thermal overloading and finally causes breakdown. If the increase in the 3rd harmonic current is monitored and detected earlier, then arrester can be repaired or replaced, thus preventing damage. The parameters of currents recorded are compared with previous measured values on the same arrester. The values are also compared with arrester of similar make and type, operating under similar conditions over a period of time.
The recommendations for measurement are:
Resistive current is to be measured after installation and then over a period of two years.
Measurements shall be carried out after severe overvoltages experienced in the system.
Lightning Arresters located in stormy weather or polluted area, shall be tested every 12 months.
Arresters, which are in service for many years shall be periodically tested to trend and monitor their condition.