A lightning protection system is an essential element of any building or facility to protect it from the damaging effects of lightning events. Testing the efficiency and the continuity of the Lighting Protection system is crucial for attaining the required lightning protection. The lightning protection system must be tested periodically for identifying faults and ensuring proper functioning.
The testing, inspection and maintenance of a lightning protection system are to be based on the IEC -3 Standards. The basic objectives of testing and inspection of a lightning protection system include:
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-To confirm that the lightning protection system fits into the requirements mentioned in the standard documents.
-To ensure that all the components of the lightning protection system are in good condition, there is no corrosion and are capable of performing their functions.
-To make sure that any recently added service or construction is properly incorporated into the lightning protection system.
The inspection and testing of the lightning protection system comprise the checking of internal and external systems. After a test or inspection is done, the test report or test log is generated and used to record the testing and servicing of the lightning protection system. This must be updated after each inspection, test or service. Inspection must be done at different stages, including:
The inspection must be done during the construction of the structure and installation of the lightning protection system. This is done to ensure the correct installation procedure, especially for the components that get concealed within the building structure. These components are part of the Structural lightning protection system or the natural components which become part of the lightning protection system.
Once all the components of the lightning protection system are installed they need to be inspected and tested. The electrical continuity of such components must be ensured. The complete lightning protection system is checked including the equipotential bonding and the earthing continuity.
The period of regular inspection can be decided based on the requirements of the structure. It is recommended that inspection or testing must be done at least once a year. The testing inspection or maintenance shall not be conducted during the threat of thunderstorms.
Once the structure is struck by lightning the lightning protection system needs to be inspected and repaired. There can be alterations made to the structure such as changes in the use of the building, installations of crane tracks, erection of radio and television aerials etc. So after every alternation or repair of the lightning protection system, the complete system needs to be tested.
According to IEC -3, during the periodic inspection and testing of a lightning protection system, the following need to be checked:
a) Deterioration of air termination elements, conductors and connections.
b) Corrosion of earth electrodes.
c) Earthing resistance value for the earth termination system.
d) Conditions of connections, equipotential bonding and fixings.
There are different techniques for testing the lightning protection system. The following are the commonly used methods for testing the reliability of a lightning protection system.
1) Resistance testing
2) Continuity testing
3) Ground or soil resistivity testing
4) Visual inspection
All the mechanical and electrical conditions of all conductors, bonds, joints and earth electrodes should be checked by the above methods. Each of the earthing or grounding points and the conductors connected to them are tested for earth resistance.
Proper testing of the lightning protection system can ensure that the structure and all its elements are safe from the effects of the lightning strike. The Standard insists that a competent or authorised person should carry out these inspections. A detailed report that includes the findings of the test and recommendations for further protection is obtained after every test. The recommendations provided must be considered, ensuring the required maintenance and upgrades are done. This will ensure the complete protection of the lightning protection system.
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Theory Lightning Arrester Test
Theory - LA Tester
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Lightning Arrester &#; Theory
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Link to Hengfeng
A Lightning Arrester is a device used on electrical power systems and telecommunications systems to protect the insulation.
and conductors of the system from the damaging effects of lightning. The typical Lightning Arrester has a high-voltage terminal and a ground terminal. When a lightning surge (or switching surge) travels along the power line to the Arrester, the current from the surge is diverted through the Arrestor, in most cases to the earth.
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If protection fails or is absent, lightning that strikes the electrical system introduces thousands of kilo Volts that may damage the transmission lines, and can also cause severe damage to transformers and other electrical or electronic devices.
Lightning-produced extreme voltage spikes in incoming power lines can also damage electrical home appliances that&#;s why it is damn crucial to the integrity of Lightning Arrester.
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Presently the monitoring of total leakage current (capacitive and resistive currents) is being used by many utilities. The Leakage Current Monitors are used to measure the Leakage Current of Surge Arrestors, and in case of high leakage current Surge Arrestors are replaced. However, it is felt that this method is not the fool proof method as the total leakage current, which is purely capacitive, does not signify precisely the health of the Surge Arrestors. There have been the cases when the Surge Arrestors have blasted even though total leakage current value was below the limit prescribed by the manufacturers.
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Resistive current is 15-30% of total current and since capacitive and resistive currents are at 90 degree face shift even considerable change of resistive current results in very small increase in the total current. Hence monitoring total leakage current may not truly indicate the degradation of ZnO disc. Degradation of long linear ZnO disc generally leads to harmonics in the leakage current when system voltage of fundamental frequency is applied. Third harmonic resistive current measurement is based on filtering of third harmonic component from the total leakage current. Leakage current of the order of about 500 micro amps is generally considered to be safe.
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The resistive part of the leakage current or the power loss can be determined by several methods given below:
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Using a voltage signal as reference
Compensating the capacitive component by using a voltage signal
Capacitive compensation by combining the leakage current of the three phases
Third order harmonic analysis
Direct determination of the power losses
Third order harmonic analysis with compensation for harmonics in the voltage
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Advance Monitoring System with &#;resistive current&#; component calculations.
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The use of advance diagnostic methods greatly reduces the chances of failure & hence avoids loses of man and money. It is therefore desirable to check the condition of Surge Arresters at regular time intervals, by measuring the resistive component of the continuous leakage current in service without de-energising the Arrester. Reliable measurements are achieved by the instruments based on the principle of &#;Voltage Signal&#; as a reference .
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Regular monitoring of LA has prevented many failures in 66 kV to 765 kV substations. The values of this current normally ranges from fractions of milli ampere to a few milli ampere, and are characterized by a resistive current variations whose value is an indicator of the deterioration of the Surge Arrester.
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The resistive component of this leakage current may increase due to different stresses causing ageing and finally causing Arrester failures.
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