FAQs on Testing and Measuring Lightning/Surge Arresters

SCOPE SA 30i+ Leakage Current Analyser for Lightning and Surge Arresters

In our previous post, we deep-dived into the various techniques and methodologies that are widely adopted for assessing the healthiness of Lightning/Surge Arresters.

In this post, we will answer the 10 frequently asked questions (FAQs) on the various aspects of testing and measuring Lightning/Surge Arresters. Let’s begin!


1. What are Third Harmonics?

A. In the context of electrical power systems, ‘harmonic’ refers to the voltage or current expressed as a multiple of the system’s fundamental frequency. Considering the fundamental frequency to be 50 Hz, Third Harmonic means 3 times 50 Hz i.e. 150 Hz.

Monitoring the Third Harmonic Resistive Component (THRC) of Lightning/Surge Arrester’s leakage current becomes important as THRC is directly related to the extent of degradation of the Arresters’ ZnO blocks.

2. Is the leakage current a 50Hz component or sum of other components?

A. The total leakage current component is the sum of all harmonic components. But out of all the harmonic components, THRC is the most important as it is directly responsible for the degradation of LAs/SAs.

3. What if the THRC value is more than the IR value?

A. Practically, this is not possible because as per IEC 60099-5 standard, the THRC value is 10-40% of the IR value, i.e. the resistive component of the leakage current. So if the THRC value increases, the IR value will increase correspondingly.

4. What happens to the resultant value after measurement if the system voltage itself has harmonic content?

A. The system’s harmonic components are compensated while conducting the THRC measurement with system harmonic compensation as per the IEC 60099-5 B2 method. Hence there is no effect of system harmonics in the THRC measurement methodology.

5. Could you please elaborate, how SCOPE’s SA 30i+ Leakage Current Analyser kit distinguishes system voltage harmonics from leakage current harmonics?

A. SA 30i+ is an advanced Leakage Current Analyser that includes an accessory called ‘Field Probe’ that automatically measures the harmonics present in the system voltage and then algorithmically compensates for the same.

6. What should be the exact position of the Field Probe?

A. It is recommended that the Field Probe be placed at the base of the Lightning/Surge Arrester.

7. Does SCOPE offer a different kit for testing and measurement of GIS Lightning Arresters (LAs)?

A. Both SA 30i and SA 30i+ offered by SCOPE can be used for GIS LA THRC measurement.

8. In the SA 30i T&M variants, will we get separate readings for IR, IC and THRC?

A. SA 30i kit measures the below four parameters:

1) Third Harmonic resistive leakage current at ambient temperature

2) Third Harmonic resistive leakage current at 200 Celsius temperature with the voltage correction factor

3) Total leakage current, and

4) Ambient Temperature.

9. Is the leakage current same for all ratings of LA of the same make?

A. No. The value of the leakage current depends on the following five parameters:

 1) Rated voltage of the Lightning/Surge Arrester

 2) OEM’s design parameters

3) Ambient temperature

4) Absorption/entry of moisture, and

5) Entry of solid micro particles.

10. How can we determine the healthiness of the LA by only observing the leakage current meter for differently rated LAs?

A. It is not always possible to determine the healthiness of a LA/SA only by observing the leakage current meter reading. Leakage current meters display only the value of the total leakage current whereas the most important parameter that needs to be measured is the THRC of the leakage current.

This is where SCOPE’s SA 30i/SA 30i+ comes handy. Unlike leakage current meters, SCOPE SA 30i variants not only measure the total leakage current but also measure the THRC at ambient temperature and at 200 Celsius thereby giving better insights into a LA/SA’s healthiness.

Summing Up

Regularly testing Lightning/Surge Arresters is pivotal to ensure their operational healthiness and safeguard your electrical infrastructure.

To learn how SCOPE SA 30i+ Leakage Current Analyser cohesively tests LAs/SAs, please visit https://www.scopetnm.com/test-and-measurements/item/75-sa-30i or write to us at marketing@scopetnm.com.

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