Testing phase comparators per IEC 61481

A phase comparator that wrongly indicates that two points carry the same phase leads to incorrect switching. In high-voltage installations the consequences are immediate. IEC 61481-1 contains the requirements for the periodic testing of phase comparators.

What does IEC 61481-1 cover?

IEC 61481-1 applies only to phase comparators: instruments that determine whether two live points carry the same phase. The standard distinguishes two versions.

Periodic testing: what do you check?

IEC 61481-1 Annex G Table G.1 gives the in-service test procedure. The order is not arbitrary: visual first, functional after.

1. Visual and dimensional inspection

Check the whole instrument for mechanical damage, deformation of the connecting cables and corrosion on terminals. Deviations in the dimensions of the insulating part are also grounds for rejection.

2. Check of the measuring element

Verify that the measuring element works correctly. A faulty measuring element means immediate rejection.

3. Leakage current under dry conditions

Measure the leakage current at nominal voltage under dry conditions. Check the measured value against the limit in the standard.

4. Protection against bridging

Test resistance to bridging under dry conditions. The method depends on the type: indoor or outdoor.

5. Spark resistance

Spark resistance ensures the instrument creates no dangerous leakage paths on contact with earthed parts.

6. Clear indication

Check that the indication of the phase comparison is unambiguously readable.

7. Visibility and audibility

Verify that visual and audible signals are clearly perceptible. A weak alarm or a poorly readable display is grounds for rejection.

Test interval

IEC 61481-1 prescribes no fixed testing interval. Annex G gives a maximum of 6 years. Use the manufacturer’s instructions as a guide for the actual interval. Before every use, a brief function test on a known voltage source.

More about testing high-voltage PPE

This article is part of a series on the periodic testing of high-voltage PPE:

• Testing insulating gloves — IEC 60903
• Testing hot sticks — IEC 60832-1 / 60855-1
• Testing voltage detectors — IEC 61243
• Testing earthing equipment — IEC 61230
• Testing insulating mats — IEC 61111

Or read the complete overview with all standards and intervals.

Questions about testing phase comparators?

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