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. Annex G of IEC 61481-1 gives recommendations for the periodic testing of phase comparators.

IEC 61481-1 applies only to capacitive phase comparators: instruments that determine whether two live points carry the same phase. Resistive phase comparators are covered by IEC 61481-2. Part 1 distinguishes two versions.

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, damage to the contact electrode and contamination or cracks in the insulating part. Deviations in the dimensions of the insulating part are also grounds for rejection.

2. Check of the testing element

Verify that the testing element (the built-in or separate self-test) works correctly. If the testing element does not work, the instrument is rejected.

3. Leakage current under dry conditions

Measure the leakage current under dry conditions at the test voltage specified in the standard. 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

This test checks that the indicator is not damaged or switched off by a low-energy spark. It may be combined with the bridging test.

6. Clear indication

Apply two test voltages with a defined phase shift and check that the phase comparator correctly indicates ‘correct’ and ‘incorrect phase relationship’. The standard sets the phase angles per class.

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.

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, carry out a visual check and check the function with the testing element as described in the instructions for use.

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.

IONIO Labs tests insulating gloves and capacitive voltage detectors, with a test report for every item. Phase comparator testing to IEC 61481 is coming soon. See all inspections and lab tests at IONIO Labs.

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