What Is a Zero-Sequence Test?
Quick answer — A zero-sequence test measures the zero-sequence impedance of a transformer, which governs the earth-fault current and the protection. It is done by applying a single-phase or zero-sequence voltage (or by exciting the windings in a defined way) and measuring the impedance. The value is used for the earth-fault protection and the system-earth-earthing, especially for a star winding with a neutral that is earthed.
What is the zero-sequence impedance test?
What it measures
The zero-sequence impedance (the impedance seen by the zero-sequence current), which determines the earth-fault current distribution and the protection setting.
How it is done
The transformer is excited so the zero-sequence current flows, or a test is run to measure the impedance; the result depends on the connection and the earthing.
Why it matters
It sets the earth-fault current and the protection and earthing coordination, so it is a special test by agreement for a transformer with an earthed neutral.
References & standards
- IEC 60076-1
- IEEE C57.12.90
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
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Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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