How Is a Transformer Neutral Earthed?
Quick answer — The neutral is earthed to hold the system at earth potential and to provide a return path for earth faults, and the method (solid, resistance, reactance or insulated) depends on the system voltage and the allowed earth-fault current. Solidly-earthed systems give a low fault level; resistance or reactance earthed systems limit the current and reduce plant stress and electromechanical torque.
How is a transformer neutral earthed and why?
Earthing methods
Solid earthing clips the neutral to earth; resistance earthing limits the current; reactance (e.g. Petersen coil) earthing compensates the capacitive current; and a high-impedance or isolated earth is used in some small systems.
Why it matters
The method sets the earth-fault current, the overvoltage on the healthy phases, and the damage to the windings, so it affects the protection and the transformer design.
Design and protection
The neutral earthing affects the required insulation and the protection coordination (earth-fault, differential, restricted earth-fault), so it must be chosen and set to match the system.
References & standards
- IEC 60076-1
- IEEE C57.12.00
Related
Related manufacturers
Acme Electric (Hubbell) · Central Moloney · CORE Transformers · Daelim Transformer (US) · Delta Star · Eaton
Related components
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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