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Sizing current transformers

You can contact the CAPSIM's specialist of this activity:
   - By email
   - By phone: +33 (0)4 42 63 61 18

This study involved sizing 156 current transformers (CT) which will be installed on the HVA grid of an industrial site in the Middle East.
Sizing the current transformers is a critical step in the correct operation of the protection plan for an industrial grid. An unsuitable current transform may result in a protection device malfunctioning.
The project also involved sizing the single-pole tori used for protection at maximum earth current.

The current transformers to be sized were of two types:
  • Current transformers intended for measurement (current measurement on high-power motors, transformer currents, generator currents, etc.),
  • Current transformers intended for protection (maximum phase current protection, maximum inverse component protection, etc.).

The sizing of the transformers allows the following technical characteristics to be defined, in coherence with the settings of the protection plan and in agreement with the technical characteristics required by the manufacturers of the associated relays:
  • Power,
  • Primary current,
  • Secondary current,
  • Safety factor (for the measurement CT),
  • Precision limiting factor (for the class 5P and 10P protection CT),
  • Minimum knee-point voltage linked to the resistance of the secondary windings (for the class PX protection CT),
  • Required behaviour with a thermal short-circuit current at 1s.

The current transformer study is an essential component in establishing the protection plan for a network. Capsim expertise ensured optimum operation of the system in this respect.

Current transformer for protection of motors
Current transformer for protection of motors

CAPSIM - 11 Boulevard de la Grande Thumine - Parc d'Ariane, Batiment E1 - 13090 Aix-en-Provence - France
Tel : +33 (0)4 42 63 61 18