Equipotential shielding of current transformer

Equipotential shielding of current transformer:

Equipotential is nothing but a constant field. creating a Constant field in a current transformer the equipotential lines are used. The Medium Voltage and High Voltage type current transformer comes with the special feature of equipotential shielding. Mostly equipotential shielding wire is used in Window types CT and Wound Types Current Transformer. In rear case, an equipotential ring is used bar types current transformer.

Equipotential shielding
Equipotential shielding With Wire

Equipotential shielding High Voltage CT
Equipotential shielding High Voltage CT

What is Wound types current transformer:

The Primary winding of The transformers is physically connected in series with the conductor that carries the measured current flowing in the circuit. Here The magnitude of the secondary current of the wound type current transformer is dependent on the turns ratio of the transformer. Mainly these types of the current transformer have used the system associated with low primary current.

Example: Low Voltage application such as induction motor starter’s (less than 5 HP) and high voltage application such as 110 KV line.

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What is Window Type Current transformer?

These types of transformer do not have the primary winding, here the primary winding considers as the main phase conductor. (R phase or Y phase or B Phase). Also this types of current transformers are coming with the split secondary core. The cores are manufactured as per the application. Two types of Spilt are most commonly used, one is, metering core and another one is protection core. But for both core’s the primary is same as the line current.

Please refer the diagram, the equipotential ring in connected in the primary winding of the current transformer. The equipotential ring is connected with the primary of the current transformer. The equipotential shield connects with primary winding by simple 1.5 sqmm cable.

What is the use of Equipotential shielding wire of the current transformer?

The equipotential ring significantly extends the service life of the transformer by preventing the deterioration of the resin in the transformer head because the ring prevents the resin from being subjected to any potential gradient. This can be seen in the figure included here, which shows the distribution of the field lines with or without the equipotential ring. This equipotential ring is a standard accessory in all ARTECHE MV Current transformers with either cycloaliphatic resin, porcelain or silicone rubber insulation.

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Equipotential shielding High Voltage CT
Use of Equipotential ring tobe

Ref: http://destin.se/wp-content/uploads/2014/11/Destin-ITMV-ARTECHE_CT_trfctMVO_EN.pdf

Normally, the Window type current transformer are used in HV voltage level their equipotential wires are used. In window type CT conductor passing through it so stress on CT material is uneven so that it creates more stress near conductor and less on other parts. so CT is design such a way that another layer provided in ct and conducting path provided and bus bar connected to this conducting parts so that potential of entire Window ct inside surface is equal and stress on CT is eliminated.


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