Products: HT Instrument Transformers

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We are one of the earliest manufactures of instrument transformers in the country. The Company has developed a full range of Cast Resin Current Transformers for 11 and 22 KV systems
Oil Insulated Instrument Transformers for up to and including 136 KV systems is being introduced by us in the market.

Indcoil covers a full range of Current Transformers both for Metering as well as protection, manufactured conforming to Indian and International Specifications. These transformers are recommended for use in Busbar Chambers, Control Cubicles, Circuit Breakers, Relays and so on. The type, Accuracy class and Burdern should be selected to suit the particular requirement.

Metering Current Transformers: These Transformers are meant for feeding measuring Instruments. The accuracy requirements of the instrument will decide the Class of accuracy of the CTs whereas the internal impedance of the instruments expressed in VA(Volt Amperes) will decide the BURDEN of the CTs. Above 100 A Primary Current, it will be economic to use Bushing type or Ring type construction will not give good accuracy for measurements. In such cases Wound Primary CTs should be selected.

Example: Current to be measured = 400 Amps
Ammeter Available = 0 to 1 Amps
Impdence of Meter = 4 Ohms
Select a CT of 500/1A, 5 VA Accuracy class 1
A ring type CT can be selected. The Bus Bar size will decide the ID requirement for the CT. A Bushing type CT is sufficient.

Protection Current Transformers:These Transformers are mainly for operation with Circuit Breakers, Relays and other Protection devices. The main characteristics of these CTs are their ability to remain without saturation in the event of a short circuit. The fault current may be many times the rated current and the CTs should be designed to drive this high current through the relays and its connected circuit. Normally they are specified as Class 5P or 10P to indicate their accuracy at fault current, followed by the fault current limit at which the accuracy required, expressed as a multiple of the rated CT secondary current


Example:5p10 10P15 and so on. SP or 10P are the accuracy class and 10, 15... are the multiplies, knows as the accuracy limit factor CTs for Differential Protection should be specified with their "Kneepoint voltage (Vk) requirements along with the permissible resistance of the CT secondary winding (Rct). The parameters for selection of CTs are given in the Relay catagalogues. By a careful selection of Vk and Rct, great economy can be achieved in selection of the right type of CTs for these applications.


Typical values:

1000/5 A, Vk > 50Volts Rct < 0.3 Ohms

1000/1 A, Vk > 250 V, Rct < 5.5 Ohms


Note: 1A sec CTs with higher Vk and Rct

The following details if furnished with enquiries can help us to quote the right type of Transformers for your specific requirement

  Type   Purpose   Ratio   Burden
  Rct*   Vk*   Accuracy   System Voltage
Limiting Dimensions and ID requirements (*For Protection class CT's only)

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