Indoor/Outdoor Instrument Transformers

The Instrument Transformers are the measuring devices for the protection and metering schemes in any power system. the primary current or voltage is transformed to the required secondary usually 5A or 1A in case of Current Transformer and in case of Voltage Transformer 63.5V or 110Volts. Not only the accuracy of the transformer of prime importance, but also isolation function, which means no matter what the system, voltage on the primary circuits. The secondary circuit needs to be insulated only for a low voltage.
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Electricfield Instrument Transformers are designed within permitted error as per the class of accuracy using best quality of electrical steel for the core and other associated material. The short time rating of Instrument Transformers is very important and must be compiled with for the protection scheme to be meaningful. The STR determine the size of construction and cost of C.T and P.T. Electricfield Instrument Transformers consists of the following categories:
1. Current Transformer Secondary 5A or 1A against any Primary Current & system voltage upto 35KV.

2. Potential Transformer Secondary 63.5V or 110V against any system voltage upto 36KV.

A. Current Transformers:

Electricfield manufactures Current Transformer in tap wound covered in bakelite mould and cast resin upto 6000Amps for L.T application suitiong the requirement of the customer with class of Accuracy 0.1 to Class 5 for metering and for protection CTs 5P, 10P accuracy limit factor 5, 10, 15, 20. The maximum burden of C.T's can be 60VA. Low voltage C.T's are used for Auxiliary C.T's Interposing C.T's Summation C.T's and core balancing C.T's apart from metering purpose. Electricfield covers full range of Current Transformers both for meteriong and protection manufactured conforming to IS: 2705 IEC AA-I and other International Standards and are type tested at C.P.R.I Bhopal. we also manufacture cast resin indoor type and bushing type outdoor current transformers with multi range ratio and potential transformer for system voltage of 6.6KV, 11 KV with standard output as per the requirement. High current ring type C.T's upto 20,000 Amps and 11 KV system voltage for use in generator bus duct can be offered. The output burden and short time rating of current transformer is related with the Accuracy Class and primary ratio. The current transformer with bar primary has limitations to give desired output with required accuracy class when the primary current is less than 100thAmps. To meet the requirement in terms of VA Burden and accurcay class, the current transformer has got to be primary wound to meet certain ampere-turns. The current transformers are categorized as under:

i) Protection current Transformers:
These transformers mainly used for 5P10 or 10P10 for operating the circuit breakers through over current and earth faults against short circuit / earth fault in the transformer or feeder line. Wherever thjere is comparison between the input and output of transformers and similar equipment like distance protection, class PS, which has higher accuracy / saturation factor is used. This is decided on the parameter of protections and its scheme.

ii) Interposing Current Transformers:
These transformers are mainly used for differential protection in order to match the ratio of main feeder current transformers. These are also used as saturable current transformers to protect the sensitive instruments from over load during fault conditions. The current transformers will saturate and thus limit the secondary current within safe limits of the instruments.

B. Potential Transfomer:

Single phase, single pole potential trnasformers, to connect between line & earth up to 300kV voltage class. Both pole potential transformers to connect between line to line up to 36kV voltage class. Three phase potential transformers, star / star connected up to 36kV vlotage class. Three phase residual voltage transformers star / delta connected up to 36kV voltage class.

B. Resin Cast Type :

These are manufactured in resin cast suitable upto 33 KV indoor application current transformers as well as Potential Transformers. The resin cast instrument transformers are superior in mechanical strengths by virtue of material apart from protection from corrosive atmosphere conditions.

B. Enquiries :

The following details furnished with your enquiry will enable us to select the appropriate Current / Potential transformers for your requirement.

  • Purpose.
  • Type.
  • Ratio.
  • Burden.
  • Accuracy Class.
  • System Voltage.
  • Knee point Voltage.
  • RCT.
  • Limiting Dimension.
  • Bus Bar or Cable size.