Instrument Transformers

Skipper has pioneered the design and manufacture of Instrument Transformers over the past three decades. Skipper Instrument Transformers are globally known for consistent accuracy, reliability and maintenance-free operation over life time. Skipper manufactures the entire range of Instrument Transformers viz. :
• Oil Filled, Outdoor
• Resin Cast, Indoor/Outdoor
• Metering Units, Indoor/Outdoord

Oil Filled Current Transformers

Skipper manufactures Oil Filled Current Transformers upto 220 kV class. Skipper make transformers are currently in operation

in challenging locations and have been delivering outstanding performance consistently for over 25 years. These

transformers comply with international quality, safety and environment  specifications standards.

Outdoor Potential Transformers

Skipper complements its range of Current Transformers with Potential Transformers.
• The PTs are usually built up of multi cores designed for Metering and Protection in dead tank construction.

• The PTs built in stacked core construction employ high permeability cold rolled grain oriented magnetic steel.
• The PTs are designed and manufactured in accordance with specific user’s specification and are suitable for Indoor / Outdoor application.

• Skipper is equipped to Design and Manufacture PTs upto 220 kV Class system voltage, with in-house Testing facilities for conducting all routine Tests. However,
Skipper also conducts Type and Special Tests to validate the design at outside NABL accredited Test Laboratories like CPRI and ERDA.


Oil filled current transformers use current transformation principle to convert highline current (in HV system) to a low current reduced by a fixed ratio. The current transformers are designed generally in live tank construction for optimum performance.

The primary winding is manufactured from copper conductor and is placed in the top housing.

The windings are rigid, concentric with uniformly distributed secondary winding to deliver high mechanical strength against short circuit forces.

The secondary windings and the cores are contained in closely fitting rigid shell. The shell is fully insulated from the top housing. The secondary leads are taken to the base passing through a hollow insulator.

Insulation is provided by electrical grade high grade Kraft paper. The fully assembled CTs are dried and oil filled under vacuum in evacuated heating chambers. Optimum insulation and long life is achieved by drying the paper insulation by heat in vacuum. Oil, impregnated under vacuum, complements the insulation.


Skipper uses brown glazed porcelain insulator with shed profile as per IEC 60815 for the CTs. Optionally grey shade porcelain and other profiles can be offered as per specific requirements. The porcelain insulator is cemented to flanges on both ends for maximum mechanical strength. The top housing contains core coil assembly and is made of corrosion resistant aluminum alloy.

The top of the tank has an oil filling plug. The CT is protected from the vagaries of weather and can withstand extreme temperature variations. Core of wound ring type are manufactured from high quality silicon steel. However, Mu-metal cores are used for select applications. Design, material and process selection ensure that all requirements relating to metering and

protection are met. The secondary winding is uniformly distributed over the circumference of the core to minimize the reactance of the winding. This also ensures accurate transformation ratio. The CT base chamber is fabricated from structural steel. This chamber is provided with secondary terminal box, oil sampling valve and earthling pads.


Skipper’s test laboratories are fully equipped with latest testing equipment and are capable of conducting all routine tests including Partial Discharge test.

Skipper oil filled instrument transformers are tested under stringent conditions for their performance, reliability and durability at NABL accredited labs such as ERDA and CRPI.

Type tests and special tests are also conducted on all new designs to verify that the product design meets all operational requirements.

Quality Management System

Skipper’s experienced and quality conscious workforce carries out quality control at each stage of production. A series of quality checks are performed at each unit

before handing over the same for the next stage. The Quality Assurance department maintains and updates all quality control documents and carries out

its own additional inspection at critical hold points. Skipper’s quality system is in accordance with ISO 9001 : 2008 and products are CE certified.

Technical Parameters
Few Successful Installations
Epoxy Resin Cast Current & Voltage Transformers

Skipper has successful utilized the advantages of epoxy cast voltage transformers for outdoor applications up to 33kV. In such cases, paper or oil insulation is not required and hence no periodic oil filtration or maintenance is needed.

The specially designed instrument transformers are cast in epoxy and put into hermetically sealed enclosures.

The dry type instrument transformers have been a great success especially in heavily polluted surroundings. Epoxy cast instrument transformers are also available for outdoor applications in special type of resin known as cycloaliphatic resin.

The current and the voltage transformers are used for stepping down the current and the voltage from high to measurable values.

The standard values of the secondary current are 1Amps and 5 Amps. Similarly the standard secondary voltages are 110V and 110/√3V. The current and voltage transformers are together known as instrument transformers and are critical to the measuring and protection system. The performance of energy meters & relays is based on the signals received from them. The instrument transformers are manufactured in compliance to IS/IEC standards.

Special Features

Current and voltage transformers up to 33kV are manufactured to suit both indoor and outdoor applications. The indoor current and voltage transformers

up to medium voltages are preferred in cast resin form over oil filled ones due to compactness, sturdiness and low maintenance. Skipper

has expertise and infrastructure to manufacture resin cast instrument  transformers up to 33 kV for indoor and outdoor applications.

Constructional Features.

The core is built from non-ageing, cold- rolled, grain oriented silicon steel laminations and is coated with heat resistant insulation. Core is annealed to reduce losses.Current transformer core is made from continuous lamination wound as a toroid.

Skipper also manufactures cycloaliphatic resin epoxy cast voltage transformers for outdoor applications up to 33kV. In such cases, paper or oil insulation is not required and hence, no periodic oil filtration or maintenance is needed.

The specially designed instrument transformers are cast in epoxy. The dry type instrument transformers have been a great success especially in heavily polluted surroundings.


Each Instrument transformer is subjected to all routine tests as per applicable standards and customer specifications.

The instrument transformers are frequently tested for type tests at reputed NABL accredited.

laboratories such as CPRI and ERDA for design validation.

Metering Units

Skipper has acquired expertise in manufacturing metering of cubicles in11 kV to 33kV voltage class suitable for indoor/outdoor applications. The company has been a major supplier to various state electricity boards, utilities and industrial units requiring medium voltage connections. The units are compactly designed

for indoor/outdoor applications keeping in mind the space limitations. The metering cubicles are supplied with side entry or bottom entry for cables as required by the customer.

The units manufactured by the company are performing successfully across the globe in widely varying environmental conditions.


Metering cubicles are supplied for three phase-three wire or three phase-four wire metering. Cubicles is divided in

two compartments; upper one for housing the meter and lower one for high voltage current and voltage transformers. The enclosures are designed to make them dust and vermin proof.

Combined Instrument Transformers

Instrument transformer includes Voltage Transformer & Current Transformer put together in a tank. Combined Instrument Transformer converts distribution class voltage & current to standardized low & easily measurable values which are used for metering for revenue purposes. When operating the current transformer between 5% of the rated current and the rated continuous thermal current, the voltage transformer shall not exceed the limits of voltage error and phase displacement

corresponding to its class within the specified range of burden and between 80% and 120% of the rated voltage.

Similarly when operating the voltage transformer between 80% of rated voltage and the rated voltage multiplied by rated voltage factor, the current transformer shall not exceed the limits of current error and phase displacement within the range of current corresponding to its class at any value from 25% to 100% of rated burden.


Skipper make Combined Instrument Transformers (11 to 33 kV) adhere to the requirements of the quality standards and our quality systems are certified as per ISO 9001-2000. These products are type tested for impulse voltage, short circuit and wet voltage withstand tests at internationally accredited laboratory ERDA in India.

Design Features

  • Single coil design located in corrosion proof tank • Vacuum impregnated oil paper insulation for coil
  • Mineral & synthetic oil free of PCB • Stable accuracy over life time
  • Hermetic sealing & oil expansion by nitrogen cushion
  • Built for long lasting life with very little maintenance required
  • Complies with IS: 2705, IS: 3156 and IEC 44-3
Technical Details