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Direct measurement of voltage in high voltage system is not possible because of insulation problem of measuring instruments. It is also not possible to use direct voltage for the system protection purpose due to its high value and high insulation problem of protective relays. Therefore, Voltage Transformers or Potential Transformers (PT) are used to step-down the high system voltage to low standard value accurately in proportion to their ratio.
Basic functions of potential transformers are:
- To reduce the line voltage to a value which is suitable for standard measuring instruments, relays, etc.
- To isolate the measuring instruments, meters, relays, etc. from high voltage side of an installation.
- To sense abnormalities in voltage and give voltage signals to protective relays to isolate the defective system.
Single phase electromagnetic PT is manufactured in two types:
1. Single Pole ( between lines & earth)
2. Double Pole (between line-to-line)
Three phase PTs are of star/star connected or star/open delta connected (Residual Voltage Transformer) type.
Potential Transformer consists of
- Primary and Secondary Windings
- Electromagnetic Core
Oil filled Potential Transformers / Voltage Transformers
For use in outdoor installations from 11KV to 33KV class. Main insulation is provided by world class insulating paper, EHV Grade Oil and good MS Metal Tanks are used along with type tested porcelain. The process control is very stringent to give the customer a trustworthy product with long life.
- Hermetically Sealed Oil Filled Outdoor Type
- Three Phase type up to 33KV Class, Voltage Class: 11KV / 22KV / 33KV
- Manufacturing as per IS & IEC standards.
- Secondary Voltage: 110V / v3 or 110V
- Accuracy Class (upto 0.2), Burden, RVF and Number of Secondary Windings as Specified.
- Single Phase type from 11KV to 145KV
Resin Cast Potential Transformers
These are for panel mounting application upto 11KV class manufactured with latest technologies.
Epoxy resin cast PT is manufactured in compliance with IEC, ANSI, VDE, BS standards and as per customer’s specification. Cores used in PT are of high quality cold rolled grain oriented steel which is annealed. HT and LT windings are designed as multi layer windings. The low voltage winding is wound on insulated bobbin. Conductors used for windings are made of electrical grade electrolytic copper. The conductors are insulated with high quality, synthetic resin based, insulating varnish. The whole encapsulation forms hermetically reeled system with primary and secondary terminals. PTs are available at single, double and three phase versions and they are of indoor and outdoor types.