36kV Current Transformer (Hair-pin type)

36kV Current Transformer

36 kV Current Transformer (Hair-pin Type) is a medium-voltage instrument transformer designed to measure high primary currents and provide scaled, isolated current signals for metering, protection, and control. The term "hair-pin type" refers to the shape of the primary conductor, which is bent like a hairpin (U-shaped), forming an integral primary winding through the transformer core.

Working Principle

A hair-pin type current transformer operates on the principle of electromagnetic induction.

When alternating current flows through the hair-pin primary conductor, it produces a magnetic field in the magnetic core. This varying magnetic flux induces a proportional current in the secondary winding.

Construction
·A typical 36 kV hair-pin current transformer consists of:
·U-shaped copper or aluminum primary conductor (hair-pin)
·Laminated or toroidal magnetic core
·Secondary winding(s)
·Porcelain or composite outdoor insulator
·Oil, SF6, or resin insulation (depending on design)
·Secondary terminal box
·Mounting base
·Nameplate
·Grounding terminal

Features
·Integral hair-pin primary conductor.
·Single primary turn with high measurement accuracy.
·Excellent electrical insulation for 36 kV systems.
·Available with one or multiple secondary cores.
·Suitable for both protection and metering.
·Outdoor weather-resistant construction.
·High thermal and dynamic current withstand capability.
·Long service life with low maintenance.

Typical Ratings
·Highest system voltage: 36 kV
·Rated frequency: 50 or 60 Hz
·Primary current: 100–3000 A
·Secondary current: 1 A or 5 A
·Accuracy class (metering): 0.1, 0.2, 0.2S, 0.5, 0.5S
·Accuracy class (protection): 5P10, 5P20, 10P10, PX
·Insulation level: 70/170 kV (typical)
·Installation: Outdoor

Advantages
·Compact construction.
·Excellent measurement accuracy.
·Strong mechanical strength.
·Simple primary conductor arrangement.
·High short-circuit withstand capability.
·Reliable long-term operation.
·Suitable for both protection and revenue metering.

Limitations
·Fixed primary conductor limits installation flexibility.
·Larger and heavier than indoor resin-cast CTs.
·Secondary circuit must never be open-circuited while the primary is energized, as dangerous high voltages can ·develop across the secondary terminals.

Applications
A 36 kV hair-pin type current transformer is commonly installed in:
·33 kV and 36 kV outdoor substations
·Medium-voltage switchyards
·Utility distribution substations
·Industrial power systems
·Renewable energy collector substations
·Transformer feeder circuits
·Incoming and outgoing feeder bays
·Generator step-up transformer connections

A 36 kV Hair-pin Type Current Transformer is a robust and accurate instrument transformer widely used in 33/36 kV outdoor substations. Its integral U-shaped primary conductor offers excellent mechanical strength, high short-circuit performance, and reliable current transformation for protection relays, energy metering, and control systems.