362kV Current Transformer (Hair-pin type)

362kV Current Transformer

362 kV Current Transformer (Hair-pin Type) is an extra-high-voltage (EHV) instrument transformer designed to accurately transform high primary currents into standardized low secondary currents (typically 1 A or 5 A) for metering, protection, and monitoring in 362 kV substations. The "hair-pin" designation refers to the primary conductor configuration, where a U-shaped (hair-pin) conductor passes through the transformer core.

Main Functions
·Current Measurement – Supplies accurate current signals to meters and energy management systems.
·Protective Relaying – Provides current inputs to protection relays for fault detection.
·Electrical Isolation – Isolates high-voltage primary circuits from secondary control equipment.
·System Monitoring – Enables SCADA and digital substation monitoring.

Construction

A typical 362 kV hair-pin type current transformer consists of:

Hair-pin Primary Conductor
-Single-turn U-shaped conductor.
-Carries the full line current.
Secondary Windings
-Metering core(s) with high accuracy.
-Protection core(s) with high saturation limits.
-Multiple independent cores may be provided.
Magnetic Core
-High-permeability silicon steel or nanocrystalline material.
-Separate cores for metering and protection.
Insulation System
-Oil-paper insulation or SF6 gas insulation (GIS applications).
-High dielectric strength for 362 kV service.
Porcelain or Composite Insulator
-Supports the live conductor.
-Provides external insulation and creepage distance.
Oil Expansion System
-Expansion bellows or conservator accommodates oil volume changes.
Terminal Box
-Houses secondary terminals.
-Includes grounding terminals and shorting facilities.

Typical Technical Specifications
·Highest System Voltage: 362 kV
·Rated Frequency: 50/60 Hz
·Rated Primary Current: 200–4000 A
·Rated Secondary Current: 1 A or 5 A
·Accuracy Class (Metering): 0.1, 0.2, 0.2S, 0.5
·Protection Class: 5P10, 5P20, PX, TPY, TPZ
·Insulation Medium: Oil-paper or SF6
·Creepage Distance: According to IEC pollution class
·Short-Time Thermal Current: 25–63 kA (typically 1–3 s)
·Dynamic Current : Up to 160 kA peak (typical)
·Ambient Temperature : −40°C to +55°C

Advantages
·Excellent measurement accuracy over a wide current range.
·High thermal and mechanical withstand capability during short circuits.
·Suitable for extra-high-voltage transmission systems.
·Reliable long-term outdoor operation.
·Multiple cores can support both metering and protection simultaneously.
·Low maintenance when properly installed.

Typical Applications
·362 kV transmission substations
·Power generation switchyards
·Grid interconnection stations
·Renewable energy grid connection substations
·Industrial EHV substations
·High-voltage transmission and distribution networks

Relevant Standards
·IEC 61869-1 – General requirements for instrument transformers
·IEC 61869-2 – Current transformers
·IEEE C57.13 – Instrument Transformers
·IEC 60044-1 (legacy standard, largely superseded by IEC 61869-2)
·Typical Primary Connection

The 362 kV Hair-pin Type Current Transformer is a critical component in extra-high-voltage substations, delivering precise current measurement, dependable protection signals, and safe electrical isolation while withstanding the demanding electrical and environmental conditions of modern transmission networks.