Outdoor 33kV Current Transformer Manufacturer in India
Current transformers in an outdoor 33kV substation face rain, dust, pollution, salt near the coast, strong sun and lightning surges, while delivering accurate signals to meters and relays for decades. AMREST Electricals manufactures outdoor 33kV CTs for substations, switchyards, utilities, industries and renewable energy projects. This guide explains what really matters when you choose one.
What is an outdoor 33kV current transformer?
A 33kV CT converts high line current into a small, proportional secondary current, usually 1A or 5A, for energy meters, protection relays, ammeters and monitoring systems, while isolating that equipment from the high-voltage line. An outdoor CT does the same job, but its insulation, housing and terminals are designed to work in open air on a switchyard structure, without the protection of a panel or building.
| Aspect | Indoor 33kV CT | Outdoor 33kV CT |
|---|---|---|
| Where installed | Inside switchgear panels and metering cubicles | On structures in switchyards and open substations |
| Environment | Clean, dry, protected | Rain, dust, pollution, UV, temperature swings |
| Insulation surface | Standard epoxy resin | Weather-resistant material with sheds for longer creepage |
| Creepage distance | Lower, suited to clean indoor air | Higher, chosen by site pollution level |
| Secondary terminals | Open terminal block inside panel | Sealed, weatherproof terminal box with cable gland |
| Hardware | Standard fasteners | Corrosion-protected fittings |
Outdoor 33kV CT designs
Single Phase Single Bushing CT
Compact construction with a straightforward primary connection, for feeder bays, transformer bays and outdoor 33kV structures.
- Metering, protection or multi-core
- Ratio, cores, class and burden per project
- Terminal and mounting as per drawing
Single Phase Double Bushing CT
Both primary terminals brought out through separate bushings, where the structure layout or connection method calls for it.
- Defined primary terminal layout
- Insulation and creepage for the site
- Customised to your datasheet
Outdoor Resin Cast CT
Windings cast in outdoor-grade cycloaliphatic epoxy that resists UV and surface tracking. Oil-free, low maintenance and no leak risk. See our MV outdoor resin cast CT range.
Oil-Immersed Outdoor CT
Active part in insulating oil inside a sealed tank with a porcelain or composite bushing. A long-established choice for outdoor utility substations.
5 things to specify for an outdoor 33kV CT
Insulation level
Highest voltage for equipment is 36kV, with typical withstand of 70kV rms and 170kVp lightning impulse. Mention if the site is above 1,000 m altitude, as a correction is needed.
Creepage distance
The surface path from HV terminal to earth. Dust or salt plus moisture makes it conductive, so polluted sites need more creepage (see table below).
Metering or protection
Metering cores (0.2S, 0.5S) for billing; protection cores (5P10, 5P20, PS) for relays; multi-core for both in one unit.
Short-time current
The CT must withstand full fault current until the breaker trips. Specify kA and duration (1 or 3 seconds) from your fault level.
Terminal box & hardware
Moisture in the secondary box is a common failure cause. Ask for a sealed box, proper cable gland and corrosion-protected fittings.
Construction
Resin cast or oil-immersed, single or double bushing, as per your structure layout and utility specification.
Creepage distance by site pollution
| Site pollution | Typical example | Specific creepage | Approx. total for 36kV |
|---|---|---|---|
| Light | Rural areas, low industry | 16 mm/kV | ~580 mm |
| Medium | Towns, moderate industry | 20 mm/kV | ~720 mm |
| Heavy | Industrial zones, near coast | 25 mm/kV | ~900 mm |
| Very heavy | Coastal, cement, chemical, desert dust | 31 mm/kV | ~1,116 mm |
Many Indian utilities specify 25 or 31 mm/kV as standard. Always follow your tender or utility specification, and tell us if the site is coastal or near a cement, steel or chemical plant.
Typical technical specifications
| Parameter | Typical requirement |
|---|---|
| Product type | Outdoor Current Transformer |
| System voltage | 33kV (highest system voltage 36kV) |
| Insulation level | 70kV rms / 170kVp |
| Application | Metering / Protection / Multi-core |
| Frequency | 50 Hz or project requirement |
| Primary current / CT ratio | Project specific |
| Secondary current | 1A or 5A |
| Accuracy class | Metering: 0.2S, 0.5S | Protection: 5P10, 5P20, PS |
| Number of cores | Single / Multiple |
| Rated burden | As required |
| Creepage distance | As per site pollution level |
| Mounting | Project specific |
Final specifications are selected according to the applicable standard, system design, site conditions and project requirements.
Get the site work right
- Never open-circuit a CT secondary while the line is live. Short it before disconnecting any meter or relay.
- Earth the CT body and one point of each secondary circuit.
- Check P1/P2 polarity; reversed polarity causes wrong metering and relay mal-operation.
- Clean insulator surfaces periodically at polluted sites, especially before the monsoon.
Built for outdoor duty
- Single and double bushing 33kV designs
- Metering, protection and multi-core configurations
- Specification-first: your datasheet reviewed before manufacturing
- EPC support: datasheet-based offers and bulk supply
- Domestic and export supply
Where they are used
- 33kV substations
- Outdoor switchyards
- Utility installations
- Industrial substations
- Solar power plants
- Wind power projects
- Outdoor CT PT metering units
- Power generation facilities
- Railway and infrastructure projects
What to send us
Share as many of these details as you have, or send your datasheet or BOQ directly.
Manufacturer, exporter and supplier
We supply outdoor 33kV current transformers for India and for projects in the following countries and regions:
- India
- United Arab Emirates
- Saudi Arabia
- Bahrain
- Iraq
- Kuwait
- Oman
- Qatar
- South Africa
- Zambia
- Tanzania
- Ghana
- Nepal
- Bhutan
- Bangladesh
- Indonesia
- Kenya
- Malaysia
- Turkey
- Zimbabwe
- and other countries
Frequently asked questions
What is an outdoor 33kV current transformer?
A CT designed for open-air installation on 33kV systems, with weather-resistant insulation, adequate creepage and sealed terminals, that converts high line current into a small secondary current for meters and relays.
Can an indoor CT be used outdoors?
No. Indoor resin and terminals are not designed for UV, rain and pollution. Using an indoor CT outdoors risks surface tracking, moisture ingress and early failure.
What creepage distance is needed for a 33kV outdoor CT?
It depends on site pollution. Heavy pollution typically needs about 25 mm/kV (around 900 mm for 36kV equipment), and very heavy or coastal sites about 31 mm/kV. Follow your utility or tender specification.
Can one outdoor CT handle both metering and protection?
Yes, with a multi-core design that has separate metering and protection cores in one body.
Does AMREST make customised outdoor 33kV CTs?
Yes. Ratio, cores, accuracy class, burden, creepage, terminals and mounting are built to your project specification.
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