11 kV 200 kVA Oil-Immersed Power Transformer: Specifications and Applications

Overview

The 11 kV 200 kVA oil-immersed power transformer is a three-phase distribution transformer that steps 11 kV primary voltage down to 0.4 kV for commercial, industrial, and rural networks. The 11 kV class is widely used in distribution systems that follow British and Commonwealth practice, and the transformer is designed and tested in accordance with IEC 60076 and GB 1094.

Key Specifications

Rated power: 200 kVA

Voltage ratio: 11 kV / 0.4 kV

Connection group: Dyn11 (standard)

Cooling: ONAN

Reference losses for the S11 type: no-load loss 330 W, load loss 2860 W, no-load current 1.3%

Design and Construction

Core

The core is made from cold-rolled grain-oriented silicon steel laminations, stacked with step-lap joints to limit no-load current and noise. The insulating coating on each lamination blocks eddy currents between sheets.

Windings

Copper conductors with class A or higher insulation are wound and dried under vacuum before oil filling, which keeps partial discharge low and dielectric strength high.

Tank

Both conservator-type and fully sealed tanks are available. The sealed design avoids oil contact with air, slowing oil aging and reducing maintenance, while the conservator design allows oil expansion with a breather and silica gel.

Environment and Installation Conditions

Maximum ambient temperature: +40 C

Minimum ambient temperature: -25 C

Altitude: below 1000 m

Relative humidity: up to 90% at 20 C (monthly average)

Installation: indoor or protected locations without fire, explosion, heavy pollution, chemical corrosion, or severe vibration

Application Scenarios

The 200 kVA rating suits the load of a small factory, a commercial building, a school, or a rural distribution feeder. At 11 kV it connects directly to medium-voltage distribution lines, and the Dyn11 connection handles unbalanced single-phase loads with low neutral displacement.

Protection and Commissioning

Primary protection: HV fuses or a ring-main unit with a fused switch.

Surge protection: surge arresters on the HV side, especially on overhead lines.

Earthing: solidly earth the tank and the neutral according to the network earthing scheme.

Commissioning checks: insulation resistance, oil level, tap position, and a dissolved gas analysis baseline.

Load checks: verify phase balance during the first weeks of operation.

Frequently Asked Questions

What does 11 kV mean in the model?

It is the nominal primary voltage; the secondary is 0.4 kV, giving a ratio of 11/0.4 kV.

What is the difference between a sealed and a conservator transformer?

A sealed tank has no air contact and needs less oil maintenance; a conservator type has an expansion tank and breather and is easier to inspect and refill.

Why is Dyn11 preferred for this rating?

Dyn11 provides a path for zero-sequence currents and keeps the neutral voltage stable under unbalanced loads, which is important when single-phase loads dominate.

What protection does the 200 kVA unit need?

HV fuses or a switch-fuse unit, a low-voltage main breaker, and surge arresters; an oil temperature alarm is recommended where loads are heavy.

Can the transformer be pad-mounted outdoors?

Yes, with a suitable weatherproof enclosure, oil containment, and the correct creepage distance for the bushings.

How often should the oil be tested?

Annual dissolved gas analysis and a periodic oil quality test per IEC 60422 give early warning of developing faults.