6 MVA Custom Power Transformers-69/3.45 KV | Jamaica 2025

Power Transformer - Transmitting powerful energy, keeping the promise of every kilowatt-hour.

01 General

1.1 Project Description

6 MVA power transformer was delivered to Jamaica in October 2025. The rated power of the transformer is 6 MVA with ONAN cooling. The primary voltage is 69 kV with +4(-2) *2.5% tapping range (OLTC), the secondary voltage is 3.45 kV, they formed a vector group of Dd0.

This custom power transformers, manufactured by SCOTECH, is a three-phase, outdoor unit designed in accordance with ANSI standards. It exhibits high efficiency, reaching 99.38% at 50% load and 99.12% at full load (0.8 pf), with no-load and load losses of 5600 W and 36800 W respectively. The exciting current at rated voltage is 0.35%, and the voltage regulation at 100% MVA and 0.8 pf is 5.3%. The transformer is built with a sealed tank made of mild steel featuring C4 anti-corrosion treatment, finished in light grey. It is equipped with three high-voltage OIP condenser bushings and three low-voltage porcelain bushings, all with spade terminals and mounted on the tank cover. Two grounding terminals are provided for safety. The unit guarantees a noise level of 66 dB and a short-circuit duration of 3 seconds. Temperature rise limits are set at 65°C for the average winding and top oil layer, and 80°C for the winding hot-spot. The transformer includes a comprehensive set of accessories such as oil and winding temperature indicators, a pressure relief device, a gas relay, surge arresters for the HV side, an off-load tap changer, oil level indicators, current transformers, an intelligent online dissolved gas monitor (HYDRAN 201R), an impact recorder, and an IP65 control cabinet. Spare parts and a series of routine and special tests, including impulse voltage withstand, heat run, partial discharge, and sweep frequency tests, are also specified to ensure reliability and performance.

Application (Where It Is Used)

• This transformer is designed for 50 Hz power systems and is typically used in:
• Step-up or step-down substations (69 kV primary / 3.45 kV secondary)
• Industrial parks, large factories, wind or solar power plants for grid connection or distribution
• Outdoor installation at altitudes ≤ 1000 m, suitable for C4 corrosion protection environments (e.g., coastal or industrial polluted areas)

Standards Compliance

This transformer is designed, manufactured and tested according to:

• IEEE C57.12.00-2021 – General requirements for liquid-immersed transformers
• IEEE C57.12.90-2021 – Test code for liquid-immersed transformers
• IEC 60076-1-2011 – Power transformers – Part 1 (partially applicable)

1.2 Technical Specification

6 MVA custom power transformers specifications type and data sheet

1.3 Drawings

6 MVA custom power transformers diagram drawing and size.

02 Manufacturing

2.1 Core

Three-leg design using high-permeability cold-rolled silicon steel. Measured no-load loss 5.274 kW (at 100% voltage) – better than 5.6 kW guaranteed. Core-to-ground insulation resistance 32.4 GΩ, low tgδ – indicating healthy core insulation.

2.2 Winding

All copper windings for excellent conductivity. Temperature rise test: HV winding 57.2 K, LV winding 49.6 K – well below 65 K limit. Winding resistance unbalance: HV 0.12%, LV 0.41% – showing uniform winding process.

2.3 Tank

Sealed tank with bolted cover, mild steel with C4 anti-corrosion. Equipped with: conservator (with diaphragm), pressure relief device, oil level gauge, oil temperature indicator, winding temperature indicator. Tank pressure test: 30 kPa / 12h – no leakage, strong structural integrity.

2.4 Off-Load Tap Changer

This off-load tap-changer, consists of three single-phase drum-type units vertically mounted on the lower side of the enclosure with linked operation. It is suitable for 72.5kV power transformers, rated at 200A, and is equipped with eight 25mm² cables (each with 6mm single-side insulation) and an 800mm operating rod (extendable upon request), enabling no-load voltage regulation.

2.5 DGA

This custom power transformers is equipped with a Hydran 201i online Dissolved Gas Analysis (DGA) system, which continuously monitors combustible gases dissolved in the oil (including hydrogen, carbon monoxide, acetylene, and ethylene) via an intelligent sensor mounted directly on the transformer valve. It provides real‑time hydrogen‑equivalent readings from 0 to 2,000 ppm, supports gas concentration alarms, hourly/daily trend alarms, and fault self‑diagnostics, enabling early warning of incipient faults in the transformer.

2.6 Buchholz Relay

The Buchholz relay of this power transformer is mounted on the connecting pipe between the main tank and the conservator, monitoring the insulating oil flow and gas accumulation. It triggers a light gas alarm for slow internal faults (e.g., partial discharge or overheating) and issues a heavy gas trip command for severe faults (e.g., short circuits), thereby promptly disconnecting the power supply to protect the transformer from further damage.

03 Testing

All technical parameters from the specification are fully matched by test results:

All key parameters meet or exceed the guaranteed values.

04 Packing and Shipping

4.1 Packing

Large custom power transformers are usually shipped without a wooden crate but with moisture-proof covering + desiccant (or wooden crates upon request). Key components (bushings, instruments) individually protected to prevent transport damage. Anti-rust and anti-humidity treatment for export shipment.

4.2 Shipping

Lifting lugs and jacking pads provided for easy loading/unloading. Impact recorder installed during transport to monitor any excessive shocks. Shipping documents include: packing declaration, center of gravity marks, forklift / lifting position marks.

05 Site And Summary

• Copper windings – Low resistance, high overload capability, unbalance ≤0.41%.
• Mineral oil + conservator with diaphragm – Prevents oil oxidation, extends insulation life.
• ONAN cooling – No fans or oil pumps, low noise (guaranteed ≤66 dB), high reliability.
• Surge arresters (3 pcs) – Integrated on HV side for lightning overvoltage protection.
• Smart online monitoring – HYDRAN 201R dissolved gas monitor + impact recorder.
• Full special tests completed – Lightning impulse, temperature rise, SFRA, dielectric loss, etc.