Dry Type Substation Transformers Technical Features

Most transformer companies offer standard engineered products only, and ask the users to make it fit their applications. Also these companies can engineer the product both electrically and mechanically to fit virtually any application. Typically companies employ three winding styles for Special Design Dry Type transformers, based on kVA, voltage and BIL requirements.

The ability to select a specific winding style assures the highest degree of mechanical strength under short circuit stress conditions and suitability for different voltage classes. The rectangular barrel wound style is the most common method in the industry for 600V and 5kV applications.

Installations of ventilated dry-type transformers do not require a liquid confinement area, automatic fire extinguishing system or fire vault. Dry type transformers use no insulating liquids, virtually eliminating the risk of local environment contamination and simplifying routine maintenance by eliminating the need to check, replace or clean liquid.

Dry-type units are relatively lightweight and can be conveniently installed on upper floors, balconies, roof trusses or roofs. Insurance companies generally offer lower premiums for installations of dry-types than for r liquid-filled transformers. General Construction Coils are vacuum-pressure impregnated (VPI) with solventless polyester resin, ensuring complete impregnation of the windings and insulation.

The finished VPI coils are incredibly strong, readily dissipate heat and are protected against moisture, dirt and most industrial contaminants. Ventilated dry-type winding designs vary depending on the voltage, basic impulse level (BIL) and current of the individual winding and/or application of the transformer. For all units, the insulation system will be 220°C regardless of the average winding rise.

Ventilated dry-type transformers are designed for indoor or outdoor applications in schools, hospitals, industrial plants, commercial buildings and any place requiring safe and dependable power.Ventilated dry-type transformers offer an economical solution and are extremely reliable when properly installed and maintained.

Transformers Enclosures

The standard indoor enclosure is NEMA 1, Category C construction. Enclosures are suitable for lifting, jacking, rolling or skidding with provisions for lifting from the transformer base. High voltage and low voltage ANSI ground pads are provided. The enclosure paint finish is neat, clean and highly resistant to corrosion. Metal surfaces are thoroughly cleaned of scale, oil, grease, rust and other foreign matter before painting. Unless specified otherwise, paint color shall be ANSI 61 (light gray). NEMA 3R and NEMA 4 outdoor enclosures are available for applications that prohibit indoor installation.

Transformer Coils:

Generally, low voltage (LV) windings less than 2,400 volts are either multi-conductor barrel or sheet conductor types. Multi-conductor windings may be more economical and preferred in smaller kVA low voltage applications in which the current and axial short circuit forces are relatively small. High voltage (HV) windings 2,400 volts or greater may be single-section barrel, multi-section barrel or disk types. Ventilated drytype coils may be either round, oval or rectangular through about 2,000 kVA. Transformers larger than 2,000 kVA generally are designed with round windings unless there are special considerations, such as limiting dimensions.

Transformer Cores:

The transformer cores are constructed of non-aging, high grade, grain oriented silicon steel laminations with high magnetic permeability. Magnetic flux densities are kept well below the saturation point. Core laminations are free of burrs and stacked without gaps. Mitered STEPLAP construction cores may be provided when specified. The core clamping brackets are designed to provide even distribution of clamping forces to the core yokes and legs. The core is electrically isolated except for the factory-installed core ground strap, which provides a single path from the core to ground.

Forced Air Cooling:

All units rated 750 kVA and higher can have added fans, increasing capacity in all current carrying parts for the fan-cooled rating and capability to add a thermometer relay to control fans. When specified, the transformer shall be provided with fans to give a forced air-cooled rating of 33% above the self-cooled rating. Control wiring (wire markers included), a thermal sensor and a fan controller will be supplied.

Audio Sound Levels

The transformer shall be designed to meet or exceed ANSI and NEMA sound levels for dry-type transformers. As an option, transformers designed at -3dB to -10dB below ANSI and NEMA standard sound levels are available.

Standard Features of MGM Transformers:

UL Listing,CSA, & CUL

Vacuum Pressure Impregnated (VPI) windings

80°, 115°, 150°C average winding rise ratings

60 Hz operation

220°C insulation system

Aluminum or copper windings

ANSI ground pads

Core ground strap

Indoor ventilated enclosure – NEMA 1

Paint — ANSI 61 finish

Provisions for lifting

Removable front and rear panels

Vibration isolating pads

(2) 2 1/2 % full capacity taps above and below nominal

Conform to NEMA, ANSI, & IEE standards for Dry Type Transformers

OSHPD Qualified

Other Options & Features

Fans for 133% FA kVA rating

Future fan wiring and control

Ground bus – full length copper

Impact indicator – Mechanical

Outdoor enclosure NEMA 3R

Paint — polyurethane overcoat

Screened ventilation openings

Enclosure — hinged panels

Enclosure — knockdown

Electrostatic Shield

Space heaters

Temperature monitor/fan controller

Thermostat for space heaters

Bus to End

Flex Leads

Low Noise