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Three-Phase Pad-Mounted Transformers

Oil-filled, three-phase transformers designed for outdoor pad-mounted power distribution.

Wafr supplies three-phase pad-mounted transformers for underground power distribution. Units are available in live-front or dead-front construction, with radial or loop-feed arrangements, copper or aluminum windings, and a range of protection and accessory options.

Key Specifications

Specification

Configuration

Power Rating

75 to 7,500 kVA

Primary Voltage

11 to 40.5 kV

Frequency

50 / 60 Hz

Feed Arrangement

Radial or Loop

HV Terminals

Live Front or Dead Front

Winding Options

Copper or Aluminum

Construction

Core

Precision-cut, burr-free, grain-oriented silicon steel, with multiple grades available to optimize core-loss efficiency.

Coils

Rectangular coil construction with wire-wound high-voltage primaries and sheet-wound secondaries, designed to minimize axial stress under short-circuit conditions and provide magnetic balancing of tap connections.

Core & Coil Assembly

Core and coil assemblies are braced with heavy steel ends to help prevent distortion under short-circuit conditions.

Cores: Cores are manufactured with precision cut, burr-free, grain-oriented silicon steel. Many grades of core steel are available for optimizing core loss efficiency.

Coils: Pad-mounted transformers feature a rectangular coil configuration with wire-wound, high-voltage primaries and sheet-wound secondaries. The design minimizes axial stress developed by short circuits and provides for magnetic balancing of tap connections. Coils are wound using the highest quality winding machines providing exacting tension control and conductor placement for superior short-circuit strength and maximum efficiency.

Core and coil assemblies: Pad-mounted transformer core and coil assemblies are braced with heavy steel ends to prevent the rectangular coil from distorting under short-circuit conditions. Plates are clamped in place using presses, and welded or bolted to form a solid core and coil assembly.

Key Features

  • Radial and loop-feed arrangements
  • Live-front and dead-front HV terminals
  • Copper or aluminum winding options
  • Mild-steel tank construction
  • Corrosion-resistant powder-coat finish
  • Self-actuating pressure-relief valve
  • Secure three-point latching cabinet
  • Removable sill for installation

Standard Features, Options & Testing

Standard Features

  • 50 Hz or 60 Hz operation.
  • 65°C average winding rise.
  • Radial & loop feed arrangements.
  • Dead and live front type of HV terminals.
  • Bolted-on cabinet with removable sill having the following depths: 19" deep for 300–750 kVA; 22" deep for 1000–1500 kVA; 24" deep for 2000–3750 kVA; 30" deep for 5000–7500 kVA.
  • Tank: Mild steel.
  • Steel HV/LV compartment barrier.
  • Padlocking facility with penta-head bolt on the HV and LV, three-point latching mechanism.
  • HV and LV compartment doors – hinged and lift-off type with 120° holding bars.
  • Stainless steel door hinges.
  • Removable sill for easy installation.
  • Three-point latching door for security.
  • Permanent nameplate per ANSI requirement.
  • ANSI tank ground pads.
  • One-inch drain valve and sampler.
  • Self-actuating pressure relief valve.
  • Four (4) lifting lugs.
  • Welded cover with hand hole.
  • Oil fill plug.
  • Removable LV neutral ground strap, as required.
  • Durable, corrosion-resistant powder coat paint finish, Munsell Green 7GY3.29/1.5.
  • Designed, manufactured and tested in accordance with the latest ANSI and IEEE standards.

Optional Features & Accessories

  • Specific customer applications and the new DOE efficiency requirements.
  • Liquid level gauge.
  • Liquid temperature gauge.
  • Pressure vacuum gauge.
  • Copper and aluminum windings available.
  • Dual high-voltage ratings.
  • Internal expulsion fuses.
  • Current limiting fuses.
  • Internal oil-immersed partial range current-limiting fuses.
  • Bayonet fuse holders with and without flapper.
  • Internal oil switch (radial or loop).
  • Under oil internal arresters.
  • Low-voltage molded-case circuit breaker.
  • Special colors.
  • Partial stainless steel design (cabinet sill and tank bottom).
  • 30", 34" or 40" deep cabinet.
  • CTs or PTs including mounting support.
  • LV externally mounted molded case breaker.
  • Externally mounted kWh meter.
  • Flip-top cabinet for low profile design.
  • Additional externally mounted nameplate.

Tests

Wafr performs routine testing on each transformer manufactured including the following tests.

  • Resistance tests of all windings.
  • Ratio tests on the rated voltage and all tap connections.
  • Polarity and phase relation tests at rated voltage.
  • No load loss at rated voltage.
  • Exciting current at rated voltage.
  • Impedance and load losses.
  • Applied voltage test.
  • Induced voltage test.
  • Full-wave impulse test.
  • Mechanical leak test.

Normal Use Conditions

Available Options

  • Liquid level, temperature and pressure/vacuum gauges
  • Dual high-voltage ratings
  • Expulsion and current-limiting fuse options
  • Bayonet fuse holders
  • Internal radial or loop oil switches
  • Under-oil internal arresters
  • Low-voltage molded-case circuit breakers
  • CTs and PTs
  • Externally mounted kWh metering
  • Partial stainless-steel construction
  • Multiple cabinet depths and configurations
  • Special colors
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