Federal Pacific Unit Substation Transformers

Unit Substation Transformers
5 and 15 KV Class
General Information

Description
Unit substation transformers are available in a wide variety of types and ratings to provide reliable and versatile electrical distribution.

The changing needs and variable load densities of industrial and commercial power systems create the need to locate transformers close to the electrical center of the load – providing flexibility for change and economical distribution of power.

Dry-type transformers are ideally suited for the applications. The ventilated air-cooled construction eliminates the concern for contamination and toxicity of cooling liquids. They do not require the expensive vaults, fluid leakage containment provisions, or fire protection systems needed for liquid filled units to satisfy National Electric Code requirements.

Lower installed costs and minimum maintenance requirements make dry-type substations transformers an ideal choice for new or existing installations.

Transformers are available in three-phase ratings from 112-1/2 KVA to 10000 KVA. All standard primary and secondary voltage ratings are provided to match load requirements to the distribution system.

Unites can be arranged for standard direct connection to high voltage and low voltage distribution protective equipment or provided as individual transformers.

Industry Standards
Unit substation transformers are designed and tested in accordance with the following standards:

• IEEE C57.12.01 General Requirements for Distribution. Power and Regulating Transformers.

• IEEE C57.12.91 Standard Test Code for Dry-Type Distribution and Power Transformers.

• NEMA 210-Secondary Unit Substations.

• NEMA TR-27 Commercial Institutional and Industrial Dry-Type Transformers.

Tested Performance
A high level of transformer reliability for trouble-free installation and operation, all transformers manufactured are tested in accordance with NEMA and IEEE Standards.

Ratio Test is performed on rated voltage connection and tap connections to assure proper turns ratio on all connections.

Polarity Test and phase relation tests are made to ensure proper polarity and marking because of their importance in paralleling or banking two or more transformers,

No-load (excitation) Loss Test determines the losses of a transformer which is excited at rated voltage and frequency, but which is not supplying a load. Transformer excitation loss consists mainly of the iron loss in the transformer core.

Load Loss Test determines the amount of losses in the transformer when carrying full rated load. These losses consist primarily of PR losses in the primary and secondary winding and ensure that specifications of the transformer design are met.

Excitation Current Test determines the current necessary to maintain transformer excitation.

Resistance Test is performed on the transformer windings and is used to determine 1 R loss.

Impedance Test is made to insure that transformer design standards are attained.

Dielectric Test (applied and induced potential) checks the insulation and workmanship to demonstrate that the transformer has been designed and manufactured to meet the insulation tests required by the standards.

Applied Potential Test are made by impressing between windings and between each winding and ground, a low frequency voltage in accordance with the following:

Induced Potential Test call for over-exciting the transformer by applying between the terminals on one winding a voltage of twice the normal voltage developed in the winding for a period of 7200 cycles. Partial Discharge (PD) is performed during the induced potential test.

Unit Substation Arrangements

Arrangements
Unit substation transformers meet a wide variety of application requirements with the highest degree of service reliability. Substations are coordinated, engineered electrical centers designed to safely step down distribution voltage to utilization voltage. It usually supplies secondary voltages ranging from 208Y/120 to 600 volts and primary voltages of 2400 to 13800 volts. They typically provide power to industrial plants, office buildings, commercial building, public buildings, hospitals and schools. The form, rating, and characteristics of unit substations and their transformers are determined by the design of the electrical distribution system and the requirements of the particular loads and installation conditions.

Incoming Line Air Interrupter Switch
The type AJII air interrupter switch, two position (open-close), three pole with manually operated, stored-energy mechanism provides quick-make, quick-break operation for disconnecting the transformer incoming line. Utilized with power or current limiting fuses, the switch provides safe, fast, and reliable protection for high voltage circuits. The AJII switch is rated 600 or 1200 amp continuous, 600 or 1200 amp load-break with a high fault closing capacity of 40,000 am asymmetrical. The 1200A switch is available with 61,000 amp asymmetrical rating (optional).

The switch compartment is bolted directly to the high voltage side of the transformer section. Cable entrance can be at top or bottom for either single or loop feed. Fuses, when specified, are located in a compartment under the interrupter switch. A hinged door allows access to fuses and is provided with a mechanical interlock to prevent the door opening unless the switch is in the “open” position. Standard fuses, when supplied, are the current limiting, non-disconnect type. Lightning arresters and key interlocks are optionally available.

Incoming Line Terminal Compartment
When a disconnect or overcurrent device is not required as an integral part of the lineup, an air-filled terminal compartment (ATC) is bolted directly to the high voltage end of the transformer section. The metal-enclosed terminal compartment matches the height and depth of the transformer section and is provided with bolt-on end panels for accessibility to terminal connections. The compartment can be arranged for single or loop feed with potheads or clamp-type terminals for either top or bottom cable entrance. Lightning arresters can be supplied when required for protection against voltage surges.

Low Voltage Distribution Sections
A complete selection of distribution and protective equipment is available to meet application requirements. Unit substation transformers are arranged for direct connection to a variety of equipment including low voltage draw-out switchgear, distribution switchboards, group mounted power panel-boards and motor control centers.

For those applications where secondary distribution equipment is not required, an outgoing air-filled terminal compartment (ATC) can be provided for top or bottom cable entrance. The compartment bolts directly to the transformer and have removable end panels for accessibility. Provisions can also be made to accommodate busway.

Features of Typical 15 KV Substation Transformer

1. Round Cylindrical coils assure proper ventilation and provide mechanical strength for fault stresses. The units are either barrel wound or disc wound (depending on voltage) using aluminum conductor with insulated coil supports.

2. Core structures are fabricated in a “stepped” configuration from special high-grade, cold rolled, silicon steel. The steel laminations are clamped at the top and bottom to absorb vertical stresses on the core.

3. 220 degree C insulation systems using Nomex* paper and resin glass laminates provides long operating life and quiet operation. The complete core and coil assembly is impregnated with polyester varnish and oven cured to make the assembly highly resistant to moisture.

4. High dielectric interphase barriers assure positive phase to phase insulating characteristics.

5. High voltage tap connections are easily accessible by removal of front panels. The centrally located taps are changed by moving jumpers between connection points when the transformer is de-energized.

6. Rugged enclosure base with provisions for lifting, jacking, towing, skidding or rolling for installation.

7. Rigidly braced low voltage bus bars arranged for proper electrical connections to the transformer. The low voltage bus is equipped with flexible connectors to the core and coil assembly to reduce transmission of vibration to the connected equipment.

8. Diagrammatic nameplate provides complete rating and connection information.

9. Vibration isolation pads isolate core and coil assembly from the base structure to reduce sound levels.

10. Optional fan cooling equipment to provide an additional 33-1/3% KVA capacity for units with self-cooled ratings of 300 KVA and above. (Provisions for future forced air- cooling are provided as standard – including sufficient current-carrying capacity on internal bus bars.) Fans and controls can be installed at the factory or can be shipped for installation at the jobsite.


Core and Coil Assembly


Core Construction
The transformer cores are made of high grade silicon electrical steel laminations with high magnetic permeability. Precision steel cutting machines are used to cut the steel laminations with precise squareness and miter and to be free of burrs.

Laminations are hand stacked to computer generated specifications to assure correct positioning for close fitting joints to minimize noise and core loss. Each lamination has an insulating coating bonded to both sides to minimize eddy-current losses.

The core legs are arranged in a “stepped” configuration to accommodate the coils and to provide maximum cooling and strength. The completed three-leg core assembly is rigidly clamped with steel members to prevent movement and to provide support for the coils.

Coil Construction
Coils are precision wound in a circular configuration using aluminum conductor material as standard. Copper conductors can also be provided as an option.

On low voltage where possible, sheet-wound secondary windings are used. The windings are separated by insulation layers and spacers. These sheet windings offer the advantage of virtually eliminating axial short circuit stresses.

Nomex insulated wire wound primary windings are placed directly over the secondary windings with a suitable insulating barrier between the coils consisting of spacers and sheet insulation applied to the proper thickness. Primary windings may be random-wound or disc-wound depending upon the design requirements. All coils are adequately braced for full short circuit capability.

Assembly
The completed coil units are placed on the core legs. Top core yokes are put into place and securely clamped. Electrical connections are made using welded aluminum or brazes copper, to ensure reliable service.

Coils may be vacuum pressure impregnated, when specified. After installation of the mounting hardware, the complete core and coil assembly is submerses and impregnated with an insulating varnish. The assembly is completely coated to provide moisture and dirt resistance as well as high dielectric strength. After dipping, the varnish is fully cured in a drying oven.

Completed core and coil assembles receive a final inspection and testing prior to installation in the enclosure. When installed, vibration isolation pads are provided to isolate the core and coil assembly from the base structure. All structural parts are grounded to prevent induced voltage buildup.
Construction
FB transformers utilize a 220 degree C insulation system that combines inorganic materials and resins to provide a fire resistant, high dielectric capability. All materials have been thoroughly tested and proven with respect to their stability at required operating temperatures.

The major components of the 220 degree C system include Nomex* paper for conductor insulation plus resin-glass laminates, silicon rubber and polyester varnish. The combination of materials is specifically chosen to assure long operating life and quiet operations.

*Nomex is a Registered Trademark of Dupont Co.

Taps
Primary windings are furnished with full capacity tap connections to provide adjustment to accommodate variations in the incoming high voltage. All units include, as standard, two (2) 2-1/2% taps full capacity above normal (FCAN) and two (2) 2-1/2% taps full capacity below normal (FCBN).

The tap connections are located in a vertical arrangement on the side of each coil. Accessible behind removable covers, the taps can easily be changed by moving jumpers between connection points when the transformer is de-energized.

Forced-Air Cooled System Operation
Unit substation transformers with self-cooled ratings of 300 KVA and above can be supplied with fans and controls to obtain additional KVA capacity. Forced circulation of air correctly applied permits the self-cooled KVA rating of the transformer to be increased by an additional 33-1/3%. (Class FA rating)

The winding temperature control panel is equipped with necessary controls for the operation of the fans:
1. Winding temperature indicator
2. Fan position test switch
3. Temperature sensing device
4. Fuses
5. Green light (auxiliary power “On”)
6. Amber light (fan operation)
7. Red light (excessive temperature)

The winding temperature indicator is furnished with three (3) sets of normally open contacts. Each contact closed as the average winding temperature reaches factory preset temperature values.

Sequence of operation is as follows:

1. When the winding indicator reaches 190 degree C (based on 150 degree C average winding temperature in a maximum 40 degree C ambient), the fan relay is energized which closed the ran-relay contact. The fans operate resulting in 33-1/3% additional KVA capacity.

2. Should the temperature increase to 200 degree C, the red light and remote alarm (if connected) operate.

3. A further increase in winding temperature to 210 degree C will operate contacts that can be used to trip the primary or secondary main breaker.

General Specification Guide

The transformer shall be ventilated. Open, dry-type construction cooled by the circulation of air through the windings. The unit shall be mounted in an indoor or outdoor enclosure finished in the manufacturer’s standard ANSI 61 light gray paint with provisions for direct connection to the primary and secondary equipment as specified. The transformer shall be designed, manufactured, and tested in accordance with the applicable NEMA, ANSI, and IEEE standards. The facility in which the transformers are manufactured shall be an ISO 9001:2000 registered facility.

Insulation Materials
All insulations materials for the primary and secondary coil assembly shall be rated for continuous 220 degree C total temperature (Class H). Insulation on the rectangular wire conductor shall be Nomex* or equivalent, which has a UL Listed 220 degree C insulation system having suitable overlapping to keep dielectric volts/mil stress within limits recommended by the insulation supplier. Layer insulation for LV strip windings shall be Nomex* or equivalent, which is a UL Listed 220 degree C insulation system having a thickness to keep volts/mil stress values no higher than values recommended by the insulation supplier.

Core and Coil Assembly
The core shall be constructed of non-aging cold-rolled, high permeability silicon steel. All core laminations shall be step-lap miter cut, free of burrs and stacked without gaps. The core framing structure shall be of rigid construction to provide full clamping pressure upon the core and provide the support points for the coils. Butt lap construction shall not be acceptable for the power ratings above 1000 KVA. The HV and LV coils shall be cylindrically wound (not rectangular) as an assembly with the HV coil wound directly over the LV coil. Coils shall be adequately braced for full short circuit capability to pass shot circuit tests in accordance with IEEE C57.12.91.

VPI Process for transformer coils:
The coil assembly is baked for 2 hours at 190 degrees C to remove moisture. Preheated coils are placed in a sealed VPI pressure/vacuum tank and impregnated with a 100% solids varnish.

Final Dip and Bake
Upon completion of the VPI process of the coils and their assembly on the core, the core top yokes are stacked, the core is clamped and all necessary leads are welded (if aluminum) or brazed (if copper) to the LV and MV bus components. At this time the complete core and coil assembly is dipped into a soft solvent based varnish of Isonel 51 or equivalent to provide a protective coating from oxidation for all bare metal parts like core laminations and core clamping hardware. The varnish used for this process must not be a hard varnish like a 100% solids material. This core and coil assembly is then baked at the proper time and temperature (usually 4-8 hours @ 175 degrees C) to cure all of the varnish.

Transformer Enclosure and Base
The transformer base shall be welded construction and shall be constructed to permit 4 point lifting using 1” diameter and 1-1/2” thick lifting eyes along the base of the transformer. The enclosure shall include provisions for rolling, skidding, lifting, and jacking for installation.
Removable panels shall not exceed 70 pounds in weight and shall contain suitably strong handles for lifting and placing. If installation space is adequate, hinged doors may be provided, when specified.
The enclosure shall be constructed of heave gauge sheet steel equipped with removable parts for access to the core and coils on the front and rear. Ventilated openings shall be furnished to meet NEMA standards. The cabinet metal must be at least 14 gauge thickness. Whenever the cabinet must be outdoor (NEMA 3R) the ventilation openings must be constructed as “back-to-back” channels. Paint for the transformer enclosure shall be an ANSI-61 light gray color of a polyurethane powder coating that is electrostatically applied conforming to UL 1332 specifications. For installation areas within highly corrosive environments stainless steel enclosures may be furnished as an option. Vibration dampening pads shall be provided to isolate the core/coil assembly from the base structure.

High Voltage Taps
Each coil shall have taps at nominally rated voltage and additional 4 taps: 2-2-1/2% above and below rated nominal voltage. Tap leads shall be terminated at the coils and equipped with provisions for changing taps under de-energized conditions.

Sound Level
The transformer shall be designed to meet the sound level standards for dry-type transformers as defined in IEEE C57.12.01-1998 or NEMA ST-20.

Forced-Air Cooling
When forced air cooling is specified, the forced-air cooling package (fans and controller) shall be provided for automatically increasing the self-cooled rating by 33-1.2%. The system shall contain 120 VAC single phase fans and a control panel with indicating lights, temperature indicator, fan position test switch, and alarm mode selector switch.

Accessories As Specified
Winding Temperature Controllers and Monitors shall be Qualitrol or equivalent. Provisions for grounding shall be provided to be welded Ground Pads or special termination hardware.

Final Tests
Final Test Reports in the proper IEEE format shall be furnished for each unit, documenting the successful passing of all required tests.

• Federal Pacific Industrial Control Transformers
• Federal Pacific Type FB Encapsulated Transformers
• Federal Pacific Type FH Ventilated Transformers
• Federal Pacific High Voltage General Purpose Transformers
• Federal Pacific Motor Drive Isolation Transformers
• Federal Pacific Unit Substation Transformers
• Federal Pacific VPI  Epoxy Shielded Transformers
• Federal Pacific K-Factor Transformers

 Power Transformer Information:

 Power Transformer Manufacturer

• ACME Transformers - With Acme Electric being in business over 80 years, they have always believed in offering there customers superior service, quality and technical expertise in the transformer market.
• AMVECO Transformers - AMVECO designs and manufactures toroids transformers, current transformers, and auto transformers. Most AMVECO products are custom designed utilizing their state-of-art proprietary CAD programs.  The AMVECO engineers can quickly generate designs in a matter of hours, if needed.
• Federal Pacific Transformers -  Federal Pacific is a division of Electro- Mechanical Corporation, a privately held, American owned company founded in 1958. Federal pacific offers dry-type transformers from .050 KVA through 10,000 KVA single and three phase, up to 34.5 KV, 150 KV BIL with UL approval through 15 KV.
• Marcus Transformer - Ever since they opened their doors for business a half a century ago, they have been a leader in innovative transformer design. As a family-owned company they are proud of the reputation they have earned for making quality-built transformers that deliver exceptional performance and savings.
• Hammond Transformers -  Hammond Manufacturing was founded in 1917 in Guelph, Ontario, Canada. In the last 3 decades it has expanded to the US and the international markets offering many types of power transformers. 
• TEMCo Transformers - TEMCo Transformer, a family-owned business which has been manufacturing and distributing electrical products since 1968. They focus on transformers that significantly reduce power consumption over 30 percent compared to competitive makes.
• GE Transformers - GE has been a key player in the energy industry for more than a century.  Since the installation of their first steam turbine in 1901. They have become number one provider of high-technology power generation and distribution equipment.
• Jefferson Electric Transformers - Jefferson Electric has been a pioneer and innovator of magnetic products since 1915. Jefferson broad line of dry-type transformers are backed by quality assurance systems so stringent that each and every unit gets thoroughly tested before it goes out there door.
• More power transformer brands - Check out more companies by clinking this link.

 Power Transformer Types

• Distribution Transformers - Distribution transformers are generally used in electrical power distribution and transmission power. This class of transformer has the highest power, or volt-ampere ratings. and the highest continuous  voltage rating.
• Substation Transformers - Substation Transformers are large devices which usually weigh tens of thousands of pounds.   They are filled with tens of thousands of gallons of heat transfer fluid.  Although they are typically 99.8% efficient in the transforming of electricity from one voltage to another, processing hundreds of Mega Volts-Amps of electricity force the liberation of hundreds of BTUs per second.
• Medical Grade Isolation
   Transformer - Medical Grade Transformers generally refer to the transformers used in medical devices as well as hospital, biomedical and patient care equipment. There are a number of strict safety rules, guidelines and laws governing the design, construction and the test of these transformers.
• Drive Isolation Transformer - They are used to isolate a drive from a main power line to prevent the transmission of harmonics that the drives produce back into the power line.  They stop drive harmonics from disrupting computers and other sensitive equipment.
• Toroidal Transformers - Toroidal Transformers are more efficient than the cheaper laminated EI types of similar power level. Some of the advantages are smaller size, lower weight, less mechanical hum, (making them superior in audio amplifier), low-off-load loss.

 Power Transformer Types

• Step-Up Transformers - A Step-Up Transformer is one whose secondary voltage is greater than its primary voltage.  This kind of transformer "steps up" the voltage applied to it. -
• Step-Down Transformers - A Step-Down Transformer is  designed to reduce voltage from primary to secondary.  They can range from sizes from .05 KVA to 500 KVA
• Isolation Transformers - An Isolation Transformer is a device that transfers energy from the alternating current (AC) supply to an electrical or electronic load.  It isolates the windings to prevent transmitting certain types of harmonics.
• Buck Boost Transformers - Buck Boost Transformers make small adjustments to the incoming voltage. They are often used to change voltage from 208v to 240v for lighting applications.  Major advantages of Buck boost transformers include; low cost, compact size and light weight. 
• High Voltage Transformer - There are many different types of voltage transformers. A High Voltage Transformer operates with high voltages. Typically, these voltage transformers are used in power transmission applications, where voltages are high enough to present a safety hazard.
• Medium Voltage Transformers - A Medium Voltage Transformer can be connected directly to a primary distribution circuit and generally has the most load diversity. These voltage transformers have installation practices that are generally in accordance with application recommendations from the Institute of Electrical and Electronic Engineers (IEEE).
• Low Voltage Transformers - A Low Voltage Transformer is an electrical device that transforms 120 volts (line voltage) into 12 volts or 24 volts (low voltage). Some uses for low voltage transformer are in landscaping lighting.
• Single Phase Transformers - In electrical engineering, single-phase electric power refers to the distribution of electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors.
• Three Phase Transformers - Three Phase Transformers must have 3 coils or windings connected in the proper sequence in order to match the incoming power and therefore transform the power company voltage to the level of voltage needed while maintaining the proper phasing or polarity.
• Custom Transformers - Custom Transformers are designed for a certain performance specifications and size requirements.  The company works with your engineering specification. 
• Industrial Control Transformers - Industrial Control Transformers are used to convert the available supply voltage to the required voltage to supply industrial control circuits and motor control loads.
• Pad Mounted Transformers - Pad Mounted Transformers are usually single phase, or three phase, and used where safety is a main concern. Typical applications; restaurant, commercial building, shopping mall, institutional. 
• Pole Mounted Transformers - Pole Mounted Transformers are used for distribution in areas with overhead primary lines. Outside a typical house one can see one of these devices mounted on the top of an electrical pole.
• Oil Filled Transformers - Oil Filled Transformers are transformers that use insulating oil as insulating materials.  The oil helps cool the transformer. Because it also provides part of the electrical insulation between internal live parts, transformer oil must remain stable at high temperatures over an extended period.
• Dry Type Transformers - Dry-Type Transformers are available for voltages up through 34.5 kV (although the most common upper limit is 15) and KVA ratings up through 10,000 (with 5000 as the usual limit). Dry-type use air as a coolant, lowering health and environmentally concerns.
• Auto Transformers - An Autotransformer is an electrical transformer with only one winding. The winding has at least three electrical connection points called taps. Autotransformers are frequently used in power applications to interconnect systems operating at different voltage classes, for example 138 kV to 66 kV for transmission. Another application is in industry to adapt machinery built for 480 V supplies to operate on the local 600 V supply.
• More power transformer types - Read further about additional transformer types and their uses.

 Power Transformer Term Definitions

• Electrical Transformers - Electrical Transformers are devices used to raise or lower the voltage of alternating current. For instance, power is transported over long distance in high voltage power lines and then transformers lower the voltage so that the power can be used by a business or household.
• Isolating Transformers - An Isolating Transformer is a transformer, often with symmetrical windings, which is used to decouple two circuits.  An Isolation transformer allows an AC signal or power to be taken from one device and fed into another without electrically connecting the two circuits. Isolation transformers block transmission of DC signals from one circuit to the other, but allow AC signals to pass. 
• Transmission Power Lines - A Transmission Line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electromagnetic or acoustic waves as well as electric power transmission. Components of transmission lines include wires, coaxial cables,  dielectric slabs, option fibers, electric power lines, and waveguides.
• Transformer Voltage - The measure of the amount of force on a unit charge because of the surrounding charge.
• Transformer Phase - Most transformer are either single phase or three phase.
• Transformer Frequency - The transformer cannot change the frequency of the supply. If the supply is 60 hertz, the output will also be 60 hertz.
• Transformer K Factor - Some transformers are now being offered with a k-factor rating. This measure the transformer's ability to withstand the heating effects of non-sinusoidal harmonic currents produced by much of today's electronic equipment and certain electrical equipment.
• Primary Voltage - The coil winding that is directly connected to the input power.
• Secondary Voltage - The coil winding  supplying the output voltage.
• Harmonic Cancellation - Harmonic cancellation is performed with harmonic canceling transformers also known as phase-shifting transformers. A harmonic canceling transformer is a relatively new power quality product for mitigating harmonic problems in electrical distribution systems. This type of transformer has patented built-in electromagnetic technology designed to remove high neutral current and the most harmful harmonics from the 3rd through 21st.
• Weatherproof - Enclosed transformers come with a weatherproof standard set by NEMA.
• Epoxy Encapsulated - A process in which a transformer or one of its components is completely sealed with epoxy or a similar material. This process is normally preferred when a unit might encounter harsh environmental conditions.
• More power transformer terms - Such as inductor, ground fault, core saturation, current transformer, faraday shield, etc.

Related Transformer Products

• Voltage Regulators - A Voltage Regulator is an electrical regulator designed to automatically maintain a constant voltage level.  It may use an electromechanical mechanism, or passive or active electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.
• AC Line Reactor - AC Line Reactors is a three phase transformer used in conjunction with AC variable frequency and DC motor drive. They are a bi-directional protective filtering device.
• Line Power Conditioners - Power or Line Conditioners regulate, filter, and suppress noise in AC power for sensitive computer and other solid state equipment.
• DC Power Supplies - Conversion of one form of electrical power to another desired form and voltage. This typically involves converting 120 or 240 volt AC supplied by a utility company to a well-regulated lower voltage DC for electronic devices.
• Rotary Phase Converters - Rotary Phase Converters are commonly used in home or small commercial or industrial settings. Rotary phase converters convert single-phase power into three-phase power. This is a very cost-effective way to power three-phase electric motors and other three phase equipment.
• Frequency Converters - A Frequency Changer or Frequency Converter is an electronic device that converts alternating current (AC) of one frequency to alternating current of another frequency.
• Voltage Converters - A Voltage Converter changes the voltage of an electrical power source and is usually combined with other components to create a power supply.
• Magnetic Motor Starters - Magnetic Motor Starters are essentially heavy duty relays mounted in boxes, often equipped with heater/thermal overloads matched to the motor they start.
• Motor Starting Auto Transformers - An Auto Transformer starter uses an auto transformer to reduce the voltage applied to a motor during start. The auto transformer may have a number of output taps and be set-up to provide a single stage starter, or a multistage starter.

For an additional resource the Best of Industry Web Directory : Electrical Power Transformer Directory section is quite useful.