1.Can air cooled transformers be applied to motor loads?

This is an excellent application for air cooled transformers. Even through the inrush or starting current is five to seven times normal running current, the resultant lower voltage caused by this momentary overloading is actually beneficial in that a cushioning effect on motor starting is the result.

2.Can transformers be used in parallel?

Yes, it is very common for transformers to be placed in parallel service. To provide maximum efficiency, voltage and impedance values must match closely.

A failure to match will cause unbalanced loading for the transformers and may lead to overheating or premature failure

3.Can Transformers develop Three Phase power from a Single Phase source?

NO. Phase converters or phase shifting devices such as reactors and capacitors are required to convert single phase power to three phase.

4.What is the difference between Insulating, Isolating, and Shielded Winding transformers?

Insulating and isolating transformers are the same. they are used to describe the isolation of the primary and secondary windings, or insulation between the two.

A shielded transformer is designed with a metallic shield between the primary and secondary windings to attenuate transient noise.

The shielded transformer is used in applications such as computers, process controllers and many other microprocessor controlled devices.

All two, three and four winding transformers are of the insulating or isolating types.

5.Will Efficiency and Heat be a Consideration?

An ideal transformer would have no losses, and would therefore be 100 efficient. In practice energy is dissipated due both to the resistance of the windings (known as copper loss), and to magnetic effects primarily attributable to the core (known as iron loss). Transformers are in general highly efficient, and large power transformers (around 100 MVA and larger) may attain an efficiency as high as 99.75%. Small transformers such as a plug- in used to power small... ... Read More

6.What is Exciting Current?

Exciting current, is the current or amperes required for excitation. The exciting current on most lighting and power transformers varies from approximately 10% on small sizes of about 1 KVA.

The exciting current is made up of two components, one of which is a real component and is in the form of losses or referred to as no load watts; the other is in the form of reactive power and referred to as KVAR.

7.How to selection the right transformer

• Determine primary voltage and frequency.
• Determine secondary voltage required.
• Determine the capacity required in volt-amperes

This is done by multiplying the load current (amperes) by the load voltage for single phase. For example, if the load is 40 amperes, such as a motor, and the secondary voltage is 240 volts, then 240 x 40 equals 9600 VA.A 10 KVA (10,000 volt-amperes) transformer is required. Always select the transformer larger than the actual load. This is done for safety purposes an allows for expansion. For 3 phase KVA, multiply rated volts x load amps x 1.73 (square root of 3) then divide by 1000.

Suppose you've got the job of designing the power distribution for an entire building, you'll have to select the service transformer and the distribution transformers. Read More

8.Is one insulation system better than other?

It depends on the application and the cost benefit to be realized. Higher temperature class insulation systems cost more and larger transformers are more expensive to build. Therefore, expensive insulation systems are more likely to be found in the larger KVA units.

• Small fractional KVA transformers use insulation class 130 degrees C
• Compound filled transformers use insulation class 180 degrees C
• Larger ventilated transformers are designed to use 220 degrees C insulation

9.Can Single Phase Transformers be used for Three Phase Application?

Yes, but the transformer output will be single-phase. Simply connect any two wires from a 3- or 4-wire source to the transformer's two primary leads. Three single-phase transformers can be used for three-phase applications. They can be used in delta-connected primary and wye or delta-connected secondary.

To avoid an unstable secondary voltage, NEVER connect wye primary to delta secondary.

10.Single Phase or three phase transformer?

Single-phase power distribution is used especially in rural areas, where the cost of a three-phase distribution network is high and motor loads are small and uncommon.

In North America, individual residences and small commercial buildings with services up to about 100 kV•A (400 amperes at 240 volts) will usually have three-wire single-phase distribution, often with only one customer per distribution transformer. Larger consumers such as large buildings, shopping centers, factories, office blocks, and multiple-unit apartment blocks will have three-phase service. In densely-populated areas of cities, network power distribution is used with... ... Read More

11.Why are Small Distribution Transformers not used for Industrial Control Application?

Industrial control equipment demands a momentary overload capacity of three to eight times normal capacity. This is customary in solenoid or magnetic contractor applications where inrush current can be three to eight times as high as normal sealed or holding currents but still maintain normal voltage at this momentary overloaded condition. Distribution transformers are designed for good regulation up to 100 percent loading, but their output voltage will drop rapidly on momentary overloads of this type making them unsuitable for high inrush applications.

Industrial control transformers are designed especially for maintaining a high degree of regulation even at eight times normal load. This results in a larger and generally more expensive transformer.

12.Can I achieve specific sound levels in a transformer?

Before selecting a transformer assure yourself that the sound levels represented have been measured in accordance with the NEMA standards. If your requirement is lower than that available from the manufacturer’s standard product, request a specific sound level on your bid.

13.How do I know when the temperature rise is too high?

Thermometers are the best way to determine the temperature.

Touch is a poor indicator of proper operating temperature for transformers. Properly designed transformers can reach 50°C (122°F) above ambient temperature. In an ambient temperature of 20°C (60°F), the total temperature can reach 70°C (190°F), which is too hot to touch.

14.What voltage power output do you need?

Voltage in the world different in the United States and Canada usually run on 110/120 and most of the rest of the world runs on 220/240 and industrial plant may use 440 to 480. Most utilities will provide a customer with one service or electrical system. You may wonder why anyone would need a transformer. Let say a new industrial plant comes in town. They have many motors in use at their company so they requested a 480Y/277 volts three-phase system. This takes care of their motor load at 480 volts and their office and plant lighting loads at 277 volts. However to operate their office machinery and incandescent lighting they require 120 volts. They also have some small horsepower motors they want to operate at 208 volts.

Since the utility will only provide them with 480Y/277 volt three-phase system, they require a transformer to provide the rest of there needs. A buck boost transformer is the ideal solution for changing line voltage by small amounts. The major advantages are their low cost, compact size and light weight. They are also more efficient and cost less than equivalent isolation transformers. When connected as an autotransformer, they can handle loads up to 20 times the name plate rating.

15.Can transformers be operated at voltages other than nameplate voltages?

Transformers can be operated. in some cases at voltages below the nameplate rated voltage. Transformer should not be operated in excess of it nameplate rating, unless taps are provided for this purpose.

Taps are provided on some transformers on the high voltage winding to correct for high or low voltage conditions, and still deliver full rated output voltages at the secondary terminals. Standard tap arrangements are at two-and-one-half and five percent of the rated primary voltage for both high and low voltage conditions.

16.What are the different frequencies of power and there uses?

The incoming electric transformers voltage is an important factor. The three common frequencies available are 50 Hz, 60Hz and 400 Hz. European power is typically 50 Hz while North American power is usually 60hz. The 400 Hz is reserved for high-powered applications such as aerospace technologies. It is also important to consider the secondary power specifications when evaluating transformers. Other specifications to keep in mind when selecting an electric transformer are: the maximum ratings of the following: secondary current and voltage rating, power and output rating. Power transformers have various configurations according to phase and connections. The most common phases are single-phase and three-phase. Both the size and expense of electric transformers increases in proportion to the number of primary windings... ...Read More

17.What is a Transformer and how does it work?

A transformer is an electrical device designed to transfer alternating current or voltage from one electric circuit to another by means of electromagnetic induction. It can be designed to "step-up" or Step-down" voltages. Because transformer has no moving parts and is a completely static solid state device, under normal operating conditions, are usually insure a long and trouble-free life. The simplest type of transformer consists of two or more coils ... ... Read More

18.What is meant by impedance in transformers?

Impedance is the current limiting characteristic of a transformer and is expressed in percentage. It is used for determining the interrupting capacity of a circuit breaker or fuse employed to protect the primary of a transformer.

The impedance of the load is expressed in ohms, and the relationship between the current and the voltage in the circuit is controlled by the impedances in the circuit. When a signal source, such as our composite video output, sees a very low-impedance circuit, it... ... Read More

19.Why should Dry-Type Transformers never be over-loaded?

When you overloading a transformer excessive temperature can cause overheating which result in rapid deterioration of the insulation and cause complete failure of the transformer coils.

20.Will the transformer be inside or outside?

For harsh environments, whether indoor or outdoor, it's critical that a transformer's core/coil, leads, and accessories be adequately protected.

In the United States, almost all liquid-filled transformers are of sealed-type construction, automatically providing protection for the internal components. External connections can be made with "dead front" connectors that shield the leads. For high corrosive conditions,... ...Read More