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Frequently asked questions
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A transformer is an electrical static equipment designed to convert alternating current from one voltage to another. It can be designed to “step up” or “step down” voltages and works on the magnetic induction principle. A transformer has no moving parts and is a completely static device, which insures under normal conditions, a long and trouble-free life. It consists, in its simplest form, of two or more coils of insulated wire wound on a laminated steel core. When voltage is introduced to one coil, called the primary, it magnetizes the iron core. A voltage is then induced in the other coil, called the secondary or output coil. The change of voltage level (or potential difference ratio) between the primary and secondary depends on the turns ratio of the two coils.
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Copper or Aluminium.
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- Construction Wise
- Single Phase Transformers
- Single Coil Transformer (EI Type)
- Double Coil Transformers (UI Type)
- Three Phase Transformers
- Torroidal Transformer
- Usage Wise
- Control Transformers
- Packaging Machine Transformers
- Lift Transformers
- Auxiliary Transformers
- Transformer for Automatic Rescue Devices in Lifts
- Battery Charger Transformer
- Transformer for Float mode
- Transformer for Boost charging
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- Helical winding
- Round Wires
- F Class Insulation
- H Class Insulation
- Rectangular Strips
- Paper Covered
- Fiber Glass Covered
- Enamelled Fiber Glass Covered
- Foil Winding
- Torroidal winding
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- Single Phase EI Construction
- Three Phase EI Construction
- Single Phase Strip Construction
- Single Coil Core Construction
- Double Coil Core Construction
- Three Phase Strip Construction
- Torroidal Construction
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Electric hum around transformers is caused by stray magnetic fields causing the enclosure and accessories to vibrate. Magnetostriction is a second source of vibration, in which the core iron changes shape minutely when exposed to magnetic fields. Around high-voltage power lines, hum may be produced by corona discharge.
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Transformers are normally provided with taps to adjust the turns ratio to compensate for this supply variance. This will allow the output voltage to be closer to the rated output voltage when the input voltage is off rated voltage. What is a Tap? Each turn on both the high and low voltage coils has the same voltage.
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In some cases, transformers can be operated at voltages below the nameplate rated voltage. In NO case should a transformer be operated at a voltage in excess of its nameplate rating, unless taps are provided for this purpose. When operating below the rated voltage, the kVA capacity is reduced correspondingly.
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- When we try to operate the transformer at lower frequency the following will happen
- When frequency (f) increases, Inductive reactance (XL) increases.
- When Inductive reactance (XL) increases, Impedance (Z) increases.
- When Impedance Increase, Current decreases.
- So we can say that:
- When we operate a 60Hz transformer on 60Hz supply source, the current will be as designed.
- But when operated a 60Hz transformer on 50Hz supply source, the current were more than what was designed.
- The extra current in this case may causes copper loss (P = I2R) and produces heat.
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- Three conditions must be met before you can connect transformers in parallel.
- The transformers must have the same primary and secondary voltage ratings.
- When making the connections, you must observe the terminal polarity of the transformers.
- All the transformers must have the same percent impedance.
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Taps are normally in the primary winding to adjust for varying incoming voltage. If the transformer is reverse fed, the taps are on the output side and can be used to adjust the output voltage.
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No. Phase converters or phase shifting devices such as reactors and capacitors are required to convert single phase power to three phases.
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Voltage regulation in transformers is the difference between the full load voltage and the no load voltage. This is usually expressed in terms of percentage.
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Temperature rise in a transformer is the average temperature of the windings and oil & insulation above the existing ambient temperature.
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- Insulation class was the original method used to distinguish insulating materials operating at different temperature levels.
- Letters were used for different designations.
- B Class – 120 Deg Centigrade
- F Class – 155 Deg Centigrade
- H Class – 180 Deg Centigrade
- The system temperature is the maximum temperature at the hottest spot in the winding.
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- Not necessarily. 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, the more expensive insulation systems are more likely to be found in the larger KVA units.
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- No. This can be compared with an ordinary light bulb. The filament temperature of a light bulb can exceed 2000 degree, yet the surface temperature of the bulb is low enough to permit touching with bare hands.
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- Impedance is the current limiting characteristic of a transformer and is expressed in percentage.
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- The Efficiency of the transformer is defined as the ratio of useful power output to the input power, the two being measured in the same unit. Its unit is either in Watts (W) or KW. It is denoted by Ƞ.
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- It is used for determining the interrupting capacity of switchgear employed to protect the primary of a transformer.
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- In any electrical machine, ‘loss’ can be defined as the difference between input power and output power. An electrical transformer is an static device, hence mechanical losses (like windage or friction losses) are absent in it. A transformer only consists of electrical losses (iron losses and copper losses). Transformer losses are similar to losses in a DC machine, except that transformers do not have mechanical losses.
- Losses in transformer are explained below :
- (I) Core Losses Or Iron Losses
- Eddy current loss and hysteresis loss depend upon the magnetic properties of the material used for the construction of core. Hence these losses are also known as core losses or iron losses. Hysteresis loss in transformer:
- Hysteresis loss is due to reversal of magnetization in the transformer core. This loss depends upon the volume and grade of the iron, frequency of magnetic reversals and value of flux density. It can be given by Steinmetz formula:
- Hysteresis loss is due to reversal of magnetization in the transformer core. This loss depends upon the volume and grade of the iron, frequency of magnetic reversals and value of flux density. It can be given by Steinmetz formula:
- In transformer, AC current is supplied to the primary winding which sets up alternating magnetizing flux. When this flux links with secondary winding, it produces induced emf in it. But some part of this flux also gets linked with other conducting parts like steel core or iron body or the transformer, which will result in induced emf in those parts, causing small circulating current in them. This current is called as eddy current. Due to these eddy currents, some energy will be dissipated in the form of heat.
- Copper Loss in Transformer
- Copper loss is due to ohmic resistance of the transformer windings. Copper loss for the primary winding is I12R1 and for secondary winding is I22R2. Where, I1 and I2 are current in primary and secondary winding respectively, R1 and R2 are the resistances of primary and secondary winding respectively. It is clear that Cu loss is proportional to square of the current, and current depends on the load. Hence copper loss in transformer varies with the load.
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- BIL is an abbreviation for Basic Impulse Level. Impulse tests are dielectric tests that consist of the application of a high frequency steep wave front voltage between windings, and between windings and ground. The BIL of a transformer is a method of expressing the voltage surge that a transformer will tolerate without breakdown.
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- 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 and less to approximately 2% on larger sizes of 750 KVA.
