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| Transformer Fundamentals |
| To order a transformer you will need to know - |
- Input voltage, single or three phase
- Output voltage
- Output current (Amps) or power required (VA or KVA)
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| ie. 240V / 110V 2Amps |
| The above basically means 240V input, 110V output at 2 amps. |
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| Optional additions may include - |
- Transformer enclosure
- Input lead and plug
- Output socket
- Fuses (Input or output)
- Handles
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| More information regarding our enclosures. |
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| Calculating transformer rating (VA or KVA) |
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| To calculate the rating of a single phase transformer - |
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| VA = Output Volts x Amps |
| ie. 240V / 110V 2Amps = 220VA |
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| Sometimes VA is shown as KVA, basically 1000 VA = 1 KVA |
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| To calculate the rating of a three phase transformer - |
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| VA = (Output Volts x Amps) x 1.732 |
| ie. 415V / 200V @ 14A = 4850VA or 4.85KVA |
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| Is Watts (W) the same as VA ? |
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| Not exactly, if your output / load is inductive (ie. a motor) it needs to be converted to VA. |
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| VA = Watts (W) / 0.85 |
| ie. 240V / 110V 400W = 470VA |
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| If the load is a large electric motor, then further upsizing of the VA may be required. |
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| Basic principals |
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| A simple transformer consists of two electrical conductors called the primary winding and secondary winding, and a steel core that magnetically links them together
These two windings can be considered as a pair of mutually coupled coils. Energy is coupled between the windings by the magnetic field that links both primary and secondary windings. |
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| Classifications |
Transformers are adapted to numerous engineering applications and may be classified in many ways:
- By power level (from fraction of a VA to over a thousand MVA),
- By application (power supply, impedance matching, circuit isolation),
- By frequency range (power, audio, RF)
- By voltage class (a few volts to about 750 kilovolts)
- By cooling type (air cooled, oil filled, fan cooled, water cooled, etc.)
- By purpose (rectifier, arc furnace, amplifier output, etc.)
- By ratio of the number of turns in the coils -
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- Step up
- Step down
- Isolating
- Variable
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| Circuit symbols |
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| Two windings and an iron core, step-up or step-down as windings are different ratios. |
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| Transformer with two windings and an iron core. |
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| Transformer with three windings, two secondary windings. |
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| Transformer with an earth screen. |
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| Three phase circuit symbols |
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| The three primary windings are connected together and the three secondary windings are connected together. This is also sometimes referred to as a polyphase transformer. |
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| The most common connections are Y-A, A-Y, A-A and Y-Y. |
| There are many possible configurations that may involve more or fewer than six windings and various tap connections. |
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