Lab # 04The Auto TransformerDescription and Working
mode:Anautotransformer(sometimes calledauto step down transformer)
is an electricaltransformerwith only onewinding. The "auto" (Greek
for "self") prefix refers to the single coil acting on itself and
not to any kind ofautomatic mechanism. In an autotransformer,
portions of the same winding act as both the primary and secondary
sides of the transformer. The winding has at least threetapswhere
electrical connections are made. Autotransformers have the
advantages of often being smaller, lighter, and cheaper than
typical dual-winding transformers, but autotransformers have the
disadvantage of not providing electrical isolation.Autotransformers
are often used to step up or step down voltages in the 110-115-120
volt range and voltages in the 220-230-240 volt rangefor example.
Providing 110 or 120V (with taps) from 230V input, allowing
equipment designed for 100 or 120 volts to be used with a 230 volt
supply (as in using US electrical equipment with higher European
voltages).
OBJECT
To study the voltage and current relationship of an auto
transformer To learn how to connect a standard transformer as an
auto transformer
Instruments and components
Transformer module Power supply module (0 - 220/380 Vac) AC
metering module (0.25/0.25 A) AC metering module (250/250 V)
Connection leads Resistance module
Procedure:1. Using your transformer, power supply, resistance
and AC metering modules, connect the circuit shown in figure. Note
that winding 5 to 6 is connected as primary winding across the 220
Vac source. The center tap of the winding, terminal 9, is connected
the one side of the load and 6 to 9 portion of the primary winding
is connected as the secondary winding.2. Place the entire
resistance module switches in their open positions for 0 load
current.3. Adjust the power supply for 220 Vac as indicated by
voltmeter E1 ( this is the rated voltage for winding 5 to 6)4.
Adjust the load resistance RL to 4400 omega5. Our output table is
as shown below:
1st reading2nd reading3rd reading4th reading
Vp
Vs
Ip
Is
Pin
Pout
