During the Red Seal Electrical IP Exam, you’ll be tested on your knowledge and applications of single phase transformers. In this blog post, we’ll be covering four important topics:
1. How to identify a single phase transformer
2. Polarity of transformers
3. Dual voltage transformers
4. Series and parallel connections of transformers
Single phase transformers are quite commonly used in step-down situations and especially for power distribution to residential homes and low voltage for electronics.
In diagrams, single-phase transformers can be identified by two conductors providing the power to the primary and two conductors connected to the secondary that provides the load.
One of the topics seen consistently in the Red Seal exam is polarity. Polarity signifies whether the voltages between primary and secondary are additive or subtractive. Usually, these questions include a voltmeter connected to both primary and secondary and ask “what does the voltmeter V read?”.
In order to solve this, follow this procedure:
If H1 and X1 on the same side, the voltage is subtractive
High voltage - low voltage = voltmeter reading
120 V - 12 V = 108 V
If H1 and X1 on the opposite side, the voltage is additive
High voltage + low voltage = voltmeter reading
120 V + 12 V = 132 V
Note: H leads are denoted as high voltage and X leads are denoted as low voltage.
Dual Voltage Transformers
At times, transformers have more than one winding on primary or secondary. The most common form of this is a dual voltage transformer where there are two windings on primary and two windings on secondary. Dual voltage transformers can operate at different levels of voltage supply and output different levels of voltage dependent on how it is wired.
If a dual voltage transformer is connected in series in the secondary, the voltage of the two windings is added while the current stays the same. As shown in the diagram below, the 12 V generated by each secondary winding is added together.
Note: The supply voltage in a series circuit is equal to the sum of the individual voltage drops, where 12 V + 12 V equals 24 V.
On the other hand, if a dual voltage transformer is connected in parallel in the secondary, the current of the two windings is added while the voltage stays the same. As shown in the diagram below, the 2 A generated by each secondary winding is added together.
Note: The total circuit current is equal to the sum of the individual branch currents for parallel circuits, where 2 A + 2 A = 4 A.
Center Tap Transformer
The most familiar type of dual voltage transformer is the center tap transformer. We use this for residential power distribution where the transformer intakes 600V in the primary and transforms it into 120/240 V. This transformer taps into center of dual voltage transformer and grounds it, and as a result, acts our neutral or identified conductor in our circuits. Furthermore, we’ll be able to get both 120 V and 240 V from the secondary with this transformer.
This is part 2 for our breakdown for transformers for the Red Seal IP exam. Stay tuned for part 3.