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- Power Developed by Synchronous Motor
- Equivalent Circuit and Power Factor of Synchronous Motor
- Working of 3-Phase Synchronous Motor
- Losses and Efficiency of 3-Phase Alternator
- Output Power of 3-Phase Alternator
- Armature Reaction in Synchronous Machines
- Working of 3-Phase Alternator
- Construction of Synchronous Machine
- Introduction to 3-Phase Synchronous Machines
- Methods of Starting 3-Phase Induction Motors
- Speed Regulation and Speed Control
- Characteristics of 3-Phase Induction Motor
- Three-Phase Induction Motor on Load
- Construction of Three-Phase Induction Motor
- Three-Phase Induction Motor
- Single-Phase Induction Motor
- Introduction to Induction Motor
- Applications of DC Machines
- Losses in DC Machines
- Types of DC Motors
- Back EMF in DC Motor
- Working Principle of DC Motor
- Types of DC Generators
- EMF Equation of DC Generator
- Working Principle of DC Generator
- Types of DC Machines
- Construction of DC Machines
- Types of Transformers
- Three-Phase Transformer
- Efficiency of Transformer
- Losses in a Transformer
- Transformer on DC
- Ideal and Practical Transformers
- Turns Ratio and Voltage Transformation Ratio
- EMF Equation of Transformer
- Construction of Transformer
- Electrical Transformer
- Fleming’s Left Hand and Right Hand Rules
- Concept of Induced EMF
- Faraday’s Laws of Electromagnetic Induction
- Rotating Electrical Machines
- Singly-Excited and Doubly Excited Systems
- Energy Stored in a Magnetic Field
- Electromechanical Energy Conversion
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Transformer on DC
In the introductory chapter, we defined an electrical transformer as an AC machine because it works only on alternating current electricity. Therefore, a transformer cannot change (increase or decrease) the value of the DC voltage. In this chapter, we shall know the reason, why a transform does not work on the direct current (DC).
![DC Transformer](/electrical_machines/images/dc_transformer.jpg)
Consider an electrical transformer as shown in Figure-1, and it is connected to a battery (or a source of DC voltage) V. When, we apply this DC voltage V to the primary winding of the transformer, it will draw a constant current (DC) and therefore produces a constant magnetic flux flowing through the magnetic core.
According to the principle of electromagnetic induction, an EMF can induce in a coil or conductor only when it is subjected to a changing magnetic field, i.e.,
$$mathrm{mathit{e}:=:mathit{N}frac{mathit{dphi }}{mathit{dt}}}$$
Consequently, the appped DC voltage to the primary winding does not induce EMF in the primary winding or secondary winding. Hence, this discussion proves that a transformer does not work on DC supply. In fact, connecting a DC supply to the primary winding of a transformer could be dangerous.
![Equivalent Circuit](/electrical_machines/images/equivalent_circuit.jpg)
The equivalent primary winding circuit of a transformer connected to the DC voltage is shown in Figure-2. In this case, there is no self-induced EMF in the primary winding to oppose the appped voltage V (according to Lenz’s law), and the current in the primary winding is given by,
$$mathrm{mathit{I_{mathrm{1}}}:=:frac{mathit{V}}{mathit{R_{mathrm{1}}}}}$$
Where, $mathit{R_{mathrm{1}}}$ is the resistance of the primary winding. Due to very small value of R1, the current $mathit{I_{mathrm{1}}}$ through the primary winding will be very large. This large current will cause the overheating and burning of the transformer or fuses will blow. Therefore, we must not connect the primary winding of a transformer to the DC supply because it may damage the transformer or may cause an electrical accident.
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