Need of Three Phase Supply - Three Phase Circuits - Basic Electrical Engineering

Summary

In this video, the need for three-phase AC supply is explained in comparison to single-phase systems. It discusses the limitations of single-phase voltage for heavy industrial loads and introduces the advantages of three-phase power, including higher output, more economical power transmission, and the generation of a rotating magnetic field (RMF) for self-starting machines. The video also highlights how three-phase systems provide smoother DC output and greater versatility, including the ability to supply single-phase power. Ultimately, it emphasizes why three-phase systems are essential for industries with high power demands.

Takeaways

• 😀 A single-turn generator produces single-phase AC voltage with low power.
• 😀 To increase AC voltage, more turns must be connected in series to form armature winding.
• 😀 A single-phase supply often does not provide sufficient voltage to power industrial loads.
• 😀 A three-phase supply is needed to provide higher voltage and power for heavy industrial machinery.
• 😀 A 'phase' refers to a circuit or winding, and 'polyphase' means many phases are connected.
• 😀 A three-phase system involves three independent AC voltages with the same magnitude and frequency but a 120-degree phase difference.
• 😀 The main advantage of a three-phase system is the higher output compared to a single-phase machine of the same size.
• 😀 Three-phase power transmission is more economical due to reduced copper and material use compared to single-phase systems.
• 😀 Rotating magnetic fields (RMF) are generated in a three-phase system, making three-phase machines self-starting.
• 😀 A single-phase motor requires additional components, like a capacitor, to simulate multi-phase behavior for self-starting.
• 😀 From a three-phase supply, you can derive three separate single-phase supplies, but you cannot generate three-phase power from a single-phase supply.

Q & A

Why is a three-phase supply needed in industrial applications?

A three-phase supply is needed in industrial applications because single-phase AC voltage is insufficient to power heavy industrial loads. Three-phase supply provides higher voltage and power, which is necessary for operating large machinery in industries.

What is the basic difference between a single-phase and a three-phase supply?

A single-phase supply consists of one AC voltage, while a three-phase supply consists of three independent AC voltages. These voltages have the same magnitude and frequency, but they are 120 degrees out of phase with each other.

What are the advantages of a three-phase supply over a single-phase supply?

The advantages of a three-phase supply include greater output from machines of the same size, more economical power transmission (requiring less copper and conducting material), the ability to generate a rotating magnetic field (RMF) for self-starting motors, and smoother DC output when converting to DC.

What is meant by the term 'phase' in a polyphase system?

In a polyphase system, 'phase' refers to an independent circuit or branch, typically represented by an AC voltage. The number of phases determines how many independent voltages are present, such as three in a three-phase system.

What is the relationship between the three voltages in a three-phase system?

In a three-phase system, the magnitudes and frequencies of the three voltages are the same, but they are 120 degrees out of phase with each other. This phase difference is crucial for the operation of three-phase machines.

Why can a three-phase system be more economical for power transmission?

A three-phase system is more economical because it allows for the transmission of power at a higher voltage, which reduces core losses and the need for more conducting material. This makes it more efficient than a single-phase system.

How does a three-phase supply create a rotating magnetic field?

A three-phase supply generates a rotating magnetic field because the three AC voltages are out of phase with each other by 120 degrees. This phase difference creates a continuous rotation of the magnetic field, which is necessary for self-starting motors.

What is a key disadvantage of single-phase motors?

Single-phase motors are not self-starting. To create a rotating magnetic field, additional components like capacitors are needed to simulate a second phase, as a single-phase system cannot generate the rotating magnetic field by itself.

What happens when a three-phase supply is converted into DC?

When a three-phase supply is converted into DC, the output voltage is smoother, with lower ripple, compared to converting a single-phase supply. This is because the three-phase system provides a more consistent and balanced waveform.

Can a three-phase supply be used to generate single-phase supply?

Yes, a three-phase supply can be used to generate single-phase supply by utilizing only two of the phases. However, the reverse is not true; a single-phase supply cannot be used to create a three-phase system.