Electrodynamometer Type Wattmeter

The electrodynamometer type wattmeter is an instrument used for measuring the power or wattage of an electrical circuit. It operates on the principle of the interaction between the magnetic fields produced by the current-carrying coils.

Components of an Electrodynamometer Type Wattmeter

The electrodynamometer type wattmeter consists of two coils:

1. Current Coil: The current coil, also known as the series coil, is connected in series with the load. It carries the load current and produces a magnetic field proportional to the load current.

2. Pressure Coil: The pressure coil, also known as the potential coil, is connected across the load. It is designed to carry a small current proportional to the voltage across the load, which produces a magnetic field proportional to the load voltage.

Working Principle

The working principle of an electrodynamometer type wattmeter is based on the interaction between the magnetic fields produced by the current coil and the pressure coil. When current flows through the current coil, it produces a magnetic field. Similarly, when voltage is applied across the pressure coil, it produces a magnetic field.

The magnetic fields produced by the two coils interact with each other, resulting in a torque on the moving coil. This torque is proportional to the product of the current and voltage. By measuring this torque, the wattmeter can determine the power or wattage of the circuit.

Fixed Current Coil

In an electrodynamometer type wattmeter, the current coil is made fixed. This is because the current coil is designed to carry the load current, which can be quite high. Making the current coil fixed ensures that it can handle the current without any mechanical movement.

By making the current coil fixed, it also simplifies the design and construction of the wattmeter. The fixed current coil is typically wound on a soft iron core, which helps to concentrate the magnetic field produced by the coil.

Advantages of Fixed Current Coil

1. Handles High Current: The fixed current coil is designed to handle high currents, making it suitable for measuring power in high-power circuits.

2. Simplified Design: The fixed current coil simplifies the design and construction of the wattmeter.

3. Improved Accuracy: By making the current coil fixed, it reduces the chances of mechanical movement and improves the accuracy of the wattmeter.

In conclusion, the current coil is made fixed in an electrodynamometer type wattmeter to handle high currents, simplify the design, and improve accuracy.