An electrodynamometer wattmeter is a type of instrument used for measuring electrical power in AC (alternating current) circuits. It operates on the principle of electromagnetic force produced by the interaction of current-carrying coils in a magnetic field. This type of wattmeter can be used for both single-phase and three-phase power measurements.
Here's how an electrodynamometer wattmeter works:
Basic Components: An electrodynamometer wattmeter consists of two sets of coils - a fixed coil (or current coil) and a moving coil (or potential coil). These coils are wound on a common frame but are electrically isolated from each other.
Current Coil: The current coil is connected in series with the circuit whose power is to be measured. It carries the load current and produces a magnetic field proportional to the current flowing through it.
Potential Coil: The potential coil is connected across the circuit voltage. It generates a magnetic field proportional to the voltage across it.
Moving System: The potential coil is mounted on a movable system that can rotate within the fixed current coil. This moving system is free to rotate and is supported by bearings.
Damping Mechanism: To ensure the movement of the potential coil is controlled and steady, a damping mechanism, often in the form of an air vane, is provided.
Force and Torque Generation: When current flows through the current coil, it creates a magnetic field. Simultaneously, the potential coil experiences a magnetic field due to the circuit voltage. The interaction between the magnetic fields of these two coils results in a mechanical torque on the moving coil. This torque causes the potential coil to rotate.
Deflection and Calibration: The amount of rotation of the potential coil is proportional to the product of current and voltage, which represents power. The angular displacement is read on a calibrated scale, indicating the power being measured.
Measurement Range and Scales: Electrodynamometer wattmeters typically have multiple ranges and scales to measure different power levels accurately. A switch allows the user to select the appropriate range for the measurement.
It's important to note that electrodynamometer wattmeters are suitable for measuring both active (real) power and reactive power in AC circuits. However, they are typically used for accurate measurement in laboratory and industrial applications, rather than in everyday electrical measurements due to their mechanical complexity.
While electrodynamometer wattmeters provide accurate power measurements, they can have limitations like susceptibility to external magnetic fields, mechanical wear and tear, and the need for periodic calibration. In modern times, electronic power measurement devices like digital power meters and power analyzers have become more common due to their convenience, accuracy, and immunity to external influences.