In electrical engineering, the "Polyphase Circuits - One-Wattmeter Method" is a technique used to measure power in a three-phase balanced load using only one wattmeter. This method is applicable when dealing with balanced loads, meaning that the impedances or currents of the three phases are equal in magnitude and have a phase difference of 120 degrees between them.
Here's how the One-Wattmeter Method works for measuring power in a balanced three-phase circuit:
Connection Setup: Connect the wattmeter in any one of the phases. The other two phases remain unconnected to the wattmeter. This is because in a balanced load, the power measurements in each phase are the same.
Power Calculation: The power reading on the wattmeter will give you the total power consumed by the balanced three-phase load. This is because the power delivered to the load is the same in each phase.
Factor Correction: Since you are only measuring the power in one phase, you need to correct the reading to get the total power for the entire balanced system. Multiply the power reading obtained from the wattmeter by the factor √3 (approximately 1.732).
Total Power = Power Reading × √3
The reason for this correction factor is because the power in a three-phase system can be calculated as the sum of the powers in each individual phase, and the phase currents are 120 degrees apart. The √3 factor accounts for the trigonometric relationship between the line and phase values in a balanced three-phase system.
It's important to note that the One-Wattmeter Method is accurate only for balanced loads, where the phase currents and impedances are equal. If the load becomes unbalanced, meaning the currents or impedances differ, this method won't provide accurate power measurements. In such cases, the Two-Wattmeter Method is typically employed for accurate power measurement.
To summarize, the Polyphase Circuits - One-Wattmeter Method is a simple and convenient way to measure power in a balanced three-phase load using a single wattmeter. It's widely used in applications where balanced loads are prevalent, such as in industrial and commercial power distribution systems.