3 Steps for Solving any Two Wattmeter Method Problem Part 1 (Electrical Power PE Exam)

How to solve every two method wattmeter problem on the Electrical Power PE Exam in three quick steps!

In Part 1 of this series, we are going to show you:

1. The three "rules" for using two wattmeters to measure the total power of a three-phase balanced or unbalanced circuit

*For example, if the negative (-) voltage reference for wattmeter 1 (W1) is on C phase, then the negative (-) voltage reference for wattmeter 2 (W2) MUST also be on C phase.

Rule #1 - The negative (-) voltage reference for both wattmeters MUST be on the same phase (both on A, B, or C).

Rule #2 - The line current measured on each phase MUST be the same phase as the positive (+) voltage reference for each wattmeter!

*For example, if the positive (+) voltage reference for wattmeter 1 (W1) is on A phase, then wattmeter 1 (W1) MUST ALSO measure the line current on A phase.

Rule #3 - The positive (+) voltage reference for both wattmeters MUST NOT be on the same phase!

*For example, if the positive (+) voltage reference for wattmeter 1 (W1) is on A phase, then the positive (+) voltage reference for wattmeter 2 (W2) MUST NOT be on A phase.

2. How to derive the two method wattmeter formula commonly seen in books depending on which phases the positive (+) and negative (-) voltage polarity for wattmeter 1 (W1) and wattmeter 2 (W2) are connected to:

P3ø = W1 + W2

In the configuration that wattmeter 1 (W1) and wattmeter 2 (W2) are shown connected in this video, we can expand this formula into:

P3ø = |VAC|·|Ia|·cos(θ-30º) + |VBC|·|Ib|·cos(θ+30º)

Click here to watch the next video (Part 2) in this series:
   • 3 Steps for Solving any Two Wattmeter...  

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