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

How to solve every two method wattmeter problem on the Electrical Power PE Exam in three quick steps! In Part 3 of the Two Method Wattmeter series, we are going to show you: 1. How to quickly identify which of the two wattmeters (W1 or W2) has the θ MINUS thirty degrees inside the cosine function, and which has the θ PLUS thirty degrees inside the cosine function WITHOUT taking the time to draw out the phasor diagrams. *It's extremely important to know how to draw both of the phasor diagrams (Part 2 in the Two Method Wattmeter Series) and how to derive the power formula commonly see in books (Part 1 in the Two Method Wattmeter Series) because in doing so you'll be able to answer just about any and every two method wattmeter question on the Electrical Power PE Exam. *HOWEVER! Time is really important during the exam because you only have a certain amount of time to answer each question. *Because of this, sometimes it is helpful to know how to QUICKLY identify which wattmeter the cos(θ-30º) and cos(θ+30º) terms belong to. 2. If the system is positive sequence (ABC), look for the negative sequence voltage. In a positive sequence (ABC) system: The A line voltage is measured from A to B (VAB) The B line voltage is measured from B to C (VBC) The C line voltage is measured from C to A (VCA) In the example circuit used in the video, wattmeter 1 (W1) is connected across A (+) to C (-). The line voltage that wattmeter 1 (W1) is measuring is the negative sequence C line voltage (VAC), NOT the positive sequence C line voltage (VCA). This means that the formula for the power measured by wattmeter 1 (W1) will have the 30º minus theta term inside the cosine function cos(θ-30º). In comparison, in the example circuit used in the video, wattmeter 2 (W2) is connected across B (+) to C (-). The line voltage that wattmeter 2 (W2) is measuring is the positive sequence B line voltage (VBC). This means that the formula for the power measured by wattmeter 2 (W2) will have the 30º plus theta term inside the cosine function cos(θ+30º). The wattmeter (W1 or W2) that has the 30º minus theta term inside the cosine function and the wattmeter (W1 or W2) that has the 30º plus theta term inside the cosine function always depends on how the wattmeters are connected. There will always be one wattmeter measuring a negative sequence line voltage, and a wattmeter that measuring a positive sequence line voltage. 3. If the system is balanced, it does not matter which wattmeter formula has the 30º minus theta term inside the cosine function, and which wattmeter formula has the 30º plus theta term inside the cosine function since the line voltages magnitude and line current magnitudes will be equal. For example, if our example circuit used in the video is balanced then: |VCA| = |VBC| = |VL| and |Ia| = |Ib| = |IL| We can use this to simplify the two method wattmeter formula for a balanced system only: P3ø = |VCA|·|Ia|·cos(θ-30º) + |VBC|·|Ib|·cos(θ+30º) P3ø = |VL|·|IL|·cos(θ-30º) + |VL|·|IL|·cos(θ+30º) P3ø = |VL|·|IL|·[cos(θ-30º) + cos(θ+30º)] Click here to start over and watch the first video (Part 1) in this series:    • 3 Steps for Solving any Two Wattmeter Meth...   __________________________________ 👉 Visit the full article on solving Two Method Wattmeter Problems: https://www.electricalpereview.com/3-... . **** PE EXAM *** 🔥 SUBSCRIBE for more videos on how to pass the NCEES® Electrical Power PE Exam!    / @electricalpereview   . 🚀 Ready to PASS the NCEES® Electrical Power PE Exam? Sign up for our FREE online study program for the PE Exam: https://courses.electricalpereview.co... . 👀 Electrical Engineering PE Practice Exam and Technical Study Guide by Zach Stone, P.E.: https://amzn.to/2zKz17u . *** FE EXAM *** ⚡ Looking for help with the NCEES® Electrical and Computer FE Exam? Visit our FE Exam Youtube Channel:    / @electricalfereview   . 👇 Ready to pass the NCEES® Electrical and Computer FE Exam? Sign up for our FREE online study program for the FE Exam: https://www.electricalfereview.com