Lecture4 - ECE 431 Electric Machinery Lecture 4 Reactive...

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1/30/2011 1 Acknowledgement – These handouts and lecture notes given in class are based on material from Prof. Philip Krein’s ECE 431 lecture notes. Disclaimer – These handouts only provide highlights and should not replace the class notes or course textbook. ECE 431 Electric Machinery Lecture 4 Reactive Power Measurement and Magnetics Review (1) 1 Copyright ©2011 Ali M. Bazzi. All rights reserved 1/30/2011 One-Wattmeter Method for Reactive Power Measurement A method using one wattmeter is proposed to measure the three-phase reactive power. The wattmeter must have independent or decoupled voltage and current measurements (Electrodynamometer). • Claim: 2 Copyright ©2011 Ali M. Bazzi. All rights reserved 1/30/2011 3 3 bc a Q V I ϕ =

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1/30/2011 2 One-Wattmeter Method for Reactive Power Measurement • Proof: 3 Copyright ©2011 Ali M. Bazzi. All rights reserved 1/30/2011 3 cos( ) cos( 90 ) but and cos( 90 ) sin( ), then, sin( ) sin( ) 3 3 sin( ) m bc a bc a o ll l o m ll l ll l m ll l P V I V I V I Z P V I V I Z Q P V I Z ϕ θ θ θ θ θ = −∠ = = −∠ = = = = = Meters In analog wattmeters, two coils displaced by γ are used, one for voltage and one for current.
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