Question: The power factor in a single phase circuit is <em>cosΦ = P / VI,</em> where P is the power read by a wattmeter, V is the voltage read by voltmeter and I is the current read by an ammeter. All the three instruments have a limiting error of ±1%. The power factor of the circuits can be known if only one meter i.e an electrodynamometer type power factor having a limiting error ±1% used. The preferred method is to use single instrument like a power factor rather than using 3 instruments because the error with using wattmeter, voltmeter and ammeter is
Answer:
MCQ: The power factor in a single phase circuit is <em>cosΦ = P / VI,</em> where P is the power read by a wattmeter, V is the voltage read by voltmeter and I is the current read by an ammeter. All the three instruments have a limiting error of ±1%. The power factor of the circuits can be known if only one meter i.e an electrodynamometer type power factor having a limiting error ±1% used. The preferred method is to use single instrument like a power factor rather than using 3 instruments because the error with using wattmeter, voltmeter and ammeter is
Correct Answer:
A. ±2%
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Related Questions
- 1. The controlling torque in single phase power factor meter is provided by :
- 2. There will be serious errors, if power factor of non-sinosoidal waveform is measured by electrodynamometer power factor meters. This is true of :
- 3. In a reed type frequency meters all the reeds :
- 4. A 53 Hz reeds type frequency meter is polarized with d.c. the new range of frequency meter is :
- 5. For a 3 phase, moving iron synchroscope<em>F<sub>2</sub></em><sub> </sub>= frequency of incoming machine<em>F<sub>1</sub></em><sub> </sub>= frequency of busbars At equilibriumΦ = ±2πf’t + ɑ ; where f’ = <em>F<sub>2 </sub></em><sub> </sub>- <em>F<sub>1.</sub></em>If f’ is positive
- 6. An electrodynamometers type of instrument is used in Weston type synchroscope while synchronizing an incoming machine to busbars
- 7. An alternator is being synchronized to the busbars whose frequency is 50 Hz. The bulbs of the synchroscope flickers at a frequency of 10 Hz. The frequency of the alternator is :
- 8. A phase sequence indicator rotates clockwise for phase sequence of <em>RYB. </em>If the phase sequence is changed to <em>BRY</em> it will rotate
- 9. In a static type phase sequence indicator which uses two identical lamp of pure resistances in the circuit of phase R and Y and inductor in phase B having inductive reactance = resistance of bulb with circuit being connected in star. The reactance is equal to the bulb resistance. If bulb connected to phase R glows brightly and lamp connected to phase Y glows dimly, the phase sequence is :
- 10. A resistance of value 10Ω approximately is to be measured by ammeter-voltmeter method with resistance of ammeter is 0.02Ω and that of voltmeter is 5000Ω. The resistance should be measured
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