SSC JE Electrical Engineering 24 Jan 2018 Evening Paper

Question : 143 of 200

Marks: +1, -0

In two wattmeter method of power calculation of a 3-phase balanced star connected system, what is the power factor of the system if one of the wattmeter shows zero r eading and the other shows a positive reading?

0
Greater than 0 but less than 0.5
0.5
Greater than 0.5 but less than 1

Validate

Solution:

ϕ= \tan^{-1}(√3({w_1-w_2}/{w-w_2}))

let one of the watt meter is zero then

w_2 = 0

ϕ=\tan^{-1}(√3w_1/w_2)

ϕ=\tan^{-1}(√3)

ϕ=60°

power factor cosϕ = .5

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