Electronics and Communication Engineering - Measurements and Instrumentation - Discussion

4. 

In 3 phase power measurement by two wattmeter method, the reading of one wattmeter is zero. The power factor of load is

[A]. 1
[B]. 0.5
[C]. 0
[D]. 0.8

Answer: Option B

Explanation:

When p.f. = 0.5, 0 = 60° and one of the wattmeters reads zero.


Kiruthiga said: (Dec 7, 2015)  
I do not understand. What p.f = 0.5, o = 60.

Badar Jahangeer said: (Dec 27, 2015)  
In 3-phase measurement O = 180, 60 degree for each wattmeter, here he told 3-phase measurement with one wattmeter is zero, the remaining two will share, so P.F = 0.5.

Babu said: (Jan 4, 2016)  
Power factor = cos $ = 0.5.

So, cos $ = 1/2,

Or, cos $ = cos 60.

So, $ = 60.

Subhankar Palit said: (Jan 5, 2016)  
tan $ = 1.732 (W1-W2)/(W1+W2).

So tan $ = 1.732 (0.5-0)/(0.5+0).

So tan $ = 1.732.

so $ = 60.

cos 60 = 0.5.

D Aiysha said: (Jan 7, 2016)  
Phase angle = 60 degree.

PF = 0.5.

W1 is positive and W2 = 0.

One of the watt meter reads zero.

Mohammad Inam Uddin said: (Aug 27, 2016)  
When the meter reading is 0 then power factor will not be 0 according to formula base the pf is 0.5 then meter reading is 0 then power factor will be 0.5.

Krishna said: (Sep 11, 2016)  
If reading of one wattmetre is = 0, then $ = 60, therefore cos $ = 0.5.

Omendra Singh said: (Jan 9, 2019)  
In 3 phase supply system phase angle is 120 b/w 3 phase.

If one wattmeter is not giving reading then one phase is off. Now phase angle b/w 2 phase is 90 and cos 90 is 0 so how answer is 0.5?

Kalyan said: (Aug 21, 2019)  
Please give me the explanation clearly to get the answer.

Sravan said: (Aug 25, 2020)  
Can anyone explain me in a simple manner?

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