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Electronics and Communication Engineering - Measurements and Instrumentation - Discussion

Discussion Forum : Measurements and Instrumentation - Section 1 (Q.No. 4)
Measurements and Instrumentation
4.
In 3 phase power measurement by two wattmeter method, the reading of one wattmeter is zero. The power factor of load is
1
0.5
0
0.8
Answer: Option
Explanation:

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

Discussion:
10 comments Page 1 of 1.
Sravan said:   5 years ago
Can anyone explain me in a simple manner?
Kalyan said:   6 years ago
Please give me the explanation clearly to get the answer.
Omendra singh said:   7 years ago
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?
(1)
Krishna said:   9 years ago
If reading of one wattmetre is = 0, then $ = 60, therefore cos $ = 0.5.
Mohammad Inam Uddin said:   9 years ago
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.
(1)
D aiysha said:   10 years ago
Phase angle = 60 degree.

PF = 0.5.

W1 is positive and W2 = 0.

One of the watt meter reads zero.
Subhankar Palit said:   10 years ago
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.
(2)
Babu said:   10 years ago
Power factor = cos $ = 0.5.

So, cos $ = 1/2,

Or, cos $ = cos 60.

So, $ = 60.
Badar Jahangeer said:   10 years ago
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.
Kiruthiga said:   10 years ago
I do not understand. What p.f = 0.5, o = 60.
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