What will each wattmeter indicate?

[Stephen30002]

Three coils with a resistance of 4 ohms and impedance of 13 ohms each are connected in wye to a 120/208 Volt panel. What will each wattmeter indicate if three single-phase wattmeters are used to measure the power?

The correct answer is 341W according to my answer sheet but I seem to keep getting 311W and I don't know what Im doing wrong. Any help would be great!

[dennisrieves]

Three coils with a resistance of 4 ohms and impedance of 13 ohms each are connected in wye to a 120/208 Volt panel. What will each wattmeter indicate if three single-phase wattmeters are used to measure the power?

The correct answer is 341W according to my answer sheet but I seem to keep getting 311W and I don't know what Im doing wrong. Any help would be great!

how did you come up with 311W? i'm having trouble with this question, not sure where to start.

[baldscreen]

Three coils with a resistance of 4 ohms and impedance of 13 ohms each are connected in wye to a 120/208 Volt panel. What will each wattmeter indicate if three single-phase wattmeters are used to measure the power?

The correct answer is 341W according to my answer sheet but I seem to keep getting 311W and I don't know what Im doing wrong. Any help would be great!

I get the same answer as you and verified it through calculator on this site: http://www.rapidtables.com/calc/electric/power-calculator.htm

Impedance Z = SQRT(4*4 + 13*13) = 8.823 Ohms
Angle Theta = ATAN (Impedance/Resistance) = ATAN (13/4) = 72.9 degrees
Total Power VA = V*V/Z = (120 * 120) / 8.823 = 1058.82 VA
Real Power Watts = Total Power * Cos Theta = 1058.82 * Cos(72.9) = 311 watts

Beats me how someone got 345 watts.

[Allenxu]

I get the same answer as you and verified it through calculator on this site: http://www.rapidtables.com/calc/electric/power-calculator.htm

Impedance Z = SQRT(4*4 + 13*13) = 8.823 Ohms
Angle Theta = ATAN (Impedance/Resistance) = ATAN (13/4) = 72.9 degrees
Total Power VA = V*V/Z = (120 * 120) / 8.823 = 1058.82 VA
Real Power Watts = Total Power * Cos Theta = 1058.82 * Cos(72.9) = 311 watts

Beats me how someone got 345 watts.

Impedance should be 13 ohms instead of 8.8

[baldscreen]

Impedance should be 13 ohms instead of 8.8

You are correct on the impedance. I was thinking of it as reactance ohms.

So, I'll try it again:

COS(Theta) = (Resistance/Impedance) = 4/13
225
Total Power VA = V*V/Z = (120 * 120) / 13 = 1107.69 VA
Real Power Watts = Total Power * Cos Theta = 1107.69*4/13 = 340.8 watts

Closer, but not quite the 345 watts given as the answer.

[Lonpadams]

PF = R/Z = 4/13 = 0.3077

E = I*R , 120 = I*13 , I = 120/13 = 9.23A

P = I*E , P = 9.23*120 = 1107.7VA

0.3077(PF) = W/1107.7VA , W = 1107.7*0.3077 = 340.84

340.84(W)/9.23A = 36.93V

36.93V/4OHMS = 9.23A

[anthony]

Three coils with a resistance of 4 ohms and impedance of 13 ohms each are connected in wye to a 120/208 Volt panel. What will each wattmeter indicate if three single-phase wattmeters are used to measure the power?

The correct answer is 341W according to my answer sheet but I seem to keep getting 311W and I don't know what Im doing wrong. Any help would be great!

120/13=9.230769231
watts is I(squared)times R.
9.230769231 (Sqaured) = 85.20710059
85.20710059 times 4 =340.8284024 watts

[amarillo1970]

Impedance should be 13 ohms instead of 8.8

I agree with you, in my calculator the result is 13.601 Ohms.