An electrical device draws 2kW power from AC mains The current differs (lags) in phase by as compared to voltage. Find (i) R, (ii) XC – XL, and (iii) IM. Another device has twice the values for R, XC and XL. How are the answers affected?



Given:
Power of an electrical device: P = 2kW
voltage: V = √50000 V
RMS value of voltage : VRMS = 223 V
tanϕ = -3/4
Formula used:
(i)
Power is given as

Here, P is the power, V is the voltage,I is the current and Z is the impedance.
Also, V
2 = 50000 V



We know that as XC>XL

Here, R is the resistance of the circuit, XL is the inductive reactance and XC is the Capacitive reactance.



Also,




Substituting we get,




(ii)
Substituting value of R we get,


(iii)
IM = Io. Here Io is the output current.
RMS value of current is



Also,



Now, if values of R, XC and XL are doubled.
Then value of tan
ϕ would remain same. Value of Z will be doubled. As power and impedance have inverse relation. Power would become half .
Hence, doubling the values of R, XC and XL would make the power half times the present one.


1
1