INEL 4085 practice exercices

A balanced three-phase 208V source supplies a balanced three-phase load. If the line current Ia is measured to be 10A, and is in phase with the line-to-line voltage Vbc, find the per-phase load impedance if the load is (a) Y-connected, (b) delts-connected.

A single phase source has a terminal voltage V=120<0° V and a current I=10<30° A , which leaves the positive terminal of the source. Determine the real and reactive power, and state whether the source is delivering or absorbing each.
The instantaneous voltage across a circuit element is v(t)=359.3cos(wt+15°)volts, and the instantaneous current entering the positive terminal of the circuit element is i(t)=100sin(wt+5°) amps. For both the current and voltage, determine: (a) the maximun value; (b) the rms value; (c) the phasor expresion, using cos(wt) as the reference.

The secondary winding of a transformer has a terminal voltage of v(t)=282.8sin(377t)V. The turns ratio of the transformer is 50:200. If the secondary current of the transformer is i(t)= 7.07sin(377t-36.87)A, what is the primary current of this transformer? What is its voltage regulation and efficiency? The impedances of this transformer referred to the primary side are: Req=0.05, Xeq=0.225, Rc=75, Xm=20.

A 10kVA, 8000V/230V distribution transformer has an impedance referred to the primary of 90+j400 ohms. The components of the exitation branch are Rc=500 kohms, Xm=60kohms. a) If the primary voltage is 7967V and the load impedance is Z=4.2+j3.15, what is the secondary voltage of the transformer? What is the voltage regulation? b) If the load is disconnected and a capacitor of -j6 ohms is connected in its place, what is the secondary voltage of the transformer? What is its voltage regulation under these conditions?