1-Phase AC Circuits

Problem 215: An industrial coil has a resistance of 32 ohms and a reactance of 24 ohms and rated 440 volts at 60 Hz. A factory will connect the coil to a 440 V, 50 Hz supply. How much percentage overcurrent will the coil suffer?

Problem 216: The open circuit voltage across the output terminals of an AC power supply is 15.2 V. When these terminals are short-circuited, a current of 3.2 A flows. When a 5-ohm resistance is placed across these terminals, the current through it is 1.8 A. Calculate the series internal resistance of the power supply.

Problem 217: A single-phase load takes 55 kW at 70% pf lagging from a 240 V, 50 Hz supply. If the supply is made 60 Hz, with the voltage remaining the same, what will be the kW load at 60 Hz?

Problem 218: A 25-ohm resistor connected in series with a coil of 50 ohm resistance and 150 mH inductance. What is the power factor of the circuit?

Problem 219: The ohmic resistance of a large magnetic contractor is measured to be 20 ohms. A 230 V is impressed on the contractor and the current is taken as 3.2 A. Neglecting core loss, determine the inductance of the contactor in mH?

Problem 220: An 8-ohm resistor is connected in series with an inductive coil and the combination is connected across a 120 V, 60 Hz source. A voltmeter connected across the resistor reads 32 V and 104 V when connected across the coil. Determine the resistance of the coil.

Problem 221: When connected to a 220-V, 50 Hz supply, an impedance coil circuit takes 5 A, but this current falls to 4.4 A when a 10-ohm resistor is added in series. Find the inductance of the coil.

Problem 222: An impedance coil, in series with a resistor takes a current of 5 A when connected to a 100-V AC source. Using a voltmeter, the voltage across the coil was found out equal to 80 V and that across the resistor equal to 30 V. Find the operating power factor of the coil.

Problem 223: A load of 20 + j35 ohms is connected across a 220 volts source. Determine the power factor and the VARS.

Problem 224: A load is rated at 115 V, 60 Hz, 10 A, and 1150 W. A coil is to be wound with a ratio of \(X_L\) to R of 5, such that when connected in series with the load on a 230-V, 60 Hz line, the load may operate normally. Solve for R.

Problem 225: Find the total impedance in rectangular for the following three series impedances: \(12\angle10^\circ\), \(25\angle15^\circ\), \(34\angle26^\circ\)

Problem 226: An impedance draws a current i = 10 cos (wt - 30°) from a voltage, v = 220 sin (wt + 30°). What is the impedance?

Problem 227: A series resistance-capacitance (R-C) circuit is connected to a 230 volt 60 cycle source. If the power taken by the circuit is 4,800 watts and the voltage drop across the resistor is 115 volts, calculate the capacitance of the capacitor.

Problem 228: A 50 and 100-microfarad capacitors are connected in series and across a 100 sin (wt + 30°) voltage. Write the equation of the current.

Problem 229: A series circuit composed of 100-ohm resistor and a 20-microfarad capacitor connected across a 240-V, 60 Hz line. Which of the following answers is WRONG?

Problem 230: A capacitance is connected to a 115-V, 25-Hz mains and takes 5 A. What current will it take when the capacitance and the frequency are both doubled?

Problem 231: An ideal inductor of 50 mH is connected in series with a 175-\(\mu\)F capacitor. The combination is then connected across a 120-V variable frequency AC source. At what frequency will this circuit take a leading current of 5 A?

Problem 232: A series circuit consisting of a variable resistor in series with a capacitance of 80 \(\mu F\) is connected across a 120 V, 50-Hz supply. To what value should R is adjusted so that the power absorbed by the series circuit will be 100 W?

Problem 233: A capacitor is rated 100 kVAR, 380 volts, 50 Hz. What will its rating be at 60 Hz, 220 volts?

Problem 234: A resistor and a capacitor are connected in series across a supply of 250 V. When the supply frequency is 50 Hz the current in the circuit is 5 A. When the supply frequency is 60 Hz, the current is 5.8 A. Find the value of the capacitance.