Quiz 2 Correl

Find the Q of a circuit when the resonant frequency is 4.468 MHz, the inductance is 47 microhenry and the resistance is 180 ohms parallel.

0.136

In a balanced three-phase wye-wye system, the load impedance at 10 + j1Ω. The source has a phase sequence abc and the line voltage Vab = 220 with an angle of 30° v rms. If the load voltage Van = 120 v rms with 0 angle, determine the line impedance

0.6 + j0.06 ohm

The per unit impedance of a circuit element is 0.30. If the base KV and base MVA are halved, then the new value of the per unit impedance of the circuit element will be

0.60

A 3 phase system supplies two, 3 phase loads connected in parallel as follows: Load 1, 80 KW and 60 leading KVAR and load 2, 120 KW and 160 lagging KVAR. Find the total line current in amperes.

129.099 A

Three capacitors of 3,4 and 5 microfarads are connected in series with a 6-volt battery. When the current stops, what is the voltage across the 3 - microfarad capacitor?

2.55

A balanced, 3 phase, 3-wire system supplies two balanced, wye-connected loads. The first one draws 6 KW at 0.8 pf lag, while the second one requires 12 KW at 0.833 pf lead. If the line current is 8A. Find current in first load amperes.

2.88 A

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?

20 A

The apparent power input to balanced wye-connected load is 30 KVA and the corresponding true power is 15 KW at 50 A. The phase voltage is

200 V

The magnitude of the complex power (apparent power) supplied by a three-phase balanced wye-wye system is 3600 VA. The line voltage is 208 v rms. If the line impedance is negligible and the power factor angle of the load is 75°, determine the load impedance.

32.67 + j15.24

A 5 MVA, 13.8 kV/480V, 5% impedance transformer is tapped at 13.8 kV line where the Thevenin's equivalent impedance is 0.5 ohm. Determine the fault current at the primary for 3-phase fault at the secondary.

3314 A

A 12 μF capacitor charged at 500 volts and a 6 μF capacitor charged at 250 volts are connected in parallel. What is the potential difference of the combination?

417V

A three phase system has line to line voltage Vab = 1500 v rms with 30 deg angle with a wye load. Determine the phase voltage.

866 vrms

An LC series circuit with an inductance L and a capacitor C has an oscillation frequency of f. Two inductors, each with inductance L and two capacitors each with capacitance C, are all wired in series and the circuit is completed. The oscillation frequency is

f

A three phase power system consists of an ideal 230 v wye connected generator which is connected through a three-phase transmission line to a wye connected load. If the impedance of the line and load are 0.06 + j0.12 and 12 + j9Ω per phase, respectively. What is the magnitude of the load phase voltage?

228 V

A 10 HP, 230 v, 60 HZ three-phase motor has an efficiency of 90% and pf of 0.85 lagging. What is the capacitance per phase in microfarads to be connected in parallel with the motor to correct the power factor to unity?

258 uF

A 480 V, 3 phase supply delivers power to a wye-connected load with impedance of 10 + j5 ohms/phase and a wye-connected purely resistive load with impedance of 15 ohms/phase. What is the average power in one phase in KW?

11.26 kW

Three parallel loads, 1, 2 and 3 have the following parameters: Load 1 - R1 = 30 ohms, L1 = 0.1061 H; load 2 - R2 = 20 ohms, C2 = 88.2 µF and load 3 - Pure resistance of R3 = 50 ohms. If these loads are fed by a 240V, 60Hz ac source, find the total current in amperes using vector diagram.

11.486 A

What is the value of RX in kohms to be connected in parallel to a 75 kohms to reduce the value of total resistance to 10 kohms?

11.7

One conductor of a three-phase line is open. The current flowing to the delta connected load through line A is 20 A with the current flowing in line A as reference and assuming the line C is open, what is the zero-sequence current of phase B?

0

A load draws current from a voltage source. The equation of the current and voltage are I = 10 cos wt and V = 220 sin wt. What is the power?

0 W

The per unit reactance's of a synchronous generator are Xd = 1, Xd'= 0.35 and Xd" = 0.25. The generator supplies a 1.0 per unit load at 0.8 power factor lagging. Calculate the voltage behind the substransient reactance

1.17 pu

In an electric system the available short circuit MVA is 750 MVA. What is the Thevenin's equivalent reactance at 34.5 kV?

1.587 k ohms

A series RLC circuit contains a resistor R of 2 ohms and a capacitor C of ½ farad. Determine the value of the inductor so that the circuit is critically damped.

1/2 H

In a balanced delta connected load, one line is open. Line a carries 20 A. Assume line a current is the reference vector and line c is open. What should be the negative sequence component of the line a current?

10+j5.77

A balanced delta connected load having impedance of 8 + j4 ohms/phase is connected in parallel with a balanced wye-connected load having impedance of 2 - j1 ohms/phase. The two loads are supplied by a balanced 3 phase source through a feeder having impedance of 0.2 + j0 ohm/conductor. The voltage at the load is 120 V line to line. Find the total power loss in the feeder in watts.

1420 W

A generator rated 600 KVA, 2400 v 60 Hz, 3-phase, 6 poles and wye-connected has 10% synchronous reactance. If a three-phase fault occurs, what will be the short circuit current?

1443 A

The per unit reactance of a synchronous generator are Xd = 1.1, Xd' = 0.24, and Xd" = 0.15. The generator is operating without load at 5 percent above rated voltage when a three-phase short circuit occurs at its terminals. If the generator is rated at 500 MVA and 20 kV, determine the sub transient current in kiloamperes.

175 kA

In a balanced, 230 V, 3 phase circuit, the line current is 90 A. The total power is measured by the two-wattmeter method. If the power factor is 100%, what is the reading in watts on each wattmeter?

17927

What is the actual voltage of the high leg (middle) for the three-phase, four wire delta grounded system 240/120 V secondary voltage?

207.8∠-30° V

A fully loaded three-phase, 2.2 kV circuit supplies 100 kW to a load having a pf of 70.7 percent lagging. Additional capacity is required in order to accommodate a greater load at the same pf. A three-phase 150 kVAR 2.2 kV capacitor bank is available. If the bank is bridged across the line at the load, how many additional kW could the line supply without overloading?

34.7 kW

The total real power absorbed by a balanced wye-connected load from a 208 V, 3 phase supply is 1,500 watts. If the load power factor angle is 20°, what is the line current in amperes?

4.43

Two parallel loads are connected across 220V, 60 Hz ac supply. The total current and power taken by the loads from the supply are 20A and 3.8 kW respectively. Load 1 consists of series R - C with R = 10 ohms and XC = 10 ohms, while load 2 consists of series R - L with unknown values. Find the current in load 2 in amperes.

4.444 A

Reactance's are connected in series: XC1 = 100, XC2 = 40, XL1 = 30, XL2 = 70. What is the net reactance?

40 XC

A relay coil carries a polarizing current of 1 A dc and a signal ac current of 3A at 50 Hz. If the coil resistance is 5Ω, power dissipated by the coil is __ watts.

5 W

A series circuit consists of a 20Ω resistor, a 0.20 H inductor and 50 microfarad-capacitor. If a variable frequency 120 V source is connected across its terminal, what is the resonant frequency in Hz?

50 Hz

An industrial load consumes 120 kW at 0.707 pf lagging and is connected to a 480 + j0 v rms, 60 HZ line. Determine the value of the capacitor in microfarads that when connected in parallel with the load will raise the pf in minimum requirement by the Philippine Electrical Code.

928.06 uF

A series circuit has R of 500 ohms, a 10 microhenry inductance L and a 4-microfarad capacitance C is connected across a 60 HZ 120 v line. Find the reactance of XL in ohms.

0.004 ohms

In a series RLC circuit, the resistance is 200Ω, the inductance is 10 mH, and the capacitance is 4μF. If the circuit is connected across 100-volt source, what is the current?

0.144

An inductive impedance, z = 40 + j30 ohms and an unknown capacitive reactance XC are connected in parallel across a 240V, 60Hz ac supply. If the total current is 5.91 A leading, find the total power factor of the circuit

0.8 pf

A coil and resistor each have a 160-V voltage across them when connected in series to 240v, 60 Hz source. If they draw a 1 ampere current from the source what is the resistance of the coil?

15 ohms

The power source feed a 100 kVA 14/2 .4 kV single-phase transformer through a feeder impedance of 38 + j140 ohms. The transformer equivalent series impedance referred to its low voltage side is 0.10 + j0.50 ohm. The load in the transformer is 90 kW at 80% pf lagging and 2.3 kV, what is the voltage at the source?

15.5∠3.0° V

A coil has an impedance of 75.4 Ω when connected a across a source of 60 Hz. The same coil yields an impedance of 54.8 Ω when connected across a source having a different frequency of 30 Hz. What is the coil's inductance?

158.6 mh

A 20 μF capacitor is in parallel with a practical inductor represented by L = 1 mH in series with R = 7Ω. Find the resonant frequency of the parallel circuit.

159.2 Hz

A coil of wire having a value of 10 + j16 Ω is connected in series with a capacitance reactance Xc. and this series combination is then connected in parallel with a resistor R. If the equivalent impedance of the circuit is 8 + j0Ω, what is the value of Xc in Ω?

16 ohms

A 50 hp, 440 v, 60 HZ, 3-phase motor operates at full load with an efficiency of 89% and power factor of 0.85 lagging. Determine the capacitance in μF per phase of a wye-connected capacitor bank to be connected across the motor terminal to improve the power factor to 0.95 lagging.

167uf

An impedance draws a current i = 10 cos (ωt - 30°) A from a voltage, v = 220 sin (ωt + 30°) V. What is the impedance?

19.1-j11

A 500 kVA, 13000/240 V, three-phase transformer with an impedance of 4.2% is connected to an infinite bus and without load. If three phase fault occurs at the secondary terminals, the fault current in ampere is

28640 A

A 5-ohm resistance and a 6-ohm inductive reactance are connected in parallel across an ac source. The currents through them are 24A and 20A, respectively. Now a capacitor is connected in series with the parallel combination. What should be the value of the capacitor reactance in ohms so that when the whole combination is connected across the same ac source the resistance and inductive reactance will have the same current as before?

4.92

A balanced delta connected load impedance of 15 + j18 Ω per phase is connected across a 230v, three-phase source. Find the total power consumed.

4336 W

An inductive impedance, Z1 = 10 + j15 ohms and capacitive impedance, Z2 = 6 - j8 ohms are connected in parallel across a 220V, 60Hz ac supply. Find the total power in watts

4392