A three phase wye delta connected, 50MVA, 345/ 34.5 Kv transformer is protected by differential protection. The current transformer on the high side for differential protection is 150:5. What is the current on the secondary side of CT’s?

A conductor has four identical strands arranged in diamond configuration. Find the GMR of the conductor in terms of the radius r of each strand.

The resistances of the same length of aluminum and copper wires are found to be equal. Find the ratio of radii of aluminum to copper.

A 15 ohm resistor connected in series with an inductor has an equivalent impedance of 30 ohms with an unknown angle. Find the power factor angle in degrees.

A 10KVA, 200/400v, 1Ф transformer is operated with pen circuited secondary Find the primary current.

A parallel RL circuit draws a total current of 17A and 1.8KW from a 120V supply. Find R.

The power factor of a 20 MW , 13 2 KV, 3Ф motor is corrected to 0 9 a 230uF capacitor. What is its initial power factor

Three identical resistors are connected in wye across 220 v, 3-phase lines. The line current is12.7 A. To what value in volts should the line voltage be changed the same line current with the resistors connected in delta?

When a V-V system is converted into Δ-Δ system, increase in the capacity of the system is _____ percent.

A small wind generator is designed to generate 50 kW of power at a wind velocity of 25 miles per hour. What is the approximate blade diameter?

A synchronous generator having a subtransient reactance of 0.15 pu and operating at 5 percent above its rated voltage supplies a synchronous motor having a 0.20 pu subtransient reactance. The motor is connected to the generator by a transmission line and a transformer of total reactance 0.305 pu. A sudden three-phase fault occurs at the generator terminals. Determine the per unit subtransient fault current.

The capacitance between any two conductors of a three-phase, threeconductor cable is 2 µF. The cable operates at 11 kV line voltage and 50 Hz. What is the charging current through the cable capacitance?

A 10-km long, single-phase short transmission line has 0.5 < 60 Ω/km impedance. The line supplies a 316.8 kW load at 0.8 power factor lagging. What is the voltage regulation if the receiving and voltage is 3.3 kV?

If the waveform of a current has form factor 1.2 and peak factor 1.7, find the average value of the current if the maximum value of the current is 100 A.

A transformer has 4 % resistance and 6 % reactance drop. Find the voltage regulation at full-load 0.8 p.f. lagging.

A 6-pole, 50 Hz, three-phase induction motor has a maximum torque of 200

N-m when it is running at a speed of 900 rpm. The resistance of the rotor is

0 25 Ω Neglecting stator impedance, determine the torque at 5 % slip.

In a certain country, the equivalent fuel reserve for power generation is 3 x 10⁶ MW-yoars. The present peak power demand is 200 GW, and the expected power consumption growth rate is 2.1 percent. How long will the fuel reserve last?

Which of the following is not a standard branch circuit among rating?

Power in balance 3-phase system is measured by the two-wattmeter method and it is found that the ratio of the two-wattmeter readings is 2 is to 1. What is the power factor of the system?

A room 8 m x 12 m i slighted by 15 lamps wo fairl uniform illumination of 100 lumens per square meter. What is the coefficient of utilization if the output of each lamp is 1,600 lumens.

A 440 -v, 70- HP shunt motor has an ammature of 0.185 Ω and field resistance of 350 Ω The current drawn by this machine is 135 A at full load. If this machine is to deliver torque equal to 175 percent of that at fullload, what would be the best resistance of its starter?

Find the amount of electrical energy expanded in raising the temperature of 45 liters of water by 75 C. Assume a heater efficiency of 90%.

A capacitor of 40 μF capacitance in series with 2,000 ohms is suddenly connected across a 200-volt source. What is the energy stored in the capacitor after 0.04 sec?

Calculate the average voltage generated in a six-turn full-pitch coil of a 25cycle alternator if the flux pole is 7.2 x 10^5 maxwells.

A 13.8 kV/440 v, 50 kVA single-phase transformer has a leakage reactance of 300 ohms referred to the 13.8 kV side. Determine the per unit value of the leakage reactance of the low base.

The sequence components of phase c current of a 3-phase system are as follows: Ic0=0, Ic1=18.4 cis88.4, Ic2=3.23 cis48.2. Find the phase b current in amperes.

A current of 20A is flowing in an RL series circuit the instant before the switch is opened. If R=10 ohm L= 10 H, find the current after 3 seconds has elapsed.

A Y-Δ connected transformer has a turns ratio of 1 If the primary line current is 5 amperes, what is the secondary line current?

What is the power given V = 4 sin3t and I = 4 sin3t?

A 40μF capacitor is supplied with a voltage of v(t) = 100sin377t. Find the current equation.

A 20mH inductor draws a current of i(t) = 100sin100t. Find the voltage equation.

For a single line to ground fault the zero sequence current is given by j3.0 pu. The current carried by the neutral during the fault is

Two single-phase transformer are each rated 75 KVA are connected in V or open delta to serve a 3-phase load of 120 KW at 0.80 power factor lagging. Determine the size in KVAR of the capacitor needed to prevent overloading of the transformers.

A time of 10 milliseconds is required for the current on a series RL dc circuit to reach 90% of its final steady state value. What is the time constant in seconds for the circuit?

A bulb having a rating of 220 volts, 75 watts is to be connected to a 110 volts source. What power will it draw if connected across 110 volts source?

A 20-HP, 110 v dc shunt motor has an efficiency of 88% and an exciting current of 4 amperes and an armature resistance of 0.04 ohm. What is the starting resistance required for full-load torque?

A coil of 50-ohm resistance and 150 mH inductance is connected in parallel with a 50 μF capacitor. What is the power factor of the circuit?

A 220-volt dc shunt motor runs at 500 rpm with an armature current of 50 amperes and an armature resistance of 0 1 Ω Calculate the speed if the torque is halved?

The capacitance reactance of a transmission line is 90,000 ohms per kilometer. Find the total capacitance reactance if the transmission line is 50 km long.

A generating station supplies peak load of 12,000 KW, 9,000 KW, and 6,000 KW. Calculate the maximum demand of the station and the energy supplies in a year if it its diversity factor and its average annual load factor is 1.2 and 0.7, respectively.

A piece of conductor 10 cm long moves across a magnetic field of 10,000 gauss at a velocity of 120 cm/sec. What voltage appears across the conductor?

The core loss of a 5 KVA single phase transformer with normal voltage applied to the primary is 75 watts. The maximum efficiency occurs 60% of full load KVA. What is the full load efficiency of the transformer at 0.80 power factor?

A 200 μH coil has a Q of 250 at resonance frequency of 800 KHZ. What is the effective resistance of the coil?

A three-phase motor is rated 50 HP, 440 volts and 85% power factor. What is the rated current if the motor efficiency is 89%?

The phase b line voltage and the phase a line current of a balanced three phase system are V = 220 sin ωt 210º and I = 10 sin ωt - 30º) respectively. What is the power of the system?

A 1 5 MΩ resistor is connected in series with a 20 μF capacitor. The voltage source is 120 volts dc. Determine the current at t = 10 seconds after switch is closed.

A dc ammeter has an internal resistance of 0.1 ohm. A shunt of 1.01 x 10-3 ohm is connected to the ammeter. What is the multiplier of the set up?

the field circuit of a 200 KW, 230 volts shunt generator is 8 A when running full-load at rated terminal voltage. If the combined brush and armature resistance is 0 03 Ω, solve for the electrical efficiency of the generator.

The PTs of a 220 KV transmission line have a ratio of 132.76 KV/ 66.375 v and are connected wye-wye. A voltmeter connected line to ground reads 66 volts, what is the transmission line voltage?

A winding is short pitched by 60 degrees electrical. Its pitch factor is:

Two conductors carrying 50 amperes and 75 amperes respectively are placed 10 cm apart. Calculate the force between them per meter.

What is the minimum required ampacity of the feeder conductors supplying a 5A, single-phase motor and a 10A lighting load?

Two exactly similar turbo-alternators are rated 5 MW each. They are running in parallel. The speed load characteristics of the driving turbines are such that the frequency of alternator one drops uniformly from 60 Hz on no-load to 57.5Hz on full-load, that of alternator two from 60 Hz to 58 Hz. How will two machines share a load of 8,000 kW?

Calculate the force that will be exerted on the scale in pony-brake test when a 20-HP, 1,400 rpm motor is operating at full-load. The length of the brake arm is 3-ft, and the tare weight of the brake is 3.75lb.

The capacitance per kilometer of a 3-phase belted cable is 0.3μF between the two cores with the third core connected to the lead sheath. Calculate the charging current taken by the five kilometers of this cable when connected to a 3-phase 50 Hz, 11kV supply.

A delta connected load of 9 +j12 /phase is supplied by a 230 v, 3-phase source through a line with an impedance of 0.06+j0.12 /conductor. Find the load voltage in volts.

A 10:1 ideal transformer has a load of 0.1μF on the secondary. What is the load capacitance, as referred to the primary?

A 110-volt shunt motor has an armature resistance of 0.8Ω and a field resistance of 220Ω At full load the motor takes 10 amperes, and the speed is 1,200 rpm. At what speed must this motor run as a generator to deliver 10 amperes to an external circuit at 110v?

In a series RL circuit, R=20Ω and L= 0 06H The current lags the voltage by <80. Determine w.

A 12-pole, 3- phase alternator driven at a speed of 500 rpm supplies power to an 8-pole, 3-phase induction motor. If the slip of the motor at full-load is 3%, calculate the full-load speed of the motor.

An alternating current is represented by i=70.7sin 520t. Determine the value of the current 0.0015 second after passing through zero and increasing positively.

A 50-kVA single-phase transformer has on full-load a copper loss of 560 watts and iron loss of 500 watts. Calculate the efficiency at 25% of full-load for a power factor of 0.8 lagging.

A 100 mw power station delivers 100 MW for 2hrs, 50 MW for 8hrs and is shut down for the rest of each day. It is also shut down for maintenance for 60 days each year. Calculate its annual load factor.

A complex current wave is represented by the equation i= 5+ 5sin(120pi)t A. Find its average value in amperes.

The core loss of a 5-kVA single-phase transformer with normal voltage applied to the primary is 75 watts. The maximum efficiency occurs 60% of full-load kVA. What is the full-load efficiency of the transformer at 0.80 power factor?

If resonant frequency is 10kHz and quality factor is 50, then

A capacitor is charged by a dc source through a resistor of one megohm. If in one second, the potential difference across capacitor reaches 80% of its final value, calculate its capacitance.

The input power to a 3-phase induction motor running without load is measured by two wattmeter method. One wattmeter indicates-220 watts and the other one indicates 940 watts. What is the no –load power factor of the motor?

In a 12-Pole duplex lap wound dc armature, each conductor can carry a current of 50 amperes. If the total armature conductor is 600, what is the rated current of the armature?

A 5-MVA, 13.8 kV/480 V, 5% impedance transformer is tapped at 13.8 kV line where the Thevenin’s equivalent impedance is 0 5Ω Determine the fault current at the primary for a three-phase fault at the secondary.

In a balanced 3-phase voltage source with phase sequence abc, phase A voltage is 127cis 0 volts. Find the line voltage Vbc

The capacitance reactance of a transmission line is 90,000 ohms per kilometer. Find the total capacitive reactance of a transmission line is 60-km long.

Estimate the distance over which a load of 15 MW at a power factor of 0.8 lagging can be delivered by a three phase transmission line having a conductors each of the resistance 1 ohm per kilometer. The voltage at the receiving end is to be 132 kV and the loss in the transmission is to be 5% of the power delivered.

A power transformer rated 50MVA, 34.5kV/13.8 kV is connected wye-wye. What is the rated primary line current?

A 50- KVA single phase transformer has a full-load a copper loss of 560 w and iron loss of 500 w. Calculate the efficiency at 25 of full-load for a power factor of 0.8 lagging.

A three- phase induction motor is taking 40 kW, the slip being 4% , stator losses amount to 800 watts, calculate the total power developed.

A 500 volts 1 $\phi$   synchronous motor is taking 50 amperes at a p.f. of 0.8 leading. The output is 25 Hp and the effective resistance of the armature is 0.25 ohm. Find the iron and friction losses.

The three unbalanced currents are : Ia= 10cis(-30^o ), Ib=0, Ic=10cis150^o . Find the phase C positive sequence current.

A 2- element series circuit consumes 700 w and has a p.f of 0.707 leading. If the applied voltage is v= 141 sin(314t + 30 ), find the circuits constants.

Two electrons in a vacuum experience a force of 2 x 10^-15 N. How apart are the electrons?

What is the current per phase in the primary windings of a 3 phase / Y connected 6,600/400 – V 500- KVA, 50 Hz transformer. Neglect no load current.

It is desired to correct the 2,400 – KVA 0.65 Lagging power factor load in a plant unity by the installation of a synchronous condenser. Calculate the KVA rating of the latter.

A transformer is rated at 550 / 220 v. With the low voltage winding shorted, it requires 25 v across the 550 v winding to permit rated current through both windings of the transformer. Calculate the percent impedance.

A 3- phase overhead transmission line is being supported by three disc insulators. The potentials across top unit and middle unit are 8 KV and 11 KV, respectively. Calculate the ratio of capacitance between pin and earth to the self-capacitance between pin and earth to the self-capacitance of each unit.

A short 3 $\phi$   line with an impedance of 6 + j8 ohms per line has sending and receiving end line voltages of 120 and 110 KV respectively for some receiving end load at a p.f. 0.9 lagging. The active power at the receiving end is nearest to

Two long straight conductors each carrying an electric current of 5A are kept parallel to each other at a separation of 2.5cm. Calculate the magnitude of magnetic force experienced by 10cm of a conductor.

A 4-pole lap-wound armature has 480 conductors and a flux per pole of 25mWb. What is the emf generated, when running at 600 rpm?

A 220V series motor takes 10A and runs at 600 rpm. The total resistance is 0 8Ω At what speed will it run when a 5Ω resistance is connected in series, the motor taking the same current at the same supply voltage

An electric heater takes 1.2 kWhr in 30 minutes at 120V. What is the current input to the heater?

A current of 20A flows through two ammeters A and B joined in series. Across A, the potential difference is 0.2V and across B, it is 0.3V. Find how the same current will be divided between the two when they are joined in parallel.

An office 17m by 8m wide, is lighted by 8 lamps has a luminous intensity of 200 Cd. Allowing an absorption loss of 4,000 lm for the reflectors, walls and ceiling, Calculate the average illuminations on the working plane.

A shunt motor runs at 500 rpm on a 200V circuit Its armature resistance is 0 5Ω and the current taken is 30A in addition to field current. What resistance must be placed in series in order that the speed may be reduced to 300 rpm, the current in the armature remaining the same.

A transformer has 4% resistance and 6% reactance drop. Find the voltage regulation at full-load unity power factor

The current in the circuit is given by i=50sinωt If the frequency be 25Hz, how long will it take for the current to rise to 25 amp?

A single phase transformer when supplied from 220V, 50 Hz has eddy current loss of 50W. If the transformer is connected to a voltage of 330V, 50Hz, the eddy current loss will be

The resistance of the field coil of a motor is 200Ω at 15 . After the motor worked for a few hours on full load, the resistance increases to 240Ω Calculate the temperature rise of the load coil assuming the temperature coefficient of resistance is 0.0042 ^oc per at 0 ^oc .

A power plant is said to have had a use factor of 48.5% and a capacity factor of a 42.4%. How many hours did it operate during the year?

A single- phase transmission line has a total resistance of 1 5Ω and a loop reactance of 0 3Ω It delivers 2MW at 11kV at a power factor of 0 8 lagging. Calculate the line voltage at the sending end.

Three 40Ω non-inductive resistances are connected in delta across 200V, 3-phase lines. Calculate the power taken from the mains if one of the three resistors is disconnected.

Power in a balanced three-phase system is measured by the two wattmeter method and it is found that the ratio of the two readings is 2:1. What is the power factor of the system?

Calculate the self-inductance of an air-cored solenoid, 40cm long having an area of cross-section 20cm2 and 800 turns.

A three-phase induction motor having an input power of 30KW running at a slip of 4%. The stator loss is 1KW and friction and windage loss is 1.5KW. Determine the motor efficiency.

An iron core has a cross-section of 500mm2and having a length of 100cm. A magnetizing force of 500AT in it produces a magnetic flux of 400μWb. Determine the relative permeability of the material.

A synchronous generator having a subtransient reactance of 0.15 pu and operating at 5 percent above its rated voltage supplies a synchronous motor having a 0.2 pu subtransient reactance. The motor is connected to the generator by a transmission line and a transformer of total reactance 0.305 pu. A sudden three-phase short circuit occurs at the generator by a transmission line and a transformer of total reactance of 0.305 pu. A sudden three phase short circuit at the generator terminals. Determine the per unit subtransient fault current.

Given a 100 kVA, 2400/240 V single phase transformer. Find the current transformer (CT) ratio at the low voltage side.

Compute for the core loss if the transformer consumes 75 watts when it is connected across a 240 V source and taking 1.4 A. The primary resistance is 0.25 ohm.

Find the GMR in terms of the radius r of each conductor in a three bundled conductor arranged horizontally.

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

A 115 kV three-phase transposed transmission line is composed of 2-ACSR 336, 400 cmil, 30/7 oriole conductors per phase with horizontal configuration: D12= 7 ft, D23= 7 ft, D13= 14 ft. The line spacing is measured from the center of the bundled conductors. The distance between the conductors of the bundle is 6 inches. The conductors have a diameter of 0.741 inch and a GMR of 0.02255 ft. Find the capacitance per phase for 20 km of the line in microfarads

A 24.6 uF capacitor stores an energy W= 12sin^2 377t J. Find the current through it.

A 25 KVA transformer supplies a load of 12 KW at a power factor of 0.6 lagging. Find the maximum KVA load at a power factor of 0.866 leading can be added without overloading the transformer.

When two resistors R1 and R2 are connected in parallel across a battery, they consume a total of 50 W and draw a total current of 5A. When the two resistors are then connected in series across the same battery, they consume a total of 225 W with the same total current of 5 A. Determine R1 and R2.

A series RL circuit is connected across a 120 V, 60 Hz source and draws a current of 0.5 A at 0.70 lagging pf. Determine the values of R and L.

Two million cubic meters of water is stored in a reservoir feeding a water turbine. If the center of mass of the water is 50 m above the turbine and losses are negligible, how much power in MWHR per second will that volume of water produce? The density of water is 993 kg/m^3

A three-phase, wye connected, 20 MW load of power factor 0.866 lagging is to be supplied by a transmission line at 138 kV. It is desired that the line losses not exceed 5 percent of the load. If the per phase resistance of the line is 0.7 ohm/km, what is the maximum length of the line?

A short three-phase transmission line of 16 km long is delivering power of 65 MW at 64.5 kV and 0.9 pf lagging. The line impedance is 0.125 + j0.4375 ohm/km. Find the line to line sending end voltage.

The shunt winding of a machine has a resistance of 80 ohm and an inductance of 4H is suddenly switched on to a 220-volt supply. Find the time taken for the current to rise to half its steady state value?

What is the force required to separate two surface with contact area of 150 sq. cm when the flux density is 2 tesla normal to the surfaces?

Water flows at the rate of 1.5 m^3/s from a height of 100m which drive a turbine connected to a 150 rpm generator. Determine the turbine brake power if the frictional torque is 600 N-m.

A pulsating direct current has a constant magnitude of 9 A for 0.02 sec and is 0 for 0.01 sec. the cycle is then repeated. What is its effective value?

A magnetic circuit consist of silicon steel 3,000 permeability of 10 cm length and cross-section of 1.5 square cm and an air gap of the same cross-section and of 2 cm length. A 0.5 ampere current flows through 500 turns. What is the field intensity at the air gap?

A short 3 phase line with an impedance of 6+ j8 ohm per line has sending and receiving end line voltages of 120 and 110 kV respectively for some receiving end load at a power factor of 0.9 lagging. What is the active power at the receiving end of the line?