DC MACHINES POWERLINE REVIEWER

80問 • 2年前

問題一覧

DC shunt motors are used for driving

machines tools

Calculate the voltage induced in the armature winding of a 4 pole, lap wound, dc machine having 728 active conductor and running at 1800 rpm. The flux per pole is 30 mWb.

655.2 V

A 4 pole wave wound armature has 144 solts with two coils sides per slot. each slot each slot having two truns. if the per pole is 20mWb and the armature rotates at 720 rpm. What is the induced voltages?

276.48 V

A 6 pole lap wound armature, having 720 conductors, rotates in field of 23.35 mWb. if the induced emf is 420 volts, what is the speed?

1720 rpm

A 440 volt 75 hp shunt motor has an armature resistance of 0.185 ohm and a field resistance of 350 ohms. The current drawn at full load is 135 amperes. What is the back emf in volts?

415.3

The direction of rotation of a dc motor is reversed by

reversing armature connections

It is a DC motor that tends to over speed when the field opened while running

shunt motor

A seperately-excited motor runs at 1045 rpm, with a constant field , while taking an armature current of 50 A at 120 V. the armature resistance is 0.1 ohms. If the load on the motor changes such that it now takes 95 A at 120 V. determine the motor speed at this load.

1004 rpm

A 500 volt shunt motor running at 720 rpm takes an armature current of 50 amp. its effective resistance 0.40 ohm. When a resistance of 1.6 ohm is placed in series with the armature, what is the new speed? Assume that load torque is constant.

600 rpm

A motor is supplying 70 N-m to a load. if the shaft of the motor rotates at 1500 rpm. determine the horsepower developed of the power

14.7

The armature and field circuits of a 230 volts shunt motor have resistance of 0.31 and 115 ohms respectively. It takes 52 Amp when operating at a certsin load. What is the hp developed?

14.4 Hp

A motor has a nameplate rating of 15 hp and 1160 rpm. Solve for the rated torque

67.9 lb-ft

A 6 pole lap wound armature having 720 conductors rotates in field of 20.35 mWb. the armature current is 78 A, what id the armature torque developed?

181.9 N-m

A 240 volt dc motor on brake test book 52 amp wheb running at 1500 rpm. the spring balance at the end of the 76 cm brake arm reads 93.5 N. What is the efficiency of the motor at this load?

0.90

A 230 V shunt motor having an armature resistance of 0.05 ohm and a field resistance of 75 ohm, draws a line current of 7A while runninh light at 1120 rpm. Determine the motor effiency when the line current at a given load is 46 A

83.9%

If the motor frame is found excessively hot which of the following is the LEAST likely cause

faulty starter

Which of the following statement is correct in case of DC series motor?

it should be directly connected to the load

If the current in the armature of dc series motor is reduced to 50% the torque of the motor will become

25% of the previous value

A 5 HP 230 volts tales 18 amperes when operating at full load. The shunt field resistance is 115 ohms and the armature resistance is 0.25 ohm. Calculate the starter resistance if the starting torque is limited tp 1.5 times the full load(take a 3-V brush drop)

9.21 ohm

The armature of a 230 volt shunt motor has a resistance of 0.18 ohm. A resistance is inserted in series with armature at the starting so as not to exceed 76 amps at starting. Calculate the value to which this resistance can be reduced when the armature acclerates until Ec is 168 volts. Brush drop is 2V

0.16 ohm

For both lap and wave windings there are as many commutator bars as the number of

winding elements

For a DC generator when the number of poles and the armature conductors is fixed, then which winding will give the higher emf?

wave windings

Which of the following components of a DC generator plays vital role for providing direct current of a DC generator?

commutator

In DC generator the critical resistance refers to the resistance of

field

The number of armature parallel paths in two poles DC generator having duplex lap winding is

A 4 pole, 12 slot lap wound armature has two coil side per slot. Assuming single turn coils and progressive winding what is the back pitch?

In a 12 pole, triplex lap wound dc armature each conductor can carry 100 A. What is the rated current of this armature?

3600 A

In a DC generator in order to reduce sparking at brushes the self induced emf in the coil is neutraized by all of the following except

dummy coils

Interpoles are connected ________ with the armature and compensating windings are connected in _________ with the armature

series, series

A shunt generator running at 1000 rpm has generated emf as 200 V. if the speed increases to 1200 rpm, the generated emf will be nearly

240 V

The emf induced in the armature of a shunt genratir is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A. the terminal voltage will be

580 V

A 50 kW 460 volt shunt generator has a voltage regulation of 8?7 percent. Calculate the no load terminal voltage

500

A shunt generator delivers 195 Amp of terminal of voltage 250 volts. The armature resistance and shunt field resistancen are 0.02 ohm and 50 ohms respectively. The iron and friction losses equal to 950 watts. What is the overall efficiency?

94%

A 10 kW 250 V shunt generator having an armature resistance of 0.1 ohm and a field resistance of 250 ohm, delivers full load at rated voltage and 800 rpm. The machine is now run as a motor while taking 10 kW at 250 V. What is the speed of the motor? neglect brush- contact drop.

774.8 rpm

A 10 kW 250 volts self excited generatir when delivering rated load, has an armature circuit voltage drop of 5% of the terminal voltage and shunt field current equal to 5% of the rated load current. Calculate the field resistance.

125 ohms

A 100 kW, 230 V shunt generator has Ra= 0.05 ojm and Rf = 57.5 ohm. If the generator has a total mechanical loss and core loass of 1.8 kW. What is the maximum efficiency of the generator can achieve? Neglect brush contact drop

90.6%

A 25 kW, 500 volt long shunt compound generator delivers a full load. it has armature, series field and shunt field resistance of 0.05 ohm, 0.03 ohm and 250 ohm respectively. What is the generated voltage allowing 3V for brush contact drop?

507 V

A 50 kW, 500 volt short shunt generator has an armature resistance series field resistance and shunt field resistance are 0.05 ohm, 06 ohm and 253 ohms respectively. What is the armature power generated?

52.13 kW

Two shunt generator A and B with ratings of 250 and 400 kW respectivelt having equal no load voltage of 260 volts and full load voltage of 240 V, calculate the load of each when the load shared is 600 kW

231 kW & 369 kW

By looking at which part of the motor it can easily confimed that a particular motor is DC motor?

Commutator

If a speed of a DC shunt motor is increased, the back emf of the motor will

increase

If the field of a dc shunt motor is opened

the speed of the motor will become very high

As the load is increased the speed of DC shunt motor will

reduce slightly

A DC shunt motor is rotating in clockwise direction as viewed from one end. The polarity of connection of the armature and field winding are reversed simultaneoulsy. The motor will

rotate in clockwise direction

The armature of a motor has of 400 active conductors the flux density in the field being 3000 gauss. The axial length of the armature is 20.32 cm. The current is 30 amperes. Determine the total force exerted in the armature

731.5 N

A 4 pole lap wound armature has 144 slots with coil sides perslot each coil having two turns. If the flux per pole is 20mWb and the armature rotates at 720 rpm. What is the induced voltage?

138.24 V

A dc machine has a 4 pole wave wound armature with 46 slots and 16 conductor perslot if the induced voltage in the armature is 480 V at 1200 rpm. determine the flux per pole

16.3 mWb

A 230 V DC shunt motor takes 32 A at full laod. The back emf on full load. if the resistance of motor armature and shunt field windings are 0.2 ohms and 115 ohm respecrively will be

224 V

The armature of a dc machine running at 1200 rpm carries 45 A in current. If the induced armature voltage is 130 V, what is the torque developed by the armature?

46.5 N-m

Calculate the Torque developed by the armature of a 4 pole lap wound dc machine having 728 active conductors and runnign at 1800 rpm. The flux per pole is 30 mWb and the armature is designed to carry a maximum line current of 100 A

347.7 N-m

A 4 poles lap wound dc machine has 728 acyibe conductor running at 1800 rpm. The flux per pole is 30 mWb. The armature current is 100 A. What is the electromagnetic power developed in armature in kW?

65.5

Which of the following loss in DC generator varies significantly with the load current?

armature copper loss

If Bmax is the maximum flux density, then eddy current loss will vary as

(Bmax)^2

The hysteresis loss in a DC generator varies with the frequency of magnetic reversals as

In case of DC machine mechanical losses are primary function of

speed

Calculate the efficiency of a 230 Volt shunt lotor from the following data: input current is 19.8 Amp, balance reading is 14 lbs, tare weight is 2lbs brake arm is 2 ft long & speed is 1100 rpm

82.4%

In which of the following applications DC series motor is invariably used?

starter for a car

A DC series motor as compared to shunt motor and compound motors, has the highest troque at the start because of its comparatively

stronger series field

Which DC motor will be suitable along with fly wheel for intermittent light and heavy loads?

cummulatively compounded motor

Differentially compound DC motor can find applications requiring

low starting torque

In a overload motor remain danger arises due to

winding getting overheated

For generating large current on DC generators which winding is generally preffered?

lap winding

In case of DC machine winding number of commutator segments is equal to

number of armature coils

The purpose providing dummy coils in a generator is

to provide mechanical balance for the motor

In DC generator the critical resistance refers to the resistance of

field

In a DC machine stray loss is the sum of

iron loss and mechanical loss

Which if the follwing losses are significatly reduced by laminating the core the core of a DC genrator?

Eddy current losses

If residual magnetism of a shunt generator is destroyed accidentally, it may be restored by connecting its shunt field

to a battery

One dc motor drives antoher dc motor. The second dc motor when excited and driven

runs as a generator

In over compounded generator full load terminal voltage is

more than no load terminal voltage

The number of armature parallel paths in two pole DC generator having duplex lap winding is

For both lap and wave windings, there are as many commutator bars as the number of

windings elements

When the shunt field of a compound generator is connected across both series field and armature. Such a connection is known as

long shunt

Drop in speed of a DC generator due to increase in load can be compensated by

increasing the input to prime mover

In case of a 4 pole DC generator provided with a two layer lap winding woth sixteen coils, the pole pitch will be

If the armature of an eight-pole dc machine were wound with a simplex wave winding. How many parallel paths would there be

2 paths

In a 4 pole 35 slos dc armature calculate the coil span

8 slots

A 4 pole dc generator with simplex lap winding has 48 slost and 4 element per slot. The flux/pole os 0.025 Wb and it runs at 1,500 rpm. What is the output voltage?

60 volts

Assuming constant field excitation calculate the no loaf voltage of a separately excited geenrator whose armature voltage is 150 volts at 1800 rpm when the speed is reduce to 1600 rpm

133 V

A 20 kW 220 volt shunt generator has an armature resistance of 0.07 phm and a shunt resistance of 200 ohms. Determine the power in the armature wjen it delivers its rated ouput

20.83 kW

DC CIRCUITS POWERLINE

premopremo remo · 75問 · 2年前

DC CIRCUITS POWERLINE