STUDY OF DC MOTORS

Name :K.L.I.M.P.B.Jayarathna

Index No : 120240E

Department : Electrical Engineering

Group : G-22

Date of Performance : 10/07/2014

Date of Submission :7/08/2014

Instructed by : Miss M.P.Manikdiwela

CALCULATIONS

R = Armature Resistance + Field Resistance = 1.4 + 0.6 Ω = 2.0 Ω

Radius of Pulley= r =0.72m2π = 0.115 m =11.5cm

For the First Observation

W = 28 lbs w = 6.6 lbs

= 28 x 0.453 = 6.6 x 0.453

= 12.684 kg = 2.989 kg

Torque (T) = (W-w) x g x r where W = Weight on the pan in kg

w = Reading of the spring balance at speed Nr in kg

T = (12.684 – 2.989) x 9.81 x 0.115

= 10.9374 Nm

Electrical Input = VI = 200 x 13

= 2600 W

Mechanical Output = ¿Nr x T) / 60

= (2 x π x 1840 x 10.9374) /60

= 2107.47 W

Copper loss = RI2 = 2x 132

= 338W

Efficiency = (Mechanical Output / Electrical Input) x 100 %

= (2107.47/ 2600) x 100 %

= 81.06 %

Mechanical loss = Electrical Input - Mechanical Output - Copper loss

Mechanical loss = 2600 – 2107.47 - 338= = 154.53 W

Converting lbs to Kilogram

1lbs = 0.453kg

Nr = Speed of the motor in rpm

OBSERVATIONS (In respective units)

V(v) I(A) Nr (rpm) W(kg) w(kg)

200 13.0 1840 12.684 2.989

196 14.2 1760 14.496 3.624

196 15.0 1660 16.308 3.986

195 15.8 1600 18.120 4.530

194 16.6 1540 19.932 4.983

194 18.0 1420 23.103 5.436

192 18.2 1400 24.009 5.979

192 18.6 1360 24.915 6.070

CALCULATED VALUES

Electrical Input (W)

Torque(Nm) Mechanical Output (W)

Copper loss (W)

Mechanical Loss (W)

Efficiency (%)

2600 10.9374 2107.47 338 154.53 81.06

2783.2 12.2653 2260.57 403.28 119.35 81.222940 13.9011 2416.49 450 73.51 82.193081 15.3316 2568.83 499.28 12.89 83.38

3220.4 16.8647 2719.74 551.12 -50.46 84.453492 19.9310 2963.78 648 -119.78 84.87

3494.4 20.3405 2982.08 662.48 -150.16 85.343571.2 21.2599 3027.82 691.92 -148.54 84.78

SPEED Vs. TORQUE

Speed (rpm) Torque (Nm)

1840 10.9374

1760 12.2653

1660 13.9011

1600 15.3316

1540 16.8647

1420 19.9310

1400 20.3405

1360 21.2599

1300 1400 1500 1600 1700 1800 19000

5

10

15

20

25

Speed vs Torque Logarithmic (Speed vs Torque)

Speed (rpm)

Torq

ue (N

m)

TORQUE Vs. ARMATURE CURRENT

Torque (Nm) Armature Current (A)

10.9374 13.0

12.2653 14.2

13.9011 15.0

15.3316 15.8

16.8647 16.6

19.9310 18.0

20.3405 18.2

21.2599 18.6

0 2 4 6 8 10 12 14 16 18 200

5

10

15

20

25

Torque vs Armature Current Power (Torque vs Armature Current)Exponential (Torque vs Armature Current)

Armature Current (A)

Torq

ue (N

m)

SPEED vs ARMATURE CURRENT

Speed (rpm) Armature Current (A)

1840 13.0

1760 14.2

1660 15.0

1600 15.8

1540 16.6

1420 18.0

1400 18.2

1360 18.6

10 11 12 13 14 15 16 17 18 19 201100

1200

1300

1400

1500

1600

1700

1800

1900

Speed vs Armature Current Power (Speed vs Armature Current)Power (Speed vs Armature Current)

Armature Current(A)

Spee

d (r

pm)

EFFICIENCY Vs ARMATURE CURRENT

Efficiency (%) Armature Current (A)

81.06 13.0

81.22 14.2

82.19 15.0

83.38 15.8

84.45 16.6

84.87 18.0

85.34 18.2

84.78 18.6

80 81 82 83 84 85 8610

11

12

13

14

15

16

17

18

19

20

Efficiency Vs Armature Current

Armature Current (A)

Efficie

ncy(

%)

COPPER LOSS Vs. ARMATURE CURRENT

Copper Loss (W) Armature Current (A)

338 13.0

403.28 14.2

450 15.0

499.28 15.8

551.12 16.6

648 18.0

662.48 18.2

691.92 18.6

12 14 16 18 200

100

200

300

400

500

600

700

800

Copper Loss vs Armature CurrentPower (Copper Loss vs Armature Current)

Armature Current (A)

Copp

er Lo

ss

MECHANICAL LOSS Vs. SPEED

Mechanical Loss (W) Speed (rpm)

154.53 1840

119.35 1760

73.51 1660

12.89 1600

-50.46 1540

-119.78 1420

-150.16 1400

-148.54 1360

1300 1400 1500 1600 1700 1800 1900

-200

-100

0

100

200

Mechanical Loss Vs Speed Polynomial (Mechanical Loss Vs Speed)

Speed (rpm)

Mec

hani

cal L

oss (

W)

DISCUSSION

1)Performance Characteristics of a DC Series Motor

As almost all motors, DC motor operates on the magnetic field induced by the field winding in the stator, interacting with the amateur winding in the rotor. (In small motors usually this magnetic field is provided by a permanent magnet)

Usually Motors are used to convert electrical energy to mechanical energy. Based on methods of windings, there are three types of DC Motors. They are;

1. Shunt excited Dc Motors2. Series excited DC Motors3. Compound excited DC Motors

Shunt Excited DC motors- The field windings are parallelly to the armature. The current through the shunt field winding is not the same current going through armature

Series excited DC Motors- since field winding is connected in series with the armature ,series field winding carries the armature current

Compound excited DC Motors -This has two field windings; one of winding connected in parallelly to armature the other winding connected in series with armatureThere are two types of compound motor connections. When the shunt field winding is directly connected across the armature terminals, it is called short-shunt connection. When the shunt winding is connected that it shunts the series combination of armature and series field, it is called long-shunt connection

Main Characteristics of a DC series Motor

Torque and Armature current characteristic (T/I) This can be shown using a curve between armature torque Ta and

armature current Ia of a DC Motor. also referred as electrical characteristic of the motor. The amount of torque that can be produced by the shaft depends on

the current passing through it (torque is proportional to the square

of the armature current.)

Speed and armature current characteristic (Nr/I) It is the curve between speed Nr and armature current Ia of a DC

motor. in an occation of selecting type of a motor to a perticular perpose

this would be an deciding factor

Speed and torque characteristic (Nr/T) can be shown using a curve between speed N and armature torque

T of a d.c. motor. also referred as mechanical characteristic

2)APPLICATIONS

DC series motors are widely used in cases where a high torque is required, but not a great speed. Because these motors are able to create high starting torques at low speed and it can be used to accelerate very heavy loads from stand still. Some applications are,

Driving cranes Steel rolling mils Electric locomotives Power tools ( hand drills, saws, power screwdrivers)

A series wound DC motor normally drives loads that require high torque and do not require precise speed regulation they are ideal for traction work where the load requires a high breakaway torque. Such uses include locomotives, hoists, cranes, automobile starters, or oil drilling rig applications. Auto mobile starters are very good example of that,

the DC series motors not using for long period of time. In a starting motor of a vehicle, it can abstract around 500A within a second, while starting the vehicle. Also DC series motors are used to drive trains, because they provide the required torque and horsepower to get massive amounts of weight moving.

Also DC series motors can work in AC current, therefore it is an universal motor.

Shunt motors are mostly used in cases where the speed and tension control are critical, therefore these motors are used in machine shop lathes, and industry process lines etc.

Applications of Shunt excited dc motors

These have fairly constant speeds against a varying load or torque. Therefore applications include situations where a constant speed is required.

E.g. Lathes, Conveyors, Fans, Machine tool drives

Applications of Compound excited dc motors

These have Combine characteristics of both shunt and series wound motors. The series winding gives good starting torque and shunt winding ensures a comparatively constant speed.

E.g. Planers, Shears, Guillotines, Printer machines, Power presses which needs peak loads at certain