EE xxxx – Laboratory Practice III

Study & Test of DC Motors

Instructed by: Mr. Lathika Attanayaka

Name : K.L.U. Sirisena

Index No : 090493R

Field : EE

Date of Exp. : 2010.11.10

Date of Sub. : 2010.11.24

Experiment:

1. Study of DC motors2. Test on DC Series motors3. Test on a separately excited DC motor

Objectives:

1. To study the basic construction of a DC machine and to get familiarized with armature windings and other associated components.

2. To study the actions of eddy current braking and mechanical braking.

3. To study the performance characteristics of DC series motor and separately excited DC motor.

Apparatus:

Part 1Dismantled DC machine

Part 2DC series motorAbsorption dynamometer1 ammeter 0-20A1 voltmeter 0-300V1 Rheostat 20A/6Ω

Part 3

3 ammeters 0-1-3-10A DC2 voltmeter 0-150-300V DC3 Rheostats 25 Ω / 10A990 Ω / 0.75A490 Ω / 2ATachometer

Calculations

Part 2 – Dynamometer

Radius of pulley (r) = Circumference/2π = 72cm/2π = 11.46cm = 0.1146 m

Sample Calculation

Input power = Electrical power supplied = V x I

For, W=23 lbs, Input Power = 202 x 13.2 = 2666.4 WT = (W-w).g.r = (12.7 - 5.443) x 9.8 x 0.1146 = 8.1502 NmOutput Power = Nrad/s .T = 201.06 x 8.1502 = 1638.68 W

Observations CalculationsWeight on pan / W

Spring balance / w

Speed/Nr Voltage (V)

Current (A)

Input Power

(W)

Torque (Nm)

Output Power

(W)lb kg lb kg rpm rad/s0 0 4 1.814 - - - - - - -28 12.700 12 5.443 1920 201.06 202 13.2 2666.4 8.1502 1638.6830 13.607 12 5.443 1880 196.87 202 13.8 2787.6 9.1688 1805.0732 14.514 13 5.897 1840 192.68 201 14.6 2934.6 9.6776 1864.6834 15.422 13 5.897 1780 186.40 202 15 3030 10.6973 1993.9836 16.329 13 5.897 1740 182.21 202 15.4 3110.8 11.7160 2134.7738 17.236 14 6.350 1720 180.11 202 15.6 3151.2 12.2258 2202.0040 18.143 14 6.350 1700 178.02 202 15.8 3191.6 13.2445 2357.7842 19.050 15 6.804 1680 175.92 202 16.2 3272.4 13.7532 2419.4744 19.958 16 7.257 1640 171.74 202 16.6 3353.2 14.2642 2449.7446 20.865 16 7.257 1620 169.64 202 17 3434 15.2832 2592.6448 21.772 16 7.257 1600 167.55 200 17.2 3440 16.3015 2731.3250 22.679 16 7.257 1500 157.08 200 18 3600 17.3201 2720.6552 23.586 16 7.257 1400 146.61 198 19.2 3801.6 18.3388 2688.65

Part 3 – Separately Excited DC Motor

Armature Resistance (Ra) = 5.1 Ω

Sample calculation (considering 1st entry)

Pin = V2.I2 = 208 x 1 = 208WCopper loss = I2

2 . Ra = 12.(5.1) = 5.1WMech. Loss = P2(0) = V2(0).I2(0) - I2

2(0).Ra = 210x0.5 – 0.52x5.1 = 103.725WPout = P2 – P2(0) = Mech. Power developed – Mech. Loss

= (Electrical power input – Armature copper loss) – Mech. Loss= (V2.I2 - I2

2 . Ra) - P2(0)= (208 – 5.1 – 103.725) W= 99.175 W

Observations CalculationsI2(A) V2(V) N(rpm) I2(0)(A) V2(0)(V) Pin(W) Copper

loss (W)Mechanical Loss (W)

Pout (W)

1 208 1500 0.5 210 208 5.1 103.725 99.1752 208 1486 0.5 210 416 20.4 103.725 291.8753 206 1478 0.5 210 618 45.9 103.725 468.3754 206 1468 0.5 210 824 81.6 103.725 638.6755 204 1462 0.5 210 1020 127.5 103.725 788.7756 204 1454 0.5 210 1224 183.6 103.725 936.6757 202 1448 0.5 210 1414 249.9 103.725 1060.3758 200 1440 0.5 210 1600 326.4 103.725 1169.8759 200 1432 0.5 210 1800 413.1 103.725 1283.175

10 198 1425 0.5 210 1980 510 103.725 1366.275

Results

(a) Speed Vs Torque

(b) Speed Vs Armature Current

(c) Pin Vs Pout

Discussion

(1).

In construction of motors, different materials are used for different application considering their electrical and mechanical properties for better performance motor configuration.

Stator –

Rotor –

Windings – copper wires

Commutators -

Brushes – Graphite,xx

(2).

A DC motor basically consists of Stator, Rotor, Commutator, Brushes (opt.) and Bearings. A brief description of each part is as belows.

And following figure gives a general idea about the construction.

(Fundamental parts of a direct current machine)

(http://www.delorenzogroup.com/dl/demo/DLelma/VirLab/A_teor_E/T_Con/Con_Gen.htm)

1 =  bearings         7 =  collector2 =  lifting eyebolt 8 =  stator3 =  bearings 9 =  brushes and brush holder4 =  shaft support flange 10= collector support flange5 =  ventilation turbine 11= cover

6 =  armature

Stator

tator stays still inside the motor while in operation. It supplies the electromagnetic field for the armature winding to exert a force on itself (armature wng) when a current passes.

Two types of stators,S

Permanent magnet Electromagnet (using a field winding)

As shown in figure, the winding is wound through the slots and thereby, magnetizing the pole shoes of the stator. Stator is constructed with the parts labeled in the figure.

(http://www.delorenzogroup.com/dl/demo/DLelma/VirLab/A_teor_E/T_Con/Con_Gen.htm)

Rotor

Rotor is the moving part of the motor. This consists of the armature winding which is wound around its slots. Usually the rotor is constructed by packing a set of laminations to minimize eddy current losses. And its shaft is mounted to the bearings of the motor.

As illustrated above the rotor arrangement is position in between of the stator pole (pole shoes).

A =  commutating pole       F =  armature conductorsB =  commutating winding G =  frame

C =  inductor coil H =  bar collector

D =  polar core I =  brushes and brush holder

E =  pole shoe L =  balancing conductors

Commutator and Brushes

Commutator is the collection of copper strips which distribute the supplied current among parallel armature winding paths.

Speed Vs Torque – DC series motor

Speed (rpm) Torque (Nm)1400 18.33881500 17.32011600 16.30151620 15.28321640 14.26421680 13.75321700 13.24451720 12.22581740 11.71601780 10.69731840 9.67761880 9.16881920 8.1502

Speed Vs Torque – Separately Excited DC motor

Speed (rpm) Torque (Nm)1500148614781468146214541448144014321425

Speed Vs Armature Current – DC series motor

Speed (rpm) Current (A)1400 19.21500 18.01600 17.21620 17.01640 16.61680 16.21700 15.81720 15.61740 15.41780 15.01840 14.61880 13.81920 13.2

Speed Vs Armature Current – Separately Excited DC motor

Speed (rpm) Torque (Nm)1500 11486 21478 31468 41462 51454 61448 71440 81432 91425 10

Input Power Vs Output Power – DC series motor

Pin (W) Pout (W)2666.4 1638.682787.6 1805.072934.6 1864.683030.0 1993.983110.8 2134.773151.2 2202.003191.6 2357.783272.4 2419.473353.2 2449.743434.0 2592.643440.0 2731.323600.0 2720.653801.6 2688.65

Input Power Vs Output Power – Sep. Exc. DC motor

Pin (W) Pout (W)208 99.175416 291.875618 468.375824 638.675

1020 788.7751224 936.6751414 1060.3751600 1169.8751800 1283.1751980 1366.275