UNIVERSITI TUNKU ABDUL RAHMAN Faculty
: Engineering and Science
Unit Cde :
Cur!e
:
Unit Title : Electrical Mac"ine!
Lecture gru#
:
E$#eri%ent : Lad te!t n DC !"unt %tr
Tutrial gru#
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Date Na%e :
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Student ID:
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UEEA()**: Electrical Mac"ine!
Lab-1
Load test on DC shunt motor
Table no. : --------
1
1
Lad te!t n DC !"unt %tr +,-ecti.e!
To understand the load characteristics of dc shunt motors. To understand the performance such as torque, speed, current and efficiency of dc shunt motors.
A##aratu!/%ac"ine! re0uired
Bac1grund t"ery A DC motor consists of a !tatr, a rtr, and other mechanical parts, such as the bearins, shaft, and the housin. The stator contains the field !indins "or permanent manets# that establish the manetic field. The rotor "also called as Ar%ature# is the rotatin part inside the stator. The rotor has its o!n !indins. A $oltae * A is induced in the armature due to the motion of its conductors relati$e to the manetic field. This $oltae is usually referred to as bac% emf and is i$en by *A
"1#
& �ffim
!here:
& is a machine constant that depends on the !indin and structural details of the motor,
� is the manetic flu' produced in the stator "(ebers#,
and ffi is the motor anular speed "rad)s# Another important relationship for the D.C. motors in$ol$es the terminal $oltae, the bac% *+ enerated by the rotation of the armature, the resistance of the armature circuit and the armature current. y &irchoffs /oltae La!, !e ha$e 0 A 2 * A "# /T m
A
!here: /T
is the terminal $oltae applied to the motor terminals, 0 A is the resistance of the armature circuit in ohms !hich, in the case of a series motor, includes the resistance of the series field coils and A is the current in the armature in amperes.
3 3
Combinin the t!o equations i$es: & �ffim 4 0 A A "3# /T 0e-arranin this equation i$es: / T 4 0 ffi
A
m
A
& �
"5#
The torque de$eloped by a D.C. motor can be calculated from the equation Tde$ & � "6#
A
!here:
Tde$ is the torque de$eloped by the motor "7m#, A is the current in the armature "A#.
or, in eneral,
8
9T 9T " 7m# 9 7 " pm# ;<.....(
ffi
:
r
1
t
=
;< 8
7
=
for output 1 load torque , t o
=
for mechanical torque , t m
=
8 out
8in
=
7
;< 8m
=
*fficiency , >
;< 8 o
=
7 ?
=
n a shunt motor, as the field !indins and the armature are in parallel connection, the armature current A is different from the field current . (hile the armature current A is dependent on the load, the field current is independent of the load conditions. As a result, the flu' for a shunt motor can be considered to remain constant. @ou !ill learn in theory that the field produced by the armature current in the armature conductors can affect the field strenth but the shunt field flu' can be considered to remain unaffected by the load. As the flu' for a shunt connected motor is independent of the armature current the only effect the load can ha$e on the speed is to increase the effect of the $oltae drop in the armature.
ne of the outcomes of this e'periment !ill be e'perimental proof of the cur$es sho!in the relationship bet!een speed, torque and current in D.C. shunt motors and an understandin of these cur$es and !hat they tell you about the motor. Comparin these cur$es for the $arious D.C. motor confiurations !ill help you select the correct motor for a i$en purpose.
2rcedure
1. Tabulate belo! the specifications of the i$en machine.
. i. 1 sho!s the connection diaram of the motor. *stablish the connections accordin to the diaram of i.1. 3. +a%e sure the startin resistance is at the +AB++ resistance position "(D+;-<#. 5. +a%e sure the field resistance is in the +7++ resistance position "(D+;-<3#. 3' T"e circuit cnnectin! are t ,e c"ec1ed ,y t"e la, !u#er.i!r'
;. Turn 7 the po!er s!itches of all modules "(+;-
11.
current 4l8! r9 a tr0ue 4 6'() 1g/% i! reac"ed' Read-u!t t"e .ltage t (66V "if required#. At each step record the speed, line current, field current and terminal $oltae. *nter the data into table 1. (hen data collection is completed, turn the control %nob of the electrodynamometer "(+;-15# slo!ly in CC( direction until it is fully CC( ITurnin the %nob too fast !ould cause the load to start roc%in, !hich is undesirableJ and then reduce the motor supply $oltae "po!er of (+;-
1. AdFust the %nob of (+;-< to +AB++ resistance position and the %nob of (+;-<3 to its +7++ resistance position. 13. !itch all rele$ant po!er supplies. 15. +easure the armature resistance "0 a# !ith a multimeter ohmmeter. Complete table-1. 16. 8lot the characteristic cur$es such as torque, speed, efficiency, input po!er and output po!er as a function of the load current "in a sinle raph sheet#.
i.1
0 a K 11.3E Voltag e V1[V]
Line curren t 11[A]
Field curren t 1F[A]
Speed N[rpm]
200 200 200 200 200 200 200 200
0.4 0.57 0.68 0.78 0.89 1.00 1.10 1.23
0.25 0.24 0.24 0.24 0.24 0.24 0.24 0.24
1498 1475 1463 1450 1432 1422 1406 1391
Arm. Torque T[kg/m] Curren t
1a[A]
<.<< <.<3 <.<; <.
0.15 0.33 0.44 0.54 0.65 0.76 0.86 0.99
Pin[W ] V111
Pd[W ] !"1a
!#cienc$
80 114 136 156 178 200 220 246
29.74 66.00 88.00 108.0 130.0 152.0 172.0 198.0
37.18 57.89 64.71 69.23 73.03 76.00 78.18 80.49
Table 1 Fr%ulae: T 7m = H.G ΞT% m a 1 4
,
8in
8
/1 1 *
=
d
b
a
"
/ 4 1
a 0 a #
a
Pd/Pin %
Pout[W ] TL
hm Pout/Pin %
0.00 0.00 45.43 39.85 90.12 66.27 133.98 85.88 176.42 99.11 218.99 109.4 259.83 118.1 299.90 121.9
8
Tffi T : 7
<
;<
ample Calculation T NM KH.G'< K< Nm I A=I L-I F
K<.5-<.6 K<.16 A P in=V l I l
K <<'<.5 KG
P d =E b I a
K"/1-a0 a#a K"<<-<.16'11.3E#'11.3E KH.E5w
8oKTw KT
200
<.5