PPT - Characteristics Of DC Shunt Motors | Electrical Machines - Electrical Engineering (EE) PDF Download

 Page 1


SPEED CONTROL of SHUNT DC
MOTOR
Characteristics Of DC Shunt Motors
Page 2


SPEED CONTROL of SHUNT DC
MOTOR
Characteristics Of DC Shunt Motors
SPEED CONTROL of SHUNT DC
MOTOR
 Effect of Armature motor’s resistance speed control on a
shunt motor’s torque-speed
 Only used in applications in which:
- motor spends almost all its time operating at full speed or
- inexpensive to justify a better form of speed control
Page 3


SPEED CONTROL of SHUNT DC
MOTOR
Characteristics Of DC Shunt Motors
SPEED CONTROL of SHUNT DC
MOTOR
 Effect of Armature motor’s resistance speed control on a
shunt motor’s torque-speed
 Only used in applications in which:
- motor spends almost all its time operating at full speed or
- inexpensive to justify a better form of speed control
SPEED CONTROL of SHUNT DC
MOTOR
 In field resistance control, lower IF è higher its speed,
& higher IF causes a decrease in speed
 there is always a minimum achievable speed by IF
control
 Minimum speed occurs when IF has maximum
permissible value
 if motor operate at its rated terminal voltage, power, &
IF then it will be running at rated speed
 this is known also as  :  “base speed”
 to achieve a reduction in this speed by IF control,
require excessive IF that may burn up field windings
Page 4


SPEED CONTROL of SHUNT DC
MOTOR
Characteristics Of DC Shunt Motors
SPEED CONTROL of SHUNT DC
MOTOR
 Effect of Armature motor’s resistance speed control on a
shunt motor’s torque-speed
 Only used in applications in which:
- motor spends almost all its time operating at full speed or
- inexpensive to justify a better form of speed control
SPEED CONTROL of SHUNT DC
MOTOR
 In field resistance control, lower IF è higher its speed,
& higher IF causes a decrease in speed
 there is always a minimum achievable speed by IF
control
 Minimum speed occurs when IF has maximum
permissible value
 if motor operate at its rated terminal voltage, power, &
IF then it will be running at rated speed
 this is known also as  :  “base speed”
 to achieve a reduction in this speed by IF control,
require excessive IF that may burn up field windings
SPEED CONTROL of SHUNT DC
MOTOR
 In armature voltage control, lower armature voltage on
separately excited motor, reduce its speed & higher armature
voltage increase its speed
 There is a maximum achievable speed, in maximum
permissible armature voltage level
 Armature voltage control would require excessive armature
voltage, which may damage armature circuit
 Armature voltage control works well for speeds below base
speed & field current control works well for speeds above base
speed
 By combining two speed-control techniques in same motor, it is
possible to get a range of speed variations of up to 40 to 1 or
more
 Shunt & S.E. motors have excellent speed control
characteristics
Page 5


SPEED CONTROL of SHUNT DC
MOTOR
Characteristics Of DC Shunt Motors
SPEED CONTROL of SHUNT DC
MOTOR
 Effect of Armature motor’s resistance speed control on a
shunt motor’s torque-speed
 Only used in applications in which:
- motor spends almost all its time operating at full speed or
- inexpensive to justify a better form of speed control
SPEED CONTROL of SHUNT DC
MOTOR
 In field resistance control, lower IF è higher its speed,
& higher IF causes a decrease in speed
 there is always a minimum achievable speed by IF
control
 Minimum speed occurs when IF has maximum
permissible value
 if motor operate at its rated terminal voltage, power, &
IF then it will be running at rated speed
 this is known also as  :  “base speed”
 to achieve a reduction in this speed by IF control,
require excessive IF that may burn up field windings
SPEED CONTROL of SHUNT DC
MOTOR
 In armature voltage control, lower armature voltage on
separately excited motor, reduce its speed & higher armature
voltage increase its speed
 There is a maximum achievable speed, in maximum
permissible armature voltage level
 Armature voltage control would require excessive armature
voltage, which may damage armature circuit
 Armature voltage control works well for speeds below base
speed & field current control works well for speeds above base
speed
 By combining two speed-control techniques in same motor, it is
possible to get a range of speed variations of up to 40 to 1 or
more
 Shunt & S.E. motors have excellent speed control
characteristics
SPEED CONTROL of SHUNT DC
MOTOR
 There is significant difference in torque & power
limits on machine under two types of speed
control
 Limiting factor in either case is heating of
armature conductors, which places an upper
limit on magnitude of IA
 For armature voltage control, flux in motor is
constant, so maximum torque in motor is:
Tmax=K fIA,max
 maximum torque is constant, regardless of
speed