6. TYPES OF DC MOTORS
• DC motor are of 3 types they are…..
1. DC SHUNT MOTOR
2. DC SERIES MOTOR
3. DC COMPOUND MOTOR
7. 1. DCSHUNTMOTOR
Armature
• The parallel combination of two
windings is connected across a
common dc power supply.
• The resistance of shunt field
winding (Rsh) is always higher than
that is armature winding.
• This is because the number of turns
for the field winding is more than
that of armature winding.
8. We know, 𝑇 𝖺 ∅ 𝐼𝑎 N 𝖺 Eb/ ∅
N 𝖺 (Vt-IaRa)
And ∅ is constant here
So , 𝑇 𝖺 𝐼𝑎
9. • The field winding is connected in
series with the armature.
• The current passing through the
series winding is same as the
armature current .
• Therefore the series field winding
has fewer turns of thick wire than
the shunt field winding.
2. DCSERIES MOTOR
10. We know, 𝑇 𝖺 ∅ 𝐼𝑎
For Dc series motor
Ia=If=I
So , 𝑇 𝖺 𝐼𝑎
Again We know
𝐸𝑏=𝑁∅𝑍𝑃/𝐴60
N 𝖺 Eb/ ∅
So, N 𝖺 1/ ∅
N 𝖺 1/𝐼𝑎
𝑇 𝖺 ∅ 𝐼𝑎
N 𝖺 1/𝐼𝑎
12. a) CUMULATIVECOMPOUND DCMOTORS
• If the two field windings i.e.
series and shunt are
wounded in such a way that
the fluxes produced by
them add or assist each
other
b) DIFFERENTIALCOMPOUND DCMOTORS
• If the two field winding i.e. series and shunt
are wounded in such a way that the fluxes
produced by them always try to oppose and
try to cancel each other.
13. APPLICATIONSOFDCMOTORS
MOTORS.. APPLICATIONS…
D.C. SHUNT MOTOR
LATHES , FANS, PUMPS DISC AND BAND
SAW DRIVE REQUIRING MODERATE
TORQUES.
D.C. SERIES MOTOR ELECTRIC TRACTION, HIGH SPEED TOOLS
D.C. COMPOUND MOTOR
ROLLING MILLS AND OTHER LOADS
REQUIRING LARGE MOMENTARY TORQUES.
14. We know the Back Emf, Eb = PØNZ/60A
(where, P = no. of poles, Ø = flux/pole, N = speed in rpm, Z = no.
of armature conductors, A = parallel paths)
Eb can also be given as, Eb = V- IaRa
thus, from the above equations N = Eb 60A/PØZ
but, for a DC motor A, P and Z are constants
Therefore, N 𝖺K Eb/Ø (where, K=constant)
This shows the speed of a dc motor is directly proportional to the
back emf and inversely proportional to the flux per pole.
15. 1. Flux Control Method
To control the flux, a rheostat is
added in series with the field
winding, as shown in the circuit
diagram. Adding more resistance
in series with the field winding will
increase the speed as it decreases
the flux.
2. Armature Control Method
When the supply voltage V and the
armature
constant,
resistance
speed
Ra are kept
is directly
proportional to the armature current
Ia. Thus, if we add a resistance in
series with the armature, Ia decreases
and, hence, the speed also decreases.
16. 3. Voltage Control Method
a) Multiple voltage control:
In this method, the shunt field is connected to a fixed exciting voltage
and armature is supplied with different voltages. Voltage across
armature is changed with the help of a suitable switchgear.
b) Ward-Leonard System:
This system is used where very
sensitive speed control of motor is required
(e.g electric excavators, elevators etc.). The
arrangement of this system is as shown in
the figure at right.
M2 is the motor whose speed control is
required.
M1 may be any AC motor or DC motor with
constant speed.
G is a generator directly coupled to M1.
18. 2. Variable Resistance In Series With Armature
By introducing a resistance in series with the armature, voltage across
the armature can be reduced. And, hence, speed reduces in proportion
with it.
3. Series-Parallel Control
This system is widely used in electric traction, where two or more
mechanically coupled series motors are employed. For low speeds, the
motors are connected in series, and for higher speeds the motors are
connected in parallel.
When in series, the motors have the same current passing
through them, although voltage across each motor is divided. When in
parallel, the voltage across each motor is same although the current
gets divided.
19. BRAKING OF DC MOTOR
Basically, there are three types of electrical braking done in a DC Motor:
1. Regenerative Braking : It is a form of braking in which the kinetic
energy of the motor is returned to the power supply system. This
type of braking is possible when the driven load forces the motor to
run at a speed higher than its no-load speed with a constant
excitation.
The motor back emf Eb is greater than the supply voltage V, which
reverses the direction of the motor armature current. The motor
begins to operate as an electric generator.
It is very interesting to note that regenerative braking cannot be used to
stop a motor but to control its speed above the no-load speed of the
motor driving the descending loads.
20. 2. Dynamic Braking: It is also known as Rheostatic braking. In this type of
braking, the DC motor is disconnected from the supply and a braking
resistor Rb is immediately connected across the armature. The motor will
now work as a generator and produces the braking torque.
During electric braking when the motor works as a generator, the kinetic
energy stored in the rotating parts of the motor and a connected load is
converted into electrical energy. It is dissipated as heat in the braking
resistance Rb and armature circuit resistance Ra.
3. Plugging : It is also known as reverse current braking. The armature
terminals or supply polarity of a separately excited DC motor or shunt DC
motor when running are reversed. Therefore, the supply voltage V and
the induced voltage Eb i.e. back emf will act in the same direction. The
effective voltage across the armature will be V + Eb which is almost twice
the supply voltage.
21. Thus, the armature current is reversed and a high braking torque is
produced.
It is used in elevators, printing press etc.
22. TROUBLESHOOTING
IN DC MOTOR
Troubleshooting DC motors can involve identifying and diagnosing
various issues that might cause the motor to malfunction. Here are
some common problems and steps to troubleshoot them:
• Motor doesn't start:
Check the power supply and ensure it is delivering the correct
voltage to the motor.
Inspect the connections between the power supply, motor, and the
control circuit.
Verify that the motor's brushes and commutator (if present) are not
worn out or damaged.
Check for any blown fuses or tripped circuit breakers.
• Motor overheating:
Verify that the power supply voltage and current ratings match the
motor's specifications.
23. TROUBLESHOOTING IN
DC MOTOR
Check for mechanical issues such as binding, misalignment, or excessive
load on the motor.
Ensure proper ventilation around the motor to prevent overheating.
Reduce the duty cycle (on-off time ratio) if the motor is being operated
in short bursts.
• Motor is noisy or vibrates excessively:
Inspect the motor's shaft and bearings for misalignment, dirt, or
damage.
Tighten any loose screws or mounting hardware.
Check the balance of the motor's armature or rotor.
• Motor doesn't stop:
Ensure that the control circuit is functioning correctly and sending the
appropriate signals to stop the motor.
Check for any obstructions in the motor's mechanical system that
prevent it from coming to a stop.
24. TROUBLESHOOTING IN DC
MOTOR
Check for any obstructions in the motor's mechanical system that
prevent it from coming to a stop.
It's essential to follow proper safety precautions when
troubleshooting DC motors, especially when dealing with electrical
components. If you are unsure or unable to diagnose the issue,
consider seeking assistance from a qualified electrician or motor
technician.
25. APPLICATIONS OF DC MOTOR IN EVs
DC motors are not commonly used in mainstream automobiles for
propulsion due to certain limitations. However, they still find limited
applications in specific automotive systems. Here are some areas where
DC motors have been historically used in automobiles:
• Electric Cars (Early EVs):In the early days of electric vehicles, DC
motors were commonly used due to their simplicity and ease of
control. They were suitable for converting battery power directly into
mechanical power for propulsion.
• Electric Scooters and Bikes:Some electric scooters and bikes have
utilized DC motors for their propulsion. These vehicles often require
lower power output and can benefit from the simplicity of DC motor
control systems.
26. APPLICATIONS OF DC MOTOR IN EVs
Electric Boats: In certain electric boats and marine applications, DC
motors were used to provide propulsion. However, modern marine
electric propulsion systems have shifted towards more efficient
alternatives like AC motors.
It's essential to recognize that with advancements in motor technology
and power electronics, newer EVs are primarily using AC induction
motors or PMSMs. These motor types offer higher efficiency, better
power-to-weight ratios, and smoother control characteristics compared
to traditional DC motors. Additionally, the use of sophisticated motor
controllers and inverters further improves the overall performance and
efficiency of modern electric vehicles.
