DAR ES SALAAM INSTITUTE OF TECHNOLOGY
DEPARTMENT OF ELECTRICAL ENGINEERING
ORDINARY DIPLOMA OF ENGINEERING
FINAL PROJECT
TITLE:DESIGNING TEMPERATURE CONTROL CIRCUIT FOR OVER
HEATING OF MOTORS AT KIBO MATCH CAMPANY LTD.
PROJECT TYPE: PROBLEM SOLVING
NAME OF STUDENT: SILVANO .E.TONGENI
ADMISSION NO: 0803015178
SUPERVISOR: D.MSANGI
PROBLEM STATEMENT
Many industries use devices like circuit breaker, fuses
and over load relay are used to cut off the supply when
motor is over loaded and cause excess current which
lead to the burnt of the motor due to the raise of
temperature. Also sometimes means of indication lamp
or alarm are provided to indicate burnt motor and is not
indicating before the burn of the motor.
This problem is found at Kobo Match Company LTD
where many motor are burnt due to overheating of the
motor which lead to the cost of rewinding of motor .
PROJECT OBJECTIVES
Main objective
To increases the life of the motor.
Specific objective
To provide a temperature sensing mechanism
which will detect the motor temperature
incase of an over current and cut off the
supply before burning of the Motor.
To provide indicating lamp this will indicate
the abnormal temperature raise from the
motor.
METHODOLOGY
 Literature review
 Studying of the existing system
 Data collection
 Data analysis
 Designing of the proposed system
 Building the prototype
 Testing the proposed system
 Report writing
LITERATURE REVIEW
• Literature review is based on:
 Protection against overload
 Causes of overheating of electric motor
 Single phasing
 Classes of insulation used in electric motor
 Temperature sensors
PROTECTION AGAINST OVERLOADS USING THERMAL
OVERLOAD RELAY
•
These relays designed for use on AC or DC provide
thermal protection against small and sustained overloads
• Each overload relay contains three bimetal elements
consisting of invar and ferronickel having different
coefficient of expansion
• Each element is fitted with a winding connected in series
with each phase of the motor when current adapted to
exceed the rating current the elements are heated and
bends
• When an incident occur the current to the load increases
bending the element and actuating the differential device
whose lateral or vertical displacement depending on the
relay model rotates a cam or shaft connected to tripping
device
SINGLE PHASING
• Single phasing can occur because of a nonclosure of one pole of a three-phase contactor or
circuit breaker, a fuse failure or similar causes
• Single phasing causes the motor to develop
insufficient torque, leading to stalling, making the
motor to draw excessive current and finally lead
to burn out unless the controller cut the supply
CLASSES OF INSULATION USED IN ELECTRIC MOTORS
• Electrical motors may operate in continuous, short time and
intermittent duty. The value of maximum torque only apply to short
time duty.
• The rated torque at which a machine can operate in continuous duty
depend on limiting temperature specified for it’s winding insulation
because the heat buildup in the winding depends on the load current
squared, it is obvious that the rated power and current will be higher
for machine whose insulation has a higher limiting temperature.
• If the motor operated at the temperature exceeding that specified
the service life of its insulation and as a consequence of the motor
itself will cut down.
• In international practice the insulating materials used in electrical
motors are divided according to the limiting temperature into seven
(7) classes
CLASS Y
• Fibrous materials made from cellulose, cotton or silk, no materials.
• Their limiting temperature is 90˚C
CLASS A
• The same materials as in class Y but impregnated with or immersed
in a liquid electrical insulating materials.
• Their limiting temperature is 105˚C
CLASS E
• Some synthetic inorganic films
• Their limiting temperature is 120˚C
CLASS B
• Materials based on mica, bonded by an impregnated with organic
resins or varnishes.
• Their limiting temperature is 130˚C
CLASS F
• Inorganic materials fabricated from mica, glass fiber or asbestos in
combination with synthetic binders or fillers
• .Their limiting temperature is 155˚C
CLASS H
• The same materials as in class F, but in combination with silicone
binders and fillers.
• Their limiting temperature is 180˚C
CLASS C
Materials used are mica,porcelain,glass and quartz with inorganic
binders or without any their limiting temperature is 180 and above.
TEMPERATURE SENSORS
Sensor
Is
a device that is used to sense or detect any particular
change in quantity that is being measured and marks an
appropriate change in its output.
THERMISTOR.
• A thermistor is the type of resistor whose resistance
varies with temperature
TYPES THERMISTORS.
• Positive temperature coefficient (PTC) thermistor
• Negative temperature coefficient (NTC) thermistor
POSITIVE TEMPERATURE COEFFICIENT (PTC)
THERMISTOR
• This is the type of thermistor where the resistance increases
with increasing temperature. This is called positive
temperature coefficient because the coefficient of temperature
is positive
• Δ R=KΔT
• Where
• ΔR=change in resistance
• ΔT=change in temperature
• K= first order temperature coefficient of temperature
NEGATIVE TEMPERATURE COEFFICIENT (NTC)
THERMISTOR
• This is the type of thermistor in which the resistance
decreases with increasing in temperature. In this type the
temperature coefficient is negative.
RESISTANCE TEMPERATURE DETECTOR (RTDs)
• These monitor the temperature of the machine
winding, motor or load bearing they are usually
applied to large motors of 1500 PH and above
• The RTD is an excellent indicator of average winding
temperature, however it is influenced by ambient
temperature, ventilation condition and recent loading
history.
TYPES OF RESISTANCE TEMPERATURE
DETECTOR (RTDs)
• Platinum temperature range -270˚C to 1000˚C
• Nickel temperature range -200˚C to 430˚C
• Copper temperature range -200˚C to 260˚C
• Tungsten temperature range -270˚C to 1100˚C
• The resistance temperature detectors (RTDs) are
useful over large temperature range.
CAUSES OF OVER HEATING IN
ELECTRIC MOTOR
The following are the causes of overheating of
electric motor
• Overload
• Single phasing
• High ambient temperature under certain
condition
• Bearing failure
• Insulation failure
• Misalignment
BEARING FAILURE
• Bearing failure also cause motor
overheating due to friction where motor
draw high current to overcome that friction
in order to produce the required speed to
drive a certain load.
• When motor draw high current lead to the
increase of temperature in motor winding
which result to the burn of motor winding.
supply
BLOCK DIAGRAM OF EXISTING SYSTEM
Controller
Loading
motor
Over current,
Bearing failure,
Insulation
failure,
Aging,
misalignment
Motor over
heating
Motor
burning
Supply
PROPOSED BLOCK DIAGRAM
Motor
protected
Controller
TEMPERATURE
DETECTOR
DATA COLLECTION
•
•
•
•
•
•
•
•
Size of motor 15HP
Current of motor 29.4 A
Voltage of motor 380V
Class of insulation is class B
Limiting temperature of motor 130˚C
Ambient Temperature 30 ˚C
Frequency 50Hz
Speed 2800rpm
DATA ANALYSIS
NEGATIVE TEMPERATURE COEFFICIENT (NTC) THERMISTOR
R (T) = Rref (1-α∆T)
∆T=T-Tref
Relation between NTC and temperature
T=130°C
T ref=30°C
∆T =130°C-30°C
∆T=100°C
At 0°C ,R=165Ω
R30°C =165(1-0.0039(30°C- 0°C))
R30°C=145.7Ω
R130°C=145.7Ω(1-(0.0039(130°C-30°C))
R130°C=88.87Ω
TRANSISTOR
Transistor
operating voltage=12V
Resistance=380ᾨ
RELAY COIL CURRENT= supply voltage
Coil resistance
Relay coil current= 12/380
I=(max)=0.031578 A
Transistor = 2N222A
ᵦ =100( for silicon silicon)
From datasheet,
Ic=0.8A
IE=Ic/B
IE=0.016A
WHERE:
IE=emitter current
IC=collector current
B is constant
Sensor (type)
THERMISTOR
 Information from the data sheet per selected thermistor NTC are:
input voltage =12 DC
monitor operating temperature (30-130)°C
Input current operating =2A
RELAY RATING
1:Electroagnetic contact 6A240Vcoil voltage
Relay setting range 1.3-1.9 type TA25DV1.8 from data sheet per
selected relay.
RELAY RATING
1.Electromagnetic contact,6A240Vcoil voltage
2.Relay setting renge1.3-1.9 type TA25DV1.8 from
data sheet
PROPOSED CIRCUIT DIAGRAM
PRINCIPLE OPRATION
When short circuit or over current occurs in the main
winding circuit it cause heat or temperature to increase
and resistance.
When temperature increase up to 130°C the thermistor.
When the thermistor senses it send the feedback to the
relay and relay will make the contact so as to switch off
the control circuit.
CONCLUSION
• This project has successfully taken an idea of solving the
problem of overheating of electric motor at KIBO MATCH
COMPANY LTD. Most of the sufficient data needed for
the design of the system were successfully collected and
analyzed and the collected data lead to the design of the
system
. By concluding the proposed system has the following
advantages.
Proposed system will protect the electric motor against overheating whatever
caused by
Overload
Single phasing
Bearing looses its alignment
High ambient temperature under certain condition
Locking of the rotor
Also the proposed system will improve the production due to reduction of time
taken during rewinding process
Proposed system will reduce the breakdown time due to fact that when the
motor reaches beyond its rated temperature the system will open circuit and
protect motor against burning
RECOMENDATION
•
Due to difficulties met in order for this system to
succeed, precise values of the components are much
necessary to achieve accuracy of the system.
• Also due to the limitation of time and unavailability of
precise components it is recommended that for the
circuit to work as expected, the part which is not working
as required should be replaced by its equivalent rather
than the approach during the implementation of this
system.
REFERENCE
1. Y.G Paithankar& S.R Bhide, Fundamental of power
system Protection
• 2. V.S Popov & S. A Nikolaev, Basic Electricity and
Electronics Mir Publishers.Moscow
• 3. Website www. Chinaproduct.com
• 4. A text book of Electrical technology –BL Theraja &
A.K Theraja. (1997)
• 5. Practical Electronics Sensors Owen Bishop (1994)