University of Bolton
School of Engineering - Electrical and Electronic
BEng (Hon’s) Electrical and Electronic Engineering
ELECTRICAL MACHINE CHARACTERISTICS ANALYSIS
(MOTORS USED IN WATER PUMPS)
NAME
STUDENT ID
: B M S P BANDARA
: 1913333
1. TYEPE OF MACHINE
In liquid transferring process water is main requirement of humans, animals. There for water transferring is most
importing factor. Nowadays electrical machines mostly used than engines because of reliability and efficiency. In
practical conditions there are both Direct Current and Alternating Current motors use for pumps. Mainly type of
motor depending on the power supply and the required capacity. DC current motors use in wide areas, which cannot
get an AC supply and those DC motors used for small capacity applications. In addition commonly DC motors using
with solar generating. When using DC supply we can see both brush less DC motors and brushes DC motors. When
using AC supply both induction motors and synchronous motors are used
AC motors
• Induction motors
§ Both single phase and three phases.
§ Used for small, medium capacity and high speed application
• Wound rotor motors
§ Ploy phases motor
§ Used for large capacity and high speed applications
• Synchronous motor
§ Used for extra large capacity and low speed applications
2. POWER, TORQUE AND SPEED CHARACTERISTIC
When we considering of power, torque and the speed of a motor all these factors are depending on the requirement of
consumer and the application. The power is the most important case of the motor and it can be depending on the
requirement. Although in the market place we can see different kind of pumps and there power will be depending of
application and consumer requirement.
If we have 3-phase supply we can choose 3-phase pump at some value of power. But we need same value of power
using single-phase supply motor physical construction will be difference but same principle is used.
When we considering about power there will be many kind of motor design and capacities to facilitate our
requirement. But we need to select a pump using performance curve as shown in below.
Figure 1
Figure 2
As shown in above figures when we selecting a pump our entire requirement should be fulfilled with the performance
curves of a selected pump.
Example: - when we select a pump it has fulfilled our suction head requirement also required flow rate according to the
total head. Then we can get required out put.
According to the consumer requirement pumps can be different type in the market place
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3 phase induction motor pump (squirrel cage and wound rotor)
3 phase synchronous motor pump
Dc motor pump (brush less or shunt motors)
Single phase pumps (capacitor start/capacitor run)
When we using single phase pump all single-phase pump use capacitor for starting purpose although we need high
power using single-phase supply we use capacitor run single-phase motor to increase the power using single-phase
supply.
Also the torque is very important factor, which are hard to start like large type of pumps. If there is no necessary
torque produced by the motor it can damage the motor also low starting torque can be accepted for small pumps.
The speed of induction and synchronous motor depending on the construction and the supply. But we can control the
speed of those motors using power electronic devices such as VFD (variable frequency devices) . Although when using
DC motors we can adjust the speed using field supply and the series resistance.
3. PHYSICAL CONSTRUCTION
Induction motor pumps
Stator
Booth squirrel cage and the wound rotor induction motor has same construction of the stator.
Normally stator winding creates using insulated copper wires. Size of copper wire and turns per one slot depending on
the capacity of the motor
Rotor
Wound rotor with slip rings
squirrel cage
Normally wound rotor construction using copper cables to creates poles same as the stator in addition it has 3 slip
rings to access the rotor using external user. From that we can feed rotor using external supply and increase or reduce the
rotor resistance there for it cause to reduce inrush current. In addition we can control the speed and also we can use it to
produced high torque. So we can use this king of motor for high torque required application like large pumps.
Squirrel cage rotor has copper conductor bars as in the figure. We call it squirrel cage rotor because these this construction
like cage of squirrel. Use for low and medium capacity of pumps.
Synchronous pumps.
Stator
In the synchronous motor stator also the same construction such as induction motor.
Rotor
Rotor construction is different from induction motor. In synchronous motors rotor should be permanent magnet or a
permanent magnet create using external field. Most of application these motors driven using power electronic device and
control the synchronous speed and produced high power at starting there for these motors can use for high torque
application at low speed.
Dc motor pumps
Because of less maintenance brush less DC motors are commonly use. Most DC motors use with solar supply systems
In this brushless DC motors we can see the both inner and outer armatures in construction although same principle is used.
As an example computer cooling fans has out armature.
4. STARTING
Starting of motor mainly decide on starting current because of high starting current directly affect for the main supply to
make a voltage drop. Therefore supply providers adding maximum demand meters and calculate the tariff because of that
those consumers have to pay more electricity bill. To reduce the bill and facilitate IEE wiring regulation starting methods
are use to start the motors.
1. Direct on load- (up to 5HP) no starting method is used load directly connected to the supply (domestic water pumps)
2. Star- delta starting- (up to 50HP) motor starting on star connection and after reach 80% of speed connected to delta
3.Autotransformer – using tap changing transformer an supply variable voltage at starting after motor reach 80% of rated
speed it connected to delta
4. Series resistor – same as previous method variable voltage obtain using resistors.
5. Soft starter – using power electronic device and get highest smoothing start (motor drawn lowest inrush current)
5. BRAKING
Normally breaking is not using on water pumps.
6. COOLING METHODS & INSULATION
Normally when we use domestic pumps we do not think about the cooling method because they have in build rotor shaft
connected cooling fan and they are do not rung very long time. Although pumps are using for industrial purposes we should
consider about the cooling method and the insulation because over heating the machine caused to reduce the efficiency and
it can be damage the insulation of windings. According to the size and the duty cycle of the pump we can see some cooling
methods are used and according to the heat produce on the motor several insulation classes are categories.
In water pumping we can see 3 kind of cooling methods
• Integrated cooling (motor dip on the water and produced heat absorb by surround water)
• Internal cooling (some liquid circulating line are made across the stator and supply the pumping liquid)
• External cooling (same principle as internal cooling but cooling liquid and external circulating method is added)
Insulation classes
According to the operation temperature suitable insulation material use for the manufacturing.
7.EFFICIENCY
Efficiency of an electric motor depends on
• Copper loss
• Core loss
• Power factor
• Operating temperature
• Stray loss
• Age of the motor
Copper loss and the core loss are increasing the raw materials and the quality of the manufacturing process. But power
factor also depending on the reactive power of the load. In this case we can see low value of power factor in single-phase
induction motor than 3-phase induction motor. Efficiency also depend on operating temperature because if there is error of
cooling method and the we did not consider about the duty cycle we can see less efficiency than rated value. Also
increasing the age of motor we cannot get same efficiency because when increasing lifetime bearings and the insulation
may be reduced. If we using brushes DC motor arc of the brushes also caused to reduced efficiency.
8. COST
Cost of a pump depending of several factors such as
• Brand name (manufacture)
• Life time
• Warranty and the guaranty
• Duty cycle
• Output power
Cost of a motor determine by the manufacture according to above mentions factor because a company withstand in market
place very long time they can sell their product easily. And if the capacity of the motor is high, cost of the motor also
increase. If there is a same size and same capacity motors they are not equal on cost because the quality of the product and
the brand name determine the cost. We can see and compare the difference cost in below figures
We can see the cost of above motors is not very close. Because the cost of an specific motor not only determine with the
capacity of the motors. Also the cost of motor determines several factor such as mentioned in above.
9. SPEED CONTROLLING TECHNIQUE
Induction motor pump
In speed controlling induction motors are used two methods
1 squirrel cage rotor – are used variable frequency drives
2 wound rotor/ slip rings – use control the rotor by adding resistors and feed the rotor using external supply.
Dc motors
1 shunt motors – control shunt file resistance and series armature resistance
2 brushless dc motors – control speed using power electronic device (PWM also used)
Speed controls of pumps not in commonly use. Speed controlling techniques are taking place in special cases such as water
treatment plants, solar panel water pumps and other flow rate control (farming) applications only. Although in our domestic
and small capacity of industrial pumps are not use speed control techniques.
References
• Human resource’s
• https://www.digikey.com/en/articles/techzone/2016/dec/how-to-power-and-control-brushless-dc-motors
• https://www.globalspec.com/learnmore/flow_control_flow_transfer/pumps/dc_pumps
• https://www.singersl.com/products/index.asp?PC=water_pumps
• https://www.electricaleasy.com/2014/02/synchronous-motor-construction-working.html