1. WRITTEN-POLE
ELECTRIC MOTORS
Presented by:
Utkalika Sahoo (4th yr
Electrical Engg.)

2. CONTENTS
•INTRODUCTION
•DIFFERENCES
•LIMITATIONS OF CONVENTIONAL TECHNOLOGY
•WRITTEN-POLE TECHNOLOGY
•CONSTRUCTION
•OPERATION
•OPERATIONAL BENEFITS
•ADVANTAGES
•APPLICATIONS
•RECOGNITIONS
•CONCLUSION
•REFERENCES
WRITTEN POLE TECHNOLOGY
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3. INTRODUCTION
• In the 1990’s, a new concept was developed in electric
motors called the Written Pole® electric motor
• This new motor type dramatically reduces starting
currents of single phase motors
• The motor uses an innovative approach of controlling
the magnetic field of the motor to reduce the starting
current requirements
• The result is a motor that has starting current
requirements of only about twice the normal running
current and, as an added benefit
• The motors have efficiencies of 90% or better
compared to conventional motors, which have
efficiencies of around 85%
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4. BASIC
DIFFERENCES….
• Rotating field is developed.
• In a convectional motor poles are fixed.
• In a written pole motors a magnet layer is
written at different places on motor’s poles
as the rotor turns.
• Written pole has much lower starting
current than traditional motors prevents
voltage dips etc….
• Slow start up speeds prevents water
hammering.

5. LIMITATIONS OF
CONVENTIONAL TECHNOLOGY
1.Dependence of speed on no. of poles of
rotor
Speed = 120 X frequency
no. of poles
2.The machine must have even no. of poles
and deviating from this condition will cause
unstability at its rated speed
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6. AN INNOVATIVE PATENTED
TECHNOLOGY
• In the 1990’s, with support from the
EPRI, the Precise Power Corporation of
Bradenton, Florida, developed a new
concept in electric motors called the
Written Pole® electric motor.
WRITTEN POLE TECHNOLOGY
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7. WRITTEN-POLE
TECHNOLOGY
• The patented Written-Pole® Technology allows the
magnetic pole pattern on the magnet layer to be
changed to a desired pattern while the machine is
rotating and therefore breaks the relationship
between rotor speed and output frequency.
WRITTEN POLE TECHNOLOGY
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8. CONSTRUCTION
WRITTEN POLE TECHNOLOGY
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Contd…..

9. Contd……
• Written Pole motors use similar construction
techniques found in conventional motors
• A continuous layer of ferrite magnets on the
surface of the rotor, along with a highdensity exciter winding contained within the
stator winding
• The basic platform consists of a conventional
steel shaft inserted into a lamination stack
containing a high resistance rotor cage
WRITTEN POLE TECHNOLOGY
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Contd…

10. Contd……
• The high resistance cage is a key factor in
limiting the starting current of Written-Pole
motors
• The stator lamination stack is constructed
using low loss electrical steel laminations
• The concentrated excitation windings are
contained within the stator structure and are
located between the main stator windings
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11. Contd……

12. Contd…..
• The actual size and quantity of the poles
generated on the surface of the rotor
depends on the rotational speed of the
machine.
• Lower speeds result in a large number of
smaller poles with shorter spans while
higher speed results in a smaller number of
larger poles with longer spans.

13. Contd……
WRITTEN POLE TECHNOLOGY
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Contd…

14. OPERATION
• A written-pole motor employs one of three
modes of operation based on the rotational
speed of the machine:
1. START MODE
2. TRANSITION MODE
3. RUN MODE
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15. Contd…….
Start mode
• In start mode a written pole produces a
large amount of hysteresis and induction
torque which helps to accelerate the motor
to its rated speed.
• W.P.T. technology is able to produce
synchronous torque over a wide range
providing gentler ramp which protects the
load from mechanical damage.
• Lower starting current so lower temp. rise
permitting high freq. starts and restarts.

16. Contd…….
tranSition mode
• As the written pole motor accelerates it
enters into transition mode during which the
excitation voltage begins to influence the
magnetic geometry of the rotor.
• Electrical synchronization is achieve before
mechanical synchronization .
• Ability to start high inertia loads.
run mode
• Excitation not reqd., motor in normal mode.

17. OPERATIONAL
BENEFITS
Feature
Conventional
WP
Speed
3,560rpm
3600 rpm
Efficiency
85%
93%
Power factor
90.5%
100%
Full-load power
53kW
40kW
Full-load torque
73.7 ft-lb
73 ft-lb
Starting torque
88 ft-lb
82 ft-lb
Full-load current
219 amps
173 amps
Locked rotor current
1450 amps
312amps
Cost (p.u.)
1.0
1.2
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18. ADVANTAGES
1. Low starting current requirements
2. Energy efficient operation
3. Unity power factor operation
4. Simple construction
5. Low temperature rise
6. High inertia starting
7. Instantaneous restart capability
8. Ride through characteristics
9. Three-phase applications
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19. Contd……
• The Written-Pole motor is designed to
operate in ambient temperatures ranging
from 32ºF to 104ºF
• However, test results show that Written-Pole
motors
have
reliably
operated
in
temperatures ranging from 42ºF to 122ºF
• They may be operated safely in the open air if
there is adequate protection from direct rain
• The motor base must be mounted on a raised
concrete pad or steel frame to avoid exposure
to standing water
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20. A WRITTEN POLE RIDE
THROUGH MOTOR USED IN A
FARM
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21. APPLICATIONS
• In a family of single and three-phase motive
power and power protection systems used by
many customers including the US Weather
Service, NASA, Federal Aviation Authority, US
Air Force and many commercial and industrial
customers.
• Agriculture purpose in rural areas.
• Conveyor belt applications.
• To run a 3-phase generator.
• At oil well beam pump.
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22. RECOGNTION
• A recipient of the R&D 100 Award in 1994,
Written-Pole technology was recognized by
R&D Magazine as one of that year's most
technologically significant innovations
• The technology has also been recognized by
numerous technical organizations including
the Professional Society of Engineers in the
United States
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23. CONCLUSION
• The written-pole motor also has
performance advantages over a
conventional induction motor including
low starting current, very high operating
efficiency, and excellent power factor.
This motor technology has the additional
benefit of being able to ride through brief
service interruptions on single-phase
power lines. When compared to the total
system costs, written pole motors are an
attractive alternative to convention threephase induction motors.
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24. REFERENCES
• S.Hoffman, B.Banerjee and S.Samotyj
“written-Pole-Revolution”. IEEE Power Eng.
6-9,1997
• A.Hannah,”Electrical field measurements on
an EPRI two pole,20-hp .written pole motor.
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25. THANK
YOU!