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Introduction to WPM,Operation, Applications
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SEMINAR ON
WRITTEN-POLE ELECTRIC
MOTORS
UNDER THE GUIDANCE OF: PROF. MR. D.K. JOSHI
PRESENTED BY: NEHA RAJPUT, TE 1st SHIFT
CONTENTS
1. Introduction : 1. Motor classification
2. Limitation of conventional technology
1. About Written-pole motors
2. Characteristics
3. Construction
4. Modes of operation
5. Merits and Demerits
6. Application
7. Experimental test
8. Case Study
9. Conclusion
10. Reference
INTRODUCTION
Electrical motors are the backbone of the electrified society and are
responsible for 2/3rd of electrical energy generated.
Distribution system : 3 phase lines main feeders and heavily congested
areas and 1 phase lines laterals and rural areas.
Challenges faced in remote areas: higher cost for constructing 3 phase
service and low operating hours of loads.
Problem: motors have high starting current and motors of sizes greater than
15hp causes problem in the lines.
Hence the written pole motor, a new technology have been proposed which
eliminates the need of three phase power.
MOTOR FAMILY TREE
LIMITATION OF CONVENTIONAL
TECHNOLOGY
Draws excessive start-up current (inrush): 6-12 times their normal running
current during start-up .
Dependence of speed on no. of poles of rotor
speed = 120 X Frequency
No. of poles
Machine must have even no. of poles and deviating from this condition
will cause unstability at its rated speed.
ABOUT
Developed by the Precise Power Corporation of Bradenton, Florida with
the support from Electric Power Research Institute(EPRI).
Concept optimizes the magnetic geometry of rotor as operating speed of
machine varies.
It gets its name from a patented technology, which "writes" magnetic
poles on the rotor during start-up.
Available in sizes upto 100hp, and start and run without exceeding the
limits of distribution lines.
CHARACTERISTICS
Single-phase
Low starting current across-the-line
High efficiency
Reliable
Instant restart after momentary power interruption
Starts high inertia loads
Eliminates flicker & line sags
High power factor during start
High starting torque per amp
Simple design (No rotating windings)
Smooth (constant torque) start
CONSTRUCTION
ROTOR
Combination of induction, hysteresis and permanent magnet technology.
Made up of a high resistance rotor cageKey factor in limiting the
starting current of WPM and provides a considerable induction torque
during initial stage of starting.
It has a continuous layer of permanent magnetic ferrite material that covers
the rotor lamination stack.
CONTD…
STATOR
Similar to a typical induction motor.
The stator lamination stack is constructed using low loss electrical steel
laminations.
Windings are similar in design and function to those used in a conventional
induction or synchronous motor.
CONTD…
The unique feature:
EXCITATION WINDING
WPM makes use of a concentrated excitation winding located at one or
two points on the stator.
Contained within the stator structure and are located between the main
stator windings.
Designed to produce a magnetic field to fully magnetize the portion of the
rotor’s magnetic layer that is immediately across the air gap from it.
Responsible for maintaining the correct pole geometry in rotor.
MODES OF OPERATION
It employs one of the three modes of operation based on the rotational
speed of the machine:
START MODE
TRANSITION
MODE
RUN MODE
Start mode
Motor produces a large amount of hysteresis and induction torque which
helps to accelerate the motor to its rated speed.
Induction torque is produced in the machine by the rotating magnetic field
of the stator.
Hysteresis torque is developed
when the magnetic fields produced
by the stator current slightly
magnetize the ferrite material.
Transition mode
The excitation coil is turned on when the motor reaches 80%- 90% of
rated speed.
The powerful excitation coil starts writing poles to the ferrite layer as the
rotor rotates.
Magnetic layer can be magnetized into any desired configuration using
exciter winding while the motor is operating.
Fig. 1 shows motor is in normal mode of operation. As the excitation had
not been turned on, the motor is running as an induction motor.
Fig. 2 and 3 shows the poles are written into the magnetic layer in the
anticlockwise direction as the rotor rotates in the clockwise direction.
CONTD…
The size and no. of poles generated are dependent on the rotational speed
of the machine AND the frequency of signal given to exciter coil.
If the exciter has constant frequency then:
1. Lower speeds result in a larger number of smaller poles with shorter
spans.
2. Higher speeds result in a smaller number of larger poles with longer
spans.
Run mode
Excitation winding is turned off.
Magentic interlocking of rotor and stator poles takes place.
The motor starts running at synchronous speed until power is cut-off.
If excessive torque is applied, causing motor to pull out of synchronism, it re-enters the transition mode and re-accelerate back to synchronism.
OPERATION DURING POWER
INTERRUPTION
MERITS
1. LOW STARTING CURRENT
These motors have starting currents comparable to conventional type:
one-fourth their size.
Reduces voltage sags no need of complex starters installation.
CONTD…
2. ENERGY EEFICIENT, UNITY POWER FACTOR OPERATION
Reduces utility bills, while decreasing the electrical load on distribution
wiring, transformers, and starting contactors.
CONTD…
CONTD…
3. THREE-PHASE
PERFORMANCE
USING SINGLE-PHASE
POWER
WPM often go beyond 3-
phase performance
reducing starting current
requirements to levels below
that of 3-phase motors and
eliminates the need for
reactive power by unity
power factor operation.
OTHER MERITS AND DEMERITS
• MERITS
1. • 3-phase applications
2. • Simple construction
3. • Low temperature rise
4. • High inertia starting
5. • Instantaneous restart
capability
6. • Low operating cost
• DEMERITS
1. • Not a self-starting motor.
2.
• Doesn’t get activated until speed is brought upto 80% of its design speed.
3.
• Size is larger than a conventional motor of same hp
4.
• Start-up and shut-down characteristics of motor do not allow it to be utilized for rapid on and off operation.
5.
• Not a familiar technology: maintenance and repair work
APPLICATIONS
1. GRAIN CLEANING
McLeod Harvester is a new approach to harvesting cereal corps. One
component is a stationary yard plant separates high protein chaff from
grain.
It also contains a rolling mill cracking seeds contained in chaff
The plant is powered with a 30hp, 1800 rpm WPM which eliminates the
requirement of 3-phase power.
Benefits: efficient and clean form of power, gradual starting of motor
reduces wear and tear on mechanical components, long term reliability.
Other applications
2.POTATO IRRIGATION 3. LAKE AERATION
4. GRAIN HANDLING 5. OIL AND GAS PRODUCTION
EXPERIMENTAL TEST
A test was conducted by Fleming- Mason Energy Corporation in June,1995
on Sheltowee Trail Country Club’s golf course irrigation system.
The Phase converter and 3-phase motor:
30hp, 240V Static Phase Converter and a
30hp,continuous duty, 3530 rpm 3-phase motor.
The Written-pole motor:
1-phase,30hp, continuous duty, 3600 rpm motor.
Motor is a high inertia external rotor design and
with ride through capabilities.
Fig.15. shows comparisons of nameplate
ratings of the motors.
Operating Characteristics
When motors are used to operate on irrigation system, amount of heads
plays a major role.
Under light loads, motors not fully utilizing their HP ratings.
Running currents and PF vary with amount of water being pumped.
CONTD…
Operating Efficiency
With WPM: adequate pressure can be maintained with 19 heads open.
With 3-phase motor: 15 heads can be operated and pressure is maintained.
With same no.of heads opened to each motor, a 2-foot bigger diameter and
better spray pattern was obtained with WPM.
Sheltowee Trail’s Assessment:
Two operational problem faced with WPM:
1. Spot watering while operating with pressure control.
2. When temperature dropped below 55 degrees, motor would shut itself off
soon after startup.
CASE STUDY
PAT TRASK’S IRRIGATION:
Calculation of Pat Trask’s irrigation cost reduction after converting from
propane fueled engine to a 60 Hp 1-phase WPM on one field of 110 acres
of alfalfa.
With propane-fueled engine:
Total watering time per crop = 384 Hours
At a fuel cost/hr of $6.50 = $2,496 per Crop
With Written-Pole motor:
Total watering time per crop = 288 Hours
At an electricity cost/hr of $2.60 = $748 per Crop
In total, the Trask family pumped 2,300 hrs to irrigate about 275-300 acres
in 2003 at a consumption rate of 5 gals/hr of propane, costing $14,375.00.
Using the Written Pole motor to irrigate the same acres, the Trask’s total
kW bill was $3,350.00 – a savings of approximately 70%.
CONCLUSION
This unique product has applications virtually anywhere that 3-phase power is either not available, or is not economical to provide.
Has performance advantages over a conventional induction motor including low starting current, very high operating efficiency, and excellent power factor.
It has the additional benefit of being able to ride through brief service interruptions on 1-phase power
Its allows one to operate much more efficiently and at a lower starting current, offer a method for powering high horsepower applications where 1 phase power is available.
References
IEEE paper: “Written Pole Motors- A practical solution to
Large HP Motor Needs?” by David E. Smart.
IEEE Paper:” Applications, Test Data and Case histories of
Single-phase Written-pole motors” by Ronnie J. Barber and
Richard T. Morash
MERIDIUM POWER : SINGLE PHASE WRITTEN-POLE
MOTORS
PRECISE POWER CORPORATION: SINGLE PHASE WRITTEN-
POLE MOTOR