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