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Workshop on Transportation systems

Technical Report

On

3-phase AC Motors for Traction Application

Jan-2015

Report No. TPTN/TR/001

Team Members:

1. Vikas Rawtiya Dy.Manager/TME 2. Subodh Prasad Sr.Engineer/DLW site 3. Abhideep Chowdhury Sr.Engineer/TSG 4. Rahul Singh Patel Sr.Engineer/CET 5. Raghuveer S Pathariya Sr.Engineer/CET 6. Ramakant Yadav Engineer/TSG

Bharat Heavy Electricals Ltd. Bhopal

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Content

1.0 Introduction

2.0 Literature survey 3 phase AC Motors for Traction Application

3.0 Current presence of BHEL in 3 phase AC Motors for Traction Application

4.0 Prospects for BHEL in 3 phase AC Motors for Traction Application

5.0 Roadmap for achieving the prospective business in Transportation system

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1.0 Introduction:

Traction motor is a vital component of transportation system. BHEL is manufacturing

various types of AC/DC traction machines for Diesel/Electric loco and DEMU/EMU

application. DC motors have been used for traction motors on railway vehicles for a

long time because of the ease of drive control and traction characteristics. After the

innovation of power electronics and computer control technologies, AC drive systems

with inverters and 3- phase AC motors became the standard traction drive system for

railway vehicles since they are easily maintained and high-performing asynchronous

motors. AC motors drastically reduced the weight of traction motors. For example, the

weight/power ratio of the asynchronous motor is almost 1/4 that of the DC motor.

Hence,now a day 3-phase AC motor is preferred for traction application.

2.0 Literature survey 3 phase AC Motors for Traction Application

DC motors with series field windings were the oldest type of traction motors. These

provided a speed-torque characteristic useful for propulsion, providing high torque at

lower speeds for acceleration of the vehicle, and declining torque as speed increased.

By arranging the field winding with multiple taps, the speed characteristic could be

varied, allowing relatively smooth operator control of acceleration. A further measure

of control was provided by using pairs of motors on a vehicle; for slow operation or

heavy loads, two motors could be run in series off the direct current supply. Where

higher speed was desired, the motors could be operated in parallel, making a higher

voltage available at each and so allowing higher speeds. Parts of a rail system might

use different voltages, with higher voltages in long runs between stations and lower

voltage near stations where slower operation would be useful.

AC induction motors and synchronous motors are simple and low maintenance, but

are awkward to apply for traction motors because of their fixed speed characteristic.

An AC induction motor only generates useful amounts of power over a narrow speed

range determined by its construction and the frequency of the AC power supply. The

advent of power semiconductors has made it possible to fit a variable frequency drive

on a locomotive; this allows a wide range of speeds, AC power transmission, and

rugged induction motors without wearing parts like brushes and commutators.

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Advantage of 3-phase induction motor over DC series motor

3-phase Induction motors are very robust and require little maintenance in absence

of brush-gear/commutator. Consequently reliability of a 3-phase locomotive is

higher.

No restriction on speed of motor in absence of commutators, AC traction motors

can easily operate at 4000 rpm in contrast to 2500 rpm in case of DC machines.

Power to weight ratio of induction motor is much higher than the DC motor.

The size of traction motor for the same output power is much less in case of a 3-

phase induction motor compared to DC motor. Therefore, with the permissible axle

load and available space in a bogie, realization of a much higher-powered loco

motive is possible.

Due to superior drop characteristics of speed Vs. torque and the fact that the motor

speed is limited by the synchronous speed, a much improved adhesion is available

in 3-phase locomotive and thus higher tractive efforts can be realized within

permissible axle load limits.

Due to lesser weight of the traction motors, the un-sprung masses in 3-phase

locomotive are low. This reduces track forces and consequently minimizes wear on

rails and disturbance to track geometry.

Latest technology in traction motors:

Permanent magnet motors:

The technology of traction electrical motors for train application has evolved from DC

motors to AC drives with both synchronous and induction motors in the last decades.

Three phase permanent-magnet (PM) synchronous motors are both smaller and

lighter than induction motors (IM) for a given torque with same cooling conditions.

However, this also implies new system challenges to be solved.

The significant advantages of PM motors compared to induction motors are:

Higher efficiency.

Higher specific power: 30% to 35% leading to 25% smaller or lighter motors for the same power rating

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Reduced need for rotor cooling since the rotor magnetization is provided by magnets

Potentially more reliable drives since the PM traction motor needs to be enclosed.

Regenerative braking is available down to really low speeds.

Some of main drawbacks of PM motor:

Due to limitations in the converter dimensioning, higher speeds can only be

reached by a controlled strategy called field-weakening since the magnets

produce a constant magnetization non-depending on the speed. The field-

weakening strategy involves higher copper losses in the stator winding to counter-

act the magnet field.

A major system aspect is that each PM motor requires its own converter due the

synchronization needed between the rotor position and the currents fed in the

windings.

The magnetic properties of permanent magnet material are temperature

dependent to such an extent that the temperature swing has to be monitored.

The material is also relatively delicate mechanically, which makes to

manufacturing more delicate.

Permanent magnets are susceptible to de-magnetization by too high temperature

and/or inverse magnetic field (possibly created by the stator windings).

Liner motor

The past, railway system is interest in the development of high speed train system

with speed up to 500 km/h. Wheeled vehicles and electric current collecting systems

have severe problems such as pantographs and third rails. To overcome these

problems, wheels can be eliminated by magnetic levitation and sliding contacts for

feeding power can be eliminated by replacing conduction with induction or radiation

at microwave frequencies, as the means for transferring electric power to the

vehicle. To achieving speed up to 500 km/h, vehicles are usually propelled by linear

synchronous motors (LSM) on the both sides of guide way with 3-phase armature

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windings and DC excitation coils wound around salient poles on the vehicle. LSM

does not use the mechanical coupling for the rectilinear movement, thus structure of

LSM is simple and robust as compared with the conventional rotary motor. LSM

system is also called as non-adhesion drive system, this non-adhesion drive system

has lots of advantages over the adhesion drive system as follows;

(1) Excellent acceleration and deceleration,

(2) Capability of climbing steep gradients,

(3) Less susceptibility to weather conditions,

(4) Quiet and smooth running.

Maglev

Maglev (derived from magnetic levitation) is a transport method that uses magnetic

levitation to move vehicles without touching the ground. With maglev, a vehicle

travels along a guideway using magnets to create both lift and propulsion, thereby

reducing friction and allowing higher speeds.

Maglev trains move more smoothly and more quietly than wheeled mass

transit systems. They are relatively unaffected by weather. The power needed for

levitation is typically not a large percentage of its overall energy consumption most

goes to overcome air resistance as with other high-speed transport. Maglev trains

hold the speed record for rail transportation.

Compared to conventional trains, differences in construction affect the economics of

maglev trains. For high-speed wheeled trains, wear and tear from friction along with

the "hammer effect" from wheels on rails accelerates equipment wear and prevents

higher speeds. Conversely, maglev systems have been much more expensive to

construct, offsetting lower maintenance costs.

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3.0 Current presence of BHEL in 3 phase AC Motors for Traction Application

Presently manufactured 3- phase AC motor for Traction application

Application Machine type Remarks

3-Ph traction motor for 6000 HP WAG9 AC Locomotive.

6FRA6068 Motor being manufactured through ToT document of CLW

3-Ph traction motor for 5400 HP WAP5 AC Locomotive

6FXA7059 Motor being manufactured through ToT document of CLW

3-Ph traction motor for 4500 HP DE Locomotive

IM4507 Motor developed after study of existing motor available for this application.

3-ph traction motor for Dual Voltage AC/DC EMUs

DMKT 53/42 Motor developed through ToT document of HOLEC.

3-ph traction motor for

25 KV AC EMU

IM3601 Motor developed inhouse with the help of corp. R &D.

Current presence of BHEL in transportation

6%

94%

Electric Loco

BHEL

Others

13%

87%

Diesel Loco

BHEL

Others

0%

100

%

Metro

BHEL

Others

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Market requirement of 3-ph motor for traction application and technological gap

Product Market requirement

BHEL Capability Technology gap

3-Ph traction motor for AC Locomotive application

Upto 1150 KW for 6000HP AC loco

1150 KW motor being manufactured through ToT document of CLW

No structured traction specific Design methodology / software available for developing suitable motors matching to control system.

BHEL needs the softwares for design of motor either with the help of Corp R & D or ToT.

3-Ph traction motor for DE Locomotive application

Upto 630 KW for 5500HP AC loco

Up to 425 KW motor developed after study of existing motor available for 4500 HP DE locomotive

3-ph traction motor for AC EMU /DEMU

300 KW AC motor for AC EMU

297 KW motor manufactured through ToT document of Holec

3-ph traction motor for metro application

100-200 kw motor as per metro requirements

Customer requirement is complete & proven system.

Only motor not required to customer.

Linear Induction/ synchronous Motor

Being used in Japan,China and Europe

NIL No capability available for designing suitable motor

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4.0 Prospects for BHEL in 3 phase AC Motors for Traction Application

Railways Vision 2020 envisages:

Gross revenue to grow from 1.2 % of GDP ( 90,000 Crs.) to 3 % of GDP (2,70,000 Crs.) -Total investment of Rs. 13,87,542 crore in ten years

Investment of Rs. 4,03,403 Cr by IR in next 10 years on manufacturing/ procurement of 5334 nos. of Diesel locos, 4281 nos. Electric locos, 50880 nos. passenger coaches EMU/DEMUs/MEMUs etc. and establishment of 2000 Kms of high speed corridors procurement through PPP projects & PUs.

Enhancement of freight share from 35 % to 50 % - Dedicated freight corridors on Western & Eastern routes.

Technology up gradation initiatives under implementations by Indian Railway in respect of IGBT Drives in Electric loco and Diesel loco in addition to AC EMU.

Stainless steel EMU with IGBT Drives also being contemplated. Heavier Axle load freight trains with higher capacity wagons being introduced for

exclusive freight Corridors requiring Higher HP Locos. Setting up of Metro development Authority in Indian Railways. A big thrust in urban metro business funding requirement revised from Rs. 57300

Cr. to 132600 Cr.

Business forecast:

250 279 247 221 200 205

711 734 824 867 8901330

428 452805

1070 1130

1598

250350

500

1500

2500

2500

490610

1120

1260

1500

1500

0

2000

4000

6000

8000

10000

12000

2012-13 2013-14 2014-15 2015-16 2016-17 2021-22

EPC/UT PROJ

FACTORIES

COACHES

LOCOS

GTO/IGBT

ELEC

CONV.

ELECTRICS

4918

3496

2425

6220

2129

10133

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Market scenario:

Railway ambitious outlay of Rs 50000 Crore for rolling stock in 11th plan.

Metro Projects for all major cities which are presently controlled by International

players. Thus there is a Large emerging market.

Requirement of locomotives for Freight Corridor.

Good scope exists for repair and rehabilitation business in DMW & Zonal Railways.

New emerging technologies like Permanent Magnet Motors, Linear Induction Motors,

Maglev, etc.

Huge market potential for EMD loco alternator & motor for supply to IR.

Repair and spare business for EMD loco Alternator and motor with sheds.

Loco production plan of DLW till 2020:

The above shows that there is huge market available for BHEL in rail transportation.

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5.0 Roadmap for achieving the prospective business in Transportation system

Currently Transportation business is addressed at either complete integration / broad integration as follows :

Coach / Loco / Metro, Bogie level and IGBT propulsion system

BHEL should develop capability to either integrate all the three broad levels or individual level as above so that BHEL can offer the desired solution in transportation system. Otherwise technology partner to be identified by BHEL for complete IGBT propulsion system through JV / ToT. To obtain prospective business in transportation, BHEL should develop capability to offer complete system rather than supply of individual component in transportation system.

Major issues:

3 Phase IGBT drives gaining popularity in EMUs and Locomotives. Due to non-availability of complete 3-phase IGBT based converter- inverter system issue of compatibility of Motors with Converter arises.

International players like SIEMENS, EMD, Bombardier are putting up their manufacturing plant in India for AC Traction Machines. They have a upper edge as they are offering complete System including Inverter.

Increased competition due to entry of local suppliers like Medha who are establishing manufacturing base for traction system in Technical collaboration with proven players.

Market competitiveness in terms of price, quality & delivery Chinese players are entering in Indian Market. Requirement of proven & complete systems/electrics by Railways.

Key success factor for 3-phase AC motor

Capability building in designing & manufacturing of 3-phase AC traction motor.

Up gradation of testing facilities of TXM &TAM. Creation of TEST faculties in CET to Address 3 phase business.

Enhancement of Spare business

Adherence to contractual delivery schedule.

Price competitiveness

Capability to offer System based solutions

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