CHAPTER III

GENERAL DESCRIPTION OF ELECTRIC ROLLING STOCK


10300 Classification of Electric Rolling Stock

Locomotives and Multiple Unit stocks are classified by means of a three/four letter code followed by a number to indicate the individual class and a series of the same.

The code letters used for ac locos and EMUs are given below : The first letter denotes the Gauge: 'W for BG and 'Y' for MG.

The second (middle) letters 'A' denotes the system of power supply for which it is suitable - A for ac & C for dc, CA for dc & ac.

The third letter for locos indicates the class of service -

'M' for Mixed traffic locos suitable for both passenger and freight services,

'G' for Freight (Goods) service locos,

'P' for Passenger services locos, and

'S' for Shunting locos.

Multiple Unit Stock is denoted by the letter 'U'.

The various classes of ac locos and EMUs at present in service on Indian Railway are as under :-

(a) ac Locosó WAG1, WAG2. WAG3, WAG4, WAG5, WAG6, WAG7,

                    WAP1, WAP2, WAP3, WAM1, WAM2, WAM3, WAM4, YAM1.

(b) ac/dc Locosó WCAM1,

(c) ac EMUsó WAU1, WAU2, WAU3, WAU4, YAU.

In addition two types of BG dc EMUs converted for ac working are in use on the Eastern Railway. Salient particulars of each type of ac and ac/dc electric locomotive are given in Table No. 3.01 & 3.02.

A set of plates containing coloured photographs of each type of ac/dc Electric Locomotives along with salient features are annexed with this chapter as a pull-out.

Salient particulars of each type of ac EMU are given in Table No. 3.03.

A set of plates containing coloured photographs of each type of ac EMUs along with salient features are attached with this chapter as a pull-out.

10301 Important Equipment of Electric Loco/EMU

1 Pantograph

1.1 For collecting power from 25 kV ac contact wire pantographs are mounted on the roof of the traction vehicles. AM 12 pantograph of Faively design has been adopted by Indian Railways for 25 kV ac electric locomotives and EMUs. These pantographs are provided with steel strips for current collection. The raising and lowering of the pantograph is by means of a pneumatically operated servo motor. This pantograph is a single pan design having two o-springs mounted on it. For keeping the pantograph in the lowered condition, main springs have been used. The suspension of pan is on plungers.

This pantograph is suitable for operation upto 140 km/h. For increasing the speed potential, improved pantograph with lower dynamic mass and independent pan heads have been used. Further, in order to improve the life of the contact wire, use of carbon strips has also been tried. Use of carbon strips for current collection has already been adopted in European countries.

1.2 Use of carbon strips necessitates change in the design of the pantograph; The pan head which is more or less rigid in case of steel strip pantograph needs to be made more flexible in the vertical, horizontal and transverse movement for carbon strip pantographs. This is achieved by improved suspension of the pan head. The speed potential of such a pantograph is of the order of 250 km/h.

The pantograph of this design have been imported from M/s Stemman, West Germany for WAG6A, from M/s SMC, Australia and M/s ETK, Austria for WAP1 and WAP3 locomotives.

2. Circuit Breaker

2.1 Since inception of 25 kV ac traction system, Air Blast Circuit Breakers manufactured by M/s Brown Boveri-Corporation were used on electric locomotives as well as on EMUs, and are still in use for about 30 years. These breakers are designed for isolation of power to the traction vehicle in the event of faults. The Air Blast Circuit Breaker needs great amount of maintenance due to inherent features like large number of parts (735 nos.), complex control block and extinguishing of arc during breaking of current in air. The life of the main contact on this account is also limited. This breaker also requires substantial amount of dry air for each switching operation.

2.2 Vacuum Circuit Breakers were introduced on electric locomotives on Indian Rlys. in the year 1985. The VCB is a simplified design with fewer number of parts (260 Nos.), have a simplified control block and self - contained interrupting medium, that is vacuum. Due to these features, the life of the main contact achievable is as high as 1 lakh electrical operations as against 20,000 operations for air blast circuit breakers. As a result, the periodicity of replacement of main contact is second POH for VCB and IOH for Air Blast Circuit Breakers. Besides, these factors, VCB also offers the advantages of reduced size, reduced weight and reduced maintenance cost as compared to these for air blast circuit breakers. The total trip-time for VCB is less than 60 milli-seconds while the same is of the order of 100 milli-seconds for air blast circuit breakers. The air blast circuit breaker is only capable of breaking the fault current with breaking capacity of 250 MVA. The VCB, besides having breaking capacity is also designed for making capacity of the same rating, i.e. 250 MVA and can handle the same level of fault current during closing also.

These circuit breakers (VCBs) were initially imported from M/s. GEC, U.K. and are presently being manufactured indigenously by GEC, Allahabad. The use of these breakers has been extended to EMUs also.

3. Transformer

3.1 Power to the traction vehicles is available at 25 kV ac single phase from the contact wire. In order to step down the voltage as well as to control the same for feeding to the traction motors, the traction power transformers are provided on the traction vehicles.

3.2 These transformers generally have a primary winding, a regulating winding, traction secondary windings and auxiliary windings. The regulating winding is designed for choosing appropriate voltage for the traction motors. The auxiliary winding is required for feeding the auxiliary motors on the locomotive.

3.3 In order to increase the h.p. of the locomotives, the traction transformers have been uprated from time to time keeping the overall dimensions unchanged on account of space constraint. The upratings have been achieved by using increased copper section of the conductor used, improved insulation scheme and in certain cases adoption of aluminium foil wound construction for minimising the losses.

3.4 The original imported transformer used in WAG1 locomotives had a capacity of 3000 kVA which was increased to 3460 kVA for WAG4, 3900 kVA for WAG-5/WAP1 and has been now further increased to 5400kVA for WAG-7 locomotives.

3.5 With the introduction of thyristorised converters, the design of the traction transformer has undergone simplification with the deletion of regulating winding. The transformer for thyristorised converter becomes a two limb construction and traction secondary winding split into 4 windings for two step sequence control.

3.6 The traction transformer necessarily has to have forced oil circulation and forced air cooling. For this purose oil pump, oil cooler and blower form an integral part of the traction transformer.

4. Tap Changer

4.1 On load tap changer Type No. 32 of M/s. Brown - Boveri Corporation has been used on most of the 25 kV ac electric locomotives. This type of Tap changer is provided on 25 kV (HT) regulating winding of locomotive transformer for controlling the voltage input to main transformer. The Tap Changer operates with the help of elaborate mechanism using an air driven Servo Motor (SMGR) and a bevel gear arrangement. Through precision adjustment and provision of transition resistance (RGR) it is ensured that there is no break of load current in-side the selector (GR) which is oil filled and the load current is broken by load switches known as CGR1, CGR2 and CGR3.

4.2 The on load tap changer presently used on electric locomotives for speed control requires great deal of maintenance on account of its inherent design and construction. Problems of flash over inside the selector and breakage of various components in SMGR and other sub-assemblies are some factors affecting to reliability of the locomotives. The development of thyristor converters for controlling the voltage input to traction motors was threfore undertaken for replacing the existing tap changer and silicon diode rectifier unit.

4.3 The thyristor converters for electric locomotives offer the advantage of maintenance reduction, smooth control of speed thereby improving the adhesion and permitting the realisation of higher tractive effort. Thyristorisation of locomotives type WAG1, WAM1, WAM2 and WAM3 is being indigenously done for realising the above benefits.

5. Traction Motor

5.1 In case of traction motor great emphasis is being given on improving power to weight ratio, keeping in view the limited space available on locomotive for mounting the same. There is continuous effort to improve the performance of traction motor by making them lighter/compact, at the same time more reliable. Indian Railways have been adopting the latest technology available for design and manufacture of traction motor. Over a period of years the traction motors have become now 2.5 times lighter specially for EMU application.

5.2 Improvements in the basic design of traction motor has become possible due to availability of new insulating materials with high thermal margins. Over the years not only new and superior materials have been developed but even the basic concepts have undergone radical changes. The method of classification of insulating material has also been changed and classification of material as generic type or chemical identity is not considered justified. With a view to classify the new insulating material correctly additional classifications are added.

5.3 Instead of dealing with individual insulating material, the specification now covers the combination and system as a whole. The new feature is added because of thermal endurance of the system which may not be directly related with thermal capability of individual materials.

5.4 The procedure for functional evaluation of insulation system also has been laid-down as per IEC 505 to evaluate the typical service life under functional test and the influence of thermal, electrical, mechanical and environmental stresses.

6. Amo Converter

6.1 Amo Converter is a special duty machine for conversion of single phase in-coming supply into 3 phase out- put supply. 3 phase supply is essentially required on most of the electrical locomotives for driving certain auxiliary equipment like blowers and compressors. The function of Amo Converter is to supply 3 phase power required for these auxiliaries.

6.2 Amo Converter of ACEC make initially imported for WAM-1/WAG-1/ WAG4 were of horizontal construction. Indigenously developed Amo Converter however is of vertical construction. The machine has mechanical construction suitable to withstand the severe vibrations encountered on locomotives. There was a provision on its top for mounting battery charger generator which has been eliminated in present Amo Converters.

6.3 The performance of indigenously manufactured Amo was not up to the level of the performance of ACEC make Amo converter, however, certain improvements like class 'F' insulation scheme, integral epoxy moulded terminal box and revised bearing scheme has led to significant improvements in reliability and performance of these Amo Converters.

6.4 As the Amo Converter offers an inherent voltage unbalance, Indian Railways are making an effort to develop suitable static converter for taking its place. Static converters are already available in imported WAG6A locomotive.

7. Motor Compressor Set

7.1 There are few locomotives equipped with imported compressor motor set from M/s. Oerlikon. Initially CLW had used motor compressor set developed and manufactured by M/s. Kirloskar Pnuematic Co. however, M/s. Elgi Equipment Ltd. have developed these motor compressors for electric locomotives and the same are being used for the last so many years by CLW. Efforts are being made by CLW vigorously for development of more sources for supply of compressors. The driving motor for the compressors have been developed indigenously by reputed motor manufacturer namely M/s. Siemens, M/s. NGEF M/s. ABB & M/s. Crompton Greaves Ltd.

7.2 Indigenously manufactured Air Compressor is a vertical cylinder air cooled machine. The compressor is directly driven through an extended crank shaft by an integral direct current motor or alternatively through a flexible coupling by 3 phase induction motor. The compressor is designed to supply compressed air to the associated equipment on 50% duty cycle in normal circumstances. It can be allowed to run continuously without causing any damage or undue wear.

7.3 The driving motor is high torque 3 phase induction motor designed for direct oh line starting. The earlier motor manufacture and supply were provided with class 'B' insulation scheme. The flexible complete assembly also incorporate the cooling fan for the compressor. With a view to improve the reliability of 3 phase induction motor certain basic design changes like 'F insulation, use of double glass cover conductor winding wire Vacuum pressure impregnation,, use of solventless varnish were adopted. The reliability of the auxilary motors have improved considerably due to these steps.

TABLE NO. 3.01 

Salient Data of Mixed/Passenger Electric Locomotives

TABLE NO. 3.02

 Salient Data of Goods Electric Locomotives

TABLE - 3.03 

Important Data of Electric Multiple Unit Stock