30100 Evolution of Electrical Rolling Stock

1 Electrical Concept

1.1 The development of mercury are rectifier for rolling stock application, wherein the dc motor could be used for traction became a single major factor for large scale application of single phase 50 Hz 25 kV for mainline electrification. Hitherto the performance of ac traction motor in locomotive had always been considered inferior to its dc counterpart and ac traction was only a compromise solution to save on the cost of OHE. The use of rectifier on the locomotive on the other hand offered an alternative of a superior locomotive to a dc locomotive. Initially water cooled mercury are rectifiers known as Ignitrons, (ignited internally through an igniting electrode) were used. Indian Railways purchased two types of locomotives of this type (WAM-1 from Europe & WAM-2 from Japan). But they gave way to neater and more reliable solution of externally fired air coated rectifiers i.e. excitrons. Excitrons had the additional advantage of reversibility i.e. converting dc back to ac and could be utilized for regeneration to a limited extent. Indian Railways imported a few locomotive of this design from Europe (WAG-1) and a sizable fleet was assembled and manufactured at CLW as well. A few Japanese locomotives using silicon rectifier were also imported (WAG-2).

1.2 With the development of High Power Silicon Diode Devices the entire technological development of ac traction stock took a new turn and more powerful units of ac locomotives were conceived. The silicon diode is simple to maintain and is extremely reliable. At present bulk of the fleet of Indian Railways consists of such locomotives.

1.3 Both with mercury are and silicon rectifiers, the voltage control is achieved by an electro-pneumatically operated tap changer. In the locomotives the high tension tap changer has been utilized. Typical Power circuit diagrams of WAG-5 and WCAM-1 type locomotives are given in Fig. 1.01 and Fig. 1.02. On some of the WAG-1 and WAM-2 locomotives, silicon rectifier with tap changer control has been replaced by the phase angle controlled thyristor convertor.

1.4 MG locomotives: These locomotives of YAM-1 class (Japanese design) are in use in a single isolated section viz. MAS-Villupuram section. They employ silicon rectifiers for conversion. Salient data on electric locomotives is given in Annexure 1.01 /A.

1.5 EMU (Electrical Multiple Units) both on MG and BG employ Silicon rectifiers for conversion and LT tap changers are used for voltage control. Salient features of EMU are given in Annexure 1.01/B. Atypical power circuit diagram of EMU type WAU-4 is also given in Fig. 1.03. Phase angle controlled thyristor convertor has also been deployed on a few 25kV ac MG EMUs in place of silicon rectifier and LT tap changer on Southern Railway.

2.0 Sources of Electric Locos

2.1 Indian Railways imported 100 WAM-1 Bo-Bo locomotives from Europe/and 36 WAM-2 and 2 WAM-3 Bo-Bo locomotive from Japan. Subsequent to this, 42 B-B high adhesion (mono motor bogies) locomotives designated as WAG-1 were imported from Europe and 45 designated as WAG-2 from Japan. Ten WAG-3 locomotive o( B-B design of higher rating were imported from Europe.

Manufacture of WAG-1 type of locomotive was taken up in Chittaranjan Locomotive Works (CLW) and later on CLW switched over to the manufacture of WAG-4 type of locomotives. After completion of 186 WAG-4 locomotives, Indian Railways switched over to 6-axle locomotive of indigenous design and CLW have "manufactured a series of WAM-4 and WAG-5 locomotives. With a view to improving the performance of the locomotive, WAG-5 locomotives with minor variations to suit specific application were also manufactured and designated as WAG-5 with different suffixes.

2.2 Eighteen prototype 6000 HP thyristor control locomotives of 3 types designated as WAG-6A, B & C were imported, six from ASEA and twelve from Hitachi in 1988. A prototype locomotive of 5000 HP capacity with high adhesion bogies, designated as WAG-7 has been designed and manufactured by Chittaranjan Locomotive Works. A new prototype control is under development.

2.3 To meet the specific requirements of higher speeds for passenger services, CLW manufactured WAP type locomotive using Co-Co flexi-coil bogies to work upto a speed of 130 km/h designated as WAP-1. This loco has been further upgraded for speed potential of 140 km/h by providing improved version of indigenously designed bogies. This loco is designated as WAP-3. A few WAM-2 locomotives were fitted with modified drive and designated as WAP-2 locomotive.

2.4 A chart exhibiting the salient features of ac electric locomotives is enclosed as Annexure 1.01/B Sheet No. 1 & 2. Major dimensions of the various locos are shown in Annexure 1.02. Load tables for various locomotives are available at Annexure 1.03. Starting tractive effort is limited to 37.5t due to limitation of bridges on Indian Railways. Brief writeups on 6000 HP microprocessor controlled thyristor locomotives are given in Annexure 1.04 and 1.05. Functional description of main circuit of thyristor EMU is given in Annexure 1.06.

3.0 Mechanical Concepts

3.1 Four axle locomotives had the following types of drives:

i) WAM1 : cordon shaft drive

ii) WAM2 and WAM3 : WN coupling drive

iii) WAG (1,3 and 4) : coupled gear drive through cordon shaft monomotor bogie European design and also built at CLW.

iv) WAG2 : Monomotor bogie with flexible rubber couplings (quill drive) arrangement (Japanese Design)

3.2 The monomotor bogie locomotives had a starting tractive effort of just under 32 tonne with motor power of 790 HP per axle. Except for a few WAG1, WAG2 and WAG3 class locomotives the bulk of the series of WAG1 and WAG4 class were manufactured at Chittranjan Locomotive Works till early seventies. The performance of these locomotives was also not found to be adequate for meeting increased operating requirements.

3.3 WAM-4 and WAG-5 locomotives which were indigeneously manufactured used Co-Co, trimount bogies of ALCO design with axle hung nose-suspended traction motors. Same design of bogie was also used in dual voltage locomotives (WCAM-1). In WAG-6A & B locomotives, with a view to have a high tractive effort and high speeds (beyond 160 km/h), 6-axle locomotive having Bo-Bo-Bo arrangement was adopted. WAG-6A locomotive utilises ASEA hollow shaft drive system whereas WAG-6B locomotive uses WN coupling. In WAG-6 locomotives high, adhesion Co-Co bogies using unidirectional motor and secondary suspension arrangement was adopted. Indigenous bogies similar to those of WAG-6C locomotive will be used in the prototype WAG-7 & 8 locomotives.

3.4 In WAP-1 locomotives, flexicoil bogie modifying the existing WDM-1 (General Motor Design) has been used. WAP3 loco utilises an improved version of this bogie.