06-03-2013, 09:40 AM
Indian locomotive class WAP-7
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INTRODUCTION
WAP 7 is a high speed locomotive indigenously developed by Chittaranjan Locomotive Works. It is capable of hauling trains at speeds ranging between 140 and 160 km per hour and is now largely used by Northern Railways (NR), South Central Railways (SCR),Southern Railways (SR), Eastern Railways (ER), South East Central Railway (SECR),East Central Railways (ECR),Central Railways (CR), Western Central Railways (WCR).
Performance
With a maximum speed rating of 180 km/h (IR restricts it to 140 km/hr), the WAP-7 has the highest acceleration figures while hauling mail/express trains. The WAP-7 can also haul loads of 24-26 passenger coaches (1430-1550t) at 110+ km/h per hour. It is also known to haul 16 heavyweight Air Conditioned coaches (1120t) in 1:40 inclines single-handedly. At a trial conducted by Indian Railways, it clocked a speed of 177 km/h. It is the most successful passenger locomotive in the Indian Railways portfolio after the WAP-4. It is used to haul premium trains like the Rajdhani Express and the Shatabdi Express apart from other regular mail/express trains.[1] It also regularly hauls other trains like the H.Nizamuddin-Thiruvananthapuram, H.Nizamuddin-Chennai, H.Nizamuddin-Bangalore, New Delhi-Sealdah and the New Delhi - Mumbai Rajdhani Expresses and Nizamuddin-Ernakulam Duronto Express.
Currently a 7000 hp version codenamed WAP 7-D with IGBT traction is under development by Chittaranjan Locomotive Works.
The most unique feature of this locomotive is that it eliminates the need to have separate DG sets for air-conditioning in long distance trains hence providing huge savings on maintenance and running costs. This technology is called HOG or "Head On Generation" where the loco transfers electric power from its pantograph to the coaches.[2][3]
A 24-coach (1500t) passenger rake can be accelerated to 110 km/h in 240 seconds (over 4.7 km) by a WAP-7; to 120 km/h in 304 sec. (6.7 km); and to 130 km/h in 394 sec. (9.9 km).
Asynchronous Motor
Modern traction motor type using three phase AC electrical supply and now the favoured design for modern train traction systems. Can be used on DC and AC electrified railways with suitable control electronics and on diesel-electric locomotives.
Axle Brush
The means by which the power supply circuit is completed with the substation once power has been drawn on the locomotive. Current collected from the overhead line or third rail is returned via the axle brush and one of the running rails.
Battery
All trains are provided with a battery to provide start up current and for supplying essential circuits, such as emergency lighting, when the line supply fails. The battery is usually connected across the DC control supply circuit.
Bucholz Relay
A device inserted in the oil cooling circuits of electric locomotive transformers to detect low oil pressure. In this event the relay trips out the power system. Often a source of spurious circuit breaker trips if not carefully calibrated.
Camshaft
Most DC electric traction power circuits use a camshaft to open or close the contactors controlling the resistances of the traction motor power circuit. The camshaft is driven by an electric motor or pneumatic cylinder. The cams on the shaft are arranged to ensure that the contactors open and close in the correct sequence. It is controlled by commands from the driver's cab and regulated by the fall of current in the motor circuit as each section of resistance is cut out in steps. The sound of this camshaft stepping can be heard under many older (pre electronics) trains as they accelerate.
Chopper Control
A development in electric traction control which eliminates the need for power resistors by causing the voltage to the traction motors to be switched on and off (chopped) very rapidly during acceleration. It is accomplished by the use of thyristors and will give up to 20% improvement in efficiency over conventional resistance control.