The Indian locomotive class WAG-7 is a class of 25 kV AC electric locomotives that was developed in 1990 by Chittaranjan Locomotive Works for Indian Railways. The model name stands for broad gauge (W), alternating current (A), goods traffic (G) engine, 7th generation (7). They entered service in 1992. A total of 1970 WAG-7 were built at CLW and BHEL between 1990 and 2015, which made them the most numerous class of mainline electric locomotive till its successor the WAG-9.
wag 5 loco pdf 47
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The WAG-7 is one of the most successful locomotives of Indian Railways currently serving both freight and passenger trains for over 31 years. Even though with the advent of new 3-phase locomotives like WAG-9 and WAG-12, all WAG-7 locomotives except ones destroyed in accidents, are in service and doing all types of duties.
The history of WAG-7 begins in the early 1990s with the aim of addressing the shortcomings of the previous WAG-5 class and remove steam locomotives from IR by a target date of 1990.[3] The WAG-5 though were great successes, had become underpowered to meet the growing demands of the Indian Railways. So in early 1990s IR decided to look for a successor the WAG-5 class. The required specification was of a 5000 horsepower locomotive.
However, even before the WAG-7 another type of electric locomotive was imported from ASEA in 1988. This locomotive was classified as WAG-6A. However WAG-6As were not selected for mass production because emergence of 3 Phase AC locomotives.[5]
However apart from Traction Motors, many other motors and equipments are provided in electric locos. These motors are collectively known as the Auxiliaries. The aim of this article is to provide an insight into the various Auxiliary Machines provided in the Electric Locos operational on the Indian Railways.
But to understand the reasons why these auxiliaries are needed, it is necessary to understand the manner in which the electric locos operate. An important part of the electric loco is the Power Circuit. A short description of the power circuit of Electric Locos operational on the Indian Railways can be seen here. The article referred to describes the main components of the Power Circuit of the Electric Locomotive comprising of the following parts:
A common feature running through all the above electrical equipments is that all of these generate a lot of heat during their normal operation. Even when they are not in use, they might generate a nominal amount of heat. Normally any electrical equipment generates heat as by-product during operation. But traction vehicles tend to generate more heat than normal. This is because day-by-day the demand on traction vehicles is increasing. But an increase in the power output more or less translates into increased size of the relevent equipments too. But a major problem with traction vehicles is that you cannot increase their size beyond a certain limit. This is due to "Loading Guage Restrictions". Hence, the power output of the locomotives has to be increased indirectly without increasing their size. This is done by "pumping"more power through the equipments and cooling them at a suitable rate at the same time.
Hence the different auxiliaries provided for cooling and other purposes in these locos is described below. All the motors are of the AC 3 Phase squirrel cage induction type and require very little maintenance and are simple and robust. They are described with regard to their relationship to the major power equipments
A flow valve with an electrical contact is provided in the oil circulating pipe. As long as the oil is circulating properly, the contacts on the relay remain closed. However, in case the MPH fails or stops the relay contacts open which in turn trips master auxiliary protection relay Q-118. This trips the main circuit-breaker(DJ) of the loco. Thus the transformer is protected.
In WAM-4 locos only one MVSL blower is provided for the cooling of the Smoothing Reactors SL 1 & 2. However in WAG-5 and other locos two blowers namely MVSL 1&2 are provided for each of the SL's. Their running is "proved*"by the Q-118 relay.
In the course of normal operation the traction motors also generate a lot of heat. This heat is dissipated by two blowers namely MVMT 1 & 2 which force air through a duct into the traction motors of Bogie-1 namely TM-1, TM-2, TM-3 and Bogie-2 namely TM-4, 5, 6 respectively. The traction motor cooling blowers require a large quantity of air which is taken from vents in the side-wall of the loco. Body-side filters are provided to minimise the ingress of dust into the loco. Their running is detected by Air-Flow sensing relay QVMT 1 & 2 (Pic-2) which in turn give there feed to the Q-118 relay.
Electric locos need compressed at a pressure ranging from 6 kg/cm2 to 10 kg/cm2. Compressed air is used for the loco's own air brake system as also for the train brakes, for raising the pantograph, for operating the power switchgear inside the loco such as the power contactors, change-over switches, windscreen wipers, sanders, etc.
In locos equipped to haul vacuum braked trains, two vacuum pumps are also provided of which at least one is running in normal service and sometimes both may have to be run if train brakes are required to be released in a hurry.
In locos equipped with internal dynamic braking resistances, MVRF blower is provided for cooling the resistances during braking. While all the Auxiliary machines run on the power supply provided by the Arno convertor / Static Convertor / Motor-Alternator set, the MVRF blower runs off the supply derived from the output of the Traction Motor itself and is connected in parallel to the Dynamic Braking Resistances.
These blowers(four in number)are provided in WCAM-1, WCAM-2, WCAM-3 locos and are used during DC line working to cool the Main Starting Resistances(MSR). The MSR is used for regulating the voltage supplied to the Traction Motors during DC line working and carry the whole current of the traction motors which results in a lot of heat generation which must be continously dissipated. The working of the MVMSR's is also proved by respective sensing relays(QVMSR's) of the diaphragm type which in turn are interlocked with the relay Q-118 in the manner described later in this article.
The auxiliary machines mentioned above are energised as per the requirements in the loco. Some of them are run continously while some may only be required intermittanly while in rare cases, some may not be required at all during the whole run of the loco. Also the working sequences of the same auxiliary machines may differ across different models of locomotives as also in different working environments. For the purpose of this article, I've described the switching sequences of the WAG-5 loco except for the case of dual power locos such as the WCAM-1, WCAM-2, WCAM-3 which will be described seperately.
Note: The control circuit of MVMSR has been modified in WCAM-1 locos and HVMSR switches have been removed.In case of failure of any MVMSR, the loco must be declared failed. However the same loco in this condition may be energized and run normally in AC line working.
Depending on the locomotive, power for the auxiliary machines is obtained through three different methods. A separate power supply arrangement is needed because the motors require three phase supply while the OHE supply is of the single phase type. So the main requirement of the power supply for the auxiliary machines is for a device which can convert single phase AC into three phase AC. It becomes a little more complicated for the dual power locomotives such as the WCAM-1, WCAM-2, WCAM-3.
This is a rotary convertor which has a combined set of windings and is used to convert the single phase supply from the Tertiary winding of the Loco transformer to Three-Phase AC which is fit for use by the various Auxiliary machines in the loco.
The Arno convertor suffers from various disadvantages chief of which is output voltage imbalance which can cause heating up of the auxiliary motors, varying output voltage because of the variations in OHE voltage, problems related to starting of the Arno, etc. To overcome these shortcomings and to improve loco reliability, the Indian Railways have started providing Static Invertor power supply for auxiliary machines in locomotives.
The MA set is used to generate power for the Auxiliary machines in both the AC as well as DC sections because the Arno cannot run in DC line supply. The MA set comprises of a DC motor coupled to an AC alternator by a mechanical coupling. When the loco is under AC line supply the DC motor of the MA Set is fed by the tertiary winding of the transformer via an auxiliary rectifier known as RSI-3. While running in DC line sections the DC motor of the MA Set is supplied directly by the OHE line supply. The switching between the AC and DC modes is determined automatically by the position of the Panto changeover switch ZPT which in turn determines the position of the Change-Over switches.
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