Indian Railways have 46,038 various types of coaches (excluding EMUs and MEMU coaches) and around 3000 of new coaches are being added annually to the system. There are two classes of the coaches called conventional and LHB being manufactured at ICF/Perambur and RCF/Kapurthala respectively.
There are three power supply systems as existing over Indian Railways to provide illumination, fan, air-conditioning and other miscellaneous needs of electricity for travelling passengers. These are
Self Generating (SG)
2×25 kW alternators for AC coach and 1×4.5 kW for non-AC coach is mounted underslung, driven by a pulley-belt arrangement when driving pulley is mounted on coach axle. Output is rectified and charges 110V DC battery for continuous power supply to AC and non-AC coaches. AC load of roof mounted packaged units is supplied by converting DC into 2×25 kVA inverters. This system is followed over trains having a combination of AC and non-AC coaches.
Two power cars each equipped with 2×750 kVA DG sets, one at each end of the train, supplies 3 phase power at 750 V AC power to each electrically interconnected air conditioned coach. The voltage is stepped down to 3 phase 400 V and supplied to standard voltage equipment on each coach. EOG system is followed for fully air conditioned train like Rajdhani, Shatabdi, Duranto, Garib Rath, Premium special trains. Import of LHB class of coaches from Germany is provided with the EOG system with a promise to provide SG system design for indigenous manufacturing. SG technology given was a complete failure and IR is still struggling to develop designs for the last 15 years.
Power is supplied from the train locomotive at the head of the train. The single phase 25 kV transformer of the electric locomotive is provided with hotel load winding which is converted to three phase AC at 750 V using 2×500 kVA inverter and supplied to the same system as that of EOG. In case of Diesel Locomotive, three phase alternator is mounted on the traction alternator and feeds the hotel load. This is the most efficient system as the cost of power is about 25% less as compared to EOG, but the system is still under development for the last 30 years. The other class of trains namely Electrical Multiple Unit and Main Line Electrical Multiple Units employs the same system for coach lighting. The system is similar to what is followed in train-set composition of train having a power unit at head as well as on tail and power the entire load of the coach for comfort.
Running of mixed LHB design AC and non-AC coach
There is a need for running a mix of AC and non-AC coaches with LHB coach design to improve passenger satisfactory, higher capacity and improved riding with less maintenance. RCF has already started manufacturing Non-AC LHB and 276 such coaches have gone into service till 31st March 2014 and working on Northern Railway, North Western Railway, Western Railway, East Central Railway and Eastern Railway. The only way to power these coaches is by EOG system as the SG design not yet successful. The electrical load of the train is about 250 kW and with a diversity factory of 80%, system loading will be around 200 kW for which the existing power cars is of over capacity.
Development history of SG AC LHB coach
For manufacturing of Non-AC LHB version, M/s LHB provided Indian Railways a design for driving the alternator with cardon shaft arrangement as per the terms and condition of the contract.
Cardon Shaft Arrangement
In this arrangement, 25KW alternator was of conventional type except belt transmission replaced with a cardon shaft which was driven by a gear box mounted on the axle. The alternator was mounted on the coach underframe to take care of space constraints in the bogie. This design was given by LHB to RCF as per the contractual condition. Based on this design, one rake was turned out to work in Shalimar rake (4545/4646). The rake turned out by RCF worked between NDLS & JAT for few days but design lapses surfaced out within a short period. The design lapse was non-damping of vibrations emerging from the track irregularities resulting failure on account of breakage of gear box & Cardon shaft, failures of fasteners provided for coupling of Cardon & gear box, shearing of flange for coupling, jamming of Cardon shaft arrangement, development of gap between torque limiter plates, breakage of gear box torque arm pin cap locking stud in Cardon shaft system and damage of fork arm bolt provided in Cardon shaft arrangement.
Failure Mode of Cardon Shaft arrangement
Alternator mounted directly on Mid Axle
RCF took initiative of developing of Permanent Magnet Alternator fitting the rotor directly on the axle of the wheel itself. The rotor consists of a solid core with embedded permanent magnets with no field windings. The stator is in two halves and provided on the axle with the help of split bearings on both sides of the alternator. The stator is held in position with a reaction rod, which is secured with the stator on one end and bogie on the other end. There is no belt drive in this system.
Constructional details of mid axle PM alternator
These type of alternators were developed by M/s Landert HMTD, Mumbai and 4 nos. of alternators with ERRUs were commissioned successfully on LHB SG ACCN coach nos. 05143 & 05146 and put on 06 to 08 months commercial trial in Shalimar Rake (4545/4646) ex. NDLS to JAT and with a lot of problems when put into service. Finally, the coaches were detached from the Shalimar Rake and sent back to RCF by Northern Railway. The defects observed were damage of bearings, grease leakage, damage/burning of stator windings & insulating material, breakage of terminal box, accumulation of copper dust and repeated control card failures in ERRU etc. Apart from above, M/s. Landert, Switzerland, who was the technical partner of M/s. HMTD, Mumbai did not technically supported M/s. HMTD. The most important issue of the design was that if the bearing fails, it results in immobilization of the coach, most severe condition of service failure and project failed.
Belt Driven Permanent Magnet Alternator
The existing Alternator used in conventional SG AC coaches cannot be fitted in the LHB-FIAT bogies due to space constraint in FIAT bogies. At this stage, Indian Railway was in look out for a smaller size alternator which can be fitted within the space available. It was well-known that the size reduces considerably with the use of a permanent magnet alternator and that gave the lead. Two numbers of belt driven 30 kW alternators with permanent magnet were developed and installed on a coach for trial. This design has been developed in close coördination of RCF, RDSO and M/s I.C.Electricals. This coach has been running in regular service since Nov. 2012 with satisfactory performance. The advantage with permanent magnet is due to reduction in the size of the rotor as it does not have winding to generate electric field, and therefore, a reduction in overall size, weight, efficiency, durability and you name the advantage, it is there. But the progress is slow for two reasons
- Only one source so far and unless there is a competition, the firm will jack up the price. Two more sources, namely HMTD and Signotron has been given dimensional fitment clearance by RDSO.
- Jacking up the price of permanent magnet in the international market by China finding the demand going up for its useful application in motors and alternators. Developers already finding difficulty in supplying the permanent magnet alternator at a reasonable cost.
- Permanent magnet alternator is going to be a major source of providing magnetic field in traction motor with the intention of reducing size and application in low floor height driving coach in metro rakes.
Financial Viability of different systems of power supply
- HOG system is considered to be the most economical for the reason the cost of generation is minimum, but the issue is that the head on locomotive is not wedded to the train. If for some reason, it is detached, there is no source of power, therefore, one power car has to remain in the system. There is one more angle to this, that if the power car become mechanically sick en route and detached then continuation of both the power cars justified even with HOG. This is the reason that there is not much enthusiasm for HOG.
- There is always debate about the economics of SG versus EOG and each group justifying in his own way. EOG favours all factors over SG, except two i.e. the earning capacity of the power car and loosing flexibility of interchangeability . For this, the initiative was taken to develop under slung mounted DG set, thus releasing the space for luggage. If this is done, all economics will shift towards to EOG system. As regards, flexibility of interchangeability, successful running of LHB coach train mix with AC and Non-AC on EOG has proved this wrong and is only a fear.
- The most important financial, practical and workable solution is to develop under slung mounted DG sets in two versions of 2×750 kW and 2×250 kW for fully AC and mix train of AC and non-AC coach . This will release 50% of the space presently used in the power car for DG set and power panels. The design of the power panel shall be so chosen to have the flexibility to draw power from HOG as well. The cost of electric energy through HOG will be much less as compared to EOG.
RDSO initiated the development process about 10 years ago, but not yet successful. This one development alone can change the complete scenario of power supply system benefitting Indian Railways in the following respect.
Energy Efficiency: The energy efficiency of SG system is very poor if the efficiency of the entire system of mechanical power generation at the train head to conversion into electrical is taken into account and works out to be around 50% as compared to 80% of EOG.
Capital and Maintenance Cost: The capital and maintenance cost of a large number of under slung mounted equipment such as alternator, pulley, belt, Electronic regulator, battery and invertor will get a go bye with the addition of maintenance cost of four numbers of DG sets and their panel. It is the total quantity of these items in SG coaches that makes the difference in all aspects of reliability and maintainability.
Indian Railway shall take up the project of development of under slung mounted DG sets power cars for EOG power supply system to help energy conservation, cost reduction, durability and maintainability.
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