In today’s world, life without electricity is unimaginable. From a small light bulb to large motors and for many other major purposes, electrical energy is the main source. As the importance of electricity in everyone’s life is increasing, it is in other way increasing the demand. As of 2016 May, 303GW is the installed capacity of utility sector in India. There is a shortage of 2.1% of total electricity in India. All this demand cannot be met alone by installing more generation. By reducing consumption, by reducing losses or by increasing private participation in energy generation, load on the utility can be decreased. By using regeneration, usage of renewable energy sources in the form of private power generation, cogeneration etc., power demand can be reduced. There is a scope for reduction of losses in many sectors, which use bulk electric supply. One such application of electric power is for batteries.
Fig 1: An Indian electric train…
Fig 2: Location of batteries in railway coaches…
In railways, batteries play a vital role. The battery used in railways is lead acid battery, which is the most popular rechargeable battery worldwide. Both the battery product and manufacture process are proven economical and reliable. These are specially designed for railway application to withstand deep cycling.
Railway batteries are typically used for rolling stock or stationary applications. Rolling stock batteries are used for locomotive starting, lighting, on board auxiliary system in engines and coaches. Stationary batteries are used as emergency backup power for railroad crossings, signal towers and signaling systems. Batteries are also used to provide illumination, fan, air conditioning, and other miscellaneous needs of electricity for travelling passengers. Hence, battery capacity, robustness, reliability and performance are important for their effective utilization. The batteries are received at railway workshop once in eighteen months to ensure the above said features. These features are ensured by conducting various tests. Discharge process which is one of the performance tests conducted on batteries to check its capacity and reliability.
In discharge test the batteries are charged and discharged for 3 cycles. Lead Acid battery uses constant current, constant voltage charge method. A regulated current raises the terminal voltage until the upper voltage limit is reached at which point current drops due to saturation. It is charged in three stages:
- Constant current charge
2. Topping charge
3. Float charge
Battery gets fully charged when current drops to a set low level. Batteries that are used in deep cycling mode can be charged up to 14.7V for a 12V battery to get the highest charge rate.
A discharge/charge cycle is commonly understood as the full discharge of a charged battery with subsequent recharge, but this is not always the case. Batteries are seldom fully discharged, and manufacturers often use the 80 percent Depth-of-Discharge (DoD) formula to rate a battery. This means that only 80 percent of the available energy is delivered and 20 percent remains in reserve.
Fig 3: Battery testing in railway workshop…
Fig 4: Control panel at railway workshop used for charging and discharging batteries…
Fig 5: Battery discharging through resistive load…
Block diagram of existing methodology :
In the existing system, during the testing of batteries for maintenance, the batteries are unloaded from the coaches and initially fully charged. The power required to charge the batteries is obtained from the grid. After charging them for 10 hours with constant value of current, batteries are discharged to a minimum level of 1.75 volts at constant current. Discharging is done through the resistive loads, i.e., dissipated through the resistors. This power is wasted and is not being utilized for any other purposes.
In the proposed methodology, various techniques are explained in which power can be conserved. The first technique is, using solar energy to charge the batteries. As it is the renewable energy, it is one of the ways of saving energy. Here battery 1 or battery 2 can be charged using the solar panel when the solar voltage falls below the set voltage automatically, it switches to the AC supply with help of the microcontroller and charges any one of the batteries. Here the switches S1 and S3 are closed. The second technique is charging a battery by the discharged power of another battery. In this technique, though the battery cannot be fully charged using another battery, remaining power can be taken from either solar or grid. Here the switches S1,S2,S3,S4 are operated. The third technique is pumping back the discharged power to the grid using synchronization technique. Microcontroller is used to control the switching operations. Keyboard and LCD display are used for better interaction of the operator with the system.
Fig. 7. Schematic diagram of the triple regenerative techniques…
Fig 8: Pilot model…
There are around 14,300 trains in INDIA and the no of batteries used in AC and NON-AC trains are 56 and 17 respectively per coach. Assuming the number of AC and NON-AC coaches in a train be 5 and 10, the capacity of the batteries used is calculated by assuming battery capacity to be minimum is 54,000Ah. Power required for one performance test is found to be 85536 kWh.
Hence for 14300 trains approximately 1.2231*e9 kwhr power can be saved.
Average commercial tariff per unit is Rs. 5.79/- and expecting a good rate as high as of 10 Rs / Unit depending upon the size of requirement by private participation. By adopting the above method, the approximate money that can be saved will be 700 crores for 18 months as the demand for installing new generating plants are also eliminated.
This Proposed method is successfully demonstrated using a pilot model:
Graph which represents the cost saving in the present and proposed method…
Graph which represents the power wasted in the present and proposed method…
Results of the triple regenerative techniques:
The results are tabulated as follows:
Future scope
This method can be adopted in all fields where batteries are used in bulk. For example, it can be implemented in KPTCL as 56 batteries are used in each substation. According to KPTCL annual report 2010-2011, there are 945 substations in Karnataka. Approximately 5 crore 82 lakhs can be saved by adopting this method in KPTCL. This proposed method is semi automatic. In future, this can be made fully automatic reducing the man power and reducing the maintenance cost. This proposed work promotes the private participation as the excess solar energy can be pumped back to the grid.
Conclusion
Regenerative techniques for Railway battery efficiency testing using solarenergy can be thus used to save a large amount of energy. Thus, using the green energy, energy can be conserved and regeneration of power adds to the amount of energy saved. Hence, electricity used and thus the cost can be minimized. Energy conservation is the foundation of energy independence as:
- Energy efficiency saves money.
• It improves the economy.
• It is environmental friendly.
• It improves national security.
• It upgrades and enhances quality of life.
This method can be adopted in all fields where batteries are used in bulk. For example, it can be implemented in KPTCL as 56 batteries are used in each substation. According to KPTCL annual report 2010-2011, there are 945 substations in Karnataka.
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