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Sunday , 24 March 2024

Energy Cost in Metro Rail–Is it getting its due?

Simulation and Commitment of Maximum Energy Consumption

In order to calculate energy consumption, bidder will have to perform simulations of the energy consumption of the train, for one or several runs over a defined infrastructure, operational and environmental conditions. Infrastructure parameters for the selected route include alignment profile (distance, height, gradient), maximum speed profile along the selected route, curves locations and radii, tunnel numbers cross sections, length and location, nominal voltage and frequency, mean voltage at the feeding point (e.g. pantograph) during train operations and position and length of neutral section(s). The mean voltage can be obtained from simulation for new infrastructure or according to experience in existing networks. In order to furnish infrastructure data, two different types of service profiles may be chosen:

1. Individual service profiles based on data from a real railway line, normally one or several lines out of the railway network where the train will be operated.

2. Standardised, typical service profiles. The standard service profiles are characterised by definitions of standard values for the identical service types being typical – yet not real – of the type of railway service.

In case of MRTS system, it is advisable to go with the first approach. However, as experienced in various projects in India, in case of new metro system, the construction of all lines is not completed when the rolling stock is tested. In case of new rolling stock procurement for existing lines, testing on complete line or on all lines is not possible due to unavailability of line in view of ongoing operations. A representative line may be selected for which energy efficiency shall be maximised during simulation and verified during testing.

Bidders shall do the simulation based on the input data provided for infrastructure and operational characteristics. The bidder should maximise use of regenerative braking within the constraints of capability of brake, time table and safe train operation.

 

 

Measurement of Energy Consumption

Measurement of energy for verification of committed maximum energy consumption is difficult and complex. Measurement has to be done under the same conditions which were considered by the bidder while doing energy calculations. In real world, the alignment keeps on changing due to various social, economic and political reasons even after train tender is awarded. This poses a big risk, since whatever energy consumption was calculated by bidder is based on a particular alignment and if the alignment changes, the energy consumption shall also change and hence the committed energy consumption is no more valid. If the infrastructure parameter has changed between simulation and test, the bid phase and commissioning phase, the simulations shall be repeated before the tests. The simulations shall be done with the same train characteristics and same simulation software and algorithm as was used during bid phase. The tests results shall then be compared with the new simulated value. Similarly, temperature can not be controlled and maintained constant in large tunnel or viaduct over the complete alignment. Generally a temperature variation of up to 5oC is considered acceptable for traction energy. If temperature varies more, the simulations shall be repeated. The voltage is never constant over the complete length of the line. A variation of 3% of voltage is generally considered acceptable, otherwise simulation needs to be repeated. TecRec 100_001 published by UIC and UNIFE provides guidelines for measurement of electrical energy for rolling stock.

Penalty Imposition

Ankur Agarwal Senior Engineer Railway and Transit, AECOM

Since the committed maximum energy consumption is a major differentiating factor, the bidder may be tempted to provide low energy consumption in order to get the tender. To ensure that the customer got what was promised, there should be a deterrent specified clearly in tender requirements. The deterrent should dissuade bidder from making any false promises and prevent from submitting any low energy consumption figure which is not feasible or a design that is not available with the bidder. This can be achieved by specifying a penalty for not meeting the committed guaranteed energy consumption. The penalty should be commensurate with the loss incurred by the operating company on the extra energy cost over the defined life of the product for all trains supplied under the contract. The calculation for energy consumption should be clearly agreed with the selected bidder before signing the contract. The recent tenders for procurement of rolling stock tenders in India have started including energy cost as part of their tender evaluation before selecting the train supplier.

One must however realize this process is complex and can lead to litigations. The penalty is generally huge and hence the stakes are high. The measurement and verification can be performed only after the complete section has been built. The results depend on the environmental factors which are also difficult to control. The factor for variations to be compensated in the measured values should be specified in the Specifications.

Conclusion

The Life Cycle Cost is finally the actual cost paid by an operator. There is a tendency to take an easy way out by the operator to decide the bid based on the Acquisition Cost alone. This practise has been followed in most of the bids till date. Some of the recent bids have broken away from this tradition and started taking into account the operating costs as well.

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