Heavy Haul Braking using Electronically-Controlled Pneumatic (ECP) brakes

GLOBAL demand for Australian coal and iron-ore is driving an expansion of heavy-haul railroading. Some of the heaviest trains in the world operate in extremely challenging conditions with consists of up to 240 wagons hauling iron-ore, magnetite and coal from the interior to ports on the coast. Australia's largest mining companies are equipping their new fleets with electronically-controlled pneumatic (ECP) brakes for increased safety and efficiency. The same is happening in Brazil and South Africa.

ECP braking requires a wire trainline to transmit electronic brake signals along the consist to apply brakes, rather than using air pressure changes in the brake pipe. Wagons receive the signal and brake simultaneously, rather than sequentially over a period of up to 2 minutes, as can be the case with pneumatically-controlled brakes. The result is more precise braking and train handling, reduced in-train forces, and shorter, faster stopping. Moreover, since the brake reservoirs are charged continually, the train can recover and get back to line speed very rapidly after a stop. Five heavy-haul railways - Fortescue Mining Group (FMG), BHP Billiton, Rio Tinto, Pacific National and Queensland Rail have adopted or are currently running ECP brakes in Australia.

 

The benefits of ECP brakes include reduced stopping time, shorter stopping distance, reduced wear on equipment, and quicker re-start after stopping. Results from real-world testing on both moderate and steep gradients, presented by Mr Jim Forrester of Norfolk Southern at the 2010 National Coal Transportation Operations and Maintenance Conference, showed significant improvements in all of these areas.

On moderate gradients, ECP-equipped trains ran at 10% higher speeds than non-ECP trains. Nonetheless, stopping distances were 404.8m on average, 36% less than a train equipped with conventional brakes. Stopping time was similarly shorter: 49 seconds versus 71 seconds. The trains resumed normal speed in 25% less time - a depleted tramline requires handbrakes to be set throughout the train while re-charging, and then released before the train is ready for movement.

 

Results were even better on steep gradients. From the same initial speed, the train stopped in 297.5m, 53% shorter than a conventional train. Stopping time was 46 seconds, versus 88 seconds for the conventionally-braked train. The ECP train resumed normal operating speeds much faster, in 2min 25s versus 1h 23min 33s for the conventional train, because the conventional train had to set its parking brakes while on a gradient.

A key benefit of the networking of the train is simplified diagnostics. The brakes on each wagon now report electronically to the locomotive, enabling in-cab reporting and troubleshooting rather than on-foot, wagon-by-wagon testing. NYAB has developed a Tramline Integrity Locomotive Test (Tilt) device which accesses the Tramline Communications Controller (TCC) diagnostics to make it easier to test trainline functions.

All of these elements are coming into play in Australia as more and more ECP-equipped trains come on line moving ore and coal from the mines to the ports, and out into the world market. South African and Brazilian railways are also taking part in the move to ECP braking. The early results reward the efforts to pioneer electronic braking to bring more and better information to the driver and more efficiency to the heavy-haul railway industry worldwide.

 

Rail Track Maintainance Prediction

In general, rail life is analysed segment-by-segment with each based on the optimum length required for effective analysis and specific track and traffic conditions. The segments are assumed to be homogeneous in that the rail life and certain key parameters will be the same for the entire segment. The rail fatigue life forecasting algorithm uses Weibull analysis techniques to predict defect growth rates and future defect levels. Studies have shown that rail develops fatigue defects as a function of the cumulative traffic that passes over it, in addition to factors such as axleload, wheel-rail contact, and rail metallurgy and cleanliness. The rate of defect formation and accumulation with traffic has been shown to follow a Weibull distribution, which is in the form of a logarithmic relationship. Thus, as the rail ages, the expected rate of defect occurrence increases significantly, corresponding to the logarithmic nature of the Weibull equation. Since complete fatigue and tonnage data is not always available, effective models, such as RailLife, employ a hierarchy of analysis approaches, which are directly related to the actual amount of available data. The output of the algorithms is an annual forecast of defect rate (defects/km/year) and cumulative defects for each segment, together with the forecast life of the rail. Rail life forecasts are based on user defined rail replacement criteria which are usually characterised by the number of defects, particularly fatigue related defects, which occur within a defined period of time, usually a year. This is the point at which it is most appropriate to replace the rail.

 

Rail grinding management software is used to manage the removal or control of rail surface defects and to maintain the rail profile, which in turn affects both rail fatigue and wear rates. Research has shown that rail grinding is extremely effective in reducing the rate of fatigue defect development and extending the rail life. Control of the wheel-rail interface through grinding has also been shown to be effective at reducing the rate of rail wear. Software tools are used to manage, plan, and monitor rail grinding and management of the rail profile. This includes comparison of actual and desired rail profile or template (Figure 3) and the development of a curve-by-curve grinding plan, which defines the number of grinding passes, pattern, and grinding speed.

 

Rating system for Safety Critical Systems based on various attributes such as Reliability, Availability, Maintainability, Etc...

We all know that Safety Critical systems are Categorized based on the Tolerable Hazard Rates (THR), which assigns them a safety integrity level (SIL). I think the next level of rating of these systems shall be based on the other attributes besides safety, since many products meet the SIL level but have different architectures and RAM data, this kind of rating will provide the vendors the comfort in choosing the right product for the environment they intend to deploy these systems. The main attributes that form as input to the rating criteria shall be:

1. System Architecture
2. Reliability
3. Availability
4. Maintainability
5. Historical Safety Record
6. System Complexity
7. Ease of Usage
8. Expandability of the system
9. Fault Tolerance
10. Cost
11. Cost of Maintenance Etc...

 

Railway Signalling using Wireless Sensor Networks

Railway Signalling is safety critical domain, where still traditional technology is in use. There are many reasons for using traditional technology; one of the main reasons being the proven Safety performance of the older systems (Relay Based). As the rail traffic is increasing and with higher speed of trains there is an acute need for modernization of Railway Signalling Technology. Even with the advent of Microprocessor based technology, the problems have not been solved. The current railway signalling technology involves huge amount of physical wiring used to receive inputs and drive outputs to the field functions, which is very difficult to maintain and up-gradation of this infrastructure is every signal engineer's nightmare. This paper proposes the use of Wireless sensor networks in Railway Signalling domain which combines the Ground base signalling and the On–Board Signalling using customized routing algorithm, which is suitable for high Speed Railway Traffic which reduces the physical wiring to the bare minimum by applying distributed architecture to the field functions which are connected by Wireless Network.

The most important part of the railways is to carry out operations like safe movement of trains, this is achieved by Signalling. The Railway signalling is governed by a concept called Interlocking. Many interlocking system still in use follow either relay based technology or the Microprocessor based technology called Electronic Interlocking System (EIS). Relay based systems are very huge in size and have cumbersome wiring to perform operations. The advent of Electronic Interlocking systems reduced the relays and wiring to some extent, but still uses traditional copper cabling to be connected to the field functions such as signals, Track Detection equipment, points (Switches). In modern signalling systems, the signal and switch status needs to be sent to the On-Board Computers in the locomotives, this involves traditional radios connected to the wayside field functions that communicate this information to the OBC. This involves laying out track loops or balises that send this information to the OBC, these loops are venerable to climatic conditions such as ballast resistance, water flooding during rains, etc. Due to the failsafe nature of these systems the cabling has to be redundant, this results in large maze of complex wiring that is very difficult to maintain and upgrade. There is need to upgrade the existing Railway Signalling Infrastructure and addition of new technologies like failsafe wireless communications which shall combine both the ground based signalling (Interlocking Systems) and the Locomotives (On Board Computers of the train) which directly leads to simple distributed architecture which are highly maintainable and easy to upgrade in future.

Safety Integrity Levels

Real Time Data Processing Techniques

Various Signal Processing Techniques are available for analysis of real time data relative to reference data:

 

Data Cluster method – This involves recording the characteristics of a parameter of a subsystem under different simulated conditions and then using this as a reference to validate the real time data. This method is different from template matching, since it not entirely based on matching the plotted characteristics.

 

Template matching – Entails comparing complete data sets with pre-recorded examples of data resulting from known fault conditions. The method can be used effectively in some circumstances, provided a representation of the data that produces good discrimination between pattern classes can be made. However, this requires a substantial amount of experimentation with different transformations of the data sets to find such distinctions, and would be a computationally intensive process.

 

Statistical and decision theoretic methods – Matches are made based on statistical features of the signal. For example, the mean and peak-to-peak value are evaluated for each vector, and plotted in feature space, whereby different patterns are distinguishable because they form clusters for each class that are located apart from the fully functioning case.

 

Structural or syntactic methods – Involves deconstructing a pattern or vector into structural components, to enable comparisons to be made on more simple, sub-segments of data rather than a complete vector. Mathematically, these methods are similar to fractal-based compression routines.

 

Principles of Train working and need for Signalling

All over the world Railway transportation is increasingly used, as this mode of transport is more energy efficient and environmentally friendly than road transportation. Trains move on steel rail tracks and wheels of the railway vehicle are also flanged Steel wheels. Hence least friction occurs at the point of contact between the track & wheels. Therefore trains carry more loads resulting in higher traffic capacity since trains move on specific tracks called rails, their path is to be fully guided and there is no arrangement of steering. Clear of obstruction as available with road transportation, so there is a need to provide control on the movement of trains in the form of Railway signals which indicate to the drivers to stop or move and also the speed at which they can pass a signal. Since the load carried by the trains and the speed which the trains can attain are high, they need more braking distance before coming to the stop from full speed. Without signal to be available on the route to constantly guide the driver accidents will take place due to collisions.

 

There are basically two purposes achieved by railway signalling.

1. To safety receive and dispatch trains at a station.

2. To control the movements of trains from one station to another after ensuring that the track on which this train will move to reach the next station is free from movement of another train either in the same or opposite direction. This Control is called block working. Preventing the movement from opposite direction is necessary in single line track as movements in both directions will be on the same track.

 

Apart from meeting the basic requirement of necessary safety in train operation, modern railway signalling plays an important role in determining the capacity of a section .The capacity decides the number of trains that can run on a single day. By proper signalling the capacity can be increased to a considerable extent without resorting to costlier alternatives.

THE COMPUTER BASED INTERLOCKING SYSTEM ARCHITECTURE

Generally following two types of redundancy techniques are used for achieving fail-safety

in the design of signaling systems:

Hardware Redundancy – In this case, more than one hardware modules of identical design with common software are used to carry out the safety functions and their outputs are continuously compared. The hardware units operate in tightly syncronised mode with comparison of outputs in every clock cycle. Due to the tight syncronisation, it is not possible to use diverse hardware or software. In this method, although random failures are taken care of, it is difficult to ensure detection of systematic failures due to use of identical hardware and software.

 

Software Redundancy – This approach uses a single hardware unit with diverse software. The two software modules are developed independently and generally utilize inverted data structures to take care of common mode failures. However, rigorous self check procedures are required to be adopted to compensate for use of a single Hardware unit.

 

Hybrid Model - The hardware units have been loosely synchronized where the units operate in alternate cycle and the outputs are compared after full operation of the two modules. Therefore, it is no more required to use identical hardware and software. Although the systems installed in the field utilize identical hardware and software, the architecture permits use of diverse hardware and software. Moreover, operation of the two units in alternate cycles permits use of common system bus and interface circuitry.

 There are two methods of programming the SSI for a particular station, namely – Geographical Programming & Free-wire Programming. Most of the SSI systems adopt geographical programming where Control Table of the station is fed to the SSI system. This gives great relief to the user as he is not required to make the circuit diagram, data for any station can be programmed very easily. However, this method does not provide flexibility in terms of change of interlocking practice or interlocking rules. Adoption of change in interlocking practice of a particular railway requires changes to be made in the executive software and entails revalidation of the software. On the other hand, Free-wire programming, which requires circuit diagram to be prepared for each station and programmed into the EPROM as Boolean expressions, provides total flexibility as any given circuit can be programmed without touching the executive software. The price, however, is to be paid in terms of preparation of circuit diagram for each station.