A case for Multi section digital Axle Counter (MSDAC) system in all applications over Indian Railways
1.???Background
Indian Railways (IR) has specified and approved multiple types of axle counters for various applications over the years. Existence of multiple specifications of axle counters can be traced back to technological developments over the years, starting with systems having discrete components like RDSO mark-1 & Mark-2 with "Single entry/ exit" and later on Universal Axle Counters (UAC- with "multi entry/ exit").
Next era in axle counter technology started with Single section digital axle counter ("SSDAC"). Subsequently, next generation of technology arrived with Multi section Digital Axle Counters ("MSDAC") via the cross-approval process. Furthermore, a variation of SSDAC with dual components was added in SSDAC specification itself and was called "High availability-SSDAC" or "HASSDAC". Over the time, all the SSDAC and HASSDAC suppliers in India have also developed and got approvals for their MSDAC systems.
Indian Railways has working installations of axle counters on all application types, i.e., station section (straight line, turnouts), and, block section (Block proving- also known as "BPAC", "Intermediate Block signalling with BPAC", "Level crossings" & "Automatic signalling"). All the above applications have working examples with most type of axle counters approved on IR.
Even though MSDAC is the predominant technology presently being used for most applications, but, usage of MSDAC in Block proving (BPAC) is slow and sporadic. This paper is an attempt to bust all myths and misconceptions related to BPAC and make a case for using MSDAC in BPAC applications due to significant benefits (lower Cost, faster deployment, higher personnel safety, ease of diagnostics & maintenance) that MSDAC brings for this application.
2. Related Provisions in Manuals and Specifications
Lets explore the provisions in Signal Engineering Manual (SEM) and RDSO specification for MSDAC system.
Signal engineering Manual 2021 stipulates the relevant guidelines, as below:
From above paras of SEM, it is evident that all type of axle counters can be used in all applications where a track circuits could be used. This provision is very clear and aligns with the world view on the subject.
Railways systems across the world (author has looked at UK and Australia specifications for axle counter applications) have defined a single specification for axle counter systems. This is due to the fact that SSDAC (Single section digital axle counter) is just a special configuration of MSDAC (multi-section digital axle counter).
Even RDSO specification for MSDAC "RDSO/SPN/176/2013" para 5.1.2 outlines a configuration of “Two detection points Single section: In straight line” as one of the various configurations of MSDAC system.
3. Why SSDAC (or HASSDAC) continue to exist ?
These systems continue to exist due to fact that SSDAC, being older technology, came to be used since much earlier and got embedded into technical schemes and tender schedules developed for Block proving applications (BPAC) by Railways.
These technical schemes and tender schedule are used repeatedly for subsequent tenders and projects for years and start getting treated as "Rules". In the process, Signalling "Principles" behind these rules get relegated to background. This conflict between rules and principles reminds me of my article published in 2016.
Additionally, procurement method of specifying separate schedules of supply and work leads to disadvantage for MSDAC. Instead, if an integrated schedule for the application (including all components like cables, location boxes and their installation) is given with supply of axle counters, then cost and other life cycle advantages of MSDAC far outweigh those of SSDAC (or HASSDAC) even for BPAC applications.
Change is taking place and various stakeholders of Indian Railways have started realizing the benefits of modern axle counters (MSDAC) and usage of MSDAC in all applications is increasing by day. There still exist few misconceptions related to use of MSDAC in BPAC applications. Rest of this article is devoted to topics relevant for BPAC applications while making a case for using MSDAC in BPAC.
4. Some basics of Block working
To start with, let’s review some of the signalling concepts for proper appreciation of rest of the discussion in this paper.
Block working: A system of operation by which it is ensured that only one train is occupying the block at a time. Before sending the next train in to the block, it is confirmed (using technical means or operational rules) that block is clear of any trains. There are various types of signalling arrangements for block working but the following two are more prevalent on Indian Railways:
Note: There is also a variation of absolute block working known as Intermediate Block signalling (IBS) and this is deployed to increase line capacity in absolute working system. In IBS system, a long block between two stations is split into two sections by providing an IB signal in the middle. The rear section is controlled by rear station itself using a train detection system like track circuit or axle counter. The section beyond IB signal is controlled by both stations through Line clear process associated with absolute block working (as explained in next section). The IB signal is also interlocked with block instrument of the station in rear.
5. Absolute Block Working
In this system of working, a train cannot enter the block unless line clear is obtained from the station in advance. The said line clear cannot be granted by station in advance unless following is conformed:
a. All reception signals have been put back to ‘ON’ behind the previous train
b. whole of the last preceding train has arrived complete
c. Line is clear up to home signal and an adequate distance beyond it
Condition ‘b’ pertains to complete arrival of the train, and this is ensured by providing an axle counter section between block section limits, i.e., at the foot of last stop signal (LSS) of station in rear and an adequate distance beyond home signal (also referred as FSS- First stop signal) of the station ahead. This way of proving complete arrival of last train is known as BPAC (block proving by axle counter) on Indian Railways.
Similarly, in IBS working the section between IB signal and home signal (an adequate distance beyond home signal) ahead is provided with an axle counter section for proving the complete arrival of train. This kind of arrangement of intermediate block signalling with block proving is known in short as “IBS with BPAC” for obvious reasons.
6.???Signalling arrangements related to "BPAC" & “IBS with BPAC”
In BPAC arrangement, one detection point of axle counting system is provided at the foot of last stop signal (LSS) of the station in rear and another detection point is provided an adequate distance beyond home signal (also known as first stop signal- FSS) of the station in advance.
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In case redundancy is required by the project (for high availability) two detection points each are provided at the two locations described above forming two parallel track sections for block proving of same section.
A typical block schematic of one of the lines of a double line block section is depicted below. For BPAC purposes, one detection point each is placed at points ‘X’ and ‘Y’ respectively thus forming a BPAC section XY that needs to be proved clear to ensure complete arrival of train.
This arrangement has been historically achieved using SSDAC (or HASSDAC) due to their early arrival on the BPAC scene and all tender schedules being geared towards specifying SSDAC (or HASSDAC).
However, if we take the total cost of BPAC project, including all cabling, erection of location boxes, termination of all cabling and related earthing (maintenance free) arrangements, it will be beneficial for railways to use MSDAC due to multiple additional advantages they offer for the Railways as proven in various railways that have already deployed BPAC applications using MSDAC.
Installation of SSDAC (or HASSDAC) at tunnels, cuttings & viaducts is highly difficult (at times not feasible) since they need erection of Full-size location boxes and large amount of cabling associated them. MSDAC systems do not need any signalling or power cables to the track side and MSDAC Evaluators are kept at relay room hence there is no need for installation of large size Location boxes at such sites with restricted spaces.
"IBS with BPAC"
IBS arrangements are depicted below in a scheme named “IBS with BPAC using MSDAC” issued by RDSO in 2008. As shown below in a diagram from referred scheme, Sections ‘N’ and ‘O’ are BPAC sections for two lines of a double line block section.
This arrangement of “IBS with BPAC” is operational for many years in hundreds of sections across Indian Railways using MSDAC. This clearly shows MSADC can always be used for BPAC application and any notion that "MSDAC can not be used in BPAC application" is completely misplaced and has no technical reasoning associated.
7.???Comparison of arrangements for BPAC using SSDAC vs MSDAC:
There is a perception that project cost of BPAC using MSDAC is higher but that is not true. When we take all the costs of additional elements (cabling /location boxes / and associated installation cost) required with SSDAC (or HA- SSDAC), we will discover that BPAC project with MSDAC comes out cheaper. This will be explained in detail in following sections.
a. BPAC using SSDAC ( or HA- SSDAC)
All electronics for SSADC (or High availability -SSDAC) including evaluation system is at trackside and thus needs following elements for each line of BPAC without redundancy.
This Means for a double line BPAC, we need 4 Nos of Location boxes, 3 km of signalling cable, 3 km of power cable, 3km of quad cable between station and location boxes near concerned signals. We will also need maintenance free earthing for electronics provided near the track. Please see following schematic depicting a typical BPAC installation showing cables and location boxes required when SSDAC (or HASSDAC) is used for BPAC.
Note: If we need to use redundancy (High availability- SSDAC) then signalling cabling necessarily must be doubled (6km of signalling cables) even if quad and power cables are shared.
b. BPAC using MSDAC
As shown in following schematic depicting a typical BPAC using MASDAC, all the signalling cables, power cables & large location boxes are completely eliminated.
As seen above, here is no need for power and signalling cables while using MSDAC for BPAC. Also, large location box is eliminated as Evaluator is housed indoors in a relay room. All the terminations, wiring, foundation and earthing related to Location boxes is also largely eliminated. This leads to significant cost reduction for the project by using MSDAC for BPAC. In addition, MSDAC based BPAC will provide benefits of reduced life cycle costs due to lesser components (lesser maintenance efforts) and lesser power consumption.
Topic of personal safety for staff working at site is also important here.?More components on trackside means frequent staff visits to trackside thus exposing them to risks associated with activities on trackside. When we use MSDAC for BPAC, components at site are significantly reduced thus reducing the risks to maintenance staff during life cycle of the equipment.
Summary of Benefits associated with MSDAC based BPAC application:
8.???Conclusions:
9. Recommendation
A guideline may be issued by relevant authorities of Indian Railways to clarify that MSDAC can also be considered in all projects and tenders where SSDAC (or HASSDAC) specification is referred due to aforementioned advantages and life cycle benefits to Railways emanating from usage of MSDAC.
This will even help suppliers of SSDAC/ HA-SSADC to choose from their alternative products that is best suited for the application since all SSDAC suppliers also have MSDAC systems approved by RDSO.??
Disclaimer: The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of any organization where author is currently associated or has been in the past.
Free Lancer - Information Technology Infrastructure
2 年Quite interesting and knowledge building
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2 年Very worthfull
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2 年Quite Insightful! Thanks for sharing.
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