Açık hatla istasyon bölgelerinin hatada güvenli anklaşman tasarımı ve PLC de gerçeklenmesi
Fail-safe interlocking design of open line and station areas and implementation with PLC
Yazar: MUHAMMED İKBAL YILDIZ
Danışman: PROF. DR. MEHMET TURAN SÖYLEMEZ
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Raylı Sistemler Mühendisliği Ana Bilim Dalı / Raylı Sistemler Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Ulaşım = Transportation

Özet:
Raylı sistemlerin iki temel karakteristiği kendisi için fonksiyonel emniyet önlemleri almayı gerektirir. Bu iki temel özellikten ilki taşımacılığın bir kılavuza bağlı yapılmasıdır. Bu durumda diğer ulaşım modlarında olduğu gibi bir tehlike anında direksiyon veya dümen gibi bir ekipmanla manevra yapılma şansı yoktur. Ayrıca yüksek hızlarda veya makas bölgelerinde bu kılavuzdan çıkarak deray olma söz konusudur. Diğer özellik ise enerji verimliliği için ray üzerinde tekerleğin rahatlıkla yuvarlanabilmesi amacıyla tren ile yol arasında çelik tekerlek - çelik ray ortamıyla düşük sürtünme kuvvetinin sağlanmasıdır. Ancak trenlerin devasa kütleleriyle beraber bu durum göz önüne alındığında trenlerin, sürücünün görüş mesafesinden çok daha uzun frenleme mesafelerine sahip olmasıyla sonuçlanır. Dolayısıyla kılavuza bağımlı ilerleyiş ve uzun frenleme mesafesi bir tehlike durumunda çarpışma veya deray gibi sonucu felakete dönüşebilecek riskleri getirir. Bu tehlikelere karşı trenler demiryolu sinyalizasyon sistemleri ile korunur. 
Sinyalizasyon sistemlerinde trenin ilerleyeceği yol, makasın bulunduğu istasyon ve sayding bölgelerinde rota prensibiyle korunurken iki komşu istasyon arası açık hat denilen bölgede ise blok kontrol prensibiyle korunur. 
Sabit bloklu sinyalizasyon sistemlerinde demiryolu hattı birim zamanda sadece tek bir trene rezerve edilen blok kesimlerine ayrılır. Bu blok kesimlerine trenler ancak anklaşmandan hareket yetkisi alarak girebilirler. Anklaşman, ekipmanların uygunluğunu ve talep edilen blok kesimiyle çakışan bir hareket yetkisinin varlığını denetler. Uygunluk teyit edilirse sadece ilgili treni bu blok kesimine alan diğer trenleri almayacak şekilde lojik bir iç kilitleme yaparak trene bloğu rezerve eder. Blok kesiminin başında bulunan sinyal açılarak hareket yetkisi verilir ve trenin bloktaki hareketi boyunca izlenerek yönetilir. 
Sabit bloklu sinyalizasyon sistemlerinde kullanılan blok prensiplerinden merkezi otomatik blok kontrol sisteminde, blok kontrolörü ana anklaşmanın bir alt sistemi olarak çalışır. Bu sistemde anklaşman, istasyon bölgesinde rota prensibiyle, açık hatta da blok kontrol prensibiyle trenin ilerleyebileceği tüm güzergahlarda korunmuş yol formu oluşturur.
Literatürde sadece rota prensibi baz alınarak yapılan anklaşman tasarım çalışmalarına ek olarak bu tez çalışmasında sabit bloklu sinyalizasyon sistemleri için merkezi otomatik blok kontrol sisteminin fonksiyonel emniyet gerekliliklerini sağlayan bir emniyet kritik yazılım tasarlanıp geliştirilmesi amaçlanmıştır.
Merkezi otomatik blok kontrolörün, açık hat bloğu için gerekli fonksiyonel emniyeti sağlayacak yazılımı IEC 61508-3 ve EN 50128 standartlarına uygun V model yaklaşımıyla öncelikle sistem modüler bir yapıda alt fonksiyon bloklarına bölünerek alt sistemlerin fonksiyonel gereklilikleri belirlenmiştir. 

Modelleme yöntemi olarak, sabit bloklu sinyalizasyon sisteminin ayrık olay sistemlerine (AOS) benzer karakteristikleri olması ve IEC 61508-3 ve EN 50128 standartlarında tavsiye edilen modelleme metotlarından olması nedeniyle sonlu durum makineleri diğer bir adıyla durum geçiş diyagramları kullanılmıştır. 
Durum geçiş diyagramlarıyla elde edilen mantıksal eşitlikler literatürdeki çalışmalardan farklı olarak PLC (Programlanabilir Lojik Kontrolör) koduna SCL (Yapısal Kontrol Dili) diliyle dönüştürülmüştür. SCL, SIL 4 (Emniyet Bütünlük Seviyesi) için EN 50128 standardında kuvvetle tavsiye edilen PASCAL dili tabanlıdır. Ayrıca IEC 61131-3 standardında tanımlanan ST (Yapısal Metin) diline tekabül eden, yüksek seviyeli bir PLC dilidir.
Sonuç olarak bu tez çalışmasında, sabit bloklu sinyalizasyon sistemler için açık hatta ve komşu iki istasyonun birbirine bakan çıkış rotaları arasında hatada güvenli bir anklaşmanı sağlayan merkezi otomatik blok kontrolörü geliştirilmiştir. Bu şekilde takip ve yön koruma fonksiyonları sağlanarak tüm açık hat üzerinde korunan bir yol formu oluşturulmuştur. Blok kontrolörü durum geçiş diyagramlarıyla modellenip mantıksal eşitlikleri SCL dilinde PLC koduna dönüştürüldükten sonra Siemens TIA Portal ve PLCSIM programlarıyla simülasyonu yapılmıştır.

Abstract:
Railways have two decisive features which specify their safety requirements. The first of these is that trains are guided by rails; accordingly, derailment has to be prevented particularly along the non-continuous guideways like points. Second characteristic is that trains move by means of steel wheels along steel rails which give advantage for energy consumption thanks to low friction. But at the same time low friction and huge mass of trains end up with much longer braking distance than driver's sight. Thus, long braking distances decrease the ability of the driver to prevent collisions with other railway vehicles. Both in case of derailment and collision, driver has no means of evading dangers as he or she has in other transportation modes. When these dangers happen, they can lead to many deaths or serious injuries which are the most significant measures for safety critical systems. For these reasons, railways shall be protected against the similar aforementioned risks by railway signalization systems.
Railway signalization basically can be classified into moving and fixed block systems. Both of them ensure safe train seperation on railway lines with block sections where a train may enter into one block when it is not occupied by other railway vehicles. In moving block system, lengths of block sections are dynamically optimized according to braking distance of successive trains and line characteristics via RBC (Radio Block Center) and onboard. On the other hand fixed block system consists of block sections that have certain length of block section which is calculated by considering braking distance and headway. These fixed lengths are implemented with track circuits or axle counters. Border of sections are limited with signals. 
Core of railway signalization is an interlocking which ensures safe movements on the protected block sections. Upon the request from dispatcher or automatically if there is a train approaching, interlocking can give moving authority into the requested block section via signals in compliance with route principle which supervises whole process during train movement. Before giving authority, block section shall be free and there shall not be any existing conflicting movement authority. If movable track elements exist on block, shall be taken in proper position. After all equipments are proper then logically locks in itself which means block section is reserved for the train. Moving authority to block section is given by open signal and supervises until release by interlocking system.
On the other hand, open lines where main tracks outside the station areas are protected by block control systems. Regardless of moving or fixed block section, block control systems shall ensure protection against opposing and following movements. Type of block control systems can be verbal, semi automatic or automatic depending on what technology is used. 
Automatic block systems can be divided into two category as centralised and decentralised automatic block systems. In the centralised automatic block systems the block controller is a part of the interlocking which supervises the open lines with block principle and station areas with route principle.
In addition to existing literature studies on interlocking design which are just handle route principle, this thesis takes a step further concept of interlocking by ensuring protection on all tracks. For this reason block controller of centralised automatic block systems are developed.
In order to design a safety critical software like failsafe interlocking system, international standards like IEC 61508, EN 50126, EN 50128, EN 50129 shall be utilized. IEC 61508 is a generic standard for all system including electric, electronic and programmable electronics (E/E/PE) components with functional safety. EN (European Norm) 5012x family special for all railway system applications. EN 50126 defines RAMS (Reliability, Availability, Maintainability, Safety) to ensure safety in terms of system perspective. EN 50129 especially specifies SIL (Safety Integrity Level) according to tolerable hazard rate (THR) per function or hour. 
EN 50128 and IEC 61508-3 recommend the utilization of  V-model in the development safety critical software. This model determines steps which related each other in lifecycle of software. System is divided into subsystems for modular approach. Then functional requirements of subsystems are determined. Afterwards the subsystems are designed using formal or semi-formal methods such as finite state machines (FSM) / state transition diagrams  or Petri nets. Then logical expression of models are converted to programming code. Each phase is tested and if any problem is detected according to cycle returns to the corresponding step and revised.  
In this thesis study, design and implementation of centralised block controller software is developed in V-cycle approach according to EN 50128 and IEC 61508-3 standards. 
In the first chapter of the thesis, aim and structure are given in detail and also contribution of thesis to literature is discussed. Afterwards in the second chapter essential terms and equipments which used in fixed block signalling are explained. Interlocking principles which are route and block principles are explained. Especially block control principle is clarified in detail in the light of reference of number 3 and 4.
In this thesis study fixed block system is used because of common use and having DES-like (Discrete Event Systems) features. In the third chapter, design and implementation methods are explained. As a design method state transition diagrams which one of the semi-formal method of DES and highly recommanded in EN 50128 and IEC 61508-3 are used. 
Diversely, existing literature studies logical expressions of state transition diagrams are converted into PLC (Programmable Logic Control) code with SCL (Structured Control Language). Due to the fact that SCL is based on PASCAL language which is highly recommanded in EN 50128 and IEC 61508-3 standards for SIL 4.  SCL also corresponds to ST (Structured Text) language which is defined in IEC 61131-3 standard as one of the PLC language. 
In the fourth chapter, an example of centralised automatic blok controller is designed with modular, scalable and fail-safe approach which are also highly recommanded in these standards. Bidirectional operation on single track which is the most complicated case is handled. With V-cycle approach first, sample open line with equipment and area is introduced. Then system is divided into subsystem with function blocks. Then functional requirements of all function blocks are determined. 
Block signal function model is created with sub-units for modular approach. Track circuit function block is  also created which also proper for axle counter owning to have same functionalities with regard to interlocking. Unauthorized train scenarios are considered and designed with state transition diagrams. 
Open line main controller function block is designed and integrated with sub-function blocks. Open line main controller communicates with other function blocks. Block controller can lock block direction and set block which gives movement authority to open line. Type of initial state of block direction is neutral type. Block is available for both directions. Between two stations on each track only one block direction per time can be used. For clearing exit signal the relevant block orientation is mandatory. With these functions, exit routes of two neighbour stations are interlocked via centralised automatic block controller.
Function blocks like block signal, track circuits, runaway and open line main controller are developed with fail-safe perspective. Block signal turns to red aspect in any failure scenario, track circuits gives occupation output until proofs related section is clear and system also detects runaways with determination of unauthorized movements.
As a result centralised automatic block controller which provides fail-safe interlocking between stations and open line is designed with state transition diagrams and then logical equoations of diagrams are converted into SCL language to PLC code. Centralised automatic block controller is implemented and simulated thanks to TIA Portal and PLCSIM programme.