Makas motoru arayüz devresi tasarımı ve güvenlik bütünlük seviyesi analizi
Design of point machine interface and safety integrity level analysis
Yazar: SERHAN SUBAŞI
Danışman: PROF. DR. SALMAN KURTULAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kontrol ve Otomasyon Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: Bilgisayar Mühendisliği Bilimleri-Bilgisayar ve Kontrol = Computer Engineering and Computer Science and Control ; Mühendislik Bilimleri = Engineering Sciences

Özet:
Demiryolu sistemlerine duyulan ihtiyaç dünyanın her bölgesinde gün geçtikçe artmaktadır. Bunun sebebi demiryolunun mevcut ulaşım sistemleri içerisinde ulaşılabilir, güvenli, hızlı ve çevreyi kirletmeyen ulaşım şekli olarak diğerlerinden ayrılmasıdır. Gelişmiş ülkelerde olduğu gibi ülkemizde de demiryolu ağına yapılan yatırımlar her geçen gün artmaktadır. İnşası süren şehirlerarası hızlı tren hatları, metro ve tramvay projelerinin tamamlanması ile beraber demiryolu günlük hayatın içerisinde insanlar tarafından daha fazla tercih edilen öncelikli ulaşım şekli olacaktır. 
Türkiye'de demiryolu inşası konusunda elde edilen sonuçlar ve başarılar ne yazık ki teknoloji geliştirme alanında çok fazla karşılık bulmamıştır. Bunun altında yatan sebepler olarak demiryolu sistemlerinde kullanılan teknolojilerin katı olarak standartlara bağlanılması ve talep edilen yüksek güvenilirlik, ulaşılabilirlik, bakım yapılabilirlik ve güvenlik değerleri olduğu söylenebilir. Tasarlanan sistemler sadece problemin çözümüne yönelik olarak değil aynı zamanda uzun ürün hayat döngüsü, çevresel faktörlere dayanım ve yoğun kullanıma karşın hatasız bir şekilde çalışmayı sürdürmelidir. 
Trenlerin yönlendirmesini yapmak üzere makasları süren elektrik motorlu üniteye makas motoru denir. Motor kendi içerisinde özel bağlantılar içermektedir. Daha basit yöntemler ile motorun sürülmesi ve konum bilgisi okunması yapılabilecek iken motora çekilen kablo sayısını azaltmak amacı ile özel bir yöntem geliştirilmiştir. 4 kablo tekniğinde makas motorunu sürmek için ve indikasyon bilgisi elde etmek için aynı bağlantıların kullanılması nedeni ile bir arayüz devresi oluşturma zorunluluğu oluşmuştur.
Tasarımı gerçekleştirdikten sonra arayüz devresinin demiryolu standartlarına uygunluğu araştırılmaya başlanmıştır. Makas motoru, sinyalizasyon sisteminin doğrudan kontrolü altında olan bir ekipmandır. Makas motoru üzerinde elde edilen bilgilerde bir hata yaşanması durumunda ölümle sonuçlanacak kazalara yol açabilir. Tasarım bu doğrultuda ele alınarak güvenlik öncelikli aynı zamanda ise güvenilirlik ve ulaşılabilirlik etmenlerini de göz ardı etmeden gerçekleştirilecektir. 
Yapılan tasarımın başarılı bir şekilde uygulandığı gözlemlendikten sonra, arayüz devresinin kullanımı hakkında risk analizi gerçekleştirilecektir. Buradan elde edilen sonuçlar ile sistemin karşılaması gereken güvenlik bütünlük seviyesi ortaya çıkacaktır. Tasarımı yapılan sistem üzerinde istenilen güvenlik seviyesine ulaşılabilirlik kontrolü gerçekleştirildikten sonra tasarım revize edilecektir. Nihai tasarım, ilgili standartlarla uyumlu ve istenilen güvenlik bütünlük seviyesine uygun olacaktır. En son olarak tasarım ile ilgili eksik veya zayıf bir nokta olup olmadığını kontrol etmek amacı ile tehlike analizi gerçekleştirilecektir. Seçilen tehlike analiz metotlarından biri tasarım üzerinde uygulanarak tez tamamlanacaktır.

Abstract:
Demand for railway systems is increasing day by day at all around the world. The reason for that railway is differentiated with respect to other existing transportation methods in terms of accessibility, safety, being fast and non-polluting alternative for transportation. Railway investments are growing in our country as well as at developed countries. People will choose railway as a preferred option for transportation in daily life with completion of intercity high-speed lines and metro and tramway lines in cities.
Unfortunately, the results and successes of construction of railways could not find any response at technology development on railway systems at Turkey. It can be explained that the railway technology development is strictly linked with standards moreover, the systems are required with high reliability, availability, maintainability and safety levels. The systems are not only designed to solve the problem but also consider to reach long product lifecycle, resisted against environmental factors and reliable functioning under frequent usage. 
Main technological component of railway systems is the Interlocking System that uses for safety train movement on the line. The Interlocking system connects to Control Centre and the field equipment on the line. Status of the field equipment are monitored continuously by the system. Control Centre takes the decisions for train movements in the station and as well as the train operation between stations. Control Centre commands are executed by the Interlocking as long as the safety principles are guaranteed The logic found on the Interlocking always works to provide the safety at all time. Therefore, the interlocking never executes non-safe logic that might causes a collision of train even the Control Centre demands a non-safe command.
In order to provide safe logic and execute commands for train operation, the Interlocking System should have proper interfaces with field equipment. The Interlocking System should control and monitor the field equipment such as wayside signals, level crossings, axle counters or track circuits and point machines. 
Trains are navigated by switches which is driven by electric powered point machine. The point machine has most complicated interface other than all field equipment. Other interfaces usually established over dry contacts and moreover power line and control line are strictly separated. AC power will be either one phase or three phase or DC voltage fed to drive point machine. Monitoring status of the point machine is again realised over dry contacts that have special behaviour while point machine is moving one position to another. 
A special method was developed in order to reduce to cable core quantity even there are some existing methods allow that the motor can be driven and position indications can be read over separate cables. The method is called 4 wire technique that only 4 cable core connections are made between the point machine and the Interlocking System. There is a necessity to develop an interface because of the same connections are used at the 4-wire technique to drive point machine as well as to obtain position indications.
Two important issues should be considered during the design of the interface. One of them is that precise transitions between power and control circuit connections are established over point machine. Any fault during the transition or connection of the power and control circuits at the same time might be resulted with extreme damage over the equipment or even false information can be read by the interlocking. Second is that the interface never provides a false indication to the Interlocking System. This could be lead a fatal accident. Therefore, safety concerns should be fulfilled by the interface system.
In order to meet with safety requirements, related standards must be defined and studied. Research activities started over compliance of the interface design with the railway standards after the design had been completed. The point machine is a device that is placed under direct control of the signalling system. In case a fault occurs while obtaining position information of the point, it might be resulted with fatal accident. Therefore, the design is carried out with safety considerations that is the prior parameter for the design without ignoring reliability and availability considerations.
First design is carried out with basic electric components such as relays and contactors. Logic itself pays attention to realize a smooth transition between control circuit connection to motor and power circuit connection to motor. The results show that the interface is working properly and safely. However later studies show that the interface is not compliant with the standards and regulations. Therefore, the design had to be rethought in terms of compliance with the related railway standards.
Logic of the interface is moved to an electronic controller which has a certification for appropriate safety integrity level for a railway application. Some relays and contactors have to be kept as a part of the interface. Therefore, the safety integrity level check for these parts of the interface must be realized as well. Relays were searched and selected as appropriate safety integrity level according to standards. But there wasn't any contactor that meets with an appropriate safety integrity level. The additional calculations should be done in order to prove that the proposed designed with selected contactors correspond to appropriate safety integrity level. The calculations show that contactors are reached the level as well as the controller and relays. Moreover, overall interface will be participated into a safety critical system such as an Interlocking System in terms of safety
A risk analysis is the last issue that must be realized in order to be sure that there is not any missing or weak point placed in the design. Fault Tree Analysis method is one of the suggested methods by the standards for risk analysis. In addition to that it is most suitable method to realize a risk assessment for our interface design. The analysis carried out together with the design in order to find non-compliant or weak points of the design. In thesis, it used to check that the interface meets with corresponded safety integrity level. It is required that the design requirements and border conditions must be considered once again before start to the analysis. Afterwards, top event should be defined to realize the analysis. In our case, it is obvious that false indication signal is selected as top event. The thesis was completed after realize quantitative and qualitative risk analysis. Results of the analysis can be used justify the interface design quality. The interface can be updated after the design checked whether compliant with defined safety integrity level. Final design is compliant with the standards and corresponded the required safety integrity level.
Studies of the thesis show that even a small system development for the safety critical railway system requires a lot of effort in terms of compliance with the standards and corresponded safety integrity level. Before starting the design process all related standards should be found and studied carefully. The requirements of the problem and standards are fulfilled by the engineers at the design. The design must be strengthened by the calculations in necessity points in order to reach corresponded safety integrity level that is defined before the design process. All in all, the thesis would be a guidance for engineers who will be worked over safety critical areas.