Alçak gerilim sistemlerinde ark flaş analizi ve koruma
Arc flash analysis and protection in low voltage systems
Yazar: GÜLŞAH DAMLA
Danışman: PROF. DR. ÖMER USTA
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Elektrik Mühendisliği Ana Bilim Dalı / Elektrik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Elektrik ve Elektronik Mühendisliği = Electrical and Electronics Engineering

Özet:
Elektrik, günümüzde en çok ihtiyaç duyulan enerji kaynaklarından biridir. Elektrik üretimi ve tüketimi her geçen gün arttıkça arızaların etkileri daha da yıkıcı hale gelmektedir. Bu nedenle elektrik enerjisinin üretimi kadar verimli, güvenli ve kesintisiz olarak kullanıcılara ulaştırılması da önemlidir.
Elektrik güç sistemlerinde elektrik kesintilerine neden olan önemli arızalardan biri ark arızalarıdır. Ark, hava ve gaz gibi yalıtım malzemelerinde iki elektrot arasında meydana gelen elektrik boşalması olarak tanımlanabilir. Elektrik güç sistemlerinde, ark arızalarında çeşitli sebeplerle meydana gelen kısa devreler ile kontrolsüz enerji, ısı, basınç ve ışık ortaya çıkmaktadır. Ark arızalarında ortaya çıkan enerji, basınç ve ısı etkileri, anahtarlama donanımlarında hasara sebep olmakla birlikte can kayıplarına ve ekonomik zararlara sebep olabilmektedir.
Bu tezde yer verilen hesaplama yöntemleri, denklemler IEEE 1584:2018 standardından alınmıştır. Standartta sabit laboratuvar koşullarında ölçülen test sonuçlarına göre ampirik denklemler elde edilmiştir. Bu nedenle hesaplama sonuçları, gerçek bir ark patlamasına maruz kalmanın verdiği tehlikeden daha şiddetli veya daha az şiddetli olabilir. Kişisel koruyucu donanım (KKD) kategorisi ve seçimi için NFPA 70E:2021 standardı kullanılmıştır.
Bu tez çalışmasında Trimble ProDesign ve Caneco BT yazılımları kullanılarak kısa devre analizi ve koruma konsepti çalışması için tesis ve ekipmanla ilgili elektriksel verileri içeren örnek bir veri merkezi alçak gerilim dağıtım sisteminin modeli oluşturulmuştur. IEEE 1584:2018 standardına göre ark flaş hesaplaması, Caneco BT yazılımının 'Arc flash risk' modülü kullanılarak gerçekleştirilmiştir. Hesap çıktısı olarak VCB, VCBB ve HCB konfigürasyonları için ayrı ayrı ark olay enerjisi, KKD giyilmesi için gereken mesafeyi belirleyen ark flaş sınır mesafesi ve KKD kategori değeri elde edilmiştir. Her pano için en kötü senaryoya göre uyarı ve bilgilendirme etiketi oluşturulması hedeflenmiştir.
Ark olay enerjisini azaltmaya yönelik çalışmalar doğrultusunda ark flaş hesaplamaları tekrarlanarak normal işletme durumu ile karşılaştırmalar yapılmıştır. Ark olay enerjisini azaltmaya yönelik çalışmalar içerisinden akım sınırlayıcı reaktör ETAP programında modellenmiştir. Son olarak hesap çıktısı olarak elde edilen uyarı ve bilgilendirme etiketi, örnek bir pano için gösterilmiştir.
Ark olay enerjisi hesaplamalarında örnek alçak gerilim sisteminin koruma ve seçicilik çalışmasından elde edilen birincil (primary) koruma ayarlarına göre uyarı ve bilgilendirme etiketi oluşturulması amaçlanmıştır. Birincil koruma arızası durumunda, yedek (back-up) koruma arızayı giderir, ancak bu daha fazla zaman ve daha yüksek olay enerjisi açığa çıkarmıştır. NPFA 70E, sistemin birincil koruma sistemindeki arızaya karşı değerlendirilmesini gerektirmez. IEEE 1584 standardına göre ark flaş analizi çalışmasında sadece üç faz arızaları ve bara tarafı dikkate alınmıştır.

Abstract:
Electricity is one of the most required energy sources nowadays. As the generation and consumption of electricity increases day by day, the effects of faults become more devastating. For this reason, efficient, safe and uninterrupted delivery of electrical energy to users is as important as its production. Potential hazards are analyzed, reduced and necessary precautions are taken.
One of the important faults that cause power outages in electrical power systems is arc faults. Arc flash incidents are a major cause of injury in the electrical industry. Apart from electric shock, 80% of burns and injuries are caused by arc accidents. Most of the high-grade burns and deaths that occur are caused by the use of clothing that is not resistant to flame and heat.
Arc flash hazard has been defined by the NFPA 70E, as "a dangerous condition associated with the release of energy by an electric arc". Air has very poor electrical conductance, so it is not easy to establish a current through it. In fact, in most electrical systems it is used as the main form of insulation. If, however through voltage spikes or failing equipment, a temporary flashover does occur, it is possible that the arcing current is sustained.
The calculation methods used in this thesis are based on IEEE 1584:2018 standard. Those equations derived from measured test results in fixed laboratory conditions. Therefore, calculation results may be more severe or less severe than the hazard presented by an actual arc flash exposure. NFPA 70E:2021 standard is used for personal protective equipment category and selection.
It is aimed to increase the safety of the personnel and reduce the damage to the equipment by keeping the arc flash incident energy level at a minimum with the methods to reduce the risk of arc flash. This can increase the level of security and can significantly reduce the time required to repair the switchgear.
Some recommendations can be considered to provide a more comprehensive arc flash hazard mitigation for the operator. Training of workers, safety culture and rules regarding operation in an environment with possible arc-flash hazard should be a common practice. PPE and arc flash labels for each switchboard or distribution panel need to be based on the arc flash risk analysis incident energy released. Workers should use insulated tools or handling equipment, or both, when working inside the restricted approach boundary or exposed energized electrical conductors or circuit parts where tools might make unintentional contact.
The effect of arc flash faults can be reduced by reducing arcing times with healthy relay coordination. Equipment manufacturers may provide a "maintenance mode" switch that allows the operator to apply a protection system change (removing the time delay) by activating only one switch. Zone selective interlocking (ZSI), opening of the breaker closest to the fault in the shortest time, can be used with taking into account the selectivity operation with the communication of two or more breakers. By placing an arc sensor in each closed compartment in the panel or switchboard, ultraviolet light information and overcurrent information are obtained through the current transformer. A trip signal is sent to the breaker with the information received from the sensors connected to the arc relay and the overcurrent information received to prevent false trips. Current limiting breakers can be used to cut off the short-circuit current as soon as possible.
The probability of arc-flash can be reduced by appropriate maintenance of the equipment. Visual inspections, thermal imaging, PD testing, and time-based testing of protection devices are some examples of preventive maintenance actions. Condition monitoring of equipment, often by online measurements and communications to upper level information systems, is an advanced tool for active maintenance.
A sample data center low voltage system is modelled in Trimble ProDesign and Caneco BT softwares. Arc flash calculations are performed using the 'Arc flash risk' module of the Caneco BT software. During the modeling phase, some companies' protection devices and settings on the market are used.
Within the scope of the study, arc fault current level calculations, arc flash incident energy level, arc flash boundary distance, necessary personal protective equipment (PPE) and electric shock hazard limits in different operating scenarios are presented for the low voltage distribution level of a data center. In line with the studies to reduce arc incident energy, arc flash calculations are repeated, and comparisons are made with the normal operating condition. The use of current limiting reactors in the studies aimed at reducing arc incident energy is modeled in the ETAP program.
It is aimed to provide a warning and information label for each distribution panel according to the worst-case scenario. Presenting the arc flash results with labels is to help protect the personnel working in the building from electric arc flash hazards. These individuals may include workers who control, maintain or operate energized electrical equipment.
All calculations of the incident energy are based on the primary protection settings from protection and selectivity study of sample low voltage system. In case of primary protection failure, the back-up protection clears the fault, but that has been required more time and effectively higher incident energy. The NPFA does not require the system to be assessed against failure on the primary protection system. Only three phase faults have been considered in the arc flash study. Earth faults have been omitted because the earth fault current is expected to be very low compared to the phase fault current. Calculations have considered busbar side.
An arc flash assessment is compulsory in the USA by the NFPA 70E, and the arc flash calculations should be carried out according to IEEE 1548 standard to determine the Personal Protective Equipment (PPE) requirements based on the hazard risk category. However, in Europe, there is currently no legal obligation to undertake an Arc Flash Hazard analysis. It is stated in the TS EN 50110-1 "Operation of electrical installations" standard that necessary precautions should be taken against electric arc hazards. In the "Personal Protective Equipment" regulation in Turkey, PPE is only defined for protection against electric shock. The regulation needs to be developed, as PPE must also be resistant to the heat intensity resulting from electric arc explosion. It is an important requirement to add the calculation of arc incident energy for the appropriate working distance and appropriate PPE category criteria to the regulation.
If properly utilised by the client, the Arc flash results shall bring the installation into compliance with the applicable standards for new installations and worker safety in operating facilities. However, the client must take all necessary additional measures and corrective actions to comply with the local health and safety requirements. PPE is seen as a last resort measure and needs to be selected adequately depending on the outcome of the risk assessment conducted by the health and safety officer.