Modeling and analysis of arc flash in high voltage power systems

One of the most important parts of the power system networks is switchgears. The occurrence of an electrical fault at the switchgears negatively affects the continuity of the electrical energy and leads to an inability of the end user to deliver the electrical energy in a healthy manner. Electrical failures are mainly caused by electrical and mechanical failures. One of the most devastating faults that cause electrical interruptions in power systems is arc failure in high voltage (HV) switchgears. The arc is a self-sustaining electrical discharge in a gas. It occurs due to gas ionization and forms a conductive connection between the electrodes with different potentials or between the electrode and ground due to ionization. An arc flash term is used for an arc that arises accidentally in an electrical installation. During the arc flash explosion, large amounts of energy which can not be controlled occurs in the form of intense heat and light. Arc flash explosion damages the equipment in the switchgears, causes electricity interruptions and causes economic losses. There is also a danger of serious burns (going to death) and many other security hazards for the staff. The arc flash can be caused by the accumulation of conductive dust, corrosion, moisture or conductive vapors, or due to the contact of animals, such as erroneous mounting of equipment, negligence of preventive maintenance work, faulty system design, or unintentional contact with energized parts during maintenance or repair of conductive devices. The reason is technical or often wrong behavior of individuals. Almost all short circuits in the electrical installation cause arc flash and enormous energies. The electrical arc event was first discovered by English scientist Sir Humphry Davy in the early 19th century. The electrical arc is generally characterized by high current and low voltage. The arc flash hazard, as defined in the IEEE 1584-2002 standard, is a hazardous condition associated with the discharge of the energy caused by an electric arc fault. The discharge of the energy is caused by the electric current flowing through the air between the unearthed conductors or between the ungrounded and grounded conductors, bringing about a temperature of about 20,000 °K. Exposure to this temperature can cause very dangerous consequences such as burns of the skin, burns, ignition of clothes. Copper, which is widely used in electrical equipment, expands 67,000 times from solid state to vapor. Air and metal expansion can cause high pressures, dense sipes and flying shrapnel. High pressures can exceed hundreds or even thousands of kilograms per square meter and personnel can rupture the eardrum. Sounds associated with these pressures can exceed 160 dB and cause hearing damage. The shrapnel and molten metal pieces reach the speed of about 300 m/sec and can penetrate the human body. In the United States, at least 2,000 people are admitted to burn centers each year with severe arc flash burns. Prior to 1982, electric shock was thought to be the greatest risk associated with energetic electricity operations. In 1982, Ralph Lee published a paper entitled "The Other Electrical Hazard, Electric Arc Blast Burns" which describes thermal events and the effects on the human body in relation to electric arc. In this article, calculations are made to determine the improved burn-up level of 1.2 cal/cm2, which is still in use today and the healing burning distance for an air arc. This paper, written by Lee, appears to be the first to evaluate the risks associated with arc flash. In 1987 Lee published the second edition of "Pressures Developed from Arcs" on arc flash hazards. This paper describes the sound and pressure effects that an arc creates in the air. In addition that there are charts to determine the pressure ripple forces depending on the fault level. At 1990, arc flash hazards and threats were identified and added the need for arc flash safety to the OSHA 29 CFR-1920 Subpart S section. Ralph Lee published two more papers examining the energy of arc faults. The empirical test data used to determine the arc energy emitted at the distances along the low voltage arc fault are shared in the article "Testing Update on Protective Clothing and Equipment for Electric Arc Exposure" published in 1997. This work was the first paper to address the directional effect of an arc in an enclosure. Equations are used to determine the arc flash energy that is turned on depending on the failure level, working distance, and the cleaning time of the arc, in other articles named "Predicting Incident Energy to Better Manage the Electric Arc Hazard on 600 V Power Distribution Systems" published in 2000. The study on this article was used by NFPA 70E in 2000 to develop safe business practices based on arc flash hazards. The only limitation here is that the arc flash equations are for low voltage (LV) applications. This work also forms the basis of the IEEE 1584-2002 standard for arc flash calculations and analysis. In this thesis, the physical and technical results of the electrical arc phenomenon will be investigated and the effects on the human body will be examined. A calculation methodology for arc flash analysis will be established and the arc energy and the methods for reducing the risk will be examined in detail. Within the scope of arc flash analysis, the distribution network starting from TEIAS transmission center to distribution centers (DC's) will be modeled on Neplan software. Then the amount of arc energy that can appear in the DC's buses will be calculated. Calculations will be made and compared using different parameters (such as short circuit current, arc current, arc duration). During the thesis, a sample network will be modeled on the Neplan software in order to determine the arc flash energy level that emerges. Arc flash analysis will be carried out through the Neplan program which calculates according to the IEEE 1584 standard used for arc flash calculations. Real relay setting values and equipment will be used during the modeling phase to calculate the arc flash energy level in a healthy and realistic way. The arc flash energy, which varies depending on the short circuit current and arc duration, will be examined by changing the parameters. The data obtained from modeling and analysis will be compared. In this context, how to interpret the parameters such as short circuit current, arc current, arc duration will be examined. After the arc flash energy level is determined, the arc flash hazard labels required for the safety of personnel and other persons shall be prepared. The personal protective equipment (PPE) to be used depends on the NFPA 70E standard. Unsafe working areas that must be observed for staff and other persons will be defined. Finally, the results obtained in the analysis and examinations conducted within the scope of the thesis study were evaluated.