Arc Flash Risk in Wind Energy Systems. Guidelines for analysis, mitigation and management

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1 Arc Flash Risk in Wind Energy Systems Guidelines for analysis, mitigation and management

2 Introduction Arc Flash incidents can result in significant damage to electrical distribution systems and injuries or fatalities to personnel involved in their operation. It is a common misconception that Arc Flash risks are mainly associated with high voltage installations. In fact, high arc energy levels can often be found in switchgear of lower voltages, nominally 690V, as these are widely used in wind turbine installations. For wind energy systems, understanding the magnitude of risk associated with Arc Flash is complicated through the need to consider not just the potential incident energy levels which occur in individual turbines, but also the effect of multiple connected turbines within the wind farm. Calculation of the worst case scenario for fault level and arc incident energy needs to take into account the detailed configuration of the distribution system, because of the contributing factors of all wind turbines. Further challenges in accurately modelling such distribution systems include the comparatively long distances between turbines and the main substation arrangement and the associated cable lengths and impedances involved, which affect protection clearance and disconnection times. At higher incident energy - and therefore higher categories of PPE protection - such equipment is heavy and obstructive however, which in turn create risks and impacts on operator performance. In addition, reliance on such equipment does not reduce potential equipment damage and downtime from Arc Flash incidents. A safer and more cost effective approach, therefore, is for owners to adopt engineering measures to minimise Arc Flash risk and operator exposure as far as possible, relying on PPE as a last resort to protect personnel from residual risks only. In this paper, we will outline a comprehensive approach to Arc Flash risk management and reduction in wind energy applications. That approach comprises three related elements: 1. Analysis 2. Mitigation approaches 3. Management of residual risk Personnel involved in working with and switching live switchgear must wear personal protective equipment appropriate to the level of Arc Flash risk to mitigate against injury. High arc energy levels can often be found in switchgear of lower voltages. 2

3 Personnel risks An arc can be initiated by a failure within electrical switchgear such as a breakdown of insulation or by the introduction of a conducting object that accidentally bridges the insulation. When an Arc Flash occurs, large amounts of energy can be dissipated in a very short time. This energy causes the ionisation and vaporisation of the conductive metal materials (highly conductive plasma), while heating of the ambient air creates a rapid volumetric expansion, known as an arc blast. In addition, Arc Flash can expose personnel to injury from flying droplets of molten metal and toxic gases from the associated combustion of materials. Personnel exposed to Arc Flash can suffer severe burns, lung damage, vision loss, eardrum ruptures, barotrauma and even death. Equipment risks Further to above, Arc Flash incidents and the associated blast cause fire in any application. The potential for such fires are a significant issue for the wind energy industry, where records show fires can lead to the complete destruction of the turbine. A high level of damage is attributed to the concentration of flammable materials, including gearbox lubricants and glass reinforced plastics in turbine nacelles, together with the difficulty accessing turbines with firefighting equipment, due to their height and, often, remote location. 3

4 Arc Flash risks in low voltage installations While Arc Flash risk is commonly associated with high voltage installations, the risk of significant arc energy in low voltage equipment is less well understood. In an analysis of more than 6,000 distribution and switchboards at low voltage at a variety of industrial sites, GSE has found that almost a quarter presented risks of NFPA 70E2 Category 3 or higher, and 6.5 percent were in the Dangerous category where PPE alone cannot provide adequate protection to personnel. Moreover, when operating and maintaining low voltage systems, protection procedures and training are less stringent. Operations are generally more frequent and are undertaken by a wider number of operators, therefore magnifying potential risks. Regulations Adequate consideration of Arc Flash risks forms part of wind farm operators responsibilities under health and safety legislation. Relevant regulations relating to Arc Flash analysis and protection include the NFPA70E Standard for Electrical safety in the Workplace. Within the UK, wind farm operators must also comply with the Management of Health & Safety at Work Regulations (1999), which requires a suitable and sufficient assessment of the risks to the health and safety of employees. Arc Flash hazard is also identified as a hazard in the Memorandum of Guidance (HSG25) in the Electricity at Work Regulations 1989, under Regulation 2. 4

5 1. Analysis Proper management of Arc Flash risk in a wind farm installation requires detailed Arc Flash analysis according to the relevant standards. The risks associated with Arc Flash depend on the likelihood of an Arc Flash incident and the severity of the event. The likelihood of an incident depends upon the number of interactions that take place with energized electrical equipment and the condition of that equipment. As a result it is dependent upon the operation and maintenance processes in use at the facility. Calculating the potential severity of an Arc Flash requires knowledge of system fault currents and protection clearance times. Typically, specialist software is used to analyse fault levels and detailed arc incident level calculations in accordance with IEEE 1584 are performed. Modelling should include multiple configurations, including single turbines operating at full capacity as well as all turbines running together. The output of this analysis is a full understanding of the incident energy levels across the distribution system, allowing appropriate mitigation measures, labelling, hazard risk categorisation and PPE requirements to be identified. 2. Mitigation Arc Flash mitigation methods use three main approaches: the reduction of Arc Flash energy, the reduction of the impact of Arc Flash or the introduction of an alternative current path to capture the arcing fault. In selecting appropriate methods, consideration should be given to the limitations of each approach, as well as its capabilities. Reduction of Arc Flash energy Normal protection schemes aim to detect short-circuit current in order to interrupt the fault. Arcing fault current is always less than the short-circuit current. Thus, an efficient protection assessment should be performed in order to select the proper settings of the overcurrent protective devices to sense the arcing fault. The challenge here is to reduce potential Arc Flash incident energy without sacrificing selectivity, in which the effect of a short circuit is minimised while the portion of the power system that must be shut down in response to the event is kept to a minimum. A modern piece of equipment that provides even faster clearing time of the fault is the arc fault detection relay. By detecting light from the flash, current - and sometimes sound - such systems can achieve clearing times of the order of 1 4 cycle or even lower. Alternatively, a light sensor or light and sound sensor technology, without regard to fault current, can be applied to decouple Arc Flash sensing from the normal protection scheme. The latter practice has the disadvantage that it increases the likelihood of a false trigger occurrence. Reduction of Arc Flash impact Remote operation and arc-resistant equipment are methods that do not reduce arcing fault energy but can protect personnel from Arc Flash. Remote operation, such as remote racking and switching, establishes distance between the Arc Flash source and the operator, placing the operator outside the Arc Flash boundary. This method is safer for operators and does not affect system selectivity but may be costly and difficult to retrofit into existing systems. In addition, remote operation does not reduce the risk of damage to adjacent equipment. Arc-resistant equipment consists of switchgear that has the capability to confine the incident energy of the Arc Flash event in the specific area of the switchgear and provides a system for pressure relief, such as venting away from the front of the switchgear and therefore protecting the operator. Arc Flash current path alternation Other approaches to mitigation involve the introduction of an alternate current path in order to transfer the arcing fault and capture it. Providing a lower impedance path than the fault path and fast transfer of the arcing fault are important factors for the success of the method. Propriety systems have been developed by manufacturers to detect and quickly disconnect a fault before an arc of significant magnitude develops that could cause damage and harm to personnel. The main categories of overcurrent protective devices are fuses and circuit breakers. Their role is to clear fault current, but they will not react as quickly or at all if the arcing current is less than their fault threshold. 5

6 3. Management of residual risk Engineering changes such as those described above can significantly reduce arc energy levels and the exposure of personnel to Arc Flash risks. Once such measures have been put in place, however, a wind farm operator must understand the residual risks, and take appropriate steps to manage them. Labelling Where Arc Flash risk is present, equipment should be clearly marked with a label indicating the Hazard Risk Category and its boundaries, in accordance with the NFPA 70E standard for electrical safety in the workplace. Training All personnel involved with the operation and maintenance of switchgear must receive appropriate training to ensure awareness of Arc Flash risks and the processes and procedures to implement in order to minimise those risks. Owners must ensure that all personnel involved in operation and maintenance activities have a suitable level of competence for those tasks. Personal Protective Equipment Staff working on, or in close proximity to, equipment where Arc Flash risk is present must use appropriate protective equipment in accordance with the level of risk present. Depending on the level of residual risk, this equipment can include one or more layers of arc resistant clothing, gloves and suitable eye and face protection. Fire Suppression Systems As highlighted earlier, the impact of fire in a wind farm application can be catastrophic due to remoteness and access. Equipment damage as the result of an Arc Flash incident and the subsequent fire is therefore significant. There are measures which can be taken to reduce the impact of fire within electrical panels including suppression systems which are able to detect high temperature and locally extinguish using non-conductive fluids or gas. Such systems help to minimise equipment damage although hazard prevention and personnel protection is the ultimate aim of Arc Flash analysis and mitigation. 6

7 How GSE Can Help GSE Systems has extensive experience of Arc Flash risk analysis and the implementation of mitigation measures in a wide range of environments around the world including petrochemical sites, oil platforms, manufacturing facilities and wind energy installations. Our services in this area include: Site surveys, protective device determination and audits of electrical management systems Risk assessment of switchgear Construction and verification of system models, including protection characteristics and Arc Flash calculations with incident energies and boundaries Arc Flash mitigation studies Implementation of remediation projects including design and installation. Equipment labelling Creation and adaptation of maintenance and operating procedures Training Annual revalidation of electrical systems We are happy to discuss client specific needs, and our offering can be tailored to suit client regulations, in-house requirements, best practice standards and international codes of practice. For further advice and recommendations please contact us at Engineering@gses.com 7

8 About GSE Systems GSE Systems, Inc. is a world leader in real-time high-fidelity simulation, providing a wide range of simulation, training and engineering solutions to the power and process industries. Its comprehensive and modular solutions help customers achieve performance excellence in design, training and operations. GSE s products and services are tailored to meet specific client requirements such as scope, budget and timeline. The Company has over four decades of experience, more than 1,100 installations, and hundreds of customers in over 50 countries spanning the globe. Information about GSE Systems is available at Worldwide Locations HEADQUARTERS MARYLAND, USA Connect with us on: info@gses.com 2016 GSE Systems, Inc.