Power system operation fault statistics reveal that a vast majority of the switchgear arc faults are caused by incorrect human actions or by aging network equipment. One way of reducing human-related or equipment-associated fault risks is to focus investments on technological solutions that enhance the operating environment.
The basic necessity of a switchgear arc fault protection system can be investigated from the probability aspect of arcing faults or from the aspect of their adverse effects.
Impacts of power system arc faults
Electric arcs may cause instant and severe burns to persons happening to stay close to the fault, when it arises. Typically, this is the case if the arc incident is caused by an incorrect switchgear operation.
The arc flash easily causes a fire, which, in addition to the immediate damage, also creates fire gases and consequential damage due to smoke and stain. The fire gases of burning electrical devices are particularly dangerous for people residing in the same area.
Equipment fault proneness - a function of time
The effective life-time of distribution network equipment is typically in the range of decades. Network companies and industrial enterprises aim at maximizing the operational lifetime of their equipment and to reach the financial goals.
As the life-time of electrical devices extends over decades, changes constantly occur in their operational proximity and the customer base they serve. The legislation and regulations may also change over the operational life-time of the equipment.
For instance, a switchgear system, which originally was intended for limited supply of power to a small population centre, may later have to supply power to a shopping mall serving thousands of customers seven days a week. The role of the switchgear system may also have become more critical. Possible power outages may cause considerable economic losses to the customers.
Furthermore, the loading of the switchgear has grown and for this reason a second power transformer has been installed in parallel with the first one. In peak load situations the transformers can be run in parallel, which also causes the short circuit power to increase. At the same time the arc fault energy and the resulting damage in case of an arc fault increase.
Changing working manners pose risks
In power systems the maintenance need of the primary system equipment is generally small. Therefore the equipment maintenance intervals tend to be fairly long. There is also just a limited need to perform local control of such components as breakers and switches. Under these circumstances the personnel will not obtain the necessary experience to work with power system components. The personnel’s lack of experience will pose an increased risk of making mistakes during maintenance work and fault clearance activities.
The probability of accidental arc faults is also increased by changes in the utility’s work staff. The fact that when the current maintenance people of the network companies reach the age of retirement, the familiarity of the new staff with the network systems decreases on a local level. In addition, the need of the network companies to outsource maintenance functions further add to the risks of human errors.
Over the years the working conditions of the devices degrade. The aging and degeneration of protective structures and auxiliary furnishing expose the equipment to dust, moisture, temperature variations and rodents. The condition of the switchgear system is also affected by stress factors and excessive loading, which may cause untightening of joints and degeneration of bushings.
Risk evaluation
The selection of the appropriate arc fault protection system preferably starts with a risk mapping, which, on one hand, focuses on the probability of the development of an arc fault, and on the other hand, on the effects of a possible arc fault.
The volume and type of investments needed to enhance the safety and security of the power system, and the reliability of the power distribution can be studied by performing risk analyses.
In the process of choosing an arc fault protection solution for an existing switchgear system, its expected remaining life-time is of significant importance. There are two alternative strategies to choose from. Either the operational life-time of the switchgear system can be prolonged by additional investments, or the whole switchgear system can be renewed.
In modern switchgear systems the probability of damage due to arc faults is comparatively low. Despite of that, it can, of technical and assembly reasons, be recommendable to provide the switchgear panel with a system-wide supervision solution serving for the whole operational life-cycle of the switchgear system.
Please contact your local ABB product or service sales* in order to perform a risk mapping for an arc incidence in your power system installation. Select your country and see the names at the bottom of this page.
An ABB solution for any application
ABB's arc fault protection systems provide appropriate solutions for both green field projects and retrofit installations. From the comprehensive and compatible arc fault protection system assortment the customers can choose their solutions according to their own preferences.
An already existing main protection scheme can be completed with an independent arc fault protection system or it can be upgraded by using protection relays with integrated arc fault protection in the basic functionality set-up. The ABB arc fault protection systems provide detection and isolation of arcing faults starting from either earth faults or from short circuits.
The arc fault protection introduction tool presents a product portfolio diagram mapping alternative strategies and solutions.
By investing in arc fault protective equipment, the safety and security of the switchgear system can be enhanced. The investment done in protection equipment will also extend the life-time of the switchgear installation, postponing possible investments in new switchgear or even substations to a later date.