infrared camera electrical maintenance
Nfpa70e, Arc Flash and safe and efficient Thermography Practices
What is an Arc Flash?
An arc flash is like a bolt of lighting that some electrical equipment is energized. It can occur spontaneously and is often caused simply by the movement of air as an electrical enclosure opens. The NFPA has recognized the great danger of the Arc Flash and tries to protect workers from the latest version of the NFPA 70E-the standard for the safety of workers at the workplace.
Arc Flash in 10-15 major incidents in the U.S. every day. Most causes of Arc Flash operator induced.
Most engineers who routinely work around energized electrical equipment are familiar with Arc Flash have seen that first hand. It is designed as a major car accident: nobody really expects it to happen for them, so people tend to drive significantly less cautious than they should. So it is with arc flash, only worse. Like driving can make a mistake, or you can do everything right when someone slams into you.
Specifically, what is an arc flash?
An arc flash is electric current flowing through an arc outside its normal path where the air is the conductor of high thermal energy (5000 º C% 2B) and generates highly conductive plasma. An Arc Flash will run all available energy and generate a volumetric explosion of gas blowing doors off electrical system and potentially generate shrapnel.
What are the causes of Arc Flash?
An Arc Flash occurs when the gap between the conductors or conductors and ground temporarily bridged. There is always a trigger event which almost always involves human intervention. Typical causes and contributing factors include:
- Accidental contact with energetic components
- Inadequate short circuit ratings
- Tracking on insulation surfaces
- Tools energetically declined share
- Wiring Errors
- Contamination, such as dust on insulating surfaces
- Corrosion of equipment, components and contacts
- Improper work procedures
Arc flash is an electric current flowing in an arc outside its normal path where the air is the conductor.
The vast majority of the Arc Flash errors occur when the door is open or opens. The National Fire Protection Agency (NFPA) is the author of NFPA 70, also known as the National Electric Code (NEC). This paper is not intended for a comprehensive overview of the available information in the code, but only highlight some of the information that may be related to thermography.
NFPA 70E is the standard for safe electrical practices.
The NEC is an electrical design, installation and inspection standards. It does not specifically address issues such as electrical maintenance and safe work practices. A national consensus was needed for safety while working around live electrical equipment. NFPA 70E is the standard for safe electrical practices. NFPA 70E addresses four specific topics: safety-related practices, safety maintenance requirements, safety requirements for special equipment and plant safety requirements. NFPA 70 suggests a Hazard / Risk Analysis before the work should be performed on electrical equipment. The core of the analysis is based on shock and arc flash boundaries that must be done by a qualified electrical engineer.
Shocks, Flash Hazards and Personal Protective Equipment (PPE) Selection
Prior to beginning work around live electrical components energized electrical work permit must be obtained and should include but not limited to the following:
- A description of the circuit, the equipment worked and location
- Reasons why the work should be performed in an energetic condition
- Description of safe working practices to implement
- Results of the Shock Hazard Analysis
- Determination of Shock Protection Boundaries
- Results of the Flash Hazard Analysis
- The Flash Protection Boundary
- Identify the necessary personal protective equipment (PPE) required to safely perform the assigned task
- Means to limit unauthorized personnel access to the workplace
- Proof of completion of a job briefing
- Energized work approval of responsible management, safety officer and owner
Before he live parts, the appropriate personal protective equipment and safe work practice are provided.
NFPA 70E provides for an exemption to secure work permits for skilled personnel who perform tasks such as testing, troubleshooting, voltage measuring, etc. as long as they use safe working practices and appropriate safety equipment. Prior to working with live parts, appropriate personal protective equipment and safe working practice are determined by performing of a shock and a Flash Hazard Analysis. A shock analysis will determine the voltage to which personnel are exposed, boundary requirements and the appropriate safety equipment necessary for the possibility of a shock to staff to minimize. The shock protection boundaries are identified as limited, restricted and prohibited for the distances associated with various voltages.
Unqualified staff are informed and warned of hazards by qualified personnel when working on or near the limited approach boundary. If an unqualified person must work within the restricted limit, it is important that they further informed of the risks and dangers and constantly supervised by a qualified person. In no case they are permitted within the prohibited limit. It is important that a Flash Hazard Analysis be conducted to protect personnel from being injured by an arc flash. The analysis provides the flash protection boundary and determining the appropriate safety equipment. The Flash protection boundary is based on the distance of energetic parts where a burn will be "compensation eligible "(2nd grade) and" incurable "(3rd grade). The guidelines provide that the flash protection boundary for systems that are 600 volts or less 4 'for clearing times of 6 cycles (0.1 seconds) and available bolted fault current of 50kA or a combination of not more than 300kA cycles. For all other bolts and fault clearing times currents, the flash protection boundary is usually determined based on the calculated incident energy of an arc fault, taking into account system voltage, available power, and clearing time (where the incident energy is the measure of thermal energy at a certain distance of the debt). If this analysis is not possible (or not implemented) implement, NFPA 70 provides guidelines (NFPA 70 Table 130.7-c9a) that can be used for the required protective equipment based on the job performed to determine. Instead of a Flash Hazard study, selection of PPE for each task is normally permitted. However, for tasks not listed in the table and clearing times other than those listed is a complete Flash Hazard Analysis is required. Using Flash Hazard Analysis and Risk Assessment Task, the following table can be used to correct PPE:
Thermography Inspection Practices Infrared cameras are used to identify problems in electrical systems for many years. Problems in electrical systems manifest themselves by connections and conductors overheat due to increased resistance, the result of loose or corroded connections, or load imbalances. An infrared camera can easily recognize these problems in a thermal image and is an excellent method for the identification of components or problem before a failure. A failure can disable an electrical system and cause significant lost production, equipment damage and bodily injury. Insurance companies use infrared electrical inspection to help determine risk and tariffs for industrial customers. More recently they have found that IR thermography can be used to predict and prevent failures to help further reduce down time equipment failure and overall safety.
Often during thermography inspections, panel covers are removed and then replaced, a method which conflicts with the requirements of NFPA70E.
Just visible cameras, infrared cameras require a direct line-of-site view an object. In most cases, surveys are hampered by cabinet designs that obscure the target components are inspected and thermal are endangered by having the cabinets or doors open in an attempt to access the internal parts to get. IR surveys of electrical systems are best done when the system is under severe, if not peak electrical load, which requires the thermographer inspection in and around live electrical components. Typically, electrical system covers removed thermography during inspections and then replaced. This approach is contrary to the requirements of NFPA 70E.
Recommendations NFPA70E they relate on Thermography Inspection
NFPA 70E recommends that only "qualified" personnel be allowed to perform maintenance within the flash protection boundary. Thermo Graphic must be accompanied by "qualified" individuals if they intend panel covers removed. Both the thermographer and the extra person should full PPE. NFPA 70E provides a way hazards and risks and the required protective equipment is based on the activity you carry around the equipment. Risk potentials are determined on a scale of 0-4, where 4 indicates the highest risk potential. For example, removing a cover bolts on 600V equipment carries a hazard / risk classification of 3 and that is to a rating of 4 on voltages greater than 600V. As this work occurs within the flash protection boundary, the necessary protective equipment. The required minimum PPE for Hazard / Risk Classification 3 work is to withstand 104.6 J / cm ², and the minimum required PPE for Hazard / Risk Classification 4 work is to resist 167.36 J / cm ². Because much of the work performed for an IR inspection requires removal of cover screws, the PPE would be required.
Infrared Windows: Remove the controllable risk
The first line in a risk assessment is eliminate the risk if possible. Infrared Windows eliminate many of risks with live inspections, because they direct view of an infrared camera live electrical components without the need to allow open electrical enclosures. They offer an excellent way to access electrical equipment safely and efficiently. In addition, half qualified technician does not need to open and unlock housings. An IR viewing window is actually an infrared-transparent material with a holder / mounting body. Thermography may even decide not to use a window to inspect the energized components at some distance from the protective cover and use a grid instead of a window. The grill must be certified IP2X (grill size should provide protection against foreign objects with a diameter greater than 12mm). This method can significantly reduce the cost and window also has the added advantage of allowing ultra sound inspection of the electrical switchgear. But the use of grills, operators will be exposed to live electrical components and they must carry the appropriate level of protection identified by the Arc Flash Hazard Analysis of the switching equipment. Infrared Windows eliminate many of the risks associated with live infrared inspections, because a direct view of infrared cameras allow live electrical components without the need to open electrical enclosures. The optics holder design depends on a number parameters: the vision, equipment lens and window size are all features of the design and shall comply with all parameters that thermographer required before a container is manufactured. It should also be included in a protective design as crystals are very expensive and in some cases, extremely vulnerable. Infrared Windows are available in several sizes and can tailor made to adapt dead fronts on the distribution and isolator boards. The larger the size of the window, the larger the field can be seen in their IR camera.
Infrared considerations in installing Windows
To correctly install infrared windows, the goals that require inspection should be identified. Typically, conventional surveys only look at the bolted connections in switching equipment. These are generally regarded as the "weaknesses" or "points most likely to fail." These may include:
- Cable connections
- Bus Bar Connections
- Isolator or circuit breaker connections
The formula for calculating the field visible through an infrared window is: FOV = 2 x tan (angle / 2) x O, where FOV is the width of the object area will be seen, the "corner" is the angular Field-of-view of the camera, and "D" is the distance from the camera (apparently the window) to the objects being viewed. Once a decision on what items to inspect the infrared window must estimate the number and the correct size to define, and where they should be installed to cover the best (and therefore maximum efficiency) guarantee. The size of the infrared window will depend on several factors, including clear aperture of the infrared camera, her ability to focus on close objects, its ability be placed as close as possible to the window, the camera's angular field-of-view and the amount of manipulation possible with the camera while viewing through the window. An important consideration is how the infrared camera to manipulate the search through an infrared window. A high degree of manipulation, the effect of increasing the size of the area inspection by a factor of 3. This means that if the object under observation is 12 inches wide, depending on various factors, it is possible that a window diameter 4-inch (for IR window size calculation) can still be used if the operator manipulates the camera from left to right or up and down.
The required size of the window depends on the following:
- the size of the objects are viewed and the distance of the panel cover;
- the infrared camera's angular field-of-view and clear aperture;
- The camera is focused on close objects and close the window to be placed.
Typically, infrared cameras have a horizontal field of view 25 °. These infrared cameras provide a wide-angle option (for example 50 °) make the user to a significantly wider field of vision, resulting in an increase in display area using the same infrared window size. This is a great advantage in certain situations, reducing the size and possibly the number of windows. Other useful features include infrared camera close focus capability, small lens diameter results in a small clear aperture, motorized focus (elimination the need to get your fingers on the lens focus ring and moving the camera away from the window) and a chassis design that facilitates movement by the window, as an articulating camera head allowing the user to look at windows above eye level or near the floor.
The View through an infrared window
An infrared window allows a camera operator inside an electrical cabinet to inspect the physical condition of the components you have chosen to inspect checked. Like traditional thermographic inspections, we can see temperature differences are very clear. You have confidence in the infrared windows that you use. They are designed to far infrared energy must broadcast them on a known transfer and therefore, even if a slight temperature difference you will be able to see that the IR-camera, able to record images for IR inspection program.
Infrared Considerations for installing Windows
Installing an infrared window requires cutting holes in expensive switching equipment. It is very important to be very sure they are installed in the correct location and that switches the ratings are not degraded in any way. Before install the following factors must be taken:
- NEMA or IP rating of the switching and IR-windows: Never Forget the installation of an IR window of a lower rating than the rating of the switchgear.
- Test Certificates: Ensure that the IR windows been tested and approved by the certification bodies such as the switches for which they were intended (ie UL, IEEE. Lloyds).
- Internal Barriers: Before removing internal Perspex / Plexiglas covers or cables, to ensure that the approval of the local security manager is first requested. In some cases, you are unable to completely remove the covers and may only be able to modify them by drilling holes or IP2X requirement for some switching equipment maintained.
- Explosion Ratings (if applicable): Some panels are placed in intrinsically safe areas and as such can never be changed in the field.
- Dielectric Clearances: If the IR windows use grills or inspection openings, must meet IP2X (13mm 0.5), and customers should be made aware of the safe space for the dielectric nature of the switching equipment that they plan to install in the window. The table on the left (from IEEE C37.20.2 Table A.3) specifies the minimum distances from live components, and it is recommended that this be considered as a standard for grills / inspection holes.
Using Infrared Windows, it is important to correct for the transmission specification of the window and the look of the component to be monitored by the IR window. One way to correct for the effects of the window by adjusting the appearance of the camera for an object of known value to the temperature reading of the camera is correct. For objects at the same temperature and atmosphere, the new image values are used.
When using IR Windows, it is important to correct for the transmission loss of the window and the look of the component to be monitored by the IR window.
Another way of using IR windows is to prepare all components so inspected, they look the same (eg with electrical tape, emissivity paint, IR-ID tags). In this case, all components are checked, have the same transfer and influence readings, therefore, the results are collected, many easier to compare.
Can Wear a Generic IR Windows Arc Rating?
Electrical switchgear takes many different shapes and sizes. The surface and volume elements of the different offices in each model, type and rating. Each case is subject to the tests determined by certification bodies such as UL, IEEE, etc. This test is completed on the cabinet assemblies and components which are not part of the meeting. Electrical cabinet designs and dimensions are infinite, and we can not or must not use the data from a cabinet design for a different design unless they are identical in every respect. This is the reason why components never wear a generic arc assessment and should be subjected to industry standard tests to confirm that they meet the minimum required level of mechanical strength and electrical properties for the environmental cabinets and assemblies that they will be incorporated.
Conclusion
Because of the frequent occurrence of Arc Flash in the industry, it is extremely important to be aware of the risks related to inspection of high voltage switching equipment and related items. Concerns about operator safety due to an arc flash event causing inspectors to adopt new practices in accordance with NFPA 70E, the standard for safe electrical practices. Flash and Shock Hazard analysis are needed in many situations. Personal Protective Equipment recommendations are also available. A new common security practice includes the use of infrared transparent windows many of the risks to eliminate live with infrared inspections because it is an infrared camera to a direct view of live electrical components without the need to open electrical enclosures.
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