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Methods of Isolating Electrical Equipment in Hazardous Areas

Background

Combustion or fire is a chemical reaction in which a combustible material combines with an oxidant to release energy. Part of the energy release is used to sustain the explosion, by utilizing existing heat or creating a vacuum to consume more oxygen.  Within a hazardous environment there are three elements necessary for a fire or explosion:

• A combustible material also known as a fuel 
• Ignition source - electrical arcing or general heat
• An oxidizer also known as oxygen

When a fuel, oxidizer and ignition source are present at the necessary levels, burning or explosion will occur. To reduce the possibility of fire or explosion, one of the key elements needs to be reduced or removed.

Another key factor in a fire or explosion are the explosive limits. These are the maximum and minimum concentration needed of a given combustible material to support a fire or explosion. To form an explosive mixture, the hazardous gas must have sufficient concentration levels. The minimum concentration of oxygen to combustible material is known as the lower explosive limit or LEL. If the concentration is below the LEL, it will not be flammable or have enough flammable material present. The same condition would apply if gas concentration is too rich, meaning it will not ignite because it will not have sufficient oxygen to sustain the fire or explosion. This is known as the upper explosive limit, or UEL. It should be noted that different gases will have different threshold limits.

In addition to the explosive limits, each hazardous material will have an autoignition temperature and a flashpoint. The flashpoint is the temperature at which the material will generate sufficient quantity of vapor to form an ignitable mixture. As the liquid is heated and reaches the flashpoint, autoignition could occur. An autoignition is the lowest temperature at which a combustible material will spontaneously ignite in a normal atmosphere. For example, if we have the heating of a combustible liquid, explosive vapors are created. As the material reaches the explosive limits creating the flashpoint. If the general atmosphere is increased, the autoignition temperature, fire, or explosion will occur.

To simplify, the specification of electrical devices into hazardous environments, IEC classification methods utilize autoignition, flashpoint, and explosive limits to place hazardous materials within groups.

The two predominant methods used for classification of hazardous environments are the NEC and IEC standards. IEC and NEC standards both classify the level of risk into three main categories:

• Continuous
• Occasional
• Not normally present

All three categories provide the likelihood of an explosive atmospheric condition within the general environments. Within the IEC standard, the general risk categories are then classified as Zones. This reflects the physical material that could provide a potential fire or explosion. From liquids and gases, the area classifications are Zone 0, Zone 1, and Zone 2. By altering the physical material to dust or fibers, the area classification numerical value changes to Zone 20, Zone 21, and Zone 22.

Referring back to the necessary requirements for an explosive triangle, we know we need ignition source, oxygen, gas and or dust combustible material in the correct mixture within the atmosphere. In order to specify electrical devices and hazardous locations, we need to identify the general Zones within each area. When working with liquids or gas, we locate the most hazardous or flammable location directly above the material. Due to the possibility of the valve leaking, at the top of the containment structure we must classify the area as Zone 1. As we move further away from the possible explosive atmospheric condition the Zone classification would be reduced to Zone 2. By altering the combustible material properties to a solid form, the area classification above the material would be Zone 20. If the dust escapes the same failed valve, the external area around the same containment unit would be classified as Zone 21. As we continue to move away from the containment unit and with reduction of Category risk, the new classification for the general area would be Zone 22.

Now that we know combustible materials whether liquid, gas and or dust will have different upper and lower explosive limits, and we understand the general heat could be the ignition source, within the IEC standards the T rating specifies the maximum surface temperature an electrical device will create. As the temperature increases, the associate rating will decrease, meaningless heat will have a higher T rating, while an increase in surface temperature will reduce the T number.

As a recap the IEC standards classify hazardous areas as environments that could contain explosive vapors, gases, and/or dust within the atmosphere. The primary categories provide the risk levels as constant, occasional, and not likely. Since elements have a variety of flammability and the physical properties could be different, IEC standards segment the types of combustible materials into Zone classifications. The most hazardous is Zone 0 or Zone 20. By reducing the risk level to have occasional explosive atmospheres the Zone classification is Zone 1 or Zone 21 and further reduction of Category risks would change the hazards classification to Zone 2 or Zone 22

Flameproof enclosure for
wireless access point (Analynk) 

Methods of Isolation/Protection

Let's take a look at each method of protection and the general application. To ensure safety in a given situation, equipment is placed in protective level categories. As mentioned before Category 1 is the highest safety level, making Category 3 the lowest risk and safety level. The general 8 protective methods are:

1. Flameproof enclosures
2. Sand encapsulation
3. Pressurization 
4. Oil encapsulation 
5. General encapsulation
6. Increased safety
7. Intrinsic safety
8. Non-sparking

A flameproof enclosure method is a type of protection where devices that are capable of igniting an explosive atmosphere are built inside an enclosure. This protective method prevents the transmission of the explosion to the external atmosphere surrounding the enclosure. This method of protection would be suitable for applications on:

• Power operated equipment
• Switchgear
• Motors
• Any equipment that produces ignition source during normal operation.

Sand encapsulation is a type of protection in which the enclosure of the electrical apparatus is filled with a finely granulated material. This ensures electrical arcs occurring within the electrical apparatus will not ignite the surrounding atmosphere.

Pressurization is a method of protection by which the entry of a surrounding combustible material is prevented by maintaining a protective gas within the enclosure. This is generally accomplished by creating a higher pressure within the enclosure than the surrounding atmosphere. This protective method would be used for any power operated equipment.

Oil encapsulation is a type of protection in which the electrical apparatus or part of the electrical apparatus are immersed within an oil-based fluid. The general application for this type of protection would be used for:

• Switchgear units
• Circuit breakers
• Transformers

Encapsulation is a type of protection in which the device that could ignite anexplosive atmosphere are enclosed within a resin. The material used would be resistant to environmental influences, heat and/or sparking from electrical components. The general application for this protective method would be used for:

• Electrical circuit boards
• Miniature motors
• Valves

Increased safety is a type of protection where measures are taken to prevent the possibility of high temperatures and the occurrence of ignition. This method includes the interior and external portions of the electrical apparatus. The general application for this protective method would include:

Connection and distribution boxes
Luminaires
Measuring instruments and devices that do not normally produce ignition within operation

Intrinsic safety is a protective method to ensure that the available electrical and thermal energy in the system is always low enough that the ignition of the hazardous atmosphere cannot occur. This is achieved by ensuring that only low voltages and currents enter the hazardous area as well as all electrical supply and signal wires are protected by safety barriers. The general application for intrinsic safety would be used for:

• Measuring and control engineering 
• Data engineering
• Low electrical valves

Non-sparking equipment and wiring process is a protective method where apparatuses are designed with low power levels and low stored energy. This ensures that arc produced during normal functionality of the equipment,  or as the result of equipment failure,  has insufficient energy to ignite the hazardous atmosphere. The general application for non-sparking protective methods would be used for:

• Motors
• Lighting
• Junction boxes
• Electrical equipment

All equipment certified for use in hazardous areas must be labeled to show the type and level of protection applied.

In summary hazardous locations could exist in multiple industries. The geographical location will dictate the general method used for classification. The European Standard or IEC provides guidance of risk into three main categories. These risk levels are then divided into Zones and have numerical values that relate to the possibility of explosive gases or dusts present within the atmosphere. Because combustible material could have a variety of explosive limits, the method of protection will be important. Nevertheless all electrical devices placed within hazardous environments will follow the device markings to ensure fire or explosion does not occur.

Wireless Process Instrumentation and Cloud-based Solutions, Part Two

Cloud-based engineering tools combined with wireless technologies continue to change the industrial control landscape by making employees more productive, making data available in real-time, and driving efficiencies in manufacturing plants. These new technologies reduce engineering hours, shorten maintenance time and make commissioning steps more efficient.  They also improve user safety, streamline usability, and significantly decrease budgets for maintenance.

A standout example of success in wireless and cloud-based tech is the adoption and growth of ADC. ADC is an abbreviation for Automated Device Commissioning, sometimes referred to as Smart Commissioning. From a practical standpoint, it is a set of engineering techniques and processes to check, inspect and test every operational component of a project. Workflows incorporating lean engineering can benefit from designing instrument configurations before the hardware is actually delivered to the facility.

ADC/Smart Commissioning can be used to: Reduce commissioning time to a fraction of the original hours needed; mechanically bind control configuration; reduce the need to verify I/O assignments; help avoid costly errors in wiring and termination; and automate intelligent device testing and documentation.

Use of ADC/Smart Commissioning promotes efficiency for automation projects. Engineers used to have to deal with repetitive and complicated tasks to get the project set up.  Now with this new approach, assisted by wireless and the cloud, teams of engineers can work on the project collectively, and at the same time, without needing to be physically at the same site.

ADC/Smart Commissioning assists engineers in confirming that the right transmitter is landed on the correct controller input/output module (I/O).  If a mismatch is determined, the engineer can fix the mismatch in real time, on-site or remotely.  Then, once the hardware configuration is confirmed, the user can wirelessly perform loop checkout as well.

As capable engineers and maintenance personnel continue to retire from the workforce, and as manufacturing companies are forced to accomplish their work with fewer experienced employees, wireless technology and cloud-based tools facilitate greater efficiency through equipment optimization, performance tracking, safety monitoring, and process reliability.

Analynk Wireless
https://analynk.com
(614) 755-5091

Wireless Process Instrumentation and Cloud-based Solutions

Wireless technologies and cloud computing systems are changing industrial communications. Industrial wireless networks and cloud-based tools, simply stated, allow manufacturing plants to do more with fewer people.

This two-part article delves into the recent trends in the use of cloud-based tools and wireless networks to help plant operators improve their application validation, improve their diagnostic selection of instrumentation, and improve device commissioning.

The benefits of wireless and mobile communications is clear. Engineers and other factory personnel can input data wirelessly via a smart phone, or a laptop computer so they can have their specific requirements recorded. Collaboration with other team members is possible, through the cloud, to determine the optimum set up for the project devices to streamline engineering decisions (and to avoid expensive mistakes upfront in the project). Information in the cloud may also be equipped for instant duplication, so projects that have many identical device configurations can be rapidly repeated.

Using a cloud-based and wireless network approach improves success in installing large numbers of new field instruments, which is common for unit expansion. Other benefits of adapting cloud-based services and wireless networks for prices control include:

• A convenient way to share and collaborate in real-time. Multiple users can visualize the transmitter configuration though a link. This saves staff time and reduces travel time for support people. 
• If a beginning user has an underdeveloped knowledge of the application, the cloud can provide readily accessible information such as compatibility charts, specification sheets, code requirements, etc … . 
• Generation of a standard data sheet so engineers don't have to spend as much time on data entry. The data sheet can be stored to support the user's necessary documentation and audit trail. 

The paradigm for instrumentation setup is changing dramatically. Cloud-based tools and wireless communications are optimizing manufacturing operations and delivering capital projects cost effectively, efficiently, and as rapidly as possible.

Under increasing pressure for improved quality, safety, and profits companies are migrating toward cloud-based application, data storage and wireless networking. These new technologies are playing a key role in improving safety, lowering operating costs, providing real-time performance data, and continuously monitor processes.

Giving Thanks on Veterans Day

Introduction to WirelessHART

WirelessHART is a subset of the HART industrial instrument communication standard as of version 7, communicating process data over 2.4 GHz radio waves. Individual instruments communicate with a common “gateway” device serving as an interface between the wireless network and a wired network or a host control system. In addition to this, though, individual WirelessHART devices also form links with one another, so that the network data routes look like a “mesh” with all nearby nodes interconnected in addition to connecting with the gateway:

In a mesh network, devices (nodes) perform double-duty as repeaters to relay data from other instruments to the gateway as needed. In other words, data transmitted from one WirelessHART instrument may not be directly received by the gateway device if that path is blocked or too far away. Instead, the data may “hop” from one device to another nearby, which then re-broadcasts that information to the gateway via a clearer path.

The purpose of a mesh network is to provide redundant data pathways in case of device failure or changes in the environment interrupting radio communication between devices. In this way, data packets may be re-routed to the gateway if the shortest route fails, in a manner similar to how Terminal Control Protocol (TCP) and Internet Protocol (IP) work together to route data segments from source to destination over the “mesh” of the Internet. This feature is often referred to in WirelessHART technical literature as the self-healing property of the mesh network.

According to the HART Foundation, reliability for a well-designed WirelessHART mesh network is 99.7300204% minimum, and typically greater than 99.9999998%.

With each WirelessHART field instrument capable of functioning as a radio repeater, the potential exists to form wireless networks larger in size than the maximum broadcast/reception range of any one device. This illustration shows what is possible:

An important consideration when planning a WirelessHART network is battery life. With the main purpose of wireless field instruments being the elimination of wired connections to the host system, the field instruments cannot rely on a host system for their electrical power needs. Lithium-based batteries currently fulfill this role as primary power source, with life expectancies of several years. Interestingly, the amount of energy required by a WirelessHART device to transmit radio-frequency data is small compared to the energy required to power its essential instrument functions (e.g. pressure measurement, temperature measurement). This means a WirelessHART device operating as a radio repeater (in addition to being a measurement device) adds little burden to its battery.

Perhaps the greatest challenge in sustaining any wireless field instrument network is ensuring network integrity despite unending changes in the physical environment around the instruments. Remember that this is an industrial, field-instrument wireless network designed to be installed in less-than-ideal physical environments. These wireless devices must somehow reliably communicate with each other despite interference from high-power electrical devices (e.g. variable-frequency motor drive units), while mounted on or near metal objects such as girders, pipes, pipe racks, large vessels, motors, enclosures, shelters, and electrical conduits. Even the ground of an industrial environment can be an impediment to robust radio communication: steel-reinforced concrete and electrical grounding grids form what is essentially a solid “ground plane” that will interfere with WirelessHART devices mounted too close to ground level. Added to all this spatial complexity is the continual presence of large vehicles and other moving machines (cranes, forklifts, manlifts, etc.). It is not uncommon for scaffolding to be temporarily erected for maintenance work in industrial areas, presenting yet one more obstacle for RF signals.

In answer to these challenges is an integral and essential component of a WirelessHART network called the Network Manager: an advanced digital algorithm usually executed by the network gateway’s microprocessor. The purpose of the Network Manager is to manage the details of the network automatically, “tuning” various parameters for optimum reliability and data throughput. Among other tasks, the Network Manager assigns “timeslots” for individual devices to transmit, determines the frequency-hopping schedule, detects and authenticates new devices added to the network, dynamically adjusts device transmission power, and selects alternative routes between devices.

In a sense, the Network Manager in a WirelessHART network continually audits and tunes the RF system in an attempt to maximize reliability. The Network Manager’s functionality does not substitute for good planning during the design phase of the WirelessHART network, but it does eliminate the need for a human technician or engineer to continuously monitor the network’s performance and make the small adjustments necessary to compensate for changing conditions. When changes occur in a WirelessHART network that cannot be compensated by the Network Manager, the real-time statistics provided by the Network Manager are invaluable to the technician or engineer assigned to update the network.


Reprinted from "Lessons In Industrial Instrumentation" by Tony R. Kuphaldt – under the terms and conditions of the Creative Commons Attribution 4.0 International Public License.