Merry Chirstmas everyone, and a joyous New Year.

Hope for 2012 to bring even great happiness and success than 2011.  Stay safe and alert this 2012 when working with electricity.

How I got started

It started when I was at Dalhousie University and was looking for a group to get involved with to help my resume and meet people in the industry.  The IEEE Student Branch seemed like a great place to start, so I started volunteering as the Secretary and the local Section, Canadian Atlantic Section invites all students to attend their meetings which is where I started to meet the people that worked in the area.

IEEE members are great people to hang out with.

One of the activities that the student branch ran was a trip around the province to visit various companies from small manufacturing, pulp and paper mills and and power generation stations.  This trip was a great time and opened my eyes wider on some of the benefits of an IEEE member.

From that point on I was a serial volunteer taking positions of Student Branch Chair (sorry Leo), section secretary, to vice-chair and regional newsletter editor and finally holding the Chair in Spokane.

That is my history as an IEEE member since 2002.

I'm a member because...

Mo El-Hawary

Some of the reasons to why I have continued with my membership has changed over the years, and others have acted in cycles.  For example, when I first joined as a student, the major reason was to get to know some of the people in the industry that I was interested in entering, and possibly help get a position in the area, and when I moved to Spokane, while I already had a job lined up, I didn't know anyone from the area and IEEE was a great starting point.

IEEE has also afforded me the ability to travel all over North America, and meet amazing people and make life long friends, whether it was a student conference in London, ON or the sections congress in Quebec City, QC and San Francisco, CA.

IEEE membership has also allowed me to learn from the giants in the industry, whether it is discussing power system analysis from the people that write the seminal text books, or learning the challenges of building the life-safety system in the Mercury program from one of the lead engineers.

(Photo Credits:
Featured Photo - UCLA IEEE Student Branch
Second Photo - Section Congress 2008 Photo page
Third Photo -  Sections Congress Facebook Page)

Modern power system design is the application of sound engineering practices to electrical systems primary develoted to the generation, distribution, and consumption of electrical power.  Ideally, this process is  governed by minimum code requirements, standards from agencies such as IEEE and ANSI, and commonly accepted industry standards.  Occasionally, the process is marred by little appreciation for tribal knowledge, incomplete understanding of standards, or the rote execution of a design with little appreciation for the application.     As engineer, we strive to avoid these pitfalls by furthering our understanding though the acquisition of additional source materials.  Unfortunately, despite the ubiquity of the internet, groups such as IEEE and ANSI don't provide their standards for free, and the availability of regionally enforced code is an area of ambiguity.  Fortunately, some manufacturers have provided resources that are invaluable to engineers:

General Electric provides The Art and Science of Protective Relaying free for download.  A quick perusal of the Bibliography for each chapter reveals the history of this document, and despite the dates, this document remains as relevant as ever.  The principals are still applied in modern protective relays, and numerous Defense Plant Corporation era facilities still employ electromechanical protection to great success.

As a modern supplement to GE's definitive guide, Schweitzer Engineering Laboratories provides numerous resources under their Literature section.  In addition to the Journal of Reliable Power, they provide white papers and technical papers outlining the methodologies used in a modern digital relay and their appropriate application.  Be warned, they do require a free account for access to their library.

Eaton publishes a Consulting Application Guide, a rather fancy name for the Eaton/Cutler-Hammer catalog of all relevant industrial equipment.  Despite the commercial nature, the first chapter provides substantial reference material on all manner of subjects.  From protection, to system layout and generation, the Eaton catalog touches on many relevant subjects.

Image provided by the Seattle Municipal Archives

Near the end of October I was shown a very poorly written Incident Energy Report.  The reason that it was given to us, a competing consulting firm, was that we designed the system and on of the action items listed was regarding the size of the transformer protection.  They said it was wrong, we checked and they were wrong.

For the record, the secondary circuit breaker of a transformer may be used for the transformer protection as long as it is no greater than 250% of the full load current of the transformer AND the up stream protection from the transformer is no greater than 600% that of the full load of the transformer.

We checked and we meet both of these requirements. Besides that, the breaker settings that we used, and they used in there report, were well within the transformer damage curves.

What’s this all about?

But that is NOT the reason I am writing this first entry, basically there are some things that every Incident Energy Report must include. Since this is more than can be covered in a single post I am going to write a 6 Part series explaining what I believe must be included in every IE Report.

The parts are:

• Part 1: Site Background Information and Scope
• Part 2: Description of the System
• Part 3: Short Circuit Information
• Part 4: Protection Coordination Information
• Part 5: Incident Energy Levels and associated Boundaries
• Part 6: Recommendations

Each one of these sections must be included in every report that you may write or receive from a consultant.  If one is missing when a review report is issued ask why it is missing.

This is not to say that each section will have to be called out within the report, depending on the scope and size of the system they may be simply broken out into line items, but they must be included.  However in this one report that I had viewed, this was not the case, and this is why I have decided to write this series of posts.  I will be adding the posts through the months of January and February and will have a detailed summary post at the end.

You have to be more Precise

When an Arc Flash Study, currently being referred to an Incident Energy Study, is completed owners and operators start to look for ways to minimize the workers exposure to high incident energies.  One of the ways that this can be done is to ensure that all work is completed in a zero energy state.

This is not always possible, and when operating disconnecting devices the worker may be in danger.  Following are some options that can be used to reduce the incident energy, and associated flash protection boundaries.

1. Tighter Protection Coordination

One of the first steps to lower the incident energy of an arc fault is to review the Protection Coordination Study surrounding the specific buses that a lower incident energy would be attractive at.  The traditional philosphy regards to protection coordination is to ensure that faults are isolated in a strictly predictable manner.  This means that there is space on the Time-Current Curves to ensure that the protective device that trips is the one that the operator expects.

These studies are coordinated at worse case, a bolted fault, and an arcing fault will always be at a lower value.  This results in the required protective device taking longer to operate than is desired.  If possible a facility may be able to use a slightly smaller fuse, or tweak the breaker settings to use less space between the protective devices and in turn allow the desired device to trip sooner.

The negative of doing this is that in higher current faults the devices may not be coordinated, this may cause an up-stream device to operate extending the range of the outage unecessairly.

2. Selective Protection Coordination

There are new technologies being developed and released to the market everyday.  One of the technologies that I have been more impressed with is the ability to have multiple sets of Time-Current Curves installed in a circuit breaker.  These curves are selectable with a switch either on the wall of the electrical room or mounted on the breaker enclosure.  This will allow the operator to change the characteristics of teh breaker and have it trip in the instantaneously for a larger range of currents.  When this happens the clearing time of a fault is significantly reduced and in turn so is the incident energy.

When the breaker is in this instantaneous range it is no longer coordinated with the devices downstream from it.  If the worker does not replace the device in its normal operating mode when work is complete there is a significant risk of it operating when there is a fault, which will then shutdown more of the facility than is required.

Another consideration to remember when this method is used is that the breaker that feeds the equipment that is to be worked on must be the one that is altered.  If that breaker is in the same enclosure, then in most cases, the next up stream breaker must be moved into the instantaneous range.  The reasoning behind this is that there is still a risk of the feeder breaker located in the enclosure faulting which would then require the upstream breaker from it to operate to extinguish the fault.

3. Install a Fuse / Breaker

If only they were this small

I have included both these options in the same line on purpose.  If you have had a representative from either of these manufacturers give a presentation on Arc Flash from 2002 til recently I am sure that you have seen the fantastic videos showing how their respective equipment is the "bee knees" with regards to Arc Flash and reducing incident energy.

I believe that the reality of the matter is somewhat more complicated than replaceing your electrical infrastructure with one product and assuming that everything is going to work out fine.

My typical rule of thumb is this, if the available fault current is high, then fuses have the faster clearing time (as little as a ¼ cycle).  However if the fault current is lower a breaker may be the better way to go.

Conclusion

What is going to be your road map to safer work conditions

There is never the perfect answer with regards to ways to reduce the Incident Energy of an Arc Flash.  Consult with the party that completed your study and with your operations people to determine what if any changes can be made to the system and operation to minimize the required PPE.  However always remember that PPE is the last line of defense and all other methods to ensure safe work procedures are employed are first.

If you have any suggestions or questions please let me know in the comments.

Arcing faults (an Arc Flash) are defined as high-impedance faults, since any fault current must travel through air, as opposed to the low-impedance path normally associated with a short circuit. A short circuit study of the electrical system is required to determine the maximum available short circuit energy, which in turn may then be used to calculate the potential incident energy available.

There are intense heat and pressure waves associated with these types of faults.  This heat and pressure wave will cause shrapnel and molten metal to explode from the point of the fault.

The core temperature of an arc fault can easily reach 5000ºC (source), for comparison the surface temperature of the Sun is only 6000 ºC and the boiling point (not melting point, but BOILING) of copper is 2500ºC.

Assuming that the electrical protective device in the circuit operates fast enough to extinguish the fault so that these extreme temperatures do not cause greater than second degree burns to the operator, the ignition temperature of the typical non-PPE clothing the operator is wearing would have been reached, this burning will cause serious harm to the operator if they are not extinguished quickly

When proper PPE is worn for the calculated incident energy at the fault, the worker should walk away from the incident with a maximum of second degree burns.