JMK Engineering Inc.

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Energy Study

What Can I Do With Incident Energy Studies?

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esp into featured imageToday, I will outline three things you can do with a completed incident energy study. Completing these tasks is an important part of any electrical safety plan, and will reduce the risks to employees performing work on energized equipment. This will also reduce the risk of an arc flash incident occurring.

Identify Key Problem Areas

An incident energy study will show you where the incident energy is dangerously high in your facility. Now that you know the incident energy on a particular bus is high, you can analyze your power system with this information in mind, and try to answer the following two questions:

  1. Why is the incident energy at this location so high?
  2. Can the incident energy at this location be lowered somehow to provide a safer working environment?

Establish Working Boundaries and Select Warning Labels

arc-flash2
An example of a warning label

Once you’ve answered the questions about your key problem areas, you might determine that the incident energy level cannot be reduced any farther. From here, what you can do is use the information in your incident energy study to establish safe working boundaries and acquire warning labels. The incident energy study should indicate the likelihood of an arc flash event occurring. Knowing the risks, you can assign appropriate working boundaries for the tasks involved with energized equipment. The incident energy study should have different “levels” assigned to each piece of equipment that is a part of the study. These levels correspond to recommended working distances, and you can use these levels to label all of your equipment so that every worker understands the risks of working on energized labelled equipment.

Select Appropriate PPE For the Job

Now you can use your newfound knowledge of the safe working boundaries to select the appropriate PPE for any job that takes place in your facility. The same levels that you used to

An example of PPE

determine working boundaries can also be used to determine PPE requirements. If for example you must work closer than the recommended working boundary, the incident energy study will recommend the level of PPE required for doing energized work at different working distances.
In order to determine what PPE you need, you’ll have to use the relevant standards. CSA Z462 in Canada and NFPA 70E in the USA both have extensive tables describing what
appropriate PPE is for the various levels of incident energy on a work site. It is important to also adhere to any and all local and regional standards for your area.
An incident energy study is required for determining safe working boundaries and PPE for the work site. Thanks for reading! If you enjoyed this article, sign up for our newsletter for more content like this, and share this article with your colleagues with buttons below.

How to best use the Power System Study Report

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If you have gone through the process of completing the power system study report, or have had an outside consultant provide you a binder with all the deliverables, now the real work begins. Having a power system study completed is not the end: it is the start. The reasons to have a power system study report completed in the first place can vary from getting incident energy values for PPE selection, to future plant expansions.

Study Report
Use the power system study report to save money and have a reliable facility.

In this article we will outline some of the more common uses of a complete power system study report. We’ll also include suggestions about how to approach the recommendations that were included.

Short Circuit Study

Let’s start at the beginning with the short circuit study. The first thing we will look at is the type of recommendations that you will be expecting to receive in the report. First there is going to be any equipment that is not rated for the existing short circuit current that is available within the facility. There are a couple of reasons for this to happen: the first is that the equipment was purchased undersized, however the more likely scenario is that there have been system changes. These changes could be either at the utility level – adding additional transmission capacity – or within the facility itself.
Typically the best way to fix these issues is to replace the equipment.
Another output of the short circuit study will be areas that are marginal. This could mean that a change in the system could exceed the fault rating on the affected equipment. For these, investigate the switching scenario that was used, and figure out if there are any additions to the plant planned in the future.  A decision will then be made to determine if the equipment should be replaced now, or flagged as an area of concern when there are system configuration changes in the future.

Protection Coordination Study

Time Current Curve Example
TCC from an ETAP example file

The protection coordination study will likely include recommendations for areas that are mis-coordinated. With the help of your consultant you can go through the areas of concern and develop a list of what needs to be changed.  With proper selective coordination, the system will operate in a predictable manner in the event of a fault or overload.
In a lot of cases it will be easy to change the settings on the relay, or LSI(G) breaker, to solve the coordination problem. If the settings can’t be changed with the existing equipment, the protection device will need to be replaced. If the mis-coordination is something that will not affect a large portion of the system, or is the same circuit (a primary fuse and secondary breaker on a transformer) the decision may be to leave the mis-coordination as it is.
Another consideration of selective coordination is the incident energy in the case of an arc flash event. Clearing the fault as quickly as possible will limit the heat energy available, and will reduce the arc flash boundary and PPE required for energized work.  These decisions will be simplfied when going through the electrical safety program.

Incident Energy Study

The incident energy study is a critical input to the arc flash analysis, which is a critical portion of the electrical safety program. If you haven’t developed an electrical safety program or an arc flash risk analysis,  a great way to start one is with an incident energy study in hand. With the incident energy known at all the equipment, you will know the arc flash boundary and can start developing PPE levels for energized work.

The Electrical Safety Program is critical workplace safety
The Electrical Safety Program is critical to workplace safety

Arc Flash Risk Analysis

The first step is to develop a risk assessment as associated with the arc flash hazard. Within the company develop a list of the various tasks that will expose workers to an arc flash hazard. From there you can determine what incident energy is considered too high of a risk for energized work, and cross-reference with the incident energy report. You can implement mitigation techniques for any areas that have a high incident energy.

Incident Energy Mitigation Techniques

There are only two methods to lower the incident energy at a bus: one is to lower the time the arc is present before being cleared, and the other is to lower the magnitude of the current.  To shorten the time that the arc is present, modifying the protection settings will work well. Sometimes this may mean sacrificing selective coordination, which is a compromise that can be made on a case by case basis.
It is harder to lower the available current. You can add impedance – add inductance or more cable – which is typically not practical, or break up the large motors onto different buses to lessen the back feed current during a fault. Neither of these are very practical, and are typically ignored.

Load Flow Study

Power system study reports can help you save money by saving energy.
A load flow study can help save energy and save money

Finally the load flow study is the place that you can really start to save money. Using the results of the load flow study report, you can see where in the system you may have opportunity to increase efficiency. We’ve already written about who can leverage a power system study: engineers aren’t the only group that can use the load flow study in their everyday work.  A couple of examples are how capital projects (power factor correction) and operations (load scheduling) can help your facility save money and pay back the cost of having a study completed in the first place.

Power Factor Correction

By ensuring that the power factor is matched as close to 1 as possible, you system will be operating with the least kW, meaning that you will be paying for the least amount of energy from the utility. The load flow study will determine the best place to install power factor correction capacitors, whether they should be staged or always online.

Load Scheduling

If your facility has a large energy draw, and a lot of motor load, then your power bill will likely be in multiple parts. Each part will have different charges. For example:

  • Energy -kWh
  • Max Demand – kW with a rolling average
  • Power Factor – too much kVAR draw

The load flow study allows you to figure out your baseline operations. You can then start making changes to how new loads are added, and determine the most cost effective way to operate the facility without hurting production.

Conclusion

There are a lot of useful projects that will optimize the operation of your facility: we have only scratched the surface with this article.  If you liked this article, feel free to share it. If you let us know, we’ll add more articles like this one, about utilizing a power system study at your facility to give your business a competitive edge.
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Short Circuit Study

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A short circuit is

an abnormal condition of relatively low resistance between two points of differing potential in a circuit, usually resulting in a flow of excess current. TheFreeDictionary

The purpose of the short circuit study is to determine the fault current available at the various buses on your system.  These are worst-case single and three phase bolted faults. With this information you can determine if your equipment is sized appropriately (or if you are designing a new system, you can size the equipment appropriately) and will not fail during a fault event.

A cool photo of an old control room – Flickr

Why do I need a short circuit study?

A short circuit study is used to determine the worst-case current scenario during a 3 phase and single phase bolted fault. This is critical design information when selecting equipment for a new design, and replacing existing equipment during upgrades. Two factors contributing to the fault current is the size – and impedance – of the transformer supplying the circuit, and the available fault current that can supplied by the utility, and on-site generation.
A short circuit study is used to determine the worst-case magnitudes of these currents. These currents will be used as design inputs when purchasing new equipment, and verify that system changes haven’t affected the maximum design currents of the equipment. The equipment must be capable of withstanding the maximum short circuit available. When a short circuit occurs, these high currents create strong magnetic forces and if the equipment design hasn’t been tested, or braced adequately, for these forces there may be catastrophic failure causing additional damage. Under normal circumstances, panels, switchboards, etc are designed to contain the fault; but this is only to a specific current rating.

When should I have a short circuit study completed?

Knowing when to get a short circuit study done isn't hard
Do you know when you get a short circuit study done?

The short circuit study will be completed, and updated during the design process, but should be reviewed  periodically to ensure that there have been no changes that affect the system. I recommend that the short circuit study be reviewed at least every 5 years, this is based on the the requirement in CSAZ462 4.3.5.1(b) regarding arc flash risk assessments. A short circuit study is one of the inputs of this risk assessment.
However, if there have been changes to the facility, it is important to update the design short circuit study with the updated information. If the changes include installation of a new utility transformer, new generation on site, or significant load modifications there is a danger that the available short circuit will increase.

How do I get one done?

Getting a short circuit study completed is very similar to any power system study as I talked about in a previous post, however there is much less data required to ensure that the output is worst-case values.
It is typical to ignore cables during the first iteration of the short circuit study. This lowers the cable impedance throughout the system resulting in higher magnitude fault currents and is used to develop the worst-case scenarios. If these values don’t cause any serious design constraints or result in values that are higher than the installed equipment can withstand, this is where the short circuit study will stop.
Additionally, if you have a smaller system with a few voltage systems, the short circuit study could be as simple as determining the maximum current your transformers will supply based on an infinte bus.  To determine this you only need to know:

  • transformer size
  • system voltages
  • transformer impedance

If the impedance isn’t marked, using typical values for the transformer design will get an answer that is close to the final answer.

Conclusions

Having a current short circuit study at your facility, regardless of the size, is very important for the safe and reliable operation of the power system. If it is a small building, this will not be difficult, and can likely be completed by hand assuming infinite bus. If you have any questions, about how to have this completed please don’t hesitate to contact us.
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