Arc Flash Analysis
You already know why you need a power system analysis at your plant, but what about actually executing the project. There a three basic way to approach getting a power system analysis completed:
- Completely In-House
- Completely contracted out
- Hybrid of both
These have their pros and cons, and depending on the size and complexity of your company and system the method that is chosen may be obvious. Below is a brief description of each method, including a couple pros and cons of each.
When you complete the power system analysis in-house, you will have the advantage of being in complete control of the end study, and as a company you will have a better understanding of the status of the power system as a hole. This is one of the less talked about advantages of having a power system analysis prepared, it gives you the opportunity to double check all your drawings and understand any oddities throughout.
Completing the power system analysis in-house assumes you have the resources within your team, including
- Skills – Someone has done these before and knows how to do this one
- Tools – The necessary software is in-house and there are staff trained in using it.
- Time – There are resources to complete all five steps to get it done.
When you outsource the power system analysis to your favorite consultant, it can be a simple matter of writing up a scope and walking away.
If you need to have multiple companies bid, I would recommend adding our free technical spec, get it when you sign up for our Power System newsletter.
This will greatly reduce the drain on internal resources, now you only need to monitor a contract and review the reports. However, when you do this you also lose some control and add to the monetary cost of the project greatly.
In summary, outsourcing the project will likely reduce you direct input greatly, while increasing the project cost.
3. Hybrid Model
A hybrid model is one that keeps your involvement high, while outsourcing the project parts that you don’t have the resources to complete, whether its time or skills. For example, assume that your company has the resources to gather all the data for the project, but doesn’t have the necessary software or anyone available that has experience in preparing a power system analysis. In this case you could outsource the model development, studies and report (steps 3-5) and prepare the scope and gather the data using company resources (steps 1 and 2).
This model has the advantage of ensuring that the data used in the analysis is accurate to site conditions as your personnel will know the site better than anyone, the cost will be kept under control as data gathering is one of the most tedious and expensive parts of the project when completed by an outside resource, and the study results and recommendations will be accurate and actionable because you had an experienced consultant prepare them for you.
The hybrid model allows the power system analysis project execution to be:
- Good input data – know one knows the facility better than the people who operate it day in and out
- Cost Effective – consultants doing what they do best, and company resources gather the necessary data
- Accurate and Actionable – experienced consultants who have the tools, and training can provide the best report.
What we think
In most cases we will always recommend some type of hybrid model, but the split will always be different and dependent on the resources of the company that we have engaged with to complete the analysis. By using a hybrid model you will be able to leverage our strengths in power system modelling and analysis to produce a great product, while using your internal resources to gather the necessary input data to keep the costs low (and value high) without sacrificing quality.
If you have a project that you want to talk to us about don’t hesitate to use the contact page, or send us a note using the form below. You will be signed up for our power system newsletter and we will get right back to you.
If you have never been involved in a power system analysis before, it may seen like a very daunting task. To help add some structure to this here are the steps involved with getting one completed, and a description of each.
- Determine the scope of the Power System Analysis
- Gather the data
- Create the Power System Model
- Run the necessary Power System Studies
- Write the Power System Analysis Report
1. What is the Scope?
Before I start any power system analysis project, or even start to price the project, I help work out the detailed scope needed for the report. This mostly has to do with, why is the power system analysis needed? The reason that it is needed will determine the specific studies that will be run, and therefore the data that will be needed in the second step. A couple of examples of this are:
- Input to the Electrical Safety program (Arc Flash Labels)
- Future Capital Expansion
- Power Quality Concerns
2. Getting the input information
With regards to usefulness, getting the necessary input information for a power system analysis is the critical step. With bad, or incomplete, information, the model and the resultant studies are not going to be accurate. If the purpose of the power system analysis is to develop labels as part of an electrical safety program, this means that PPE will be selected based on the outputs of the analysis, being wrong will put electrical workers at a higher risk than they expect.
Garbage in, garbage out.
Gathering the information is typically both the hardest and most time consuming part of a power system analysis. It requires combing through existing drawings, and then verifying that this information matches the installed conditions. Some of the information that is required for an arc flash analysis are:
- Nameplate information of:
- Circuit breaker settings
- Fuse settings
- Cable and Raceway information
- conductor size and configuration
- conductor length
- raceway material (ferrous or non-ferrous)
A lot of this information can only be verified behind the enclosure doors, and since this hypothetical scenario is for an arc flash anaylsis, there is no recommended PPE, therefore it must be completed de-energized. For a lot of facilities, this requires coordination with already busy shutdowns, etc. Planning is the key to any successful power system analysis
3. Putting the Data Together
The next step along the journey to a completed power system analysis is putting all the data that was gatherd in the previous step into a power system model using the software of choice, my preference is ETAP, but there are other great options out there.
Creating the power system model is mostly data entry, and is pretty straightforward, but care is taken to ensure that all the data is correct so that the resulting studies are not misleading.
4. Running of the Power System Analysis Studies
Which studies are necessary will depend greatly on the scope of the project that was figured out in Step 1 above. In Power System Analysis in Industry I talked about the 3 that I always recommend:
- Short Circuit
- Protection Coordination
- Incident Energy (Arc Flash)
These studies allow you to prepare updated labels for your equipment, determine if there are any existing equipment that needs to be replaced on short circuit duty, and ensure that the protection coordination of your plant is adequate for your operations.
5. Writing the Power System Analysis Report
Finally comes the report. With all the information above, the report will summarize the results of the studies and provide any recommendations. The report is the most important power system analysis deliverable. With a detailed report, you will be able to create action items for any of the issues that were discovered, and have a great base point to build and improve the quality and reliability of the power system at your plant.
I help clients of all industries and situations through all these steps. We have started preparing a detailed checklist based on these 5 important steps. If you are interested in getting a copy when its done fill out the form below, or here. When you sign up we will send you our template power system analysis technical specification that you can include in your next RFP.
As always please don’t hesitate to contact us if you have any questions!
Jeff MacKinnon, P.Eng.,PE
There is a misconception that I hear every month or so when talking to clients and other engineers, it is that since CSA Z462 isn’t written directly into the law of the land that it doesn’t have to be followed.
Well, they are right that it isn’t written in the Provincial Regulations, with the exception of BC where it is referenced as an acceptable standard, but they do reference the Canadian Electrical code CSA C22.1, and C22.1 references CSA Z462.
For example in Nova Scotia Occupational Health and Safety Act paragraph 120 (1) states:
An employer shall ensure that an electrical installation is designed, installed, assembled, operated, inspected, serviced, tested, maintained, repaired and dismantled in accordance with the latest version of CSA standard CSA C22.1, “Canadian Electrical Code Part 1”, Safety Standard for Electrical Installations”.
When you open the Canadian Electrical Code Part 1 (CEC), there are two rules in Section 2 that stand out:
Rule 2-304 (1)
No repairs or alterations shall be carried out on any live equipment except where complete disconnection of the equipment is not feasible.
and Rule 2-306 (1)
Electrical equipment such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centres that are installed in other than dwelling units and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn persons
of potential electric shock and arc flash hazards.
These rules both point to appendix B in the standard with notes on the rules that point the reader to CSA Z462 as an acceptable method to meet the intent of these rules. To my understanding this hasn’t been tested in the court of law, but it would be negligent not to use CSA Z462 as the minimum standard when developing a safety program in your company.
Not only CSA Z462
That doesn’t meant that CSA Z462 is the only standard that can be used, NFPA has a comparable standard numbered 70E that says all the same things as CSA Z462, but in standard units vs metric.
Using Nova Scotia as the example, using the current version of CSA Z462 (or NFPA 70E) as the standard when developing your electrical safety program is the most prudent means to ensure the safety of your employees and compliance to local law.
CSA Z462 is the accepted industry standard regarding electrical safety in the workplace, and the 2015 revision allows tight integration into your existing Occupational Health and Safety program. By using CSA Z462 as the standard in your facility you reduce incidents in number and severity, and will be compliant with the local laws.
If you would like to talk more about how we can help you integrate CSA Z462 into your safety program contact us here. If you aren’t ready to integrate CSA Z462 into your safety program click here and sign up to our monthly newsletter.
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.
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
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.
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
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.
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.
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.
Be sure to follow us on Twitter and like our page on Facebook!
Main Image Source