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Power System Modelling

Power System Study Deliverables

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Now that you have decided on the project framework that you are going to go with and you understand the scope of the power system study, you need to prepare the list of deliverables.

Power System Report drafting
Let’s outline the power system study report

There are 3 items that must be included in every report, and there are some things that should NEVER be included in a power system study report body. There are some sources of information that are important to have as backup to both you as the client to evaluate the consultants expertise in the area, and also to educate the non-electrical workers and managers in your company.

Power System Study Deliverables

The 3 overall deliverables that should be included at the end of the project are:

  • Power System Study Report, complete with recommendations
  • Updated drawings with any new information – onelines, switchgear drawings, etc.
  • Power System model in the software of your choice – complete with any custom libraries.

Depending on the scope of the study, you may want to include the following:

  • Capital Budget estimates to implement selected recommendations
  • Updated Electrical Safety Program Documents
    • Typically labels from the incident energy study
    • Updated information for Energized Work Permits

Now lets describe the critical parts of each of these.

Power System Study Report

We outlined the sections that will be included in the report when we discussed scope, but there we only mentioned the specific study results and a section for recommendations.
The report isn’t the place to educate the reader about what the different studies are, the pro and cons of different methodologies, or discussing why it was a good idea to have the study completed. If the report will be distributed to people that don’t have an electrical background and need to be brought up to speed, here’s the tip I use at JMK Engineering:

Include appendices with articles and short whitepaper reports describing what the studies are and how they can be used. This keeps the report on topic, but expands the audience of the complete report.

Introduction

The introduction is the place in the report where the reader is orientated as to what this report is all about. The introduction should include the purpose and scope of the report, the methodology used to gather data and study the system, and standards that were referenced during the work. The sub-headings include:

  • Purpose
  • Scope
  • References
  • Definitions
  • Assumptions and Limitations
  • Project Methodology

Study Analysis Sections

Each study – short circuit, protection coordination, incident energy and load flow – will have their own chapter in the report.  Each of these will have the following sub-sections:

  • Introduction
    • Study specific scope items
    • Study specific source information – utility supply, motor loading assumptions for load flow, system configurations reviewed, etc
    • Thresholds used for warning and critical for the results.
  • Study Results
    • This is only a summary of the results including separate tables for the warning and the critical items.
  • Study Recommendations
    • These recommendations are for the what needs to be done, not the how.  It could be that all the critical lines need to be addressed, but it could be a procedural change (don’t put the system in that configuration)

Appendices

This is where the report starts to grow. The appendices will include the complete analysis outputs for the various studies, including all TCCs for the protection coordination studies. The appendices should also include any pertinent source information that was used in developing the model and report. Here is an example list of appendices that I have included in past reports:

  • Original Proposal (including scope, etc)
  • Data Collection Sheets
  • Relevant Correspondence
    • With the client, utility, suppliers and anyone else that provided useful information that was used in the analysis.
  • Incident Energy Labels
  • What is Short Circuit, Selective Coordination, Incident Energy and Load Flows.
    • This is 4 different articles in one appendix.

Updated Drawings

Next the drawings that are affected by the study and its recommendations need to be updated. What I have found is the drawings lag behind the changes in the field over time, and during the data collection effort we find a number of conflicts, equipment added or removed and settings changed.  The power system study is the perfect opportunity to as-built all these drawings.
The oneline is always caught, but there are other drawings that should be looked at for inconsistencies.  These can include:

  • Threeline diagrams
  • Motor Schematics
  • Switchgear and MCC Drawings
  • Panel Schedules

Power System Model

If you are having an outside resource develop the model, we still recommend you receive a copy of the model and any custom library items electronically. Ideally this will be included on a thumbdrive and included in the report as an appendix.  The best reason for this is that the power system study report is not a static thing, as the system changes it will be updated, and per CSA Z462 and NFPA70E it should be updated no less than every 5 years. After doing all the work – and spending the money – to get the original completed, it is much easier to update with changes than go through the entire process every 5 years.
If the contractor moves along, or doesn’t have good data retention practices, you will lose this data. Get a copy for your records.

Optional Deliverables

The list of deliverables is not exhaustive, and depending on the scope of the power system study you will include others.  Two that I recommend are capital budgets and electrical safety program updates.

Capital Budget Development

You likely have a capital budget cycle that is used to determine what capital projects will be completed in the coming years.  Based on the recommendations outlined  in the report, there are typically additional engineering and installation that will be needed to fulfill the recommendations and make the system safe. To develop these budgets there is some initial engineering design required, but the entire design does not need to be completed in most cases. To present a complete package to management, and allow business decisions to be made, the capital budget report should include the following for each recommendation:

  • Recommendation and why it is needed (Scope)
  • Options – if there are any
  • Capital cost for each option in today’s dollars
    • This should include engineering, procurement, and installation/construction

If there are similar recommendations, like setting changes to relays, these can be grouped.

Electrical Safety Program Updates

If you included an incident energy study in your report, and you have an existing electrical safety program, you will want to make any necessary updates. This may include adding information to the energized work permits, adding new labels and updating the training information

Conclusion

The deliverables related to a power system study are not just labels and an output for the software. To be useful, informative, and actionable we need to include everything mentioned above.  A good consultant will include all the critical deliverables even if you haven’t included them in the RFP, however the lowest price may cut out most of them and provide the bare minimum.
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Getting a Power System Study Completed – Who does what?

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Now that you have determined that you need a power system study, and you have developed the scope of the project, you need to determine how you are going to get the study completed. To start with there are a lot of questions that need to be answered. Do you buy the software and tackle it yourself? Do you hire an outside company to put it together? How you answer these questions will determine the next steps, but we are 90% sure what the best option will be at the end.

Teamwork is key for a successful power system study
Teamwork is key for a successful power system study – Flickr

 

Getting Started

There a three basic way to approach getting a power system study completed:

  • Completely In-House
  • Completely contracted out
  • Hybrid of both

These all have their pros and cons, and depending on the size and complexity of your company and system the method that is chosen will be self-evident. I will explain the pros and cons of the two extremes, all in-house and all contracted out and then explain why I think a hybrid option is typically the best answer, even with the added administration over completing the project inhouse.

InHouse

The main advantage with completing the power system study inhouse is control. If you, or a co-worker, is completing the study they already have access to the equipment, or know who does.

Outsourcing

The advantage of having an outside resource do the work for you is that you can put together the project scope, pick your favorite consultant and walk away for the most part until they have questions, and finally are ready to present the report.  With this method you have to facilitate the consultant with getting the information and then answering any questions that they may have.

Hybrid Model

The hybrid model is a combination of both, completing the areas that you are competent and have resources available for inhouse, and then outsourcing the areas that you may be weaker – or don’t have the resources available – to a competent consultant.  A common split would be for the owner to gather all the data required and update the drawings, and the consultant build the model with this information and produce the report.
The reason I think that this is the preferred method, and will help keep the project schedule and costs reasonable is because it will allow you to leverage your strengths (knowledge of the system, process, business, etc) and limit your weakness such as knowledge of the modeling software, interpreting the results, working with utilities, etc. These are all tasks and areas that you may not work with on your day-to-day business, but a reputable consultant will.

Our Recommendations

There is no right model for every situation, however we almost always recommend some type of hybrid model. The site should retain control of the Electrical Safety Program, developing the risk matrix, and even gathering the input information. However, outside resources will typically be more efficient for developing the system model, the incident energy report and at times even the data gathering around the site.
Always work with your consultants to divvy up the work in a way that leverages the strengths and limits the weaknesses of each group.
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Data Requirements for Power System Studies

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Now that we have an understanding about the importance of good data collection for power system studies, and how to prepare a plan for data gathering, now we need to understand exactly what is needed for each power system study type and specific pieces of equipment. However, there is some information that is needed no matter what study is being completed.

Pole mounted utility transformers.
The size and type of the utility transformers make a huge difference

What do they all need?

  • Utility information
  • Nominal system voltage levels
  • System configuration with the following equipment:
    • Transformers (with impednance, voltage and configuration),
    • Configuration switches and circuit breakers
    • Switchgear, mccs, switchboards, etc down to the voltage level you are interested in
  • Any large motors and other generation on the site.

With this minimal information you can prepare an adequate short circuit study that will give you values for the short circuit on any of the buses above. These will be very much worse case as we haven’t gathered any additional impedance information.  This study would be useful for design and specification purposes when you are purchasing equipment for a new facility.

Short Circuit

What information needs to be added to get a decent short circuit, well it is everything above and the following:

  • Distribution equipment short circuit withstand and full load information
  • Transformer ratings
  • Protection equipment manufacturer information, complete with full load rating and short circuit withstand ratings.
  • Cables connecting distribution equipment, complete with size, type, configuration and length
  • Lumped motor and non-motor loads at all distribution equipment

With this information you will be able to determine the worse case fault scenarios based on your system configuration and determine if there is any equipment that hasn’t been designed to withstand that level. If there is, this is the first thing that must be addressed in your facility.

Protection System

The additional information that is required for your protection system includes everything that is needed to determine how your protection is going to activate in the event of a fault as determined by the short circuit study.
For this you will need to determine the following:

  • Trip characteristics of all relays
  • Tripping times for all breakers
  • Complete manufacturer information for the fuses in your system
  • Manufacturer information for all moulded case breakers
  • Any large motors, and their protection broken out. This is to ensure that the protection is coordinated with the worse case starting current.
  • For large motors the interial load, and starting times may be required, along with any design type information.

With this information in the model, time current curves, commonly called TCCs can be developed and reviewed to determine if the system will operate in the event of a fault as intended.  If there are any overlapping areas that may be cause for concern, this is where they should be addressed.  If there is a fault, predictability in how it will be cleared is very important in the aftermath. If multiple protection devices activate it is much harder to determine the cause if there isn’t much visable damage.

Incident Energy

Getting into the meat and potatoes of the studies. As I mentioned in the previous episode, incident energy, and the resultant arc flash risk analysis, is the single most cited reason when I ask why the prospective client is interested in getting a study completed.  This is where a lot of time and care needs to go into gathering the data necessary for the study, and where the previously stated numbers related to time come into pLineup ready to start gathering data for a power system study.lay.
Along with all the information that was gathered for the barebones short circuit and protection coordination, more detailed informaiotn on the imedances withint the system and loads need to be gathered. All information, for any place that the electrical safety program required a detailed label, based on whether or not there will be energized work, needs to be put together.

What type of loads?

This information amounts to the following, starting at the load.  All motors 25hp and above need to be broken out.  The actual size whether it is 25hp or 50hp isn’t as important as they are broken out.  Induction motors contribution fault current for short periods of time, and the magnitude is proportional to the motor size and intertia.  This fault current, is not “seen” by the protection relay upstream and doesn’t account for how quickly the protection will clear the fault, however it does contribute energy into the incident energy value.  However, it is not a linear relationship, therefore a large number of small motors will not contribute the same values as a single large motor, therefore it is important to break out the larger motors, I like to use 25hp as the break point, and then lump the remaining motor load.

How are the loads fed, what is the impedance?

The cable information, including the size, configuration, raceway material and length is needed from the load to the MCC, or distribution panel.  This all contributes to the overall impedance of the cable, and affects how much energy that motor can contribute. If the length is hard to determine, walk it down and err on the shorter side. Since this fault current doesn’t affect clearing time of the protection, erring on less impedance will give you a worse case incident energy everytime. In a future episode I will discuss why this is important, in short it has to do with the time portion of the incident energy equation.
The motor protection, including overloads and MCP is good to have here, it is not critical, but since you will likely be in the bucket gathering the data, it is better to have it now.  It will be important if qualified workers are needed to complete energized work at a local motor disconnect, or within the bucket itself.
If the detailed cable information mentioned for the motor feeds wasn’t gathered during the short circuit it is important to get it here.

Load Flows

When you have all this information, the load flow is mostly complete, we need to get into the operational details.  We have already mentioned the motors, and breaking them out, now we need to start thinking about the non-motor loads, and just as importantly, what is a good “demand factor” that can be applied to these.
For example, for all the other studies we assume that that motor or load is running at 100% kW, however this is rarely the case.  For an accurate load flow, load factor percentages need to be added to determine the loads and then the resultant report can then be checked against any metering information that you may have at your facility to determine that it is accurate.
If this information is hard to come by, a good starting point may be as follows:

  • Motors  greater that 250hp – 100%
  • Motors 100hp to 250hp – 75%
  • Motors less than 100hp –  50%
  • Non-motor load – 75%

From this iterations can be made to get closer to actual values that can be used as a basis of the report.

Conclusions

Now that you know why you may need a power system study at your facility, how to get started with getting the studies completed, and with this series how to gather the data necessary for great reports.  The next step is to get started.
If you need assistance send us a email with a brief description of your system and how to get back to you.  We look forward to hearing from you.
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Plan you Data Collection Effort

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In the first post of the series we talked about why having good information and data is critical for an accurate power system study.  If you haven’t read that one yet, stop reading an check out Data Collection for Power System Studies and then head back here. This article will talk about the planning process of getting all this critical information together, and the last post of the series will be cataloging what information is required for specific devices, equipment, etc.

Data Collection Planning
Getting the Planning Process Together

How to get it

The data required as outline is a lot to swallow in one go, however at your facility and elsewhere most of this information is can likely be found on existing drawings, cable schedules, operations/maintenance manuals, lockout tagout procedures, maintenance databases, relay testing reports, etc.  the first step after knowing what is needed, is to start brainstorming where this information can be found already, and then verifying the accuracy of this information.
In the content library we have developed data gathering sheets that you can use to help organize your thoughts, and start filling out this information.

Use existing information

Existing data from old reports, single line diagrams

Have a central location/database to put all the information

It is important to have a central location for all this data, the data sheets in the SparkyResource library is one way, a equipment database, or spreadsheets all work.  If you are completing the study in house, adding the information directly in the model is another great way. ETAP and other modeling software have methods to track the validity of the equipment information, or you can circle and note in the model where the information is complete, or what is missing.

Plan out how you are going to get it

Plan it out, have a digital camera to keep track of everything that you look at.  I like to take a picture of the equipment number label, and then the nameplate.  There is a column in our data collection sheets where you can add the image numbers to keep track of them later.
If you are consultant going to a site to gather data, make sure that you or your site contact coordinates with maintenance, and have someone from that department go around the site with you.  They typically know the site and the equipment better than anyone else.
When you have a grasp on the information that you need, and what is missing, a plan can be put together to start gathering the rest of it in the field.  Gathering data on live equipment can be a risky procedure, and be sure to consult your facilities electrical safety program on the best method to start. If your facility doesn’t have an electrical safety program in place, and the power system study is supposed to help with the development of it, then working in an de-energized state is the most prudent way to go.
Take note of the current status of all switches, breakers etc. before you get in there, this is important to determine the “normal” operating situation for the model.

Get out into the field.

This can make it difficult to gather the information and open MCC buckets, etc, however it doesn’t have to be all gathered at one time. Plan around existing outage and maintenance schedules to gather the information while the equipment is down already.  If there is an unscheduled outage, before the equipment is re-energized consult with the operator to wait until the data is gathered, coordinate with the various teams in the field to gather the data in a piecemeal way as they are going about hteir normal work.

Make sure everyone is safe and not taking unnecessary risks

If you are using outside resources, they may have their own safety program in place, and be able to help expedite the process. It is very important to remember that opening equipment to develop a safety program is not the best way to get the information. If at all possible de-energize.  It will take 5min or so per bucket. A scheduled shutdown will never take as long as one that is un-scheduled, especially if it causes an fault or arc flash event.  That equipment will be unavailable longer, not to mention the possible injury to workers.

Data Quality

The quality of the infromation that you are gathering is critical to the development of the model.  This is something we talked about in the first post of this series Data Collection For Power Series

“the results from the power system model are only as good as the data that is used to create it”

This is also talked about in the EasyPower Webinar – Garbage in Garbage Out.  It is useful to check this out before starting the actual collection process.

What’s Next

The last post in the series we will be talking about what is the data that you need to start putting together.  It is important to hang around and check out that post.  Be sure to be kept up on the posts by following us on Twitter and like our page on Facebook. And if you liked this article be sure to share with the buttons below and sign up for our newsletter (the form is below) where you will get these posts in your inbox and special offers.

Data Collection For Power System Studies

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What Is Needed When Gathering Data For Power System Studies

Data Collection is about gathering the data necessary for building an accurate model of your power system. This model will be the basis for the various studies that we mentioned last week, and without accurate data the model will not be as useful as you need it to be.

Time to stat gathering that data.
Time to stat gathering that data.

Why having complete and accurate data is important

First the results from the power system model are only as good as the data that is used to create it. If the data is not correct, then the model that is created will not be accurate. In fact incorrect data will lead to poor results in the incident energy study which is very sensitive to the fault levels on the system. It is very important to get accurate impedance information, this includes cable configurations, transformer data, etc.
Collecting the data for the first time is a very labour intensive prospect, and can account to 50% of the cost of getting the initial study completed.  That’s one of the reasons I mentioned before about getting the data together, and getting more than one report completed at the same time.  The incremental cost in negligible compared to the total cost of the project.
When your facility has good single line diagrams, manuals, and data in other forms, this will speed up the collection process.  However it is always a good idea to verify all this data in the field, especially for larger, active facilities where changes are being made on a constant basis.  When this is completed once, the model can be used as a change management tool. One of the software vendors have a great webinar describing how you can use their software to manage change in the entire facility

How long to expect?

Data Collection can cost a lot of money
Managing cost and time is important

You can expect that the data gathering stage of the project will take about 2hours for every substation, switchgear lineup and MCC, and 0.1 hours for every load, including motors, panels, etc.  If your facility is spread out or has a lot of specialty equipment these numbers may need to be increased.  This will give you an idea on how long you can expect to take to gather all the data for your facility.
We have included forms in the content library that will help you gather this information. We based the information required on the recommendations of ETAP.

How much do you need to gather?

Depending on what set of studies you are planning to have completed, the detail of the data that needs to be gathered will be slightly different. It is my opinion that you have at least the 4 studies completed that we mentioned last week in, The Critical 4, they are Short Circuit, Protection Coordination, Incident Energy and Load Flow. These 4 studies build upon each other, and as such they need increasingly more and better detailed information.  Lets start at the top, what do they all need?

  • Utility information (MVA, X/R min and max)
  • Nominal system voltage levels
  • System configuration with the following equipment:
    • Transformers (with impedance, voltage and configuration),
    • Configuration switches and circuit breakers
    • Switch gear, mccs, switchboards, etc down to the voltage level you are interested in
  • Any large motors and other generation on the site.

With this minimal information you can prepare an adequate short circuit study that will give you values for the short circuit on any of the buses above. These will be very much worse case as we haven’t gathered any additional impedance information.  This study would be useful for design and specification purposes when you are purchasing equipment for a new facility.

What’s Coming Up

On Wednesday I will lay out the specific data that is required for each of those critical four.  They all build upon each other, and will require collecting data in the field and interviewing operators and maintenance to understand how the facility operates.
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