How to Properly Design and Size A Generator

Introduction

Specifying and sizing a generator for your project can be an overwhelming task . . . but it doesn’t have to be! Collicutt and MTU have a great tool available to assist with this task and simplify it as much as possible.

The tool is called PSSPEC and it is available for download using this link.

What follows is a brief introduction to the PSSPEC tool and how it can be used. This is not meant to be a detailed user manual but it does provide enough detail to get you off to a great start on your generator sizing project.

Should you have questions, want training on the tool, or need further assistance, please reach out to our Collicutt team at the contact information at the bottom of this article.

Getting Started

Once you download, install, and open PSSPEC, you will see the following screen:

 

Select the “Start a New Sizing Project” button. The following screen will appear and this is where the real work begins!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

From this screen you can enter:

  • Customer data and add new customers
  • Project specific Notes
  • The Basic generator information – This is where generator information such as; frequency, voltage, fuel type, rating type, temperature rise, load factor percentage, UL2200 requirements, customer supplied cooling system, and PMG requirements are checked.
  • Specific Site Conditions – this contains the location, elevation, and temperature data
  • Intermittent Loads – This is where you define the loads that your generator will be expected to handle (there is more information on this below).
  • Intake and Exhaust information
  • Advanced options – this allows you to select the % THVD limit

Note that this is an active menu system so an entry in one menu adjusts the menu selections in the other areas.

Once you are completed your entries, click on the “Accept” button and the following screen appears.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Adding Loads

This is where you need to understand the electrical loads that your generator will be powering.

A project’s electrical loading contains a sequence of steps that are defined by the user. Within each step, loads are placed that fit the requirements of the application. All loads within a step are assumed to start at the same time, and steps occur sequentially one after another once the previous step has reached steady state (i.e., generator set has fully recovered to nominal voltage).

PSSPEC offers templates to use for many different types of loads (see graphic below). These templates allow easy selection of the needed variables for the selected load type. The PSSPEC application makes assumptions based on the load type, load criteria, and information entered by the PSSPEC user and populates default values for each load parameter accordingly.

 

 

 

You can select these loads for a particular step by selecting the step and clicking on the “Add Load” button. The screen shown above appears and you select one of the options which will bring you to a screen that allows you to adjust specific parameters for the selected load.

One you are finished adding load steps and loads, you can select the “Sizing and Rating” button on the left side of the screen. This starts the generator sizing and selection process.

 

Sizing and Rating

When you click the “Sizing and Rating” button, PSSPEC runs its calculations and selects the recommended best fit generator using all of the data that you have provided. This is illustrated in the graphic below.

 

 

Note that this window will also display oversized and undersized generator sets that may meet project requirements.

Any generator set in the list can be selected and a sizing report can be generated to provide a ‘mini spec sheet’ for the user. Multiple sizing reports can be created for different generator set models. Just select the generator sets you are interested in and click the Report button that shows up on the left of the screen (see the graphic below).

 

 

These reports can be used as a convenient quality check to ensure the generator selected meets your design requirements and then included as part of your generator specification package. If you find errors or things that you missed you can go back through the process described above and make the changes and additions and recreate the report to include your changes.

In Conclusion

This was a very condensed tutorial which illustrated only a small fraction of PSSPEC’s capabilities. The best way to understand it’s capabilities is to dive in and start sizing some of your projects!

If you would like us to provide some training for your organization or just need to have some questions answered, be sure to call us or email us at the link below.

888-682-6888    info@collicutt.com

 

Note: Sizing of the generator is the responsibility of the “engineer of record.” Input data and the output from PSSPEC must be reviewed and approved by the responsible engineering firm.

 

Finally, see these article for related content:

 

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Do You Need a Generator Specification? Let Our Software Do the Work For You!

Many of Collicutt’s long time customers are engineering firms. One of the things these engineering firms need for each project is a prepared set of bid packages for each major scope of work on that project. These bid packages will be sent out to potential suppliers of that scope of work so that the supplier can propose a solution complete with an accurate price.

The Challenge

This means that the bid package must have sufficient detail to get price certainty. Without this detail, prices between suppliers will be difficult to compare and the engineering firm will have no way of knowing if they are selecting the best solution.

To solve this problem, the bid package must contain a specification that defines the exact performance details for the piece of equipment or structure under development.

One of the most important specifications that these engineering firms need to complete is an emergency generator specification. This specification defines the generator that will provide emergency power should the power grid fail. Among many things, this specification needs to contain requirements for the following:

  • Submittal process
  • Quality assurance process
  • Warranty
  • Approved manufacturers and approved manufacturing locations
  • Industry standards compliance (UL, CSA, ANSI, NFPA, EPA, etc.)
  • Performance requirements
  • Engine requirements
  • Alternator requirements
  • Electric load definition
  • Switchgear requirements
  • Fuel type(s) and fuel system requirements
  • Environment constraints (emissions, altitude, temperature, size, noise, etc.)
  • Control and monitoring
  • Overcurrent and fault protection
  • Voltage regulation
  • Enclosure requirements
  • Installation, interconnections (fuel, cooling-system, exhaust-system, grounding and electrical connections)
  • Commissioning, testing, and start up
  • End user training
  • Life cycle maintenance

Although it sounds simple enough, the creation of specification like this can be a complicated and daunting task!

The Solution

So, what do you do if you are in this situation and don’t have a detailed specification for an emergency power generator set but need one for your project?

You can leverage our unique sizing software to estimate the generator capacity required for your project as well as create your own set of specifications. Just answer a detailed list of questions and the software will prepare an MS Word style document that you can further edit to fit your bid specification package.

Call us or email us at the link below for assistance or download our software using this link and build your own custom specification!

888-682-6888    info@collicutt.com

You can also download the 260kW NG genset spec that is attached to this post to get an idea of what a generator spec looks like.

Finally, see this article for related content – Don’t Make This Mistake When Buying Your Generator!

 

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