How to Properly Design and Size A Generator


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.



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:


Want to learn more? Collicutt has a new PSSPEC webinar available that will give you a thorough walk through on how to utilize the tool.


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Preserving an Engine

Preserving an Engine

Have you considered the affects of not preserving your equipment before putting it into long term storage?  Or “Parking it along the fence?” as so many people refer to it.  How many of you have started up a unit after storing it and noticed it was no running as it was before or experienced a catastrophic failure?  Maintaining spare equipment and redundant machinery in a prime state, ready for operation is critical.

Storing Equipment That Has Recently Been Operable

1. Clean the engine of any dirt or debris.

2. Get the engine running so the oil is hot.  Drain and install clean oil filters.

3. Preserve the engine with preservative oil.  Remove rocker arm covers and gear train covers. Spray these with a preservation oil.  For gas engines, remove spark plugs and spray preservation oil into each cylinder.  Spray each spark plug and install back in place.

4. Seal all intake, exhaust and any other open ports.

5. Relieve the tension on belts to prevent fatigue and deterioration.

6. Spray or brush preservation oil on exposed machined surfaces.  Remove fuel from filters and drain fuel injection pump.  Grease rod threads, joints, linkages, etc.  Remove batteries and store indoors on a trickle charger.  Place a waterproof cover over the equipment.

7. If possible, rotate the alternator on a monthly basis.  Prior to being put back into service, all alternators and switchgear should be visually inspected and have its insulation tested using a megger.

8. When placing the equipment back into service, all equipment must be removed of its preservation oil and be filled with normal, manufacturer approved oil.  Coolant should be tested and an analysis performed.

Engine manufacturers may have other or a variant of steps to be performed.  Always consult the operation and maintenance manual for the proper preservation procedure.

How Can We Help?

The best way to avoid a costly failure perform the steps above – or consult Collicutt Energy for a quote to perform a preservation or de-preservation on your equipment.

During this preservation, we can perform an inspection on the equipment.  This inspection would identify suggested repairs to occur either now or when the equipment is planned to be placed back in operation.  Knowing the condition of your equipment and ensuring it does not further deteriorate saves repair costs in the future.

Take Action

Take action now and schedule an inspection and/or preservation today to ensure that your equipment is ready for when you need it!

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