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Power Design Pro Tip: Understanding and Using the Load Summary Page

Power Design Pro Tip: Understanding and Using the Load Summary Page

3/17/2015

This is the sixth article in our series about Power Design Pro™ software and it discusses the load summary page which includes generator sizing, load grouping and load shedding. The load shedding feature can be especially useful for analyzing paralleled gensets or generators that run fire pumps, as the pumps are typically operated with no other loads to ensure fire fighter safety.

The opening screen of the load summary page:

  • Summarizes the characteristics of all entered loads.
  • Sizes the generator and displays the selected genset configuration (engine and alternator).
  • Displays the load effects on the genset (load level, voltage and frequency dips, and harmonic distortion).
  • Summarizes the projects limits (from the project setup page).
  • Allows the user to manually select the generator product family.
  • Allows the user to manually select the genset (engine and alternator combination).

Being able to select any generator and evaluate how it performs with the input loads is a significant advantage over competitive sizing programs which only provide limited options.  Power Design Pro™ also allows the users to choose single unit configurations or parallel solutions for any application.

Sizing Method
While the program automatically selects the recommended size for the generator, it allows the user to select a desired engine/alternator combination. This flexibility allows the user to see the effects of generator size on transients (voltage and frequency) and harmonic distortion.

The generator is sized based on multiple criteria. Some of the criteria limits are set on the project page and others are limits that are set when entering the loads. The program sizes the generator to achieve the following results:

  • Load level less than the sited rated generator capacity.
  • Load’s peak loading is less than the generator’s peak load/surge capacity.
  • Load level less than the user-specified maximum load level (entered on project set-up page).
  • Voltage dip less than the specified limit (determined by project set-up and individual loads).
  • Frequency dip less than the specified limit (determined by project set-up and individual loads).
  • Harmonic voltage distortion less than the specified limit (determined by project set-up).

Power Design Pro™ is the only generator sizing program in the market that performs full harmonic analysis. Harmonic analysis is the process of projecting the various harmonic current spectrums of the entered loads against the source impedance of the alternator and then calculating the resulting total harmonic voltage distortion (THVD). With Power Design Pro™, the resulting voltage distortion is fully mapped and its effects on the sine wave are displayed.

Documentation
The documentation tab provides access to additional documentation and drawings. This includes spec sheets, installation drawings, emission certificates, and a specification text document that matches the selected product family. The specification text is a Word document that includes full designer notes.

Load Summary
The load summary section totals the input load information. It uses this information to size the generator to the user-specified limits. Think of this information as a general sizing solution that could be applied to any suppliers’ generator.

Generator Summary Information
The selected generator is listed based upon rated kW, site de-rated kW, engine displacement, and selected alternator size. The values listed under the generator description provide information about the operating characteristics of the selected genset (engine/alternator combination) with the input loads.  This information provides verification that all the key sizing criteria are being met. It also supports the ability to evaluate how any selected generator will perform against the input load.

Load List Summary
For each load, a summary of the input data is displayed.  The list also shows the status of each load’s running, starting, and harmonic characteristics in addition to its voltage and frequency dip limits. The results of each load sequence are totaled to provide summary information for the load sequence. 

Load Shedding
The load list also provides the ability to shed off entire load groups. This allows users to evaluate the capability of the generator system to handle a portion of the total load list. This is very helpful in analyzing parallel generator system operation when all generators are not on the generator bus. It is also very helpful when analyzing applications with a fire pump and optional standby circuits. For most applications, the generator controls and feeder breakers are designed so these two load groups don’t run at the same time to ensure fire fighter safety. The “shed” function allows all the loads to be entered and then the user can easily toggle between which loads are running.

Power Design Pro™ is a powerful program with many load management features assuring you obtain a properly-sized generator that meets your specific requirements.
Click here for more information about Power Design Pro™.


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