CEE Relays Ltd

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FAQs: Using Diversity Factors in PTW
Both motors and loads can have diversity factors applied to them. These are used, for example, if a 500kW motor is only running at 250kW, then a 0.5 diversity factor should be applied. 

In PTW, diversity is expressed as a "Load Factor" which is intended to model the size of the driven or absorbed load compared to motor or load rating rather than the proportion of time the motor or load is in service.  For motors, this has the following implications:
  • If the "Global (Options)" or "Individual" tick boxes are selected in the Component editor, the Load Factor will affect the motor's power factor and efficiency.  
  • Motor models can actually represent several machines of the same size by entering a figure in the "Number of Motors" box.  When load factors are applied, it is assumed that all motors are in service, with loads based on the load factor. For example, if the "number of motors" is 4 and the "load factor" is 0.25, this will model the case when four motors are operating at one quarter load (not one motor at full load).
  • Short circuit studies do not take Load Factors into account.  Therefore Load Factors cannot be used to model cases where only a proportion of system load is in service when a fault occurs.

For these reasons it is recommended that complex systems with large numbers of motors model the motors individually - diversity can be applied simply by taking selected motors out of service before running the Load Flow or Short Circuit study.  
Depending on the Load Specification selected in the load-flow set-up, the diversity factors might not be taken into account. Please refer to PTW's on-line help (click the Help button from the load-flow set-up dialogue box) for more information. 
If you have any more questions, then please contact us.