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Fault Induced, Delayed Voltage Recovery Analysis

Since the Great Northeast Blackout of 2003, Altran has been researching traditional power system models, power system load representations, and the design and operation of transmission and distribution systems. Our research indicates that the accuracy of today’s power system models need to be enhanced by the addition of new load models that more accurately represent distribution system customer loads during Fault Induced, Delayed Voltage Recovery (FIDVR) conditions.

At this time, Altran is prepared to work with clients to evaluate

  • Impact of remote, EHV, three phase short circuits on distribution system load models.
  • Need to upgrade models to understand transmission system performance with enhanced customer load models.
  • Cost effective system enhancements that mitigate local impacts when three phase faults occur at remote locations.

 

To uncover weaknesses in distribution system design and operation and the resultant impact on transmission system operability, Altran’s Subject Matter Experts (SME) are prepared to

  • Meet with client distribution system operations SME, transmission system operations SME, and protection and control SME to discuss risks and impacts.
  • Use client short circuit models to develop voltage profiles across the distribution system when three phase short circuits occur at remote locations.
  • Use client transmission system models to develop voltage profiles across the transmission system considering Fault Induced, Delayed Voltage Recovery.
  • Modify client distribution system models to predict Fault Induced, Delayed Voltage Recovery at selected distribution substations when three phase faults occur at remote locations.
  • Develop recommendations for corrective action.

 

These concerns are best illustrated using Figure 1 which shows:

  • Voltage along a distribution line is maintained at, or above, nominal value during peak load conditions (black line).
  • Voltage along a distribution line decays substantially during fault conditions at remote locations (red line).
  • Voltage along a distribution line does not recovery immediately when the remote fault is cleared.

 

The dashed lines in the figure below represent critical load voltages for HT – High Torque Motor Loads and LT – Low Torque Motor Loads.  The concern is that existing load flow models represent motors as constant power loads.  Our analysis indicates that the existing representation is adequate for low torque and variable torque mechanical loads, that is, fans and pumps.  However, our analysis indicates that the existing representation is unacceptable for high torque mechanical loads, that is, air conditioners, refrigerators, and air compressors.  Moreover, our analysis indicates that high torque motor loads will stall in less than 3 cycles (50 milliseconds) when a three phase fault occurs at remote locations.

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