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Power-Flow Didn't Converge

When power-flow does not converge by the number of Newton-Raphson iterations set in the Solver mask, the following dialogue is shown:

Error message due to non-converging power-flow

The following may cause this error:

  • The number of iterations is not large enough
  • Poor choice of initial bus voltages for Newton-Raphson algorithm

No Type (PV, PQ or SLACK) Was Defined for Bus X

Depending on the input file format, check the following to resolve the problem:

  • Excel: check that for bus X in the Bus page, the bus type is defined as either ‘PQ’, ‘PV’ or ‘SLACK’. The type string should be upper-case.
  • PSS/e: check that for bus X in the bus data section of the RAW file, the 4th data entry (column 4) is either 1, 2, 3, or 4.

At Least One Machine Must Be Connected to SLACK Bus X

To resolve this problem, verify a machine is connected to bus X. Also ensure the status of the machine is set to in-service.

Invalid Reactive Power Limits for Machine X

To resolve this error, verify the lower reactive power limit for machine X is less than or equal to the upper limit.

Tolerance Value Must Be Positive

To resolve this error, ensure the Newton-Raphson tolerance in the Simulation settings tab of the Solver mask is greater than zero.

Maximum Number of Newton-Raphson Iterations Must Be Greater than One

To resolve this error, ensure the iteration limit in the Simulation settings tab of the Solver mask is greater than one.

No SLACK Bus Was Defined. Power-Flow Requires at Last One SLACK Bus

At least one bus should be defined as a slack bus when using either Excel or PSS/E as the input format. Ensure that the Bus Type column (on the ‘Bus’ page for Excel, or the 4th column of a bus data record in the RAW file) for at least one bus is the slack bus type ('SLACK' in excel file and 3 in the RAW file).


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