# 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:

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).