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Starting Times

Notes Regarding Starting Time.

The calculated starting time is based on a direct on line start (D.O.L) using a motor with an average starting torque of 1.3 times the motor full load torque.

Centrix will generate a warning if this calculated starting time exceeds 12 seconds.

In general small motors (11 kw or less) would not accommodate a 12 second start time but these motors usually have a higher average starting torque ratio which reduces the starting time. Similarly large motors (above 90 kw) can accommodate longer starting times but may not have a starting torque ratio as high as 1.3

When a warning is generated it is recommended that you check with your motor supplier that the motor will start the fan. Generate a torque speed curve and forward this to your motor supplier.

Generally the warning can be ignored if a variable speed drive is to be used but if the DOL starting time exceeds 20 seconds and the motor is small it is safer to check.

Star delta starters are generally not recommended for starting fans due to the shape of the torque speed curve. The starting characteristics of the motor using a star delta starter should be carefully investigated. It may be necessary to use a larger motor size when using star delta starters. Auto transformers or electronic starters are preferred over star delta starters.