Drive Transformer Sizing

This document refers to G&L PiC application note AN000017 and provides information on the sizing of the transformers for use with G&L Centurion Servo Drives (DSM100, DS100, DS200, and AS100) and motors (SSM, FSM, and HSM).

This PiC Application Note applies to all G&L Centurionä drives (DSM100, DS100, DS200, and AS100) and motors (SSM, FSM, and HSM).

This application note provides information on the sizing of the transformers for use with G&L Centurion Servo Drives.  The approach taken is conservative.  In many cases a smaller transformer may be selected if performance requirements are known and guaranteed not to change. G&L Centurion Servo Drives do not require transformers for isolation, except for the DSM100 which requires an AC Line Filter for EMC Compliance.  A transformer may be required however, to match the voltage requirements of the drive to the available service.

KVA Rating Sizing Method

To size a transformer the power output (KVA) of each axis must be known.  This can be derived by calculating the horsepower for each axis and converting that horsepower into units of watts.  If you are supplying power to more than one motor and drive, simply add the KVA ratings together from each calculation to get a system KVA total.

Transformer KVA Rating = (Sum of the average output power of each motor) x Power Factor

Note:  The power factor of 2.0 is used to account for the power factor and losses of the system.  This factor should minimize secondary line voltage sagging in the transformer during peak current periods.

If you are using the Systex sizing program, the average speed and average torque data has been calculated and can be used in the above equation.

Example

If you are using a DS130 drive and SSM490 motor, and you are not sure of the exact speed and torque in your application.  Look at the speed/torque curves for the selected drive/motor combination as shown in the Centurion section of the Product Guide.  Select the values for the worst case continuous speed and torque.  The SSM490 with a DS130 is capable of 3,000 RPM and a torque of 75 lb-in.

Note:  The speed/torque curves are based upon a drive module input voltage of 230 VAC.  For a 115 VAC input voltage, the maximum speed is reduced by half.

You should select a transformer with a minimum rating of 5.3KVA.