Transformers
Drive Output High Frequency Transformers
Drive output high frequency transformers match the rated drive output voltage with motor rated voltage. On PWM (Pulse Width Modulated) drives, the rated drive output voltage is typically defined by the line voltage (mains) to which the drive is connected, while the motor rated voltage is often given and cannot be changed.
These transformers typically see high current ripple and voltage spikes coming from PWM drives and have to be designed appropriately. Transformers must be able to withstand, the operation with high PWM switching (carrier) frequency and fundamental motor frequency.
Unless isolation is required by the applications, these transformers are typically made as auto transformers, which makes them smaller than isolation transformers. One should also note that the size of high frequency transformers is much smaller that the size of an equivalent transformer designed for low frequency which sometimes permits the use of a smaller drive.
Step-Down Transformers
If the PWM drive is connected to 400 V line, and if motor is rated 220 V, without an output transformer (or L-C filter), the 220 V motor will be subjected to voltage pulses and current ripple of much higher level than necessary (400V/220V). This kind of application would likely cause premature insulation failure and motor overheating.
A step-down output transformer (400/220 V in this example) would normalize the motor exposure to voltage pulses and current ripple appropriate to 220 V level, extending motor life and acting as an motor output filter.
An additional benefit of a step-down transformer is that its application practically increases the drive/transformer combination’s current rating by the voltage ratio, which sometimes permits the use of a smaller drive.
Step-Up Transformers
In an opposite example, if drive is connected to a 220 V line and motor is rated 400 V, without a step-up transformer, the drive could not reach the full motor voltage at all, thus limiting the speed and power range.
A step-up transformer (220/400 V in this example) would increase the voltage to the full level required by the motor, thus permitting full motor speed and power.
Step-up transformers practically reduce the drive/transformer combination’s current rating, which sometimes leads to the use of larger drive.
SPINDEL Electronics provide drive output transformers rated from low to very high frequency motor applications, up to about 1000 Volts and 1000 Amps. We use modern simulation tools and an abundance of experience to specify an optimal drive output transformer for every application.
Scott-T Transformers for Two Phase Motors
Some motors/spindles, especially the older ones, are built as 2 phase motors. Stator windings on such spindles consists of two coils, resulting in four available stator wires.
Scott-T transformers convert the 3 phase drive output to 2 phase voltage/current as required by the motor winding. In addition, primary-to-secondary voltage ratio can be made to match drive and motor voltages. Often, these transformers are made for high frequency applications.
