BENSHAW Rsi S Series, Instruction Manual, Page: 383 / 398

371
Applying Drives to Single-Phase Input Application
Figure-2 Typical Single-Phase Configuration
Power(HP), Input Current and Output Current
When using a three-phase VFD with single-phase input, derating the drive’s output current and
horsepower will be necessary because of the increase in DC bus ripple voltage and current. In
addition, the input current through the remaining two phases on the diode bridge converter will
approximately double, creating another derating consideration for the VFD. Input current harmonic
distortion will increase beyond that with a three-phase supply making the overall input power
factor low. Input current distortion over 100% is likely under single-phase conditions without a
reactor. Therefore, the reactor is always required. Do not use a motor and drive of the same rating
when using single phase input. This will result in poor performance and premature drive failure. The
selected drive for single-phase current ratings must meet or exceed the motor current rating.
Input Frequency and Voltage Tolerance
The single-phase current ratings are valid for 60Hz input only. The AC supply voltage must be
within the required voltage range of 240/10% to –5% to maximize motor power
production. Standard product with three-phase voltage input has an allowable range of +10% to –
15%. Therefore, a stricter input voltage tolerance of +10 to –5% applies when using the drive with a
single-phase supply. The average bus voltage with single-phase input is lower than the equivalent
of a three-phase input. Therefore, the maximum output voltage (motor voltage) will be lower with a
single-phase input. The minimum input voltage must be no less than 228Vac for 240 volt models
and 456Vac for 480 volt models, to ensure motor voltage production of 207Vac and 415Vac,
respectively. Thus, if full motor torque must be developed near base speed (full power) it will be
necessary to maintain a rigid incoming line voltage so that adequate motor voltage can be
produced. Operating a motor at reduced speed (reduced power), or using a motor with a base
voltage that is lower than the incoming AC supply rating (ex. 208Vac motor with a 240Vac supply),
will also minimize the effect of voltage deprivation. ( 240VAC Input
208V motor, 480VAC Input
400V motor )