Chapter 12 Single-Phase Rating
12-2
12.2 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. When using a motor that is selected by the
three-phase drive rating criteria when using single-phase input, it may result in poor
performance, premature drive failure. The selected drive of single-phase current ratings
must meet or exceed the motor current ratings as indicated in Table 1.
12.3 Input Frequency and Voltage Tolerance
The drive ratings in Table 1 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 as 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.
12.4 Wiring and Peripheral Device
It is important that input wiring and branch circuit protection be selected based on the
drive’s single-phase input current rating indicated in Table 1-2.