S200: Voltage Sag Standard

Semiconductor F47 and F42 standards relate to the ability of equipment to ride-through voltage dips of various magnitudes and duration. F47 requires that semiconductor equipment tolerate transient voltage sags or dips on the AC power line: voltage dip to 50% of nominal for 200 ms, 70% of nominal for 0.5 second, and 80% of nominal for one second. F42 specifies how to test for compliance with F47. To robust the S200 for F47 type voltage sags, power the S200 using AC line voltage and phasing as described below.

AC S200 Control Power
240 VAC, one-phase
AC S200 Bus Power
Three-Phase, 240 VAC
DC S200
DC power supply operated from three-phase, 240 AC line

AC Control Power
The use of 240 VAC, single-phase, nominal for control power results in the control voltage remaining within the drive control voltage specification (85 VAC to 265 VAC) during an F47 50% sag (deepest F47-specified sag). Powering the control with 240 VAC also maximizes the ride-through time for larger amplitude sags because more energy is stored in the control bus capacitor.

AC Bus Power
If three-phase 240 VAC is available for bus power, it provides much better F47 ride-through than either single-phase 240 VAC or 120 VAC because F47 and F42 standards mandate that in a three-phase system, only one phase of the three phases is sagged at a time. If the AC S200 is powered by three-phase 240 VAC, it keeps its bus capacitors reasonably well-charged by pulling power from the one line-to-line voltage that does not sag.

With single-phase AC bus power, a full torque acceleration of the motor to high speed during an F47-mandated voltage sag has the potential to drag the bus voltage down. If only the internal bus capacitors of a 3 A / 9 ARMS S200 are supplying the full 3 kW peak output power, the bus voltage sag rate is 13 V/ms.

A single 10 to 20 ms motor acceleration during a 50% F47 voltage sag has the potential to drop the bus voltage about 50%. Options to handle this problem are:

 
  • Limited hold-up time of 20 to 30 ms is achieved by adding additional capacitance on the bus. Wire an external 1,500 uf or higher, 450 VDC, aluminum cap across the +Bus to -Bus. In this case, simply wire a rectifier or surge limiter between the drive AC terminals and the cap to help charge the external capacitance at power up. The bus voltage does not return to normal until the line returns to normal, so multiple accelerations during the sag are a problem with this option.
  • Monitor the line voltage and quickly pause the machine when the voltage sags.
  • Combination of the previous two points.
  • A robust, costly option to ride through all F47 mandated voltage sags when three-phase 240 VAC is not available, is either to double the peak power capability of the motor/drive system, or to derate the motor's maximum speed 50%. If a motor's top speed can be achieved with a 50% low bus voltage, the worse case F47 voltage sag of 50% is tolerated with little or no effect on motor performance.
  • If three-phase power is available within the plant, but at higher voltage than 240 VAC, consider adding a power transformer to step it down to 240 VAC for use as AC bus power for the S200 drives in the machine. This is also a robust option.

 

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