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This information is cannot be found in ATV catalogs or datasheets, because there are several factors that play role.
All our ATVs ,except ATV212, uses DC bus capacitors to balance voltage ripples in DC bus caused by input rectifier (3-phase diode bridge). As long as there is voltage in DC bus, the drive will work.
Energy from DC bus voltage is consumed by the motor that is driving the load. This means if the motor will not be operated, then short (several seconds) interruption in ATV main AC supply will not cause ATV to switch off.
Despite there is small discharging resistor conencted to DC bus, the DC bus will not fall below undervoltage level even after 5 seconds.
Situation is very different, if the motor is operated. Then the DC bus voltage starts descending immediately with AC supply loss.
The slope of DC bus voltage descend strongly depends on the load. More energy consumed by load means faster fall of DC bus voltage.
When DC bus voltage falls below undervoltage fault level, the drive will go to fault and if there is no external 24V DC supply for control parts used, the drive will also switch off.
In several ATVs, fortunately there is function called undervoltage prevention. Using this function, it is possible to configure prevention from loosing DC bus by setting: Stp [Stop type Ploss] = DC maintain and configuring the prevention level UPL.
With this setting, if motor has been running and DC bus voltage drops below UPL, the drive will use kinetic energy from the all rotating parts (rotor, shaft, impeller) to supply DC bus. It will look like drive is braking the motor in order to get energy from the motor to supply DC bus. Of course the load speed will go steadily down. The slope of motor deceleration depends mainly on the inertia, the load itself and whether external 24V DC is used to supply ATV electronic circuits. Deceleration will be smaller if the load is small, but with high inertia.
This function of maintaining DC bus will be active during the interval set by MMS [Dc bus maintain time] parameter. After this time, ATV will not keep DC bus, so it will switch off.
Maintain DC bus is possible with ATV630, ATV930, ATV340 drives.
To sum up:
The time to overcome AC supply loss using ATV process or ATV340 drives using maintain DC bus function depends on the energy that is available in form of kinetic energy in all rotating parts (motor+load). For its calculation it is necessary to know the inertia, load (also load dependence of speed) and the operating speed just before loosing ATV mains power supply. External 24V DC supply for control parts (if remains present during power interruption) also helps to save certain energy and prolong possible DC bus maintain time.
All our ATVs ,except ATV212, uses DC bus capacitors to balance voltage ripples in DC bus caused by input rectifier (3-phase diode bridge). As long as there is voltage in DC bus, the drive will work.
Energy from DC bus voltage is consumed by the motor that is driving the load. This means if the motor will not be operated, then short (several seconds) interruption in ATV main AC supply will not cause ATV to switch off.
Despite there is small discharging resistor conencted to DC bus, the DC bus will not fall below undervoltage level even after 5 seconds.
Situation is very different, if the motor is operated. Then the DC bus voltage starts descending immediately with AC supply loss.
The slope of DC bus voltage descend strongly depends on the load. More energy consumed by load means faster fall of DC bus voltage.
When DC bus voltage falls below undervoltage fault level, the drive will go to fault and if there is no external 24V DC supply for control parts used, the drive will also switch off.
In several ATVs, fortunately there is function called undervoltage prevention. Using this function, it is possible to configure prevention from loosing DC bus by setting: Stp [Stop type Ploss] = DC maintain and configuring the prevention level UPL.
With this setting, if motor has been running and DC bus voltage drops below UPL, the drive will use kinetic energy from the all rotating parts (rotor, shaft, impeller) to supply DC bus. It will look like drive is braking the motor in order to get energy from the motor to supply DC bus. Of course the load speed will go steadily down. The slope of motor deceleration depends mainly on the inertia, the load itself and whether external 24V DC is used to supply ATV electronic circuits. Deceleration will be smaller if the load is small, but with high inertia.
This function of maintaining DC bus will be active during the interval set by MMS [Dc bus maintain time] parameter. After this time, ATV will not keep DC bus, so it will switch off.
Maintain DC bus is possible with ATV630, ATV930, ATV340 drives.
To sum up:
The time to overcome AC supply loss using ATV process or ATV340 drives using maintain DC bus function depends on the energy that is available in form of kinetic energy in all rotating parts (motor+load). For its calculation it is necessary to know the inertia, load (also load dependence of speed) and the operating speed just before loosing ATV mains power supply. External 24V DC supply for control parts (if remains present during power interruption) also helps to save certain energy and prolong possible DC bus maintain time.
Released for:Schneider Electric Vietnam
