Installation of mains failure buffering of casting kettle

In order to guarantee safety during the casting process, we looked for solutions to move the casting kettle back to safe position in the event of a power failure.

In principle there are 2 possibilies for this.

Capacitive energy storage:

• DC link voltage decreases in the event of a power failure
• No power limit

Kinetic energy storage:

• DC link voltage constant
• Maximum buffer size dependent on motor design

Sizing of the components

Input data

Servoaxis

• Power Unit: HMD01.1N-W0036-A-07 NNNN
• Motor: MSK070C-450-NN-M1-UP1-NNNN
• Gear: i =1:956

Power Measurement (worst case Scenario)

Determination of power and energy requirements (worst case scenario)

Dimensioning capacitive energy storage

• Determination of the DC lower voltage
• Draw the torque and speed curve in the motor characteristic curve and read off DC lower voltage

• With DC lower voltage and the EnergyEI, determination of the necessary DC capacity

A minimum capacity of 80mF is required to ensure that the intermediate circuit voltage drops in the event of a power failure and simultaneous movement of the axis.

Dimensioning kinetic energy storage

In the data sheets of the motors, the mechanical performance is given and not the electrical one. Therefore, the value is converted with an eta = 0,85 --> PDC_max = 2,5kW => Pmech = 2,9kW.

Energy to buffer kinEnergy = 6,2 kWs

Selection criteria:

• The full power is not available over the entire speed range.
• Higher base from the speed and motor interia results in an higher kinetic energy

• Motor MAD100C-0150 with no external intertia
• Power unti HMS-W0036
• Bufferspeed n = 7000 rpm

Solution

The kinetic buffer was chosen as the solution. The figure shows an energy storage motor from Bosch Rexroth as an example.