gefran TPD32-EV Manuel D'instruction page 496

A2.5.4 Install an SCR Overvoltage Protection Device
When the "TPD32-EV FC" unit is used as a motor/generator field supply, should be need to install on the load
an Overvoltage Protection Device (OVDP, i.e. crowbar ) to prevent faults in the thyristors and / or varistors of
the device
The purpose of the voltage clamp is to provide a means to let the DC output current to the load decay if the power
is interrupted to the field controller while the device is adjusting the current on the load.
In these cases the load current decreases very rapidly generating voltages proportional to the rate at which the
current decreases. These voltages can damage the field controller and/or the motor wire insulation.
The voltage clamp is connected directly across the DC output power connections to the load and during normal
operation it appears as an open circuit.
Below the Block Diagram with the Overvoltage Protection Device.
Do not remove AC power until the field controller output current is zero. Equipment damage
c :
Aution
can occur.
496
Figure A2.5.4: Block diagram of Field exciter control + Overvoltage Protection Device
TPD32-EV-...-E
External Bridge
2Q / 4Q
M
—————— TPD32-EV ——————
TPD32-EV-CU
Control Unit
External I/O
R-TPD32
OVPD
TPD32-EV-FC
External Field
R-TPD32
2Q / 4Q