TECHNICAL USER´S MANUAL
5
Thyristor modules
3.2 Installation
CAPACITOR AND DISCHARGE MECHANISM: The recommended capacitor voltages for a 400V
PFC system with and without a detuned filter reactor are listed in Table 3.1. A suitable detuned
filter reactor is recommended to avoid the risk of resonance and reactor acoustic noise.
Table 3.1:
Capacitor voltages for PFC with and without a detuned filter reactor
PFC type
Recommended Capacitor
Voltage Rating (V)
No detuned filter reactor
400
7%
440
14%
480
Switching action takes place within 10ms upon receiving the 24VDC trigger signal given that
the capacitors were appropriately discharged. If the capacitors remain charged, switching action
might be delayed. In point welding and similar applications where capacitors are required to be
switched on and off frequently, the capacitors must be equipped with a discharging. High power
resistors or discharge reactors are recommended to increase switching speed and frequency.
Discharge resistors need to be selected carefully to achieve desired discharge rate. Figures
3.1 and 3.2 show the relationship between the discharge resistance and discharge time for
12.5kVAr, 25kVAr, 50kVAr and 80kVAr PFC systems employing two and three discharge resistors,
respectively. The discharge rates are almost identical for systems with a 7% detuned filter reactor
and without a detuned filter reactor. If a detuned filter reactor is not used, the discharge may be
obtained from 7% curves on Figures 3.1 and 3.2.
The recommended power ratings for common discharge resistor values are listed in Table
3.2. These power ratings allow for safety margins. Avoid use of power resistors lower than the
given ratings. Avoid thermal coupling between the modules and power resistors by keeping a
clearance distance of 150 mm in all directions.
Do not place discharge resistors directly
underneath the modules!
