TECHNICAL USER´S MANUAL
7
Thyristor modules
Figure 3.2:
The effect of discharge resistance on discharge time for 7% (189Hz) and 14%
(134Hz) detuned reactor PFC with two discharge resistors. 7% rates may be used if no reactor
is employed.
Table 3.2:
Recommended power ratings for discharge resistors
Resistance (kΩ)
Resistor Power (W)
5.6
100
10
50
18
25
22
25
39
10
56
10
69
5
SUPERFAST FUSE SELECTION: Each thyristor module should be connected to the line through a
“superfast” branch fuse. Depending on the module type, recommended fuse current and voltage
ratings are listed in Table 3.3.
Table 3.3:
“Superfast” fuse ratings for each thyristor module
Model
Current (A)
Voltage (V)
Power (kVAr)
12kVAr
35
NH AC 690
12.5
25kVAr
63
NH AC 690
25
50kVAr
125
NH AC 690
50
80kVAr
200
NH AC 690
80
MITIGATING HIGH
di/dt
: When the thyristors are triggered, the current is initiated at the gate-
cathode junction. The current spreads to the entire junction area as it increases. If the current
time rate of change (
di/dt
) during this process is faster than the charge carriers in the junction,
then the thyristor may get damaged. Absolute maximum
di/dt
ratings for thyristor modules are
presented in Table 3.4. If these values are exceeded, the thyristor modules might be permanently
damaged. Detuned filter reactors limit the
di/dt
. If a detuned filter reactor is not used, then a
current limiting reactor with a minimum of 20µH inductance is recommended to protect the
module and maintain a long life expectancy.
Table 3.4:
Absolute maximum
di/dt
ratings for module types
Model
di/dt
(A/µs)
12kVAr
50
25kVAr
100
50kVAr
140
80kVAr
140
