7300A User Manual
3-2
LED labelling Signalling
Power supply for electronics.
Power supply fault (flashing).
No reference Neutral (flashing).
Thyristor firing request in ‘Burst mode’, ‘Single-cycle’ and
‘Advanced single cycle’ modes.
Reminder: ‘Advanced single-cycle’ is only available with 4S and 6D three
phase load configuration.
Thyristor firing request in ‘Phase angle’ mode.
Firing modes
3. Chapter 3 FIRING MODES
3.1. GENERAL AND FIRING MODE SIGNALLING
7300A power thyristor units can be controlled with one of the following thyristor firing types:
• thyristor firing angle variation (‘Phase angle’, code PA)
• a series of supply voltage cycles with zero crossing firing
(‘Burst mode’, codes C16, C64, FC1, ASC)
Two indicators (green ‘ON’ and ‘HEAT’ LEDs) are included on the front panel in all
versions, either basic or with options.
The indicators correspond to the thyristor firing mode as shown in the table below.
Table 3-1 Firing modes and base LEDs on front panel
ON
HEAT
HEAT
During normal operation with zero-crossing switching, the ‘HEAT’ LED flashes to match the
thyristor firing periods.
In normal operation in ‘Phase angle’ mode, the ‘HEAT’ LED varies in brightness depending on
the firing angle, with maximum brightness during full firing.
3.2. BURST MODE (codes C16 and C64)
‘Burst mode’ firing is a proportional cycle which delivers a series of whole supply cycles
to the load. Thyristor firing and cut-off is synchronised with the supply and occurs at zero crossing.
t
Load
Voltage
T
M
TF
T
NF
Thyristor firing in ‘Burst mode’ can be
described by the firing time (T
F
) , non-firing
time (T
NF
) and modulation time (T
M
)
where T
M
= T
F
+ T
NF
and the Base Cycle Time is
equal to the number of cycles firing at 50% of
the duty ratio (or 50% of the power supplied to
the load):
T
B
= T
F
= T
NF
.
The Base Cycle time is equal to 16 cycles for
code C16 and 64 cycles for code C64.
Figure 3-1 Thyristor firing for one of the
phases, in ‘Burst mode’
