Delay Triggering With Burst Firing - CD Automation REVEX PA User Manual

REVEX
PA from 35A to 90A

14.6 Delay Triggering with Burst Firing

The Delay Triggering firing is used
the control a primary of transformer
coupled with the
resistances on the secondary (N.B.
don't connect cold resistances on
the secondary like: Superkanthal,
Molybdenum, Platinum, Tungsten,
Quartz Lamp).
For an inductive
transformer), switching
thyristors at zero crossing can
generates transient over currents
that can blow the fuses, to avoid this
problem you must use the Delay
Triggering. This firing delay the first
half cycle of Burst for an angle from
0 to 100° relative to the zero.
For understand the
Triggering firing, we have represented the waves generate by vectors that rotates in counterclockwise:
Without Delay Triggering
y
V
2
l
2
i
2
i
1
i
3
l
3
V
3
over currents is reduced and the fuses don't blow.
The angle alpha is the delay to have i1=0 and this angle depends on the power factor.
The delay angle suggest for most applications is 80°.
Without Delay Triggering
normal
Voltage
load (ex
the
0
Zero
crossing
voltage
Delay
With Delay Triggering
V
2
V
1
X
l
1
Transient over-current
Current
y
l
2
V
1
i
2
Delay Angle
l
1
i
3
l
3
V
3
60
User's manual
With Delay Triggering
Delay angle
(0° to 100°)
Voltage
Current
0
Zero
crossing
voltage
Without delay at zero crossing
when V1 is to zero (projected on
the X axis) the unit switch On.
In this case the instantaneous
value of the currents are i1, i2 and
i3 and this condition, for the curve
of magnetization, could generate
transient over currents that can
blow the fuses.
X
With Delay Triggering the firing of
the thyristor are triggered with a
delay until the instantaneous value
of the current i1=0, i2 positive and
i3 negative like represented.
In this case the risk of transient