Delay Triggering With Burst Firing - CD Automation Revo CL User Manual

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16.3 Delay Triggering with Burst Firing (DT+BF
The Delay Triggering DT firing is used the control a primary of transformer coupled with the normal
resistances on the secondary (N.B. don't connect cold resistances on the secondary like: Superkanthal,
Molybdenum, Platinum, Tungsten, Quartz Lamp).
For an inductive load (ex transformer), switching the 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, besides all the
first burst start with soft start ramp to reduce the inrush current during the cycle of magnetization.
Without Delay Triggering
Transient
over-current
0
Zero
Crossing
Voltage
For understand the Delay Triggering firing, we have represented the waves generate by vectors that
rotates in counterclockwise:
Without Delay Triggering
V
2
I
i
3
I
3
V
3
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.
With Delay Triggering the firing of the thyristor are triggered with a delay until the instantaneous value
of the curret i1=0, i2 positive and i3 negative like represented.
In this case the risk of transient 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°
CD-Eng-REVO-CL-1PH-60-210A-Thyristors-Units
Current
Voltage
y
2
i
2
V
1
x
i
1
I
1
REVO CL
bFdt bFdt bFdt bFdt
)
With Delay Triggering
Delay angle
(0° to 100° )
0
Zero
Crossing
Voltage
With Delay Triggering
I
V
2
2
i
3
37
User's Manual
Voltage
Current
y
V
1
i
2
Delay Angle
α
I
1
I
3
V
3
x