IMR01M01-E16
24
7.12 Protection Function for Control of Primary Side of a Transformer
If momentary power failure occurs during execution of the control of primary side of a transformer, inrush current is generated.
Protection function for control of primary side of a transformer is to protect the thyristor from the inrush current.
With this protection function enabled, when momentary power failure occurs, the instrument determines that the secondary side
of a transformer was disconnected and suppresses the output. When the instrument is automatically reset from the breakdown
(momentary power failure), the soft-start function suppresses the inrush current.
To use this protection, the following parameters need to be set.
• Protection function for control of primary side of a transformer (t)
• Determination set value in case of a break on the secondary side of the transformer (a)
• Output limiter setting in case of a break on the secondary side of the transformer (h)
• Soft-start time in case of break on the secondary side of the transformer (u)
For the setting range of parameter, refer to page 16.
For the setting procedure, refer to page 13.
Operation chart
Determination of break and release of secondary side of transformer
• Determination of break
While control of primary side of a transformer is executed, if the current transformer (CT) value goes below the determination set
value in case of a break on the secondary side of the transformer, it is judged to be a break (momentary power failure).
Below is a formula to convert the determination set value in case of a break on the secondary side of the transformer (a) into the
current value (A).
Current value [A] = Maximum load current set value [A] × Effective output voltage [%] × (100 % − Determination set value in
case of a break on the secondary side of the transformer [%])
• Determination of release
While the phase angle is 20 % or more, when the current goes over the determination set value in case of a break on the
secondary side of the transformer by 0.3 A (instrument of 45 A or more: 1 A), it is judged to be a release from a break
(momentary power failure).
22.1 %
(Phase angle 20.0 %)
Current (A)
Effective output voltage (%)
0
70.7 %
(Phase angle 50.0 %)
100.0 %
Determination set value in case of a
break on the secondary side of the
transformer
Computed heater current value
Insensible range of protection function for
control of primary side of a transformer
Operating point of output limiter in
case of break on the secondary side
of a transformer
When the input value of the current
transformer (CT) goes below this
point, it is judged to be broken and
protection is executed.
During the “break” state, the displayed
value flashes.
Output limiter ON range when the secondary
side of the transformer is broken.
Output limiter setting range when secondary side of transformer is disconnected.
When momentary power failure occurs, if the output from the instrument is smaller than the
output limiter set value in case of a break on the secondary side of the transformer, control
continues with the same level of output kept.
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