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1VLM000651, Rev.3, en 2014.01.21
2. Application and settings
a)
VT Guard Pro
VT Guard Pro should be connected in open delta configuration of three single-phase VTs, as shown in Fig. 22.
Nominal voltage level of the winding used for open-delta configuration should be 100/3 V or 110/3 V and it should
be design at least for nominal current 4A.
Manufacturer does not guarantee proper operation and performance of
VT Guard Pro in case of its use in different applications or at different
voltage levels. In such case contact manufacturer for further details.
In case some other device for ferroresonance elimination is already
installed in the open-delta winding of VT, it has to be removed from this
circuit before VT Guard Pro installation.
Live end of the open delta configuration (da1 - terminal on Fig. 22) should be connected into X1:1 terminal, earthed
end (dn3 - terminal on Fig. 22 to the X1:2 terminal. In case, the earth-fault protection device is already connected in
open delta configuration, the VT Guard Pro should be connected in parallel to such protection device.
Fig. 2 – Connection diagram of VT Guard Pro
Factory default setting for the threshold voltage of VT Guard Pro (effective voltage level when the device is activated)
is 20 V and time delay (time between reach of threshold voltage and dumping action – introduced in order to keep
functions of external protection device unaffected) is 1,4s. These settings cover the majority of the applications, but
can be changed if necessary. In that case, the device has to be disconnected from the power (both functional and
diagnostic part) at least for 20s before setting change. The setting change is done by jumpers, after opening the
cover– one jumper is for threshold voltage selection, the other for time delay Fig..
Possible adjustment:
Threshold voltage ……………..20, 25, 30 V
Time delay …………………….0,4; 1,4; 2,4; 3,4s
b)
VT Guard Pro-D
The internal settings (threshold voltage, time delay) and connection of the functional part (Terminals X1:2, X1:2)
Fig. 3– Jumper setting
