84
DMC3S - Manual - 08 - 2021
U
VT
<
Fun_74VT.ai
U
2
U
2
≥
U
2
VT
>
74VT-AL-K
74VT-AL-L
74VT-BK-K
74VT-BK-L
“1”
≡
CB CLOSED
I
2
I
2
≥
I
2
VT
>
Max(
U
L1
...
U
L3
)
≤
U
VT
<
Max(
I
L1
...
I
L3
)
≥
I
VT
>
Min(
U
L1
...
U
L3
)
≥
U
VT
<
|I
L1(k)-
I
L1(k-1)|
|I
L2(k)-
I
L2(k-1)|
≤
I
VT
<
|I
L3(k)-
I
L3(k-1)|
&
&
&
&
&
&
&
&
&
S
R
Q
S
R
Q
&
≥
1
≥
1
t
VT-AL
T
0
RESET
BLOCK 25/32P/67/67N
ATTIVA 51N(E)
U
2
VT
>
I
2
VT
>
t
VT-AL
I
VT
>
I
VT
<
≤
I
VT
<
≤
I
VT
<
(ON=1
≡
Autoreset enabled)
(ON=1
≡
Reset key)
Self-reset 74VT
CB closed
Reset key
Reset ThySetter
Remote Reset
(ON=1
≡
remote reset)
(Remote interface reset)
Reset LEDs
74VT Block out
TR
IP
PI
NG M
AT
RI
X
(LE
D+R
EL
AY
S)
ON
≡
Enable 74VT
74VT Enable
A
A
B
C
D
E
G
H
E
G
H
D
B
C
Alarm 74VT
Block 74VT
Enable (ON
≡
Enable)
Block1 input (ON
≡
Block)
Block1
BLK1 74VT
Block1
Binary input INx
T
0
Logic
INx
t
ON
INx
t
ON
INx
t
OFF
T
0
n.o.
n.c.
INx
t
OFF
Functional diagram of the VT monitoring function (74VT)
Activates 74VT when one or more phase voltages is lost and no negative sequence current is available (to discriminate disymmetric short circuits).
Activates 74VT when all three phase voltages are lost with e generator under load.
Activates 74VT when all three phase voltage are absent during line power up (VT not connected), and checks that none of the three currents are greater than
IVT>. To not activate 74VT on closing to a polyphase shirt circuit, IVT> must be set to a value lower than ICC (but greater than the maximum load inrush
current). In any case the breaker must be closed, otherwise 74VT activates with the machine stopped.
Inhibits activation of 74VT on polyphase short circuits, by setting the flip-flop when the current variation of at least one phase is subject to a pulse
variation. The inhibition of 74VT automatically resets when all three phase voltages return above the threshold and the negative sequence voltage
falls below the threshold.
The activation of 74VT is maintained when at least one of conditions A, B and C is satisfied. The function 74VT can be reset manually (so long as the
automatic reset conditions in point D are satisfied) or automatically, if configured to do so by the user.
Activation of 74VT can be inhibited by a block command applied to a digital input.
Activation of 74VT is always reported. The voltage inverse protections can also be blocked, if so configured by the user.
