FUNCTION CHARACTERISTICS
267
NVA100X-D - Manual - 02 - 2016
CT supervision - 74CT
Preface
The CT monitoring function is employed to issue an alarm when secondary phase CTs side H and side
L and/or phase input of the relay failure are detected.
Interruptions are detected by means of a symmetry criterion of the
I
L1
,
I
L2
,
I
L3
input currents.
The symmetry factor is calculated comparing the minimum and maximum of the fundamental compo-
nents of the three phase currents
I
LMIN(H)
/
I
LMAX(H)
and
I
LMIN(L)
/
I
LMAX(L)
.
Operation and settings
The starting of the timer occurs if both the following conditions are fi lled:
I
LMIN(H)
/
I
LMAX(H)
<
S
(H)
< for CTs side H or
II
LMIN(L)
/
I
LMAX(L)
<
S
(L)
< for
CTs side L;
I
LMAX(H)
>
I
(H)
* for CTs side H and
I
LMAX(L)
>
I
(L)
* for
CTs side L
where
I
(H)
* and
I
(L)
*: maximum phase current threshold
S
(H)
< and
S
(L)
< : element pickup values
t
S(H)
< and
t
S(L)
<
:
operate time
If both conditions are fi lled over the
t
S(H)
< and
t
S(L)
<adjustable time an alarm is issued.
The output may be assigned to the selected
S(H)<TR-K
and
S(L)<TR-K
output relays inside the
Set \ CT supervision-74CT side H
and
Set \ CT supervision-74CT side L
submenu; the same for ad-
dressing the LED indicators
S(H)<TR-L
and
S(L)<TR-L
.
Logical block (Block1)
If the
S<-BLK1
parameter is set to
ON
, and a binary input is designed for logical block (Block1), the
CT supervision function is blocked off whenever the given input is active. The trip timer is held in re-
set condition, so the operate time counting starts when the input block goes down.
[1]
The
S<-BLK1
parameter is available inside the
Set \ CT supervision-74CT side H
and
Set \ CT supervision-74CT
side L
submenu.
All the parameters are common for A and B Profi les.
Note 1 The exhaustive treatment of the logic block (Block 1) function may be found in the “Logic Block” paragraph inside
CONTROL AND MONITORING
section
—
A)
B)
Current asimmetry monitoring - 74CT
I
(H)
*
I
(L )
*
α
I
LMIN(H)
I
LMIN(L)
I
LMA X(H)
I
LMA X(L)
tg
α
=S(H) <
tg
α
=S(L)<
TRIP
NO TRIP
CT monitoring logic diagram - 74CT
Fun-74CT.ai
&
0
T
t
s
<
t
S<
I
LMIN
/
I
LMAX
<
S
<
S
<
TRIP
P
ING
M
ATRIX
(LED
+R
EL
AY
S
)
Trip S<
Start I*
BLK1 S<
I
LMAX
>
I*
I*
Enable (ON
≡
Enable)
Block1 input (ON
≡
Block)
&
&
S<BLK1
Block1
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
I
L1
I
LMAX
I
L2
I
L3
I
LMIN
I
LMIN
I
LMAX
S<TR-K
S<TR-L
RESET
