
FUNCTION CHARACTERISTICS
47
NA20 - Manual - 04 - 2022
Undercurrent - 37
Preface
One operation threshold, adjustable (
I
<
def
) with adjustable delay (
t
<
def
).
The threshold operates with definite time characteristic.
Operation and settings
Each of three currents are compared with the setting value (
I
<
def
). The start and trip logic may be
selected
OR
or
AND
.
With
OR
selection, a start is issued when at least one of the three currents goes down the adjust-
able threshold (START); with
AND
selection, a start is issued when all the three currents go down
the adjustable threshold.
After expiry of the associated operate time (
t
<
def
), a trip command is issued; if instead the currents
exceed the threshold, the element is restored.
The element can be enabled or disabled by setting
ON
or
OFF
the
State
parameter inside the
Set
\ Profile A(or B) \ Undecurrent-37 \
I
< Element \ Definite time
menu.
The undecurrent element may be disabled by means MMI. During the command, the trip output
relays I<TR-K (with latched or no-latched operation mode and, de-energized or energized logic) are
forced in the rest state, the“
37 DISABLED
” message is displayed and all the LEDs flash until the
command is ended.
The following block criteria is available:
Logical block (Block1)
If the
I<BLK1
enabling parameter are set to
ON
and a binary input is designed for logical block
(Block1), the protection is blocked off whenever the given input is active.
The trip timer is held in reset condition, so the operate time counting starts when the input block
goes down.
[1]
The enabling parameter is available inside the
Set \ Profile A(or B) \ Undercurrent - 37
\
I< Element \ Setpoints
menu, while the
Block1
function must be assigned to the selected binary
input inside the
Set \ Inputs \ Binary input INx)
menus (INx matching).
The parameter may be adjusted independently for both profiles
A
or
B
.
Note 1 The description of the logical block (Block 1) function may be found in the “Logic Block” paragraph inside CONTROL AND MONITORING section.
General operation time characteristic curve for the undercurrent element - 37
I
<
def
t
I
t
<
def
TRIP
General logic diagram of the undercurrent element - 37
all-F37.ai
I
L1
,
I
L2
,
I
L3
I< Element
Start I<
Trip I<
t<
def
I<
def
State
Block1
BLK1I<
&
I<BLK1
Start I<
&
AND
OR
Logic37
Содержание NA20
Страница 207: ...APPENDIX 207 NA20 Manual 04 2022...