46
NV021 - Manual - 08 - 2012
CHARACTERISTICS
Positive sequence undervoltage - 27V1
[1]
Preface
The protection has an adjustable threshold and defi nite time characteristic.
Enabling or disabling is provided by means ThySetter, the element can be temporarily blocked by
keyboard command.
Operation and settings
The positive sequence voltage is calculated as:
U
1
=(
U
12
+e
+j120°
·
U
23
+e
-j120°
·
U
31
)/3
where
U
12
,
U
23
and
U
31
are line voltages and with e
-j120°
=-1/2-j√3/2, e
j120°
=-1/2+j√3/2
The voltage of the positive sequence is compared with the threshold (
U
1
<
def
).
A start is issued when the positive sequence voltage falls below adjustable threshold (START).
After expiry of the associated operate time (
t
U1
<) a trip command is issued; if instead the voltages
drops below the threshold, the element it is restored.
The element can be enabled or disabled by setting
ON
or
OFF
the
State
parameter inside the
Set \
Profi le A(or B) \ Positive sequence undervoltage-27V1 \ U1< Element \ Defi nite time
menu.
The user can disable the 27V1 protection by means of a keyboard command (DISABLE 27 FUNCTION
BY OPERATOR). During this command, the output trip relays (manual or automatic reset, normally
energized or de-energized) are forced to idle state, the “Disable 27-27V1” message is displayed “and
all the LEDs fl ash until the end of the command.
Breaker failure (BF)
The undervoltage element can produce the Breaker Failure output if the
U1< BF
parameter is set
to
ON.
The parameter is available inside the
Set \ Profi le A(or B) \ Positive sequence undervoltage
- 27V1 \
U1< Element \ Setpoints
menu.
[2]
Logical block (Block1)
If the
U1<BLK1
enabling parameter is 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.
[3]
The enabling parameter is available inside the
Set \ Profi le A(or B) \ Positive sequence un-
dervoltage - 27V1 \
U1< Element
\ Setpoints
menus, while the
Block1
function must be assigned to
the selected binary input inside the
Set \ Inputs \ Binary input IN1(x)
menus (IN1 or INx matching)
.
All the named parameters can be set separately for
Profi le A
and
Profi le B
.
Nota 1 La funzione è signifi cativa solo in applicazioni su rete trifase
Note 2 The common settings concerning the Breaker failure protection are adjustable inside the
Breaker Failure - BF
menu.
Note 3 The exhaustive treatment of the logical block (Block 1) function may be found in the “Logic Block” paragraph inside
CONTROL AND MONITOR-
ING
section.
—
U
1
U
1
<
t
t
U1
<
TRIP
General operation time characteristic for the positive sequence undervoltage elements - 27V1
U
1
U
1
<
t
t
U1
<
TRIP
General operation time characteristic for the positive sequence undervoltage elements - 27V1
all-F27V1.ai
U1< Element
MMI
Start U1<
Trip U1<
t
U1< def
U
1
<
def
State
Block1
BLK1U<
&
U1<BLK1
Start U1<
&
U1<BF
Trip U1<
&
U1<BF
&
U
1
Disable 27 functions by operator
General logic diagram of the positive sequence undervoltage elements - 27V1
all-F27V1.ai
U1< Element
MMI
Start U1<
Trip U1<
t
U1< def
U
1
<
def
State
Block1
BLK1U<
&
U1<BLK1
Start U1<
&
U1<BF
Trip U1<
&
U1<BF
&
U
1
Disable 27 functions by operator
General logic diagram of the positive sequence undervoltage elements - 27V1