100
FUNCTION CHARACTERISTICS
— Positive sequence undervoltage - 27V1
Preface
The element has an adjustable threshold with time definite delay.
Enabling or disabling may be performed through Thyvisor: it can be temporarily blocked by keyboard
command.
Operation and settings
The positive sequence voltage is calculated as:
U
1
=(U
L1
+e
+j120°
·U
L2
+e
-j120°
·U
L3
)/3
where e
-j120°
=-1/2-j√3/2, e
j120°
=-1/2+j√3/2.
The positive sequence voltage is compared with the setting value (U
1
<
def
). Voltages under the as-
sociated pickup value are detected and a start is issued. After expiry of the associated operate
time (t
U1
<
def
) a trip command is issued; if instead the voltage 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) \ Positive sequence undervoltage-27V1 \ U1< Element \ Setpoints menu.
User can disable the 27V1 protection threshold from the keyboard. During this command, the trip
output relay (U <and / or U << thresholds) are forced to reset state, the message “Disabled 27-27V1-
37P-37Q” is displayed and all LEDs blink until the end of the command.
Breaker failure (BF)
U1< threshold can be associated to BF (H) and BF (L) protection by activating the relative parameter
in the matrices “Selection of function tripping for BF (H)” or “Selection of function tripping for BF (L)”
in relevant BF menus
[1]
:
• Set \ Profile A (or B) \ Breaker failure - BF side H
• Set \ Profile A (or B) \ Breaker failure - BF side L
VT supervision (74VT)
The element may be blocked whenever the VT supervision function is active, so that no unwanted trip
can arise if any fault on the VTs secondary circuits (break, fuse trip, etc) are detect;
[2]
the Block fun-
ctions enable from 74VT parameter
74VT-BK-ENis available inside the Set \ VT supervision -74VT.
Note 1 The common settings concerning the Breaker failure protection are adjustable inside the Breaker Failure - BF menu.
Note 2 The exhaustive treatment of the VT supervision function may be found in the “VT supervision - 74VT” paragraph inside CONTROL AND MONI-
TORING section.
t-int-F27V1.ai
U
1
U
1
<
t
t
U1
<
General operation time characteristic for the positive undervoltage element - 27V1
TRIP
all-F27V1.ai
General logic diagram of the phase positive sequence undervoltage elements - 27V1
U1< Element
MMI
Start U1<
Trip U1<
t
U1<
def
U
1
<
def
State
Block1
BLK1U<
&
U1<BLK1
Start U1<
&
&
U
1
74VT
Disable 27-37-81 functions by operator
XMR-D EQUIPMENT MANUAL
Ed. 2.9 - 02/2021
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