Undervoltage Protection - ABB REU 610 Technical Reference Manual

REU 610
5 . 1. 4 . 3 .
24
Voltage Relay
Technical Reference Manual
at definite- time characteristic or the calculated operate time at ID M T
characteristic elapses, the stage generates a trip signal. The stage is reset in 7 0
ms after the phase- to- phase voltages have fallen below the set start value of
the stage.
The conventional overvoltage stages have a settable drop- off/ pick- up ratio,
which is adjustable between 0.9 5 ...0.9 9 , the default being 0.9 7 .
The settable drop- off/ pick- up ratio enables the voltage
protection to satisfactorily work with a voltage regulator, for
instance, such as a tap changer. The tap changer step is often
1.67 % , which is less than the drop- off/ pick- up ratio of voltage
relays. This can cause a situation where the voltage protection
remains active even though the tap changer already has changed
the voltage.
O v er v oltage p r otec ti on b as ed on n egati v e p h as e- s eq u en c e
v oltage
W hen the calculated negative phase- sequence voltage value U
set start value of the stage U
start time. W hen the set operate time at definite- time characteristics or the
calculated operate time at ID M T characteristics elapses, the stage generates a
trip signal. The stage is reset in 7 0 ms after the calculated negative phase-
sequence voltage value has fallen below the set start value of the stage.
The negative phase- sequence voltage is calculated as follows:
+ ×
8 D 8
=
8
V
a = 1∠ 120°
2
a = 1∠ - 120°
The negative phase- sequence value is scaled to the amplitude of the measured
voltage. On a network with a reverse phase order, the calculated negative
phase- sequence value has the same amplitude as the measured voltage signal.
S tage U > can be set to be blocked when one of the measured phase- to- phase
2
voltages falls below 0.15 × U
S tage U > has a fix ed drop- off/ pick- up ratio of 0.9 6.
2
Un d er v oltage p r otec ti on
The undervoltage protection can be based on either conventional voltage
measurement or the calculated positive phase- sequence voltage.
>, the stage generates a start signal after a 5 0 ms'
2
+ ×
D 8
. The selection is made in S GF 4 .
n
1MRS755769
ex ceeds the
2s
( 1)