ABB REU 610 Technical Reference Manual page 24

REU 610
24
Voltage Relay
Technical Reference Manual - ANSI Version
When the conventional protection mode is selected and the phase-to-phase
voltages exceed the set pickup value of the high-set element, 59P-2, the
element generates a pickup signal after a ~ 50 ms' pickup time. When the set
operate time at definite-time characteristic or the calculated operate time at
IDMT characteristic elapses, the element generates a trip signal. The element
is reset in 70 ms after the phase-to-phase voltages have fallen below the set
pickup value of the element.
The conventional overvoltage elements have a settable drop-off/pick-up ratio,
which is adjustable between 0.95...0.99, the default being 0.97.
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.
Overvoltage protection based on negative phase-sequence
voltage
When the calculated negative phase-sequence voltage value U
set pickup value of the element 47, the element generates a pickup signal after
a 50 ms' pickup time. When the set operate time at definite-time
characteristics or the calculated operate time at IDMT characteristics elapses,
the element generates a trip signal. The element is reset in 70 ms after the
calculated negative phase-sequence voltage value has fallen below the set
pickup value of the element.
The negative phase-sequence voltage is calculated as follows:
2
+ ×
U a U
=
ab bc
U
2
3
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.
Element 47 can be set to be blocked when one of the measured phase-to-
phase voltages falls below 0.15 × U
Element 47 has a fixed drop-off/pick-up ratio of 0.96.
+ ×
a U
ca
(VT). The selection is made in SGF4.
n
1MRS755972
exceeds the
2
(1)