3.Underfrequency Protection; Connections; 1.Protection Signal Routing - ABB REX 521 Technical Reference Manual, Standard Configurations

1MRS 751802-MUM
11.6.3.1.
11.6.4.
11.6.4.1.
Protection Relay
Technical Reference Manual, Standard Configurations
85% 115%
t(s)
70%
100
60 s
10
3 s
1
70 80 90 100 110 120 130
UNDERVOLTAGE
U< = 0.85 x Un, t> = 60 s, DT
U<< = 0.7 x Un, t> = 3 s, DT
OVERVOLTAGE
U> = 1.15 x Un, t> = 60 s, DT
or U> = 1.09 x Un, k = 0.2, p = 2, IDMT
U>> = 1.3 x Un, t> = 0.1 s, DT
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Underfrequency protection
The underfrequency protection is included in the functionality of the protection relay
of the measurement cubicle. The underfrequency protection includes two protection
stages: a low stage f< and a high stage f<<.
In this application two load shedding groups are used. The low stage f< is used for
disconnecting the load shedding group 1. The high stage f<< is used for
disconnecting the load shedding group 2.
The trip signal of the f< stage is connected to the power output relay PO2 via Trip 2
signal. This trip signal is used for disconnecting the outgoing feeders of the first load
shedding group.
The trip signal of the f<< stage is connected to the power output relay PO3 via
Trip 3 signal. Also the residual voltage stage Uo>>, under- and overvoltage
protection trips are connected to this power output and those signals have to be
connected to all outgoing feeders. Therefore the trip signal of the high stage f<< will
be connected to all circuit breakers of the outgoing feeders. All outgoing feeders are
included in the load shedding group 2.

Connections

All the necessary settings for the connections and signal routings can be set via the
Relay Setting Tool or the local HMI.
Protection signal routing
The trip signal (Trip 1) of the residual voltage stages Uo>> and Uo>>> protection
function are routed to the high speed power output HSPO1 (x4.2.1/2/3/4).
130%
DT operation
60 s
IDMT operation
0.1 s
U/Un(%)
REX 521
197