Siemens siprotec SJ62 User Manual page 278

Substation Layout
Protective Func-
tionality
Synchronization
Before Connecting
the Generator
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
2.18 Reverse-Power Protection Application with Flexible Protection Function
A 110-kV line connects the substation to the utility grid on high-voltage side. Circuit-
breaker CB1 belongs to the utility grid. The switch-disconnector separates the substa-
tion from the utility grid if necessary. The transformer with a ratio of 10:1 transforms
the voltage level to 11 kV. On low-voltage side, transformer, generator and the two
feeders are connected on a busbar. The circuit-breakers CB2 to CB5 disconnect con-
sumers and equipment from the busbar.
Table 2-23 System data for the application example
Generator nominal power
Transformer nominal power
Nominal voltage of high-voltage side
Nominal voltage of busbar side
Nominal primary CT current on busbar side
Nominal secondary CT current on busbar side
Nominal primary VT voltage on busbar side
Secondary primary VT voltage on busbar side
The 7SJ64 protective relay will disconnect the substation from the utility grid in case
the generator feeds back energy into the utility grid (protective function P rev>). This
functionality can be achieved using a flexible protection function. Disconnection will
also be initiated if frequency or voltage fluctuations occur in the utility grid (protective
functions 81, 27-1, 59-1, 67-1, 67N-1). The protective relay obtains the measured
values via a three-phase current and voltage transformer set and a single-phase con-
nection to the generator voltage transformer (for synchronization). Circuit-breaker
CB2 will be activated in case of disconnection.
The transformer is protected by a differential protection and inverse and definite time
overcurrent protection functions for the phase-to-phase currents. In the event of a
fault, circuit-breaker CB1 in the utility grid will be activated via a remote link. Circuit-
breaker CB2 is activated in addition.
Time overcurrent protective functions protect the feeders 1 and 2 against short-circuits
and overload caused by the connected consumers. The phase-to-phase currents and
the zero currents of the feeders can be protected by inverse and definite time overcur-
rent protection elements. Circuit-breakers CB4 and CB5 are activated in the event of
a fault.
In addition, the busbar could be equipped with the 7UT635 differential protective relay
for multiple ends. The current transformers required to this end are already included
in Figure 2-91.
In most cases, it is the power customer who is responsible for restoring normal system
operation after disconnection. The 7SJ64 relay tests whether the synchronous system
conditions are satisfied. After successful synchronization the generator is connected
to the busbar.
The voltages required for synchronization are measured at the transformer and at the
generator. The voltage at the transformer is measured in all three phases since they
are also necessary to determine the direction. A generator supplies the phase-to-
phase voltage Vca across a star-delta transformer to device input V4 (see Figure 2-
92).
Power System Data
S = 38.1 MVA
N,Gen
S = 38.1 MVA
N,Transformer
V = 110 kV
Nom
V = 11 kV
Nom
= 2000 A
I
N,prim
= 1 A
I
N,sec
V = 11 kV
N,prim
V = 100 V
N,sec
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