Functions
2.18 Reverse-Power Protection Application with Flexible Protection Function
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
298
Table 2-25 System data for the application example
Protective Functionality
With protection device 7SJ64, the control system is disconnected from the generator upon the generator's re-
versed feeding into the power supply company's power system (protection function P reverse>). This function-
ality is realized by means of a flexible protection function. Additionally, the disconnection is effected by fluctu-
ations in frequency or voltage in the power supply company's power system (protection function f<, f>, 27-1
PICKUP, 59-1 PICKUP, 67-1 PICKUP, 67N-1 PICKUP). This protection receives measured values via a
three-phase current and voltage transformer set as well as a single-phase connection to the generator's voltage
transformer (for synchronization). In case of disconnection, the circuit breaker CB2 is triggered.
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.
Overcurrent protection 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 overcurrent 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 2-107.
Synchronization Before Connecting the Generator
In most cases, it is the power customer who is responsible for restoring normal system operation after discon-
nection. The 7SJ64 relay tests whether the synchronous system conditions are satisfied. After successful syn-
chronization 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 2-108).
Wiring Diagram, Power Direction
Figure 2-108 shows the wiring of the device for reverse power protection and synchronization. The power flow
in positive or forward direction occurs from the high-voltage busbar (not shown) via the transformer to the low-
voltage busbar.
Power System Data
Generator nominal power S
Nom,Gen
= 38.1 MVA
Transformer nominal power S
Nom,Transformer
= 38.1 MVA
Nominal voltage of high-voltage side V
Nom
= 110 kV
Nominal voltage of busbar side V
Nom
= 11 kV
Nominal primary CT current on busbar side I
Nom,prim
= 2000 A
Nominal secondary CT current on busbar side I
Non,sec
= 1 A
Nominal primary VT voltage on busbar side V
Nom,prim
= 11 kV
Nominal secondary VT voltage on busbar side V
Nom,sec
= 100 V
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