Specifications

Overcurrent Protection SIPROTEC 7SJ81
5/7SIPROTEC Compact · SIEMENS SIP 3.01 · Edition 3
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It has the following functions:
• TRIP via the displacement voltage V
E
• Two instantaneous elements or one instantaneous plus
one user-defi ned characteristic.
• Each element can be set to forward, reverse or
non-directional.
• The function can also be operated in the insensitive mode
as an additional short-circuit protection.
Fig. 5/5 Directional determination using cosine measurements for
compensated networks
(Sensitive) ground-fault detection
(ANSI 50Ns, 51Ns / 50N, 51N)
For high-resistance grounded networks, a sensitive input
transformer is connected to a split-core low-power current
transformer (also called core-balance CT). The function can
also be operated in the normal mode as an additional short-
circuit protection for neutral or residual ground protection.
Negative-sequence system overcurrent protection (ANSI 46)
By measuring current on the high side of the transformer,
the two-element phase-balance current/negative-sequence
protection detects high-resistance phase-to-phase faults
and phase-to-ground faults on the low side of a transformer
(e.g. Dy 5). This function provides backup protection for
high-resistance faults through the transformer.
Breaker failure protection (ANSI 50BF)
If a faulted portion of the electrical circuit is not discon-
nected when a trip command is issued to a circuit-breaker,
another trip command can be initiated using the breaker fai-
lure protection which trips the circuit-breaker of an upstream
feeder. Breaker failure is detected if, after a trip command
is issued and the current keeps on fl owing into the faulted
circuit. It is also possible to make use of the circuit-breaker
position contacts (52a or 52b) for indication as opposed to
the current fl owing through the circuit-breaker.
Automatic reclosing (ANSI 79)
Multiple re-close cycles can be set by the user and lockout
will occur if a fault is present after the last re-close cycle.
The following functions are available:
• 3-pole ARC for all types of faults
• Separate settings for phase and ground faults
• Multiple ARC, one rapid auto-reclosure (RAR) and up to
nine delayed auto-reclosures (DAR)
• Initiation of the ARC is dependant on the trip command
selected (e.g. I
2
>, I>>, I
p
, I
dir
>)
• The ARC function can be blocked by activating a binary
input
• The ARC can be initiated from external or by the PLC logic
(CFC)
• The directional and non-directional elements can either
be blocked or operated non-delayed depending on the
auto-reclosure cycle
• If the ARC is not ready it is possible to perform a dynamic
setting change of the directional and non-directional
overcurrent elements.
Flexible protection functions
The SIPROTEC 7SJ81 enables the user to easily add up to
20 additional protection functions. Parameter defi nitions
are used to link standard protection logic with any chosen
characteristic quantity (measured or calculated quantity).
The standard logic consists of the usual protection elements
such as the pickup set point, the set delay time, the TRIP
command, a block function, etc. The mode of operation for
current, voltage, power and power factor quantities can be
three-phase or single-phase. Almost all quantities can be
operated with ascending or descending pickup stages (e.g.
under and overvoltage). All stages operate with protection
priority.
Voltage
Current
Parameter
Pickup
df/dt
f
t
Time
FRV˳
34

Function 1
Function 2
Function 20
TRIP
command
3V0, U1, U2
3I0, I1, I2
V measured
I measured
Standard protection logic
(simplified diagram)
Measured-value
processing
Threshold

Fig. 5/6 Flexible protection function
for Low-Power CT and VT Applications – Application sheets
5_6_Visio-fl exProFunc-us.pdf