Overcurrent Protection Relay for Low-Power Current Transformer Applications
The SIPROTEC Compact 7SJ81 provides 4 low-power current transformer inputs and optionally 3 low-power voltage transformer inputs. With the same low-power current transformer (LPCT) a wide range of primary rated line currents can be covered. Objects with rated currents in the range from 20 A to 2500 A can be protected when using low-power current transformers.
The following low-power current transformer ratios are suitable for the following primary current operating ranges
300 A/225 mV for a primary operating current range of 60 A to 630 A
600 A/225 mV for a primary operating current range of 120 A to 1250 A
1250 A/225 mV for a primary operating current range of 250 A to 2500 A
100 A/225 mV for a primary operating current range of 20 A to 200 A
SIPROTEC 7SJ81 is a multi-functional motor protection relay. It is designed for protection of asynchronous motors of all sizes. The relays have all the functionality to be applied as a backup relay to a transformer differential relay. The relay provides numerous functions to respond flexibly to the system requirements and to deploy the invested capital economically. Examples for this are: exchangeable interfaces, flexible protection functions and the integrated automation level (CFC). Freely assignable LEDs and a six-line display ensure a unique and clear display of the process states. In combination with up to 9 function keys, the operating personnel can react quickly and safely in any situation. This guarantees a high operational reliability.
Inputs for Low power CTs and VTs according IEC 61869-6 (formerly IEC 60044-7 and IEC 60044-8)
Removable terminal blocks
Binary input thresholds settable using DIGSI (3 stages)
9 programmable function keys
Buffer battery exchangeable from the front
USB front port
2 additional communication ports
integrated switch for low-cost and redundant optical Ethernet rings
Ethernet redundancy protocols RSTP, PRP and HSR for highest availability
Relay-to-relay communication through Ethernet with IEC 61850 GOOSE
Millisecond-accurate time synchronization through Ethernet with SNTP
The SIPROTEC Compact 7SJ81 relays can be used for line/feeder protection of high and medium-voltage networks with grounded, low-resistance grounded isolated or a compensated neutral point. The relays have all the functionality to be applied as a backup relay to a transformer differential relay.
The SIPROTEC Compact 7SJ81 offers highest reliability at major functionality by the synergy of reliable algorithms with newly developed hardware. The reliability is proven by the experience in the field of almost 1,000,000 SIPROTEC devices.
The relay provides numerous functions to respond flexibly to the system requirements and to deploy the invested capital economically. Examples for this are: exchangeable interfaces, flexible protection functions and the integrated automation level (CFC). Freely assignable LEDs and a six-line display ensure a unique and clear display of the process states. In combination with up to 9 function keys, the operating personnel can react quickly and safely in any situation. This guarantees a high operational reliability.
Commands for the ctrl. of CB, disconnect switches (isolators/isolating switches)
Control through keyboard, binary inputs, DIGSI 4 or SCADA system
User-defined PLC logic with CFC (e.g. interlocking)
Operational measured values V, I, f
Energy metering values Wp, Wg
Circuit-breaker wear monitoring
Minimum and maximum values
Trip circuit supervision (74TC)
Fuse failure monitor
8 oscillographic fault records
– IEC 61850
– IEC 60870-5-103
– DNP 3.0
– MODBUS RTU
– Ethernet redundancy protocols RSTP, PRP and HSR
Ethernet interface for DIGSI 4
USB front interface for DIGSI 4
4 low-power current transformer inputs
0/3 voltage inputs
3/7 binary inputs (thresholds configurable using software)
5/8 binary outputs (2 changeover/Form C contacts)
1 life contact
Pluggable voltage terminals
for Low-Power CT and VT Applications– Applications
The SIPROTEC 7SJ81 unit is a numerical protection with low
power CT and VT inputs. The device performs control and
monitoring functions and therefore provides the user with a
cost-effective platform for power system management, that
ensures reliable supply of electrical power to the customers.
The ergonomic design makes control easy from the relay
front panel. A large, easy-to-read display was a key design
The integrated control function permits control of disconnect
devices, grounding switches or circuit-breakers through
the integrated operator panel, binary inputs, DIGSI 4 or the
control or automation system (e.g. SICAM).
The integrated logic characteristics (CFC) allow the user to
add own functions for automation of switchgear (e.g. interlocking)
or switching sequence. The user can also generate
user-defined messages. This functionality can form the base
to create extremely flexible transfer schemes.
Operational measured values
Extensive measured values (e.g. I, V), metered values (e.g.
Wp,Wq) and limit values (e.g. for voltage, frequency) provide
improved system management.
The SIPROTEC 7SJ81 units can be used for line protection
of high and medium-voltage networks with grounded,
low-resistance grounded, isolated or a compensated neutral
Event logs, trip logs, fault records and statistics documents
are stored in the relay to provide the user or operator with all
the key data required to operate modern substations.
The relay provides all the functions for backup protection for
transformer differential protection. The inrush suppression
effectively prevents unwanted trips that can be caused by
SIPROTEC 7SJ81 can be used as a backup protection for a
wide range of applications.
Switchgear cubicles for high/medium voltage
All units are designed specifi cally to meet the requirements
of medium-voltage applications. In general, no separate
measuring instruments (e.g., for current, voltage, frequency,
…) or additional control components are necessary in the
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