Motor Protection Relay
The SIPROTEC Compact 7SK81 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 rangefrom 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
The SIPROTEC 7SK81 is a multi-functional motor protection relay. It is designed for protection of asynchronous motors of all sizes. The relays have all the required functions 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 VTs and CTs 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
Commands for the ctrl. of CB, disconnect switches (isolators/isolating switches)
Control through keyboard, binary inputs, DIGSI 4 or SCADA system
User-defi ned PLC logic with CFC (e.g. interlocking).
Operational measured values V, I, f
Energy metering values Wp, Wq
Circuit-breaker wear monitoring
Minimum and maximum values
Trip circuit supervision
Fuse failure monitor
8 oscillographic fault records
– IEC 61850 Edition 1 and 2
– IEC 60870-5-103
– DNP 3.0
– MODBUS RTU
– Ethernet redundancy protocols RSTP, PRP and HSR
Ethernet interface for DIGSI 4, RTD box
USB front interface for DIGSI 4.
4 current inputs
0/3 voltage inputs
3/7 binary inputs (thresholds confi gurable using software)
5/8 binary outputs (2 changeover)
0/5 RTD inputs
1 live-status contact
Pluggable voltage terminals.
The SIPROTEC Compact 7SK81 unit is a numerical motor protection relay for low power CT and VT inputs. It can perform control and monitoring functions and therefore provide 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 factor.
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-defi ned messages. This functionality can form the base to create extremely fl exible transfer schemes.
Operational measured value
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.
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 7SK81 relay is specifi cally designed to protect induction-type
The 7SK81 units can be used for line protection of high and medium-voltage networks with grounded, low-resistance grounded, isolated or a compensated neutral point.
The 7SK81 relay provides all the functions for backup protection for transformer differential protection. The inrush suppression effectively prevents unwanted trips that can be caused by inrush currents.
As a backup protection the 7SK81 devices are universally applicable.
Switchgear cubicles for high/medium voltage
All units are designed specifi cally to meet the requirements of high /medium-voltage applications. In general, no separate measuring instruments (e.g., for current, voltage, frequency, …) or additional control components are necessary.
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