Overcurrent protection for low-power current transformer

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 /225mV for a primary operating current range of 20 A to 200 A 

The 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 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.

Hardware

• 4 current 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

• Instantaneous and definite time-overcurrent protection (phase/neutral) (50, 50N, 51, 51N)
• Directional time-overcurrent protection (phase/ground) (67, 67N)
• Directional sensitive ground fault detection (67Ns, 50Ns)
• Overvoltage protection, zero-sequence system (59N)
• Inrush restraint
• Trip-circuit supervision (74TC)
• Undercurrent monitoring (37)
• Overload protection (49)
• Undervoltage/overvoltage protection (27/59)
• Forward-power, reverse-power protection (32)
• Power factor (55)
• Overfrequency/underfrequency protection(81O/U)
• Circuit-breaker failure protection (50B/F)
• Intermittent ground fault protection
• Directional intermittent ground fault protection (67Ns)
• Automatic reclosing (79)
• Fault locator (FL)
• Lockout (86)

Line protection

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 point.

• 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
• 6-line display
• 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.