Siemens SIPROTEC 7SJ85 Overcurrent and Feeder Protection Relay

Overview

The Siemens SIPROTEC 7SJ85 is the overcurrent and feeder protection device of the modular SIPROTEC 5 series. Siemens designed it specifically for the protection of feeders and lines, and with its modular hardware and the DIGSI 5 engineering tool it combines protection, control, automation, monitoring and Power Quality – Basic functions in one bay device. One unit can protect up to nine feeders using up to 40 analog inputs, which makes it a natural choice for medium-voltage switchgear, ring main systems, industrial substations and capacitor bank installations.

Seven Star LLC supplies the Siemens SIPROTEC 7SJ85 to utilities, oil and gas operators, switchgear builders and industrial plants in the Sultanate of Oman and across the GCC. Because every SIPROTEC 5 device is configured to order, our engineers in Muscat work from your single-line diagram, CT and VT data and communication requirements to define the hardware variant and function scope before the order is placed.

Protection Principle of the Siemens SIPROTEC 7SJ85

The Siemens SIPROTEC 7SJ85 measures phase and ground currents and voltages through its current and voltage transformer inputs and evaluates them against configured protection stages. Its core functions are non-directional and directional definite-time and inverse-time overcurrent protection for phases and ground (ANSI 50/51, 50N/51N, 67 and 67N), supplemented by instantaneous high-current tripping, negative-sequence protection, thermal overload, under- and overvoltage, frequency and rate-of-change-of-frequency protection, and circuit-breaker failure protection. For compensated or isolated networks, sensitive ground-fault detection uses methods such as 3I0, V0, transient ground fault, cos φ, sin φ, harmonic detection, admittance and pulse detection, and intermittent ground faults are detected with automatic blocking to avoid message flooding.

Directional elements in the Siemens SIPROTEC 7SJ85 allow directional comparison protection on lines with infeed at both ends, with direction information exchanged over protection interfaces, IEC 61850 GOOSE or pilot wires so that faulty sections in closed rings are isolated quickly without long grading times. Further functions include automatic reclosing, synchrocheck, switchgear interlocking, arc protection with a dedicated plug-in module, fault locator plus for inhomogeneous line sections, point-on-wave switching, a phasor measurement unit to IEEE C37.118, and capacitor-bank protection with peak overvoltage (59C), current-unbalance (60C) and differential (87C) stages.

Engineering Design of the Siemens SIPROTEC 7SJ85

The hardware follows the SIPROTEC 5 modular concept. Siemens offers five predefined standard variants of the Siemens SIPROTEC 7SJ85, each with four current-transformer and four voltage-transformer inputs, ranging from a 1/3 x 19-inch housing with 11 binary inputs and 9 binary outputs to a 5/6 x 19-inch housing with 59 binary inputs and 33 binary outputs. Beyond these, the I/O can be expanded with 1/6 expansion modules up to a 2/1 x 19-inch width, with a large display, a small display or no display. The modules carry a standard protective coating, which Siemens describes as giving the highest availability even under extreme environmental conditions.

Communication starts with a fixed integrated electrical RJ45 Ethernet interface for DIGSI 5 and IEC 61850 reporting and GOOSE. Two slots accept optional communication modules for IEC 61850-8-1, IEC 61850-9-2 client, IEC 60870-5-103 and -104, Modbus TCP, DNP3 serial and TCP, and PROFINET IO including S2 redundancy, with PRP and HSR for seamless network redundancy and IEEE 802.1Q VLAN partitioning. Cybersecurity functions include role-based access control, security event logging, signed firmware and IEEE 802.1X authenticated network access, in line with NERC CIP and BDEW Whitepaper requirements.

Key Features of the Siemens SIPROTEC 7SJ85

The Siemens product profile and SIPROTEC 5 catalog list these strengths of the Siemens SIPROTEC 7SJ85.

• Protection of up to nine feeders with up to 40 analog inputs in a single device.
• Five standard variants with 4 CT and 4 VT inputs, 11 to 59 binary inputs and 9 to 33 binary outputs.
• Full compatibility between IEC 61850 Editions 1, 2.0 and 2.1, plus IEC 60870-5, DNP3, Modbus TCP and PROFINET IO protocols.
• Reliable data transmission through PRP and HSR redundancy protocols and time synchronisation using IEEE 1588.
• Graphical logic editor (CFC) for automation functions such as busbar switchover sequences inside the device.
• High-performance fault recording with a buffer of up to 80 s at 8 kHz or 320 s at 2 kHz.
• Power Quality – Basic values including THD, TDD, harmonics, voltage unbalance, dips and interruptions.
• Web browser access to device information, vector diagrams, single-line and display pages for diagnostics.

Industrial Applications

Siemens lists selective tripping of short circuits in radial networks, lines with infeed at one or two ends, parallel lines and open or closed ring systems as the main duty of the Siemens SIPROTEC 7SJ85, together with backup protection for differential relays on lines, transformers, generators, motors and busbars. In Oman this maps onto 11 kV and 33 kV medium-voltage feeders, primary substations for industrial estates, ring networks in oil and gas fields, and incoming and outgoing feeders in power and desalination plants. Underfrequency load shedding with automatic frequency relief also supports grids with growing solar and decentralised generation.

Capacitor bank functions make the Siemens SIPROTEC 7SJ85 relevant for reactive-power compensation and harmonic filter installations at industrial users in Sohar, Duqm and Salalah, while the transformer voltage controller functions support tap-changer control on two- and three-winding transformers. Seven Star LLC supplies the Siemens SIPROTEC 7SJ85 with engineering support in Muscat. Where a site standardises on other ranges, we also supply relays such as the ABB REF615 feeder protection relay, the Schneider Electric MiCOM P139 and the ABB REF542plus.

Technical Specifications

The data below for the Siemens SIPROTEC 7SJ85 comes from the Siemens product profile and the SIPROTEC 5 catalog, Edition 7; the final order code is generated in the SIPROTEC 5 order configurator.

How to Order

To request the Siemens SIPROTEC 7SJ85, send Seven Star LLC your single-line diagram, CT and VT ratios, auxiliary supply voltage, required binary I/O and the substation protocol in use. We will help define the variant and function points, quote the device for delivery in Oman and the GCC, and you can download the Siemens product profile and catalog extract from this page.

For the automation side of the same project, see the Siemens SCALANCE XC208 switch and Siemens CPU 1515-2 PN.