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Products»Smart Line»S24 Series»High-impedance differential protection» Variant 7 High impedance differential protection

The S24 Variant 7 provides numeric high impedance differential protection solution for busbar, transformer, generator and motor applications where fast clearance of faults is required with high stability against external fault conditions and fast & reliable performance against internal faults.

It is a member of the S24 series, which is part of the EuroProt+ Smart Line. Members of the Smart Line also offer a wide range of functions but they do so in a small, compact enclosure so that they can be installed in locations with limited space available for the protection equipment.

The S24 series contain special selections of the EuroProt+ modules and functions, composed with cost effectiveness in mind. Depending on the standard configuration chosen (Variant 1, Variant2,…), the IED is adapted to the protection of medium-voltage feeders in isolated neutral, resistance earthed, compensated and solidly earthed networks. Once the application-specific settings have been defined for  the standard configuration IED, it can be put into service directly. Areas of application include protection functions for a large variety of applications, e.g. transformer differential and restricted earth fault protection, frequency and voltage based protection, motor protection, thermal overload protection.

The EuroCAP configuration tool, which is available free of charge, offers a user-friendly and flexible application for protection, control and measurement functions to ensure that the IED-EP+ S24 devices are fully customisable.

General features

  • Native IEC 61850 IED with Edition 2 compatibility
  • Standard module layouts with options
  • 24 HP wide rack size (height: 3U)
  • The pre-defined factory configuration can be customized to the user’s specification with the powerful EuroCAP tool
  • Different HMI types: advanced HMI with color touchscreen and black-and-white display with 4 tactile push buttons. An embedded web server and extended measuring, control and monitoring functions are also available for both types
  • User configurable LCD user screens for the HMI-type color touchscreen, which can display SLDs (Single Line Diagrams) with switchgear position indication and control as well as measuring values and several types of controllable objects
  • Various protection setting groups
  • Enhanced breaker monitoring and control
  • High capacity disturbance recorder (DRE) and event logging:
    • DRE for up to 32 analogue and 64 digital signal channels
    • Event recorder can store more than 10,000 events
  • Mounting methods: Flush mounting; Semi-flush mounting; Din rail mounting
  • Wide range of communication protocols:
    • Ethernet-based communication: IEC61850; IEC60870-5-104; DNP3.0 TCP; Modbus TCP
    • Serial communication: DNP3.0; IEC60870-5-101/103; MODBUS, SPA
    • Legacy network based protocols via 100Base-FX and 10/100Base-TX (RJ45)
  • Optional communication ports: Fiber optical Ethernet (MM/ST, SM/FC), RJ45, Serial POF, Serial glass fiber, RS-485/422
  • Handling of several communication protocols simultaneously

The S24 Variant 7 provides numeric high impedance differential protection solution for busbar, transformer, generator and motor applications where fast clearance of faults is required with high stability against external fault conditions and fast & reliable performance against internal faults. This operating principle requires stabilizing resistors in each phase and a non-linear resistor (metrosil) is generally required across the relay circuit.

The high impedance relay can be configured either for three-phase protection (87T, 87B) or restricted earth fault (87N) applications, according to the ordering option labeled "Number of differential currents":

  • By selecting "1", a CT+/5153 current input module is applied in the device, where only the 4th current channel is assigned to the High Impedance Restricted Earth Fault Protection, and the first 3 current input channels are utilized for overcurrent protection.
  • By selecting "3", a CT+/5116 current input module is applied, and its first 3 channels (three phases) are assigned to the phase-segregated High Impedance Differential Protection.

The integrated CT supervision function (CT50) with a sensitive differential element provides CT open circuit detection in the secondary wiring circuits of the CT.



  • High impedance differential protection solution for busbar, transformer, generator, reactor and motor applicationss
  • Integrated CT supervision function
  • According to the relay configuration:
    • High impedance restricted earth fault protection (87N) with conventional current-based current protections such as 50, 51, 50N, 51N, 50BF
    • High impedance differential three-phase protection (87T, 87B)
Protection & Control functions

Depending on the desired option, the Variant 7 configuration either measures the three phase currents and one differential current (87N), or it measures the three phase differential currents only. The main functions are the high impedance differential function (1 or 3 phase) with its CT supervision counterpart (both described in the High Impedance Differential Protection Technical Guide).

Note that the additional functions (50, 50N, 51, 51N, 60, 68) are avaliable only in the option with one differential current (87N).

Protection & control functions IEC ANSI *Inst.
Breaker failure protection functions CBFP 50BF 1
Three-phase instantaneous overcurrent protection function I >>> 50 1
Residual instantaneous overcurrent protection function Io>>> 50N/50G 1
Three-phase time overcurrent protection function I>, I>> 51 2
Residual overcurrent protection function Io>, Io>> 51N/51G 2
Current unbalance function 60 1
Inrush current detection function I2h> 68 1
High impedance differential protection technical guide 3Id>/Id> 87P/87N 0
*The INST. column contains the numbers of the pre-configured function blocks in the factory configuration.These numbers may be different in order to meet the user’s requirements.
Protecta products can be ordered by using an Order Code. This code specifies the hardware and the configuration.
Please always refer to a valid Order Code when placing an order.
The Order Code page can be opened by clicking the link below.
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