Current Differential Relay - 87L

  • GARD 8000 - Current Differential Relay thumb
  • GARD 8000 - Current Differential Relay thumb
  • GARD 8000 - Current Differential Relay thumb
GARD 8000 - Current Differential Relay

Product Description

Current Differential Protection - GARD 8000® System
The Current Differential Protection Module in the GARD 8000® System is a proven current-only, high speed line protection system. The advantages with current-only schemes are well known:

  • potentials not required
  • unaffected by CCVT transients
  • never overreach, never underreach
  • is not affected by mutual coupling on parallel lines
  • unaffected by power swings

Current Differential Protection was traditionally reserved for short line applications due to the limitation of the required pilot wire. However, with the advantage of new communications technology, digital communications become increasingly available for longer lines as well.

Current Differential Relaying is unquestionably the simplest form of line protection, requiring very few settings to be entered for the actual line. The GARD 8000® Current Differential Protection System provides high-speed fault clearing and high sensitivity without compromising security.

The GARD 8000® Current Differential Protection System can be used for two- or three-terminal lines as well as tapped load applications.

The GARD 8000® Current Differential Protection System is suitable for series compensated lines and is inherently phase selective, making it an excellent choice for single pole trip applications.

The GARD 8000® Current Differential Protection Module can be complemented with an independent full Line Distance Protection Module within the same GARD 8000® chassis for full redundant Pilot Protection or as channel failure back-up for the Current Differential Protection. The Distance Protection Module provides additional protection elements such as voltage elements, recloser and synch check.

The two protection modules can be applied in pilot schemes over the same communications channel, or use independent communications interfaces. Or each can be provided with an independent communications interface and use a third as a common redundant channel.

It has been shown that using independent protection modules within the same chassis with redundant power supplies and redundant communications interfaces provides a higher degree of redundancy than physically separate protection devices. A direct comparison based on component failure rates between conventional, redundant Main 1 and Main 2 pilot protection, with redundant pilot protection within one GARD 8000® chassis shows an increased MTBF (Mean Time Between Failure) of a factor of 10 in favor of the GARD 8000® hardware configuration.

  • A complete Current Differential Protection in the GARD 8000® Protective Relay and Communications System
  • Stand-alone or together with a GARD 8000® Distance Protection Module as communications independent back-up
  • Duplicates the highly successful RFL 9300 measuring principle with added features
  • Unaffected by up to +/- 4 ms channel asymmetry, giving a tolerance of 8 ms difference in transmit and receive path delays
  • Dual Breaker option for breaker and a half or ring bus applications
  • Single Pole trip
  • Ideal for series compensated line applications
  • 3U or 6U chassis depending on number of functional modules included
  • Supports NERC/FERC security standards
  • Phase-segregated measurement; three phase elements, one ground element
  • High speed operation; 10 ms minimum
  • Single or redundant communications interface
  • Extensive Sequence of Event Reporting
  • Digital fault records in COMTRADE; 32 samples per cycle
  • Supports DNP 3.0
  • 10 Year Warranty
  • A wide range of communication interfaces to choose from:
    • T1/E1, electrical or fiber
    • RS 449, 56-768 kbps
    • X.21, 64-768 kbps
    • V.35, 64-768 kbps
    • G.703, co-directional, 64 kbps
    • C37.94 fiber
    • Fiber, multi-mode or single-mode; up to 80 km
  • Two- or three-terminal line applications

AC Current Inputs

Nominal 1 or 5 A
Continuous 4 times nominal
One second 100 times nominal
Burden <0.2 VA for 5 A nominal
<0.05 VA for 1 A nominal


Frequency 50 or 60 Hz (selectable)

Current Differential Elements

Bias 5A nominal 1.0 - 30.0 A
1A nominal 0.2 - 6.0 A
Slope 1 0-200%
Slope 2 0-200%
Cross-over point 5A nominal 1.0 - 30 A
1A nominal 0.2 - 6.0 A
High Set Trip 5A nominal 10 - 30.0 A
1A nominal 2 - 6.0 A
CT ratio 40 - 4000

Communication Interfaces

  • T1/E1; 1.544 Mbps/2.084 Mbps for direct connection to a SONET/SDH multiplexer
  • RS 449; 56/64 kbps - 768 kbps for connection to a CSU/DSU or a T1 multiplexer
  • X.21, V.35; 64 - 768 kbps
  • G.703; co-directional, 64 kbps
  • C37.94 fiber
  • Fiber; 64 - 768 kbps, as specified in the following table:

Overcurrent Fault Detectors

5A nominal 1.0 - 30.0 A
1A nominal 0.2 - 6.0 A

Instantaneous/Definite Time Overcurrent Elements

5A nominal 1.0 - 50.0 A
1A nominal 0.2 - 10.0 A
Time delay 0.01 - 1.00 seconds

Time Overcurrent Elements

5A nominal 0.20 - 25.00 A
1A nominal 0.04 - 5.00 A
Time Dial 0.05 - 15.00
US Moderately inverse
Very inverse
Extremely inverse
IEC curves Type A / Type B / Type C
Wavelength & Emitter TypeFiber TypeConnector TypeSystem GainTypical Distance
ANSI C37.94 Multimode ST 25 dB 1 km/0.6 miles
1300nm LED Singlemode ST 19 dB 27 km/17 miles
1300nm Laser Singlemode ST 6 dB 59 km/37 miles
1550nm Laser Singlemode ST 30 dB 90 km/56 miles

Available Files

Files Available in the Customer Area

Please visit Operating Manuals or Product/Software Downloads to download relevant files. Requires RFL Customer Account.

    GARD 8000® Manual – August 2012
    GARD 8000 SYSTEM - Instruction Manual
    GARD 8000® Bias Setting Guidelines and Examples for the GARD 87L (Current Differential Module)
  • Bias Setting Guidelines and Examples 87L

Please visit Operating Manuals or Product/Software Downloads to download relevant files. Requires RFL Customer Account.

GARD 8000® Emulators

The RFL GARD 8000® Emulator will simulate a complete GARD Protective Relay and Communications system without the need for an actual GARD chassis. The Emulator will allow the user to pre-configure a system by selecting which RFL Modules are included in the final system, thus allowing for whole chassis configuration to be saved and loaded into an actual GARD chassis. Conversely files saved from an actual GARD chassis can be loaded into the Emulator. The Emulator will familiarize the user with the web driven capabilities of the GARD 8000 System and can be used as a teaching tool in the field. The GARD Emulator will show typical examples of GARD status situations. Note that because this is an emulator there are slight differences in menu options from an actual GARD chassis, also note that when the ‘Save’ button is clicked in configuration mode all configurations are accepted.

The Emulator Software is conveniently loaded into the users PC. The software, when loaded, also includes a user manual which will step you through using the Emulators. Examples of how the Emulator can interact with a GARD chassis are also described.

Please note that there are specific Emulators for the Image software that is loaded into the GARD 8000®, please download the correct version for your machine. Different versions do not work with different images.

If you should have any questions please call our Customer Service department at 973-334-3100 x226 and they will be glad to provide assistance.

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