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RADHL (Legacy)

Pilot wire differential relay

Pilot wire differential relays are traditionally used for protection of short to medium length two terminal cables or overhead lines. This application requires a dedicated metallic pilot wire between the line ends. Pilot wire differential relays thus provide an effective means of dedicated protection of a selected line section.

The RADHL pilot wire differential relay can also be used for protecting lines with two or more terminals, using one relay per line end. For example, in a three terminal application, three relays are interconnected via the pilot wires. Phase and ground faults are detected on the line. All line ends are tripped even if the fault current is coming from one line end only.

RADHL offers a compact protection assembly with the optional functions forming a complete protection terminal, including backup protection functions. To supplement the basic differential relay function, the different versions of RADHL relay with current supervision also provide backup overcurrent and ground fault protection.

The RADHL relay configuration with the RXHL 411, combines phase and earth current protection with the proven differential relay concept. This configuration also includes a three-phase thermal overload relay and a breaker failure backup relay. Autoreclosing is available as an option.

Via the RXHL 411, phase and earth current service values in primary or secondary values and fault information can be presented through the relay text window of the HMI (Human Machine Interface).

The RADHL differential relay has 5 kV, optionally 15 kV, pilot wire isolation. Supervision equipment is additionally offered to detect and alarm for pilot wire problems. 1000 or 2000 ohm pilot wires of low cost communication type may be used. The standard supervision equipment extends also for multi-terminal applications.

The RADHL relay has several mounting options for 19'' rack or panel mounting.

Main Features:

  • Phase and earth-fault protection for cable and overhead lines
  • Protect lines with two or more terminals
  • High-speed operation (1-2 cycle)
  • Stability ensured for external faults
  • All line ends trip for fault current from single end
  • Pilot wire voltage limited to 60 V permits use of low cost communication wires (100 V)
  • 5 kV basic insulation level and 15 kV with pilot wire isolating transformers
  • 1000 ohms and 2 µF pilot wire capacitance
  • 2000 ohms and 0,7 µF with pilot wire isolating transformers
  • Direct trip contacts and trip flag indicator
  • Test switch included

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