Products Multi Function Protection Relays

L-PRO Transmission Line Protection Relays

L-PRO 4000 Transmission Line Protection Relay
L-PRO 4000 Transmission Line Protection Relay
L-PRO 4500 Transmission Line Protection Relay
L-PRO 4500 Transmission Line Protection Relay

The L-PRO is a digital, microprocessor-based line distance protection system that provides comprehensive distance based line protection for medium to extra-high-voltage transmission lines. Apply the L-PRO for high-speed distance and directional protection and complete control in multi-breaker applications typically found in ring or breaker-and-a-half substation arrangements.

The L-PRO comes in two models with different builds to suit specific market requirements. Model 4000 is a 3U or 4U 19 inch rack model whereas model 4500 is in an E12 case size and has dual rated 1A and 5A CT inputs. Model 4500 also has optional PRP redundancy communications. The user software is common to the two models.


  • Primary and backup protection on transmission and sub-transmission lines (using pilot protection schemes)
  • Single and multi breaker applications (i.e. ring-bus and breaker-and-a-half capability, including breaker failure and individual breaker monitoring requiring single pole/three-pole auto-reclosing)
  • Ideal for multi-circuit line applications (to monitor mutual coupling via additional VT and CT inputs)
  • Backup protection for generators, transformers and reactors

Features and Benefits

  • High-speed 5 zones of phase and ground distance functions
  • Fully integrated breaker protection and control for 2 breakers
  • Ultimate flexibility with selectable “Single Pole”, “3 Pole” and “Single and 3 Pole” tripping and reclosing
  • 4 shot recloser with dead line/dead bus control and sync check
  • High quality fault recording and event log

Flexible Communications

  • State-of-the-art communications to accommodate the industry’s latest network-based communications
  • Ethernet ports with 2 unique MAC addresses that easily accommodate network access security needs

Substation Automation

  • IEC 61850 Station Bus on dedicated Optical/Copper Ethernet Ports included at no extra cost
  • Optional PRP (IEC 62439-3) communication redundancy in model 4500
  • Enhanced DNP3.0 Level 2 SCADA communication protocol including user-selectable point lists, class support and multiple master station support

Easy to Use

  • Flexible programmable logic for building customized schemes with ProLogic™ statements – 24 control logic statements (total of 192 statements)
  • User-friendly, Windows®-based relay setting and record analysis software

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