Broken Conductor Protection in numrAL FDR22 Relay

Broken Conductor Protection in numrAL FDR22 Relay
Updated: | 6 min read

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Introduction

A broken conductor or open circuit fault is one of the most difficult faults to detect in power systems. It often does not cause a significant increase in current, making it hard for standard overcurrent relays to sense.

The Challenge

Standard unbalance protection (ANSI 46) uses negative-sequence current (I2) to detect faults. However, at low load levels, the negative-sequence current produced by a broken conductor can be very small — sometimes even smaller than the normal unbalance present in the system. This makes it risky to set sensitive pickup values without causing false tripping.

The Smart Solution: I2/I1 Ratio

The numrAL FDR22 relay from Lauritz Knudsen uses Broken Conductor Protection based on the I2/I1 ratio (Negative-sequence current to Positive-sequence current).


This ratio remains relatively constant even when load changes, making it a much more reliable way to detect broken conductors or open circuits.

Key Features of FDR22 Broken Conductor Protection

  • Uses I2/I1 ratio for accurate detection
  • Pickup setting adjustable from 20% to 100%
  • Time delay setting from 0.01 sec to 100 sec
  • Works effectively on both single-point and multiple-earthed systems

Why It Matters

Broken conductor faults can lead to dangerous voltage unbalance, equipment damage, and safety risks. The advanced Broken Conductor Protection in the numrAL FDR22 relay helps detect such faults quickly and reliably, enhancing system safety and protection.

Conclusion

For reliable detection of broken conductors, the Lauritz Knudsen numrAL FDR22 feeder protection relay offers a smart and sensitive solution using the I2/I1 ratio.


Takeaway: Don’t rely only on standard unbalance protection — use dedicated Broken Conductor Protection for better safety.

About the Author

author

Rajesh R Shirodkar,

DGM-Corporate Communication

Rajesh Shirodkar is a seasoned marketing and business leader with over 20 years of experience in the automation and electrical industry, spanning marketing communications, sales, business development, and software solution selling. He has led successful brand transformation initiatives and high-impact marketing programs, including branding and account-based marketing campaigns, as well as industry events that drive visibility, engagement, and growth. With expertise in brand building, lead generation, solution selling, and sales enablement, Rajesh is known for translating technology and business offerings into compelling value propositions and delivering sustainable growth through strong stakeholder collaboration.

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