Frame Leakage Protection 

By on

Image
Frame Leakage Protection Principle
While not as popular as it once was, frame leakage protection does still have some use in some circumstances.  In essence frame leakage is an earth fault type protection.  A current transformer installed in a connection from the frame to earth monitors  any fault current and operates an instantaneous relay. 

The fault measuring connection is the only link to earth.  All other connections, including the frame of any switchgear or controlgear assemblies are insulated from earth. 

The main reason for using frame leakage to its ability to detect low levels of fault current.  An example would be a d.c. rail  traction system, where the return rail is insulated (in addition to the switchgear) and by the use of frame leakage protection it is possible to detect high impedance faults away from the switchgear.

In practice it is invariably difficult to fully insulate any item of equipment from earth.  Resistance values of 10 ohms or so would be typical. 

Tip: while insulating the entire switchgear frame,  care must also be taken to use insulating cable glands and in ensuring that no inadvertent earth connections are made.

With the inclusion of transformer neutral earthing, generators, double and sectioned bus bars implementation of frame leakage becomes more complex.  Modern numerical relays are cost effective and provide a large number of features, making them an attractive alternative to the implementation of frame leakage.



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus

  1. naban's avatar naban says:
    4/18/2013 4:16 PM

    If we fix a relay to each of the feeders and one for main switchboard frame if a fault develops in any of the feeders only that feeder will trip,otherwise all feeders won't get supply/power


Comments are closed for this post:
  • have a question or need help, please use our Questions Section
  • spotted an error or have additional info that you think should be in this post, feel free to Contact Us



How to Size Current Transformers

The correct sizing of current transformers is required to ensure satisfactory operation of measuring instruments and protection relays. Several methods...

Restricted Earth Fault Protection

The windings of many medium and small sized transformers are protected by restricted earth fault (REF) systems. The illustration shows the principal of...

Are We Losing Professional Integrity

I have been thinking recently that there appears to be less professional integrity around than when I first started my career in electrical engineering...

Understanding LV Circuit Breaker Fault Ratings

I think this post is going to be helpful to several of our readers. While the IEC low voltage circuit breaker Standard [IEC 60947-2, Low voltage switchgear...

Fire Resistant and Fire Retardant Cables

Fire resistant and fire retardant cable sheaths are design to resist combustion and limit the propagation of flames. Low smokes cables have a sheath designed...

Electrical Engineering

Electrical engineering is a field that covers a wide variety of sub-fields, including electricity and electronics. It is a field that goes back to the...

Capacitors - Energy Storage Application

Capacitors have numerous applications in electrical and electronic applications.  This note examines the use of capacitors to store electrical energy....

MIT OpenCourseWare

MIT OpenCourseWare, makes the materials used in teaching all MIT subjects available on the Web, free of charge, to any user in the world.

Cable Sizing Tool

Our cable sizing tool is one of the more popular tools on the site.  The tool enables cables to be sized in compliance with BS 7671 (the IEE Wiring Regulations...

RLC Circuit, Resistor Power Loss - some Modelica experiments

Modelica is an open source (free) software language for modelling complex systems. Having never used it before, I thought I would download a development...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note