Differential protection, the good old days 

By on


Image reproduced from
'Network Protection and Automation Guide, by Areva
This morning I was explaining how differential protection works to a junior engineer.  To give him something to read I opened up the NPAG (Network Protection and Automation Guide, by Areva) and turned to Chapter 10  ‘Unit Protection of Feeders’.  I was immediately confronted with Marz and Price, circulating current systems, balanced voltage systems, high impedance series connected relays, illustrations like the one shown, etc. ... and remembered my early years.  A time when if you mentioned differential protection to an electrical engineer, they would turn and run in the opposite direction.

Now, I’m not sure if this applies to everyone, but the systems I have been involved with for the past few years have employed numerical relays for differential protection.  Install the two relays, connect together with an optical fibre and gone are all the problems of trying to do this using wires/current between the relays.   I think this is a pretty clear example of how changes in technology have vastly simplified something.  Not only has it simplified the application of differential protection, it also comes with a host of advancements – being able to use CTs manufactured to different specifications as an example.

Numerical relays and optical links may not be the answer to every situation, but I think they make life easier for most of us. 



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



Lead Acid Batteries

Lead acid batteries are cost effect and reliable, making them suitable for many applications.This note examines topics of interest associated with the...

Windows Live Writer and myElectrical

When making adding a Note to our site we have a great online WYSIWYG editor and things are pretty simple.  However, if you prefer you can write, manage...

Gas Insulated or Air Insulated Switchgear

Various arguments exist around SF6 Gas Insulated (GIS) and Air Insulated (AIS) medium voltage switchgear. Recently we had to change a GIS design to AI...

Differential protection, the good old days

This morning I was explaining how differential protection works to a junior engineer. To give him something to read I opened up the NPAG (Network Protection...

Battery Sizing

This article gives an introduction to IEEE 485 method for the selection and calculation of battery capacity.

Control Theory

Control theory looks at how systems work and are controlled from a mathematical view.  This note gives a brief introduction to some of the concepts – more...

The ac resistance of conductors

In a previous article I looked at the dc resistance of conductors and in this article we turn our attention to ac resistance. If you have not read the...

Generator Sizing & Operation Limits

When selecting a generator, there are inherent limits on the active and reactive power which can be delivered. Generators are normally sized for a certain...

Lighting - Lamps

Lamps are the essential part of any luminaire. These are the light generating components. Since the advent of electrical lighting in the middle of the...

LED Replacement Light Bulb

The inventor of the first visible light-emitting diode makes history again this year as it begins to show customers a 40-watt replacement GE Energy Smart...

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