CT Specs – Part 2 – Class P Application

Preamble

Part 1 of this blog presented an overview of Australian & IEC standards for Class P type Current Transformer (CT) specifications.  This blog presents the application of Class P type CTs in actual site conditions.  This process can be confusing due to the diverse methodology presented in the literature. 

I have conducted an in-depth review of at least 20 publications, including the 3 major relay manufacturers’ manuals, to prepare this blog.  It has taken more than a week of full-time study to present this blog clearly and logically!

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CT Specs – Part 1 – CT Overview & Class P

Preamble

Even experienced engineers find Current Transformer (CT) specifications daunting and confusing.  A good understanding of CT specification and performance are essential for safety of personnel and equipment.  Let us not panic—help is on the way! 

The previous blog on ‘CT Specifications – Gold Report’ presented a site problem due to incorrect CT specifications.  

This blog presents the specification for Class P type protection CTs as per Australian Standard AS60044.1 and International Standard IEC 60044.1.

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CT Specifications – Gold Report

Good old technical conference papers are gold strips. 

New-age conferences are networking and business trips! – Sesha

Preamble

In my ‘About This Site’ blog, I said that a good, two-page technical report is worth more than its weight in gold! This blog is one of them.  This is slightly longer because I have included a detailed explanation. If you are a non-technical person, you can still read the Introduction, The Problem, The Fireworks, and the Site Recommendations.  You will enjoy it! 😊

Introduction

Current Transformers (CT) are used in power systems to step down large currents.  Stepped down currents are used for measurement (as inputs to Ammeters) and protection (as inputs to relays).  This blog is about a major site issue due to an incorrect CT specification for differential protection of a large utility grid transformer.  Continue reading →