Brief Introduction to Current Transformers and Its Applications.

In part 6, we talked about the concept of CT polarity, including a brief overview of the various types involved. In part 7, we will discuss the concept of CT grounding, and how it can be used to ensure its safe operation.

If this video was helpful for you, please consider subscribing to GeneralPAC.com. Our goal is to make Power Systems intuitive. Our corporate sponsor for this topic is AllumiaX.com, from Seattle Washington. Contact them for industrial and commercial power system studies like short circuit, coordination, and arc flash studies. AllumiaX.com, also performs advanced studies like power quality, motor starting, grounding grid, reliability, transient stability, and snubber circuit studies.

Let us start by first establishing the basic concept of grounding. In simple terms, “grounding” is the process of electrically connecting any type of electrical equipment to the “ground”. We can also refer to it as the “Earthing” process.

By following this procedure, we can safely protect all types of equipment from electrical “surges”, along with providing the necessary protection for the working personnel against “electric shocks”.

If we consider the case of a current transformer, then it is necessary to ground the secondary side, in order to ensure protection of the equipment attached to the secondary terminal. The equipment could be a relay or a measuring device.

In order to understand how grounding works, let us consider a single phase CT model.

For a single phase CT, we shall ground the neutral wire present on the secondary side. This ensures adequate protection of the secondary side equipment. On the other hand, if we had left the CT “ungrounded”, this would cause the secondary voltage “Vs” to rise to abnormal values.

The voltage rise is due to the presence of “stray capacitances”. In basic terms, these capacitances can occur between any two surfaces at a close distance from each other.

In the case of a current transformer, a stray capacitance exists between the high voltage and the low voltage winding, another capacitance exists between the high voltage winding and the ground, and a third capacitance will occur between the low voltage winding and the ground.

They are practically unavoidable, and they cause an electrostatic charge to build up on the secondary winding. Which causes dangerously high secondary voltages, which is very dangerous for electrical workers. Furthermore, it can potentially damage the equipment connected to the secondary terminal of the current transformer

It is for these reasons why grounding a current transformer is highly recommended.

A good engineering practice is to ground the current transformer in an accessible location, which will make it easier to remove it for testing purposes.

Keep in mind that all current transformer circuits are to be grounded at a single point “only”. This is to avoid the occurrence of multiple ground loops which can cause the relay connected to the secondary winding, to trip under false conditions. We will be discussing this concept in more detail in a later series.

We will now sum up the discussion by drawing a three phase wye-connected current transformer model.

Following the same grounding terminology, we ground a three phase CT model by connecting the neutral points of the three windings together, which is followed by connecting them to the grounding grid at a single point “only”.

We will now conclude the series of “Current Transformer and its applications”. More advanced discussions for current transformer applications, will be covered in different topics.

The examples used in this tutorial are derived from the “Instrument Transformers Application Guide” by “ABB”. Rest assured, these are good and accurate examples. If mistakes are found, they will be described in detail on general pac.com

We hope you have a continued interest in this topic and series as a student or professional. We also hope you find this content useful and enlightening. Please consider subscribing to GeneralPac.com… Making Power Systems Intuitive.

#### Greetings from the GeneralPAC Team!

We make high-quality Power Systems Video Tutorials on complex topics that are free and open to everyone!  Thank you so much for supporting us through Patreon so can continue doing good and valuable work.

What is Patreon and why do we use it?

Patreon is a fantastic portal that allows our fans and community to make monthly contribution (like Netflix subscription) so we can continue creating high-quality power systems video tutorials. In return, you get access to incredible perks like voting on future topics, getting your questions answered, access to VIP Q/A webinars with the creators of GeneralPAC, and much more! We THANK YOU for supporting us

Why do we need your support?

An incredible amount of time and effort is needed to develop high-quality video tutorials. Each video (Part 1 for example) takes approximately 10 hours to complete which includes learning the concept ourselves, brainstorming creative ways to teach and explain the concepts, writing the script, audio recording, video recording, and editing. It's no wonder why Hundreds-of-Thousands of people have watched, liked, subscribed, and left positive comments on Youtube channel. Your support truly makes all the difference.