Aug 29, 2015

Current Transformer - Winding Check


urrent Transformer! - Successful commissioning? HEARTfelt Welcome, dear friends of protection and control engineering!

The commissioning of current transformers is divided into several test steps. An ever-overlooked test is the so-called winding sense test or the polarity check. Only on the basis of this important test we can prove that the secondary current transformer winding was also wound correctly. This is particularly important for differential protection. Additional protection functions with chained sizes, such as:

🌐 Distance Protection

🌐 Out-Of-Step-Protection

🌐 Reverse Power Protection

🌐 Underexcitation protection

are also equipped with direction-dependent algorithms. Conclusion: Without the winding check the world can't go on. But to how to test it? Here we go:

The old measuring method employed by our ancient forebears still works perfectly. We connect an analogue multimeter to the secondary side and select a very narrow DC measuring range. On the primary side, we briefly apply the DC voltage of a 9 V monobloc battery and observe what happens to the multimeter needle. The needle deflection enables us to determine the direction of the secondary flowing current.

"Simple, but clever"

After the test is complete, apply an alternating current to avoid a one-sided pre- magnetization.

A special measuring method devised by Omicron superimposes a direction-defined saw-tooth amplitude over the injected test current to provide a suitable measuring device for determining direction (CPol- Tool©). Testing with this system in the field has proved to be extremely effective.

The commissioning test of current transformers is incomplete without an appropriate winding check. It can be carried out quickly at any time by simple means and at an early stage to avoide later anger within the framework of the "hot commissioning"!

This article and the figure are excerpts from my book "The Bible of Generator Protection Engineering"!

HEARTfelt Greetings Alexander Muth

Safety Notice

Failure to observe the following points can result in death, serious injury or material damage!

Hazardous voltages may be present when carrying out the tests and checks described in this manual. The safety rules and regulations regarding electrical systems must be strictly observed at all times. The generator must always be shut down when working on the primary system; appropriate grounding and short-circuiting facilities are to be provided at the respective workplaces. When carrying out a primary check on a turbine set, take care to ensure that no overheating of the turbine occurs.

The work described in this manual may only be carried out by qualified personnel, who must be conversant with the relevant safety regulations and safety measures as well as the warnings in the manuals provided by the suppliers of the various components. The contents of this manual 10

must not construed as work instructions. All statements in this manual must be carefully considered in light of the safety rules and regulations. The information presented in this manual does not claim to be complete.