Why we measure Tan Delta?
Questions about Tan Delta Testing
What is tan delta test?
What is insulation?
What is capacitor and ideal capacitor?
Why we measure tan delta?
Theory of Tan Delta Testing?
What is a tan delta test?
TD test is the most common technique used to asses the insulation of theTransformer, Motor, Circuit Breaker, Generator. And to remember, it is an AC test ! We use Alteranate Voltage and Current instead of DC Voltage. There are two reasons. First of all, all results of AC testing are more repeatable than DC testing. Secondly, DC testing tends to be more destructive than AC testing since it leaves some free electrons inside the insulation. And in case that insulation has some voids imperfections inside, you're increasing the probability of partial discharge inside that particular insulation. So we use this test to see if our acid has had some mechnical deformation and to see what is the state of our insulation, how old is our insulation and how much more time do we have untile it falls. So Tan Delta test will help us to do some predictive maintenance.
What is insulation?
lEEE defines it as Material or a Combination of Suitable Non-Conducting Materialsthat Provide Electrical lsolation of Two Parts at Different Voltages. In short, insulation is something we put between two conductors and if we don't want any electricity running between the two conductors.
What is capacitor and ideal capacitor?
Actually whenever you have two different electrical potentials and there is always a dielectric in between. We also have a Capacitor that can hold electrical charge. And this is a formula for two paralell plates Capacitor. Because there are many other types of capacitors but the sake of simplicity we'll use the most simple one.
C= Capacitance in Farads
ε= Permittivity of dielectric (absolute, not relative)
A = Area of plate overlap in square meters
d= Distance between plates in meters
In ideal conditions, the capacitive current leads the applied voltage by 90 degrees. The definition of ldea Transformer is Current is leading and Voltage is lagging. There is also something we call Real Capacitor and that fellow does not have phase shift of 90 degrees, but less.
Why we measure Tan Delta?
We test it because we want to know the state of our insulation -or-how far are we from the insulation breaking. Since insulation has avery non linearcharacteristic-a very small increase in resisitivecurrent can suddenly make the insulation break.
Theory of Tan Delta Testing
TD test is often used on High Voltage assets, such as power transformer, current and voltage transformer, bushing, generators, motors and surge assets. The following picture is three phase two winding transformer.
We should guarantee all terminals of same winding must be shorted. We wll also connect short-circuit to the high-voltage side and low-voltage side with a thin wire. And we don't expect big current to run to be generated in this test. We actually need to measure three capacitances between the high voltage. They are CH、CL、CHL.
There are two ways of expressing Tan Delta: Absolute and Percentage.
The Difference between the two is Percentage is Absolute value multipled by 100.
Why we do this - because Delta is usually a very small angle (often less than 1degree).
Tangens of 0.25°=0.0043633508 and that multiplied by a 100 and rounded is 0.436 %
Tangens of 0.5°= 0.0872686 and that multiplied by a 100 and rounded is 0.872 %
Tangens of 0.75°= 0.0130907171 and that multiplied by a 100 and rounded is 1.309 %
So it's more practical to express Tan Delta in Percentage.
If you are interested in Tan Delta Test of Transformer, click here to find more information.
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You may not know about tan delta test.
Click here to find iec standards about tan delta tester.
