×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Tangent Delta Test

Tangent Delta Test

Tangent Delta Test

(OP)
Hi,can someone tell me more about tangent delta test especially for auto-transformer i.e. purpose of tangent delta test and test procedures.

RE: Tangent Delta Test

Tan-delta test (European) is almost identical to the "power factor" test (American).  

In both cases we are applying a high-voltage to the insulation (up to 10kv but no more than normal L-G voltage) and measuring the phase angle of the resulting current.
The insulation itself is primarily capacitive (power factor 0.0), but contamination introduces some resisitve component (can raise power factor above 0.0).  The higher the power factor, the more likely contamination is present in the insulation. Also the magnitude of the current is also measured which enables calculation of insulation capacitance.  All of these parameters can be trended over time for even better diagnostic value.  There is a lot that goes into interpreting the data... Doble Engineering is a great resource in this area.

Back to the difference between Tan-delta test and "power factor".  In both cases we are characterizing the angle delta between voltage and current.  Tan delta is the tangent of this angle while power factor is the cos of this angle.  For almost any insulation specimen, this angle will be less than 10 degrees and the cos and tan are virtually identicial.  I prefer to talk in terms of power factor because it is a concept already familiar to most electrical types.

RE: Tangent Delta Test

Tan-delta test is intended for determining the degree of degeneration of high voltage insulation. That insulation is part of the capacitance between the line, or windings, and earth, or between two windings. The loss factor of such capacitor gives a very reliable information about the degeneration of insulation, so that high loss factors correspond to high degeneration. That meassurement must be performed at the working voltage, and there is a well known an documented procedure based upon the so called "Schering Bridge".

RE: Tangent Delta Test

I should offer a correction to my discussion on similarities between power factor and tan delta.  

They ARE very nearly identical for most test specimens.  But my reasoning was incorrect.... cos and tan are not equal for small angles, but sin and tan are equal.  The tan delta looks at the tangent of the angle delta which is "complementary" to the power factor angle theta (ie delta = 90-theta).  The trigonometry gives the same result, since cos(theta)=sin(delta) which is very near to tan(delta).

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources