Skip to main content

Dielectric frequency response (DFR) analysis for moisture measurement in transformer


The dielectric response is a unique characteristic of the particular insulation system. The increased moisture content of the insulation results in a changed dielectric model and, consequently, a changed dielectric response. By measuring the dielectric response of the equipment in a wide frequency range, the moisture content can be assessed and the insulation condition diagnosed.

The test connections and modes are the same as used in a traditional transformer insulation power-factor test with the difference being the test is performed at a low voltage, up to 200 Vp-p, and the test is performed at frequencies from 1 kHz to 1μHz. 

In this Figure the response curve for oil-impregnated paper. This curve shows a frequency vs. dissipation factor relationship.
  • The higher frequencies display the moisture and aging of the cellulose.
  • Moving from left to right the frequency is reduced and the oil conductivity properties are displayed. In the millihertz range, the insulation geometry comes into play.
  • As the moisture properties of the cellulose change so does the shape of the curve.
The most common techniques used to measure this response are frequency domain spectroscopy (FDS) and polarization and depolarization current (PDC) methods. Using the frequency domain spectroscopy, the dissipation factor of the insulation system under test is measured by frequency sweep. The FDS allows fast measurements at high frequencies but requires long measurement times at frequencies down to 0.1 millihertz.
After the test is completed the results must be compared to a standard to determine the actual moisture content. IEC 60422 and IEEE 62-1995 have defined moisture classifications.

Labels

Labels:

Comments

Post a Comment

Popular posts from this blog

RCM(Reliability Centered Maintenance):Basic Seven Questions to be asked

To evaluate any asset or system with the RCM(Reliability Centered Maintenance) process Following seven questions are to be asked, What are the functions and associate performance standards of the system in present operating condition? How the system is failed to fulfill its functions? What are the causes for the failure of its functions.? What happen when its function failure occurred? In what way each failure matter or failure significance or consequences? What can be done to prevent or predict the failure? What happen if any proper proactive task cannot be found to prevent or predict the failure? Any team ask this basic Seven question to the system or the asset to be evaluated via RCM process for determination the maintenance requirement to be done easily. #RCM #realibility
Post a Comment
Read more

What is Arc Flash Studies?How it is carried out?

In order to identify the specific arc flash hazard at a given piece of equipment within a  given facility, an arc flash study must be performed. Outcome of Arc flash Study? Identify the Arc Flash Protection Boundary (this is the closest approach allowed before PPE must be worn).  arc flash equipment labeling Fault current and coordination analysis  recommendations for PPEs Arc Flash Incident Energy Mitigation Strategies How Arc flash Study carried out? There are several software packages available, similarly to short circuit study and coordination study software packages, to facilitate this analysis by a qualified professional electrical engineer.  Following seven steps to be carried out to done complete Arc flash study of the facility.      1.Gathering all as built documentation of the facility The starting point of study is to accumulate  all documentation like Electrical and earthing drawing etc. If...
Post a Comment
Read more