This content has restricted access, please type the password below and get access.
Protected: From the Desk of the President
Enter your password to view comments.
This content has restricted access, please type the password below and get access.
This content has restricted access, please type the password below and get access.
This content has restricted access, please type the password below and get access.
Transformers Maintenance and Testing
By Anzar Hasan
Power transformers are designed to have a very long operational life. However, there is no definitive consensus regarding how to determine their specific useful life. While there are transformers that have been in service for 30 to 40 years, there have also been major transformer failures and fires for those in service for relatively shorter periods of time. It is fair to conclude that while transformers are generally reliable, external interference and internal cumulative hazards often lead to premature failure.
The issues that affect the useful life of transformers may be categorized in two areas: manufacturing defects and operational issues. Manufacturing defects may result in service outages and shorten the expected life of transformers. In this issue, we are focusing on the operational issues that affect the reliability and premature failure of transformers, including the following:
All of the above result in insulation failures that in turn cause short circuits and arcing. In the case of mineral oil-filled transformers, which are ignitable, this will further cause rupturing and fire.
In general, most transformer evaluation decisions are driven by occupancy, size of transformers and loading. My review of risk assessment reports that span several years reveal a vast deviation in evaluation of transformers and recommendations. In addition to standard tests such as dielectric absorption testing, ratio testing, etc., below are some suggested evaluation tips for transformers > 5,000 kVA, furnace and special purpose transformers, and GSUs:
NOTE: For meaningful evaluation, the results should be trended and interval of testing adjusted accordingly. If this is not done, a recommendation is warranted.
The results of overall power factor tests on power transformers reflect the insulation condition of the windings, barriers, tap changers, bushings and oil. Modern oil-filled power transformers should have power factors of 0.5 percent or less, corrected to 20°C (68°F), for individual windings to ground (CH and CL) and interwinding insulations (CHL). The IEEE transformer specification states that the power factor of the insulation system shall not exceed 0.5 percent at 20°C.
Several insurance companies, manufacturers and electrical testing companies recommend PF testing every three-to-five years. Often this is not practical because the testing can only be completed offline. For this reason, users are reluctant to perform this important testing. For GSUs, furnace and special purpose transformers, a great option to consider is installing continuous power factor monitoring systems.
The above suggested evaluations tips may increase reliability and prevent the premature failure of transformers. If you have any questions, please feel to contact me, as our team is always ready to help.
Part owned by GAPS, an XL Group company
Services | About Us | Careers | Contact Us | Home
5018 Bristol Industrial Way, Suite 203
Buford, Georgia 30518
Boiler & Property Consulting Copyright 2015 •
Site Design by Mighty 8th Media