TRANSFORMERS

 

The cornerstones of Hour Electric's preventive program are oil sampling, electrical testing and visual inspection. Together, these three methods provide the information to analyze the condition of your transformer and switchgear and to determine the steps needed to assure reliability and top performance.

 

Electrical Testing

 

Recommended Intervals:

 

Liquid filled Transformers:

• 1. Liquid-filled transformers should be tested and inspected every one (1) to three (3) years, depending on the environment of the transformers and its load.

• 2. They should be tested any time that there has been a severe fault on the secondary side of the transformer, or any time that a problem is suspected in the transformer.

 

Dry Type Transformers:

• 1. Dry type transformers should be cleaned every six (6) months to one (1) year, depending on the environment of the transformer location.

  2. They should be electrically tested every one (1) to three (3) years, depending on the environment and the load, or any time there has been a severe fault on the secondary side, or if a problem is suspected in the transformer.

 

Electrical tests accurately measure these important values:

 

• Insulating value of insulation (DC Megger)

• Resistive and Capacitive loss (DC Hipot)

• Power Factor (tests of transformers & bushings)

• Relationship of primary and secondary voltages (TTR)

• Trip levels and accuracy of relays and low, medium and high voltage circuit breakers

 

Test results are compared to manufacturers specifications and/or performance standards set by NETA, IEEE and NEMA, and establish a baseline for comparison with future tests. Repairs or calibration needed to bring equipment into specification can be easily identified, and post repair testing assures that proper corrective action has been taken.

 

In many cases, testing identifies the need for simple repairs and adjustments that preclude costly repairs and downtime in the future.

 

Tests Performed
The suite of tests include the following:

 

• Dielectric Absorption

• Insulation resistance test, winding-to-winding and winding-to-ground.

• Turn to Turn Ratio Test: to determine actual vs. calculated voltage

• Power Factor Test: to assess condition of electrical insulation in high voltage apparatus

• Breaker and relay tests of contact resistance, conductivity, insulation resistance, current and /or voltage trip levels

 

Equipment Used

• Microprocessor based circuit breaker test sets for high current injection

• 5KV Insulation Resistance testers

• Automated Insulation Power Factor Test Set

• Protective Relay Test Set

• Digital Low Resistance Ohmmeters

• 10KV automated power factor test set

• Turn to Turn Ratio Test Set

 

Repairs
Our breaker and relay test process compares the performance of your equipment to manufacturer’s maintenance specifications. In addition to testing, our electrician's perform on-the-spot repairs such as:

 

• Cleaning cubicles

• Burnishing and adjusting contacts

• Lubricating moving parts

• Retrofitting trip units

• Repairing faulty subassemblies

 

More extensive repairs are performed by returning the faulty item to the supplier and installing a new item or on a subsequent site visit.

 

Test Report and Analysis
After the test program is completed, a test report is compiled and submitted to our customer. The test report presents the actual data taken at the customer’s site and the results of any calculated values. Out of specification conditions are highlighted and maintenance recommendations are presented