Electrical Power Equipment Maintenance and Testing Flashcards

This technical overview covers the maintenance protocols for insulating mediums and the fundamental categories and testing of power transformers. The first segment discusses sampling, purification methods like centrifugation and vacuum dehydration, and specific requirements for alternative fluids like RTemp, FR3, and sulfur hexafluoride gas. The second segment focuses on transformer design categories, core and shell construction, and field acceptance tests such as insulation resistance and turns ratio. Would you like a summary of the next technical segment regarding transformer oil testing or overhaul procedures?

What is the recommended period for natural precipitation to occur in oil before removal to allow water and solids to settle?

Undisturbed for at least $24\,\text{h}$.

What is the ideal temperature range for accurately filtering insulating oil through a filter press?

Between $20\,\text{°C}$ and $40\,\text{°C}$.

At what back pressure threshold should filter paper in a filter press be replaced?

Approximately $75\,\text{psi}$.

What is the recommended filter density for mobile cartridge-type filters used with transformer oil?

0.5\,\text{\mu m}.

What are the temperature requirements for applying full load to an RTemp transformer?

Top oil temperature must be at $-15\,\text{°C}$ or above.

In Envirotemp (FR3) quality tests, what is the recommended stand time for the ASTM D1816 test to allow air to escape?

$15\,\text{min}$.

What is the dielectric strength threshold at which a sample of askarel must be sent to a laboratory for moisture testing?

$26\,\text{kV}$ or less.

At what temperature and pressure does sulfur hexafluoride ($SF_{6}$) gas liquefy on the lower end of the vapor pressure curve?

$-20\,\text{°C}$ at a pressure of $50\,\text{psig}$.

What is the rating of a forced air-cooled transformer compared to its self-cooled rating?

$133\,\%\text{ of the self-cooled rating}$.

What is the ventilation requirement for dry-type transformers installed in vaults or restricted spaces?

A minimum of $100\,\text{ft}^{3}\text{ per minute per kilowatt (kW)}$ of transformer loss.

What is the standard altitude limit for transformers of standard temperature rise?

$3300\,\text{ft}$.

For a transformer coil rating greater than $5000\,\text{V}$, what is the minimum insulation resistance (IR) value suggested by NETA?

25,000\,\text{M\Omega}.

What is the accepted difference margin for a Transformer Turns Ratio (TTR) test compared to calculated values?

Not greater than $0.5\,\%$.

How is the Polarization Index (PI) calculated during an insulation test?

The ratio of the $10\,\text{min}$ insulation resistance reading to the $1\,\text{min}$ reading.