MGVCL Exam Paper (30-07-2021 Shift 1)
Determine maximum permissible load which a 15 MVA, ONAN cooled transformer to IS : 2026 can take for 6 hr, if the initial load on it was 12 MVA. The weighted ambient temperature is 20˚C. Assume the permissible load kVA as a fraction of rated kVA is 1.25.
There is one IEC guideline, number is IEC 599, Statement of guideline is that "If the ratio of carbon dioxide and Carbon monoxide in Dissolve gas analysis test result is more than 11, it is predict that the condition of paper insulation inside the transformer is poor." For healthy condition this ratio will be between 4 to 11.
Condition of good conductor: σ/ϵω >> 1 Equation is given by: The constant ratio = σ/ϵω = 44913.6 σ/ϵω >> 1. hence sea water is a acting as a good conductor Since attenuation is 90%, so transmission is 10% So, e^(-αx) = 0.1
Attenuation constant = √(σμϵ/2) = 0.702 -αx = ln(0.1) x = 3.27 m
Bus Type - Known Parameter - Unknown Parameter Load Bus -P, Q - V, phase angle Generator Bus - P, V (magnitude) - Q, Voltage phase angle Slack Bus Voltage - magnitude and phase angle - P, Q
EXAMIANS