Question

A 4 pole turbo generator rated at 20 MVA, 13.2kV, 50 Hz has an inertia constant of H = 8.5 kW-s/kVA. It is supplying rated power at 0.8 pf. When a fault occurs that reduces the electical output to 40% of its initial value. Find the accelerating torque at the time when fault occurs?

• A. 61 kNm
• B. 75 kNm
• C. 122 kNm
• D. 100 kNm

Answer 1

The correct option is A 61 kNm

Output power before fault $=20\times 0.8=16MW$

Output power after fault $=\frac{40}{100}\times 16=6.4MW$

Accelerating power, $P_{AG}=16-6.4$

$P_{AG}=9.6MW$

Accelerating torque, $T_A=\frac{P_{AG}}{\omega }=\frac{9.6\times {10}^6}{2\pi \times \frac{1500}{60}}$

$=\frac{9.6\times {10}^6}{50\pi }$

$T_A=61115.5Nm$

$=61kNm$