- 1 A Discuss The Advantage Of Using A Variable Speed Drive Instead Of A Throttling Valve In A Pumping Application 5 1 (61.36 KiB) Viewed 90 times
1. (a) Discuss the advantage of using a variable speed drive instead of a throttling valve in a pumping application. [5 marks) (b) An incident on the road would force a car to stop suddenly, decelerating to rest within one second. If the car uses regenerative breaking the motor would be required to produce a counter-torque, in order to absorb the kinetic energy in the car. During testing, you measure the energy that would be absorbed by the electrical machine in such a scenario, and you find it to be 0.018 kWh. The gear ratio of the car's gearbox is M = 0.44, where n, is the number of teeth in the load gear and nm is the number of teeth in the motor gear. The load and motor inertia are Ju = 7.21 kg m2 and JM = 0.99 kg-m2 respectively. Damping and the load torque (TL) can be neglected. If the motor can only produce up to 500 Nm of counter- torque, determine if this is sufficient to stop the car in that scenario. NOTE 1 kWh = 3,600,000 J. Neglect electrical machine losses. [12 marks] (c) A three-phase wind turbine generator is rated at 690V (line-to-line) and 2.3 MW. It operates at a power factor of 0.85 (lagging) at its rated conditions. The manufacturer tries to reduce the cost of the cables carrying the generated power to the converter at the base of the tower. They install new cables that can only carry a current up to 2,200 A, otherwise they will overheat and burn. Determine if the manufacturer designed the system sufficiently safe, or if the cables will overheat when the turbine produces the rated power. [3 marks]