VIII Using figures describe the solid-state voltage regulator.
UNIT 11AC GENERATOR FREQUENCY CONTROL
AIMS OF THE UNIT: - to describe ac generator frequency control - to understand grammar point `Infinitive`
TASKS 1 Do your best to answer the brainstorming questions. 2 Read the text for general understanding. 3 Make up questions to the text. 4 Find the sentences with the new words in the text. Give the Kazakh or Russian equivalents of the words. 5 Write sentences with the new vocabulary. 6 Do the given exercisesfor better remembering the topic.7 Study grammar point ‘Infinitive ` do the tasks and find the sentences with infinitives in the text. 8 Speak on the topic. Given schemes and questions will help you to remember and understand the topic. 9 Find more information about the topic. Do some research, create slideshow or a project work and present them.
1 What is the function of CSD? 2What is the purpose of the CSD?
Because of the fixed number of poles, the only means of fine-tuning the output frequency is controlling rotor rpm, often done by using CSDs. CSDs receivedrive power from hydraulic power, pneumatic power, or the accessory drive section of an engine.It is for this reason that on most aircraft a CSD unit is located between the aircraft engine and the ac generator. On helicopters, the main generators are mounted on an accessory gearbox that is driven by the main transmission. The purpose of the CSD is to transfer and convert aircraft engine variable-speed rotation to a constant-speed rotation, which drives the generator. The CSD consists of a variable-displacement hydraulic pump, constant-displacement hydraulic motor, and a governing system. The governing system controls the rate of flow from the pump, thereby controlling the speed of the motor. There are several other components in the CSD that are necessary for self-regulating constant-speed operation. Among these components are three output-driven gear pumps: the charge pump, replenishing pump, and scavenge pump. A gear on the CSD output shaft drives these pumps, the limit governor, and basic governor. The pump wobbler and the pump section of the cylinder block assembly form the variable displacement pump in the CSD. The pump wobbler consists of an outer stationary shell and an inner race. The inner race is separated from the wobbler shell by bearing rollers. It is free to turn with the pump pistons, which are always in contact with the race during operation. Two control pistons in the CSD housing move the wobbler sideways to vary the output of the pump. The CSD functions in three different phases of operation: overdrive phase, straight-through phase, and underdrive phase. When the engine input rpm is less than the rpm required for the generator, the CSD makes up the difference in rpm. The CSD does this by causing the pump wobbler system to respond to governor signals. This response causes the pump to supply more oil to the motor. The difference between the input and output rpm depends on the quantity of oil pumped by regulating the wobbler pump. Anytime the motor wobbler (output) is rotating faster than the cylinder block assembly (input) the CSD is in overdrive. When the input rpm equals the required output rpm, the rotary motion transmits through the CSD without hydraulic action. The pump wobbler would, theoretically, be positioned through the action of the governor to be concentric with the cylinder block assembly. In this condition, the pump neither sends oil to the motor nor accepts oil from the motor. The motor pistons lock in position against the motor wobbler, forcing the wobbler to rotate at the same speed as the cylinder block assembly. Since the drive starts in underdrive and operates normally in overdrive, this straight-through condition is only temporary. When engine input rpm exceeds the output rpm requirements for the generator, the CSD acts to subtract from the input rotation. The wobbler pump accomplishes this in response to the governor signal. The pump-motor action for underdrive is the reverse of the action required for overdrive. In the underdrive phase, the pump performs in a negative pumping action. The generator load opposes the driving force of the CSD, so it always tries to slow the wobbler. The cylinder block assembly then rotates faster than the motor wobbler. Excess input torque is dissipated in the reverse pumping action to the charged oil system. Whenever the motor wobbler is rotating more slowly than the cylinder block assembly, the CSD is in underdrive.
EXERCISES FOR BETTER REMEMBERING THE TOPIC
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