What causes turbine overspeed?
A turbine overspeed accident can be caused by a lightning-induced power surge, a fouled pilot valve, an electrical fault, operator failure, or any of a few dozen other problems. These systems are built to cut the energy supply to the turbine so that it will coast to an orderly stop.
What is the purpose of overspeed test?
Turbine overspeed events lead to costly and dangerous catastrophic failures. Therefore the overspeed system has to be periodically tested to ensure the system has the adequate response time to protect the turbines, plants and personnel.
How is turbine speed controlled?
A steam turbine governor is a component of the turbine control system that regulates rotational speed in response to changing load conditions. The governor output signal manipulates the position of a steam inlet valve or nozzles which in turn regulates the steam flow to the turbine.
What causes a steam turbine to trip?
Many events can cause a turbine trip, including: turbine overspeed condition where the turbine accelerates over its design speed, typically by 10% low vacuum in the secondary cooling loop, or condenser. lubrication failure for any number of reasons.
What is turbine overspeed?
Background. The steam turbine overspeed event occurs when little or no energy is being consumed by the driven equipment, whether a generator, pump or compressor, and too much steam is provided to steam turbine.
What is turbine overspeed trip?
The overspeed trip system protects personnel and plant systems by preventing missiles that can result when turbines disintegrate at higher than normal rotational speeds. It also protects against financial losses of an extended outage and premature turbine replacement.
What is a governor valve?
The governor valve is a mechanical valve used in non-electronic hydraulically controlled transmissions. It varies governor pressure proportional to vehicle speed. If the vehicle is traveling around 20 mph, there should be around 20 psi in the governor’s circuit. The output shaft drives the governor valve.
Why speed control is required in a turbine?
The speed controller compares the speed reference value with the actual speed of the turbine and accordingly provides an output for the throttle valve lift. The reference speed signal ensures that the highest permissible rate of speed is consistent with the safe operation of the turbine.
Why is overspeed bad?
Left unchecked a prop overspeed can lead to hub or blade failure and a subsequent severe vibration from the imbalance. Pull the throttle and slow the plane down, and you can usually regain propeller speed control, at least temporarily. pressure is lost in the prop dome. makes prop overspeed in twins much less likely.
What is minimum governor speed?
Minimum speed: The Minimum speed is nothing but the speeds at the minimum radius of rotation of the balls without tending to move either way is called as minimum speed. 8. Governor effort: The mean force working on the sleeve for a given change of speed is termed as the governor effort. 9.
What is the cause of motoring in alternator?
Tripping Schemes Motoring of a generator occurs when the energy supply to the prime mover is cut off while the generator is still on line. When this occurs, the generator will act as a synchronous motor and drive the prime mover.
How is overspeed test done on a turbine?
Testing of the overspeed bolt consists of running the turbine up to the trip point (typically 112% of rated speed); h owever this is a risky operation for several reasons. First, there is no guarantee that the turbine will actually trip at 112% until the testing has been completed.
How does overspeed protection work on an Emerson turbine?
The Emerson electronic turbine overspeed protection system (OSP) prevents excessive turbine speed that could lead to equipment damage. Overspeed protection is achieved by using a two – out -of -three voting trip system. This system is completely independent of the turbine speed governor.
How many trip bolts are used in a turbine?
One trip bolt assembly is used for each trip channel and each assembly is provided with independent on-load test facilities. The bolt has its centre of gravity a short distance from the axis of rotation and, at low speeds, is held retracted by a spring.
What is the purpose of the overspeed trip?
The overspeed trip is the final protection against catastrophic failure of the turbine following a load rejection, causing the unit to become disconnected from the power system.