How long does it take to warm up a steam turbine prior to start up?

They should be warmed up and cooled down slowly to minimize the differential expansion between the rotating blades and the stationary components. Large steam turbines may require approximately five to nine hours to warm up.

Why is it that we need to have a long period of starting and stoppage time for the steam turbine system?

To reduce excessive vibrations the turbine speed must be kept constant for a longer period of time. Typically, such a stop is done at 1000 rpm. If during run-up no excessive vibrations occur it is not necessary to heat-up the machine on intermediate speed.

What should be done during warming through a steam turbine?

Warming-through a steam turbine Obtain clearance from the bridge to turn the shaft. Engage the turning gear and rotate the turbines in each direction. Start the sea water circulating pump for the main condenser. Then start the condensate extraction pump with the air ejector recirculation valve wide open.

Why steam turbine is preheated before operation?

Steam turbine must be preheated to evaporate and purge all condensate before spinning up to speed. Liquid damages blades. Also turbines are built to close tolerances so thermal expansion should be unified to near normal running dimensions.

Why is it necessary to have pre warming in turbine?

The pre-heating rises the parts temperature before the actual start-up begins. It changes the thermal state of the turbine and causes smaller maximal stress during the initial period of the start-up.

What should be done before starting the steam turbine?

The correct starting procedure for steam Turbine Generator onboard ship is as follows: Check turbo generator lube oil sump level and drain it for water. Replenish it if level is less than normal. Start the lube oil priming pump from the local station and check the lube oil pressure.

Why warming up of steam turbine is important?

Steam turbines have to be warmed slowly to avoid excessive differential expansion of the various components, rotor stress, and potentially reduced service life. If the rotor and shell don’t warm and expand at a uniform rate, it can cause rubbing or binding between rotating and stationary components.

What is critical speed of turbine?

Critical speed of the turbine is the rotor speed at which natural frequency of the assembled rotor (rotor shaft with discs, blades, shrouding strips etc in assembled condition) becomes equal to the operating speed. This is usually a expressed as a range (critical speed range). There are multiple critical speeds.

Why is vacuum required in a steam turbine?

In other words, the specific volume of water at a given pressure is many times lower than that of steam. A vacuum is maintained in the condenser so that steam can easily flow and more work can be extracted from the steam in the turbine; this is the reason why vacuum is maintained in condensers.

What is bleeding in steam turbine?

It is the process in which expanded steam is extracted from the expansion path to utilize it for some purpose. Bleeding in a steam power plant is always performed in advance of the closing of expansion.

What happens to steam when it leaves the turbine?

When the steam leaves the turbine, its temperature has dropped, and it has lost almost all its elevated pressure. Some of the pressure drop also occurs across the diaphragm, which is a component between the outer wall and inner web. The diaphragm’s partitions direct the steam toward the rotating blades.

How long does it take for a steam turbine to start up?

Large steam turbines may require approximately five to nine hours to warm up. While smaller units have more rapid start-up times, steam turbines differ appreciably from reciprocating engines, which start up rapidly, and from gas turbines, which can start up in a moderate amount of time and load follow with reasonable rapidity.

What is the difference between the different types of start-up turbines?

The difference between the above types of start-up consists in the fact that in the former case steam supplied to the turbine has greater than casing metal temperature, while in the latter two cases, depending on the boiler characteristics, steam temperature can be lower or higher than the casing temperature.

What are the pre-requisites for the operation of steam turbine?

Prior to supplying steam to the turbine, the steam supply pipelines have to be drained and heated up. In case of turbines with cooling water preheating and low-pressure (LP) by- pass, prior to supplying steam the regeneration and dumping systems have to be started. 1.1 Run-up to idle run and synchronisation