What is differential expansion of steam turbine?

Differential Expansion of Steam Turbine:- It is the difference between the rotor expansion and the Casing Expansion. It is +ve if rotor expands more than casing. It is -ve if casing expands more than rotor. During initial startup diff Exp. is +ve as rotor mass is less and expands at more faster stage than casing.

What is axial displacement in steam turbine?

Axial shift of steam turbine is basically happen when high-pressure steam enters into the turbine steam chest after that high-pressure steam exerted an axial force on the turbine rotor in the direction of the axis of the rotor at that time turbine rotor displaced it’s position in few mm.

What is relative expansion?

The relative expansion (also called strain) divided by the change in temperature is called the material’s coefficient of linear thermal expansion and generally varies with temperature.

What is axial shift?

16 April 2021. Axial Shift of Steam Turbine. Axial shift on the Rotors comes due to two components. Direct Pressure Thrust: It is the axial thrust due the diff of the pressure X Area component across the moving stage blading and Discs. Velocity Component: It is due to diff.

What are the reasons for high vibrations in steam turbines?

TOP 22 REASON’S BEHIND STEAM TURBINE VIBRATION IN POWER PLANT

• Unbalance of the steam turbine rotor.
• Unbalanced of steam turbine rotor parts.
• Loss parts of steam turbine cylinders.
• Deposited on steam turbine blades.
• Damage of journal bearings.
• Rotor shaft axial shift.
• Differential expansion.

What is the expansion of steam?

Steam engines and steam turbines use the expansion of steam to drive a piston or turbine to perform mechanical work. The ability to return condensed steam as water-liquid to the boiler at high pressure with relatively little expenditure of pumping power is important.

What is float in steam turbine?

Thrust Bearing Float:- It is the total axial movement of the Rotors between the working and the Non working Pads of the Thrust Bearing. It is measured by moving the rotors from the extreme end of the working pads to the extreme end of the Non working pads or vice versa Reading is measured by Dial Gauges .

What is differential expansion?

Differential Expansion on a turbine is the relative measurement of the rotor’s axial thermal growth with respect to the case. Rotor Expansion on a turbine is the absolute measurement of the rotor’s axial thermal growth with respect to the turbine’s foundation.

Why is solid low expansion on heating?

The atoms themselves do not expand, but the volume they take up does. When a solid is heated, its atoms vibrate faster about their fixed points. The relative increase in the size of solids when heated is therefore small.

What is the cause of steam turbine vibration?

The vibration is caused by insufficient clearance between stationary and rotating parts, as well as a shaft located off-center in its bearing. Again, the rubbing causes friction between stationary and rotating parts, localized heating of the rotor metal at the contact point, and shaft bending.

What causes vibration in turbine?

How is vibration measured on a steam turbine?

Vibration is measured either in terms of displacement, velocity or acceleration. Vibration displacement is always measured as Peak to Peak, a measure of the total excursion of the rotor or machine casing in MILS or MICROMETERS. Vibration velocity and Acceleration are measured as Zero to Peak or RMS.

What is the differential expansion of a steam turbine?

For all practical purposes, “Differential Expansion” would be zero. Which of course, never happens. The turbine casing is exposed to steam on its inner surface only, while the turbine rotor is enclosed within the turbine casing, and in nearly all cases is significantly lower mass than the casing.

What happens when steam is added to a turbine?

When steam is first admitted to a turbine the rotor will heat up faster than the turbine casing. Thus the rotor will grow faster axially than the turbine casing grows axially. This difference in expansion is called differential expansion.

Why the expansion of turbine shaft is not equal to turbine casing?

Due to this temperature differences, the expansion of turbine shaft will not be equal to that of turbine casing. A steam turbine has a fixed end and moving end. Both the ends are supported on independent pedestals. When turbine is in service, superheated steam (temperature above 540 degree celsius) is admitted into the turbine.

Why do turbine rotors have long rotor diffrential expansion?

Long rotor diffierential expansion is the norm – due to the physical implications of the fact that – while the turbine casing is relatively much more massive than the rotor, and is exposed to high temperature steam on its inner surfaces only, the much less massive turbine rotor is emersed in steam.