Turbine diff expansion can be positive or negative and depends on the convention used. The usual convention is that positive expansion is rotor expanding faster (hotter) than fixed components. Expansion is dictated by steam flow, gland steam temperatures etc
my LP turbine differential expansion increase ,when rated gland steam temperature maintain.
differential expansion is refer to differential distance between rotor blade and fix blade.rotor expand toward generator and casing expand toward control valve.when temperature increase ,expansion in casing and rotor.so rotor mass is less than casing which rotor expand more than casing.
Differential expansion means gap between fixed Blade & rotating blase of a turbine.. When steam enters into the turbine, rotor tends to expand towards generator side & casing tends to expand towards control valve side. If differential expansion increase then there is a possibility of reducing axial gap between rotor & fixed blades. When differential expansion is positive its means rotor expand more than the casing expansion. There is a limit upto +ve 5. If increases than +ve 5 it means we have to check front side tie rods status.
by controlling main steam flow
Lp turbine diaphragm breaks due to positive pressure inside the condenser because of steam expansion.
Interlock system is in turbine for protect the turbine. different types of interlocks in turbine 1. high vibration, 2. Bearing oil Temp,3. vacuum related, 4. over speed, 5. differential expansion, 6. casing expansion, 7. lube oil header Pressure. 8. Axil shift. etc... . this interlocks is keep the turbine in safe mode in any abnormalities.
HP Turbine is High Performance Turbine LP Turbine is Low Performance Turbine
it's the thermal expansion in the casing of hp or ip turbine can be noticed by journal or thrust bearing when moving <<
The TSI system is Turbine Supervisory Instrumentation system, consists of multiple instruments, including speed sensors, speed monitors and so on. The system continuously monitors the steam turbines of all important parameters, such as: rotational speed, overspeed protection, eccentricity, shaft vibration, cover vibration, axial displacement, differential expansion, and thermal expansion. The system helps to improve the availability of steam turbine unit.
1. Low vacuum at high loads 2. High HRH temp 3.High steam flow 4. high gland steam temperature
casing and shaft are made of alloy steel they are supposed to expand when heated (at/2 *length of turbine.).wherea is coefficient expansion of material.t=finaltemperature ( of casing or shat)-ambienttemperaturel=length of turbine in meter
cold start up of a steam turbine has to be done after a rather long period of shut down - when turbine case and chest temperature are fallen down dramatically. turbine constructor heating ramps mast be followed in order to avoid thermal stresses on the metal of turbine case , valve case and rotor to avoid also height differential expansion between rotor and case that could lead to contact between case and rotor because of the different thermal inertia of the two parts.when the heating is complited the turbine can be started checking closely the differntial expansion recorders.when at speed the unit can be sincronyzed (usually at 3000 rpm) and then loaded according to the related load ramp.(megawatts\ minute)