TURBINE ROLLING

OBJECTIVE OF TURBINE ROLLING:-
To bring the unit on load and raised on rated output within optimum time but also without under stress on the turbine components.
Warming up and startup of the turbine during various steam condition of or turbine metal temperature condition are given by the manufacturer in the form of few startup curves.

TYPE OF UNIT STARTUP:- A unit start up described on the basic of  turbine metal temperature as given 

(1) Cold startup :- 
HPT metal temperature is less then 150°C.
Shut down time greater than 5 days
rolling steam pressure 40 kg/cm²
rolling steam temperature 350 °C.
Soaking time 1 to 1.5 hours
Load gradient 3 mw/min.

(2) Warm startup:- 
HPT metal temperature is between 150°C to 350°C.
Shut down time greater than 48 hours.
rolling steam pressure 60 kg/cm²
rolling steam temperature 400 °C.
Soaking time half hours
Load gradient 5 mw/min.

(3) Hot startup:- 
HPT metal temperature is greater than 350°C.
Shut down time less than 8 hours.
rolling steam pressure 85 kg/cm²
rolling steam temperature 485 °C.
Soaking time 15 minutes.
Load gradient 10 mw/min.

STARTUP CONSIDERATION (1) During startup the turbine is subjected to non steady state operation. (2) This cover the operating condition where speed, steam pressure & temperature changes with time. (3) Under this condition turbine components which are exposed to temperature changes subjected to thermal stress and expansion. (4) For turbine life point of view it is very much necessary to limit the extent of these temperature changes. (5) To take care of the above factor the operator has to follow the recommendation from turbine stress evaluator and start the rolling procedure by following criteria curves X-1 to X-7 right from beginning.

STATING PREPARATION
After having accomplishing the heating check & note down the following reading on a log sheet before rolling of the steam turbine.
Turbine metal temperature
Metal temperature of steam supply pipes before MSV &  ESV.
Metal temperature of steam admission line 
Metal temperature of hot reheat
Metal temperature of IVs
Metal temperature of IPT & HPT top/bottom.
Steam parameter before MSV.
Differential expansion of HP rotor, IP rotor,  & LP rotor.
Axial shift
Total expansion of HPT\IPT
Condenser vacuum
Eccentricity of rotor.
Turbine drain valve opening status.


UNIT STATUS BEFORE TURBINE ROLLING

1:- TG on barring gear & all turbo supervisory parameters are normal.

2:- Boiler is light-up condition with one or two oil elevation are in service.

3:- HPBP & LPBP is in charged condition.

4:- Boiler load index is 90 to 100 t/hr.

5:- steam parameters are ready for rolling.

6:- MS pressure 25 to 30 kg/cm² HRH Pressure 8-12 kg/cm² (for 200/210 to 350 MW units).

7:- MS and HRH temperature 320°C to 350°C (for cold rolling). 

TASKS INVOLVED IN TURBINE ROLLING 

1:- Seal steam chargine & vacuum pulling.

2:- MS line warmup & chargine.

3:- HPBP chargine.

4:- LPBP charging.

RESETTING OF STEAM TURBINE

1:-When turbine is trip due to electrical or mechanical protection resetting of turbine is required.

2:- In this condition trip oil is drained then SV & CV remain closed.

3:- So trip oil is require for ESV, CV, ISV & IVC in open condition and required  secondary oil pressure for opening the HPCV &IPCV.

4:-Trip oil is generated after resetting of turbine.

5:- Now reset the turbine we have to:- 

(a) Reset the unit or master trip relay. (b) Bring the starting device to zero.
Unit or Master Trip Relay can be reset :-

1:- resetting boiler master fuel trip relay

2:- all generator trip telay reset.

3:- turbine electrical protection to be reset.

The zero position of starting device generates:-

1:- Startup Oil  2

:- Auxiliary startup oil 
(A) Auxiliary startup oil required for reset trip gear

(B) Startup oil is required for opening ESVs & IVs.

(C) It is also ensure that the control valve opening are are prevented still ESVs and IVs are opened.

ROLLING CRITERIA        

For KWU units CRITERIA BEFORE OPENING OF ESV                                                                                
X₁ Criterion: T_MS > Tm_CV + X₁(T)    T_MS    = Main Steam temperature ahead of high pressure bypass station Tm_CV  = Midwall temperature of main steam control valve.       
X₂ Criterion: Tss < Tm_CV + X₂(T)       Pms   =Main Steam pressure before HP Bypass used for calculating Saturated Steam Temperature TssTm_CV =Midwall temperature of main steam control valve.       
X₃ Criterion: T_MS > Tm_Strainer + X₃(T)      T_MS     = Main Steam temperature ahead of high pressure bypass station Tm_Strainer =Mean wall temperature of main steam strainer. 

CRITERIA BEFORE OPENING OF CONTROL VALVES                   

X₄ Criterion: T _MS > T_SS + X₄(T)T _MS = Main Steam temperature ahead of high pressure bypass station P _ms = Main Steam pressure before HP Bypass used for calculating Saturated Steam Temperature T_ss
X₅ Criterion: T _MS > T m _HPS + X₅ (T)T _MS = Main Steam temperature ahead of high pressure bypass station T m _HPS = Mean rotor temperature of HP Shaft (Simulated).      
X₆ Criterion: T_RH > Tm _IPS + X₆ (T)T_RH = Reheat Steam temperature ahead of intermediate bypass station Tm _IPS =Mean rotor temperature of IP Shaft (Simulated).  

CRITERIA BEFORE SPEEDING UP TO RATED SPEED                                  
X₇ Criterion: T _MS < Tm _HPS + X₇(T)T _MS = Main Steam temperature ahead of high pressure bypass station Tm _HPS =Mean rotor temperature of HP Shaft (Simulated).     
CRITERIA BEFORE LOADING THE GENERATOR                                          
X₈ Criterion: T _RH < T _RH + X₈(T)T _RH = Reheat Steam temperature ahead of intermediate bypass station T _RH =Mean rotor temperature of IP Shaft (Simulated).

Opening of ESVs & IVs (1) Before opening of stop valve following (a) drain should be open:- (b) MS strainer drain. (C) HRH strainer drain. (d) Seat drain before ESVs. (e) Seat drain before IVs. (2) TSE selected in admission mode  (3)Trim device should be on. (4) Following SLCs of following equipment is on. (a) Oil pressure &turning gear on (b) LP water injection on (c) AOP SLC should be on. (d) Vacuum pump SLC shoud be on. (e) SOP SLC should be on.