Ansaldo Gas turbine_component_HCO or RDS_part3

Ansaldo Gas turbine_component_HCO or RDS_part3

in this part we will discussion the most problems for HCO 
system during operation

click her for part1

click her for part2

1-    Load rejection and GT fast unloading: the RDS is automatically deactivated

A fast unloading == a load rejection it is considered fast unloading when:

a-      The load gradient is > EK.LEIST.101 (load change of about 13 MW/min)

b-      The load reduction is > E.LEIST.101 (load difference of about – 15 MW).

                   In case the rotor is not in the NULL position G.HSO.01 after delay K.HSO.11, a GT trip.

                When the RDS has been deactivated due to a load rejection, it is necessary to wait that

                K.HSO.04 (e.g. 1 h) has elapsed before a new activation of the RDS. 

  

2-        GT Shut Down: It is automatically disconnected after the fuel stop valve(s) closure   

3-         GT Turning gear operation and standstill:

a-    During turning gear operation for cooling, the RDS system is under pressure and the secondary chamber is pressurized

b-    In case of fault to the RDS system, the turning gear operation is performed also with the depressurized RDS system. However in this condition a GT start is NOT ALLOWED since the shaft shall be in the NULL position before attempting

       a GT start up.

c-    In case of interval turning and GT standstill the RDS system is not pressurized

d-    Maintenance on the RDS system

                 Warning: In case it is required to totally exclude the RDS system with the GT at        

                               Standstill or in turning gear mode in order to perform maintenance job, 

                                 it is Necessary to switch off manually all pumps, to deactivate all manual

                                  Sequences and to interlock pumps (otherwise they will start again due to

                                  The low pressure protection logic).To perform maintenance job, all system                                            Shall be TOTALLY DEPRESSURIZED

4-     The following actions are required (necessary fundamental condition: GT speed < S.TURB.05):

a. Switch off the RDS pump (if just in operation) and disconnect the pumps at the  

     Switchboard by smooth action (in order to avoid undesired automatic start).

b. Switch off the RDS‐SEQUENCE

c. Open SEC CH return valve (MBA53AA005)

5-      When the pressure in the RDS system has decayed it is possible to perform work on the RDS system

6-      When the lube oil has been removed from the RDS system, after work completion, the RDS system must be refilled with oil, after that, during cool down turning, the RDS system is pressurized.

When the RDS system is filled with lube oil, the RDS‐Sequence shall be switched on for automatic operation. This action activates automatically the shutdown branch of the RDS sequence. Since during the depressurization of the system the RDS pressure has dropped below P.HSO.02, the main and secondary channels are at first vented and purged. Then the solenoid valves are positioned by the RDS sequence in order to bring the shaft in the NULL position and the secondary channel is pressurized.

7-      Additional warnings:

a-    The accumulator pre‐charge is monitored by the control system via the filling time of the accumulators. The accumulator pre‐charge shall be controlled at regular intervals.

b-    The closure of not used optional tapping points must be checked at regularly maintenance activity in order to avoid potential leak.

c-    Before activating again the RDS system when the RDS system has been deactivated due to a fault, it is necessary that the fault event has been removed.