GT8C2

en HTCT 690 558 Var. 52 A

Compressor Blow-Off System

GT8C2

HTCT 690 558 Var. 52 A en

Revision History

Revision Date Content of Change Document Pagestotal :

A 10-1-2003 Description edited and completedDiagram HTCT 319 617A replaced withHTCT 319 617A

12

GT8C2

en HTCT 690 558 Var. 52 A i

Contents

1 GENERAL DESCRIPTION........................................................................................... 11.1 Function ................................................................................................................ 11.2 Design ................................................................................................................... 11.3 Principle of Operation.......................................................................................... 2

1.3.1Standstill........................................................................................................... 21.3.2Start-Up............................................................................................................ 21.3.3Operation ......................................................................................................... 31.3.4Shut-Down ....................................................................................................... 31.3.5Emergency Trip................................................................................................ 3

1.4 Safety and Monitoring Equipment ...................................................................... 4

2 APPENDICES............................................................................................................... 62.1 Designation of Parts ............................................................................................ 6

Diagram......................................................................................... HTCT 319 617A

GT8C2

ii HTCT 690 558 Var. 52 A en

Blank page

GT8C2

en HTCT 690 558 Var. 52 A 1

1 GENERAL DESCRIPTION

1.1 FunctionDuring start-up and shutdown, the compressor blow-off system bleeds aportion of the compressor air into the environment. This compensates for thevolume flow mismatch during operation at low speed.

1.2 DesignDiagram HTCT 319 617A shows the design in schematic form. The mainparts of the system are:- compressor blow-off system MBA81, with:

two blow-off valves MBA81 AA011 and AA012after the second stage of thecompressor (Pressure stage 1)one blow-off valve MBA81 AA021after the fifth stage of thecompressor (Pressure stage 2)one blow-off valve MBA81 AA031after the 11th stage of thecompressor (Pressure stage 3)

- blow-off valve hood MBA81 HA800, with:silencer MBA81 BS001

- control air system for 1st and 2nd stage valves MBX69, with:pressure reducing valves MBX69 DP001 and DP002feed orifices MBX69 BP001 and BP002safety relays MBX69 AA001 and AA002

- control oil system for 1st and 2nd stage valves MBX48, withpilot valves MBX48 AA001 and AA002orifices MBX48 BP010 and BP011

- control air system for 3rd stage valve MBX37, withsolenoid, pilot valve MBA81 AA031A

- washing connection control withsolenoid valve MBX69 AA011two way valve MBX69 AA012solenoid valves MBX69 AA012A

non-return valve MBX69 AA13- safety and monitoring equipment- piping.

GT8C2

2 HTCT 690 558 Var. 52 A en

1.3 Principle of Operation1.3.1 Standstill

Blow-off valves MBA81 AA011, AA012, AA021 and AA031 are normally open.During off-line washing of the compressor, blow-off valves MBA81 AA011,AA012 and AA021 are closed by pressurized air supplied by the compressoron the wash cart. Solenoid valves MBX69 AA011 and AA012A are open, twoway valve MBX69 AA012 is closed.Blow-off valve MBA81 AA031 is closed by control air of system MBX37.Solenoid pilot valve MBA81 AA031A is open.For functional testing the blow-off valves can also be closed by compressedair.

1.3.2 Start-UpThe force of the built-in springs holds the blow-off valves MBA81 AA011,AA012, AA021 and AA031 open. The passage of pilot valve MBA81 AA031Ais also open.A portion of the air being moved by the compressor escapes through valvesMBA81 AA011, AA012 and AA021, the blow-off valve hood and silencerMBA81 BS001.Another portion of the air taken in by the compressor can discharge into theopen through blow-off valve MBA81 AA031, the exhaust diffusor and thenthrough exhaust system MBR01.Hydraulic control oil system MBX48 for blow-off valves MBA81 AA011, AA012and AA021 is supplied with oil from system MBX42. Pressure builds up topilot valves MBX48 AA001 and AA002.Control air system MBX37 builds up pressure to pilot valve MBA81 AA031Afor blow-off valve MBA81 AA031.Control air system MBX69 is supplied by compressor air. The air is cooled incooler MBX69 AC002, and dried in condensate trap MBX69 AT003.The air flows through one of the two filters MBX69 AT001 or AT002. (Manualchange over is possible even during operation).The air then flows to safety relays MBX69 AA001 and AA002 for blow-offstages one and two through reducing valves MBX69 DP001 and DP002 andsupply orifices MBX69 BP001 and BP002.When the gas turbine reaches the preset percentage of nominal speed, pilotvalves MBX48 AA001 and AA002 for blow-off valves MBA81 AA011, AA012and AA021 switch over. The oil flows to safety relays MBX69 AA001 andAA002, and changes them over.

GT8C2

en HTCT 690 558 Var. 52 A 3

Control air flows to the blow-off valves MBA81 AA011, AA012 and AA021 andcloses them.The flow of control air and the closing time for blow-off valves MBA81 AA011,AA012 and AA021 is determined by supply orifices MBX69 BP001 andBP002 and the pressure after reducing valves MBX69 DP001 and DP002.The pressure after the reducing valves is set during commissioning.Solenoid pilot valve MBA81 AA031A for the third stage blow-off valveswitches over. The air flows into the piston of blow-off valve MBA81 AA031and closes this valve.

In spite of the silencer, it is impossible to preventincreased sound emissions (sound level 105 dBA)during blow-off.

1.3.3 OperationThe four blow-off valves are closed during operation of the gas turboset.

1.3.4 Shut-DownLoad is removed from the gas turboset with the blow-off valves closed. Thenafter a preset time of idling (cool-down phase) the turboset is disconnectedfrom the grid and shutdown.Pilot valves MBX48 AA001 and AA002 switch over. The oil pressure in safetyrelays MBX69 AA001 and AA002 collapses, and spring force discharges thecontrol oil through the pilot valves and switches over the safety relays. Thecontrol air discharges to the environment, the pressure in blow-off valvesMBA81 AA011, AA012 and AA021 collapses. The blow-off valves are openedby spring force.Pilot valve MBA81 AA031A switches over to the setting "blow-off valvesopen". The control air discharges to the environment and blow-off valveMBA81 AA031 of stage three are opened by spring force.

1.3.5 Emergency TripDuring an emergency trip of the gas turboset, pressure in hydraulic safetysystem MBX42 and with it in control oil system MBX48 collapses immediately.Non-return valves MBX48 AA011 and AA012 remove the load from the safetyrelays, which then switch over. The control air pressure collapses and theblow-off valves MBA81 AA011, AA012 and AA021 open.Pilot valve MBA81 AA031A switches over to the setting "blow-off valvesopen". The control air discharges to the environment and blow-off valveMBA81 AA031 of stage three is opened by spring force.

GT8C2

4 HTCT 690 558 Var. 52 A en

1.4 Safety and Monitoring EquipmentMBA81 AA011 H, L, M; AA012 H, L, M; AA021 H, L, M; and AA031 H, L,M: Limit switches to blow-off valvesOne limit switch H monitors the "Open" setting of each blow-off valve,MBA81 AA011, AA012, AA021 and AA031.Two limit switches L and M monitor the "Closed" setting of each blow-offvalve MBA81 AA011, AA012, AA021 and AA031. Incorrect positioning of theblow-off valves is signaled to the control room by means of a general alarm.Start-Up: an interlock prevents start-up of the gas turboset unless all fourblow-off valves are open.At a preset percentage of nominal speed, if one of the blow-off valves is notopen, first an alarm is initiated in the control room and progress of the start-up program is interrupted for a preset time.If all blow-off valves are opened during this time, further progress of thestarting program is enabled. Otherwise the gas turboset is tripped.If then within a preset range of nominal speed only one of the blow-off valvesMBA81 AA011, AA012, AA021 and AA031 moves away from the openposition, the gas turboset is tripped.Operation: If only one limit switch Closed (L and M) of one of the blow-off valves moves from the closed position, a load shedding is initiated.

MBA81 AA031 H, L, M: Limit switches to blow-off valveThe limit switch H monitors the "Open" setting of valve, MBA81 AA031.The limit switches L and M, monitor the "Closed" setting of blow-off valveMBA81 AA031.Start-Up: An interlock prevents start-up of the gas turboset unless theblow-off valve is open.At a preset percentage of nominal speed, if the blow-off valves are not open,progress of the start-up program is interrupted for a preset time.If the blow-off valve is opened during this time, further progress of thestarting program is enabled. Otherwise the gas turboset is tripped.If blow-off valve MBA81 d AA031 moves from the open position within apreset range of nominal speed, the gas turboset is tripped.Operation: If only one limit switch Closed (L and M) moves away fromthe closed position, a load shedding is initiated.

GT8C2

en HTCT 690 558 Var. 52 A 5

MBA81 AA031 R: Measurement of position of valve MBA81 AA031The measurement monitors the position of blow-off valve MBA81 AA031 anddisplays it in the control room.Incorrect position of the blow-off valve initiates an alarm in the controlroom.

MBX69 AA012 H: Limit switch to two-way valvesThe limit switch H monitors the closed position of two-way valve MBX69AA012. It initiates an alarm in the control room if the valve is in the openposition during compressor off-line washing.

MBX69 CP001 and CP002: Pressure measurementsPressure measurements MBX69 CP001, and CP002 monitor the control airpressures after reducing valves MBX69 DP001 and DP002 and indicatethem locally.

MBX69 CP005: Differential pressure measurementThe measurement monitors the differential pressure across control air filtersMBX69 AT001 and AT002 and indicates it locally.

GT8C2

6 HTCT 690 558 Var. 52 A en

2 APPENDICES

2.1 Designation of PartsKKS-No. DesignationMBA33 Water drainMBA80 CompressorMBA81 Compressor blow-off systemMBA81 AA011 Blow-off valve, pressure stage 1MBA81 AA011H Limit switch, "Open"MBA81 AA011L Limit switch, "Closed"MBA81 AA011M Limit switch, "Closed"MBA81 AA012 Blow-off valve, pressure stage 1MBA81 AA012H Limit switch, "Open"MBA81 AA012L Limit switch, "Closed"MBA81 AA012M Limit switch, "Closed"MBA81 AA021 Blow-off valve, pressure stage 2MBA81 AA021H Limit switch, "Open"MBA81 AA021L Limit switch, "Closed"MBA81 AA021M Limit switch, "Closed"MBA81 AA031 Blow-off valve, pressure stage 3MBA81 AA031A Solenoid pilot valve, stage 3MBA81 AA031H Limit switch, "Open"MBA81 AA031L Limit switch, "Closed"MBA81 AA031M Limit switch, "Closed"MBA81 AA031R Measuring of blow-off valve positionMBA81 BS001 SilencerMBX35 Control air supplyMBX36 Control air SystemMBX37 Control air SystemMBX42 Hydraulic safety systemMBX48 Control oil system for blow-off valvesMBX48 AA001 Pilot valve for MBX69 AA001MBX48 AA002 Pilot valve for MBX69 AA002MBX48 AA011 Non-return valveMBX48 AA012 Non-return valveMBX48 BP010 OrificeMBX48 BP011 OrificeMBX69 Control air system for blow-off valvesMBX69 AA001 Safety relay, pressure stage 1MBX69 AA002 Safety relay, pressure stage 2

GT8C2

en HTCT 690 558 Var. 52 A 7

MBX69 AA004 Shut-off cockMBX69 AA005 Shut-off cockMBX69 AA006 Shut-off cockMBX69 AA007 Shut-off cockMBX69 AA011 Solenoid valveMBX69 AA012 Two-way valveMBA69 AA012A Solenoid valveMBA69 AA012H Limit switch OpenMBX69 AA013 Non-return valveMBX69 AC002 Air coolerMBX69 AT001 FilterMBX69 AT002 FilterMBX69 AT003 Condensate trapMBX69 BP001 Feed orifice for MBX69 AA001MBX69 BP002 Feed orifice for MBX69 AA002MBX69 CP001 Pressure measurement, control air, blow-off stage 1MBX69 CP002 Pressure measurement, control air, blow-off stage 2MBX69 DP001 Pressure reducing valve for stage 1MBX69 DP002 Pressure reducing valve for stage 2

GT8C2

8 HTCT 690 558 Var. 52 A en

Blank page