STEAM TURBINE OPERATION

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Steam turbines are started based on operating instructions which is developed by original equipment manufacturer.

Start-up includes a sequence of actions followed as according to various parameters.

During start-up of turbine maintaining the limit values of operating parameters.

Start-up of turbine is a complicated operation as it consists of starting of various equipment and auxiliary systems.

Turbine start up is a transient & non-stationary actions like,

  • Transient heating
  • Varying steam flows
  • Acceleration of rotors

Three basic phases can be distinguished in the process of steam turbine unit

Turbine preparation to start-up,
Running-up to idle run and synchronization,   
Loading.

o   Turbine to start-up begins with turning gear or barring gear.

o   The turning gear operated by electric (electric turning gear)  or hydraulic (hydraulic turning gear) 

o   Before start up of turbine it is thermally stablished

o   its deflection line must coincide with the gravity deflection line.

o   Rotor cooling down during standstill would be leading to its thermal bent due to faster cooling from the bottom, which would lead to rubbing and damage of labyrinth seals of blades & shaft.

o   Prior to cold start, the turbo-set rotating system should be rotated using turning gear as long as possible.

o   The turning gear can be switched off only when the highest temperature of HP & intermediate pressure (IP) inner casing is lower than 100⁰C.

o   If needed, the turning gear can be switched off for 15 min after a day of barring, and after 2 days of barring – for about 30 min on the condition that vacuum is broken and gland steam supply is switched off.

o   The maximum time of turning gear standstill depends of the type of turbine.

o   Prior to repeated switch on of the turning gear, turbine rotor must be manually turned by one revolution in order to check if rubbing has not taken place. If rubbing is found it is necessary to wait until the rotor rotates freely and only then the turning gear can be repeatedly switched on.

  • Before starting of barring gear turbine lub oil system should be started.
  • The turning gear can be switched on only when all jacking oil pumps are in operation.
  • After starting the oil system and turning gear, the condensation system can be started, that is cooling water, air ejection and condensate pumping systems.
  • Simultaneously, gland steam system is started to prevent air in-leakage.
  • Gland steam must have appropriate temperature and pressure which must be controlled during start-up.
  • Prior to supplying steam to the turbine, the steam supply pipelines have to be drained and heated up.
  • In case of turbines with cooling water preheating and low-pressure (LP) bypass, prior to supplying steam the regeneration and dumping systems have to be started.

Run-up to idle run and synchronization

One can distinguish three major types of start-ups:
• From a cold state – when HP and IP inner casing temperature is lower or equal 170C,
• From a warm start – when HP and IP inner casing temperature is lower or equal 430C,
• From a hot state – when HP and IP inner casing temperature is greater than 430C. 

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