System to control axial thrust loads for steam turbines

In a steam turbine (T) having a low pressure section (LP), an intermediate section (IP), and a high pressure section (HP), a thrust bearing (B) being positioned between the high pressure section and the low and intermediate pressure sections, apparatus (10) for dynamically controlling a resultant net thrust of the turbine (T) caused by changes in the operating condition of the turbine so to maintain the net thrust within a predetermined acceptable range of thrust, the apparatus comprising:

• sensing means (14) continuously sensing loads on the thrust bearing;
• valve means (CV1-CV3) for balancing pressures between locations within at least one of the sections of the turbine;
• and,
• control means responsive to the sensing means sensing a change within the turbine indicative of a change in net thrust which exceeds a predetermined limit to activate the valve means and, using only internal pressure within the turbine, balance the pressure within the section of the turbine so to maintain net thrust within the acceptable range and prevent damage to the turbine.

A method of dynamically controlling the net thrust within a steam turbine (T) comprising:

• continuously measuring the loads on opposite sides of a thrust bearing (B) on one side of which are located low and intermediate pressure sections (LP, IP) of the turbine and on the other side of which is a high pressure section (HP) of the turbine;
• calculating changes in the thrust load of the turbine between two points in times;
• determining if any calculated change in thrust load exceeds a predetermined limit the result of which will cause the net thrust to move outside of a range of acceptable net thrust;
• and,
• activating a control valve (CV) in at least one section of the turbine to timely balance pressures within that section using only internal pressure within the turbine, balancing of the pressures maintaining the net thrust within the acceptable range and preventing damage to the turbine.

Apparatus (10) for controlling net thrust in a steam turbine (T) in response to changes in the operating condition of the turbine, the turbine including a thrust bearing (B) positioned between low and intermediate pressure sections (LP, IP) of the turbine and a high pressure section (HP) thereof, the apparatus comprising:

• sensing means (14) continuously sensing loads on the thrust bearing;
• valve means (CV1-CV4) for balancing pressures between locations within the high pressure section of the turbine;
• control means responsive to the sensing means sensing a change within the turbine indicative of a significant change in net thrust to activate the valve means to adjust the pressure within the high pressure section of the turbine and maintain the net thrust within a predetermined range of thrust and prevent damage to the turbine;
• and,
• the high pressure section of the turbine including a balance position an a control valve (CV4) of the valve means having its pressure inlet on the upstream side of the balance piston and its pressure outlet on the downstream side thereof, thereby to balance the pressure across the piston when the control valve is activated.

Apparatus (10) for controlling net thrust in a steam turbine (T) in response to changes in the operating condition of the turbine, the turbine including a thrust bearing (B) positioned between low and intermediate pressure sections (LP, IP) of the turbine and a high pressure section (HP) thereof, the apparatus comprising:

• sensing means (14) continuously sensing loads on the thrust bearing and including a load sensor (14) located on opposite sides of the thrust bearing;
• valve means (CV1-CV3) for balancing pressures between locations within the high pressure section of the turbine and including a plurality of control valves each of which has a pressure inlet and a pressure outlet, the control valve inlet being connected to a higher pressure region of the high pressure section of the turbine than the outlet of the control valve;
• and,
• control means responsive to an output from each load sensor sensing a change within the turbine indicative of a significant change in net thrust to activate the valve means to adjust the pressure within the high pressure section of the turbine and maintain the net thrust within a predetermined range of thrust and prevent damage to the turbine.

In a steam turbine (T) having a low pressure section (LP) an intermediate section (IP), and a high pressure section (HP), a thrust bearing (B) being positioned between the high pressure section and the low and intermediate pressure sections, apparatus (10) for dynamically controlling a resultant net thrust of the turbine (T) caused by changes in the operating condition of the turbine so to maintain the net thrust within a predetermined acceptable range of thrust, the apparatus comprising:

• sensing means (14) continuously sensing loads on the thrust bearing;
• valve means (CV1-CV4) for balancing pressures between locations within at least one of the sections of the turbine;
• a packing for sealing the section against steam flow and including packing elements located at intervals along the length of the section, with control valves (CV1-CV3) of the valve means balancing the pressure on both sides of a packing element;
• control means responsive to the sensing means sensing a change within the turbine indicative of a change in net thrust which exceeds a predetermined limit to activate the valve means and balance the pressure within the section of the turbine so to maintain net thrust within the acceptable range and prevent damage to the turbine;
• and,
• a balance position (P) installed in the section with a control valve (CV4) of the valve means having its pressure inlet on the upstream side of the balance piston and its pressure outlet on the downstream side thereof, thereby to balance the pressure across the piston when the control valve is activated.