Overview of Jacking oil system:

Purpose:

The jacking oil system performs the following purposes:

•  Prevents metal to metal contact in the journal bearings by producing a hydrostatic oil film when the rotational shaft speed is too low to create a continuous hydrodynamic oil film.
•  Reduces the break away torque during run-up of the steam turbine rotor.

Function:

 This is reached by the following functions:

• Generates jacking oil pressure and flow.
• Guides and distributes jacking oil to the steam turbine journal bearings. 
• Drains the jacking oil into the bearing pedestal

Components:

 The following components are needed as a minimum:

• Jacking oil pump

• Pressure limiting valve

• Flow control valves

• Forwarding and distribution piping

• Lube oil tank

Principle:

1.The jacking oil system protects the turbines journal bearings during start-up and shut-down. The shaft of the steam turbine rests on the journal bearings.

2.Before the shaft is turned, jacking oil is supplied to the bearings to lift the shaft so that it floats on an oil film rather than on the metal surface of the bearings.

3.The jacking oil pump supplies the jacking oil system. This pump is an axial piston type, which is located on the lube oil tank. The Lube oil system feeds the jacking oil pump from downstream of the lube oil filter. A common AC motor drives both the jacking oil and turning gear pump

 

4.A pressure limiting valve maintains the pressure in the jacking oil system in accordance with the operating data. The oil passes through a flow control valve before entering each bearing. It drains into the bearing pedestal and flows back to the lube oil tank through the drain pipe lines, together with lube oil returning from the lube oil system.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hydrostatic Turning Gear :

Purpose:

 The turning gear system performs the following functions:

• Continuously turns the rotor at low speed before start up and after shut-down.
• Ventilation, caused by the blades, prevents bending due to temperature differences between top and bottom, caused by natural convection after stand still of the hot turbine. 
• Avoids the rubbing of blading and seal strips due to rotor bending during restart.

Function:

This is reached by the following functions:

•  Pressure generation (motor / hand)
• Pressure control
• Engaging / disengaging of turning gear
• Turning of rotor
• Hydraulic control

Components:

 Therefore the following components are needed as a minimum:

• Turning gear pump
• Hydro motor with drive pinion
• Sliding piston
• Control solenoid valves (creep speed, rotary, engaging) 
•  Pressure control and reducing valves
• Hand pump

System Description:

 

1.The turning gear system rotates the turbine shaft so that it will not bend, due to uneven temperature distribution. The lube oil supply downstream of the lube oil filter feeds the turning gear pump, which is driven by the same AC-Motor that drives the jacking oil pump.

2.The turning gear pump is an axial piston type, which is located on the lube oil tank. Oil that is discharged from the pump is guided to the common turning gear housing, which consists of an axial movable drive pinion, a coupled radial piston motor and a control block.

3.To engage the drive pinion, a solenoid valve is activated, which exerts lube oil pressure on the piston of the drive pinion.

4.The piston moves axially against a spring force in the direction of the gear rim on the turbine shaft. At the same time, creep speed operation of the radial piston motor is started by the force from the pressure reduced oil from the turning gear pump to assure engagement of the drive pinion.

After engagement, controlled by a limit switch, the full pressure from the turning gear pump is supplied to the radial piston motor turning the shaft with full turning gear speed.

Then the engagement solenoid valve is switched off, the turning gear remains engaged by the positive torque of hydraulic motor.

Two solenoid valves, one for creep speed and the other for full speed, control the turning gear oil supply.

For disengagement, the normal speed solenoid valve is switched off, the torque becomes negative (speed of steam turbine > speed of hydraulic motor) and the pinion wheel is driven out of engagement by the action of the helicoil spline on the shaft. Finally a spring forces the wheel out off the engagement and fully home into the opening of the engagement cylinder.

Operation and Supervision:

The jacking oil system and the turning gear system belong to the same function group controller. The turning gear pump and the jacking oil pump are driven by one common AC motor. Turning gear operation without jacking oil switched on is not allowed, because the bearings can be damaged due to insufficient lubrication. Therefore the operation of both systems is described here together.

The operation is fully described in the operation manual, which should be read carefully. Nevertheless, the most important facts are listed in this section.

Operating Method:

The system may be operated using the following methods:

• Manual operation from the control room via operator station and function group controller.

• Automatic operation by automatic start-up and shut-down sequencer.

　

Normally the system will be operated using the automatic sequencer. However, during system checks, routine maintenance or maintenance the system has to be operated manually.

System start up sequence:

Before any operation may take place, the following systems have to be in operation:

• Lube oil cooling system, i.e. closed cooling water system.

• Lube oil system.

Start up procedure:

before start-up, the steam turbine must be on turning gear for the following periods of time!

Shaft standstill Minimum turning time

less than 1 day 2 hours

up to 7 days 6 hours

7 - 30 days 12 hours

more than 30 days 24 hours

• In case the above mentioned times can not be met, the turbo group should be operated in a speed range of 550 - 600 rpm for approximately 20 minutes.

• First the jacking oil system is started, then the turning gear system must be engaged manually.

• Before the turning gear system is put into operation, the rotor must be rotated manually with the hand pump. This is to ensure free movement.

• The turning gear system is automatically switched-off if the speed is above a certain value.

• The jacking oil pump is switched-off at approximately 90 % speed.

Supervision:

During start-up the following has to be supervised:

• Jacking oil & turning gear pump motor switches-on.

• Turning gear engages.

• Turbine shaft speed is equal to turning gear speed.

• The jacking oil pump switches-off above 90 % steam turbine shaft speed.

Normal operation:

During normal operation the jacking oil and turning gear pumps are shut-down, i.e. the systems are "not in operation". However, the function group is active (on automatic) and will switch-on both pumps when needed.

Supervision:

During normal operation the following has to be supervised:

• Function group on "automatic".

• Jacking oil & turning gear pump motor is switched-off.

Shut down:

• The jacking oil pump starts at 90 % below full speed.

• The turning gear is engaged if the turbine speed is below 4 rpm.

• The turning gear operation is switched off, if the turbine metal temperature falls below a certain value.

Supervision:

During shut-down the following has to be supervised:

• Jacking oil pump is starting.

• Turning gear is engaged if turbine speed is less than 4 rpm.

• Turbine speed equal to turning gear speed when the turning gear is engaged.

Emergency Operation:

Automatic operation failure:

1.If the automatic turning gear operation does not work, the shaft has to be turned manually:

• Check if the lube oil system and jacking oil system is in service.

• Push the jog push button on the local panel to engage the gear and turn the turbine shaft manually with the hand pump.

• Turn the shaft by 180° as follows.

• Every 5 min. during the first 2 hours.

• Every 10 min. during the next 10 hours.

• Every 30 min. until the turbine metal temperature is low enough to switch off.

• Do not use excessive force to turn the shaft as this can cause serious damage. Instead, check for proper shaft lift and engaging of the turning gear. If the shaft will not turn, wait until the unit is cold and try again. If it still does not move, investigate the cause.

2.In case of an emergency the turning gear system may be switched-off for a maximum of 15 minutes after one day and 30 minutes after 2 days steam turbine shut-down. However, the vacuum in the condenser must be broken and the gland steam system switched-off.

AC power loss:

In case of an AC loss the steam turbine will trip. In order to safely run-out the turbine shaft, jacking oil is needed. Typically the following solutions are used:

• Stand-by jacking oil pump unit driven by a DC motor dedicated for run-out and consequent rotor turning for cool down.

• Emergency diesel generator to cover all essential power users to safely shut-down the plant. This solution requires no DC- backup jacking oil pump.