VIEWS: 10,425 PAGES: 32

Elements of the turbine governing
As with any conventional control system, a
  turbine governing system comprises three
  basic components:
• The setpoint controller,
• the actuator or actuators, and
• the controlled process.

                                SETPOINT CONTROL       CONTROL LOOP
   INPUT PROCESSING             CAM, AUTO                     FEED BACK
  FROM GEN FREQUENCY                                          RUNNER BLADE POSITION
                                    GOVERNOR STATUS               GOVERNOR OK
                                    MONITORING,FUZZY LOGIC BASED
                                    HEALTH MONITORING, GENERAL
  AUTO-SYNCHRONISER                                               CONTROL OUTPUTS
                                    PURPOSE CONTROL LOGIC
 GOVERNOR CONTROL LOGIC I/P                                        STATUS IND.
                                    DISPLAY PROCESSING AND SCADA
                                    COMMUNICATION INTERFACE.
                                                              SCADA COMMUNICATION &
                                                              PROGRAMMING INTERFACE
 GENERATOR FREQUENCY                                    AVR ‘’ON’’ COMMAND
                                      MODULE           VOLTAGE LOWER PULSE TO AVR
 PHASE ANGLE                                            VOLTAGE RAISE PULSE TO AVR
           Setpoint controller

• The setpoint controller portion of the turbine
  governing system determines the basic operating
  function of the hydroelectric generating unit.
• The operating parameters and controller strategy
  used in the setpoint controller determine what
  conditions the turbine governing system responds
  to, and what action is taken by the turbine
  governing system.
                 PID control
• A common computing algorithm is the PID. Speed
  or power errors, or both, are inputs to a typical
  PIDgovernor on a hydroelectric unit.
• The PID gains should be independently adjustable
  to achieve the desired dynamic performance.
• There     are     several   possible    structural
  implementations of the basic PID control
  algorithm that have been used in hydroelectric
  turbine governing systems.
• An actuator is the connection between the setpoint
  controller and the controlled process. The output or the
• actuator should be able to effect a change in the
  controlled variable of the process.
• Most controlled variables related to the control of a
  hydroelectric generating unit require the mechanical
  positioning of the controlledvariable, such as the wicket
  gates or turbine blades
• The actuator system compares the desired turbine
  actuator position command or setpoint with the actual
  actuator position, and it provides the necessary work to
  hold the actuator output at the desired value.
                   Controlled process
•   The hydroelectric generating plant consists of four basic elements that are
    necessary to generate power from
•   water: a means of creating head, a conduit to convey water, a hydraulic
    turbine, and an electric generator.
•   The dam creates the operating head necessary to move the turbines,
    establishes the amount of water storage available for power production, and
    impounds the water supply necessary for the daily or seasonal stream flow
    release pattern.
•   The turbine governing system controls the operation of the hydraulic turbine
    to achieve the desired operating results.
•   The water levels, water flow rate, turbine speed, generator output frequency,
    and generator output power are parameters that are affected by the operation of
    the turbine governing system.
•   The design of the turbine governing system determines which of these
    parameters has the highest priority in the operation of the hydroelectric
• The turbine converts the potential energy of water into
  mechanical energy, which in turn drives the generator.
• Water under pressure enters the turbine through the
  wicket gates and is discharged through the draft tube
  after its energy is extracted.
• The amount of power the turbine is able to produce
  depends on the head on the turbine, the rate of flow of
  water passing through the unit, and the efficiency of
  the turbine.
• Modern turbines can develop power from almost any
  combination of head and flow. .

• The generator converts the mechanical power
  produced by the turbine into electrical power.
• Generator interaction with the power system
  can be complex, and it can result in lightly
  damped response poles that can be stimulated
  by fast governor action, producing undesirable
  power oscillations.
             Water passage
• Water is the medium through which energy is delivered
  to a hydroelectric turbine for the purpose of
  generating electric power.
• Often, there are constraints placed on water levels,
  flows, or pressures that require certain elements of the
  water-handling system to be included within the
  boundaries of the “controlled process” for the turbine
  governing system.
• Brief descriptions of the main elements of the water
  system for a hydroelectric generating unit follow:
                 Head pond
• The head pond is the water impoundment used as
  an energy source for the hydroelectric unit. Some
  stations may have a very large storage capacity,
  and others may have essentially no storage
• The size of the head pond storage affects the rate
  at which the hydroelectric generating unit can
  affect the head pond water level. The head pond
  may also be called the reservoir, forebay,
  headrace, headwater, or the pool elevation.
          Water CHANNEL
• The water CHANNEL comprises all of the
  structures used to convey water from the head
  pond to the turbine.
• The water CHANNEL may include an intake
  structure, a penstock, one or more surge tanks, and
  a spiral case.
• The composite water CHANNEL inertias and
  elasticity of these structures contribute to the
  water hammer effect that impacts the performance
  of the turbine governing system.
                   Draft tube

• The draft tube conveys the water from the
  discharge side of the turbine to the tailrace. It is
  normally a part of the powerhouse structure, and it
  is designed to minimize exit losses.
• The inertia of the water in the draft tube also
  contributes to the total water inertia that impacts
  the performance of the turbine governing system.
  In some applications, this effect is significant.
            Shutdown control

• Historically, protective shutdown of the unit has
  commonly been accomplished by using the
  primary turbine governing control actuator.
• Typically, a shutdown valve, either solenoid
  operated or mechanically operated, is used to
  override the turbine control actuator’s control
  valve and force the primary turbine control
  servomotor to close at its maximum rate
            Speed sensor source
• The rotating speed of the turbine is detected by the turbine
  governing system in order for the system to respond to
  changes in speed.
• methods used to detecting turbine speed are
• Mechanical speed sensing
• Direct connection
• Mechanically coupled connection
• Motor-driven ballhead
• Electronic speed sensing
• Speed signal generator
• Shaft-mounted speed source
   Speed signal generator (SSG)
• An SSG consists of a gear or toothed wheel that is
  mechanically coupled to the turbine or generator
• Passive magnetic pickups or active proximity
  pickups sense the passage of the SSG gear teeth to
  produce a frequency that is proportional to the
  speed of the turbine.
• Active proximity pickups are able to sense the
  rotational speed down to zero speed, making this
  approach usable for a full range of speed switch
  functions including creep detection.
       Automatic shutdown
• Automatic shutdown is the process of stopping the
  unit under normal conditions.
• A typical automatic shutdown closes the turbine
  control servomotor at a controlled rate until the
  unit generation is approximately zero set value .
  At that time, the unit breaker is tripped and the
  turbine control servomotors are fully closed.
• The operation of field breakers, excitation
  systems, and other auxiliary systems are also
  included in the automatic shutdown process.
     Emergency stop pushbutton

• Generally, emergency stop pushbuttons are located
  strategically at major system components such as at the
  unit breaker, the governor control panel, and the unit
  control board.
• When an emergency stop is initiated, the unit is
  generally shut down by opening the unit breaker,
  closing the turbine control servomotors at their
  maximum rate, removing excitation, and shutting down
  all auxiliary systems.
   Generator air braking system

• The generator air braking system may
  consist of a dedicated air compressor,
  pressure vessel, piping, brake/ jacking
  cylinders, and pressure monitoring devices.
• Devices located with the turbine governing
  system may operate the air braking system,
  or it may be operated by other parts of the
  unit control system.
         Startup blade position
• The blades may be prepositioned to a steeper off-
  cam position for startup of the turbine. This
  provides greater developed torque for a faster
  breakaway. This steeper angle also results in less
  loading of the unit’s thrust bearing on startup.
• After synchronizing to the power system, the
  blades return to their on-cam position, which
  results in some increase of power output of the
  generator. This automatic pickup of generation
  after synchronization helps to avoid problems with
  reverse-power protective relaying on the unit.
Hydraulic pressure supply system

• The hydraulic pressure supply system also
  called Oil pressure unit ( OPU) uses
  various oil pressures and levels to control
  the pressure pumps, issue alarms, and to
  shut down the unit under abnormal
           Black start capability

• In certain applications, a unit will be required to
  perform a “black start,” which requires the ability to
  start the unit without any AC power available to the
  unit. Often, where black start capability is required, a
  DC-powered oil pressure pump is provided to produce
  sufficient hydraulic oil pressure to start the unit.
• This DC-powered oil pressure pump uses the station
  battery system for operating power. Generally, the flow
  output from this DC-powered oil pressure pump is not
  required to produce the oil flow specified for the main
  AC-powered oil pressure pumps.
           Black start capability
• For black start capability, it is only necessary to be
  able to build sufficient oil pressure to start the unit
  within a specified time frame.
• Therefore, a unit with a separate oil pressure pump
  used to build oil pressure for a black start may
  have an output flow of one-fourth or less of the
  flow produced by the main Ac powered pumps.
• After a black start, the main AC-powered oil
  pressure pumps are usually powered by the output
  of the generator just started, thus allowing
  continued normal operation of the unit.
     Oil cleanliness control
Initial component cleanliness
• The initial cleanliness of the components used in
  the hydraulic turbine control servomotor system is
  one of the most important influences in
  establishing the desired degree of oil system
• During the installation of the hydraulic system
  components, it is important to mechanically clean
  all system components prior to final installation.
         Overspeed switch
• Historically, the preferred method of detecting
  unit overspeed for protective shutdown of the unit
  has been
• the use of a mechanically driven speed switch.
  Mechanically driven overspeed switches have
  been specified
• for the purpose of achieving highly reliable
  overspeed detection for this protective function.
 Electronic switch using magnetic
        or optical pickups

• Magnetic or optical pickups normally sense
  the speed of the turbine shaft from the
  frequency produced by the passage of the
  teeth, slots, or optical stripes on a device
  that is mechanically coupled to the turbine
  or generator shaft.
              Speed switches
• Speed switches are devices used to operate an
  electrical contact as a function of the unit speed.
• Speed switches may be driven mechanically from
  the turbine shaft, or they may be driven
  electrically from a speed probe sensing the
  passage of the teeth of a gear or toothed wheel.
• Speed switch functions may also be derived from
  sensing the frequency of the generator voltage
             Remote control
• The term “remote control” can have several
  meanings in the hydroelectric generating
  industry. One common usage of the term
  “remote control” refers to control of the unit
  from a point within the powerhouse that is
  physically removed from the turbine
  governing system. issued from the plant
  controller to the unit control system.
              Remote control

• Some typical functions within the turbine governing
  system that are controlled remotely are as follows:
• a) Speed reference (speed changer)
• b) Generation setpoint (load changer)
• c) Servomotor limit
• d) Permanent speed droop
• e) Speed regulation
• f) Automatic generator braking system
• g) Governor gain settings
             Remote indication

• The turbine governing system may provide electrical
  outputs signals to drive remote-indicating instruments
  to indicate operating conditions of the unit.
• Some typical remote indication outputs that may be
  provided by a turbine governing system are as follows:

To top