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What is the purpose of the Bulk Electric System in BC?
To transfer power from large remote generating stations to the load centers in the Lower Mainland and Vancouver Island
What is the responsibility of the Generation Coordinator?
- -The overall operation of the generation portfolio to meet reliability requirements
- -More focused on the ‘Big 7’ generating stations
- -operation of the Automatic Generation Control (AGC)
What is the responsibility of the Plant Operator?
- -Supports the GC
- The 24x7 monitoring and control(starting, stopping, load control) of BCHydro generating facilities (except GMS & PCN)
What is PSOSE short for? What is the responsibility of PSOSE?
- -Power Supply Operations and Support Engineers
- -PSOSE is responsible for operating the generation system from an economics point of view
What is the Operating Responsibility and Operating Authority of the Plant Operator
- Operating Responsibility:-All water conveyance equipment
- -All generation equipment covered under WPP with a generation capacity LESS than 100 MW
- -All dispatchable IPPs (ALH, ICG)
- Operating Authority:NO Operating Authority is delegated to the Plant Desk
What does the term “head” mean?
The difference in height of the water between the surface of the reservoir(top) and the surface of the tailrace
Describe a storage type dam
- The intake(top of penstock) is well below the surface of the reservoir.
- The reservoir level may fluctuate quite a lot without significant affect to power production.
- The reservoir is allowed to fill during freshet and stores the water
Describe a run-of-the-river type dam
- There is little or no water storage on this dam type.
- Plant output relies on seasonal river flow or output of another upstream Dam.
- This Dam type may not be able to run year round when water flows are low
Describe a diversion type dam
- Changes the course or flow of a river or stream for the benefit of another dam.
- Diverts water behind a run-of-river or storage dam with a generation facility.
What is a reservoir
The body of stored water that is created by the construction of a dam
What is a tailrace
The section of riverbed that is immediately downstream of the turbine discharge(draft tube)
What does the term Power Release Facility mean
All the equipment involved in the power generation aspect of a hydro-electric generator
What does the term Non-Power Release Facility mean (NPRF)
All the equipment involved in moving water through/past the dam that are not power generation related
What is an Intake Gate? Where is it typically installed
- -The gate that blocks/ allows water from entering the penstock.
- -Located at the top of the penstock
- -Used to control the flow of water into the penstock during normal operation.
- -This gate must be set at and remain greater than 90% open during normal operation.
- -It is raised and lowered by hydraulic operation
Explain the purpose and function of the bubbler system
- -In freezing climates where ice build up is an issue, a bubbler system is employed to reduce the amount of icing.
- -Compressed air is forced through a perforated tube creating turbulence in the water, thus preventing freezing around the intake gates
What is a Trashrack? Where is it typically installed?
A metal grid/rack for blocking large debris from entering penstock. Located at the open end of the intake structure in reservoir forebay
What is a Penstock? Where is it typically installed?
Large tube/pipe structure used to deliver water from the intake structure to the scroll case of turbine
What is a Surge Tower? Where is it typically installed?
- Large tower in the reservoir, (connected to penstock), that is above the height of the reservoir
- Ensures penstock not affected by water hammering or surging through ventilation
- Surge tower is open to the atmosphere at the top, which allows air to freely escape or fill the penstock when it is being filled or drained.
- This air must be allowed to escape or fill, otherwise it will become pressured or negative pressured in the penstock causing damage in the headworks or penstock itself
What is a Scroll Case? Where is it typically installed?
- A snail-like looking structure that ensures equal pressure of water on all portions of the runner. Located at the bottom of penstock
- Provides even water flow into the turbine from all sides. The snail shaped spiral winds around the turbine inlet and decreases the diameter of the penstock
Explain the purpose and function of the stay vanes
- Used to direct the water at the correct angle towards the wicket gates.
- They are permanently welded to the Stay Rings
What is a Wicket Gate? Where is it typically installed?
Controls the flow of water into the turbine. Located at end of scrollcase right before turbine
What is a Turbine? Where is it typically installed?
The 'runner' that spins and converts kinetic energy to mechanical energy. Located at bottom of penstock after scrollcase
What is a Draft Tube? Where is it typically installed?
- The tube that directs water to flow back to the river(tailrace).
- Located right after the turbine runner
- The second purpose of the draft tube is to act as a suction head(or negative pressure) on the runner blades, increasing the turbine’s efficiency
What is the energy transfer process that occurs in the production of electricity in a hydro-electric generator?
- Potential Energy: the stored water behind the dam, or water that is upstream at a greater elevation, possesses potential energy
- Kinetic Energy: as the force of gravity pulls water downstream or through a penstock, the velocity of the water creates pressure which spins the turbine
- Mechanical Energy: the kinetic energy of the water creating the spinning action of the turbine is converted to mechanical energy
- Electrical Energy: the mechanical energy of the turbine rotates a shaft that also spins the rotor magnets which induces electrical energy on the stator coils
What two factors dictate the amount of power a hydro-electric generating unit can output
- Water pressure acting on turbine: The amount of head (elevation difference from reservoir to tailrace)
- The volume of water stored or available
What are the two main types of turbines? Describe the principle of operation of each
- Impulse Turbines: All of their rotational energy is derived from the velocity of the water
- Reaction Turbines: Their rotational energy is derived from the velocity of the water AND
- the pressure drop across the blades(pressure differential)
Which type of reaction type runner is used for medium head plants? Describe how it uses water to create rotational energy on the turbine shaft?
- Francis Reaction Type Turbine:
- -The velocity of the water through the scroll case is directed through the wicket gates
- -As the water exits the runner through the draft tube, negative pressure is created to further increase rotational energy and efficiency
Which type of reaction type runner is used for low head plants? Describe how it uses water to create rotational energy on the turbine shaft?
- Propeller Type Reaction Turbine(Kaplan):
- - Guide Vanes give the water a circular motion as it enters the runner
- - The Kaplan Style runners are designed with adjustable blades to maintain efficiency as load drops
Which type of impulse type runner is used for high head plants? Describe how it uses water to create rotational energy on the turbine shaft?
- Pelton Type Impulse Runner
- - Several nozzles at the bottom of the penstock strike bowl shaped buckets on the runner. This jet of high velocity water spins the turbine
- -The water is discharged to the atmosphere inside the runner housing
What are the three types of runners used based on height of head
- High Head: Pelton Type Runner Impulse Turbine
- Medium Head: Francis Type Runner Reaction Turbine
- Low Head: Propeller Type Runner (Kaplan) Reaction Turbine
What is the purpose of the Turbine Guide Bearing and Generator Guide Bearing
-Keeps the rotating shaft in proper POSITION
What type of machines does BC Hydro use for the majority of their energy production and why
- Large three-phase AC synchronous machines
- These machines are used as they can produce both real(active) and reactive power
In principle, how is an alternating current waveform generated by a hydro-electric generator
- A DC current is applied to the field windings on the rotor.
- The DC current produces a magnetic field around the rotor.
- As the rotor turns, it induces a voltage on the stator.
- The voltage on the stator causes current to flow out of each stator winding
What are the two types of rotors? Which are used on hydro-electric generators and why
- Cylindrical Rotors
- –mostly in thermal applications
- Salient Pole Rotors
- –normally designed to rotate on a vertical axis
- -designed to act as a magnet with north and south poles to carry DC current
- -are designed to run at slower speeds by increasing the number of poles
What formula represents the relationship between speed and frequency on a hydro-electric generating unit?
RPM = 120 x frequency/Poles
In which component, the rotor or the stator, is the alternating current waveform induced
AC waveform induced in the STATOR
To get a 3 phase alternating current, the stator windings are spaced ___ degrees apart.
What is the purpose of bearings in a hydro-electric generator
- To support the enormous weights of the generators and turbine runners against gravity
- To support the enormous forces imposed by dynamic forces of rotation
What is the Lift Pump
Used to supply lubricating oil between the thrust pad and collar during startups and shutdowns to prevent damage
What is the purpose of delivering cooling water to generator components?
Components must be protected from excess heat for efficient operation, reduced wear and protection of sealing surfaces
What is the purpose of the unit circuit breaker
- -Protects the generator from load and fault current originating from the BES
- -synchronizes the generator to the rest of the Bulk Electrical System
What is the purpose of the generator isolation disconnect
This is the Isolation point when isolation is required for the generator only
What is the purpose of the iso-phase bus
Isolates each phase conductor leaving the stator by enclosing it in a metal enclosure (insulated from conductor)
What is the purpose of the synchronizing and protection VTs
- -stepping down voltage for metering and protection
- -stepping down voltage for synchronizing the generator to the BES
What is the purpose of the surge arresters
Protects the system from over-voltages by diverting the high voltages to ground
What sources can generating stations get their AC station service from
- -from the operating generators at the powerplant through Station Service Transformers
- -from Tertiary windings of main transformers
- -from a line feeding in from another station
- -from a standby generator powered by diesel engine
- -from a DC Battery Bank
Why do substations have DC station service
Some station service equipment is designed to run on DC (normally by AC via a rectifier)
Where are the service transformers located in a station with a generator bus
Between the Generator Bus and the Station Service buses
Where are the service transformers located in a station without a generator bus
Between the Stepped-up Transmission Voltage and the Station Service buses
What is the purpose of the thrust and guide bearings in a hydro-electric generator
- Thrust Bearings: supports the weight (static loading) and turbine hydraulic thrust
- Guide Bearings: keeps the rotating shaft in position
When does the Lift Pump start and when does it stop during both startups and shutdowns of hydro-electric units?
- The pump is started before the wicket gates are opened
- The pump is stopped when rotor speed reaches 90%
- -The pump automatically starts when rotor speed drops below 90%
- -The pump stops when the unit is completely stopped, or may even run longer to cool surfaces
- -The pump will automatically start if creep is detected
What is the purpose of the braking system? When does the braking system come on during a shutdown of a hydro-electric unit?
- To bring a generator unit to a complete stop as quickly as possible after a shutdown
- The brakes are applied when:
- -the generator CB is open
- -the turbine wicket gates are fully closed
- -the generator unit has decelerated to a preset speed(maybe 25%)
What is the purpose of the generator cooling equipment
To dissipate heat away from the generator, rotor and bearings
What is the IEEE definition of what a governor system is?
In essence what does this mean for hydro-electric unit operation?
- -The combination of devices and mechanisms which detect speed deviation and convert it into a change in servomotor position.
- -When the unit changes speed, there should be a corresponding change in the wicket gate position to return the unit to synchronous speed (with the rest of the system)
What are the three main subsystems of a governor system?
What is the purpose of each?
- -Control Subsystem: mechanical and electrical components that monitor the speed and power output of the system (initiate changes to waterflow when required)
- -Hydraulic Subsystem: hydraulic valves and servomotors that effect the changes to the water flow by moving wicket gates
- -Hydraulic Oil Subsystem: oil storage and delivery system that ensures adequate pressure in the hydraulic system (in order to perform its operations)
What is the primary function of the governor when the unit is NOT connected to the power system
To control the speed of the generator (the RPMs)
What is the primary function of the governor when the unit IS connected to the power system
- -To control the frequency of the electricity generated
- -To control the power output of the generator (the MW)
What is the purpose of the Wicket Gate Servomotor
The actual large hydraulic cylinders which adjust the shift ring to move the wicket gates
On what principle does the governor system operate
What is meant by Gate Position and what are the two ways it can be controlled
- Gate Position: the relative amount the gates are open between closed (0%) and the Gate Limit
- 15F: Frequency Setter: the unit is NOT synchronized to the system, and the speed of the unit can be varied by opening/closing wicket gates to match the system frequency
- 65P: Power Setter: The unit IS synchronized to the system, opening/closing of wicket gates will vary the output (MW) of the generator
What is meant by Actuator Lock
- A failure of governor control
- -Loss of MW feedback
- -Failure of speed control signal
- -Loss of DC excitation
What is meant by Actuator Lock Free
- A condition where Gate Limit is lowered to Gate Position
- The lock free limit switch (33LF) closes to establish 'Actuator Lock Free' status
- -A full open DC bias signal is placed on the pilot valve
- -wicket gates follow gate limit which allows unit to be raised and lowered (MW) using gate limit controls
In a hydro-electric generator what is the purpose of the exciter
- Controls the generators terminal voltage
- Creates the magnetic field on the rotor
- Counteracts system disturbances and dampens system oscillations
What three factors affect the voltage induced in the stator of a hydro-electric generator
- -Strength of magnetic field
- -Rate of change of the magnetic field
- -Length of the conductor exposed to the magnetic field
What is the most practical method of controlling the voltage on an AC hydro-electric generator? How is this achieved?
- -By adjusting the strength of the magnetic field
- -by controlling the DC current flowing in the excitor(the electric current flowing in the windings of the electromagnets)
What is the secondary purpose of the exciter and what components are used to provide this response?
- To counteract system disturbances:
- -Exciter: briefly increasing/decreasing terminal voltage
- -Field Windings: inductance on field windings is effective in dampening system oscillation
In general, how does a static exciter work
The exciter converts AC from the generator to a controllable DC which is fed to the field windings
What is meant by the term Field Flashing? What are the two options for Field Flashing and which is typically used?
- Providing a DC source for the purpose of starting up a generator
- -AC Source: existing AC source, such as StationServ., which is converted to DC (typically used)
- -DC Source: station Battery bank (protected by diodes from feedback)
What is the purpose of the Field Breaker
- Protects and isolates the exciter from the generator field
- (energize/ de-energize exciter)
What is the purpose of the Brushgear
- Provides the rotating connection to the field windings
- (delivers the DC current)
The Automatic Voltage Regulator has two control modes, a 70V and a 90V.
Which one is manual and what does this mean to the operator?
- 70V: Manual: Operator must make manual adjustments to excitor
- 90V: Automatic: Operator would not need to chase voltages as it fluctuates (changing power factor from connected loads)
What additional exciter facilities are there and what purpose do they serve?
- Current Limiter: limits excitation current during generator startup and over rides voltage regulator inputs to reduce the exciter output current during disturbances
- Minimum Excitation Limiter (MEL): regulates the minimum excitation level (based on magnitude and phase relationship) to prevent under-excitation and potential danger of becoming out of synchronization
- Volts/Hz Limiter (VHL): Limits excitation as frequency decreases during shutdown. Also protects unit (trips unit) from over voltage if above 60 Hz for too long
- Power System Stabilizer (PSS): receives digital data that monitors system disturbances in order to increase/ decrease exciter current (field current) to aid in damping system power oscillations
What are the three quantities that must be matched for synchronizing to take place?
- Voltage Magnitudes
- Frequency of the Voltages
- Phase Angle between the Voltages
- -A synchroscope can monitor and check all three of these variables
What is the consequence of not matching the voltage magnitude variable when synchronizing a unit
- A sudden rise in MVARs will flow (instability to area voltage)
- possible instability to incoming generator and all generators on system
What is the consequence of not matching the frequency variable when synchronizing a unit
A sudden change in MW flow
What is the consequence of not matching the phase angle variable when synchronizing a unit?
- Extreme wear on the moving mechanical parts of the incoming generator
- - the rotor will ‘snap’ into place to match the system phase angle
What is the difference between a generating station auto synchronizer and a transmission station synchronizer
- The generation synchronizer will have outputs to:
- -change the speed of the generator
- -change the exciter voltage
- -monitor the phase angle for tolerable limits to close CB when all conditions met
- The station synchronizer will simply just monitor all quantities until within tolerable limits to close CB
What is AGC?
Automatic Generation Control: automatic control system for balancing generation to load and maintaining a constant system frequency
What does AGC use as an indicator that generation and load are not in balance
ACE: Area Control Error: instantaneous (real time) calculation that represents the discrepancy between the generation supply and the total Load requirements (MW) of the Balancing Authority
Which mode of AGC is typically used by BC Hydro Balancing Authority
Tie Line Bias Control: monitors both frequency control and tie-line control
How long does a typical hydro-electric unit take to come to a complete stop following an auto stop
10 Minutes to come to a complete stop in Auto
What should be done if an auto stop incomplete sequence alarm comes in
- -Start up the Unit again
- -Call out staff to investigate
What other mode of operation are some generators capable of running in? Describe this mode of operation.
- The Generator acts as a motor on the system, drawing MW
- -this mode is useful for voltage control during light load periods (by varying MVARs)
What is the basic process for putting a shutdown unit into generate mode
- -A successful start sequence
- -Synchronization to the grid
- -The Unit CB closes
- -The unit may now generate within its capability curve
What is meant by the term “prohibited zones”?
- Prohibited Zones: generator speeds (rpms) that the unit should not operate in, and be ramped through as quickly as possible
- -rough load zones
- -cavitation zones
What is cavitation
The formation of empty cavities in a liquid by high forces and the immediate implosion of them. Rapid changes of water pressure, such as in a turbine, causes cavitation
What is meant by the “torque angle” of a hydro-electric generator
- The angular separation between the rotor's rotating magnetic field and the stator’s magnetic field.
- To increase/decrease the output of the generator, the torque angle is increased/decreased by opening/closing of the wicket gates
What is the 65P of a hydro-electric unit used for
- Governor Load Reference Setpoint:
- - controls the wicket gates for increasing/decreasing MW output
- -Unit speed can’t be appreciably increased due to the fact it is electrically synchronized to the system speed
What is meant by the term governor droop
- -The response of a generators governor to changes in system frequency can be plotted to form a curve, which when shown graphically illustrates the governors characteristic curve, or Droop Curve
- -A response 'Lag' is built in to avoid over-reacting to frequency deviation
What is meant by the term isochronous?
Do we normally operate units in isochronous?
- -Isochronous: a Governor will constantly make adjustments to its generator output in its quest to achieve a perfect 60 Hz
- -Units are not operated in this way (unless islanded)
What effect does varying the excitation have on the strength of the field on the rotor
-Increasing the strength (voltage) of the exciter increases the strength of the field of the rotor.
What does varying the field do to the MVars the unit is producing or absorbing
- -Increasing the strength of the rotor field increases the MVars the Unit is producing
- -Decreasing the strength of the rotor field decreases the MVars the Unit is producing
What net effect does varying the excitation voltage have on the terminal voltage of the machine and the station bus voltage
Varying the Exciter voltage can control the terminal voltage of the Unit in order to support system voltage on the station bus
What is meant by the term “synchronous condense” mode
- Synch-Condense mode allows the Unit to be run as a motor instead of a generator
- -'Negative' Angular Seperation in relation to Stator AC Waveform
- The Unit is on-line, spinning in synchronization, and is used for voltage control
What is the reason for admitting compressed air into the draft tube during synchronous condense mode operation
Removes the water, which reduces the load that the Motor (generator in Synch-Cond. Mode) is putting on the system
Do the MVars have to be taken off a generator before it can be put in synchronous condense mode
NO. Because the Unit will remain connected to the system
What are the two main reasons RPG is run
- -Prince Rupert area outage (loss of 2L101)
- -2L101 (or some other facility) is scheduled OOS (RPG is required to meet load requirements)
What are the special procedures for Blackstart of RPG units
- - There is a 5 minute time period from the time the Unit reaches 3550 rpm (59 Hz) to when the Unit CB is closed to restore AC station service
- -Air capacity limited to 5 start attempts
- -Battery capacity is 3 hours
- -Spectra Energy must be called to ensure an adequate Natural Gas supply
Fully explain what a Capability Curve is
- Describes graphically the various limits that a generator can operate within and maintain stability:
- MVAR (Excitation)
- Heat (Rotor Field & Stator Windings)
What are the typical prestart conditions for large Francis type turbines
- Penstock full and Intake gate open 100%
- Governor pressure and auxilliary equipment normal
- Voltage Regulator, Lift Pump, Unit Brakes, Gate Locks in 'AUTO'
- Unit in 'AUTO' & 'REMOTE' control
- All Relay Protections and speed switches normal
What are the typical Autostart conditions for large Francis type turbines
- Field Breaker, if open, will close
- Brakes are released
- Cooling water valve opens
- Lift Pump forces oil into Thrust bearing
- Gate Locks released and Governor Shutdown solenoid will 'pick up'
- Wicket gates opened to 20% snap starting the unit (BreakAway Position)
- Speed-No-Load solenoid 'picks up'
What mode does a Unit need to be in to be started from FVO
What is the basic process of putting a shutdown unit into Generate mode
- Successful Start sequence
- Synchronization to the grid
- Unit CB closes
- Unit now may generate within capability curve
What is the relationship between PSOSE and Grid Operations
- PSOSE takes an overall 'Big Picture' view
- Triple Bottom Line Objective:
- -Basepoints for Big 7 Plants provided for GC