Electricity From Wind and Power Grid Flashcards
What are the 2 types of generators and how are they different?
- Permanent Magnet Machine (PMM): Have a core of powerful magnets. When the magnets rotate around conducting wires, it creates electricity. They do not require external power supply.
*Less common in wind turbines - Induction Generators: Induction generators have an external AC electricity source from the grid that powers a rotor inside a stationary stator.
- Induction generators are widely used in wind turbines due to their simplicity.
Extra: The rotor is the moving part of an electromagnetic circuit. The stator is the stationary part of an electromagnetic circuit that is connected to the electrical grid. It contains both the rotor and a set of armature coils that encircle the rotor. The stator is supplied with an electrical current which generates a magnetic field inside the armature coils. At this stage, the generator operates as a motor and starts to drag the rotor behind it. Once the rotor begins to turn more due to the kinetic energy from the blades of a wind turbine, the magnetic field inside the stator also starts to rotate. When this occurs, the speed of the induction motor is slightly slower than the synchronous speed of the magnetic field inside the stator. This rotating magnetic field results in an alternating electromagnetic force (EMF) inside the armature coils. The fluctuating magnetic field disturbs the electrons inside the coils, causing them to switch directions continually. At this point, the machine starts to run faster than the synchronous speed of the magnetic field and begins to generate electricity. Finally, the armature coils carry the alternating current to the grid, which gets distributed through transmission lines to the electrical outlets in buildings.
What is “Capacity Factor” and how is it calculated?
Capacity factor is the percentage of full load in a year.
The capacity factor is the average power generated, divided by the rated peak power.
Example: Let’s take a five-megawatt wind turbine. If it produces power at an average of two megawatts, then its capacity factor is 40% (2÷5 = 0.40).
According to the ScienceDirect website “The capacity factor measures the overall utilization of a power generation facility or generator fleet. The capacity factor is the annual generation of a plant (or fleet of generators) divided by the product of the capacity and the number of hours in a given period. In other words, it measures the actual generation of a plant in relation to the maximum value it could generate in a given period without any interruption. As power plants sometimes operate at less than full output, the annual capacity factor is a measure of how many hours in the year the plant operated and at what percentage of its total output.”
Describe what the “Power Curve” chart for a wind turbine is and how it can be used.
X axis is Wind Speed in meters per second (m/s)
Y axis is Power in megawatts (MW)
The chart shows wind turbine’s energy generation performance during a range of wind speeds. Manufacturer power curve data can be compared to current operational data to evaluate repowering needs.
Extra
“As wind turbines age, their annual energy production decreases, and while the decrease is slight – generally accepted at about 2% per year – it can significantly extend the return on investment (ROI) period for owners. It’s important to note that even though the decrease in power is attributed to “aging,” it starts almost immediately after the turbine is installed. This is why wind turbine power curve upgrades can be so critical for long term performance (and profits). While power decreases are typical of various types of machinery, wind farm operators have technology on their side. Thanks to global studies and research collaborations, many wind turbine blade retrofit options are available to help recover lost efficiency and even improve production.”
Source: https://weatherguardwind.com/wind-turbine-power-curve-upgrades-cost/
Explain what “rated output” and “actual output” are and how they are different.
- Rated Output: The optimal wind turbine performance reported by the turbine manufacturer.
- Actual Output: Wind turbine performance in operation with mechanical and environmental factors involved.
*Variables for actual output:
- Blade length in meters
- Wind speed in meters/second
- Air density in kg/meter^{3}
- Power coefficient
- Wind direction
- The intrusion of water vapor
- Thermal expansion
- Equipment corrosion and wear and tear
What is “Nominal Voltage” and why is it important?
- “Nominal voltage is a value assigned to a circuit or system to designate its voltage class conveniently (e.g. 120/240 volts, 300 volts, 480Y/277 volts). The actual voltage at which a circuit operates can vary from the nominal voltage within a range that permits satisfactory operation of equipment.”
- Nominal voltage is used as a voltage reference to describe batteries, modules, or electrical systems. This is the supply circuit system voltage to which the unit may be connected.
The LRSC wind turbine generator:
1) Has how many poles and what does than mean?
2) What is the frequency in hertz of the generators output, what does than mean, and what is the standard in the USA?
3) Is our generator synchronous or a-synchronous and what does than mean?
4) What is a doubly fed induction generator?
5) Is it an induction or permanent magnets generator?
1) 6 poles, meaning there is 3 negative and 3 positive areas. Number of individual field coils on to rotor. (Common: 4, 6, 8, 10)
2) Frequency = 60 hertz which is the industrial standard for electricity in the United States.
3) Asynchronous: Produces electrical power when its rotor is turned faster than the synchronous speed. The output power increases or decreases with the slip rate.
4) It’s a doubly fed generator. About 80% of the used generators are double fed induction generators (DFIG), so that we can state that DFIGs are most commonly used worldwide.
5) Induction Generators: Induction generators have an external AC electricity source from the grid that powers a rotor inside a stationary stator; as opposed to a Permanent Magnet Machine that has a core of powerful magnets. Doubly Fed means both the rotor and stator windings are fed with 3 phase AC signal.
1) What does the “power converter” in a wind turbine do?
2) What are the two main parts of a power converter and what do they do?
1) The power converter manages the frequency from the generator to match the grids frequency (60 Hz in U.S.).
2) Integrated Gate Bipolar Transistor:
A rapid switch that regulates AC frequency cycle strength or adds cycles to match the desired frequency.
&
Capacitor:
Stores power short term
1) In order to produce power at 60 Hz our turbine generator must spin at what rpm?
2) What is it called when the generator’s spins at a lower rpm that the set point above.
3) What is it called when the generator’s spins at a higher rpm that the set point above.
1) 1,200 rpm = our generators set point to make 60 Hz
2) Sub-synchronous
3) Super-synchronous
What does the “sync switch” do?
Sync Switch will cose when the generator is in sync with the grid allowing power to transmit to it from the turbine.
Define “Ampacity”
ampacity - The amp carrying capacity of the cable
“Ampacity is defined as the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Also described as current-carrying capacity.”
What is the “Power Converter’s Charge Contractor” and what does it do?
Power Converter’s Charge Contractor (CCONT): Connects the capacitors to the grid
The CCONT is used to pre-charge the DC Link capacitors
1) What is the ROVC and the other name for it?
2) What does it do?
ROVC
1) Rotor Over Voltage Contactor
“Crowbar”
2) Protects the generator from grid induced transient power
“Protects the DC Link from high voltage resulting from grid faults
induced onto the stator.”
Explain what “switching” or opening the transformer does to the electricity flowing in the turbine.
“Switching” the turbines transformer disconnects the “high side” of the transformer (where the love feeder cables are) from the “low side” that transmits electricity in and out of the turbine tower.
Does “Switching” the transformer to open de energize towers farther down the feeder line?
No
The in series feeder line is still live with energy flowing.
What is the stick called that is used to “switch” open and closed a transformer?
Stand off stick,
Hot Stick
or
Shotgun
