Quiz 3 Flashcards
(61 cards)
1
Q
Define power electronics
A
Power electronics is the application of solid-state electronics for the control of the conversion or transmission of electric power.
2
Q
What is a semiconductor material?
A
A material whose conductivity can be controlled by applying an electric field.
Isolator –> open switch
Conductor –> closed switch
3
Q
How is a semiconductor made?
A
Its conductivity is regulated by adding impurities during
manufacturing process —> doping.
4
Q
What is an ideal power switch?
A
- Ideal switch: instant turn on/off
- Made of semiconductor material: Si, SiC, etc
5
Q
What is the characteristics of a real power switch?
A
Real switch: switching losses, voltage drop and losses on the R_on (conduction losses)
6
Q
What are some types of semiconductors
A
diode
diode rectifier
Thyristor
Transistors:
-Mosfet
-IGBT
7
Q
What are some characteristics of a diode?
A
- Non-controllable semiconductor valve (no gate)
- Positive voltage across the
terminals –> turn on - Negative voltage & zero current –> turn off
8
Q
what are some characteristics of a diode rectifier?
A
- Convert AC to DC voltage
- Very simple topology, no control required
- Can operate at a very large
range of operating points:
can reach very high voltages/
currents - Unidirectional power flow
- Not clean dc-voltage (a lot of harmonics)
9
Q
What are some characteristics of a Thyristor?
A
- Controllable AC to DC conversion
- Gate voltage necessary to turn on
- Converter has bidirectional power flow
10
Q
What are some characteristics of a MOSFET transistor?
A
- Can switch with high
switching frequencies - Is used typically in low power – low voltage power
converters
11
Q
What are some characteristics of a IGBT transistor?
A
- Has lower switching
frequency than MOSFET
(due to higher losses) - Can handle much higher
current and voltage
–> typical application large grid converters or machine drives
12
Q
Where are DC/DC converters used?
A
TV
Smart devices
Other household appliances
13
Q
What are thyristors used for?
A
very low sw. freq. very high voltage/current —> HVDC, grid control
14
Q
What are IGBT transistors used for?
A
low sw. freq. high voltage high current
—> machine drives
15
Q
What are MOSFET transistors used for?
A
high sw. freq. low voltage/current —> chargers,
DC/DC converters
16
Q
SiC compared to Si IGBT
A
Can withstand higher voltages
Lower conduction losses
Much lower switching losses
Can handle higher operating temperatures (>250 C)
17
Q
What are some characteristics for shunt capacitors?
A
- Capacitors connected in parallel to the ac-transmission lines
- Locally produce reactive power increasing the efficiency of the grid and boosting the voltage of that node
- Low flexibility into tuning the required reactive power using discrete number of capacitors
18
Q
What are some characteristics of STATCOM (= Static Synchronous Compensator)?
A
- Active power factor correction using power converters
- Medium voltage (multilevel) converters are usually used (e.g. MMC, CHB converter)
- They can be controlled to produce precise amounts of reactive power
+
They can support the grid in
case of faults.
19
Q
What two concepts can power system reliability be divided into?
A
1) Security: Short term operation
2) Adequacy: Long term operation and planning
20
Q
Define power system security
A
The ability of the power
system to withstand sudden disturbances such as short circuits or non-anticipated loss of the system components.
1) Security refers to the degree of risk in its ability to survive imminent disturbances (contingencies) without interruption of customer service
2) It relates to the robustness of the system in a context of imminent disturbances and depends on the power system operating condition before the disturbance and the contingent probability of disturbances
21
Q
Define Power System Adequacy
A
The ability of the system to supply the aggregate electric power and energy requirements of the customers at all times, taking into account scheduled and unscheduled outages of the system components.
22
Q
What are some Applications of Reliability Analysis?
A
- Estimation of reliability of supply and interruption costs
- Investment planning
- Application of concessions
- Design and evaluation of different measures
- Establishment of standards for security of supply
- Operation and Maintenance
- Emergency planning
- Risk and vulnerability assessment
- Sizing of back-up system (both power and energy)
23
Q
How do you calculate SAIFI?
A
Total Number of Customers Interruptions/ Total Number of Customers Served [No./year]
24
Q
How do you calculate SAIDI
A
Total Duration of Customers Interruptions/ Total Number of Customers Served [Min./year]
25
How do you calculate CAIFI?
Total Number of Customers Interruptions/ Total Number of Customers Interrupted [No./year]
26
How do you calculate CAIDI?
Total Duration of Customers Interruptions/ Total Number of Customers Interrupted [Min/year]
27
How do you calculate ASAI?
Total Number of Delivered Costumer Hours/ Total Number of Costumer Hours [-]
28
What are some examples of implimentations in a smart grid?
1. New components
– Smart meters
– BLL and BLX
2. New technologies for use in EPS
– ICT in EPS
– Electrical storage
– Solid state transformer
3. New strategies
– DSM
* Peak shaving
* Electric vehicles in distribution systems
– DG
– Dynamic line rating
* OH-line
* Cable
– Network reconfiguration
4. The heart (the enabler) of smart grid
29
Why is smart grids a good idea?
* Environmental
* Less losses
* Less land need
* Less raw materials
* Less visual impact
* Decreased EMF etc.
* Economy
* Less losses
* Utilize low “electricity
prices”
* Reduce the need for
regulating power.
* Less new power lines
30
What are BLX or BLL?
* OH line covered with insulation
* Not full insulation (no personal saftey)
* Still need for poles
* Still visibilitet issue
* Mostely used at MV.
* Less need for tree safe lines
* Survive branches but not trees
* Reduce number of ”small” faults
* Cheaper then cable
* Repair time as OH-line
31
describe electricity storage in the distribution grid
* Reduce losses in the transformer
* Limit the peak.
* Harmonics mitigation
32
Describe Solid state transformers (SST)
So much more then a transformer:
* Transformation
* More compact and lightweight installation
* Easy to add storage
* Less dependent on the need for inductive material
* Less environmental impact (no oil)
* Better voltage control (more exact)
* More remote control will be possible
* More information about the substation will be available
* Protection from disturbances, e.g. PQ.
* Reactive power compensation ±Q
Issues:
* Losses in the converters
* Lack of short circuit power
33
Describe Demand side mangement
* Let the load
– React on availability of electricity/electricity price
– Support the grid at capacity deficit (reduce curtailment etc.)
– Support the grid during fault
* Suitable loads
– Large heatpumps
– Industrial processes
– Electric heating
– Dish washers etc.
– Charging of electric cars
– All (almost at least)
34
pros and cons with load control (DSM)
+ Loads are distributed in different areas.
+ Close to the other loads
+ Cheaper
- Hard to control
- Uncertian about available capacity
- Peak shaving, limtited by the flexibility of the customers
35
Pros and cons with storage (DSM)
+ Placement and design adaptable after need
+ Esier to control
+ Ancillary services
- Expensive
- Peak shaving, limtited by size of the storage
36
Describe some characteristics of distributed generation
* Production close to the consumption (reduce losses?)
* Use existing infrastructure, grid, roof, walls etc
* Enables small installations, investments from households.
* Mainly solar, wind and small scale hydro
* Reduce CO2 emissions
* Less dependence on large producers?
37
Describe load connecting converters
* Both for the DC and AC loads
* Current use
– Control the load
– Make the operation more efficient
– Fulfill grid codes
– Adapt to technical differences
* Create business opportunities (ancillary services) e.g.
– Power Quality issues mitigation
– Act as frequency support (temporary engagement)
– Frequency control (continuous engagement)
– Act as voltage support (temporary engagement)
– Voltage control (continuous engagement)
– Congestion management
– Providing emulated inertia
– Short circuit power
38
Describe Production connecting converters
* Both for the “DC” and “AC” production.
* Current use
– Make the production more efficient
– Control the production
– Fulfill grid codes
* Updates of grid codes
– EU, dependent on type of production. = req. on the control.
* New business opportunities e.g.
– Power Quality issues mitigation
– Act as frequency support (temporary engagement)
– Frequency control (continuous engagement)
– Act as voltage support (temporary engagement)
– Voltage control (continuous engagement)
– Providing emulated inertia
39
Describe Storage connecting converters
* Current use
– Make the grid operation more efficient
– Fulfill grid codes
– Grid following/forming
* New business opportunities.
– Power Quality issues mitigation
– Act as frequency support (temporary engagement)
– Frequency control (continuous engagement)
– Act as voltage support (temporary engagement)
– Voltage control (continuous engagement)
– Congestion management
– Providing emulated inertia
40
Describe interconnecting converters
* Allow dual ways power flow.
* Grid(s) following (and grid forming)
* New business opportunities e.g.
– Power Quality issues mitigation
– Act as voltage support (temporary engagement)
– Voltage control (continuous engagement)
41
Describe Multiport converters
* Several input and outputs
* All can act both input and outputs
* Grid following and grid forming
* New business opportunities e.g.
– Power Quality issues mitigation
– Act as voltage support (temporary engagement)
– Voltage control (continuous engagement)
42
What is concidered normal operation for the power grid?
* Voltage
* Frequency 49,9-50,1 Hz
* Transmission of power within limits
* Reserve power available
* System ready for (n-1) faults
43
how does Energy in = Energy out in the power system?
* The difference between production and consumption of power in a given moment is stored in or taken from the rotational energy of the generators in the system
* Result of difference: Frequency deviation
44
How does the operation of the system react to a faul?
* Spinning reserve (increase generation)
* Thermal power plants
* Hydro power
* Load shedding (decrease load)
* Demand side response
* Disconnection of large heat pumps
* Disconnection of none prioritized loads
* Rotational load shedding
45
Why does frequency increase/decrease?
* Frequency
decrease due to
Loss of production
* Frequency
increase due to
Loss of load
46
How does frequency regulation work in practice?
* Operator (SvK) keeps an eye on the frequency
* Primary control
– Stop the frequency drift
* Secondary control
– Restore the frequency
* If it deviates, the operator will activate bids on the regulation market
* Activation automatic (aFRR) or by phone call (mFRR)
47
Define congestion
when the producers and consumers of electric energy desire to produce and consume in the amounts that would cause the transmission network to operate at or beyond one or more transfer limits, the system is said to be congested.
48
What is the price area method?
* Market is first solved as uncongested, and generation and load in each bid area is determined. If transfers between areas do not exceed limits, then this solution, with one system wide market price, is used.
* If transfers exceed limits, then each area is separately settled using only the bids for that area and the transfer constraint
* By that way, the transmission capacity can be optimized, and the transfers are kept within limits.
49
what is the counter trade method?
* Market is first solved as uncongested, and generation and load in each bid area is determined. If transfers between areas do not exceed limits, then this solution, with one system wide market price, is used.
* If transfers exceed limits, the TSO purchase to power (accept higher bids) in the area with deficit and sells (reimburse the producer that did not got the bid due to the constraint in the other area.
* The difference is an extra cost in grid operation.
50
What are Ancillary services?
* Providing services to the grid
* Frequency control
* Voltage control
* System Restoration
* Other services
51
What is fast frequency support?
* FFR (Fast frequency support) shall stop the rapid drop in frequency
* Actived by frequency deviation
* Time to full activation: 0.7, 1. 1.3 s and operated 5-7 s.
* Providers
* Natural providers
* Connected with large
inertia
* Emulating providers
* Industry (e.g. system
that can withstand short
outages)
* Other load (e.g. system
that can withstand short
outages)
* Short term overload of
generators (e.g. Wind
turbines)
52
What is frequency containment reserve?
* FCR is used to stabilize system frequency after the big drop has
been shown.
* Frequency Containment Reserve – Normal (FCR-N)
* Within ±0,2 % of normal frequency
* Activation time 63 % within 60s and 100 % within 3 min
* Frequency Containment Reserve – Disturbance (FCR-D)
* Outside ±0,2 % of normal frequency
* Activation time 50 % within 5s and 100 % within 30 seconds
* Providers
* Production units
* Industry load
* Other loads
53
What is Frequency Restoration
Reserve?
* FRR services are active power reserves used to restore the frequency back to 50 Hz and by that also reset the activated FCR resources
* mFRR (manual FRR) proactive manner and suppress structural unbalances
* Activated within 15 min
* aFRR (automatic FRR) manage remaining and fast unbalances
* Activation based on TSO signal, time 120 s
* Providers
* Generation units (Hydro)
54
What is replacement reserve?
* RR are active power reserves that can be used to support or restore FCR and FRR resources that have been activated due to system imbalances.
* Activation time: Minutes
* Providers
* Generation units (Hydro)
55
Describe voltage control
* Fast voltage control
* Normal Voltage Control, is used to maintain system voltage quality and more specifically dynamic security
* Normal voltage control
* Normal Voltage Control, is to control the voltage at network nodes within the predefined target range, during normal operation
* Current providers
* Capacitor banks
* Synch. generations units
* Potential providers
* Power electronic connected production and loads.
56
Describe System Restoration
* Black start
* Be starting point after an outage
* Current providers
* Selected production units (Hydro, thermal)
* Potential providers
* VSC-HVDC
* Islanding
* Run a part of the system in case of a major outage.
* Potential providers
* VSC-HVDC, industry with in-house production,
production units.
57
What are some other services that could find a market in operation management?
* System Stability Services
* Power Flow/Congestion Management
* Power Quality Services
58
How are planned outages handeled in a meshed grid?
* Make sure that nothing gets over loaded
* Assure still N-1
59
How are planned outages handeled in Ring built grids?
* Possible feed from other direction
* Alert the customers and make the interruption as fast as possible
60
How are planned outages handeled in radial grids?
* Alert the customers and make the interruption as fast as possible (plan well)
* Back-up if long (especially sensitive customers)
61
How are non-planned outages handled in the grid?
1. Break the current and disconnect the faulted part (Automatically)
2. Auto-reclose (if allowed)
3. Try to connect in a different way
4. Make sure that nothing gets overloaded
5. Reestablish N-1 (if applicable)
6. Fix the fault and reconnect
