Quiz 3 Flashcards
What is reliability?
The ability of an item to perform a required function,
under given environmental and operational conditions
and for a stated period of time (ISO 8402):
Power system reliability two concepts:
1) Security: Short term operation
2) Adequacy: Long term operation and planning
Goal for power providers
(Safety first). Always provide power to consumer
What is power system security?
Short term. The ability of the power system to withstand sudden
disturbances such as short circuits or non-anticipated loss of
the system components.
What is power system adequacy?
The system should always be working.
Long term.
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
When do we use reliability analyses? (Applications of reliability analysis) (9 st)
Estimation of cost of reliability of supply and interruption (what is worth to do, what kind of reliability do we need?)
Investment planning
Application of concessions
Design and evaluation of different measures
Establishment of standards for security supply
Operation and maintenance (a lot of this)
Emergency planning (sabotage)
Risk and vulnerability assessment
Sizing of back up system (both power and energy)
Concession?
The right to build powerlines.
System to avoid having excess powerlines
You need to do reliability analysis to prove that you are able
Back-up system?
Diesel generators, but try to avoid usage. For important societal things, police, hospitals maybe grocery stores.
Trade-off economics and reliability?
High reliability: high investment cost/operating cost
Low reliability: cost of failures
Classification of power system reliability
HL-I: generation facilities
HL-II: generation and transmission facilities
HL-III: generation, transmission and distribution facilities
Why 3? To be able to see where the system is failing. Different indices for the different classes.
HL-III indices
SAIFI
SAIDI
CAIDI
CAIFI
(ASAI)
SAIFI
System Average Interruption Frequency Index (how often per year in Sweden, in some countries per day) [no. /y]
SAIDI
System Average Interruption Duration Index (how long is the power out) [min/y]
CAID
Customer average interruption duration index [min/y]
CAIFI
Customer Average Interruption Frequency
Index [no. /y]
Indices equation
Look up (L13 slide 13)
ASAI
Average System Availability Index [pu]
What can you use HL-III indices for?
Impact of refurbishing
Impact of extension
Know where to make investments
(To keep up the reliability)
Equation for expansion
See L13 slide 16
In Sweden, where are the interruptions mainly?
Low voltage (0.4 kV) bc there are a lot of them, and they don’t have a lot of impact
(more in 12 kV, and much less in 24 kV and <10 kV)
Low SAIDI high CAIDI indicates?
Interruption concentrated to a few customers
Causes of interruption
Most common: weather phenomenon (mostly storm), lightning, material/method (impurities in materials, mistreated in installation), mechanical impact (man-made, ex dig of cable)
Why is reliability different in developing countries? (not really in the quiz)
Weak institutions (big investments - long-term planning needed. In Sweden grid is an income!)
Power system is being constructed (a lot is happening, urbanisation)
Poverty
Demands of renewable energy sources
Fast growing populations
(Harsh climates (hot countries - max need when hottest for AC, easily stresses the system. In Sweden in winter we have natural cooling while max need))
(Unstable politically)
Measure outage in developing countries
Multi-tier framework (much less “hard” than SAIFI and SAIDI)
Measures in hours available electricity, not considering power quality
How to improve reliability?
Add redundancy -more power lines feeding from both directions. Look for hotspots, where it breaks most often.
Should we improve reliability (in Sweden)?
Maybe more local backup rather than big investments
A paradigm shift in power distribution/grids? (4)
Central production -> distributed production
Controllable generation -> intermittent generation (renewables)
Uncontrollable loads -> controllable loads (ex. avoid buying when expensive, stresses the system less, win-win)
Products -> services (what it should do for us more important than how, as DH instead of electrical heating)
Purpose smart grids?
“How to manage”
Grid will require measurements, control and distribution of the right information to the right part at the right time. Often called smart grids
Smart grids and security
These grids are possible to hack, opposite to traditional mechanical systems
Definitions smart grids (one of them)
Increased use, both more efficient and by providing new services, of electric power systems, both exisiting and future, by utlizing new components, technologies and strategies
- Jimmy
Why smart grids?
Environmental
- less losses
- less land needed
- less raw materials
- less visual impact
- decreased EMF etc
Economy
- less losses
- utilize low “electricity prices”
- reduce the need for regulating power
- less new powerlines
DSM stands for
Demand side management
Smart meter
Shows actual consumption in your electricity bill, every month. (Earlier they estimated your yearly consumption/12) (per timme from nyår)
Drawback before: If changed behavior - long time until bill “catches up”
Drawback now: higher bill during winter
Purpose: to realize what takes a lot of energy, per hour. Also possible to pay based on spot price (possible to adapt), you can also pay average per month or fixed price etc. Also possible to turn off consumption remotely.
Smart meter emergency possibilities
It is possible to turn off customers if there is a deficit of power, which type of customers can be disconnected to have the least social impact. Ex. every second home, you can borrow from your neighbour. Or disconnect big customers. Concept that works for grid and social.
BLX or BLL
Normally blue
OH-lines covered with insulation. Insulation that somewhat protects the cable, but not insulated enough for personal safety.
Shorter repair time (easier access with OH), reduce number of small faults
Electricity storage in the distribution grid benefits
Reduces losses in the transformer, limit the peak, harmonics mitigation.
You can even out the load in a way that you don’t have to build extra lines in for example Stockholm.
So far only Li-Ion batteries
Reason for ICT (information and communication tech.) in the EPS (electrical power system)
Transmission: for protection and control/supervision
Subtransmission: protection, control/supervision! and measurements!
Local: Control/supervision! and measurements!
0,4kV: Measurements! and communication with/bw customers!
! = increased communication
SST?
Solid state transformer
MV AC/DC link -> LV AC/DC
10-30 kV 50 Hz -> 10-30 kV -> 0,4 kV -> 0,4 kV 50 Hz
DSM meaning for load
Let the load
- react on availability of electricity/electricity price
- support the grid at a capacity deficit
- support the grid during fault
Suitable loads for DSM
large heatpumps
industrial processes
electric heating
dish washers
charging of electric cars
(almost all loads, that can be turned off for one hour)
DSM loads pros and cons
+ loads are distributed
+ close to other loads
+ cheaper
- hard to control
- uncertain about available capacity (if its already off, you can’t turn it off)
- Peak shaving, limited by the flexibility of the customers
DSM storage pros and cons
+ placement and design adaptable after need
+ easier to control
+ ancillary services
- expensive
- Peak shaving, limited by size of the storage
DG stands for
Distributed generation
Why DG?
production close to consumption (reduce losses)
use existing infrastructure, grid, roof, walls etc.
Enable small installations, able to attract investments from households
Mainly solar, wind and small-scale hydro
Reduce CO2 emissions
Less dependence on large producers? (but they are needed either way)
Dynamic rating, what and why?
Impact on a line for a certain load
Measurement of temperature and windspeed along OH-line => base capacity on this
(Now we check winter load on a summer line, which wont happen (cooling in winter) we are not using the line to full capacity) => Increased capacity on about 15-30%. Correct most of the time.
Interesting especially for windpower but also transformer.
What is a hybrid AC/DC system?
A converter based system, a parallell system where benefits of AC/DC can be used.
Load connecting converters, current use (4)
Control the load
Make operation more efficient
Fulfill grid codes
Adopt to tech. differences
Load connecting converters, possibilities (8)
Power quality issues mitigation
Act as frequency support (temporary engagement)
Frequency control (continuous engagement)
Voltage support (temporary engagement)
Voltage control (continuous engagement)
Congestion management
Providing emulated inertia
Short circuit power
Difference support and control
Support = temporary engagement
Control = continuous engagement
Production connecting converters, current use (3)
Make the production more efficient
Control the production
Fulfill grid codes
Production connection converters, possibilities (6)
– 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
What does converters mean to the grid?
They are good for the grid, opens up a lot more controlling. Parts only there for control can be removed. Also, good with double network for reliability
Storage connecting converters, current use (3)
– Make the grid operation more efficient
– Fulfill grid codes
– Grid following/forming
Storage connecting converters, possibilities (7)
– 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
Why interconnect converters?
- Allow dual ways power flow.
- Grid(s) following (and grid forming)
- Possibilities:
– Power Quality issues mitigation
– Act as voltage support (temporary engagement)
– Voltage control (continuous engagement)
Why use multiport converters
- Several input and outputs
- All can act both input and outputs
- Grid following and grid forming
- Possibilities:
– Power Quality issues mitigation
– Act as voltage support (temporary engagement)
– Voltage control (continuous engagement)
SST services (6)
Installation can be much more compact and easier to “form” as convenient
More measurements can be done
Remote control possible
Less environmental impact (no oil)
Protect from disturbances, you don’t have transfer reactive power
Easy to add storage
SST drawbacks
Drawbacks: In total, today more losses and can’t transfer short circuit current only load current (fuses etc must be adapted to the limited current)
Beneficial if you need any of the services
In which application is NOT power electronics usually used?
Electric heating
What ”services” can power electronics contribute with?
Control (in some way) or DC power supply
In which types of studies can the reliability analysis be useful? (6)
Investment planning
Application of concessions
Emergency planning
Risk and vulnerability assessment
Sizing of back-up system
Estimation of reliability of supply and interruption costs
Power System reliability can be divided in to two concepts, security and adequacy. In what of the aspect(s) below to they differ?
Time horizone
What is/are drawbacks using solid state transformers compared to conventional transformers?
Higher losses and lack of short circuit power. The lack of short circuit power could make it hard to secure
selectivity.
How does load vary?
Predictable, cyclic during day, depending on season
Which are considered base electric production units?
Nuclear, hydro and biomass
Which are considered intermittent production units?
Solar and wind
Which are considered peak production units?
Gas turbines
operation keep the frequency affects
the whole system
operation keep the voltage affects
local part
operation do not overload affects
local part
operation keep it up and running affects
local and whole system
What is “normal” operation
- voltage (within requirement, preferably little above to keep down current)
- frequency (49,9-50,1 Hz)
- transmission of power within limits
- reserve power available
- system ready for (n-1) faults
frequancy deviaton occurs because of
difference between production and consumption
Storage need for basic operation planning
A lot of power for a long time (as pumped hydro, batteries, hydrogen, compressed air)
Storage need for after fault operation
A lot of power for a short time (as batteries, high power capacitors, super magnetic, high power flywheel)
frequency decrease bc
loss of production
frequency increase bc
loss of load
Frequency - primary control vs secondary control
Primary - stop the frequency drift
Secondary - restore the frequency
