Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

ENM125 Sustainable electric systems > Quiz 3 > Flashcards

Quiz 3 Flashcards

1
Q

What is reliability?

A

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):

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Power system reliability two concepts:

A

1) Security: Short term operation
2) Adequacy: Long term operation and planning

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Goal for power providers

A

(Safety first). Always provide power to consumer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is power system security?

A

Short term. The ability of the power system to withstand sudden
disturbances such as short circuits or non-anticipated loss of
the system components.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is power system adequacy?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

When do we use reliability analyses? (Applications of reliability analysis) (9 st)

A

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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Concession?

A

The right to build powerlines.
System to avoid having excess powerlines
You need to do reliability analysis to prove that you are able

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Back-up system?

A

Diesel generators, but try to avoid usage. For important societal things, police, hospitals maybe grocery stores.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Trade-off economics and reliability?

A

High reliability: high investment cost/operating cost
Low reliability: cost of failures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Classification of power system reliability

A

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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

HL-III indices

A

SAIFI
SAIDI
CAIDI
CAIFI
(ASAI)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

SAIFI

A

System Average Interruption Frequency Index (how often per year in Sweden, in some countries per day) [no. /y]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

SAIDI

A

System Average Interruption Duration Index (how long is the power out) [min/y]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

CAID

A

Customer average interruption duration index [min/y]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

CAIFI

A

Customer Average Interruption Frequency
Index [no. /y]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Indices equation

A

Look up (L13 slide 13)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

ASAI

A

Average System Availability Index [pu]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What can you use HL-III indices for?

A

Impact of refurbishing
Impact of extension
Know where to make investments

(To keep up the reliability)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Equation for expansion

A

See L13 slide 16

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

In Sweden, where are the interruptions mainly?

A

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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Low SAIDI high CAIDI indicates?

A

Interruption concentrated to a few customers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Causes of interruption

A

Most common: weather phenomenon (mostly storm), lightning, material/method (impurities in materials, mistreated in installation), mechanical impact (man-made, ex dig of cable)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Why is reliability different in developing countries? (not really in the quiz)

A

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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Measure outage in developing countries

A

Multi-tier framework (much less “hard” than SAIFI and SAIDI)
Measures in hours available electricity, not considering power quality

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
How to improve reliability?
Add redundancy -more power lines feeding from both directions. Look for hotspots, where it breaks most often.
26
Should we improve reliability (in Sweden)?
Maybe more local backup rather than big investments
27
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)
28
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
29
Smart grids and security
These grids are possible to hack, opposite to traditional mechanical systems
30
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
31
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
32
DSM stands for
Demand side management
33
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.
34
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.
35
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
36
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
37
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
38
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
39
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
40
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)
41
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
42
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
43
DG stands for
Distributed generation
44
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)
45
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.
46
What is a hybrid AC/DC system?
A converter based system, a parallell system where benefits of AC/DC can be used.
47
Load connecting converters, current use (4)
Control the load Make operation more efficient Fulfill grid codes Adopt to tech. differences
48
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
49
Difference support and control
Support = temporary engagement Control = continuous engagement
50
Production connecting converters, current use (3)
Make the production more efficient Control the production Fulfill grid codes
51
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
52
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
53
Storage connecting converters, current use (3)
– Make the grid operation more efficient – Fulfill grid codes – Grid following/forming
54
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
55
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)
56
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)
57
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
58
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
59
In which application is NOT power electronics usually used?
Electric heating
60
What ”services” can power electronics contribute with?
Control (in some way) or DC power supply
61
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
62
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
63
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.
64
How does load vary?
Predictable, cyclic during day, depending on season
65
Which are considered base electric production units?
Nuclear, hydro and biomass
66
Which are considered intermittent production units?
Solar and wind
67
Which are considered peak production units?
Gas turbines
68
operation keep the frequency affects
the whole system
69
operation keep the voltage affects
local part
70
operation do not overload affects
local part
71
operation keep it up and running affects
local and whole system
72
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
73
frequancy deviaton occurs because of
difference between production and consumption
74
Storage need for basic operation planning
A lot of power for a long time (as pumped hydro, batteries, hydrogen, compressed air)
75
Storage need for after fault operation
A lot of power for a short time (as batteries, high power capacitors, super magnetic, high power flywheel)
76
frequency decrease bc
loss of production
77
frequency increase bc
loss of load
78
Frequency - primary control vs secondary control
Primary - stop the frequency drift Secondary - restore the frequency

ENM125 Sustainable electric systems (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions