math bollen - power quality and dg.pdf
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1
Power Quality, distributed generation, and intermittent
sources of energy
Math BollenSTRI AB
Ludvika, Sweden
2
What is Power Quality?
• Interaction between the power network and its customers.
• Voltage quality: network impacts customer equipment.
• Current quality: customer equipment impacts the network.
• Many other definitions exist.
3
What’s the difference?
• Network and system operators have no control over the generation.
• Generated power is non-predictable and/or highly variable.
• Generator units do not contribute to ancillary services.
4
Power Quality and DG
• 1. Voltage quality impacts the DG units.• 2. DG units impact the current quality and
through the network other customers.• 3. Tripping of DG units impacts system
security and reliability.
5
1. Voltage Quality and DG
T&D network
DGvoltage
6
Voltage Qualitya Matter of Design
• Normal operation (variations)• Units should tolerate the existing levels of voltage quality like all
other equipment.• Normal events
• Units should tolerate normal events (capacitor switching, transformer energizing).
• Abnormal events• The immunity against abnormal events is part of the economic
optimization of the DG units.• The approach is the same as for normal equipment
7
2. Current Quality and DER
T&D network
DERother
customers current
8
Current QualityA Multi-Dimensional Problem
Low-frequency harmonics
High-frequency harmonics
Voltage variations
Voltage flicker
UnbalanceTransformer energizing dips
Capacitor-energizing transients
Tap-changer operation
Voltage dips due to faults Frequency swingsHarmonic resonances
9
Hosting Capacityaddressing one dimension at a time
Per
form
ance
index
Penetration levelHostingcapacity
Limit
more investment
10
Hosting Capacity: Examplerm
s vo
ltage
%DG
95% 10-minute
99% 3-
seco
nd110%
106%
11
3. Tripping of DG Units
voltageT&D network
DGothercustomers trip
Sudden loss of large amounts of DG will cause reliability, security, and quality problems in the power system.
12
Potentially Dangerous Events
0 50 100 150 20049.2
49.4
49.6
49.8
50
50.2
50.4
50.6
Time [s]
Fre
quen
cy [
Hz]
0 10 20 30 40 50
-15
-10
-5
0
5
10
15
Time [Cycles]
Vol
tage
[kV
]Frequency swing due to loss of large power station
Voltage dip due to a fault not properly cleared by the protection
13
Immunity Requirements
• Protection (maximum tripping time)• No protection mal-trip• No unintentional islanding• (Thermal) limits of DER components
• Immunity (minimum tripping time)• Limited risk of massive DER tripping• Reliability of grid connection
14
Voltage Tolerance of DER100%
Duration
Res
idual
voltag
e Immunity requirementIm
mun
ity p
erfo
rman
ce
Protection requirement
15
Further work
• Hosting-capacity approach• Stochastic models of load and DG.• Performance indices and objectives for a
wide range of disturbances.• Tripping of DG on voltage events
• Reliability methods to be applied.• What is an acceptable risk?
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