Quality of supply management by means of
interruption statistics
and voltage quality
measurements
Gerd H. Kjølle, Helge Seljeseth and Jørn Heggset,
SINTEF Energy Research
Frode Trengereid,
Norwegian Water Resources and Energy Directorate
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Introduction
„ The paper focus on statistics of reliability of supply and
voltage quality in Norway
„ The documentation is an important basis for the quality of
supply regulation and management
„ Interruption recordings are standardized using the fault and
interruption information tool FASIT
„ Voltage quality measurements are based on IEC and
CENELEC standards ( i.e. EN50160 etc)
„ Interruption data presented for 6 years: 1995 – 2000
„ Voltage quality data presented for the period 1992 - 2001
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Quality of supply REGULATION in Norway
„ The ”new” Norwegian Energy Act from 1991
„ Mandatory reporting of interruptions > 3 min. from 1995
„ Revenue cap regulation of network companies from 1997
„ Quality dependent revenue caps from 2001: The Cost of
Energy Not Supplied arrangement
„ Further quality of supply regulations expected from 2004:
„ Specific requirements for measurement of voltage phenomena?
„ Minimum standards for the reliability of supply?
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Key figures reported 1995-2000
Number of
interruptions
per delivery
point
Annual
duration per
delivery
point
[hours]
Duration per
interruption
[hours]
ENS per
Energy
supplied
[%]
Interrupt-ion
costs
[million €]
Total average
per year
3,0
5,2
1,7
0,03
90
Average for
notified
interruptions
0,8
2,2
2,9
0,01
29
Average for
non-notified
interrupt-ions
2,2
3,0
1,3
0,02
61
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Energy not supplied 1995 - 2000
%
ENS referred to energy supplied
0,05
0,045
0,04
0,035
0,03
0,025
0,02
0,015
0,01
0,005
0
Total ENS
Due to notified interr
Due to non-notified interr
1995
1996
1997
1998
1999
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2000
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Interruptions in overhead vs cable
networks, average 1995 - 2000
Number or hours per year
Annual number and duration of interruptions at the
distribution level, 1995 - 2000
8
7
6
5
4
3
2
1
0
Overhead network
Cable network
Number of interruptions
Annual interruption duration
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Main causes for energy not supplied
Distribution system
Unknown/
not
specified
32 %
Other
1%
Technical
22 %
Environmental
40 %
Human
5%
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NEW 2001/2001 survey in Norway on interuption
and voltage quality costs
NOTE! Preliminary results for residential
customers only!
„ Direct worth:
„
„
„
„
Duration 1h:
Duration 2h:
Duration 4h:
Duration 8h:
„ Willingness to pay
2,4 Euro/kWh ENS
2,4 Euro/kWh ENS
2,3 Euro/kWh ENS
2,1 Euro/kWh ENS
„
„
„
„
Duration 1h:
Duration 2h:
Duration 4h:
Duration 8h:
1,5 Euro/kWh ENS
1,2 Euro/kWh ENS
1,1 Euro/kWh ENS
0,8 Euro/kWh ENS
The TRUTH…… somewhere in between
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Voltage Quality measurements
„ Initially 43 PQ monitors in 1992 and close to 70 by the end
of 2000.
„ Database: 4,4 GB from 624 locations (~700.000 files).
„ All PQ parameters (EN50160) except flicker measured.
„ Anonymous data to minimize data filtering risk.
„ Possible to sort measurement locations by location
parameters like % overhead line vs. cable, voltage level etc
„ Database strength
„ many locations, several years measured (number of PQ parameters)
„ Database weakness
„ Very varying measurement period, no flicker measurements
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Examples of measurement results
„ Flicker has not been reported as a significant problem in
Norway except for in one region in northern Norway.
„ This problem in Mo i Rana developed and got worse after
measurement equipment was chosen in 1991/1992.
„ The two main reasons for the increase of flicker in that
specific region were:
„ Considerable reduction in short circuit capacity in that region of the
network due to the deregulation of the power market. (The
operational pattern of the power stations is very dependent of the
spot market price.)
„ Permanent damage of the local SVC due to a fire.
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Examples of measurement results - LEVELS
Distr.
THD
5 % level
50 % level
95 % level
0,52 %
1,4 %
3,8 %
High V
THD
5 % level
50 % level
95 % level
0,49 %
1,0 %
1,9 %
High voltage
Distribution
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Examples of measurement results - CAUSES
„ Low to moderate level of harmonics due to a high % of
linear load
„ One of the main reasons for a relatively large number of
short interruptions in the Norwegian distribution network
are the low number of arc suppression coils in the medium
voltage overhead lines.
„ Switching of capacitor banks without any mitigation
against switching transients have caused many of the
measured transients of moderate frequency.
„ Synchronized switches on capacitor banks are not yet very
common in Norway.
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Examples of measurement results - TRENDS
„ Slightly increased
harmonics
„ (Slightly increased
flicker) – signifficant
increase in one
location
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OVERHEAD vs. CABLE NETWORK
(Distribution network)
„ The number of short interruptions, voltage dips and
transient overvoltages are verified to be significant higher
in overhead line networks compared to cable networks
„ The higher number of short interruptions is strongly
related to the low number of arc suppression coils in
medium voltage overhead line networks in Norway.
„ Short interruptions in overhead vs. cable networks:
„ average of 19 vs. 6 per year
„ Transient overvoltages in overhead vs. cable networks:
„ 11 times more transients
„ 2,4 times higher average magnitude.
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CUSTOMER COMPLAINTS
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Conclusions
„ Results from 6 year of mandatory reporting of interruptions
and 10 years of voltage quality measurements
„ The reliability level in terms of ENS is slightly improving
„ The voltage quality has shown no significant change,
except for a moderate increase in harmonic voltages
„ There is a relatively high number of short interruptions,
mostly due to few installed arc suppression coils
„ The data base of interruptions and voltage measurement
is steadily improving
„ These data and statistics are important as a basis for the
quality of supply regulation and management in Norway
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THANK YOU
for your
attention
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