Quality of Supply Standards:  Is EN 50160 the answer? Abstract
From a regulatory perspective, the European Union has been a leader in developing and implementing quality of supply standards through its implementation
of European Norm 50160.  Some countries have used EN 50160 as the basis for their national quality of supply regulations.  But the standard’s statistical models allow eight hours per week of unregulated power quality, and utilities compliance (or non-compliance) is assessed regardless of the severity of any events.
This paper will outline the state of EN 50160 today: its benefits and possible areas of improvement, including those suggested by the European utility regulators themselves. The standard will be compared to national quality of supply standards from countries around the world to identify best practices and contrast the differences.  In conclusion,
a framework for quality of supply regulation will be proposed that will ensure that compliant utilities are providing a level of service that meets their customers’ expectations.
I.  Review of EN 50160
History:
The history of EN 50160 dates back to 1989 and the European Union directive 89/336 for Electromagnetic Compatibility.  Intended to ensure the reliability of distribution networks (and proper operation of equipment connected to them), the so-called EMC Directive led to a 1989 definition of the physical characteristics of the low and medium voltage distribution systems by the organization UNIPEDE, and finally in 1994 a standard on “Voltage characteristics of electricity supplied by public distribution systems”.  This standard was developed by
a working group under CENELEC (European Committee for Electrotechnical Standardization) and was given the designation European Norm 50160, or EN 50160 [1]. Scope:
The original mandate for EN 50160 was limited to low and medium voltage distribution systems and specifically the following characteristics of the supply voltage:  frequency, magnitude, waveform and symmetry of the three-phase voltages. Low voltage is defined with an upper limit of
1 kV RMS and medium voltage with an RMS value between 1kV and 35 kV.  In the original scope, higher voltages were not considered.
Supporting the requirement to define voltage characteristics in terms of frequency, magnitude, waveform and symmetry, EN 50160 provided definitions and in some cases measurement methods and compliance levels for 10 characteristics of the supply voltage:
• Power frequency
•Supply voltage variations
•Rapid voltage changes (and Flicker)
•Supply voltage dips
• Short interruptions
• Long interruptions
• Temporary overvoltages
•Supply voltage unbalance
• Harmonic voltage
• Mains signaling voltage
Supply voltage characteristic Statistical Evaluation Compliance limit Power frequency
95% of the time in 1 week 100% of the time in 1 week 50 Hz ± 1%
50 Hz + 4% to -6% Supply voltage variations
95% of the time in 1 week Uc ± 10% Rapid voltage changes (and Flicker) 95% of the time in 1 week Plt ≤ 1
Supply voltage dips    1 year None given 1 Short interruptions    1 year None given 2 Long interruptions
1 year None given 3 Temporary overvoltages    1 year
None given Supply voltage unbalance 95% of the time in 1 week <2%
Harmonic voltage 95% of the time in 1 week 95% of the time in 1 week See Figure 1 THD <8% Mains signaling voltage
99% of the time in 1 day
9% @ 100 Hz 1% @ 100 kHz
reactive power什么意思
Table 1:  EN 50160 Compliance Limits
1.  Indicative value of 1000 dips/year provided
2.  Indicative value of “several hundreds” of short interruptions/year provided
3.  Indicative value of 50 long interruptions/year provided
Figure 1:  Harmonic limits in EN 50160
Issues with EN 50160
The primary issues preventing EN 50160 from being a comprehensive power quality standard can be broken down into five main points:
1.  As a consensus-driven standard, with equal representation from all countries, it reflects the lowest common agreed-upon value for PQ limits.
2.  Many of the most costly and most common PQ phenomena (dips, swells and interruptions) do not have compliance limits but only indicative values.  In his paper “End use perceptions of Power Quality – A European Perspective” [2]  Roman Targosz estimated the cost of dips and short interruptions within the EU at 86.5 Billion euro out of a 150 Billion euro estimated total cost of power quality.
3.  The scope is limited to medium voltage (35kV) networks and below.
4.  Measurement methods for each characteristic are not defined.  By allowing utilities to evaluate compliance with undefined measurement methods, it will be impossible to compare results or apply fair noncompliance penalties.
5.  Many characteristics are evaluated for less than 100% of the measurement interval.  This allows:
• No limit on supply voltage
variations, flicker, voltage unbalance, individual harmonics or THD for 8.4 hours/week
• No limit on mains signaling for 1.7
hours/week
8.0%
2.0%
5.0%
1.0%
6.0%0.5%  5.0%
0.5%1.5%0.5%
3.5%
0.5%
3.0%
0.5%
0.5%0.5%  2.0%
0.5%
1.5%0.5%
0.5%0.5%1.5%0.5%
THD
357911131517192123H a r m o n i c  O r d e r
II.  Alternative National Quality of Supply Standards
To provide the most accurate comparison, medium voltage compliance limits for all national standards are used when compared to EN 50160.
A.  Norway
History:
Regulation of quality of supply began in 1991 with the passing of the Energy Act.  In 1995 mandatory reporting of interruptions greater than three minutes was added and 179 network companies were req
uired to report key figures on voltage quality.  On January 1, 2005 the Norwegian Water Resources and Energy Directorate (NVE) put into force “Regulations relating to the quality of supply in the Norwegian power system” [3]. Scope:
The NVE regulations apply to all network voltage levels.  The regulations provide definitions and in some cases measurement methods and compliance levels for the following supply voltage characteristics: • Frequency
•Short interruptions
•Long interruptions
• Flicker Pst
• Flicker Plt
• Interharmonic voltage
•Temporary overvoltages
•Voltage dips
• Voltage variations
• Harmonic voltages
• Mains signaling voltage
•Rapid voltage change
• Voltage unbalance
Supply voltage characteristic Statistical Evaluation Compliance
limit
vs.EN50160 Power frequency 100% of the time  50 Hz ± 2% Different Supply voltage variations 100% of the time  Uc ± 10% Same
Rapid voltage changes    1 change/day
Up to 24 changes/day
>24 changes/day 6%
4%
3%
Harder
Flicker 95% of the time in 1 week
100% of the time in 1 week Pst <= 1
Plt <= 0.8
Harder
Supply voltage dips None given None given Same Short interruptions    1 year None given Same Long interruptions    1 year None given Same Temporary overvoltages    1 year None given Same Supply voltage unbalance 100% of the time <2% Harder
Harmonic voltage Mean value for 10 minutes
Mean value for 10 minutes See Fig. 2
THD <3%
Harder
Harder
Mains signaling voltage None given None given Easier Table 2:  NVE Directorate Compliance Limits
0.0%  1.0%  2.0%  3.0%  4.0%  5.0%  6.0%7.0%8.0%
THD
357911131517192123
Figure 2:  Comparison of EN 50160 and NVE Harmonic Voltage Limits
How NVE regulations address identified limitations in EN50160:
1.  By focusing on just one country, Norway
has been able to raise the compliance limits
on rapid voltage changes, flicker, voltage unbalance and harmonic voltage.  Higher order (above the 25th ) harmonic limits have
been established, and the RMS variation
averaging period for supply voltage
magnitude is reduced from 10 minutes to 1
minute.  2.  Like EN 50160, dips, swells and interruptions still do not have compliance limits.  NVE does require mandatory reporting of long interruptions (greater than 3 minutes) and further classifies interruptions as notified (where the customer was informed in advance of an impending interruption) and non-notified.  This is a necessary first step to establishing compliance limits but does not set targets.  3.  The scope is expanded up to and including 245 kV.    4. Measurement methods for each characteristic are not clearly defined.  This clause “Measurements of the quality of supply shall be carried out in accordance with the relevant standards prepared by the International Electrotechnical Commission – IEC or the European Committee for
Electrotechnical Standardization – CENELEC.” should be expanded to list the specific standards required for each characteristic.  5.  Steady-state characteristics have compliance limits for 100% of the measurement period, with the exception of mains signaling voltage.  Limitations of NVE regulations with respect to EN 50160:  1.  Mains signaling voltage compliance limits not defined.  2.  While frequency limits are defined for 100% of the measurement period, the
compliance limit has been reduced from 1% to 2%.
B. China
History:
In 1998 the State Grid Corporation of China produced “Management requirements for
the technical supervision of grid power quality” and in 2004 “Management requirements for the voltage quality of the power system and reactive power for the State Grid Corporation of China”.  Most of
the compliance standards have been developed between 2000 and 2004.
Scope:
Compliance limits apply at all voltage levels.  The national standards are based on IEC standards including measurement methodologies, compliance limits and PQ monitoring product requirements.  Standards specific to compliance limits are GB/T 12325-2003 “Admissible deviation of supply voltage”, GB 12326-2000 “Voltage fluctuation and Flicker”, GB/T 14549-1993 “Harmonics”, GB/T 15543-1995 “Admissible voltage unbalance factor”, GB/T 15945-1995 “Admissible deviation of frequency for power system”, and GB/T 18481-2001 “Temporary
and transient overvoltages” How Chinese standards address identified limitations in EN50160:
1.  The GB/T standards have higher compliance limits on frequency, rapid voltage changes, flicker, temporary overvoltages and low-order harmonic voltages.
2.  Dips, swells and interruptions still do not have compliance limits.
3.  The scope is expanded up to and including 500 kV.
4.  Measurement methods for each characteristic are clearly defined for voltage harmonics (IEC 61000-4-7) and flicker (IEC 61000-4-15).  Other characteristics need clearly defined measurement methods.
5.  Steady-state parameters have compliance limits for 100% of the measurement period, with the exception of mains signaling voltage.
Supply voltage characteristic Statistical Evaluation Compliance
limit
vs.EN50160 Power frequency 100% of the time  50 Hz ± 1% Harder Supply voltage variations 100% of the time  Uc ± 10% Same
Rapid voltage changes <= 1000/hour
Other 4%
2%
Harder
Harder
Flicker 95% of the time
100% of the time  Pst <= 1
Plt <= 0.8
Harder
Harder
Supply voltage dips None given None given Same Short interruptions    1 year None given Same Long interruptions    1 year None given Same Temporary overvoltages    1 year √3 per unit Harder Supply voltage unbalance 95% of the time <4% Easier
Harmonic voltage Mean value for 10 minutes
Mean value for 10 minutes Odd <2.4%
Even <1.2%
THD <3%
Harder
Harder
Harder
Mains signaling voltage None given None given Easier Table 3:  GB/T Compliance Limits

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