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Introduction
Expected electricity parameters are defined in the delivery location, i.e. in the location of its transfer from the supplier's distribution network into the consumer's consumption network. This accomplishes the act of electricity supply according to Act No. 169/1995 Coll., Section 6, Subsection 1.
Electricity parameter evaluation can be broken down into two basic categories.
Reliability of supplies including long-term interruptions and outages. Various global indicators, for example the UNIPEDE methodology, can measure the reliability of electricity supplies:
- annual outage count
- average outage duration
- aggregate annual duration of outages
- electromagnetic interferences spreading through wiring
- harmonic
- voltage variations
- drops and short-term outages
- voltage asymmetry
- transfer and distribution of signal through power lines
- network frequency variations
- temporary power surges - pulse interferences
other phenomena that have to do with load changes, switching operations or atmospheric effects.
TopStandard electricity parameters (product properties that can be rightfully expected)
According to current legislation, the supplier is obliged to ensure and maintain standard electricity parameters.
The basic requirement following from the legal regulations is stipulated in section 6, subsection 2 of Act No. 169/1995 Coll.:
"Electricity is supplied of a quality which corresponds to recommended technical standards." In judging electricity parameters,
we always have to take into account that the tolerance ranges of the standard electricity properties are codified in current
technical standards.
The European standard EN 50 160 gives a comprehensive overview of standard properties of electricity in low and high voltage distribution networks, including methods for their measurement and evaluation. This standard is included in the Czech standards system as:
ÈSN EN 50 160 - voltage characteristics of electricity supplied from public distribution networks
PNE 33 3430 - 7 - voltage characteristics of electricity supplied from public distribution networks
These standards state the ranges or values of major voltage characteristics that can be expected by every user under normal operational conditions. As well as these values, the standards also state the calculation of average values of the basic quality indices of electricity for a given time period.
Brief overview of the basic quality characteristics of supplied electricity
Network frequency
Rated frequency of supply voltage is 50 Hz. The mean value of the basic harmonic frequency must fall within the following range:
50 Hz ± 1 percent (i.e. 49.5 ... 50.5 Hz) for 99.5 percent of the year
50 Hz + 6 percent -4 percent i.e. 47 ... 52 Hz) all of the time
Supply voltage
Supply voltage is given by the rated voltage of the network (Un).
Standardized rated voltages are declared in the "ÈSN IEC 38 - Standardized IEC Voltages" standard.
- Low voltage networks - for three-phase four-wire networks
- Un = 230 V between the phase and neutral wire
Un = 400 V between phase wires - High voltage networks - for three-phase networks (generally three-wire) - with a 50 Hz frequency
- Un = 3, 6, 10, 22 and 35 kV
- Very high voltage networks
- Un = 110 kV
Voltage variations
Not counting interruptions, 95 percent of average effective supply voltage values in 10-minute measuring intervals must fall within a Un ± 10 percent range.
Up until 2003, the ÈSN IEC 38 standard allowed for deviations from rated voltage in low voltage 230/400
V networks amounting to +6 percent and -10 percent.In 110 kV networks, only the maximum voltage is declared (123 kV).
It is expected that in the year 2000, the ÈSN IEC 38 standard will be replaced by ÈSN 33 0120.
Rapid voltage fluctuations (flicker)
Rapid voltage fluctuations don't usually exceed 5 percent Un in low voltage networks and 4 percent Un in high voltage networks.
Short-term voltage drops
The expected number of voltage drops during a year can vary from several dozen up to one thousand. Most of the drops last for less than one second and the fluctuations are less than 60 percent. In some areas, there can be frequent 10 to 15 percent drops caused by switching consumer appliances on and off.
Short-term voltage outages
The annual number of outages during the year varies from several dozen up to several hundred. Roughly 70 percent of the short-term interruptions may last for less than one second.
Long-term voltage outages
The annual number of outages lasting for longer than three minutes may be less than 10, but depending on the area, the number can reach as high as 50. The guide values don't include planned and announced outages.
Other quality parameters are:
Temporary power surges at network frequency
Transient power surges
Voltage asymmetry
Harmonic voltages
Inter-harmonic voltages
Signal voltage in supply voltage
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