What is power quality?
Electric power quality (EPQ) is the degree of compliance of electrical energy parameters at a given point in the electrical system with a set of normalised EPQ indicators.
In other words, the quality of electrical energy is a set of characteristics in which power consumers can operate normally and perform the functions inherent in them.
EPQ at the place of production does not guarantee its quality at the place of consumption. EPQ before and after switching on the electric receiver at the point of its connection to the electrical network may be different.
Main Indicators of Electricity Quality
According to GOST 13109-97 there are 11 indicators of the quality of electricity:
- steady state voltage deviation
- voltage swing
- dose flicker
- voltage curve distortion factor
- the ratio of the nth harmonic component of the voltage
- negative stress unbalance factor
- zero sequence voltage imbalance factor
- frequency deviation
- duration of voltage failure
- pulse voltage
- overvoltage coefficient
Voltage deviation
One of the parameters of power quality is voltage deviation.
The voltage deviation is determined by the value of the steady-state voltage deviation. For the value of voltage deviation, the following standards are established:
Normally permissible and maximum permissible values of the steady-state voltage deviation at the terminals of the electricity receivers are respectively +5 and +10% of the rated voltage of the electrical network.
The value of voltage deviation is determined when the process duration is more than one minute.
Normal voltage tolerances. Normally, the tolerance of the voltage is considered to be in the range of 5%, that is: +/- 5% (from 209 V to 231 V).
Maximum allowable voltage deviations. The maximum permissible voltage deviation is considered to be a range of 10%, that is: +/- 10% (from 198 to 242 V).
The following standards apply for the electricity quality indicators defined above: positive and negative voltage deviations at the point of transmission of electrical energy should not exceed 10% of the nominal or agreed value of the voltage during 100% of the time interval of one week.
Important: do not confuse the requirements of GOST to the quality of electricity in the network (GOST R 54149-2010 "Electrical Energy. Electromagnetic Compatibility of Technical Means") and GOSTs describing the quality of power supply for electrical appliances (eg. GOST R 52161.2.17-2009 "Safety of household and similar electrical appliances”). GOST of power quality imposes requirements on the essence of the electricity supplier, and it is this GOST that you can rely on if you need to make demands on the supplier if the power supply is poor. Moreover, the requirements for the quality of the power supply in the instrument documents determine the requirement for the instruments to operate normally over a wider range of current parameters. For devices, as a rule, the voltage range from -15% to +10% of the nominal is set.
PROPERTIES OF ELECTRIC ENERGY, INDICATORS AND PERPETRATORS
Properties of Electrical Energy |
EPQ Indicator |
The Most Likely Culprits of CE Deterioration |
Voltage Declination |
Steady State Voltage deviation dUy |
Power supply organisation |
Voltage Fluctuations |
Scope voltage change dUt Dose Flicker Pt |
Variable load consumer |
Non-sinusoidal voltage |
The distortion factor of the sinusoidal voltage curve KU The ratio of the n-th harmonic component of the voltage KU(n) |
Non-linear load consumer |
Asymmetry of the three-phase voltage system |
Voltage unbalance factor by reverse sequence K_{2U} Voltage unbalance factor for zero sequence K_{0U} |
Unbalanced load consumer |
Frequency deviation |
DF Frequency deviation |
Power supply organisation |
Voltage failure |
The duration of the volatage drop Dtp |
Power supply organisation |
Voltage pulse |
Impulse voltage U_{imp} |
Power supply organisation |
Temporary overvoltage |
Time overvoltage coefficient |
Power supply organisation |