The quality of electricity. Requirements for the quality of electricity

The quality of electricity needs to be expressed in quantitative terms to assess the supply network. Providers are required to maintain compliance with GOSTs such characteristics as voltage and frequency fluctuation. Depending on the connected consumers, the values of the main indicators change, which can lead to the failure of household appliances with significant deviations.

What affects the characteristics of the supply network?

The quality of electricity depends on a huge number of factors that change indicators beyond the limits set by the regulations. So, the voltage may be too high due to an accident at the substation. Underestimated values appear in the evening or in the summer season, when people return home and include TVs, electric stoves, split-systems.

The quality of electricity according to GOSTs can vary slightly. In very poor supply networks, consumers have to use voltage regulators. Control over the characteristics is entrusted to Rospotrebnadzor, which can be handled with the arising inconsistencies.

The quality of electricity can depend on the following factors:

• Daily fluctuations associated with uneven connection by consumers or with the influence of tides at sea stations.
• Changes in the air environment: humidity, the formation of ice on the supply wires.
• A change in the wind, when the power is produced by the windshields.
• The quality of the wiring, over time, it wears out.

Why do we need the main characteristics of the supply network?

The quantitative value and deviation errors of the parameters are established in accordance with GOST. The quality of electricity is stated in document 32144-2013. It was required to legitimize these indicators because of the risk of ignition of consumer devices, as well as the disruption of the operation of electrical devices sensitive to voltage surges installations. The latest devices are distributed in medical institutions, scientific centers, military facilities.

The electricity quality indicators were updated in 2013 due to the development of the energy market and the emergence of new electronic devices. Consider electricity as part of its delivery as products that meet certain criteria. If the established characteristics are rejected, providers may be subject to administrative liability. If, however, due to the fault of the incoming voltage, people were injured or could suffer, then criminal responsibility may already arise.

What happens to consumers in the event of a deviation from normal diet?

The parameters of the quality of electricity affect the duration of the operation of the connected devices, often this becomes critical in production. The productivity of lines falls, the energy consumption increases. So on the shaft of the motors, the torque decreases when the values of the mains supply drop. The service life of the lighting lamps is shortened, the light flux of the lamps becomes smaller or flickers, which affects the output in the greenhouses. A significant effect is on the processes of other biochemical reactions.

According to the laws of physics, reducing the voltage with a constant load on the motor shaft leads to a rapid increase in current. This, in turn, leads to malfunctions in the operation of safety switches. As a result, the insulation melts, in the best case, fuses are burning , at worst the windings of engines, electronics elements are irreparably damaged. Under similar circumstances, the electricity meter starts to rotate at a higher speed. The owner of the premises suffers losses.

Criteria for assessing the supply network

What does GOST contain? The quality of electricity is determined by the characteristics of three-phase networks and the 50 Hz common in the home:

• The steady-state value of the voltage deviation determines the characteristic value at which consumers can function without failure. The lower normal limit from 220 V is set at 209 V and the upper limit is 231 V.
• The range of variation of the input voltage is the difference between the effective and amplitude values. Measurements are performed per cycle of the parameter drop.
• The dose of flicker is divided into short-term within 10 minutes and prolonged, determined by 2 hours. Indicates the degree of susceptibility of the human eye to the flicker of light, the cause of which was the oscillation of the supply network.
• The impulse voltage is described by the recovery time, which has a different value depending on the cause of the jump.
• Coefficients for assessing the quality of the supply network: the distortion of sinusoidal, the values of temporary overvoltage, harmonic components, asymmetry in the reverse and zero sequences.
• The interval of the voltage dip is determined by the recovery period of the parameter set in accordance with GOST.
• The deviation of the supply frequency leads to damage to the electrical parts and conductors.

The fixed deviation of the input quantity

The indicators of the quality of electricity try to make the corresponding nominal values prescribed in the legislative acts. Attention is paid to the errors that arise when measuring U and f. If there are errors, then you can apply to the supervisory authorities to hold the electricity supplier accountable.

General requirements for the quality of electricity include the parameter of supply voltage deviation, which is divided into two groups:

• Normal mode, when the deviation is ± 5%.
• The limit of the permissible mode is set for oscillations ± 10%. This will be a minimum threshold of 198 V and a maximum of 242 V for a 220 V network.

The voltage recovery should occur in a time interval of not more than two minutes.

The range of the change in the supply network

The power quality standards contain supervision of such a parameter as the oscillation of the voltage components. It sets the difference between the upper amplitude threshold and the lower one. Taking into account that the tolerances of the deviation of the parameter from the established one are within ± 5%, then the limit regime can not exceed ± 10%. A 220 V supply network can not fluctuate more or less than 22 V, and 380 V operates normally within ± 38 V.

The resulting range of voltage fluctuations is calculated by the following expression ΔU = U _max -U _min , in the standards the results are given in% according to the calculations ΔU = ((U _max -U _min ) / U _nominal ) * 100%.

Instability of the input value

The power quality system includes flicker dose measurements. This indicator fixes a special device - a flickermeter, which removes the amplitude-frequency response. The obtained results are compared with the sensitivity curve of the visual organ.

The admissible limits for changing the dose of flicker are set by GOST:

• Short-term fluctuations should not be higher than 1.38.
• Long-term changes must be within the value of the parameter 1.0.

If we are talking about the upper limit of the indicator of the chain of incandescent lamps, then it is required that the result fall into the following boundaries:

• Short-term fluctuations - the indicator is set to 1.0.
• Continuous changes in the parameter are 0.74.

Perceptible differences

Measurements of the quality of electricity include measuring such a component as the pulses of the supply voltage. It is explained by sharp downturns and electricity rises within the selected interval. The reasons for this phenomenon can be the simultaneous switching of a large number of consumers, the effect of electromagnetic interference due to a thunderstorm.

Periods of voltage restoration are established, which do not affect the work of consumers:

• The causes of the fluctuations are a thunderstorm and other natural electromagnetic interference. The recovery period is no more than 15 microseconds.
• If the pulses are due to uneven commutation of consumers, the period is much longer and equal to 15 ms.

The greatest number of accidents at substations occurs due to a lightning strike in the installation. At once the insulation of the conductors suffers. The amount of overvoltage can reach hundreds of kilovolts. For this, protective devices are provided, but sometimes they do not stand, and residual potential is observed. At these moments, failure does not occur due to the strength of the insulation.

The duration of the decline in the input quantity

The measured parameter is described as the voltage drop, which falls within the limits ± 0.1U _nominal for an interval of several tens of milliseconds. For a 220 V network, the change in the figure is allowed up to 22 V, if 380 V, then not more than 38 V. The depth of the recession is calculated according to the expression: ΔU _n = (U _nominal -U _min ) / U _nominal .

The duration of the decay is calculated according to the expression: Δt _n = t _k -t _n , here t _k is the period when the voltage has already been restored, and t _n is the reference point, the moment when the voltage drop occurred.

The quality control of electricity obliges to take into account the frequency of occurrence of dips, determined by the formula: Fn = (m (ΔU _n , Δt _n ) / M) * 100%. Here:

• M (ΔU _n , Δt _n ) is defined as the number of decays at a specified time at a depth ΔU _n and duration Δt _n .
• M is the total account of the decline during the selected period.

Why is the magnitude of the recession necessary?

The parameter of the decay time of the input quantity is required to estimate the reliability of the supply energy in quantitative terms. This indicator can be affected by the frequency of accidents at the substation due to negligence of personnel, lightning. The result of the study of the failures are the forecasts of the degree of failure in the network under consideration.

Statistics allow you to draw approximate conclusions about the stability of the supply of electrical energy. The electricity provider is provided with the recommended data for preventive measures at the facilities.

Frequency deviation

Compliance with the frequency within certain limits refers to the necessary requirement of the consumer. With a decrease of 1%, losses are more than 2%. This is expressed in economic costs, a decrease in the productivity of enterprises. For an average person, this leads to increased amounts in receipts for payment for electricity.

The speed of rotation of an induction motor depends directly on the frequency of the mains. Heating heaters have lower efficiency with a decrease in the parameter less than 50 Hz. If the values are too high, there may be damage to consumers or other mechanisms that are not designed for high torque.

The frequency deviation may affect the operation of the electronics. So on the TV screen there is interference when the indicator changes by ± 0,1Hz. In addition to visual defects, the risk of micronutrient failure is increasing. The method of combating the deviations in the quality of electricity is the introduction of reserve feeder nodes, which allow in an automatic mode to restore the voltage at specified intervals.

Coefficients

For normal operation of the power supply network, the following coefficients are introduced:

• Nonsinusoidality of the stress curve. Distortion of the sinusoid occurs due to powerful consumers: electric heaters, convection ovens, welding machines. If this parameter is deflected, the service life of the motor windings is reduced, the operation of the relay automatics is disrupted, the drive systems with thyristor control fail.
• The temporary overvoltage is a quantitative estimate of the impulse change in the input quantity.
• The Nth harmonic is a characteristic of the sinusoidal character of the voltage characteristic obtained at the input. The calculated values are derived from the tabular data for each harmonic.
• The unbalance of the input value by the reciprocal or zero sequence is important to take into account in order to avoid cases of uneven phase distribution. Such conditions occur more often when the mains supply is cut off, connected by a star or a triangle.

Types of protection against unpredictable changes in the supply network

The improvement of the quality of electricity must be carried out within the time limits specified by law. But the consumer has the right to build the protection of his equipment using the following means:

• Power stabilizers guarantee the maintenance of the input value within the specified limits. Qualitative energy is achieved even with deviations of the input value by more than 35%.
• Uninterruptible power supplies are designed to maintain the functionality of the consumer for a specified period of time. The power of the devices is due to the accumulated energy in its own battery. When the electricity is cut off, the uninterruptible power supplies are able to maintain the functionality of the whole office equipment for several hours.
• Devices to protect against voltage surges operate on the principle of a relay. After exceeding the input value of the set limit, the circuit is opened.

All kinds of protection have to be combined to ensure full confidence that expensive equipment will remain intact during the accident at the substation.