Electricity quality is required to be expressed in quantitative terms to assess the supply network. Providers are required to maintain compliance with GOST specifications such as voltage and frequency fluctuations. Depending on the connected consumers, the values of the main indicators change, which, with significant deviations from them, can lead to the failure of household appliances.
What affects the characteristics of the mains?
The quality of electricity depends on a huge number of factors that change indicators in excess of the limits established by the standards. 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 turn on televisions, electric stoves, split systems.
The quality of electricity according to GOSTs may fluctuate slightly. In very poor supply networks, consumers have to use voltage stabilizers. The control over the characteristics is assigned to Rospotrebnadzor, where you can contact in case of inconsistencies.
Electricity quality may depend on the following factors:
- Daily fluctuations associated with uneven connection by consumers or with the influence of ebbs and flows at offshore stations.
- Changes in the air: humidity, ice formation on the supply wires.
- Change in the wind when the visor produces power.
- The quality of the wiring, over time, it wears out.
Why do we need the main characteristics of the mains?
The quantitative value and the error of the deviation of the parameters are set according to GOST. The quality of electricity is spelled out in document 32144-2013. It was required to legalize these indicators because of the risk of fire of consumer devices, as well as the malfunction of electrical appliances sensitive to voltage drops of installations. The latest devices are common in medical institutions, research centers, and military facilities.
Electricity quality indicators were updated in 2013 due to the development of the energy sales market and the advent of new electronic devices. Consider electricity as part of its supply should be as products that meet certain criteria. If the established characteristics are rejected, administrative liability may apply to providers. If, due to fluctuations in the incoming voltage, people were injured or could have suffered, then criminal liability may already arise.
What happens to consumers with deviations from normal diet?
The parameters of the quality of electricity affect the duration of the connected devices, often this becomes critical in production. The productivity of the lines decreases, the energy consumption increases . So on the motor shaft decreases the torque when the values of the supply network. The service life of lighting lamps is shortened, the luminous flux of the lamps becomes less or flickers, which affects the products in greenhouses. A significant influence is exerted on the processes of other biochemical reactions.
According to the laws of physics, a decrease in voltage with a constant load on the motor shaft leads to a rapid increase in current. This, in turn, leads to malfunctioning of the circuit breakers. As a result, the insulation melts, in the best case, fuses burn , in the worst, motor windings and electronics are irreparably damaged. Under similar circumstances, the meter begins to rotate at a higher speed. The landlord suffers losses.
Mains Evaluation Criteria
What does GOST contain? The quality of electricity is determined by the characteristics of three-phase networks and circuits common at home with a frequency of 50 Hz:
- The steady-state value of the voltage deviation determines the value of the characteristic at which consumers can function without failure. The lower normal limit is set from 220 V to 209 V and the upper one is 231 V.
- The magnitude of the change in input voltage is the difference between the values of the current and amplitude. Measurements are carried out per cycle of the parameter difference.
- The flicker dose is divided into short-term within 10 minutes and long, determined by 2 hours. Indicates the degree to which the human eye is susceptible to flickering light, caused by fluctuations in the supply network.
- The pulse 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: by the distortion of the sinusoidality, the values of the temporary overvoltage, harmonic components, asymmetry in the reverse and zero sequences.
- The voltage dip interval is determined by the recovery period of the parameter set according to GOST.
- Deviation of the supply frequency leads to damage to electrical parts and conductors.
Input Deviation Fixed
They are trying to make power quality indicators consistent with the established ratings prescribed in legislative acts. Attention is paid to errors arising from measurements of U and f. If there are errors, then you can contact the supervisory authorities to prosecute the electricity supplier.
General requirements for the quality of electricity include the deviation parameter of the supply voltage, which is divided into two groups:
- Normal mode when the deviation is ± 5%.
- The limit of the permissible mode is set for fluctuations of ± 10%. This will be for a 220 V network a minimum threshold of 198 V and a maximum of 242 V.
Voltage recovery should occur in a time interval of not more than two minutes.
The scope of the mains change
Electricity quality standards contain supervision of such a parameter as the fluctuation of voltage components. It sets the difference between the upper amplitude threshold and the lower. Given that the tolerances of the deviation of the parameter from the set fit within the ± 5% limit, then the swing limit mode cannot exceed ± 10%. The 220 V power supply network cannot 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 standards the results are indicated in% according to the calculations ΔU = ((U max −U min ) / U nominal ) * 100%.
Input value instability
The power quality system includes flicker dose measurements. This indicator is fixed by a special device - a flicker meter, which removes the amplitude-frequency characteristic. The results are compared with the sensitivity curve of the visual organ.
GOST established the permissible limits for changing the dose of flicker:
- Short-term fluctuations should not exceed 1.38.
- Long-term changes must be within the value of parameter 1.0.
If we are talking about the upper limit of the indicator of a chain of incandescent lamps, then it is required that the result fall into the following boundaries:
- Short-term fluctuations - the indicator is set equal to 1.0.
- Long-term parameter changes are 0.74.
Tangible differences
Measurements of the quality of electricity include measurements of such a component as pulses of the supply voltage. It is explained by sharp drops and rises in electricity within the selected interval. The reasons for this phenomenon may be the simultaneous switching of a large number of consumers, the influence of electromagnetic interference due to a thunderstorm.
The periods of voltage recovery that do not affect the operation of consumers are established:
- The reasons for the differences are a thunderstorm and other natural electromagnetic interference. The recovery period is not more than 15 μs.
- If the pulses appeared due to uneven switching of consumers, then 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. Insulation of conductors immediately suffers. The overvoltage can reach hundreds of kilovolts. Protective devices are provided for this, but sometimes they cannot withstand, and residual potential is observed. At these times, a malfunction does not occur due to the strength of the insulation.
Input Duration Duration
The measured parameter is described as a voltage drop falling within ± 0.1U nominal over an interval of several tens of milliseconds. For a 220 V network, a change in the indicator is allowed up to 22 V, if 380 V, then no more than 38 V. The recession depth is calculated according to the expression: ΔU n = (U nominal −U min ) / U nominal .
The duration of the decline is calculated according to the expression: Δt n = t k −t n , here t k is the period when the voltage has already recovered, and t n is the reference point, the moment when the voltage dropped.
The quality control of electricity requires taking 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 drops in the set time at a depth of ΔU n and duration Δt n .
- M - the total account of recessions during the selected period.
Why do we need a recession?
The parameter the duration of the decline in the input quantity is required to assess the reliability of the supply energy in quantitative terms. This indicator may be affected by the frequency of accidents at substations due to the negligence of personnel and lightning. The result of a failure study is prediction of the degree of failure in the network in question.
Statistics allows you to make approximate conclusions about the stability of the supply of electrical energy. The electricity provider is provided with recommended data for preventive measures at the plants.
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, reduced productivity of enterprises. For the average person, this leads to increased amounts in electricity bills.
The speed of rotation of an induction motor directly depends on the frequency of the supply network. Heating TENs have lower performance with a decrease in the parameter below 50 Hz. With overestimated values, damage to consumers or other mechanisms that are not designed for high torque can occur.
Frequency deviations can affect the operation of the electronics. So on the TV screen, interference occurs when the indicator changes by ± 0.1 Hz. In addition to visual defects, the risk of microelement failure increases. The method of combating power quality deviations is the introduction of redundant supply nodes, which allow automatic restoration of voltage at set intervals.
Odds
For the normal operation of the supply network, the control of the following coefficients has been introduced:
- Nonsinusoidality of the voltage curve. Sinusoid distortion occurs due to powerful consumers: heating elements, convection ovens, welding machines. With deviations of this parameter, the service life of the motor windings decreases, the operation of relay automation is disrupted, the thyristor control drive systems fail.
- Temporary overvoltage is a quantitative estimate of the pulse change in the input quantity.
- The nth harmonic is a characteristic of the sinusoidality of the voltage characteristic obtained at the input. The calculated values are obtained from the tabular data for each harmonic.
- The asymmetry of the input quantity in the reverse or zero sequence is important to consider to exclude cases of uneven phase distribution. Such conditions occur more often when the supply network is disconnected, connected according to the star or triangle scheme.
Types of protection against unpredictable changes in the mains
Improving 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 conditioners ensure that the input value is kept 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 health of the consumer for a specified period of time. The devices are powered by the accumulated energy in their own battery. With a power outage, uninterruptible power units are able to maintain the operability of the equipment of the whole office for several hours.
- Surge protection devices operate on the principle of a relay. After exceeding the input value of the set limit, the circuit opens.
All types of protection have to be combined to ensure complete confidence that expensive equipment will remain intact during an accident at a substation.