Electricity is characterized by three main parameters, including frequency, voltage, and the shape of its curve. Frequency refers to the active power balance characteristic. The voltage in power systems is a characteristic of the reactive power balance. At the same time, each individual element of the energy system affects the overall generated electromagnetic field, which, of course, affects the quality of energy supplied to consumers. In this article, we will consider what are the indicators of power quality, their regulation and control methods, as well as measurements.
Content:
- Consideration of key indicators
- Measurement methods
Consideration of key indicators
The quality of electricity is determined by the level of ratio to the established values of certain indicators. All parameters of electrical energy most of the time in a day (95%) must comply with the normal established values and not exceed this limit.
GOST 13109-87 divides quality indicators into two categories: basic and additional. The main ones determine the properties of electricity. This subgroup includes 9 voltage characteristics and 1 frequency characteristic. Let's consider a number of key indicators in more detail.
Voltage deviation. Has the greatest impact on consumer performance. Loads, voltage levels and other parameters can change over time. Based on this, the voltage drop value is also variable. At the same time, a significant reduction in stress at industrial enterprises has a negative impact on the overall labor productivity, negatively affects the vision of the working personnel. Also, voltage reduction affects the duration of most technological processes in electrothermal and electrolysis plants. In addition, a voltage level mismatch with the required values results in a loss of voltage and power.
In networks up to 1 kV, the permissible voltage deviation ± 5%, maximum ± 10%. In 6-20 kV networks, the maximum deviation value is ± 10%.
The range of voltage change. This power quality parameter is the difference between the peak or rms value before and after the change. The repetition rate of these changes can be from 2 times / min. up to 1 time / h. Such abrupt changes in a three-phase network can be caused, for example, by the operation of an arc steel-making furnace or a welding machine. The regulation of voltage fluctuations is based on the need to protect people's eyesight. A separate swing value is set for each type of lamp. To ensure compliance with this quality indicator, it is recommended to use a separate power supply for electrical receivers of the lighting network and power loads.
Dose of voltage fluctuations, which is analogous to the previous indicator of the quality of electrical energy, they are interchangeable. The rationing of the dose of fluctuations in power grids is carried out only if there are certain devices in them.
Voltage dip duration. Failure is a sharp decrease in voltage, after which it is restored back to its original or approximate value after a certain time interval. The duration of the dip reflects the time from the initial moment of the dip to the moment of its recovery. The duration of the failure can be either in one period or in tens of seconds. According to GOST, this parameter can reach 30 seconds in networks up to 20,000 Volts.
Impulse voltage is similar in description to a failure, but its duration is different, ranging from a few microseconds to ten milliseconds. The permissible values of this indicator of the quality of electricity are not standardized by the standard.
The voltage characteristics are also four coefficients: harmonic component, non-sinusoidal curve, zero and negative sequence.
The characteristic of the frequency is the deviation. The largest frequency deviation occurs when loads are changing at a slow rate and the power reserve is small. Normal permissible deviation is ± 0.2 Hertz, maximum ± 0.4 Hertz. In post-emergency modes, the deviation interval is admissible from + 0.5 to - 1 Hertz (no more than ninety hours per year).
Additional indicators of power quality are a form of recording the main ones. This includes the following 3 coefficients that characterize the voltage: amplitude modulation, as well as the unbalance of phase and phase-to-phase voltages.
Measurement methods
There are three main types of instruments with which you can measure indicators:
- measuring - are a clamp meter with an indication unit; determine only the nominal values of the parameters, are used for daily control;
- analyzers - in addition to determining the nominal parameters, they are able to analyze phase imbalance, losses, and are able to assess energy losses; used to carry out one-time measurements;
- recording devices - are stationary devices, perform the same functions as analyzing devices, but for a long time; they allow you to build any necessary graphs.
To ensure the reliability of the functioning of power systems, it is necessary to comply with the power quality indicators to certain requirements. For this, they are rationed. In order to timely monitor the compliance of parameters with standard values, control is necessary. Quality control is carried out by the working personnel of energy enterprises.
The duration of the measurement of each indicator is at least twenty-four hours, while the frequency of control established by the international state standard and is 1 time in two years, except for voltage deviation (2 times in year).
This issue is discussed in more detail in the video:
So we examined the main indicators of the quality of electricity, their regulation and measurement methods. We hope the information provided was interesting and informative for you!
It will be helpful to read:
- What is overvoltage in the network
- Earthing resistance measuring instruments
- Causes of electricity losses in networks
