Power quality = power + quality?

Power quality, in a general sense, refers to high-quality power supply, including voltage quality, current quality, power quality and power quality.

It can be defined as: the deviation of voltage, current or frequency that causes the malfunction of the electrical equipment or does not work properly, including frequency deviation, voltage deviation, voltage fluctuation and flicker, three-phase unbalance, temporary or transient over-voltage, Waveform distortion (harmonics), voltage dips, interruptions, transients, and continuity of power supply.

In modern power systems, voltage sag and interruption have become the most important power quality issues. among them:

1, voltage quality. It is the deviation of the actual voltage from the ideal voltage, reflecting the concept of whether the power supplied by the power supply enterprise to the user is qualified. This definition can cover most power quality problems, but it cannot include power quality problems caused by frequency, nor does it include the impact and pollution of power equipment on grid power quality.

2. Current quality. It reflects the change of current closely related to voltage quality. In addition to the constant frequency and sinusoidal waveform requirements of the AC power supply, the power user also requires the current waveform to be in phase with the supply voltage to ensure high power factor operation. This definition contributes to the improvement of grid power quality and the reduction of line losses, but does not summarize most of the power quality problems caused by voltage.

3. Power quality. Its technical meaning refers to voltage quality and power supply reliability, and non-technical meaning refers to service quality. Including the speed of the power supply company's response to user complaints and the rationality and transparency of the price of electricity.

4, the quality of electricity. It includes the current quality and the rights, responsibilities and obligations of the electricity consumers in the interaction and influence of the power supply and the electricity supply, and also whether the power users pay the electricity fee on time and in full.

Main indicator for measuring power quality

Indicators for measuring power quality include: voltage deviation, frequency deviation, voltage three-phase imbalance, harmonics and interharmonics, voltage fluctuations, and voltage flicker.

1. Voltage deviation: The voltage deviation refers to the unstable supply voltage and the voltage rise or fall.

2. Frequency deviation: All grids have the same grid frequency requirements and will not change due to different power users. Frequency deviations have corresponding regulations in each country.

3. Voltage three-phase unbalance: The value of the three-phase voltage exceeds the specified standard.

4, harmonics and interharmonics: the frequency is an integer multiple of the fundamental wave of the sinusoidal current or voltage called harmonics. Non-integer multiples are collectively referred to as interharmonics.

5. Voltage fluctuations and flicker: Regular changes in the voltage within the grid are called voltage fluctuations, or random variations in the magnitude of the variation between 0.9 and 1.1. Flicker refers to the visual impact of voltage instability on lamp illumination.

Small industries and major products involved in power quality

The small industries involved in power quality include:

1. Reactive power compensation;

Divided by voltage level: mainly divided into high voltage reactive power compensation and low voltage reactive power compensation;

Divided by different products and functions, the main reactive power compensation equipment: TSC, LC passive power filter, SVC, STATCOM (SVG).

2. Harmonic control;

Active filter (APF), passive filter.

3. Power quality testing;

4. Other power quality issues.

Power quality metrics

Indicators for measuring power quality include: voltage deviation, frequency deviation, voltage three-phase imbalance, harmonics and interharmonics, voltage fluctuations, and voltage flicker.

1. Voltage deviation: The voltage deviation refers to the unstable supply voltage and the voltage rise or fall.

2. Frequency deviation: All grids have the same grid frequency requirements and will not change due to different power users. Frequency deviations have corresponding regulations in each country.

3. Voltage three-phase unbalance: The value of the three-phase voltage exceeds the specified standard.

4, harmonics and interharmonics: the frequency is an integer multiple of the fundamental wave of the sinusoidal current or voltage called harmonics. Non-integer multiples are collectively referred to as interharmonics.

5. Voltage fluctuations and flicker: Regular changes in the voltage within the grid are called voltage fluctuations, or random variations in the magnitude of the variation between 0.9 and 1.1. Flicker refers to the visual impact of voltage instability on lamp illumination.

What are the national standards for power quality?

1. Power supply voltage deviation (GB/T 12325—2008)

2. Voltage fluctuation and flicker (GB/T 12326—2008)

3. Harmonics of the utility grid (GB/T 14549-1993)

4. Three-phase voltage imbalance (GB/T 15543-2008)

Characteristics of power quality

Power production companies cannot fully control power quality. Some power quality changes are caused by power users (such as harmonics, voltage fluctuations, and flicker), or natural disasters and non-control factors.

The energy indicators for supplying electricity at different times are usually different, and the quality of power is constantly changing in space and time.

Causes of power quality

1. Nonlinear problems in power system components

The nonlinear problems of components in the power supply system are: harmonics generated during normal operation of the generator; harmonics generated by various transformer devices in the power grid; harmonics generated by direct current transmission; amplification of harmonics by the transmission line after high voltage effect. In addition, the installation of parallel capacitors in the substation and other factors will also cause the emergence of harmonics. Among these factors, the direct current transmission factor is the main factor for generating harmonics in the power system.

2, non-linear load

The proportion of non-linear loads in industrial and domestic electricity is large, which is the main source of harmonics in power systems. The main load of nonlinearity is the electric arc furnace, and the arc delay of the arc furnace and the severe nonlinearity of the arc generate harmonics.

In the daily life and production load of residents, the volt-ampere characteristics of fluorescent lamps used are also non-linear, and there are also serious harmonic currents generated, and the highest content is the 3rd harmonic. In addition, the use of high-power rectification and frequency conversion devices will also have severe harmonic current generation, which seriously affects the safety of the power grid.

3, power system failure

Power quality can also be affected by internal and external faults during power system operation. For example, various natural disasters, artificial abnormal operations, various line short circuits, changes in the operating state of the generator and excitation system when the power grid fails, etc. Quality has a big impact.

Harmonic hazard

The main hazards of power harmonics are:

1. Cause series resonance and parallel resonance, amplify harmonics, causing dangerous overvoltage or overcurrent;

2, the generation of harmonic losses, so that the efficiency of hair, power and electrical equipment is reduced;

3. Accelerate the insulation aging of electrical equipment, making it easy to break down, thus shortening their service life;

4. Make equipment (such as motor, relay protection, automatic device, measuring instrument, power electronic device, computer system, precision instrument, etc.) operate abnormally or cannot operate correctly;

5. Interfere with the communication system, reduce the transmission quality of the signal, destroy the correct transmission of the signal, and even damage the communication equipment.

Method of controlling power harmonics

There are three main types of harmonic control measures:

The first is active management, that is, starting from the harmonic source itself, by improving the electrical equipment so that it does not produce or generate less harmonics;

The second is the end-of-pipe governance, that is, starting from equipment or systems affected by harmonics to improve their ability to resist harmonic interference;

The third is passive governance, that is, by installing a power filter, preventing harmonics generated by harmonic sources from being injected into the grid, or preventing harmonics of the power system from flowing to the load end.

Due to the extensiveness and complexity of harmonic sources, active governance methods are affected by factors such as equipment structure, efficiency, cost, reliability, etc., and can only solve some problems. The terminal governance method and passive governance method are still the current power harmonic problem. The main method. For example, the harmonic resonance amplification caused by the reactive compensation capacitor is suppressed by the series detuning reactor, and the filtering is performed by installing a passive power filter and an active power filter in the system.

Measures to improve power quality

Measures to improve power quality include:

First, adjust the load and reduce the sensitivity of the load. If a power user who requires a particularly high load power quality is only able to meet the requirements in the short term, the power company must take the necessary measures together with the power user. Reduce load sensitivity and reduce power quality.

Second, to improve the power grid, power companies install the necessary equipment to suppress or eliminate power disturbances.

The common power quality adjustment device has relatively simple functions, for example, an active filter APF, a dynamic voltage restorer DVR, etc., and the device that fully realizes the power quality of the power user is a power quality regulator, and the composition thereof is mainly a capacitor to be connected in parallel. The inverter and the series inverter are coupled together.

The parallel inverter performs nonlinear load harmonic current and reactive power compensation. The PWM current control technology is used to adjust the DC voltage of the capacitor. The series inverter uses PWM voltage control technology, which mainly controls the output voltage to achieve sensitivity to suppress harmonics and reduce load.

Since the power quality regulator is composed of an inverter connected in series and in parallel, it has the structural features of both, and the waveforms of current and voltage in the network can be simultaneously adjusted, and the application of the power quality regulator is greatly solved. The emergence of power quality problems in the power grid.

FEATURES:

High intensity and reliability

High quality, Low power requirement and low cost

IC compatible , Easy assembly

Meet RoHS EU Directive

ESD 2000V