In modern society, electrical energy is one of the most widely used energy sources, and its degree of application is one of the main indicators of a country ’s development level. With the development of science and technology and the national economy, the demand for electrical energy is increasing, and at the same time, the requirements for electrical power quality are becoming higher and higher.
Power quality; harmonics; PQA; power quality analyzer.
1. Power quality and indicators
An ideal power system should supply users with a constant frequency and a sinusoidal waveform at a specified voltage level. In a three-phase AC power system, the voltage and current of each phase should be in a symmetrical state with equal amplitude and 120 ° phase difference. Because the parameters of each component of the system are not ideally linear or symmetrical, coupled with imperfect control methods, different load properties and the randomness of their changes, operating operations, various failures, etc., this ideal state does not exist in practice. Therefore, the concept of power quality was born.
Power quality can be defined as: voltage, current, or frequency deviations that cause electrical equipment to malfunction or fail to work properly. Its content involves frequency deviations, voltage deviations, electromagnetic transients, power supply reliability, waveform distortion, three-phase unbalance, and voltage fluctuation And flicker.
With the emergence of new power loads and their increasing requirements for power quality, power quality problems have gradually attracted the attention of power companies and power customers. The main reasons are as follows:
1) In order to improve labor productivity and automation level, a large number of computer-based control equipment and electronic equipment are put into use, and these devices are very sensitive to power quality. A computing center that loses voltage for two seconds can destroy dozens of hours of data processing results or lose hundreds of thousands of dollars in output value. The continuous finishing production of today's automation equipment, whether it is variable speed drag or robot, working machine or automated production line, such as flexible manufacturing system or computer integrated manufacturing system, they are very sensitive to interference and abnormalities in the power distribution system, even One second of abnormality may cause confusion inside the factory. The tolerance of these users for unqualified power is strictly limited to only 1 to 2 frequency cycles of continuous power frequency.
2) Significant changes have taken place in the load structure of modern power systems, such as semiconductor rectifiers, thyristor voltage regulation and frequency conversion adjustment devices, steel-making electric arc furnaces, electrified railways and household appliances. The rapid development of loads, due to their nonlinearity, impact The unbalanced and unbalanced power consumption characteristics cause the voltage waveform of the power grid to be distorted, or cause voltage fluctuations and flickers, and three-phase unbalance, and even cause system frequency fluctuations. These will cause serious interference or "pollution" to the power quality of the power supply. ".
3) Electrical energy is a commodity. Under the electricity market operation mechanism, different power generation companies, including independent power producers, compete on the power generation side. The transmission and distribution system (ie, power company) is separated from power generation. The user provides the service of transferring electrical energy, and the user side can also participate in price control as an independent entity. Such an open and encouraging competitive operating environment will inevitably put higher and higher requirements on power quality, and promote the development and continuous improvement of power quality standardization.
The power quality is different from the general product quality, and has the following characteristics:
1) Quality indicators (such as harmonics, voltage fluctuations, and flicker three-phase unbalance) that are not entirely determined by power production enterprises are often caused by user interference;
2) For different power supply (or power) points at different (or power) moments, power quality indicators are often different, that is to say, power quality is in dynamic changes in space and time.
2. Application of power quality analyzer
The power quality analyzer can measure and analyze different aspects of power quality, and provide theoretical basis and data support for the next step of power quality management.
1) Harmonic measurement：
Among the various indicators of power quality, harmonics are the most common due to disturbing loads. This is because non-linear loads are growing rapidly, and the harmonic levels of the power grid are constantly increasing. Due to harmonic interference, electrical equipment abnormalities and accidents There is a trend of increasing year by year, so the harmonic standards of public power grids play an important role in controlling the harm of harmonics and ensuring the safety, economic operation and normal production of power grids and users.
2) Voltage fluctuation and flicker:
l Voltage fluctuations in the power grid are generally caused by fluctuating loads. The main fluctuating loads are:
l Steel-making electric arc furnace;
l Loads where the motor starts frequently, such as rolling mills or winches, etc .;
l Intermittently energized loads, such as resistance welding machines and arc welding machines.
l Hazards of voltage fluctuation and flicker
l Electric lighting flashes, causing visual fatigue and even unbearable;
l Motor, screen image distortion, swing, roll and brightness changes;
l The speed of the motor is uneven, which affects the quality of the product and even damages the motor
l Electronic computer monitoring and control equipment are not working properly.
3) Three-phase voltage unbalance:
l Three-phase unbalance has the following application environment impact, and abnormal operation of the device for a long time will cause damage to the device.
l The impact of asymmetric operation on the generator;
l Induction motor runs under unbalanced voltage
l Asymmetrical operation of the transformer;
l Relay protection and false start of automatic device;
l Non-characteristic harmonics of the converter;
l Interference with computer systems;
l Increase of transmission line loss;
Voltage is one of the important indicators of power quality. The quality of the voltage has an important impact on the safe and economic operation of the power system, as well as ensuring the safe production and product quality of users and the safety and life of electrical equipment. The reactive power compensation and reactive power balance of the power system are the basic conditions for ensuring the voltage quality.
There have been a lot of researches on the damage of power quality indicators to electrical equipment. However, different indicators of power quality have different effects on different equipment, especially when there are multiple indicators of power quality Impact is a very complex issue.
In order to solve the related electrical problems caused by power quality, a power quality analyzer is needed to provide data for engineers to analyze the problem and find out the cause.
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