Definition of power quality issues
Power quality includes voltage quality, current quality, power quality, and power quality. The IEEE 22nd Standards Committee defines the following related power quality issues:
Voltage dip: The effective value of the voltage or current is reduced to 0.1-0.9 of the rated value for a duration of 0.5 cycles to 1 minute, and the system frequency is still nominal.
Voltage interruption: The line loses voltage in single or multiple phases within a certain time range (less than 0.1 of rated value). According to the duration, it is divided into instantaneous power off (0.5 cycle to 3 seconds), temporary power failure (3 seconds to 60 seconds) and continuous power failure (more than 60 seconds).
Harmonics and Interharmonics: A sinusoidal voltage or current whose frequency is an integer multiple of the fundamental frequency of the power supply is called a harmonic, and a sinusoidal voltage or current containing a non-integer multiple of the fundamental wave is an interharmonic. Harmonics are caused by the nonlinear nature of power systems and electrical load equipment. The harmonics are mainly generated by induction motors, static inverters, cycle inverters and arc equipment. Interharmonics can cause visual flicker in the lighting device.
Voltage fluctuation (flicker): The voltage fluctuation is a regular or random change of the voltage amplitude within the normal range of variation (90%-110% of the rated value), and the voltage fluctuation will produce an illumination flicker of about 6-14 Hz. The phenomenon is called flicker. Voltage fluctuations and flicker are mainly caused by industrial loads such as electric welders, rolling mills and electric arc furnaces. Flicker is a subjective perception of lighting fluctuations and an important and effective indicator of the impact of voltage fluctuations on electrical equipment.
In addition, there are other power quality issues, such as voltage asymmetry, three-phase unbalance, overvoltage, undervoltage, and so on.
Harm of power quality problems
The decline of power quality will not only affect the normal and safe power supply of the power supply system, but also bring various hazards to the power system, which directly affects personal safety and economic efficiency. Therefore, the power quality problem has serious consequences. appears in:
(1) Voltage fluctuations and flicker
It will cause unstable operation of the electrical equipment, and the voltage amplitude will exceed the allowable range due to fluctuations in voltage. In addition, due to the voltage fluctuation caused by the electric arc furnace steelmaking operation, the rotating electric machine will generate additional loss, which will reduce the working efficiency and life of the motor.
(2) Short-term interruption of voltage
Typical transient voltage deviations are usually caused by external environmental influences such as lightning and strong winds, and may also be malfunctions of internal equipment or control devices. The large-scale use of various precision instruments and equipment controlled by computers and microprocessors is increasingly sensitive to the quality of power supply. According to a market survey by IBM, 48.5% of computer data loss is due to power quality.
(3) Harmonic hazards
1. Harmonics increase the additional transmission loss of the utility grid, reducing the efficiency of power generation, transmission and use of electrical equipment;
2. Harmonics will make the measurement results of the electrical instrument incorrect;
3. Harmonics can affect or even seriously affect the normal operation of electrical equipment. For example, harmonics generate additional torque to the motor, resulting in undesired mechanical vibration, noise, and additional copper loss, iron loss, and overvoltage. Local overheating, insulation aging, shortening equipment life;
4. Harmonics can cause malfunctions of protection devices such as relay protection and automatic devices;
5. Harmonics can cause significant interference to adjacent communication systems and reduce communication quality. When the harmonic frequency is equal to the natural frequency of the system, parallel resonance is generated, and the harmonic is amplified several times or even several times.
(4) Reactive power
Reactive power mainly reduces the use efficiency of power generation equipment and transmission equipment, increases the capacity of equipment, and increases equipment and line losses. Reactive power also increases the voltage drop across the line and transformer. If it is an impact reactive load, it will also cause the grid voltage to fluctuate drastically, which seriously affects the quality of the power supply. Typical phenomena include automatic clock reset, computer crash, abnormal operation of programmable controller, abnormal operation of communication system, overheating capacitor in neutral line, damage to motor due to overheating, loss of output due to loss, inaccurate meter measurement, relay protection and automatic device error Action, equipment insulation aging, accelerated line loss and transformer loss.
(5) Three-phase imbalance
1. Make the rotating motor generate additional heat and vibration, which has a great impact on safe operation and normal output:
2. causing the semiconductor converter device to generate additional harmonic currents (non-characteristic harmonics);
3. Causes a variety of protections with a negative sequence component as the starting component to malfunction (especially when harmonics are present in the power grid), which poses a serious threat to the safe operation of the power system;
4. In the low-voltage distribution line, it will affect the normal operation of the computer, causing the life of the lighting lamp to be shortened (high voltage) or insufficient illumination (low voltage) and damage to the TV;
5. Three-phase unbalance will also increase the power grid loss; for communication equipment, it will increase its interference and affect the normal communication quality.
Automotive Fuse
Automotive Fuse, ie Car Fuse, is the name we are often called. Its official name is "fuse protector." The use of Automotive Fuse Block is very similar to that of household fuses, which act as a circuit protection barrier when the circuit current is abnormal and exceeds its rated current. Vehicle fuses are broadly divided into two types of fast-blow fuses and slow-blow fuses.
A car is made of Car Fuse, Automotive Switches and other kinds of Automotive Accessories, and the Automotive Switches including Automotive Rotary Switches, Automotive Battery Switches, Automotive Rocker Switches
Inline Fuse Holder include high-current fuses and medium-low current fuses. Medium and low current fuses are generally easier to reach. Low-to-medium current fuses can be broadly classified as chip fuses (including automatic fuse box mini-fuse), plug-in fuses, screw-on fuses, and tube fuse box fuses. Among them, we are able to access medium-sized ATO or small-size fast-acting chip fuses. Chip fuses can carry small currents, short pulse currents, such as headlamp circuits, post-glass defrosting, and more.
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