By analyzing the causes of line voltage mutation, its influence on microelectronics production enterprises and the improvement methods of voltage mutation in China at present, the protective measures that can be taken are put forward.
The abrupt change of line voltage generally refers to the abnormal fluctuation of power grid caused by fault or abnormal load switching. The reasons are generally as follows.
1 surge
Surge means that the effective value of the output voltage is higher than the rated value 1 10% for one or several cycles. There are two kinds of surge: external surge and internal surge. External surge mainly comes from lightning, and another source is the large electrical load in the power grid. Generally, during heavy load switching, the power grid will suddenly unload or load, resulting in high-voltage inrush current.
Internal surge often occurs in electrical equipment on low-voltage power lines. Such as refrigerators, air conditioners, elevators, electric welding machines, air compressors and other inductive loads.
2 high voltage sharp pulse
High voltage spike pulse is mainly caused by lightning strike, arc discharge, electrostatic discharge or switching operation of large electrical equipment. The peak voltage reaches 6000v, and the voltage duration ranges from one ten thousandth of a second to half a cycle (10ms).
This pulse voltage is abrupt and discontinuous. Once it is generated, it will cause great damage to electrical equipment, which is one of the potential threats to electrical equipment.
3 transient overvoltage
Transient overvoltage refers to the pulse voltage whose peak voltage is as high as 20kv, but its duration is between one millionth of a second and one ten thousandth of a second. Overvoltage, also known as power frequency voltage rise, is mainly due to the action of circuit breaker or the occurrence of short circuit fault, which makes the power system regain some temporary stability after the transition process.
All electrical equipment is in the big family of public power grid. Under the action of power frequency power supply, due to the accumulation of capacitance effect of long-distance no-load lines, the voltage distribution along the lines is uneven and the terminal voltage is the highest, resulting in instantaneous overvoltage of electrical equipment. The damage caused by transient overvoltage to electrical equipment is no less than that caused by high voltage sharp pulse.
4 voltage sag
Voltage sag refers to a low voltage state in which the effective value of voltage is between 80% and 85% of rated value and lasts for one or several cycles. Voltage sag is the most common power problem, accounting for 87% of power problems. Large equipment is often turned on or connected to a large power transformer.
Voltage sag has a very serious impact on high-tech and precision equipment with high voltage quality requirements. Especially the impact on computers, from the suspension of keyboard and other interface devices to data loss and file destruction; The sudden voltage drop will also damage the components in the computer and shorten the service life of the computer.
The destructive consequences of sudden changes in line voltage, especially instantaneous overvoltage (peak voltage) and voltage sag, on microelectronic devices are shown in the following four levels:
(1) Mechanical equipment is mainly damaged by lightning. The damage of this kind of lines is mainly caused by natural lightning, not man-made control factors. Under normal circumstances, the harm caused is also extremely serious.
(2) In the process of power supply operation of the whole equipment, because the power supply is too large, or the machinery is running at the same time, this leads to the short circuit phenomenon of mechanical equipment under the same power supply, thus causing damage to different mechanical equipment and causing a series of economic losses.
(3) If the instrument is disturbed by the outside world and cannot clearly display pictures or related information, it will also lead to the damage of mechanical equipment, thus shortening its service life.
In order to make microelectronic equipment work normally and prolong its service life, it is necessary to prevent threats from the power grid. The most effective method is to use high-performance anti-interference AC regulated power supply to supply power to instruments and equipment, so as to isolate the "pollution" of instruments and equipment in the power grid, such as surge peak voltage, surge current, harmonic distortion and voltage fluctuation, eliminate or weaken the harm of various interference sources and induced lightning strikes from the power grid, and form a local "purified" power supply.
At present, there are many kinds of AC regulated power supplies on the market, and the applicable objects are also different. The AC regulated power supply of microelectronic equipment shall have the following performance:
(1) High reliability: The reliability of the AC regulated power supply itself must be high. The one that can work continuously and has the longest mean time between failures should be selected. Prevent the failure of AC regulated power supply from affecting the normal work of equipment and even damaging the hardware or software of instruments and equipment.
(2) Excellent anti-interference performance: The anti-interference performance of the AC regulated power supply directly affects the "purification" degree of the power grid. The input and output should be completely isolated, and the AC regulated power supply with good shielding device and filter absorption circuit should be selected.
(3) Strong overvoltage protection function: it has the function of eliminating lightning disaster and restraining surge voltage. Surge protectors are generally installed to reduce the destructiveness of peak voltage, and the surge current resistance is greater than 15000A.
(4) Small waveform distortion: The waveform distortion of the output voltage of AC regulated power supply should be less than 5%. Even in the case of high harmonic content in the power grid, the output voltage can still maintain a sinusoidal waveform with a total harmonic content of less than 5% through the absorption of the internal filter circuit of the AC regulated power supply.
(5) All kinds of protection functions are complete: AC regulated power supply should have protection functions such as overvoltage, overvoltage and short circuit, which can not only protect its own safety, but also protect the safety of microelectronic equipment.
For extremely important precision equipment, uninterruptible power supply (UPS) can be used as its power supply. Uninterruptible power supply is a constant voltage and constant frequency power supply with inverter as the main component. It consists of inverter, battery pack and control circuit.
When the grid voltage is normal, the UPS uses the grid power to charge itself. When the power grid is abnormal, the uninterruptible power supply releases the electric energy stored in the battery for the load to use. It can effectively solve the problems of power failure, lightning peak, surge, frequency oscillation, voltage mutation, voltage fluctuation, frequency drift, voltage drop, pulse interference and so on. However, the general investment is large and the maintenance cost is high.
With the constant change and development of power industry, people pay more and more attention to the use of power transmission, and systematically analyze the various security of power transmission network.
Usually study the power supply situation and fault behavior used in a certain area. It is known that under normal circumstances, the power supply network is seriously damaged, which leads to the "pollution" of the power supply network and ultimately affects the stability of power supply equipment and instruments. Many power supply personnel can't clean the power supply lines carefully during maintenance and inspection, and then under the long-term influence of the external environment, their network lines suffer from "pollution", which ultimately affects the stability of power supply.
As a public power grid, it is connected with thousands of loads, some of which are inductive, capacitive and switching power supplies. , which not only obtains electric energy from the power grid, but also adversely affects the power grid itself, worsens the power supply quality of the power grid or local power grid, and causes voltage fluctuation of the power grid. Therefore, while solving the influence of sudden change of power grid voltage, we should also strengthen the control of access load, reduce or eliminate the "pollution" to the power grid, and make it clean, reasonable and standardized in the use of electric energy.
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