The hazards and solutions of power quality problems

introduction:

Power supply is the heart of information systems and electronic products. The quality of AC power determines whether information systems and electronic products can work normally. Therefore, only by understanding the quality issues of AC power supply can we provide effective solutions. The quality problems of AC power supply include the following types.

1. Power quality issues

1. The voltage variation range is too large, the grid power supply is insufficient, the power supply department adopts step-down power supply, or it is located in a remote area and has excessive losses, resulting in low voltage; the grid consumes too little electricity, resulting in high voltage. If the voltage is too low, the load will not work properly; if the voltage is too high, the service life of the load will be shortened or the load will be burned.

2. The cause of waveform distortion (or harmonics) is the use of switching power supplies in power electronic equipment and electrical equipment such as rectifiers, UPS power supplies, electronic speed control equipment, fluorescent lighting systems, computers, microwave ovens, energy-saving lamps, and dimmers. The harm of harmonics to public power grids mainly includes:

1) The components in the public power grid generate additional harmonic losses, which reduces the efficiency of power generation, transmission and transformation equipment. When a large amount of third harmonics flows through the neutral line, it will cause overheating of the line or even a fire;

2) Affects the normal operation of various electrical equipment. In addition to causing additional losses, it can also cause mechanical vibration, noise and overvoltage in the motor, cause serious local overheating of the transformer, cause overheating of capacitors, cables and other equipment, cause insulation aging, and shorten service life. causing damage;

3) It will cause local parallel resonance and series resonance in the public power grid, thereby amplifying the harmonics, greatly increasing the aforementioned hazards, and even causing serious accidents;

4) It will cause relay protection and automatic devices to malfunction, and make electrical measuring instruments inaccurate;

5) It will cause interference to adjacent communication systems. In the mild case, it will generate noise and reduce the communication quality. In severe cases, it will cause information loss and make the communication system unable to work normally.

3. Surge (also called surge or surge) refers to the effective value of the output voltage being higher than 110% of the rated value in an instant (a few milliseconds) and lasting for one or several cycles. It is the main culprit of damaging precision electronic equipment. . In addition to being caused by lightning strikes, it is also mainly due to the high voltage generated by the sudden unloading of the power grid when large electrical equipment connected to the power grid is turned off and on.

1) The impact of surges on sensitive electronic and electrical equipment has the following types.

Damage: voltage breakdown of semiconductor devices; damage to the metallized surface of components; damage to printed circuit boards or contact points; damage to triacs/thyristors...

Interference: lockup, thyristor or triac out of control; part of the data file destroys the data processing program; errors: errors and failures in receiving and transmitting data; unexplained failures...

Premature aging: components age prematurely, the life of electrical appliances is greatly shortened, and the output sound quality and picture quality are reduced.

2) Which electrical equipment will be damaged by surges? Electrical equipment containing microprocessors is extremely vulnerable to damage by surges, including computers and auxiliary equipment, program controllers, PLCs, fax machines, telephones, answering machines, etc.; program-controlled switches, Radio and television transmitters, film and television equipment, microwave relay equipment; products in the home appliance industry include televisions, stereos, microwave ovens, video recorders, washing machines, dryers, refrigerators, etc. Survey data shows that 63% of electrical equipment that has problems during the warranty period are caused by power surges

4. Spike wave (or high-voltage spike pulse) refers to a voltage with a peak value of 6000V and a duration from 10-4 to 10ms. This is mainly caused by lightning strikes, arcing, static discharge or switching operations of large electrical equipment.

Its main hazards are: when the peak pulse amplitude is very large, it will damage the input filter, rectifier and even the main oscillator of the switching power supply of the industrial computer. In addition, its spectrum is very wide, and it will also enter the computer and cause interference.

5. Transient overvoltage and transient overvoltage refer to pulse voltages with peak voltages up to 20,000V but duration of 10-6s-10-4s. The main cause of its occurrence and possible damage is similar to high-voltage spikes, mainly caused by lightning.

Its main hazards are: advanced electronic equipment such as measurement, monitoring, protection, communication, and computer networks with large-scale integrated circuits as core components, and electronic equipment composed of large-scale CMOS integrated components are generally susceptible to transient overvoltage and overvoltage. The disadvantage of weak current tolerance is that transient overvoltage will not only cause malfunction of electronic equipment, but also cause interference, data loss, or temporary paralysis of electronic equipment; in severe cases, it can cause component breakdown and circuit board burnout, causing The entire system is paralyzed.

6. Voltage sag/drop refers to a low-voltage state in which the effective value of the mains voltage is between 80-85% of the rated value, and lasts for one to several cycles, or even longer. The causes include the startup and application of large equipment, the starting of large motors, or the connection of large power transformers, main power line switching, line overloading, etc.

Its main harm is: the impact on the computer ranges from causing the keyboard and other interface devices to suspend operations, to causing data loss and file destruction. The voltage sag will also damage the components in the computer and shorten its life. Voltage sag is the most common electrical problem, accounting for 87% of electrical problems.

7. Three-phase voltage unbalance refers to the unequal phase voltage or unequal line voltage between each phase. It is caused by the unbalanced load of each phase, which is related to the user load characteristics, and is also related to the planning and load distribution of the power system. Relevant standards stipulate that the allowable value of unbalance in the normal operation mode of the power system public connection point is 2%, and it shall not exceed 4% in a short period of time. Harm to the transformer: When the three-phase load is unbalanced, the transformer is in an asymmetric operating state, causing the transformer's losses to increase (including no-load loss and load loss). According to the transformer operating regulations, the neutral current of the transformer during operation shall not exceed 25% of the rated current of the low-voltage side of the transformer. In addition, unbalanced operation of the three-phase load will cause the zero-sequence current of the transformer to be too large, increase the temperature of local metal parts, and even cause the transformer to burn out. Impact on electrical equipment: The occurrence of three-phase voltage imbalance will lead to several times the occurrence of current imbalance, inducing an increase in reverse torque in the motor, thereby causing the temperature of the motor to rise, efficiency to drop, energy consumption to increase, vibration to occur, and output loss; shortening the service life of electrical equipment, accelerating the replacement frequency of equipment parts, and increasing equipment maintenance costs; causing excessive unbalanced current to flow into the neutral line, causing the neutral line to thicken. Impact on line loss: Increase line loss, and the impact is different depending on the load mode. Taking the three-phase four-wire connection method as an example, when one phase is heavily loaded and two phases are lightly loaded, the line loss increment is smaller; when one phase is heavily loaded and one phase is lightly loaded, the load on the third phase is Under average load, the line loss increment is larger; when one phase is lightly loaded and two phases are heavily loaded, the line loss increment is the largest. When the three-phase load is unbalanced, regardless of the load distribution situation, the greater the current imbalance, the greater the line loss increase.

8. Noise interference (or noise) refers to radio frequency interference (RFI), electromagnetic interference (EFI) and other various high-frequency interferences, which originate from electromagnetic waves or high-frequency wave induction. Noise is caused by motor operation, breaker operation, motor controller operation, broadcast emissions, microwave radiation, and electrical storms. Its main hazards are: causing the computer CPU to misjudge actions. In severe cases, it may burn out the CPU and other computer accessories, causing radio transmission interruption; the induction is conducted to the surrounding environment, causing other electronic equipment to fail to work normally; it can cause the civil aviation system to fail. Work failure, poor communication, computer operation errors, and automatic equipment malfunction.

The AC parameter regulated power supply designed by Ochis can solve the above power supply problems due to the following characteristics.

1. Wide voltage stabilization range and high output accuracy: the actual working range of input voltage can reach 120V∽300V for single phase and 210V∽515V for three phases, which can effectively solve the problem of excessive voltage changes.

2. The total recovery time of 10-40ms effectively solves the problem of voltage sag/drop.

3. Input and output isolation design and unique frequency-selective parameter excitation oscillation function can realize input and output bidirectional anti-interference, effectively solving noise interference, harmonics, surges, sharp waves, transient overvoltage and other induced lightning power quality problems.

4. The three-phase magnetic flux balance and complementary function achieved by the unique magnetic circuit design enables it to output stable and balanced three-phase and line voltages when the input voltage and load impedance fluctuate or are seriously unbalanced. Effectively solve the problem of three-phase phase and line voltage imbalance.

5. Magnetic saturation circuit magnetic circuit design, with automatic protection function for output load short circuit, reduces the voltage to zero with almost zero reaction time, effectively protecting the load and its own equipment from damage.

6. The circuit design has no electronic components, no mechanical adjustment devices, simple structure, reliable operation, low failure rate, and can be regarded as semi-permanent equipment, which will eliminate worries.

Aoqisi parameter regulated power supply consists of isolation transformer, lightning protection and anti-interference filter, and wide range balanced fast voltage regulator. It can automatically, quickly and steplessly stabilize the voltage, eliminate all kinds of power pollution, output high-quality power, and effectively ensure the reliable operation of electrical equipment, thereby doubling its service life.

Under normal operating conditions, the input power is transmitted through the primary and secondary electromagnetic couplings of the voltage regulator that are isolated from each other and the frequency change of the secondary inductance parameters. The LC energy storage element absorbs system energy to generate excitation oscillation. Make the local magnetic circuit enter a nonlinear working state. while utilizing its equivalent parameters to oscillate the narrow rectangular properties. The forced filter in the oscillation loop and a large time constant are used to obtain good frequency selection, anti-interference and purification performance. When the input voltage or load changes, the compensation electromagnetic circuit that synchronously tracks the change instantly generates a reverse tracking compensation amount, which is quickly, steplessly, and without transition added to the output end, thereby quickly maintaining the stability of the output voltage.