The harm and solution of power quality problems

1. The voltage variation range is too large

The power supply of the power grid is insufficient, the power supply department adopts the voltage reduction, or it is located in a remote area, and the loss is too much, resulting in low voltage. The power grid uses too little electricity, resulting in high voltage.

If the voltage is too low, the load cannot work properly. If the voltage is too high, the service life of the load will be shortened or the load will be burned.

2. Waveform distortion (or harmonic Waveform. Distortion)

Common waveform distortion refers to multiple harmonics of the standard power waveform. The cause of grid 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, dimmers, etc., or the secondary power supply itself.

The hazards of harmonics to the public power grid mainly include:

1) It causes additional harmonic losses in the components of the public power grid, reducing the efficiency of power generation, transmission and transformation equipment. When a large amount of third harmonics flows through the neutral line, it will cause the line to overheat or even cause a fire;

2) Affecting 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 severe local overheating of the transformer, overheating of capacitors, cables and other equipment, aging of insulation, shortening of life, and even 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 electrical measurement instruments to measure inaccurately;

5) It will interfere with the neighboring communication systems. In mild cases, 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. Power surges

It means that the effective value of the output voltage is higher than 110% of the rated value in an instant (several milliseconds) and lasts for one or several cycles. It is the main culprit for damaging precision electronic equipment. In addition to being caused by lightning strikes, it is mainly caused by 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.

[page] Hazards of power surge:

Computer technology has developed to this day, with multi-layer, super-scaled integrated chips and dense circuits, and the trend is towards higher integration, smaller component gaps, and thinner wires. A few years ago, a square centimeter of computer chips had 2,000 transistors, while today's Pentium has more than 10,000,000. This increases the probability of computers being damaged by surges. The design and structure of computers determine that they should work within a specific voltage range. When the surge exceeds the level that the computer can withstand, the computer will have garbled data, damaged chips, and premature aging of components. These symptoms include: unexpected data errors, failure to receive/transmit data, loss of documents, malfunctions, frequent maintenance, unexplained failures and hardware problems, etc. Lightning surges far exceed the level that computers and other electrical equipment can withstand. In most cases, they cause immediate destruction of computers and other electrical equipment, or permanent loss of data. Even a small 20-horsepower induction engine starting or shutting down can generate a 3,000-5,000-volt surge, causing computers that share the same distribution box to be damaged or interfered with every surge, which happens very frequently.

The impact of surges on sensitive electronic and electrical equipment can be of the following types:

destroy

Voltage breakdown semiconductor devices

Damage to the metallized surface of components

Damage to printed circuit board traces or contact points

Destroys triacs/thyristors...

interference

Latch-up, loss of thyristor or triac control

Partial data file corruption

Data processing program error

Errors and failures in receiving and transmitting data

Unexplained malfunction...

Premature aging

Premature aging of components and greatly shortened life of electrical appliances

Output sound and picture quality deteriorates

● What electrical equipment can be destroyed by power surges?

Electrical equipment containing microprocessors is very susceptible to damage from power surges, including computers and auxiliary equipment, program controllers, PLCs, fax machines, telephones, answering machines, etc.; program-controlled switches, radio and television transmitters, video equipment, microwave relay equipment; and household appliances, including televisions, stereos, microwave ovens, video recorders, washing machines, dryers, refrigerators, etc. Survey data show that 63% of electrical equipment that has problems during the warranty period is caused by power surges.

4. Spikes (or high voltage spikes)

Refers to a voltage with a peak value of 6000V and a duration from one ten-thousandth of a second to one-half cycle (10ms). This is mainly caused by lightning strikes, arcing, static discharges, or switching operations of large electrical equipment.

harm:

This kind of spike interference is particularly harmful in steel mills, rolling mills, or places where thyristor equipment, electric spark equipment, electric locomotives, etc. are used in large quantities. Its amplitude can reach hundreds of volts or even thousands of volts, and the pulse width is generally in the order of μS. Lightning often invades in the form of spike pulses. When the amplitude of the spike pulse is large, it will damage the input filter, rectifier, and even the main oscillator of the industrial computer switch power supply. In addition, its spectrum is very wide, and it will also penetrate into the computer to cause interference.

5. Transient overvoltage and temporary overvoltage

Refers to a pulse voltage with a peak voltage of up to 20,000V but a duration between one millionth of a second and one ten-thousandth of a second. Its main cause and possible damage are similar to high-voltage spike pulses, mainly caused by lightning.

harm:

Advanced electronic equipment such as measurement, monitoring, protection, communication, computer network, etc. with large-scale integrated circuits as core components are widely used in various fields of power, aviation, national defense, communication, radio and television, finance, transportation, petrochemical, medical treatment and other modern life. These electronic equipment composed of large CMOS integrated components generally have the disadvantage of weak tolerance to transient overvoltage and overcurrent. Transient overvoltage will not only cause electronic equipment to malfunction, or cause electronic equipment to be interfered with, data lost, or temporarily paralyzed; in severe cases, it can cause component breakdown and circuit board burning, paralyzing the entire system.

6. Voltage Sags & Brownouts

Refers to the low voltage state where 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. Its causes include: starting and application of large equipment, starting of large motors, or access to large power transformers, switching of main power lines, line overload, etc.

[page] Hazards:

Voltage sag is the most common power problem, accounting for 87% of power problems. The power supply may cause a short-term voltage drop for some reason. Its impact on the computer can be as minor as causing the keyboard and other peripheral devices to stop working, or as serious as causing data loss and file corruption. Voltage sag can also damage components in the computer, shortening their lifespan.

7. Three-phase voltage unbalance

It refers to the unequal voltage or phase angle between phases, which is caused by unbalanced load on each phase.

The harm and impact of three-phase imbalance

Three-phase imbalance refers to the asymmetric voltage of each phase of the three-phase power supply. It is caused by the unbalanced load added to each phase of the power supply, which is a fundamental load configuration problem. The occurrence of three-phase imbalance is related to the user's load characteristics, and is also related to the planning and load distribution of the power system. "Allowable Unbalance of Three-Phase Voltage of Power Quality" (GB/T15543-1995) is applicable to AC rated frequency of 50 Hz. Under normal operation of the power system, the voltage imbalance at the PCC point connection point caused by the negative sequence component. The standard stipulates: The allowable value of imbalance under normal operation of the common connection point of the power system is 2%, and it shall not exceed 4% for a short time.

Harm to transformers. In production and life electricity, when the three-phase load is unbalanced, the transformer is in an asymmetric operating state. This causes the transformer's losses to increase (including no-load losses and load losses). According to the transformer operation regulations, the neutral line current of the transformer in operation shall not exceed 25% of the rated current of the transformer's low-voltage side. In addition, unbalanced operation of the three-phase load will cause the transformer's zero-sequence current to be too large, the temperature of local metal parts to increase, 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. Induced reverse torque in the motor increases, which causes the temperature of the motor to rise, efficiency to decrease, energy consumption to increase, vibration, output loss and other effects. The imbalance between phases will shorten the service life of electrical equipment, accelerate the frequency of equipment component replacement, and increase the cost of equipment maintenance. Circuit breaker The allowable current margin is reduced, and overload and short circuit are prone to occur when the load changes or alternates. Excessive unbalanced current flows into the neutral line, causing the neutral line to thicken.

Impact on line loss. In the three-phase four-wire connection mode, the line loss is the smallest when the three-phase load is balanced; when one phase is heavily loaded and the two phases are lightly loaded, the line loss increment is small; when one phase is heavily loaded, one phase is lightly loaded, and the load of the third phase is an average load, the line loss increment is large; when one phase is lightly loaded and the two phases are heavily loaded, the line loss increment is the largest. When the three-phase load is unbalanced, no matter what the load distribution is, the greater the current imbalance, the greater the line loss increment.

8. Noise Interference (or Noises)

Refers to radio frequency interference (RFI) and electromagnetic interference (EFI) and other high-frequency interference. Originated from electromagnetic waves or high-frequency wave induction, it is a high-frequency change, ranging from 15-100% potential disturbance on the normal power frequency of 50Hz. Motor operation, circuit breaker operation, motor controller operation, broadcast transmission, microwave radiation and electrical storms can all cause noise.

harm:

Excessive noise may cause the computer CPU to misjudge, and in severe cases may burn out the CPU and other computer components, and may cause wireless transmission interruption.

The induction is transmitted to the surrounding environment, causing other electronic devices to malfunction.

It can cause the civil aviation system to fail, communications to be disrupted, computer operation errors, and automatic equipment to malfunction.

The Ochis AC parameter power supply integrated regulator plays an important role in improving the power supply quality of the distribution network. The device has the following functions: (1) Maintaining a constant voltage on the load side when the primary voltage fluctuates or when there is a short-term power outage of 2-3 cycles; (2) Maintaining a balanced three-phase voltage on the load side when the primary voltage is unbalanced and has harmonics; (3) Compensating for the current harmonics and reactive power on the load side so that only active current is provided on the grid side; (4) Compensating for the unbalanced current harmonics on the load side so that the grid side current is three-phase balanced;

(5) Various microscopic power interference pollution can be eliminated.