Learn about harmonics and harmonic handling methodsQPC
What are harmonics?
Harmonics is an unwanted interference that directly affects the quality of the power grid and should be taken into account when the total harmonic currents are higher than the allowable limit. Harmonic current is a current whose frequency is a multiple of the fundamental frequency. For example, a 250Hz line on a 50Hz grid is a 5th harmonic.
The 250Hz current is an unusable power flow with devices on the grid. Therefore, it will be converted to heat energy and cause loss.
- Introduction What is a capacitor and compensation capacitor reactive power
Effect of harmonics
Harmonics can cause the cable to overheat, damaging the insulation. The motor can also overheat or cause noise and fluctuations in the torque on the rotor leading to mechanical resonance and vibration. Capacitors overheat and in most cases can lead to dielectric destruction. Electrical displays and lights may flicker, protective devices may cut off power, computers may fail (data network) and measuring devices may give incorrect results.
How are comedy lines created?
Harmonic currents and voltages are generated by nonlinear loads connected to the power distribution system. All electrical energy converters used in different forms in the power system can increase harmonic noise by injecting harmonic current directly into the grid. Common nonlinear loads include motor starters, electric drive systems, computers and other electronics, electronic lamps, soldering supplies, etc.
Solutions to reduce harmonic emissions from inverters?
The transformers themselves contain nonlinear elements that are the source of harmonics. However, the harmonic current more or less depends on the structure of the drive system and the load, if using a large motor (compared to the power transformer) or increasing the motor load will increase the harmonic current. Therefore, in order to reduce harmonics, industrial manufacturers are forced to use low harmonic frequency inverters or use external filtering methods. In which, in order to reduce the harmonic current, it is necessary to increase the AC, DC inductance or increase the number of rectifier valves in the rectifier and reduce the harmonic voltage caused by the harmonic current to increase the transformer capacity, reduce the transformer impedance or increase the voltage. short circuit capacity of the source.
Method to minimize harmonics
1. Using an inverter: ABB’s harmonic reduction converters provide a simple harmonic lowering solution incorporated in the inverter. These inverters use harmonic reduction technology without the use of external filters or multi-pulse transformers. Harmonic minimization inverters produce low-order harmonics on the side input with less than 5% total distortion current.
Therefore, ABB’s harmonic reduction inverters provide a simple, low-cost solution to meet stringent power quality standards.
2. Use resistor coil to filter harmonics in the compensation capacitor
Improving grid quality
In inverters with 6-pulse diode bridge, the grid-side current is non-sine and contains bi-harmonic components, especially 5th and 7th order components. It is represented by a distorted current pattern, which can be up to 30-50 %. In ABB’s harmonic reduction inverter, the use of DTC (Direct Torque Control) method and filter will reduce the harmonic current to less than 5%. The result is a sinusoidal current that makes the shape of the mains voltage almost distortion-free.
Need to have regulation to control harmonics soon
Ideally, the alternating current on the electric utility grid supplied to consumers should be sinusoidal. However, the existence of nonlinear elements on the supplier’s grid as well as on the load side causes harmonics to appear, affecting the operation of the grid and equipment. Typical nonlinear elements are the steel cores of transformers, motors (saturation properties of ferromagnetic materials), power semiconductor devices such as diodes, and thyristors of converters. Usually the 3rd harmonic is suppressed by the delta windings in the transformer (along with the power loss), but other odd harmonics (maximum values are 5th and 7th order) still. spread along the line, causing power loss, adversely affecting the operation of equipment, especially three-phase motors… not to mention the higher harmonics can cause electromagnetic waves to propagate in space, affecting radio transceivers.
Therefore, when investing in construction, it is necessary to choose equipment that causes less harmonics and use additional means to minimize harmonics. At the same time, the state management agencies should also consider and soon have specific regulations to control harmonics.
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