What Is Harmonics? - Active Filtration & Passive Filtering
Harmonic Definition:
Harmonics is a form of interference that is characterized by complete oscillation over the fundamental industrial frequency spectrum. The harmonic component in the AC source is defined as the sine component of a wave period with an integer frequency equal to the fundamental frequency of the system.
fh = h.fb; h = (n * p) ± 1; h is the harmonic, n is a positive integer, p is the number of pulses (2, 6, 12, 18, ...)
An arbitrary waveform is the sum of sine waveforms. When homogeneous from one cycle to another, it can be described as basic sine waves and multiples of the fundamental frequency, which means that it consists of the basic sine wave and the sequence of sine wave harmonics. High, called the Fourier series.
f (t) = ΣAn * sin (n * pi * t / T); n is the number of harmonics, An is the amplitude amplitude, T is the period
When both positive and negative half cycles of a waveform are homogeneous, the Fourier series has only odd harmonics. Since most harmonics generators have a uniform waveform, in reality we only need to consider the odd harmonics h = 3, 5, 7, ..., 21, ..., 49, ...
The cause of the harmonics:
Because of the nonlinear loads in the electrical system. The input voltage of the nonlinear load is sinusoidal, but it is distorted and has no sinusoidal shape.
The electronic equipment has PWM switching circuits, rectifiers, inverters such as DC-DC, AC-DC, DC-AC, Inverter, DC Drive. Diode, Transistor, SCR, IGBT, ... Especially the dedicated switch circuit for battery system.
Systems of variable supplies such as welding machines, transformers, mill mills, steel rolling machines, tole rolling machines, switching equipment such as computers, DC power supply, ...
Harmonics:
The resonance in the electrical system is the resonance of the LC circuit, divided into parallel resonance and series resonance, both of which occur when high harmonics are present. Parallel resonance causes overcurrent and serial resonance causing overvoltage. If the voltage and current resonance amplitudes are large enough, capacitors and other electrical devices will suffer severe damage.
Harmonics Standard:
According to IEEE & IEC standard is I_THD = 12% (max) (Ratio = Isc / I_load deman = 50 ÷ 100), V_THD = 5% (max) (<6kV). There are a number of specific regulations on this standard for different sectors such as the military, information systems, hospitals, etc..
Composite Analysis:
Visible power: S = UI, kVA; Working power: P = UICosθ, kW; Reactive power: Q = UISinθ, kVAr
S2 = P2 + Q2, pf = P / S, tagθ = Q / P
S2 = P12 + Q12 + D2, D2 = S2 - (P12 + Q12); D: Distortion Power
Vrms = V1 * Sqrt (V12 + V12 + ... + Vn2)
Irms = I1 * Sqrt (I12 + I12 + ... + In2)
THD-V = Vthd% = (Vh / V1) * 100%
THD-I = Ithd% = (Ih / I1) * 100% = TDD; Total distortion
Harms of Harmonics:
Economic losses: Electricity losses, damage to electronic equipment, electrical switchgear and control devices; Increasing current and wire size, ...
Defective switchgear and capacitor banks: Trip CB (ACB, MCCB, MCB, ...), convergence, explosion, causing noise to the capacitors, destroying the dielectric in the capacitor, heat the CB - Busbar, Busway, ...
Stabilization of electrical system: Stabilization of electronic relay, conductor heating, flux loss and distortion.
Influence on engine start-up processes: Harmonic waves cause deviations in calculation functions, resulting in angular error, torque vectors, flux vectors in the control process inside the soft star, inverter, etc. This leads to a faulty number of defaults or loss of control, which results in incorrect startup of the computation process or failure to start up.
Deviation of the measuring device: Deviation of the measuring devices for the network such as V, A, Hz, Pf, kW, kVA, kVAr, kWh, kVArh, KVAh, Σ KVAh, Σ kVArh, ...
Stabilization of the radio system: Stabilization and frequency deviation for information systems such as television, radio, unstable transmission of electronic equipment, etc.
Solution:
Conducting survey, measurement, analysis and system design by specialized power quality analyzers:
Methods of filtration:
Harmonic filter for equipment
Active positive humor
Passive harmonics
Integrated filtering
