What is harmonics? – Reasons makes harmonics- Harmonics filter systemAdmin
Definition of harmonics filter reactor
Harmonics filter reactor is a noisy form, featured by complete vibration on basic industrial spectral frequency. Harmonics filter reactor in AC power is definited as sin of a wave period with frequency is equal with integer times of basic frequency in that system.
fh = h.fb; h = (n*p) ± 1, in that, h is harmonic step, n is positive integer, p is impulse number ( 3, 5, 7, …,21,…49, …)
An any frequency form is sum of sin’s frequency forms. When identifying from this frequency to other frequency then it can be described as sin’s basic frequencies and multiply of basic frequencies., ie, both sin’s basic frequencies and string of sin’s high hormonics forms, called Fourier.
f(t) = ∑An*sin(n*pi*t/T) ; n is number of harmonics step, An is amplitude of harmonics steps, T is cycle.
When half of negative and positive cycle of frequency form is identified, then Fourier’s string only contain odd harmonics steps. Because almost devices generate normal harmonics have identifying frequency form, thus in reality, we only attention to odd harmonic frequencies. ( h=3, 5, 7,…49, …)
Reasons generate harmonics.
Due to non-linear load forms in electric system. Input voltage of non-linear is sin’s forms but it is distorted and different from sin’s forms.
Electronic devices has rectifier switch circuit and inverter switch circuit as: DC – DC, AC – DC, DC – AC, Inverter, DC Drive,…In that, Diode, Transistor, SCR, IGBT, … generate main components. Especially, dedicated convert circuts for battery’s system.
Components system has power supply always changed such as: welder, transformers, motor of crusher, steel rolling machine, rolling mill, switching devices such as: Computer, DC sourse…
Resonance in electronic is resonance of LC circuit, devided into parallel and serial resonance. Both will appear when has high harmonics. Parallel resonance made over current and serial resonance made over voltage. If resonance’s amplitude of voltage and current is big enough is capacity panel and another electric devices will be severely damaged.
Point of Common Cuopling (PCC)
Limit of harmonics current would change, depend on score against circuit breaker and max basic current in PCCC.
Ratio = Isc/ I_load deman
Standard and Regulations of Harmonic frequencies.
According to IEC là I_THD = 12%(max), V_THD = 5 %(max). There are some regulations for this standard depent on each career such as: military, informatic system, hospitals… will be regulated for each career.
Phân tích tính toán khi có sóng hài:
Apparent power: S = UI, kVA; Active power: P = UICosθ, kW; Reactive power: Q = UISinθ, kVAr
S2 = P2 + Q2, pf = P/ S, tagθ = Q/ P
S2 = P12 + Q12 + D2, D2 = S2 – (P2 + Q2); 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 demand distortion
Harm of Harmonics.
Harm of economy for factory: Power loss, damaging electronic devices, switch devices and control devices; increase the current and the size of cables.
Damaging switch devices and capacity: Trp CP ( ACB, MCCB, MCB…), swelling capacity, damaging capapcity, make a noise for capacity, destroy dielectric in capacity, heating for poles CB – Busbar, Busway…
Unstable for electric system: Unstable for electric delay, heat the current, loss of magnetic flux and distorting moment in transformer, motor…
Deviation of the measuring devices: Deviation of the measuring devices for electric networks such as: V, A, Hz, Pf, kW, kVA, kVAr, kWh, kVArh, KVAh, ∑ KVAh, ∑ kVArh, …
Unstable for wireless system: Unstable and deviation of frequencies for information system such as television, radio, unstable for receiving and broadcasting of electronic devices…
Doing research, meassurement, analysis, design systems:
- Filter for Components
- Active filter
- Passive filter
- Hybrid filter
For more details, please contact with Mr. Vinh: 0908 488 633/ 0969 553 557
You can see our video on youtube with (Design guided by Hữu Vinh)