How to size Active Harmonic Filter & Static Var Generator?

In today’s industrial and commercial environments, maintaining optimal power quality is paramount. Non-linear loads, such as variable frequency drives and rectifiers, introduce harmonics and reactive power issues that can compromise system efficiency and equipment lifespan. Implementing Active Harmonic Filters (AHFs) and Static Var Generators (SVGs) can mitigate these challenges, but accurate sizing is crucial for their effectiveness.

Understanding the Basics

Active Harmonic Filters (AHFs): AHFs are designed to detect and compensate for harmonic currents in real-time, ensuring that the current waveform remains as close to sinusoidal as possible. They are particularly effective in environments with high levels of harmonic distortion.

Static Var Generators (SVGs): SVGs provide dynamic reactive power compensation, stabilizing voltage levels and improving power factor. They are essential in systems where voltage fluctuations and reactive power demands are significant.

Ikonmac Active Harmonic Filter (AHF) device

Capacity Determination of Active Harmonic Filter

Based on the experience of the power quality industry, two formulas are commonly used to estimate the capacity of harmonic suppression.

(1) Centralized governance: Estimate the configuration capacity of harmonic governance based on industry classification and transformer capacity.

\[ I_h = \frac{S \times K}{\sqrt{3} \times U \times \sqrt{1 + \text{THD}_i^2}} \times \text{THD}_i \]

S ─── Transformer rated capacity

U ─── Rated voltage on the secondary side of the U-transformer

I_h ─── Harmonic current

THD ─── Total current distortion rate, with a range of values determined based on different industries or loads

K ─── Transformer load rate

Industry Type	Typical harmonic distortion rate %
Subways, Tunnels, High-speed trains, Airports	15%
Communication, Commercial buildings, Banks	20%
Medical Industry	25%
Automobile manufacturing, Ship manufacturing	30%
Chemical / Petroleum	35%
Metallurgical Industry	40%

(2) On site governance: Estimate the configuration capacity of harmonic governance based on different load devices.

$$ I_h = K \times I_N \times \frac{\mathrm{THD}_i}{\sqrt{1 + \mathrm{THD}_i^2}} $$

I_h─── Harmonic current

THD_i ─── Total current distortion rate, with a range of values determined based on different industries or loads

K ─── Transformer load rate

Load type	Typical harmonic content %	Load type	Typical harmonic content %
Inverter	30~50	Medium frequency induction heating power supply	30~35
Elevator	15~30	Six pulse rectifier	28~38
LED Lights	15~20	Twelve pulse rectifier	10~12
Energy saving lamp	15~30	Electric welding machine	25~58
Electronic ballast	15~18	Variable frequency air conditioning	6~34
Switching Mode Power Supply	20~30	UPS	10~25

Ikonmac Static Var Generator product thumbnail image for reactive power compensation

Capacity Determination of Static Var Generator

(1) Estimate based on transformer capacity:

20% to 40% of the transformer capacity is used to configure reactive power compensation capacity, with a general selection of 30%

Q_compensate = 30% × S

Q_compensate─── Reactive power compensation capacity

S ─── Transformer capacity

For example, a 1000kVA transformer is equipped with 300kvar reactive power compensation

(2) Calculate based on the power factor and active power of the equipment:

If there are detailed load parameters, such as maximum active power P, power factor COSθ before compensation, and target power factor COSθ after compensation, the actual compensation capacity required for the system can be directly calculated:

Q_compensate = K × P × (tanθ₁ - tanθ₂)

Q_compensate─── Reactive power compensation capacity

P ─── Maximum power

Q ─── Average load coefficient (generally taken as 0.7-0.8)

Understanding the Basics

Ikonmac Active Harmonic Filter product thumbnail image for power quality solutions

Capacity Determination of Active Harmonic Filter

Based on the experience of the power quality industry, two formulas are commonly used to estimate the capacity of harmonic suppression.

(1) Centralized governance: Estimate the configuration capacity of harmonic governance based on industry classification and transformer capacity.

\[ I_h = \frac{S \times K}{\sqrt{3} \times U \times \sqrt{1 + \text{THD}_i^2}} \times \text{THD}_i \]

S ─── Transformer rated capacity

U ─── Rated voltage on the secondary side of the U-transformer

I_h ─── Harmonic current

THD ─── Total current distortion rate, with a range of values determined based on different industries or loads

K ─── Transformer load rate

Industry Type	Typical harmonic distortion rate %
Subways, Tunnels, High-speed trains, Airports	15%
Communication, Commercial buildings, Banks	20%
Medical Industry	25%
Automobile manufacturing, Ship manufacturing	30%
Chemical / Petroleum	35%
Metallurgical Industry	40%

(2) On site governance: Estimate the configuration capacity of harmonic governance based on different load devices.

$$ I_h = K \times I_N \times \frac{\mathrm{THD}_i}{\sqrt{1 + \mathrm{THD}_i^2}} $$

I_h─── Harmonic current

K ─── Transformer load rate

THD_i ─── Total current distortion rate, with a range of values determined based on different industries or loads

Load type	Typical harmonic content %
Inverter	30~50
Medium frequency induction heating power supply	30~35
Elevator	15~30
Six pulse rectifier	28~38
LED Lights	15~20
Twelve pulse rectifier	10~12
Energy saving lamp	15~30
Electric welding machine	25~58
Electronic ballast	15~18
Variable frequency air conditioning	6~34
Switching Mode Power Supply	20~30
UPS	10~25

Capacity Determination of Static Var Generator

(1) Estimate based on transformer capacity:

20% to 40% of the transformer capacity is used to configure reactive power compensation capacity, with a general selection of 30%

Q_compensate = 30% × S

Q_compensate─── Reactive power compensation capacity

S ─── Transformer capacity

For example, a 1000kVA transformer is equipped with 300kvar reactive power compensation

(2) Calculate based on the power factor and active power of the equipment:

Q_compensate = K × P × (tanθ₁ - tanθ₂)

Q_compensate─── Reactive power compensation capacity

P ─── Maximum power

Q ─── Average load coefficient (generally taken as 0.7-0.8)