Reactor for capacitor

What role does the Reactor play in the system? Reactor works when combined with capacitors? To better understand this electrical device, let's follow the entire article below with BTB Electric.

1. What is a Reactor?

A reactor is an electrical device consisting of a coil (copper or aluminum) wound around a ferromagnetic core of constant reactance. When current flows through the coil of the reactor, a magnetic field is generated, and this magnetic field produces an induced voltage to slow down the current variation in the coil. Based on the above characteristics, Reactor is used for the purpose of limiting current fluctuations when there is a sudden change in the power grid.

Reactor manufactured by BTB Electric company

2. How does the reactor protect the capacitor?

Reactor for Capacitor, Detuned Harmonic Reactors, Harmonic Filter Reactor,  is a different name for Reactor installed in series with a capacitor for the purpose of limiting high-order currents pass through the capacitor.

For Capacitors connected to electrical systems with harmonic components (the presence of a voltage whose frequency is a multiple of the fundamental frequency of 50Hz) will cause the capacitor's total impedance to decrease.

When the total impedance of the capacitor decreases, the current on the capacitor will increase, the larger the harmonic component, the higher the current on the capacitor, exceeding the allowable capacity, causing the capacitor to fail.

For Reactor it will be completely opposite when there is a harmonic component present

Based on the above characteristics of the device, we see the need to use capacitors in series when the power system has a large harmonic component.

Capacitor manufacturers recommend using Capacitors in series with Reactor when THDu >3% to prolong APFC system life, reduce waveform distortion and improve power quality.

3. Structure and working principle of Reactor

Structure of Reactor

Reactor has a simple structure

Through the image you can also see, the Reactor has a fairly simple structure with only 1 coil wrapped around the ferromagnetic core, for the 3-phase Reactor, the number of coils and iron cores also increases.

Working principle of reactor

For AC circuits, the inductance will be proportional to the frequency of the current. That is, the higher the frequency, the greater the inductance. At this time, the current through the Reactor will be smaller. Therefore, using Reactor in industrial equipment will help to lose high harmonics

Reactor, when integrated with the capacitor, also avoids high-order current (harmonic current) on the capacitor causing overcurrent, overheating, even damage to the capacitor, thereby helping to increase the life of the capacitor and improve the quality better power for the system.

Due to their constant characteristics, Reactors are often installed in industrial inverters. So the electric motor will operate smoother and more durable when reversing and changing speed.

4. Classification of Reactor for capacitors

Reactors have many classifications and are common as follows:

- According to voltage:

- According to the harmonic filter properties

- According to insulation level

- By phase number

5. How to choose Reactor for capacitors

Usually we think that just buying a Reactor and connecting it in series with a capacitor is enough, but it's actually not that simple. From the expression we can see that with resistor R = 0, the circuit Capacitor in series Resistance will occur resonance phenomenon of LC circuit causing fire resistance and capacitor explosion when ZC = ZL

Currently, Reactor manufacturers usually have inductance rates of 6%, 7%, 13% or 14%, respectively, with resonant frequencies will be 204Hz, 189Hz, 139Hz and 134Hz. To avoid resonance of the LC circuit, the above resonant frequency must be less than the frequency of the lowest harmonic present in the power supply network.

In order to know the lowest harmonics present in the power supply network, it is necessary to use specialized test and measurement equipment, experience has shown that

* For loads that are Inverters there are usually harmonics of 5, 7, 11 and 13. At this point we have to choose the resonant frequency in the range 174Hz to 210Hz. So we need to use Reactor is 6% (204Hz) or 7% (189Hz)

* For loads that are high-frequency smelters or electric vehicle charging stations, there are usually 3, 4, 5, 7 harmonics. We need to use a Reactor with a rate of 13% or 14% (134Hz).

6. What should I pay attention to when choosing Reactor for capacitors?

Because when connecting the capacitor to the Reactor in series, the capacitor terminal voltage will increase, so according to the following formula

      In there:

          Uc: capacitor terminal voltage

          Us: system voltage

          p: % of inductance of reactor (6%, 7%, 13%..)

For 400V power systems, it is often recommended to use capacitors with voltage 440V for Recator 6%, 7% and capacitors with voltage 480V for Recator 13% or 14%

7. Reactor application for capacitors

After selecting the Reactor, we proceed to install the capacitor system with Reactor as shown.