# ABC of Chokes

## 1. Definitions (in compliance with EN61558-20)

**Choke:**

Apparatus consisting of one or more windings with a frequency dependent impedance, working by the principle of self-inductance, whereby a magnetising current produces a magnetic field leading through a magnetically active core or through air.

**AC Choke:**

Choke where the magnetising current produces a magnetic alternating field, which alternates its polarity depending on the frequency.

**Biassed Choke:**

Choke where the magnetising direct current produces a magnetic field with a single polarity, while a superimposed alternating current modifies the direct magnetic field depending on the intensity of its current and its frequency.

**Rated Current:**

Current assigned to the choke by the producer, including the harmonic currents, if any, which influences the warming up of the choke. Rated Choke

**Power:**

Sum of the products of rated voltage drop and the rated current at the rated frequency of the different windings.

**Rated Inductance:**

Inductance of the choke, assigned by the producer for the set operational conditions of the choke.

**Rated resistance:**

Direct current resistance of the winding of the choke, assigned by the producer for the set operational conditions of the choke.

**Rated Voltage Drop:**

Voltage along a winding of a choke, assigned by the producer for rated current and rated frequency.

**Rated Input Voltage:**

The distribution voltage (in the event of three-phase systems between the outer conductors) assigned to a choke for the set operating conditions.

**Rated Frequency:**

The frequency assigned to the choke for the set operating conditions.

**Overload-proof Choke:**

Choke, where the temperature does not exceed fixed threshold values if the choke is overloaded and which continues to fulfil all EN61558 requirements once the overload is removed.

**Conditionally Overload-proof Choke:**

Overload-proof choke equipped with a protective device, which opens the current circuit or reduces the current in the circuit if the choke is overloaded, and which continues to fulfil all EN61558 requirements once the overload is removed or the protective device is replaced or reset.

- Examples of protective installations are: Fuses, overload release relays, thermal links, a thermal fuse link, temperature limiters, PTC resistors and automatically triggered mechanical protection switches.
- In the event of the protective release through a protective device that cannot be replaced or reset, this does not mean that the choke will continue to operate.

**Unconditionally Overload-proof Choke:**

Overload-proof choke without protective device, where the temperature during an overload will not exceed set threshold values due to its design, and which will continue to operate and fulfil all EN61558 requirements once the overload is removed.

## 2. Fundamentals

**B=jωL**

Whereby Δu is the voltage at the coil and L is the (ideally constant) inductance. The above-mentioned formulas serve the purpose of a rough estimate and assume an ideal choke (without ohmic resistance and internal capacitance).

General circuit diagram:

ΔU Voltage drop

f Frequency

L Industance

### Voltage Drop (ΔU):

angular frequency

Voltage drop (per phase in the case of a three-phase choke)

### Rated Choke Power (SN):

Energy Content (LI^{2}):

Units employed:

I Ampere/A

S Volt-Ampere/VA

L Henry/H

f Hertz/Hz

## 3. Operation

**Ambient temperature: **

The ambient temperature of the choke at rated power must not exceed the rated ambient temperature specified on the rating plate (the choke can be operated temporarily at a maximum temperature of 10°C over ta ).If the rated ambient temperature is continuously exceeded, the rated current must be reduced:

Duty cycle:

The specified rated current refers to the operating mode S1 (continuous operation). If operated in a sequence of established identical cycles (intermittent operation) a choke with smaller rated power can be employed in many cases.

The duty cycle (DC) of the choke is calculated as follows:

In order to avoid impermissible heating, the cycle duration (load time + off-load time) is limited to 10 minutes. With the help of the factor F it is possible to calculate the rated power of the choke:

ED/% | 100 | 80 | 70 | 60 | 50 | 40 | 30 | 20 |

F | 1,0 | 0,89 | 0,85 | 0,77 | 0,70 | 0,63 | 0,55 | 0,45 |

**Installation altitude:**

Chokes are designed for operation up to a maximum altitude of 1000m above sea level. If an equipment is installed at a higher altitude, the rated current must be reduced: ## 4. Types of Chokes

**Small Chokes**

The power ranges listed here are in conformity with the requirements of EN61558. In the same sense, these types of chokes are naturally also available in higher power classes and with a voltage up to 12kV.

**Line Commutation Choke:**

Choke to limit the feedback on the line of commutating semi-conductors (for example input rectifiers of frequency converters).

The effective value of the current consumption of such systems is significantly improved.In the industry, it is customary to indicate the voltage drop in percent of the line voltage.

Example: Choke 4% at 3x400V line

**Motor Choke: **

Choke for the limitation of the voltage rate of at the motor terminals, which is caused by the pulse-width modulation of the frequency converter.

**AC Smoothing Choke: **

Choke for smoothing the ripple current (waviness) of a rectified AC voltage.g.

**Filtering Circuit Choke: **

Choke used to build a choked compensation system in combination with a capacitor. A parallel resonance of the capacitor with the power converters in the same grid is prevented. Furthermore, a small reduction in harmonic currents in the line is achieved. Due to the higher load by harmonic currents and the individual design of the oscillating circuit, it is compulsory to define the expected current spectrum as well as the capacity value.

**Choke for Absorption Circuits:**

Choke used to build an absorption circuit (L-C-series tuned) in combination with a capacitor. This system represents a very low resistance to the respective harmonic and absorbs the resulting harmonic currents where they occur (for example powerful drives).The setting of the inductance of these chokes is very sensitive and has to be done within very narrow tolerances.Due to the extremely significant harmonic load it is compulsory to define the expected current spectrum.

**Large Chokes:**

Chokes in the larger power range fall under the EN60289 standard.Similar definitions and applications with the same effect apply.Our product range comprises chokes from 0.03 to 900kVA rated power and a maximum rated voltage up to 12kV.