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The use of 5-core chokes

13 August, 2015

A comparison with alternative solutions

In order to be able to transfer large loads using low voltage inverters, they are increasingly connected in parallel nowadays. Thus, the current load of the individual inverters is less, and it is also possible to use high switching frequencies that enable a sinusoidal current with a low THDI (Total Harmonic Distortion) to be produced from the start. At first, this may sound very good and advantageous. However, this also means that the downstream elements must meet specific requirements.

One of these is common-mode noise which can occur due to parallel connected inverters and the resulting fluctuating intermediate circuit voltages. For smooth operation, this must be filtered, because especially in applications where the load is connected in delta, the common-mode noise leads to an unbalanced power supply.

The solution is a current-compensated choke that has a high inductance for the currents from common-mode noise, thereby attenuating them. Finally, the parasitic currents are eliminated by connecting capacitors to earth downstream of the choke. At the same time the rated current for a current-compensated choke can flow through the choke virtually unhindered. However, this is undesirable when operating an inverter because the choke must also have a defined inductance in order to smooth out the rated current.

Consequently, the choke must be designed so that both application cases can occur simultaneously. This document examines this topic in typical three-phase core sections.

For further product information you can find details on our CNW 910 three phase 5 limb mains choke together with our CNW MD 835 liquid cooled motor choke.

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