Danfoss VLT 6000 HVAC Instrukcja Obsługi Pobierz pdf (Strona 37)

VLT

6000 HVAC

37MG.60.B1.02 - VLT is a registered Danfoss trademark

Introduction to

HVAC

■■

■ LC filters for VLT 6000 HVAC

When a motor is controlled by a frequency converter,

resonance noise will be heard from the motor. This

noise, which is caused by the design of the motor,

occurs each time one of the inverter switches in the

frequency converter is activated. Consequently, the

resonance noise frequency corresponds to the

switching frequency of the frequency converter.

For the VLT 6000 HVAC, Danfoss offers a LC filter to

dampen the acoustic motor noise.

This filter reduces the voltage rise time, the peak

voltage U

PEAK

and the ripple current ∆I to the motor,

thereby making current and voltage almost sinusoidal.

The acoustic motor noise is therefore reduced to a

minimum.

Because of the ripple current in the coils, there will be

some noise from the coils. This problem can be solved

entirely by integrating the filter in a cabinet or similar.

■■

■ Examples of the use of LC filters

Submersible pumps

For small motors with up to and including 5.5 kW

rated motor power, use a LC filter, unless the motor is

equipped with phase separation paper. This applies

e.g. to all wet running motors. If these motors are

used without LC filter in connection with a frequency

converter, the motor windings will short-circuit. If in

doubt, ask the motor manufacturer whether the

motor in question is equipped with phase separation

paper.

Long motor cables

If screened/armoured motor cables longer than 150

m or unscreened/unarmoured motor cables longer

than 300 m are used, a LC filter should be applied.

The LC filter reduces the capacitive earth leakage

currents and the voltage peak loads.

NB!:

If a VLT frequency converter controls several

motors in parallel, the motor cables must be

added up to give the total cable length.

Well pumps

If immersion pumps are used, e.g. submerged pumps

or well pumps, the supplier should be contacted for

clarification of requirements. It is recommended to

use a LC filter if a VLT frequency converter is used for

immersion operations.

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