Capacitor bank for Motor drivers

Shunt Capacitor banks usually used for power factor improvement/ elimination of harmonics from the supply system. Voltage dip in the supply system usually arises due to load fluctuations in the grid but still using of capacitor banks will save your power and stabilize your supply system.

Dear Sir,

Could you please guide on selecting capacitor bank size to avoid voltage dips.

Selection of capacitor banks is most easy providing that the existing power factor and KVAR absorbed by your system are measured.capacitor banks will be selected interms of reactive power (KVARs) which can be directly derived from the power tables.

Yes you can in principle, many VSD's have terminals that are connected to their internal DC bus. The energy stored in a capacitor is .5*C*V^2 (half C V squared). The usable energy is in the difference between the normal bus voltage and the minimum voltage necessary for the VSD to function. Plugging some numbers in shows that you'll need a huge amount of capacitance to provide even a few seconds of protection. Jeff

Dear Sir,

Thank You very much for your help.

The Problem we are facing is malfuctioning of the 60 HP DC motor driver (415 V AC input) even during a small dip in the voltage. What can we do to maintain steady voltage for motor driver?

What sort of dip, is it dropping all the way to zero? How long does it drop for?

Also, check if the VSD monitors the input voltage, it may be faulting when it sees the power is failing. What brand and model is the drive? Thanks Jeff

Be Careful here!

You may have other issues in your power system. Can you install a power quality monitor nearby with date stamping? You need to know what is going on in your system and make corrections to your system. Are you familiar with the ITI curve? Your drive should be able to ride through anything inside this envelope. If it does not check with the drive vendor on adjustments you can make to the drive to handle the ride through. Change or installing capacitors without understanding the problem can lead to even more troubles with harmonics.

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... DC motors with VSD drivers ...

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This requires DC Filter Capacitor Bank of thousands µF to filter Ripples in rectifier O/P

And

support In-Rush current taken by a motor @ start; if it is not thru a "Soft-Starter" .

If the the motors are at different loctios & you have a single-DC-Power-Source then it will be better to have individual Capacitor Banks close to the motor-start-gear.

adam #1 & #3

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Shunt Capacitor banks usually used for power factor improvement/ elimination of harmonics from the supply system.

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The Question is " ... DC Filter Capacitor Bank ...

You are refering to Power-Line [AC Ditribution system about Power-Factor-Correction the Capacitor-banks connected on to off-set the Over-all-Lagging Loads; corrected by introducing leading PF load.

This does not increase the load on Power-Source but cancells some of the Lagging-load & causes to increase PF.

More over these "Capacitor-banks " do not supprt the power lines in decreasing Dips in power-lines except the purpose described by you ie improving of PF for example 0.5 towards 0.7 or better [towards UNITY PF which is an ideal but never attainable]

it is clear from the question that the motor is a DC motor and not the power supply, in other words the DC is obtained by introducing rectifier units to supply the motor, inwhich case shunt capacitors could be used to filter the AC upstream of the rectifier unit leading to improvement of power factor (lagging) and stabiliziation of power system. Certainly capacitor banks do not decrease the power Dips which might arise due to load fluctuations.

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