Flicker Caused by Motor/Load 3

[baldwon]

I have a situation where a 60hp motor is driving a reciprocating compressor. I believe that the nature of the reciprocating compressor (loading/unloading of valves) is causing a high frequency voltage flicker which can be seen in the incandescent lighting. When motor is not running flicker ceases.

Does anyone have any experience with a problem of this nature and what can be done to eliminate this problem?





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[jraef]

If it happens not only when starting but also while the motor is running full speed (and when the unload valve cycles), I'd say your power system is too weak, i.e. you need a bigger transformer / service drop from the utility. You must be running right near full capacity of the system and when the relatively small addition to the load happens as the valve closes it causes a voltage drop severe enough to dim your lights.

"Venditori de oleum-vipera non vigere excordis populi"

 

[aolalde]

I think the flicker is caused by the torque variation in the crankshaft of the reciprocating compressor. To eliminate it direct coupled motors have high rotating inertia. A flywheel could be added. Consult NEMA MG1 20.82 Pulsating Stator Current in Induction Motors.

 

[jbartos]

Comment: When the flicker becomes objectionable, it should be removed.
Capacity of the supply system should be increased to reduce the voltage drop caused by the fluctuating load.
The effect of voltage flicker depends on the frequency of occurrence. An occasional dip, even though quite large, is rarely objectionable.

 

[busbar]

The IEEE Red Book [Std 141-1993] §3 discusses flicker. Source stiffening and isolation are the simple cures.

 

[jbartos]

Suggestion: Reference:
IEEE Std 241-1997 IEEE Recommended Practice for Electric Power Systems in Commercial Buildings,
page 137, equation 4:
modified for the original posting HP, namely:
60HP Motor x 5kVA/HP x 6%/600kVA = 3% flicker
where
60HP is the motor with NEMA Code Letter having 5kVA/HP
6% is the transformer impedance
600kVA transformer
The estimated 3% dip associated with the motor starting reaches full border line of irritation at 10Starts/Hour.
The reciprocated compressor may be causing many dips per hour.

 

[RonShap]

Sometimes replacing the magnetic type flourescent ballast with a good quality electronic model will compensate.

 

[edison123]

baldwon,

a wild shot - is it possible that your motor starter/contactor is chattering under load (due poor pitted contacts area, improper/insufficient contactor operating-coil voltage etc.)

 

[Danfossegypt]

Hi baldwon,

i think what u really need is a capactor bank to compensate the reactive power, really i donot know how to size a capacitor bank for a 60HP motor, but i think it is easy.
voltage is strongly related to reactive power,
increasing the load(a cylinder start to waork) will need more power,i.e more current leading to more voltage drop on the terminal voltage of the motor, so the reactive power at the recieving end will decrease, if the motor didnot found a reactive power source he will try to get it from the power system, which will leads to more voltage drop.

i hope this would help and i hope you are not connecting a capacitor already.

 

[busbar]

There is an IEEE Working Group draft online paper at

http://grouper.ieee.org/groups/1453/drpaper.html

 

[jbartos]

Suggestion: Visit

http://www.abb.com/GLOBAL/ABBZH/ABB...DA6D4D88D7C1256882002BE167/$file/capA05en.pdf

for:
In 1999 the new SVC Light was commissioned. SVC
Light has all the benefits of the classic SVC and will also
eliminate flicker problems.

 

[Marke]

Hello baldwon

If you are seeing a modulation on incandescent lighting, that would suggest that there is a major voltage fluctuation. In this situation, the effect on discharge or flourescent lighting would be very severe.
If this is happeneing while the motor is operating, the voltage fluctuation during start must be extreme, unless there is some other circustance that we are not aware of.

In many territories, it is common to require that the voltage disturbance during start is limited to less than 5% of the line voltage. If the disturbance is higher, you must reduce start current or increase supply capacity. If you supply is within these limits, then the current variations expected due to loading changes will be much less than this and will not affect incandescent lighing. The first place I would look at is the strength of the supply.
As an off the wall thought, if you are using a soft starter with an energy saving function, you can get this type of characteristic due to the energy saving function operating incorrectly. If there is instability (not uncommon with these devices) then you can get supply modulation.

Best regards,

Mark Empson

http://www.lmphotonics.com