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WHY VOLTAGE FLUCTUATION EFFECTS ONLY STARδ SYSTEMS

03/13/2012 9:09 PM

IN OUR PLANT WE ARE HAVING 220KV/33KV SUBSTATION ON WHICH SUDDEN VOLTAGE FLUCTUATION CAME, IT EFFECTS ONLY STAR&DELTA SYSTEMS (STAR DELTA MOTORS WITH OPERATING VOLTAGE OF 440V,FURNACE TRANSFORMERS WHICH ARE CONNECTED BY THE STAR AND DELTA SWITCH WITH OPERATING VOLTAGE OF 33KV).WHY THIS VOLTAGE FLUCTUATION EFFECTS ONLY STAR&DELTA SYSTEMS

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#1

Re: WHY VOLTAGE FLUCTUATION EFFECTS ONLY STARδ SYSTEMS

03/13/2012 11:09 PM

Firstly please stop yelling in capital letters.

Based on what you are saying I think the answer is that the voltage drop you are seeing on the 440V system (powering the motors) is due to voltage sag at the transformer(s) supplying the 440V system (33kV/440V ?). High motor starting current causes voltage sag.

Perhaps I am reading this wrong, it could also mean that a system wide voltage fluctuation could have upset the motor protection (perhaps causing them to trip out) but not the furnaces because the furnaces have a better ride-through ability (due to being resistive).

More information is needed to answer this question properly.

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#2
In reply to #1

Re: WHY VOLTAGE FLUCTUATION EFFECTS ONLY STARδ SYSTEMS

03/13/2012 11:28 PM

I'm glad that you could make some sense out or that, I couldn't.

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#3

Re: WHY VOLTAGE FLUCTUATION EFFECTS ONLY STARδ SYSTEMS

03/14/2012 2:25 AM

Typical equipment that is likely to cause voltage fluctuations are large motors, heating loads and furnaces. The primary cause of voltage changes is the time variability of the reactive power component of fluctuating loads. Such loads include arc furnaces, rolling mill drives, and main winders all of which are loads with a high rate of change of power with respect to the short-circuit capacity at the point of common coupling (PCC). Small power loads, such as starting of induction motors, welders, boilers, power regulators, electric saws and hammers, pumps and compressors, cranes, and elevators also can be sources of flicker.

Other causes are capacitor switching and on-load transformer tap changers, which can change the inductive component of the source impedance. Variations in generation capacity of wind turbines, for example, also can have an effect. Sometimes, voltage fluctuations are caused by low-frequency voltage inter-harmonics.

more links

http://northpower.com/network/services/voltage_fluctuations

http://www.fpl.com/residential/power_quality/pqr_faqs.shtml

http://www.engrreview.com/Editorial_pages/2010/jannuary_10/power_techbyte_01.html

Limits for Voltage Fluctuations in the Electricity Supply Sy..

A guide to voltage fluctuation and light flicker

Voltage Fluctuation and Flicker

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#4

Re: WHY VOLTAGE FLUCTUATION EFFECTS ONLY STARδ SYSTEMS

03/14/2012 2:35 PM

A little more information please. I believe the cause of your voltage fluctuations has been amply addressed.

Information such as the voltage you are seeing on the 440 volt transformer as well as the 33 KV transformer if possible with all the equipment operating would be helpful.

It would also be helpful to know if you've added any equipment lately or when you noticed the voltage fluctuations.

I'm not clear on whether or not the fluctuations are occurring in the entire plant or just in 440 volt transformer.

Assuming That none of the transformers are operating above their rated KVA the problem could potentially be minimized by re tapping the transformers. Adjusting the supply voltage to the higher end of the 440 volt transformer rating, then adjust the output voltage of the 440 volt transformer to the higher end of the motors operating range.

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#5

Re: WHY VOLTAGE FLUCTUATION EFFECTS ONLY STARδ SYSTEMS

03/14/2012 11:21 PM

star delta systems have inherently unstable voltage due to a lack of continuous grounding between the primary and secondary transformers.

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