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Lalit Shukla
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Join Date: May 2012
Posts: 26

Alternator Frequency

08/05/2013 7:31 AM

Dear All

alternator standard frequency is 50 Hz, if we reduce frequency from 50 to 49 then are the effect on electrical KW

example if Kw 14 MW on 50 Hz what are the KW on 49 HZ

if star delta motor load are 7 Mw & drive motor load are 7 Mw

& effect on motor efficiency & life
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PWSlack
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#1

Re: Alternator Frquency

08/05/2013 7:41 AM

Never mind that. If the motors are driving pumps then pump performance will fall off, altering the economics of the operation rather more than simply the change in life of the motors!

Stay at 50Hz.

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Lalit Shukla
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#2
In reply to #1

Re: Alternator Frquency

08/05/2013 7:52 AM

thanks for Reply

pump discharge decrease but is input power of star delta motor also decrease. ie if it getting load 60 KW is new KW is less than 60 Kw
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PWSlack
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#4
In reply to #2

Re: Alternator Frquency

08/05/2013 8:08 AM

This is folly. Stay at 50Hz.

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Anonymous Poster #1
#3

Re: Alternator Frquency

08/05/2013 8:06 AM

http://cr4.globalspec.com/thread/82029
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lyn
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#5

Re: Alternator Frequency

08/05/2013 11:09 AM

Sure, why not do it.

Since you don't know how calculate the difference, it shouldn't bother you that efficiencies of most devices will suffer and all your clocks will run slower.
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tcmtech
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#6

Re: Alternator Frquency

08/05/2013 1:32 PM

This sounds like mis directed penny pinching to me.

If you want to have maximum profit at the least operating cost never take short cuts or underfunded the service and maintenance departments. Go after the managements paychecks. That's usually where the most money is going that does the least good for the betterment and longevity of a company in the end.
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jack of all trades
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#7

Re: Alternator Frquency

08/05/2013 3:34 PM

Don't !

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pillay
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#8

Re: Alternator Frequency

08/05/2013 11:17 PM

Whats the idea behind this.R U trying to save energy , than forget it on power circuits.
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vishram lele
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#9

Re: Alternator Frequency

08/05/2013 11:28 PM

Hi Lalit,

Lowering the operating frequency of alternator will increase the burdon on the excitation circuit of the alternator; Excitation Circuit = AVR + Exciter Stator + Exciter Rotor+ Rectifier Assembly + Main Rotor, and inturn will incresae the losses (I2R Losses, whith the very little benefit on the Iron Losses).

To avoid the over burdoning on the excitation circuit, you need to reduce the output KVA of the alternator, this can not be calculated with an imperical formula, but needs to restrict the Excitation Values same as Full Load 50 Hz.

Lowering the frequency will further increase the No Load Current drawn by the Induction Motors, which is again a loss.

If you want to get max Efficiency, please talk to the Manufacturer of the Alternator and ask for the Efficiency Graphs at various PF and various Load Conditions. As per my experience the Max Efficiency is arround 85 - 90 % of Full Load.

I certainly do not advocate lowering Frequency will save money, rather it will take a penny more from your pocket.

Regards,

Vishram Lele
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PWSlack
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#10

Re: Alternator Frequency

08/06/2013 8:17 AM

If it were a good idea, then why is nobody else doing it?

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4wsilver
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#11
In reply to #10

Re: Alternator Frequency

08/06/2013 9:24 AM

The main problem with lowering the frequency is that the core flux density goes up. Many motors and generators of current design do not have much margin. If the core goes to saturation then damage will occur. Design for alternators take into account that there will be some fluxuation but if you try to run at less than rated (50 HZ) continuously you will not have the tolerance available for short term variance. There probably would be little damage at 49 but if the frequency drags down during starting you could get into big problems. Going into saturation destroys equipment, not just overheats it.
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1capybara
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#13
In reply to #11

Re: Alternator Frequency

08/09/2013 11:58 PM

4w silver, u r obviously someone who's got up from their desk, gone out into the field, and actually understands how things work... and so you are 100% right. thx! :)

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dhayanandhan
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#12

Re: Alternator Frequency

08/06/2013 12:07 PM

Dear Mr. Lalit Shukla,

This topic/similar topics have been discussed several times.

If the frequency falls down, the motor speed will fall down - considering 50 C/s. Frequency, drop to 49 C/s.speed will drop to 98% - fall of 2 % and for the Pumps, fans etc., capacity will varyas Proportional to the speed, Pressure will vary as Proportional to the SQUARE of the speed, and the Power will vary as CUBE of the SPEED.

Further, as replied in Post No. 9, the EXCITATION CURRENT, will INCREASE, the Power Factor will vary etc.

DHAYANANDHAN.S
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Users who posted comments:

1capybara (1); 4wsilver (1); Anonymous Poster (1); dhayanandhan (1); jack of all trades (1); Lalit Shukla (1); lyn (1); pillay (1); PWSlack (3); tcmtech (1); vishram lele (1)

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