Author Topic: What is going on hear  (Read 1113 times)

Offline thedoc298

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What is going on hear
« on: September 27, 2019, 03:22:31 AM »


The power factor correction capacitor came out to be 166Uf, all good, for 15000/60 nst.

The capacitive reactance for 166uf is just about 16 ohm

So this comes out to  120/16 is 7.5 amps.

So accross my nst mains without nothing else running is going to be pulling 7.5 amps line to neutral.

How is that a advantage..?....Or


So if a single nst masures 43mh across its line and Neutral and I add a 166uf across line and neutral for pfc,  the current pulled will be about 155ma and without the 43mh it would jump to 7.5 amps from 16 ohms of capacitive reactance. Either side of the 43mh the current climbs up very fast.

Looks like the only way to use power factor correction is to know the inductance you are putting the capacitor across.

Is this even close


Offline MRMILSTAR

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Re: What is going on hear
« Reply #1 on: September 27, 2019, 05:21:21 AM »
That is essentially correct. You need to know the reactance (inductive and capacitive if any) of the load to know the actual PFC capacitance that you need.  You are trying to achieve a phase shift of zero degrees between the voltage and the current at the load. If that were achieved you would have a totally resistive load. In practice, zero degrees (PF =1) can't be achieved with reactive loads but it can be brought closer to zero with PFC.

After determining your PFC capacitor value, this will only be optimum for a particular load. If you change the load, you will have to change the PFC capacitor. On my control cabinet, I provide a bypass switch to eliminate PFC if I want. This allows me to use a different load if I want.
« Last Edit: September 27, 2019, 05:24:10 AM by MRMILSTAR »
Steve White
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Offline thedoc298

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Re: What is going on hear
« Reply #2 on: September 27, 2019, 05:05:14 PM »
That is essentially correct. You need to know the reactance (inductive and capacitive if any) of the load to know the actual PFC capacitance that you need.  You are trying to achieve a phase shift of zero degrees between the voltage and the current at the load. If that were achieved you would have a totally resistive load. In practice, zero degrees (PF =1) can't be achieved with reactive loads but it can be brought closer to zero with PFC.

After determining your PFC capacitor value, this will only be optimum for a particular load. If you change the load, you will have to change the PFC capacitor. On my control cabinet, I provide a bypass switch to eliminate PFC if I want. This allows me to use a different load if I want.

Thanks again for taking the time for a good confirmation reply, also sounds like the pf would be dynamically changing on the fly. Guess I will make a box and switch caps in and out or just off.

Getting close to first light. Thanks again

Offline MRMILSTAR

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Re: What is going on hear
« Reply #3 on: September 27, 2019, 06:04:56 PM »
Set the PFC with your coil in operation. Find the capacitance that gives you the lowest wall current with your coil in operation. After that is set don't change it again unless you change the design of your coil. I use the bypass switch if I want to use my control cabinet to power some other non-TC type of device, which of coarse would require a different PFC capacitance.

Large industrial plants frequently use adaptive PFC devices. They use a bank of capacitors that can be switched in or out as needed as the load changes throughout the day. The capacitor switching is controlled by a computer in real time.
« Last Edit: September 27, 2019, 08:09:12 PM by MRMILSTAR »
Steve White
Cedar Rapids, Iowa
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Offline DashApple

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Re: What is going on hear
« Reply #4 on: September 27, 2019, 06:20:57 PM »
I have done both using manual PFC with high voltage transformers and it dose work within a range , as said knowing the inductance of the circuit helps in selecting a capacitor .


I have also have built a system that uses a industrial PFC controller to control 12 capacitors and will actively try and maintain a PFC , I have had good results with test trials .


On a high voltage transformer setup with inductive ballast and auto PFC i was able to hit 0.98 PFC during arcs , there are limits to this as the PF controller was never intended for this and is abit slow , but the principle is there .

Offline thedoc298

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Re: What is going on hear
« Reply #5 on: September 28, 2019, 04:43:03 AM »
Thanks all, its really nice to have others verify what you are thinking, takes some of the edge off. Really learn alot.

Offline thedoc298

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Re: What is going on hear
« Reply #6 on: September 28, 2019, 04:47:46 AM »
I have done both using manual PFC with high voltage transformers and it dose work within a range , as said knowing the inductance of the circuit helps in selecting a capacitor .


I have also have built a system that uses a industrial PFC controller to control 12 capacitors and will actively try and maintain a PFC , I have had good results with test trials .


On a high voltage transformer setup with inductive ballast and auto PFC i was able to hit 0.98 PFC during arcs , there are limits to this as the PF controller was never intended for this and is abit slow , but the principle is there .

Guess I will be making a decade box, at least it will look kool. That would be fun to watch it change on the fly and know why. Thanks

Offline Hydron

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Re: What is going on hear
« Reply #7 on: September 28, 2019, 01:01:33 PM »
Unless your mains supply is right on the limit of tripping breakers (with only a 15kV/60mA NST I would expect plenty of margin) it's not critical to get the perfect power factor or even make any correction at all! If you set it up for perfect power factor at the nominal load, then it should still help for any load that is not wildly different - it's not gonna suddenly stop working for a load slightly off the design point.

Offline thedoc298

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Re: What is going on hear
« Reply #8 on: October 01, 2019, 05:08:43 AM »
Unless your mains supply is right on the limit of tripping breakers (with only a 15kV/60mA NST I would expect plenty of margin) it's not critical to get the perfect power factor or even make any correction at all! If you set it up for perfect power factor at the nominal load, then it should still help for any load that is not wildly different - it's not gonna suddenly stop working for a load slightly off the design point.

Yep, for my first low power, think I will skip. Thanks for tip.

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Re: What is going on hear
« Reply #8 on: October 01, 2019, 05:08:43 AM »

 


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