Power factor

[Ingenieur]

Have fun.

Always
it is an aquired frame of mind
some never get the knack

 

[Besoeker]

I think the inductor along with capacitor is used for ripple control in the output. The ripple current has a frequency and inductor is there to limit its di/dt.

Not so.
There are reactors on the input lines. Typically a few tens of uH to limit di/dt for the semiconductors in the input bridge. In good designs, there is also a DC reactor for VFDs. This limits DC ripple current and input harmonics.

 

[mbrooke]

sometimes used as filters

sometimes used to absorb VAr for pf control (often during faults, transients, switching)
look up TCR thyristor controlled reactor
the can provide proportional VAr compensation
often in conjunction with TSC thyristor switched capacitors for a +/- Q
tuned LC filters for 5, 7 harmonics (and a net baseline C for pf improvement)
with active TSC and TCR all on a common bus
the 3rd harmonic is typically handled by a delta iso/matching/step up xfmr

Stupid question. Is this like a STATCOM?

 

[Ingenieur]

Stupid question. Is this like a STATCOM?

same general class of devices FACTS
it can do both + and - VAr
it is an active voltage source convertor where as the tsc and tcr are basically ss switching devices to put reactive loads online (tcr proportionally and tsc 2-state)

 

[mbrooke]

same general class of devices FACTS
it can do both + and - VAr
it is an active voltage source convertor where as the tsc and tcr are basically ss switching devices to put reactive loads online (tcr proportionally and tsc 2-state)

tsc, tcr, ss? Sorry. :ashamed1:

 

[Ingenieur]

tsc, tcr, ss? Sorry. :ashamed1:

ss solid state, vs contactors

tsc thyristor switched capacitor
tcr thyristor controlled reactor

 

[mbrooke]

ss solid state, vs contactors

tsc thyristor switched capacitor
tcr thyristor controlled reactor

Thanks

 

[Sahib]

Not so.
There are reactors on the input lines. Typically a few tens of uH to limit di/dt for the semiconductors in the input bridge. In good designs, there is also a DC reactor for VFDs. This limits DC ripple current and input harmonics.

MOV's would do a better job of limiting di/dt (of a transient) on the input side, relegating inductor to play the role of limiting harmonics and short circuit current.

 

[Besoeker]

MOV's would do a better job of limiting di/dt (of a transient) on the input side,

Not really.

 

[Sahib]

Clarification please.

 

[mbrooke]

Clarification please.

While I am fuzzy on what Besoeker is saying, MOVs short when the reach a certain voltage. This "clamps" or shunts the voltage and stops when it falls below a certain value.

 

[Besoeker]

Clarification please.

On what exactly?

 

[GoldDigger]

On what exactly?

I think that he needs to be told that what you want to do is time average the energy in a lossless way, not absorb and waste the energy in the sharp edged waveform.

 

[Besoeker]

I think that he needs to be told that what you want to do is time average the energy in a lossless way, not absorb and waste the energy in the sharp edged waveform.

My requirement was to limit di/dt. A MOV can't do that. I think he needs to understand that.

 

[mbrooke]

One last question regarding power factor, moving on to a big picture type deal. This is an excerpt from a report on the August 14, 2003 black out:

Immediately following the separation, the Connecticut transmission voltage reached high levels: more than 385 kV on the 345 kV system, and 130 kV on the 115 kV systems. This was a result of several factors: the static capacitors remaining temporarily in service; load being lost; reduced reactive losses on transmission circuits; and the loss of generation to regulate the system voltage. The Millstone units changed from full reactive output (lagging) during the separation transient, to absorbing VARs (leading) after the separation. Overvoltage protective relays operated, tripping both transmission and distribution capacitors across the Connecticut system. In addition, the load in the part of Connecticut that was still energized began to increase during the first seven to ten minutes following the event. This increase was most likely due to customers restoring load that had tripped during the transient. The load increase, combined with the capacitors tripping, resulted in transmission voltages dropping from high to low voltages within five minutes. The voltage on the 115 kV system fell to approximately 100 to 105 kV.

Question being, how do you generate VARs? My understanding is that generators deal with either a reactive or capacitive load, being either slowed down and sped up every 1/2 cycle, rather than actually making them? :dunce:

 

[Ingenieur]

One last question regarding power factor, moving on to a big picture type deal. This is an excerpt from a report on the August 14, 2003 black out:





Question being, how do you generate VARs? My understanding is that generators deal with either a reactive or capacitive load, being either slowed down and sped up every 1/2 cycle, rather than actually making them? :dunce:

this might help, a good basic description of a synchronous generator (electrical and mechanical speed are synchronized, no slip)
http://www.egr.unlv.edu/~eebag/Synchronous Generator I.pdf

it can supply or absorb VAr depending on the load
it can have a leading or lagging pf
the key is the angle between to field and the rotor

 

[mbrooke]

this might help, a good basic description of a synchronous generator (electrical and mechanical speed are synchronized, no slip)
http://www.egr.unlv.edu/~eebag/Synchronous Generator I.pdf

it can supply or absorb VAr depending on the load
it can have a leading or lagging pf
the key is the angle between to field and the rotor

Same would hold true for a permanent magnet AC generator? (Hypothetical question)

 

[winnie]

I believe that the general concept would hold true for a PM synchronous generator, however with such a generator you don't have the ability to adjust the field strength in order to control if that generator is a supplier or consumer of VARs.

-Jon

 

[Besoeker]

One last question regarding power factor, moving on to a big picture type deal. This is an excerpt from a report on the August 14, 2003 black out:








Question being, how do you generate VARs? My understanding is that generators deal with either a reactive or capacitive load, being either slowed down and sped up every 1/2 cycle, rather than actually making them? :dunce:

Synchronous motors have been used for PFC since before Adam was a boy - and I'm older than Adam!
They were sometimes known as Synchronous Condensers.

 

[mbrooke]

I believe that the general concept would hold true for a PM synchronous generator, however with such a generator you don't have the ability to adjust the field strength in order to control if that generator is a supplier or consumer of VARs.

-Jon

I think I am starting to get it... so its possible for the generator to act like a capacitor or inductor? But where does the load stand then? ISn't PF a function of the load and the generator takes which ever?