Power factor

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Besoeker

Besoeker

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Sahib said:
As you say ''used these for limiting di/dt in power electronics'', it seems to imply ''i'' of higher frequency as the slope of ''i '' i.e di/dt increases with increase in frequency of ''i''.

What a self contradiction!
Click to expand...
No contradiction, old chap.
 
I

Ingenieur

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Sahib said:
Introduction of a series capacitor in the lamp circuit with inductance will reduce the overall impedance presented to the power supply and if such an act is not part of the original design, it would likely increase the current through the lamp above its design value with consequent reduction in its rated life due to nature of tungsten filaments at the lamp ends.
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slope does increase with frequency
assume 2 signals, unit magnitude 1A
f1 = 1 Hz
f2 = 10 Hz
start at zero crossing
1/4 cycle positive slope, then 1/2 cycle negative, the 1/4 positive, repeat
let's focus on the first 1/4 positive

time duration for 1 cycle: 1/1 = 1 sec, 1/4 cycle = 0.25 or 1/4
f1 di/dt ~ delta I / delta t = 1/(1/4) = 4 A/sec

time duration for 1 cycle: 1/10 = 0.1 sec, 1/4 cycle = 0.025 or 1/40
f2 di/dt ~ delta I / delta t = 1/(1/40) = 40 A/sec
much 'steeper'

another way to look at this
Xl = j (2 Pi f) L
as f increases, so does X and it 'chokes' or suppresses the higher frequencies

it can be said as 'slope' (di/dt) increases so does impedance
 
Besoeker

Besoeker

Senior Member
Location
UK
Ingenieur said:
slope does increase with frequency
assume 2 signals, unit magnitude 1A
f1 = 1 Hz
f2 = 10 Hz
start at zero crossing
1/4 cycle positive slope, then 1/2 cycle negative, the 1/4 positive, repeat
let's focus on the first 1/4 positive

time duration for 1 cycle: 1/1 = 1 sec, 1/4 cycle = 0.25 or 1/4
f1 di/dt ~ delta I / delta t = 1/(1/4) = 4 A/sec

time duration for 1 cycle: 1/10 = 0.1 sec, 1/4 cycle = 0.025 or 1/40
f2 di/dt ~ delta I / delta t = 1/(1/40) = 40 A/sec
much 'steeper'

another way to look at this
Xl = j (2 Pi f) L
as f increases, so does X and it 'chokes' or suppresses the higher frequencies

it can be said as 'slope' (di/dt) increases so does impedance
Click to expand...

With all the respect merited, I think you totally missed the point.
Rate of change current or di/dt can be detrimental to the operation of power semiconductors. Or even kill them.

For example, this can happen in variable speed DC drives where SCRs are used to convert fixed voltage, fixed frequency to variable voltage DC.
The SCR is essentially a solid state switch. Turn it on at whichever part of the cycle is required and the current will rise at whatever rate the external circuitry allows. Without line reactors, the di/dt could exceed the capability of the SCR which is typically in the order of several hundred Amps per microsecond for converter grade devices.

It's a transient, not a steady value which is what you presented.
 
I

Ingenieur

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Besoeker said:
With all the respect merited, I think you totally missed the point.
Rate of change current or di/dt can be detrimental to the operation of power semiconductors. Or even kill them.

For example, this can happen in variable speed DC drives where SCRs are used to convert fixed voltage, fixed frequency to variable voltage DC.
The SCR is essentially a solid state switch. Turn it on at whichever part of the cycle is required and the current will rise at whatever rate the external circuitry allows. Without line reactors, the di/dt could exceed the capability of the SCR which is typically in the order of several hundred Amps per microsecond for converter grade devices.

It's a transient, not a steady value which is what you presented.
Click to expand...

was not talking about interaction with a IGBT's etc.
only the physics of the choke

di/dt is not steady state
I've had a ton of schooling and experience on various types of convertors
built them up from raw components
for example
ECE 2250 : Power Electronics Circuits & Applications
also a good exposure in FACTS/HVDC courses
the current course is on PV and wind generation, convertors are essential
been working with SS convertors since the mid 80's
 
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mbrooke

mbrooke

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Location
United States
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Technician
Ingenieur said:
was not talking about interaction with a IGBT's etc.
only the physics of the choke

di/dt is not steady state
I've had a ton of schooling and experience on various types of convertors
built them up from raw components
for example
ECE 2250 : Power Electronics Circuits & Applications
also a good exposure in FACTS/HVDC courses
the current course is on PV and wind generation, convertors are essential
been working with SS convertors since the mid 80's
Click to expand...



Shot in the dark, is this what you are referring to?


https://www.youtube.com/watch?v=ZOTGuWCfS-A
 
Besoeker

Besoeker

Senior Member
Location
UK
Ingenieur said:
was not talking about interaction with a IGBT's etc.
only the physics of the choke

di/dt is not steady state
I've had a ton of schooling and experience on various types of convertors
built them up from raw components
for example
ECE 2250 : Power Electronics Circuits & Applications
also a good exposure in FACTS/HVDC courses
the current course is on PV and wind generation, convertors are essential
been working with SS convertors since the mid 80's
Click to expand...
But you still missed the fundamental point.
No problem.
 
I

Ingenieur

Senior Member
Location
Earth
chokes are increasingly used for active Q compensation/pf correction
using thyristor controllers

we have 4 major players in the area
ABB
Alstom
Westinghouse
Mitsubishi


their FACTS/HVAC divisions are local
 
mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Ingenieur said:
chokes are increasingly used for active Q compensation/pf correction
using thyristor controllers

we have 4 major players in the area
ABB
Alstom
Westinghouse
Mitsubishi


their FACTS/HVAC divisions are local
Click to expand...


These provide smoothing and absorption of harmonics created by switching valves?
 
Sahib

Sahib

Senior Member
Location
India
Besoeker said:
With all the respect merited, I think you totally missed the point.Rate of change current or di/dt can be detrimental to the operation of power semiconductors. Or even kill them.For example, this can happen in variable speed DC drives where SCRs are used to convert fixed voltage, fixed frequency to variable voltage DC.The SCR is essentially a solid state switch. Turn it on at whichever part of the cycle is required and the current will rise at whatever rate the external circuitry allows. Without line reactors, the di/dt could exceed the capability of the SCR which is typically in the order of several hundred Amps per microsecond for converter grade devices.It's a transient, not a steady value which is what you presented.
Click to expand...
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.
 
I

Ingenieur

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Location
Earth
mbrooke said:
These provide smoothing and absorption of harmonics created by switching valves?
Click to expand...

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
 
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