Inductor has no high inrush current

[Ingenieur]

So what angle is it because that's what your diagram in post #51 shows.

No it isn't
it is the phase ang v to i
the cos of which is pf

 

[Besoeker]

170923-1511 EDT

Fig. 3.2 above is a good illustration of the AC current in an RL switched AC circuit.

If you can visualize from this plot what happens if the time constant is very long and turn on occurs at a steady state current peak, then you can see why the upper limit of peak current is just 2 times the steady state peak.

.

Totally agree.

 

[Ingenieur]

170923-1511 EDT

Fig. 3.2 above is a good illustration of the AC current in an RL switched AC circuit.

If you can visualize from this plot what happens if the time constant is very long and turn on occurs at a steady state current peak, then you can see why the upper limit of peak current is just 2 times the steady state peak.

.

:thumbsup:
The 2x concept is very important to understand

 

[Besoeker]

No it isn't
it is the phase ang v to i
the cos of which is pf

Power factor isn't really relevant to transients.

 

[GoldDigger]

matters not what you nor I call it
v = iz hold true for transient analysis

Actually it does not. Under transient conditions as well as under steady state conditions the voltage depends on the time derivative and time integral of the current. Unless you are trying to say that z itself depends on those time functions of current rather than being a circuit constant. In general we have L and C constant for linear circuits and the resulting impedance depends directly on Z_L and Z_C, which are in turn related to L and C by the frequency of the sinusoidal component we are looking at.
One way or another V=IZ is an oversimplification IMO.

 

[Ingenieur]

Power factor isn't really relevant to transients.

The dood that wrote text thought so
hence revisited in the chapt 'simple switching transients'
this course obviously had many prerequisites

I can't explain it with an iphone lol
took me 50 hrs of class
triple that in study time
math derivation and model simulation to get a fundemental understanding
by no means an expert: but the author and my prof were
hopefully a bit rubbed off on me

 

[Besoeker]

The dood that wrote text thought so

He gives a definition of steady state power factor which I suspect few electrical engineers, myself included, would disagree with.

 

[Ingenieur]

Actually it does not. Under transient conditions as well as under steady state conditions the voltage depends on the time derivative and time integral of the current. Unless you are trying to say that z itself depends on those time functions of current rather than being a circuit constant. In general we have L and C constant for linear circuits and the resulting impedance depends directly on Z_L and Z_C, which are in turn related to L and C by the frequency of the sinusoidal component we are looking at.
One way or another V=IZ is an oversimplification IMO.

perhaps the concept is an oversimplification
the application of it not so much
it is the fundamental tool to begin analysis
gets easier with a constant freq and assuming ckt parameters are constant
although it still applies if freq and ckt parameters are not constant
I like 'simple'

 

[Ingenieur]

V = L di/dt
volts = H x A/s or volts = Ohm x s x A / s = Ohm x A or V = I x R

,

 

[Ingenieur]

He gives a definition of steady state power factor which I suspect few electrical engineers, myself included, would disagree with.

let's hope not :lol:

then he applies the associated angle to derive transient equations

 

[Besoeker]

let's hope not :lol:

then he applies the associated angle to derive transient equations

Not in the copy and paste you posted.
Let's just stick with the simple:
i(t)=v/r(1-e^(-t(r/l))

 

[Besoeker]

V = L di/dt
volts = H x A/s or volts = Ohm x s x A / s = Ohm x A or V = I x R

,

Excellent promo for SI no matter where you copied it from..............

 

[gar]

170923-1659 EDT

The simplified math model of this circuit consists of two components.

1. The DC circuit exponential decay curve for current for R and L.

2. The steady state sinusoidal curve for current based on R, L, and frequency.

These two components are added together to obtain the actual current.

The time of turn on relative to the steady state current curve determines the constant in front of the 1-e transient component. If the initial inductor current is zero, then the transient component current has to be equal and opposite in value to the instantaneous value of the steady state current when it is projected back to time t = 0. This all results from the initial current condition of the inductor being 0.

.

 

[Ingenieur]

Not in the copy and paste you posted.
Let's just stick with the simple:
i(t)=v/r(1-e^(-t(r/l))

sure it is
those are successive pages post 46

 

[Ingenieur]

Excellent promo for SI no matter where you copied it from..............

:happyyes: I knew you'ld get a kick out of that lol

 

[Electric-Light]

Zero crossing turn-on is indicated against inductive loads like motors and transformers.

 

[GoldDigger]

Zero crossing turn-on is indicated against inductive loads like motors and transformers.

Actually a voltage zero crossing into an inductive load will result in the highest possible magnetic flux in the winding since flux will start at zero (or if you are unlucky with residual magnetism a high positive value) and increase for an entire half cycle. In the steady state there will be remaining negative flux at the time of the positive zero crossing, and so the transient flux starting from a voltage zero will be significantly worse, potentially driving the core into saturation for even more excess current.

For capacitive load, OTOH, you do want to turn on at voltage zero crossing, at a time when charge will be zero in a normal equilibrium cycle. The current will be high, but no higher than the steady state current.
If you turn on at voltage peak the inrush current will only be limited by the incidental or designed series inductance and resistance in the circuit.

 

[FionaZuppa]

simple RC or RI ckt will not see "inrush".

Typo? double typo? no inrush for RC is sure news to lots of folks I'll bet.

Inrush defined as larger than steady state.

not sure what you mean.

there is no inrush for simple RC or RI ckts.

 

[GoldDigger]

not sure what you mean.

there is no inrush for simple RC or RI ckts.

It is nonstandard terminology and confusing to use RI for Resistor-Inductor. Much more common would be RL for that purpose.
Especially when you do not use subscripts, I is pretty much reserved for current.

 

[mbrooke]

Question- what if you have an air choke inductor? Will these present low inrush since there is now iron core to dump flux into?