I simulated a resonant Pole Pig (7,200v) in LTSpice, here are my results.
ScottH, Wed Mar 22 2017, 11:10AMI don't know how to include core saturation, but here is a 7.2kV Pole Pig with a 0.35uf resonant cap added in series. The voltage went from 7,200v with no cap--to nearly 70,000v with resonant cap.
By any chance, is it possible to factor in the properties of a transformer core and/or shunt inductance (for MOTs) in Spice?
Re: I simulated a resonant Pole Pig (7,200v) in LTSpice, here are my results.
Dr. Slack, Wed Mar 22 2017, 02:28PM
We call that a parallel capacitor, not a series capacitor, in engineering circles. The capacitor is connected across the transformer output terminals, and you're measuring the voltage across it.
A series capacitor would be connected in series with a load, and you'd measure the output voltage across the load.
With a K1 of 0.99, there's very little leakage inductance. If you want to model the shunts of a MOT, then decrease this value. Try setting K1 to 1.0, to see whether a transformer with no leakage is much different. Setting it to a lower value will decouple the secondary inductance from any shorting effect of the primary and supply.
You appear to be resonating the primary/secondary inductances, with the 0.5ohm primary resistive ballast failing to short circuit these. This was probably the defect in my thinking, the presence of the primary ballast. Without it, the low mains supply impedance would short-circuit both primary and secondary inductance, leaving nothing to be resonant. Try the simulation again with zero ballast resistance to check whether this is the case.
I think there is a way to factor in the core magnetics, but I've never done it myself. Try google. There's plenty of interesting insights to be gained from this simple model without worrying about saturation. You can mimic saturation very crudely by decreasing the inductances.
Dr. Slack, Wed Mar 22 2017, 02:28PM
We call that a parallel capacitor, not a series capacitor, in engineering circles. The capacitor is connected across the transformer output terminals, and you're measuring the voltage across it.
A series capacitor would be connected in series with a load, and you'd measure the output voltage across the load.
With a K1 of 0.99, there's very little leakage inductance. If you want to model the shunts of a MOT, then decrease this value. Try setting K1 to 1.0, to see whether a transformer with no leakage is much different. Setting it to a lower value will decouple the secondary inductance from any shorting effect of the primary and supply.
You appear to be resonating the primary/secondary inductances, with the 0.5ohm primary resistive ballast failing to short circuit these. This was probably the defect in my thinking, the presence of the primary ballast. Without it, the low mains supply impedance would short-circuit both primary and secondary inductance, leaving nothing to be resonant. Try the simulation again with zero ballast resistance to check whether this is the case.
I think there is a way to factor in the core magnetics, but I've never done it myself. Try google. There's plenty of interesting insights to be gained from this simple model without worrying about saturation. You can mimic saturation very crudely by decreasing the inductances.
Re: I simulated a resonant Pole Pig (7,200v) in LTSpice, here are my results.
klugesmith, Wed Mar 22 2017, 02:46PM
Isn't the analog circuit simulator variant we call LTSpice formally named Switcher-something?
It's supposed to stand out among Spices for efficient, practical modeling of switching power converters.
They have very fast transitions in and around magnetic components, usually combined with feedback regulation that works on a much longer timescale.
Point being, LTSpice certainly features nonlinear magnetic element modeling. But I've never explored that. Who has?
It isn't necessary for the exercises Dr Slack has been guiding in this thread.
A simple exercise in nonlinear magnetic modeling might be a Joule Thief circuit. If the transistor is ideal, then I think the circuit won't oscillate without a saturating core.
klugesmith, Wed Mar 22 2017, 02:46PM
Isn't the analog circuit simulator variant we call LTSpice formally named Switcher-something?
It's supposed to stand out among Spices for efficient, practical modeling of switching power converters.
They have very fast transitions in and around magnetic components, usually combined with feedback regulation that works on a much longer timescale.
Point being, LTSpice certainly features nonlinear magnetic element modeling. But I've never explored that. Who has?
It isn't necessary for the exercises Dr Slack has been guiding in this thread.
A simple exercise in nonlinear magnetic modeling might be a Joule Thief circuit. If the transistor is ideal, then I think the circuit won't oscillate without a saturating core.
Re: I simulated a resonant Pole Pig (7,200v) in LTSpice, here are my results.
ScottH, Wed Mar 22 2017, 04:21PM
I have some more results
For MOT shunts, would a K value of .66 be appropriate? What is the primary or secondary coils inductance on a MOT?
ScottH, Wed Mar 22 2017, 04:21PM
Dr. Slack wrote ...
We call that a parallel capacitor, not a series capacitor, in engineering circles. The capacitor is connected across the transformer output terminals, and you're measuring the voltage across it.
A series capacitor would be connected in series with a load, and you'd measure the output voltage across the load.
With a K1 of 0.99, there's very little leakage inductance. If you want to model the shunts of a MOT, then decrease this value. Try setting K1 to 1.0, to see whether a transformer with no leakage is much different. Setting it to a lower value will decouple the secondary inductance from any shorting effect of the primary and supply.
You appear to be resonating the primary/secondary inductances, with the 0.5ohm primary resistive ballast failing to short circuit these. This was probably the defect in my thinking, the presence of the primary ballast. Without it, the low mains supply impedance would short-circuit both primary and secondary inductance, leaving nothing to be resonant. Try the simulation again with zero ballast resistance to check whether this is the case.
I think there is a way to factor in the core magnetics, but I've never done it myself. Try google. There's plenty of interesting insights to be gained from this simple model without worrying about saturation. You can mimic saturation very crudely by decreasing the inductances.
We call that a parallel capacitor, not a series capacitor, in engineering circles. The capacitor is connected across the transformer output terminals, and you're measuring the voltage across it.
A series capacitor would be connected in series with a load, and you'd measure the output voltage across the load.
With a K1 of 0.99, there's very little leakage inductance. If you want to model the shunts of a MOT, then decrease this value. Try setting K1 to 1.0, to see whether a transformer with no leakage is much different. Setting it to a lower value will decouple the secondary inductance from any shorting effect of the primary and supply.
You appear to be resonating the primary/secondary inductances, with the 0.5ohm primary resistive ballast failing to short circuit these. This was probably the defect in my thinking, the presence of the primary ballast. Without it, the low mains supply impedance would short-circuit both primary and secondary inductance, leaving nothing to be resonant. Try the simulation again with zero ballast resistance to check whether this is the case.
I think there is a way to factor in the core magnetics, but I've never done it myself. Try google. There's plenty of interesting insights to be gained from this simple model without worrying about saturation. You can mimic saturation very crudely by decreasing the inductances.
I have some more results
For MOT shunts, would a K value of .66 be appropriate? What is the primary or secondary coils inductance on a MOT?
Re: I simulated a resonant Pole Pig (7,200v) in LTSpice, here are my results.
johnf, Wed Mar 22 2017, 06:14PM
I think you got your R1 and R2 values around the wrong way
correcting this will reduce your resonant ring up voltage.
So now you need real values inductance of both windings inductance of one winding with the other shorted this gives leakage inductance. resistance of both windings and idle current no load (core loss)
johnf, Wed Mar 22 2017, 06:14PM
I think you got your R1 and R2 values around the wrong way
correcting this will reduce your resonant ring up voltage.
So now you need real values inductance of both windings inductance of one winding with the other shorted this gives leakage inductance. resistance of both windings and idle current no load (core loss)
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