HenryOhm
Electrical
- Jun 22, 2005
- 60
All,
We are looking at upgrading an old Ward Leonard loop with DC gens to AC synchronous generators. The DC motors involved would be retained. We are a remote operation with utility power an impossibility.
I am trying to estimate what levels of ripple current one would expect from ~1600kW machine with a 6-pulse thyristor drive solely feeding a DC motor (pump application).
It would seem to me now that, somewhat similar to determining the depth of notching on the AC side, that the determination of ripple current should use the subtransient reactance (direct-axis) of the machine, not the transient, or synchronous, for the commutating inductance of the source.
Just want to be sure. The use of the subtransient in my attempted calculations give me perhaps acceptable though not ideal ripple current. But, any higher levels of source reactance lead to much higher unacceptable levels of ripple current.
I'm sorry, I know this question may seem a bit obtuse. But somehow, similar to notching, my mistaken impression at first was that since the system was not dealing with a sudden load shift (from the motor's perspective, re transient reactance) much less a serious short circuit (ie subtransient used), that the synchronous might be the value to use. Much of the material I have researched uses examples involving utility power and transformer reactances, neither at play for us.
Finally, my calculations are only meant to give me a better feel for whether specifications given the contractor should require current ripple testing post-installation, 12-pulse SCR's or PWM (we have 6-pulse SCR's throughout our installed base thus the preference here), a calculation prior to manufacturing showing the calculated ripple current, etc. So, any input along those lines would be greatly appreciated.
Thanks for any and all help.
We are looking at upgrading an old Ward Leonard loop with DC gens to AC synchronous generators. The DC motors involved would be retained. We are a remote operation with utility power an impossibility.
I am trying to estimate what levels of ripple current one would expect from ~1600kW machine with a 6-pulse thyristor drive solely feeding a DC motor (pump application).
It would seem to me now that, somewhat similar to determining the depth of notching on the AC side, that the determination of ripple current should use the subtransient reactance (direct-axis) of the machine, not the transient, or synchronous, for the commutating inductance of the source.
Just want to be sure. The use of the subtransient in my attempted calculations give me perhaps acceptable though not ideal ripple current. But, any higher levels of source reactance lead to much higher unacceptable levels of ripple current.
I'm sorry, I know this question may seem a bit obtuse. But somehow, similar to notching, my mistaken impression at first was that since the system was not dealing with a sudden load shift (from the motor's perspective, re transient reactance) much less a serious short circuit (ie subtransient used), that the synchronous might be the value to use. Much of the material I have researched uses examples involving utility power and transformer reactances, neither at play for us.
Finally, my calculations are only meant to give me a better feel for whether specifications given the contractor should require current ripple testing post-installation, 12-pulse SCR's or PWM (we have 6-pulse SCR's throughout our installed base thus the preference here), a calculation prior to manufacturing showing the calculated ripple current, etc. So, any input along those lines would be greatly appreciated.
Thanks for any and all help.