DC offset as it pertains to article 240

[mbrooke]

Few questions regarding this phenomenon in 600 volt and under power systems. What causes DC offset during a short circuit fault? Why isn't the sine wave like that of a load, just greater in magnitude? How does the X/R ratio effect it, if at all? Also does DC offset play a role in how symmetrical vs asymmetrical is applied to molded case circuit breakers?

 

[topgone]

It is more due to the existence of a fault at the moment other than the crossing point of the voltage wave. Add to that the impedance of the circuit which tries to resist any change in current (inductive).

 

[MyCleveland]

Read over attachment....

I have been stuck on the complex math involved with summing bus points to calculate X/R.

Anyone willing to help me with the math please contact me.

 

[mbrooke]

It is more due to the existence of a fault at the moment other than the crossing point of the voltage wave. Add to that the impedance of the circuit which tries to resist any change in current (inductive).

Thank you- but why is that? More detail

Read over attachment....

I have been stuck on the complex math involved with summing bus points to calculate X/R.

Anyone willing to help me with the math please contact me.

Heavy stuff. I've tried to do the same but in order to determine at which point a CT will saturate to determine bus bar differential over current settings. Relays with internal operate and restraint or those that are High Z really make it a no brainier.

But you still have to know it breaker interrupting wise.