What is the concept of Impedance protection for synchronous Generator(turbo/hydro)? Does impedance protection refer to distance protection or it is something about minimum impedance limit of Gen?

Moreover, what is voltage balance protection for Gen? Is it similar to unbalance loading or negative phase sequnce?

 

Speedtronic, "Impedance Protection" is most likely related to a "Loss-Of-Field" disturbance. That is, the condition can be better represented by transforming the generator's measured parameters into an impedance having magnitiude and phase-angle.

However, there are limitations regarding its use. If required details can be provided.

Regards,
Phil Corso ([email protected])

 

Loss of field? Does it mean that up on loss of field generator will start to absorb reactive power from system & that must be limited or stopped?

Please give some theoretical description.

 

Speedtronic, as you know a synchronous generator delivers, or exports, inductive (lagging) kVAr to the system. If field current is reduced the "magnetic connection" between stator and rotor disappears. This condition manifests itself mechanically by rotor acceleration, assuming the prime mover still provides input. Thus, it is said that the machine operates asynchronously.

The electrical manifestations are: terminal voltage decreases (assuming there is significant impedance between it and other generators); armature current increases; kW output reduces; but, inductive kVAr output reverses, i.e., becomes negative. Then, it is said that the machine draws, or imports, lagging kVAr from the system.

If the generator's performance is plotted on a four-quadrant rectangular graph having reactance as its vertical axis and resistance as its horizontal axis, then the machine's operating condition can be represented by a point in the first-quadrant, say R, X. A line from the origin to R, X, represents its impedance, Z. As the event continues the path from R, X drifts (in most cases seconds, in rare cases tens of seconds) into the fourth-quadrant, where R is positive, but X is negative. The "impedance protective relay" is designed to detect the transgression, and trip the machine!

Regards,
Phil Corso

<b>Moderator's note:</b> error corrected according to Mr. Corso's comment in his next message. This now says "armature current increases" according to his correction.

 

Speedtronic... in my earlier reply, my comment that armature current "decreases" is incorrect. I should have said "increases!"

Phil Corso

<b>Moderator's note:</b> This error has been corrected according to Mr. Corso's comment in his message. It now says "armature current increases" according to his correction.

 

hi...

can you explain what the under impedance protection?

thank you
[email protected]

 

Sajad...

are you referring to under-excited operation as related to Impedance-Protection?

Regards,
Phil Corso