Impedance in parallel with surge arrester 1

[MikiBg]

Hi all!
Connection of impedance in parallel with surge arrester at 36/0.4 kV power transformer terminals is required by tender documentation.
What is the purpose of this impedance and how it should be dimensioned?
Regards,
Miki

 

[7anoter4]

I don’t know how the arrester will operate with parallel impedance.
I found only this article referring [close to] to this issue.
In order to test [only] the surge arrester model a resistance is inserted parallel. The resistance value is approx. 10^9 ohm .See:

http://www.ece.mtu.edu/faculty/bamork/Trans_Param/data05.PDF

 

[waross]

Given the contrasting response of capacitors and inductors in response to the rapid rise of a typical lightning induced surge, impedance may be too broad a term. I have seen capacitors connected at motor terminals downstream of the conventional surge arrestors as a last line of defense against over voltages. ( No, the capacitors were NOT for power factor correction. The capacitors were not large enough to make a difference to the power factor of a 3000 HP motor. Large synchronous condensers were used for whole plant power factor correction.)
Did you mean resistance?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crshears]

My utility employs what are called "surge capacitors" in gas-insulated switchgear line terminations "to serve two purposes - to slow down the incoming transients into the GIS and help the breakers' Short Line Fault (SLF) capability so they can be qualified as 80 kA breakers."

Another application is where they are used in combination with series reactors to switch high-voltage capacitors by means of independent-pole-operation circuit breakers, also to slow down incoming transients and purportedly to ease the duty on the IPO breaker contacts.

Why they were specified in the circumstances under consideration might be a question to direct to the engineering department that created the tendering documentation in the first place.

Hope this helps.


CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[cuky2000]

Below is an excerpt from Eaton, MV switchgear to minimize the impact of the very fast transient attributable to the vacuum circuit breakers switching transient.

Recommendations from manufactureres suggest that the combination of metal oxide arrester (zinc Oxide - ZnO) in parallel with a resistor (R) and also connected in series with a surge capacitor to form a device known as ZORC.

The resistor R is sized to match surge impedance of the load cables,typically 20 to 30 ohms and here is a simplify explanation how this device works to mitigate the overvoltage:
1) Under normal operating conditions, impedance of the capacitor is very high, effectively “isolating” the resistor R and ZnO from the system.
2) Under high frequency transient conditions, the capacitor offers very low impedance, thus effectively “inserting” the resistor R and ZnO in the power system as cable terminating network.

The resistance minimizing reflection of the steep wave-fronts of the voltage transients and prevents voltage doubling of the traveling wave. The ZnO element limits the peak voltage magnitudes.

The combined effects of R, ZnO, and Capacitor of the ZORC device provides optimum protection against high frequency transients by absorbing, damping, and by limiting the peak amplitude of the voltage wave-fronts.

Please note that the ZORC is not a lightning protection device. If lightning can occur or be induced in the electrical system, a properly rated and applied

 

[Pafi]

I have also read articles about surge protection (for HV motors, transformers) using surge arresters in combination - parallel - with RC filters where R approx.30 Ohms and capacitor approx. 0.25-0.5 uF.

 

[MikiBg]

Thank you all, specially cuky2000. I suppose they meant on what he is referring to as ZORC.