Resonance Grounding 3

[nightfox1925]

What are the advantages and disadvantages of resonance grounding and when it is applied? I have encountered the same description in an IEEE handbook but it simply says..it very complicated to use. Are there any info on this? I am curious.

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[Marmite]

Resonant grounding (Arc suppression coil, Petersen coil) is used by utilities to improve the transient performance of high voltage overhead lines, and hence the reliability of supply to customers. Around 80% of faults on O/H lines are transient and result in no permanent damage. A tunable reactor is connected in the transformer neutral to earth. The value of the reactance is chosen such that the reactance current neutralises the capacitance current, and the current at the point of fault is theoretically zero and unable to maintain an arc. One downside is there is insufficient fault current to operate normal feeder protection. Sensitive wattmetric protection can be used however. Some companies allow this situation to persist indefinitely, others shunt the coil after 30 secs or so and allow the normal protection to operate to clear the fault, if it's still there. Also, the phase/earth voltage on the healthy phases increases which can overstress insulation and cause polymeric surge arrestors to melt. The other major downside is cost.
Regards
Marmite

 

[nightfox1925]

Thanks marmite. Do you have any useful link or literature that I may use to expund further?

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[Marmite]

There's some information on the following website.

http://www.trenchgroup.com/Trench Group/Trench_EarthFault/Trench_EarthFaultProtection.html

You could also try Google for arc suppression coil or petersen coil.
Regards
Marmite

 

[prc]

Thank you Marmite for the good explanation.May be too basic-why the fault current is zero at fault point?Why on falling line voltage a current is not flowing back to transformer neutral?
There is another application,used in some countries.A neutral reactor is connected to the neutral of three phase shunt reactor -I am told for reducing arcing on single phase to line fault. How this compares with ARSC?

You have said some users allow the line fault to continue indefinitely.Then will not the supply in that line get affected?

 

[Marmite]

PRC, there are many text books which will explain the theory of arc suppression coils in detail if you are interested. In answer to your last point, don't forget that 80-90% of overhead line faults are transient, such as lightning, wind borne debris, tree contact, squirrels etc. This is where the ASC is of real benefit. If you have a downed conductor then you will of course have loss of supplies and/or voltage problems downstream and will need to locate and repair the fault. Although the coil theoretically makes the fault current zero, you would still have a live high voltage conductor on the ground which is highly dangerous. This is why I prefer the coil to be shunted after 30 secs. In the UK where I work ASC's are applied to the 11kV O/H system which is predominantly either single phase unearthed or 3 phase 3 wire unearthed construction and with no neutral conductor. All pole mounted transformers are either 3 phase with Delta HV windings or single phase connected between 2 phases. The ASC operation has no effect on the phase to phase voltage, but does affect the phase to ground voltages as the star point is displaced. The voltage to ground of the 2 healthy phases can increase to the full phase to phase voltage, but the voltage to customers is unaffected as they are all fed from Tx's connected phase to phase.
Regards
Marmite

 

[RalphChristie]

prc:

The value of reactance is chosen such that the reactance current neutralises capacitance current. The current at fault point is therefore nil and unable to maintain the arc

reactance current = due to the tuneable reactor
capacitance current = due to line capacitance

Other downside for this kind of grounding is the fact that the reactor has to be tuned everytime the system changes. And that faults on different parts of the system may result in different values of fault-current.

One reference given in the Green Book (142-1991 GREEN BOOK IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems):
AIEE Committee Report, "Application of Ground Fault Neutralizers,"
Electrical Engineering, vol. 72, July 1953, p. 606.




Regarding your last question: Ain't you refering to resistors? With reactance grounded systems (not resonant grounding) there can be problems with power frequency overvoltages under arcing earth fault conditions. The mining industry in South Africa experienced such problems in the mid 1970s, if I remembered correctly a Pretorius-guy where involved with it. Will have to check through some of my papers.

Regards
Ralph

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[nightfox1925]

Thank you gentlemen for all the valuable posts

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata