Muhanad Sharaf/USABB/ABB Phone: +1 614 818 6393 , Mobile: +1 614 397 4150

07/31/2012 07:40 PM

To Normann_Fischer@selinc.com,

cc Albert J Keri/USABB/ABB@ABB, bob_morris@selinc.com

bcc

Subject Fw: Broken Conductor Detection on Transmission Line

Hi Normann,

I have not heard from you in a long time and hope you've been in good health and all is well with you.

I really wanted to have a closure to the subject matter that started back in Chicago during the conference.

So, I set out to do my own independent looking into it and have the last word based on established mathematical tools including symmetrical components.

Attached below is my work that shows Phase-A is re-created by the delta-backfeed with no distortion in phase or in magnitude. This agrees with my colleague Albert Keri's earlier statements.

What you had demonstrated to me at the conference is true whether Phase-A is lost or intact. In brief, polarity is the key thing and when you were summing the two healthy phases which are in series in the Delta after loss of the third phase, the sum was equal to the lost phase but inverted. However, that is true whether Phase-A is lost or not. And that same sum is actually reversed again when measured with respect to the polarity of the lost phase. Again, the attached work depicts that.

Actually, what you had thought is true for Delta(HV) - WYE-G(LV) configuration though the inverted phase is on the HV side and about half of the PU Ph-N voltage. So, there is a distinction between WYE(HV) - Delta(LV) and Delta(HV) - WYE(LV) configurations as far as voltages are concerned under no load and with a radial feed (only one feed source). Under load, the relative magnitudes of load currents for WYE(HV) - Delta (LV) are 1, 1, 1 (Outside of Delta) and 0.5, 0.5, 1 (or 1,1,2) for Delta(HV) - WYE-G(LV) for a phase loss.

The conclusion in the attachment is the same for 3X1, 3-legged core, 4-legged core, or 5-legged shell transformers. So, the loss of phase for a WYE-G(HV) - Delta(LV) configuration is not affected by the transformer core form as it is the case in the rare configuration of WYE-G - WYE-G where loss of phase on a 3X1 transformer results in complete loss of phase on both sides but not on a 3-legged core transformer where the flux sharing re-generates the lost phase just as the delta electrically does in the WYE-G - Delta configuration.

Open Phase Analysis in BW.PDFOpen Phase Analysis in BW.PDFOpen Phase Analysis.PDFOpen Phase Analysis.PDF

Best Regards,

Muhanad N. SharafSenior Electrical Engineer, P.E.ABB Inc.Integrated Services Instrumentation, Control, & Electrical579 Executive Campus DriveWesterville, Ohio 43082-8870Phone: +1 614 818 6393Mobile: +1 614 397 4150email: muhanad.sharaf@us.abb.com

Broken Conductor ScenarioElectrical Oneline

Muhanad N. Sharaf, P.E.Senior Electrical Engineer

Printed by EasyPower

GEN BUS 13.8

kV

345 k

V

138 k

V

345 k

V

EMER. FEED 13.8

kV

GEN

138KV TRANS SYS

345KV TRANS SYS

AUX LOAD15 MVA

TX-1450 / 750 MVA345 - 138 kV8%

GSUT450 / 750 MVA138 - 13.8 kV7.69%

EMERGENCY XFMR20 / 26.67 MVA345 - 13.8 kV7%

1-26

6.8

Partr

idge

/acs

sA

CSS

, 0.2

5 m

i.

OPEN

CB NORMALLY OPENAUX LOAD CB

Phase-A conductor broke off while Emergency XFMR is energized with no load.

Can this Loss-of-Phase be detected on the delta side of the Emergency XFMR?

Positional Protection Technique (Transient-Based Protection for Detection of Broken Conductors)Muhanad Sharaf to: Albert J Keri 06/21/2012 05:10 PM

Phone: +1 614 818 6393 , Mobile: +1 614 397 4150

From: Muhanad Sharaf/USABB/ABB

To: Albert J Keri/USABB/ABB@ABB,

Albert,

This is the IEEE paper I ran into a couple of months ago. I downloaded it yesterday and it is interesting to read.

Detection of Broken Conductors .pdf

The concept is simple but it doesn't seem to be promising in the specific case of detecting a broken conductor with no prior load. Aside from its ability to make a distinction for the type of fault in addition to pinpointing its location, the scheme philosophy is basically built on the phenomen where a sudden change of power flow or interrupt of current due to a fault (e.g. high short-circuit current or very high-impedance fault which is similar to a broken conductor scenario) causes high-frequency voltage signal. In the case of a broken conductor, the reflected and refracted transient waves are propagated into the healthy conductors (or phases) via the mutual coupling between the broken and the healthy ones.

As the paper mentions, the magnitude of this fault-generated high frequency voltage signal is influenced by two factors (i) fault inception angle, and (ii) the pre-fault loading in the broken conductor (See Page 1166). The paper does not treat the case where there is little or no load prior to loss of one phase potential; nor does it provide a minimum sensitivity for this technique to detect a broken conductor.

Whether the interruption of excitation current will generate a good enough magnitude of high-frequency voltage signal for the transient capture unit to be able to declare a broken conductor incident is not known. But, it certainly must first be answered before we can say this technique is a solution.

Muhanad N. SharafSenior Electrical Engineer, P.E.ABB Inc.Integrated Services Instrumentation, Control, & Electrical579 Executive Campus DriveWesterville, Ohio 43082-8870email: muhanad.sharaf@us.abb.com