f08-ballotresults

8/13/2019 F08-BallotResults

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IEEE C57.12.90 Sect. 11 WG Ballot Results Note: Re visions to the balloted text are highlighted in column 1.

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Jerry Corkran (unresolved negative ballot ): My vote willchange to a positive if the procedure is revised to agree with IEC14 -563 Temp Rise Draft which states the following in section7.5 of this standard regarding how to determine the averagetemperature rise of a three phase transformer:7.5 Determination of average winding temperature The average winding temperature is determined viameasurement of winding resistance. On a three - phasetransformer the measurement should preferably be associatedwith the middle limb, but this recommendation should be

disregarded for low resistance star connected winding. The negative applies to both Distribution and Power. I believewe should harmonize our standard with the IEC documentreferenced.

The March 2006 meeting minutes documentsthe original proposal for a standard coolingcurve format: at least one measurement bemade on all windings within 4 minutes ofshutdown and that a minimum of 4 be madeon all windings as B - phase may notnecessarily give the highest temperaturerise which lead to the WG consensus tomeasure winding resistance on all phases. Balloters comment is unresolved.

c) The first hot resistance data point used todetermine the time zero hot resistance of thewinding shall be taken as quickly aspossible after shutdown and after coresaturation disappears the inductive effectsdisappear and in any case, no later than 4 minutes after shutdown. In order to achievecore saturation in a short time period, theDC power supply voltage should be largeenough to provide sufficient 'volt -seconds'to saturate the cores in a short time.

The DC source should be selected such thatit can also provide sufficient current to keepthe core saturated without causing excessiveheating of windings. A series resistor addedto the circuit will decrease time tostabilization.

c) When a transformer s are has awinding connected in delta, all affectedlimbs must involved core legs shall besaturated unless the delta is open during

Steve Synder: The first hot resistance data point aftershutdown and after core saturation the inductive effects disappear , and in any case In order to achieve largeenough to provide sufficient volt -seconds to saturate the cores

Thang Hochanh : Phrase to be added at the end of section 2identified by without causing excessive heating of windings:Series resistor added to the circuit will decrease the time tostabilization.

Juan Castellanos : (1) Change the phrase When transformers areconnected in delta, all affected limbs must be saturated toWhen a transformer has a winding connected in delta, allinvolved core legs shall be saturated, unless the delta is open

Accepted

Accepted

(1) Accepted


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shutdown for stable and accurate readings.Special attention is required to ensure thatall the cores in a circuit such as ones in aWhen performing winding resi stancemeasurements on a transformer that utilizes series transformer s often utilized inconjunction with on for load tap changerschanging , care is required to ensure that thewhole circuit, consisting of the main andseries transformer windings, is are a lso

saturated before stable readings of thecombined winding resistances can beobtained.

during the shutdown

(2) Remove the phrase Special attention is required to ensurethat all the cores in a circuit such as the ones in a seriestransformer often utilized in conjunction with on load tapchangers, are also saturated before stable readings can beobtained due that there is no way to ensure the individualsaturation of each core, but only as a whole circuit.

Comment on resolution:

I agree with the spirit of the paragraph care is required toensure that the whole circuit is saturated but see no way toensure that each core individually (main, series, preventive auto,tec.) reaches saturation. The saturation is verified as a wholecircuit, therefore the phrase consisting of the main and seriestransformer windings to my understanding is not adding value.

(2) Balloter a ccepts with comment asnoted.

d) The hot resistance versus time data shallbe used as the basis for correction to timezero. The cooling curve format shall consistof a series of measured hot resistance pointsbeginning with the first hot resistance datapoint in accordance with c) and ending witha hot resistance data point taken no soonerthan 10 minutes from shutdown. All hot resistan ce data points taken within the 10 -minute period after shutdown shall berecorded at no longer than 30 -secondintervals for distribution transformers and15 -second intervals for power transformers .

Juan Castellanos: Use hot resistance instead of resistance throughout this item.

Steve Synder (unresolved negative ballot ): The resistanceversus time data in accordance with c) and ending with aresistance data point taken no sooner than 10 minutes fromshutdown. All resistance data points taken within the 10 -minuteperiod after shutdown shall be recorded at no longer than 30second intervals for distribution transformers and 15 secondintervals for power transformers. For distribution transformersthe resistance data points shall be recorded at no longer than 30 -second intervals for a minimum of 10 points. For powertransformers, the resistance data points shall be recorded at nolonger than 15 -second intervals up to the 10 -minute period aftershutdown. (I recommend we allow up to 30 -second intervals for power transformers too.)

I would vote negative on the basis of the comments I made(sorry). The main "sticking point" for us right now is therequirement to develop a 10 -minute cooling curve for adistribution transformer. That's why I proposed a certain

Accepted

The WG wrestled with defining the numberof data points to obtain a statisticallyaccurate cooling curve and could not agreeon a discrete number. By establishing aminimum time for the test duration and amaximum time interval for recording data the WG consensus was that the data pointsthereby recorded would be sufficient toobtain an accurate cooling curve. W hen aseries of resistance -time measurements ismade on only one terminal pair of adistribution transformer, a measurementshould also be made on each of the otherphases of the winding within 4 minutes ofshutdown in order to use the seriesresistance -time data to determine thecorrection to time zero for the other phases.Using digital instrumentation, a 15 -second


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minimum number of data points (10), which if recorded at 10second intervals (our preference), would allow the first windingbe completed usually around 2 minutes from shutdown. This permits us to jump onto one of the secondarywindings at about 2:20 minutes after shutdown and still get agood curve on that winding. At the conclusion of that timeperiod (another 1:40 minutes), we re -energize the unit for anhour or more to stabilize temperatures again, and then do asecond shutdown to finish the secondary windings, and repeatthe primary winding measurement if it looks suspect. We have

used this technique for many years and have produced excellentmeasured results, we think.

I had proposed we allow up to 30 second intervals for bothpower and distribution class transformers (we typically use 10seconds in distribution). I think I suggested this range toappease other commenters that wanted some other time interval. It is the 10 -minute cooling curve that is a problem for us. I don'tknow if this helps, but attached is a spreadsheet containing acouple cooling curves from a typical heat run test, to helpillustrate our technique. In this example the data collection wascompleted inside of 4 minutes. (See Attachment A).

recording interval for power transformers isachie vable. Balloters comment isunresolved.

e) The hot resistance -time data collected ind) shall be extrapolated to the instant ofshutdown using a computerized curve fittingprogram to determine the hot resistance -timecooling curve. The hot resistance -timeminimal least squares of the data collectedshall be fitted to an exponential decay curveor otherwise suitable curve shall define thebest statistically fitting resistance -timecooling curve using the method of leastsquares.

Juan Castellanos: (1) Use hot resistance instead of resistancethroughout this item.

(2) Change the phrase The minimal least squares of the datacollected fitted to an exponential to The method of leastsquares applied to the data collected and fitted to anexponential

Don Platts (Y): The last sentence doesnt make sense to me.Can we re -word it? My suggestion - - The curve shall be anexponential decay curve (or other suitable curve) fitted to a leastsquares analysis of the data which minimizes the r valu e.

Mark Perkins: While I think this is an improvement in the

(1) Accepted

(2) Accepted

Accepted

Accepted


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IEEE C57.12.90 Sect. 11 WG Ballot Results Attachment A

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0 0.5 1 1.5 2

T im e in M in u t e s

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0.531

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8/26/03Opposition Heat Run

HV Hot Resistance Curve

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T im e in M i n u t e s

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0.58

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8/26/03Oppositi on Heat Run

X1 - X2 Hot Resistance Curve

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