GEH-230W StPersetles GEH-230V INSTRUCTIONS. f:. l I ' INSTRUMENT TRANSFORMERS DRY AND COMPOUND-FILLED TYPES. GENERAL. E,LECTRIC

Transcription

1 i. ' r f:. l I ' I. : I INSTRUCTIONS INSTRUMENT TRANSFORMERS DRY AND COMPOUND-FILLED TYPES. GENERAL. E,LECTRIC GEH-230W StPersetles GEH-230V

2 2 TECHNICAL DATA This book presents GENERAL INSTRUCTIONS whih apply to all dry and ompound-filled instrument transformers. The desriptive bulletins listed below ontain ADDITIONAL TECHNICAL DATA - suh as harateristi ratio and phase-angle urves, and dimensions - for speifi transformers. These bulletins an be obtained on request. Information on instrument transformers not listed below, and on those with speial features an also be obtained on request. Your letter should: a. Inlude all information on the transformer nameplate; b. Clearly state your speifi questions. Address all requests for bulletins and information to your nearest General Eletri apparatus sales offie. POTENTIAL TRANSFORMERS TYPE NO. BULLETIN TYPE NO. BULLETIN INDOOR TYPES INDOOR TYPES (ont.) E-21_ (240 to 2400 V) GEC-235 JEF-5-769, _ (4200 to 4800 V) -469 JEG-5 E-22 _ (240 to 2400 V) -235 YT-1557-M -999, JE-1 _ ( 4200 to 4800 V) JE JEA-3 OUTDOOR TYPES -769 GEC-448 JE JEB JE-41 _ (2400 volts) -770 JEB _ (4200 to 7200 V) -666 JEB _ (7200 to V) -608 JE-42_ (2400 volts) -770 PORTABLE TYPES _ (4200 to 7200 V) -666 E-6 GEC-755 (7200 to V) -608 JE CURRENT TRANSFORMERS TYPE NO. BULLETIN TYPE NO. BULLETIN INDOOR TYPES OUTDOOR TYPES JCA-0 GEC-1245 JCA-0 GEC-1245 JCH JCP JCP JKB JCS JKB JKL JKB JKL JKD JKL JKD JKM JKD JKM JKH JKM JKH JKP JKH JKR JKP jkr JKW JKR-2-(10 to 800 A) -958 JKW ,. _ ( A) -959 JKW JKS JW JKS JL JS-1 '':. (replaed by JKS-5) -333 PORT ABLE TYPES JS-2'':_(replaed by JCS-0) -332 JP-1 GEC-929 JS-5 JY JP JP JY-9'''---- (replaed by JCH-0) -955 JP KC JP *Disontinued type; no longer available These rnstrutions do not purport to over all details or vonalions in equipment nor to provide for every pouib/e ontingeny to be met in onnetion with installation, operation or morntenone. Should further mformatron be desired or should partiular problems arise whih ore not overed suffiiently for the purhaser's purposes, the motler should be referred to the General fledn Company. www. EletrialPartManuals EletrialPartManuals. om om 0

3 INSTRUMENT TRANSFORMERS DRY AND COMPOUND-FILLED TYPES The several types of transformers overed by these instrutions inlude indoor and outdoor instrument transformers, portable instrument transformers, split-ore urrent-measuring sets, and auxiliary transformers. These instrutions apply also to Type Y transformers, whih are not stritly standard but whih utilize the mehanial onstrution of standard transformers. For information on the installation and are of transformers with unusual ratings of frequeny, seondary voltage, urrent, et., onsult the nearest sales offie of the General Eletri Company. When any speial information is requested, give the omplete nameplate data in order to indentify the transformer. HANDLING When unpaking and handling the transformer, exerise are not to damage the insulation. Make an inspetion to see whether any damage has oured during shipment. Transformers that are reshipped to the point of installation, even though this be done by truk, should be supported only by the ore or mounting supports. Do not use the bushings or leads as handles. DRYING OUT Transformers that have been subjeted to submersion or have been stored for some time in a damp plae should be dried out previous to installation. When drying out is neessary the following method should be used. Allow the transformer to stand not less than 12 hours in a room of an approximatel:f even temperature, and reord that temperature. Measure the resistane of the seondary winding. Short-iruit the primary winding and apply an adjustable voltage to the seondary winding. Adjust the voltage so that suffiient urrent will flow in the winding to raise its temperature to approximately 80 C. The rate of rise should not exeed 6 C per half hour. The winding temperature should be held at approximately 80 C until the transformer is dry. The amount of urrent neessary to obtain a winding temperature of 80 C varies beause of the variations in losses and opper densities in the different types of transformers. It is advisable to start with a urrent not greater than 2 amperes in the seondary of a potential transformer, or not greater than 5 amperes in the seondary of a urrent transformer. Gradually inrease this urrent until the proper heating is obtained. Inreases of urrent should be made autiously with frequent heking of the rise in temperature of the winding. The temperature of the winding may be determined onveniently by the resistane-hange method. Sine the resistane of a opper winding inreases approximately one per ent for eah 2-1/2 C, the temperature rise may be alulated by measuring the "before" and "after" resistanes and finding the perentage inrease in resistane. For example, if the "after" resistane is ohm and the resistane at the starting (room) temperature is ohm, the, m perentage mrease 1s --o =0.22 =22 - o, whih orresponds to a temperature rise of 22 x = 55 C (approximately). The approximate winding temperature at any time is the temperature rise at that time added to the starting (room) temperature. When failities for measuring resistane are not available the temperature may be taken by plaing the bulb of a spirit thermometer (do not use a merury thermometer) on eah oil as lose to the winding as the insulation will permit. The bulb of the thermometer should be overed with lean dry otton waste so that the bulb will have as nearly as possible the atual temperature of the oil. In the ase of urrent transformers of high urrent ratings the atual temperature of the primary winding an be quite losely obtained by plaing the bulb of the thermometer diretly on the primary terminal. TESTING Dieletri Tests If it is desired to make insulation tests after the drying out period, or at any other time, 3

4 GEH-230W Instrument Transformers, Dry And Compound-Filled Types these tests should be made in aordane with Amerian Standard C for Transformers, Regulators, and Reators (superseding A.I.E.E. Standards No. 4 and No. 14 ). These rules should be stritly followed, both as to the value of test voltage and in the method of appliation. (Note that periodi field tests of insulation should not exeed 65% of the fatory test voltage. Oasional tests should not exeed 75% of the fatory test voltage.) Polarity Tests Convenient methods for testing polarity are given in Amerian Standard C-57, the Eletrial Metermen's Handbook published by Edison Eletri Institute, and General Eletri Company's publiation GET-97. Ratio and Phase-Angle Tests Refer to Eletrial Metermen's Handbook and G-E publiations GET-1725 and GET-97. MOUNTING When onneting instrument transformers into power or distribution lines, it is important to make the onnetion in suh a manner as to avoid plaing line strains upon the terminals of the transformers. Where the primary leads onsist of ables, as in the ase of ertain outdoor transformers, are should be taken not to bend the leads sharply where they enter the bushing. The onnetion should also be made so as to prevent swaying of the ables. Where the primary leads are brought out through stud-type bushings or so-alled fixed terminals, are should be exerised to prevent either longitudinal or transverse strains upon the bushings. Instrument transformers of the "window" type (without primary winding) should be installed so that the weight of the transformer is not arried by the bus but by the mounting feet. For high-urrent transformer ratings, 2000 amperes and above, there may be some interferene from the field of the return bus unless the bus enters are kept at a minimum distane of 15 in. apart; for ratings above 5000 amperes this distane should be not less than 24 in. In ase this type transformer is used with more than one primary turn, the loop should be at least 24 in. in diameter. Care should be taken to see that the seondary leads are twisted losely together and arried out without passing through 4 the field of the primary ondutors. It is not neessary that the bus exatly fill the window, but the bus or buses should be entralized. For ratings of 1000 amperes and less, these preautions are generally unneessary. Ambient Temperature Instrument transformers must not be subjeted to an ambient temperature (temperature of the ooling air) higher than for whih they are designed unless ertain preautions are taken. Most transformers are designed to operate on a daily average ambient temperature not exeeding 30 C. This rule permits rated load in an ambient temperature up to 40 C for a few hours a day, provided the average value does not exeed 30 C. A few designs, partiularly for use in enlosed swithgear, will operate satis fatorily in an ambient temperature of 55 C. Generally, the allowable ambient temperature for a partiular transformer is marked on the nameplate. Appliation of instrument transformers in various ambient temperatures should be made in aordane with Amerian Standard C-57. CONNECTIONS The resistane of all primary and seondary onnetions should be kept as low as possible to prevent overheating at the ontats, and partiularly in the ase of urrent transformer seondary iruits, to prevent an inrease in the seondary burden. WARNING: Always onsider an instrument transformer as a part of the iruit to whih it is onneted, and do not touh the leads and terminals or other parts of the transformer unless they are properly grounded. (See Grounding). Also, do not open the seondary iruit of a urrent transformer while the transformer is energized. Seondary Connetions Current-transformer seondary iruits must not be open while primary urrent flows. Breaking the seondary iruit while primary urrent is flowing is espeially to be avoided. In both ases, the entire primary urrent beomes the exiting urrent whih auses the ore to saturate and may indue voltage dangerous to human life aross the seondary terminals. Also, the transformer ore may be damaged (by being magnetized; see DEMAGNETIZING.) Therefore, if it should be neessary to hange seond-

5 ' J ary onnetions while primary urrent is flowing, the seondary terminals must be short-iruited while the hange is being made. Take are not to disturb ground onnetions. Most indoor urrent transformers are supplied with an enlosed seondary terminal blok whih an be sealed. When shipped, the over of the terminal blok is in the reversed position beause the short-iruiting devie between the seondary terminals is losed. The proedure for making seondary onnetions is as follows: Remove the over, attah the servie leads, open the short-iruiting devie by loosening the srew or nut and turning the bridge to the open-iruited position, and then retighten the srew or nut. Turn the over 180 degrees from the shipping position, and reinstall it on terminal blok. The over annot be replaed after the servie leads are in plae until the short-iruiting devie is opened. CAUTION: Do not short-iruit the seondary of a potential transformer. Grounding The asings and frames of instrument transformers should always be grounded. The seondaries should also be grounded lose to the transformers. Grounding of instrument transformers should be made in aordane with A.I.E.E. Standard No. 52, Marh 1951, Appliation Guide for Grounding of Instrument Transformers Seondary Ciruits and Cases. On instrument transformers, the grounding of the feet also grounds the ores, asings, and frames. If it is neessary to hange the seondary onnetions, be areful not to disturb ground onnetions. Instrument Transformers, Dry And Compound-Filled Types GEH-230W Seondary Leads When planning installations of urrent transformers, the resistane voltage drop of the seondary leads should be inluded in alulating the seondary volt-ampere burden arried by the transformer. This total burden should be kept within limits suited to the transformers used. For many onditions, seondary leads whose resistane does not exeed that of 100 iruit-feet of No. 10 Awg opper wire (200 feet of wire) are satisfatory. This resistane is 0.2 ohm, requiring 5 volt-amperes at 5 amperes. However, this burden is too great for transformers designed for low volt-ampere metering burdens. For suh transformers, lower lead resistane is neessary. In the ase of potential transformers the voltage drop in the seondary leads may affet the indiations of the onneted instrument and meters. For the usual onditions, leads of 50 iruit-feet of No. 10 Awg opper wire ( 100 feet of wire) are satisfatory. The above instrutions regarding the length and size of the leads to be used should be onsidered as general. In ases where instruments and instrument transformers have been furnished as a unit by the fatory, no hange should be made in the length or size of leads whih might hange the volt-ampere burden in them. If any hange is needed onsult the nearest sales offie of the Company. Seondary Burdens When alibrations are furnished with transformers, it is important that the onneted burden be in agreement with the burden used in alibration. If it beomes neessary or desirable to hange the onneted burden, and if there is any question regarding the effet of suh a hange on the auray of the transformer, the nearest sales offie of the Company should be onsulted. Questions regarding the maximum allowable burdens should also be referred to the Company's nearest sales offie. If transformer alibrations are required, it is important that omplete information be furnished the Company, inluding the number of devies to be onneted in the seondary of eah transformer, the rating of the devie and type if the devie has more than one urrent or voltage, apaity, size, and length of leads to be used, the frequeny of the iruit, and the method of onnetion. Polarity In wiring instrument-transformer iruits, it is neessary to maintain the orret polarity relation between the line and the devies onneted to the seondaries. For this reason, the relative polarity of eah winding of a transformer is indiated by a marker H 1 (or a white spot) on or near one primary terminal, and a marker X 1 (or a white spot) near one seondary terminal; and in some ases by white bushings. Where taps are present, all terminals will be marked. The primary leads will be H 1, H1, H1, et., in order and the www. EletrialPartManuals EletrialPartManuals. om om 5

6 GEH-230W Instrument Transformers, Dry. And Compound-Filled Types seondary terminals XI' x2) x3, in order, and the tertiary, if present, Y1, Y 2, Yl, in order. H 1, always indiates the same instantaneous polarity as X1, or Y1 Signifiane of Polarity Markings When onnetion is made to a seondary terminal having a polarity marking similar to a given primary terminal, the polarity will be the same as if the primary servie ondutor itself were detahed from the transformer and onneted diretly to the seondary ondutor. In other words, at the instant when the urrent is flowing toward the transformer in a primary lead of a ertain polarity urrent will tend to flow away from the transformer in the seondary lead of similar polarity. When onneting instrument transformers with meters or instruments, refer to the Instrutions furnished with the meters or instruments involved. MAINTENANCE When working with urrent transformers, always make ertain that the seondary winding is either losed through the instrument iruit or that it is short-iruited at the terminals. Also, do not disturb ground onnetions on either a urrent or a potential transformer. After instrument transformers for indoor installation have been installed, they should need no are other than seeing that they are kept lean and dry. Transformers for outdoor installation should reeive the same are in operation as power transformers of similar design and of similar voltage rating. Considerable are should be exerised to make and keep the resistane of all ontats in the seondary iruit as low as possible. Cleaning of Bushings Dirt or other ontaminants on the surfae of a bushing may ause a derease in the flashover voltage. Danger of flashover ours when the surfae oating is partly onduting, usually as a result of moisture. In some loations, operating onditions are suh that a periodi leaning of the bushings is desirable, at whih time all foreign matter should be removed from the under, as well as the upper, sides of the pettioats. When the dirt is loose, a wet loth may serve. If this method proves inadequate, arbon tetrahloride or ammonia may 6 be effetive. After leaning a bushing by any of the above methods, wash the surfae thoroughly with lean water to avoid leaving foreign material. FUSES Potential transformer fuses are intended primarily to protet the line rather than the transformer, although the modern fuse will afford protetion to the transformer in a large number of ases. With the exeption of the urrent-limiting fuses, suh as the Type EJ-1, potential-transformer fuses are not designed to open the maximum short-iruit urrents whih may flow when a short iruit ours in the transformer. For this reason, urrent-limiting resistors should be used in series with the fuse when neessary to limit the urrent to a value whih the fuse an interrupt satisfatorily. Replaing Fuses Many potential transformers are equipped with two fuses. However, when suh transformers are installed on a grounded iruit, it is ommon pratie to substitute a brass tube (or a "solid" onnetion) for the fuse in the grounded line. This is to establish a permanent unfused ground at all times. Do not disturb this onnetion when replaing a fuse. The fuses of some types of potential transformers, 3000 volts and below, are supported by a hinged over. If it is neessary to replae a fuse while the transformer is onneted to an operating iruit, the over should be opened by an insulated hook. After the new fuse is inserted, the over should be losed also by means of the insulated hook, whih should be of suffiient length to prevent the operator from being burned in ase a short iruit exists in the transformer. The artridge fuse may be replaed by the Type EJ-1, Size A. In testing fuses for ontinuity of iruit, not more than 0.25 ampere should be used. In replaing Type EJ-1 fuses or in substituting the EJ-1 for the ES-1 or the artridge fuse, are should be taken to selet a fuse unit with the nearest voltage rating above line-to-line voltage of the iruit regardless of the rated voltage of the transformer. Do not use fuse units of higher voltage ratings as undesirable overvoltages may result. One permissible exeption to this general rule is the use of the Size A, Type EJ-1 fuse in Type JE-2 transformers.

7 In this ase the s1ze A fuse an be used on either 2400-volt delta iruits or 2400/ 4160-volt grounded "Y" iruits. DEMAGNETIZING If by aident a urrent transtormer beomes magnetized, it should be demagnetized in the following manner before being used for preision work: Connet at least 50-ohms resistane in series with the meters or instruments in the seondary iruit. Bring the primary urrent up to as near full load as possible and gradually redue the series resistane by one-ohm steps until it reahes zero, being areful not to open the seondary iruit in the proess. DIFFERENTIAL PROTECTION Standard General Eletri urrent transformers may be used for differential protetion through a onsiderable range of burden and overurrent. This range is limited by the differene in burden, the maximum overurrent, and the mehanial and thermal short-time rating. Information regarding these points may be obtained from G-E publiation GET-97 or fwm the nearest sales offie of the Company. INDIVIDUAL TYPES OF TRANSFORMERS Outdoor Instrument Transformers Bushings of outdoor instrument transformers sometimes beome broken. For the replaement of bushings on a ompound-filled transformer it is reommended that the transformer be returned to the fatory. For the replaement of bushings where the asing is not filled with ompound, aess is gained by removing a portion of the transformer ase. Conduit onnetions an be made to the seondary of a dry-type transformer having flexible seondary leads, by loosening the srews whih hold the bushing in plae, removing the bushing, and inserting onduit fitting in plae of the porelain bushing. Portable Transformers When used under ordinary onditions, portable transformers, both potential and urrent, exept split-ore urrent transformers, will not vary more than 1 per ent from their marked ratio. When better auray is required, the ratio and phase angle ertifiate should be used. By means of this ertifiate orretions an be made to within 0.1 per ent on ratio and to within 3 minutes on phase angle. Instrument Transformers, Dry;.And Compound-Filled Types GEH-230W Portable potential transformers have terminals arranged with thumb nuts. Double-rated transformers have four primary terminals. Conneting links are used to make onnetions for the different ratios. Care should be exerised to lamp the links firmly in plae in order to obtain good ontats. Sine ertain portable urrent transformers have no primary windings, the able arrying the urrent to be measured is threaded through the opening in the transformer. The seondary of a single-rated transformer is not tapped. The rating is obtained by use of one turn of able through the hole, and other ratings may be obtained by threading two or more turns through the hole. The ratings are shown on the nameplate. The seondary of a multi-rated transformer is tapped and the different ratios are obtained by onneting to the proper taps, as shown on the nameplate. Other types have self-ontained primary windings as well as a hole in the ore for higher ratings. The lower ratios are obtained by onneting the urrent to be measured to the orret binding posts as shown on the nameplate. Other ratings may be obtained by threading the able, whih arries the urrent to be measured, through the hole in the ore one or more times as shown on the nameplate. Still others have all ratings self-ontained. Changes in ratio are made by means of metal links loated on top of the transformer. The six-rated transformers also have a tap in the seondary. Three of the ratios are obtained by using the full seondary winding with the proper arrangement of links on the primary winding; the other three ratios are obtained by using the tap in the seondary winding with the primary links in the same positions as before. All onnetions are shown on the nameplate. High-&uray laboratory standards are multirated. All ratings are obtained by onneting the urrent to be measured to the proper terminals, whih are marked on the over. The lower urrent ratings are proteted by fuses inserted in the over adjaent to the orresponding terminals. Unsrew the ap in order to replae a fuse. All portable urrent transformers, exept the split-ore type, are provided with a short-iruiting swith on the seondary. This swith should always be losed whenever it is neessary to 7

8 ' GEH-230W Instrument Transformers, Dry And Compound-Filled Types.,.,., open the seondary iruit with the transformer onneted in the line. This short-iruiting swith should always be opened after making onnetions. Split-ore Current Measuring Sets Certain split-ore urrent transformers are intended to be used only with the instrument and leads with whih the transformer is alibrated. The sales on the ammeters are marked to read primary amperes diretly, and the ammeters should not be used to measure urrent unless used with the transformer with whih they are alibrated. Changes in ratio are made by turning the rotating swith in the ammeter. Split-ore urrent transformers should not be used around any ondutor whih is not insulated for the full voltage of the iruit. The butting ore surfaes must be kept lean and free from any dirt as a very slight opening M) I N S T R U M E NT between the two halves of the ore will affet the alibration of the set. Current-measuring sets onsisting of a split-ore urrent transformer alibrated with an indiating ammeter and leads will have an auray of plus or minus 2 to 3 per ent of full sale, and with a reording ammeter and leads, an auray of plus or minus 3 to 5 per ent of full sale. A urrent adapter is used with the split-ore transformer for measuring small urrents. With the orret size of terminals attahed to the adapter, insert it in plae of the fuse in the utout. Clamp the split-ore transformer into the round loop of the adapter and read the ammeter. Compute the line urrent from the formula on the nameplate of the adapter. The use of the urrent adapter does not affet the auray of the urrent measuring set, and it may be used with sets having either the indiating ammeter or the reording ammeter. D E P A R T M E N T GENERAL fj ELECTRIC WEST LYNN, MASS.,,