Document EvMDy6aN9zLrO3Nw0gYGRwwVx

y f V? - 4 ;?V*s j .. i c \ I:. ,! A' f -- 4 . '; % {. - - ?. '-. ;;'.,:.=// ..;. v -' A-A jAA -.>A .-. . -.. r `,v >. :'-v '..y,;;;~. .:.. _.. . .>' - ' ' V - {; :, . r ' V: ' i - .I' ""! ,r **"-*'.; H.: ' *. ' .. ' ', ' A 'Vf' ' . "* . . 'Y *`s '. ' , . ' ' ''. . ' . Megohm Brl4?et General Radio Company Tyoe 544&, AC operated - 90 volt*, aerial So* 171* This Is a direct-ourrent Wheatstone bridge V for measuring high resistances, bridge balance being obtains! thru . uss of a vacuum tube voltmetStv Hango* 0.1 megohm to 10,000 megohms, covered by a dial and 5"Position multiplier switch* ,A resistance of 1,000,000 egohas can be detected,;., . Teat &lectrod*s| 'Two concentric nickat cylinders (or brass, nickel plated) with feat. Obtained from General SlactriC Company. The inner electrode has outside diameter of 2.0" and height of 3.25", with area of 104 sq. cm. The outer electrode has inside diameter of 3" and like hiight of 3.25*, with area of 19 sq. cm. The distance between electrodea is therefore 0,1 inch or 0.254 cm. By theory the electrode constant, area/l*ngth, ia 102/0.254 or 752 where 191 is the average area. In practice the cell Constant su' plied by General Electric Company is used. For the electrodes now in use,.the cell - constant was given as 815* , Glass Plate* Pyrex, about 3-1/2w diameter with concentric grooves to assist in spacing the electredes. Obtained from General Electric Co. Oven* Cenco-OeKhotensky drying oven with two holes in back wall for porcelain tubes fbr lead wires. Holes must bo avoid oven heating clamant s Shleb occupy 2" paths vertically and horizontally intersecting at the center of the Circular wall. . '' r ' .. ' , 1 .. * Lead ^iresi Provide two flexible leads to connect the electrodes in oven to the posts of the bridge. The portions exposed to oven temper ature art bared and then covered with porcelain beads. Provide also a flexible lead to ground the bridge to a water pipe. Clean the la&ds, beads, and porcelain tubes periodically. : A- . .. ' - Asafgnfely.^f. .. ' ': a-: - v, - The grooved glass piste i placed in an 000 cc. beaker. The clean electrodes are placed in the grooves of the glass plate with the Connector posts directly opposite in order to give the widest possible spacing to reduce' surfacs conductivity. The cylinders should be very close.to equidistant. The apparatus should be dried for 2 hours at 100C. before use. , Heat the sample to be tested to about H0C. on a hot plate and pour into the electrode assembly until the level of the liquid Is 1/4 To 1/2" above the electrodes. Care must bs used to make sura that the / D$W 330769 i '' STLCOPCB4077413 W: 4 . V-' ; {- i. '7 m- ? i.*r --* -w*y Y ? 1c I Ii- 'V I# ! 5 -i 3 {.- { fI DIRECTIONS FOR TEST NO._________________________ SUBjECT:----Resistlvltyof Liquid Aroolors - Page 2. ------------------- METHOD: __________- ' ' : lip of the container * from which ths liquid Is poured, 1 clean. Tilt the beaker In such manner that all air bubbles in the Aroclor will rise to the surface, ` S- : r{ f -* -'"S./'i .. -*A' V' ' ?* ,l' ' C //::' " .'A-'""-" . ` ' Air cool tb lO-lOtoC, then without removing thermometer, tranafer to the oven which te maintained at lOCf^C, end connect the electrodes t the two flexible wiree which lead to the megohm bridge, When the ErooloT cotsaa to temperature (100C*), remove thermometer, check centering of electrodes, and procode to measurements. :Measurement.. wlttiMsaohE*.Bri&aa. ^ .. Connect, the two lead wires to the megohm bridge with the lead from the outer electrode to the W8 unknown post of the bridge} the inner eleotrode to the "a* unknown post. Connect the GROUND post on th left aide to a water pipe. Swing the spring connector, pivoted on the *0* post, to the LOW poet. Connect the attachment cord to the 110 V power supply* : ,; -Y";-': - with the Aroclor at 1C0C., turn the control knob (OHP3RVH5-0H&HGS) to the GH3GK position. Throw all 3 switches at the rear of the Panel to OH. After 2 minutes bring the galvanometer pointer to aero by means of the. 2IR0 ADJUST knob. . Then tum ths control knob to CHARG3 for one minute, Turn the knob to OPERATE and return the galvanometer pointer to aero by adjustment of the MULTIPLE BI switch and the megohm dial. Read after one minute. Repeat the CHARGE and OPERATE positions for verification, , The resistivity of the Aroclor is the product cf the ''multiply hyn reading times the dial reading times the electrode constant* Report in units of 10 oh/W'4# rounded off to two significant figures. Example* "Multiply by" reading * 100 Megohm dial reading 5*4 ohm Electrode Constant 815 cm Resistivity s IDO x 5,4 x 815 * V - 4*4 x ID* oagohas/cm3 .; Y;;\* 440 x 109 ohfi^cm^ v Values for rasietlvlty are qualified by designation of temperature and voltage. These are lOCrC, and 90 volts for the test above. Like conditions are used at Plant B, Mineral Electric Company de termines resistivity at 1D0C., 500 volts D,0* oS\N 330770 STLCOPCB4077414 IS3 I ,-T . V. I I K :; i: y DIRECTIONS FOR TEST NO._________________ subject:_--Resistivity of Liquid Aroclors - Page 3. METHOD:. pAr?.,ftf.,AgraratKi , _ .. The "Operating Instructions", General Radio Form 458-, which accompany the megohm bridge, rooits details of installation, measurements, uses, and construction/ illustrated by figures and circuit and wiring diagrams, Ro attempt is mads to reproduce such information here. The operator should acquaint himself with the contents of the G.R, manual and refar tft it for maintenance of tubes and parts. When not in use the megohm bridge should be dosed and stored In cabintt, . For the removal of Aroclor from electrodes and glassware, a series of covered jars is maintained containing 1 gallon or more of cleaning fluid to a depth of 5" or more. The first 3 jars contain "motosolve" - a mix ture of 2 parts mineral spirits and 1 part carbon tetrachloride. The last jar contains pure carbon tetrachloride for a final wash. As the solutions become spent the first wash is dlsc&rddd and replaced with the second wash being used to prepare the &otosolvs To Glean the Test Cell* Four out the Aroclor upon removing frw oven at 100C, Let drain for a few minutes. Rinse once in beaker with a little Kotosolve which is discarded. While still warm, immerse parts in the first ISotosolve wash, dipping in and out several times. Repeat. . Ithe second wash pslng brush over all surfaces. Continue with third feotosolve^iraih and final wash with pure carbon tetraohlorf.de. Inspect carefully. Dry in oven at 100C, for 1 hour. Store under bell jaw until used. Dry again befors ^ae. Zf the electrodes show any tarnish, polish them with a paste of rouge on a soft cloth. .Clean the glassware as necessary with warm chromic acid solution lt2CjrO'/ H2S0^). Refer to General Sledtrlo Company methods H-3992863 and 8-3984092 for other precautions in cleaning electrodes and glassware* . -' , '' ' : V. , Calibration and Reproducibility A reference cample of Aroclor 12$4 should be maintained for checking purposes. Resistivity of tfcigsssaple should be determined seal-monthly or whenever abnormal values are encountered In testing production. Before one reference sample is exhausted another sample should be obtained in order that a number of simultaneous determinations say be made upon the old and new samples. For a rough check on the condition of the bridge, one or more cartridge- type resistances of known approximate value should be kept on hand for r periodic or emergency verification of the ester itself, - DSW 330771 STLCOPCB4077415 if jr- \ V l ' -f 3 fs: l ) Iv I r ( y# e DIRECTIONS FOR TEST NO.______________ _ subject:_------ Raslgt-ivlty of -Liquid--A-roclors - Page 4-------------------- METHOD::_________________________________________ ____i=_________________________________ __ Prior to each test* General Sleetrio prescribes cheeking the electrodes with & standard Aroclor or oil for resistivity value. Agreement with expected value within 20% Is necessary before proeeding. At least two aamplee of the Aroclor under examination are tested. These mstahow agreement within2G5f* * ' . Sffr^ ftf Ve^eMe* '/ 1* Bridge readings will vary depending upon the time elapsed after closing the circuit switch* The current flowing immediately after closing the switch is greater then after the switch has been in for several minutes*1 Conforming to cannon practice, one minute Is allowed for "electrification1* before reading the bridge mater*. 2* The resistivity of Aroclors is lowered by the presence of polar im purities such as ferric chloride or hydrochloric acid* These polar impurities affect the resistivity to a greater extent in the more liquid Apoclora than in the viscous Aroclor# (Reft H*B. Glass)* I 3* Treatment with Fullers earth has the effect of increasing the resist ivity* A chart illustrating time of treatment versus resistivity and power factor has been prepared by the General Slectrlc Company " their 1941 methods* * 4* Because the resistivity may vary with the time of heating at the test temperature* 100G.* the assembly and heating of the teat cell should be uniformly performed as described* 5* Conforming to General Electric specifications* the resistivity is measured at 100C* The usual effect of temperature on resistivity is that if the d'.alectrio contains moisture* the application of hsat will reduce the moisture content and simultaneously increase the resistivity. In the case of a thoroughly dry dielectric* however* increase in tamp- erature usually has the reverse effect* Prolonged heating of a di ;' electric* if In excess of safe or conservative working temperature* is isjinjurious and tends to hasten the breakdown of the material by de composition or chemical change* The General Electric Company specifies that Aroclor 1254 after heating at 100C. for 96 hours shall show no I: loss ir resistivity* b, The resistivity of a dielectric with alternating currents is usually less than with continuous currents and decreases progressively as a rule with increase in frequency owing to dielectric energy losses. 7* Btoost cleanliness of all apparatus - beakers* containers, electrodes, thermometer, etc* - coming in contact with the Aroclor is necessary to prevent contamination* DSVM 330772 STLCOPCB4077416 ; ` V H ' )) DIRECTIONS FOR TEST NO.__________ SUBJECT:--:--------Resistivity of Liquid Aroolors - JPage-jk M ETHOD:_____________- . ____________________:_________:________!____--_____ Resistance (synfcol E)t Obstruction to electric flew, the ratio of voltage () to current (X) in a conductor or closed circuit. (R s 3/1, Ohm's law). The practical unit of resistance is the ohm. Electrical 'Resistiritis at The current which flows between two conductors insulated from each other by a dielectric ie made up of two components (1) that which flows thur* the dielectric itself and (2) that which flows through a surface film of moisture or other seal-conducting material (oil, dust, or foreign matter). The components are designated respec tively as nvolume resistivity* end as "surface resistivity'1. , Volume Resistivityf Symbol p (Greek letter "rho".) Also called specific resistance. Defined as the resistance between two opposite faces of a unit cube of the substanoe. p RA/L where A Is cross-sectional area and L is length of the current path thru the substance. The practical unit f resistivity is the ehl*-eenii*terQ(oh-em,) The resistivity f *roclors is reported in multiples of 10 ohm-cm. A volum resistivity of 740 x 10? ohm-ca is equivalent to saying that the resistance offered by the substance between two opposed parallel faces of 1 sq. cm. each, placed 1 cm. apart is 740 x 109 ohms. Following the practice of the General Electric Company, resistivity Is measured with the substance under test (Argclcr at 100C. "Resistivity" as applied to Arc elors always refers to volume resistivity. Surface Resistivity* (symbol S, Greek letter "Sigma") is defined as the resistance between two opposite edges of a squat* surfacd film. The practical unit is the ohm-cm (between opposite edges of a film 1 cm. square) $ * Bb/l where R le resistance of a rectangle of film of length 1 and breadth b. Measurements of surface resistivity are applied to solid dielectrics rather than to liquid. For most materials the surface resistivity is much lower than the volume resistivity. Atmospheric humidity conditions at time of measuring may frequently greatly alter the surface resistivity. FABtcm 1-30-45 DSW 330773 STLCOPCB4077417 If t .!j? ,Xf ( I ^3 4) f t' V 1) DIRECTIONS FOR TEST NO.._________________ SUBJf<^T; Resistivity of Liquid Aroclors - Page 6. M ETHOD:_______________ ;:: Resistivity of, Various Plalep.trlflJl Rsfereneet Standard Hand-book fop Electrical Engineers, , ' - . Courscyi Sleotrical Condensers. SOLIDS .................... Paraffin Fused Quartz (ordinary temp.) Mica, Madras or Bengal Mica, Canada Glass (ordinary temp.) Rubber Bakelits tfnglazed Porcelain (ordinary temp ) Marfcls LIQUIDS '. . Transformer Gil A Transformer Oil B Pratts Astral (kerossns) Castor Oil -: :: : L : Stlyl Aleohol linseed Oil Olivs Oil Water, Distilled /roclor 1254 (100C,, 500 ?) FAB:cm 1-30-45 . \. Resistivity In ohm-ca., 1 to 10,000 x 10*5 0.1 to 10,000 x IQ15 10 to 130 x 1012 0.44 to 22 1012 10 to 10,000 x 1012 100 x 10,000 x DO12 0.5 to 3 x 10u 100 to 1,000 x 1012 0.1 to ID x 109 490 x 10? 3,100 x 10* 470.000 x IQ9 30,000 x 10* 3.3 x 10* 50 x 10* . 1.000 x 107 70xlD9 100 to 800 x 10? DS\N 330774 STLCOPCB4077418