Document 0R7OD9JGoeG3QXw6JxGbbmnJ

;r 3i. r) i DIRECTIONS FOR TEST NO* 14-35-41 SUBJECT: Resistivity of Liquid Aroclors * p* *. i* - f i-'j r-c-v-pPF* METHOD: ., Besistanee Measurements Detween Condnotore w : r _ I i >*y I- 'r`r.%3-j; -; f . .- -. . >>' < - , ,,, Apparat .... ^pip^^e|^3eli^l_ ; -*-- J?v3 '* vy. ., TypS^pdiS, ACj^^fUt -- . ^f^ 90'voits, serial No* 171* This is a direct-current Wheatstone bridge for measuring high resistances, bridge balance being obtained thru use of a vacuum tube voltmeter* Hangs: 0*1 megohm to 10,000 megohms, covered by a dial and 5-position multiplier switch* A resistance of 1,000,000 megohms can be detected* Test Electrodes: Two concentric nickel cylinders (or brass, nlokel plated) with feet* Obtained,from General Electric Company* The inner electrode has outside diameter of 2*8" and height of 3*35", with area of 164 sq* to* ^he outer electrode has inside diameter of . 3" and like height of 3*25", with areaicf 193 sq* cm* The distance between electrodes is therefore 0*1 inch or 0*254 cm* By theory the electrode constant, area/length, is 191/0*254 or 752 where 191 is the average area* In practice the cell constant supplied by General Elec tric Company is used* For the eldetrodes now in use, the cell constant was given as 615* : V ' . . ; v ' : ... . Glass Plate: Pyrex, about 3-1/2* diameter with concentric grooves to assist in spacing the electrodes* Obtained from General Electric Co* '' ' .. . Oven: Cenoo-DeKhotensky drying Oven with two holes in back wall for porcelain tubes for lead wires* EEblos must avoid hven heating elements which occupy 2" paths vertically and horizontally intersect ing at the center of the circular wall* w Lead Wires: Provide two flexible leads to connect the electrodes in oven to the posts of tbs bridge* The portions exposed to oven tem perature are bared and then covered with porcelain beads* Provide also a flexible lead to ground the bridge to a water pipe*_ Clean the leads, and ^orcl^In tubes; periodicfij^^ ^`u Ife,... Asfembly of TeaPlibll' - . .. y*\-' --> The grooved glass plate is phased la an 600 ce* beaker* The clean electrodes are placed in the grooves of the glass plate with the con nector post8 directly opposite in order to give the widest possible spacing to reduce surface conductivity. The cylinders should he very dose to equidistant* The apparatus should he dried for 2 hours at 100*C, before use. Heat the sample to be tested to about 110*C* 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 be used to make sure that the SW 330726 STLCOPCB4077370 r Page Ho# 2 Test Ho# 14-65-^41 ~ Resistivity of Liquid Aroclors lip of the container, from which the liquid Is poured, is clean# Tilt the beakerin such manner that aHalrbubbles Inthe Aroclor will .rise tq thh $*<**' ... " ...... ~ " ....... _ ^ oooj^^||^^l04:_^^^^%id.tho^^^^riiig tSl^^pIter,' for to the oven which is maintained,atlOO*C#andconneet the elec trodes to the two flexible wires which lead to the megohm bridge# When the Aroclor eernes to temperature (100*C#), remove thermometer, eheck centering of electrodes, and proce&e to measurements# . : Measurement with Megohm Bridge . Connect the two lead wires to the megohm bridge with the lead from the outer electrode to the LOW unknown post of the bridge; the inner electrode to jhe "t* unknovai post#...Connect the GROUND post on the left side to a water pipe# Swing the spring connector, pivoted on the "Gr* post, to the LOW post. Connect the attachment cord to the 110 T power supply# ;;V With the Aroclor at 100*C#, turn the control knob (CHECK-OPERATE- CHARGE) to the CHECK position# Throw all 3 switches at the rear of the Panel to OH# After 2 minutes bring the galvanometer pointer to zero by means of the ZERO ADJTJSTknob# __ _ __ ___ _ ___ Then turn the control knob to CHARGE for one minute# Turn the knob to OPERATE and return the .galvanometer pointer to zero by adjust ment of the MULTIPLY BY 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 of the "multiply by" reading times the dial reading times the electrode constant# Report in units of 10 ohm/cm*., rounded off to two significant figures# Examples \ -" ' .- "Multiply by" reading s 100 , Megohm dial reading . 5#4 ii.Electrode Constant ;-x 815 Values for.resistivity are qualified by designation Of tempera ture and voltage# These are 100*0# and 90 volts for the test above Lika conditions are used at Plant B* General Electric Company de termines resistivity at 100*C#, 500 volts D*C# DSW 330727 STLCOPCB4077371 ,r s A'j, 7,OJV..T ) VV' Page Ho* 3 Test No* 14-05HL1 -- Resistivity of Liquid Aroelors i^are^of Apparatus 3#?^ - A The "Operating Instructions", s General Radio form .458-,' which le megohm ;^ridgeV^rcc4t^*ntaile of: installation, meer- ` operatorshoaldacquaiiit tents of the G*R* manual and refer to it for maintenance of tubes ' andparts* Nhen not in use the megohm bridge should be closed and stored in cabinet* . ....... " For the removal of Aroclor from electrodes and glassware, a . series of covered Jars is maintained oontalnlng 1 gallon or more of cleaning fluid, to a depth of 5* or more* The first 3 jars contain . ftaotoSolva" -- a mixture of 2 parts mineral spirits and 1 part car- s*" bon tetraehloride. The; last jar contains ;^ure carbon tetrachloride ' for a final wash* As the solutions become apentthe first wash is discarded ani replaced with the second wash, others in turn are moved up, the final wash being used to prepare the Motosolve. To Clean the Test Cell; Pour out the Aroclor upon removing from oven at 100*C* Let drain for a few minutes. Rinse once in beaker with a little Motosolve which is discarded* Hhile still warm, immerse.. parts in the first Motosolve wash, dipping in and out several times. Repeat in the second wash using brush over all surfaces* Continue with third Motosolve wash and final wash with pure carbon tetrachloride. Inspect carefully* Dry in oven at 100*C* for 1 hour* Store under bell jar until used. Pry again before use* A " If 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 (K?Grs07 H2SO*) Refer to General Electric Company methods H-8992863 and EH3984092 for other precautions in clean ing electrodes and glassware. - .* Calibration and Reproducibility .... >> 1 ' preference sampleof Arrclojrl2$4 should be maintained for check ' ing RedlSi4|r|ty of sSjpjftj^ps deteri|ii|eft^||mi-- ^swntl^yl^liheneyis^CL^rmal encoittitered in t 1 r duct!on. Before one referencesampl* 'is exhausted another sample, hh should be obtained in order that a number of simultaneous detendft- 1 J n\ ations maybe made upon the old fund new a'amples* Tot a rough check on the condition of the bridge, one or more cartridge--type resistances of known approximate value should be kept on hand for periodic or emergency verification of the meter itself* Prior to each test. General Electric proscribes checking the electrodes with a standard Aroclor or oil for resistivity value* Agree ment with expected value within 20$ is necessary before procedlng* At least two samples of the Aroclor under examination are tested. These must show agreement within 20$. DSW 330728 STLCOPCB4077372 w Page Ho* 4 Test Ho. 14r-35-4L -- Resistivity of Liquid Aroclors _ . ; Bffeet of 'Variables _ . _, . : s 1. Bridge readings will vary depending upon the time elapsed af ter elosing tLe' eirealt: sviteH*^|Bie .eurrent flowing immediately af-- ' v- ter cildt|ag the great^fe^hin after^^ewitch^s^enjin .. allowed for "electrification* before reading the bridge meter* ^ 8 The resistivity of Aroclors Is lowered by the presence of po lar impurities such as ferric ehlorldf or hydrochloric acid* These polar impurities affect the resistiviiy to a greater extent in the more liquid Aroclors than in the viscous Aroclors (Reft H.B. Glass)* 3* Treatment with Pullers earth has the effect of increasing ' the resistivity* A chart illustrating time of treatment versus re-- sistivity and power factor has been prepared by the General Eleetrle Company -- their 194L methods. ' 4. Because the resistivity nay very with the time of heating at the test temperature, 100*C, the assembly and heating of the test cell should be uniformly performed as described. ..... 5* Conforming to General Electric specifications, the resistivity is measured at 100*C* The usual effect of temperature on resistivity is that if the dielectric contains moisture, the application of heat will reduee the moisture content and simultaneously increase the re sistivity. In the case of a thoroughly dry dielectric, however, in crease in temperature' usually has the reverse effect. Prolonged heat ing of a dielectric, if in excess of safe or conservation working tem perature, is Injurious and tends to hasten the breakdown of the ma-- terial by decomposition or chemical change. The General Electric Com pany specifies that Aroclor 1254 after heating at 100*C. for 96 hoars at 100*C* shall show no loss in resistivity* : 6* 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. v a . . VT /ifrs -v*T\n^ . A-?1 * ; r- 7* Utmost cleanliness of all Apparatus - beakers, containers*-*, electrodes, thermometer, etc. -- coming in contact with the Aroclor is necessary to prevent eontemlnat iom* ........... .... ........... Definitions Resistance (symbol R): Obstruction to electric flow. The ratio of voltage (E) to eurrent (i) in a conductor or closed circuit. (R E/l. Ohm's Law). The practical unit of resistance is the ohm. Electrical Resistivities: The current which flows between two conductors Insulated from each other by a dielectric is made up of two components (l) that which flows thru' the dielectric itself and (2) that which flows through a surface film of moisture or other semi-- DSW 330729 STLCOPCB4077373 ; Page Ho* 5 Test No* 14*65-41 -- Resistivity of Liquid Aroclors <r? v. .eonduoting material(oil, dust, <*r foreign, natter;*; ..These components are designated respectively as "volume resistivity^ and as "surface Spggggfg ~ ` '~ '&$&>.............................................. ..................................... " l^^f'^lolume Jleilst'i^ityi J,-#^iho!t^ (Greek/Letter "rPfifr.yAlso _ ctfLied specific resistance* Defined as the resistance between two opposite faces of a unit cube of the substance* p RA/L where A Is cross sectional area and L ls length of the current path thru the substance* The practical unit of resistivity is the ohlt-centimeter (ohm-cm*)* The resistivity of Aroclors is reported in multiples of 10 ohm-cm* A volume resistivity of 740 x 10 ohm-cm is egiivalent to saying that the resistance offered by. the substance between two opposed paral lel faces of 1 sq* 'em* each, placed 1 cm* apart is 740 x 10 ohms. Fol lowing the practloe of the General Sleotric Company, resistivity is measured with the substance under test (Arodor at 100*C* "Resistivity' as applied to Aroclors always refsrs to volume resistivity* .. Surface Resistivity: (symbol S, Greek letter "Sigma") is defined as the resistance between two opposite edges of a square surface film0 The practical unit is the ohm-cm (between opposite edges of a film 1 cm* square) S * Rb/l where R is resistance of a rectangle of film of length 1 and breadth b* , '? Measurements of surface resistivity are applied to solid dielec trics rather than to liquid* For most materials the surface resis tivity is much lower than the volume resistivity^' Atmospheric humidity conditions at time of measuring may frequently greatly alter the surface resistivity* , ^ ' ti T DSW 330730 STLCOPCB4077374 y Page Ho* $ Test Ho* 14-35--41 -- Resistivity of Liquid Aroclors Resistivity of Various Dielectrics Reference: Standard Hand-book for Electrical Engineers* Coursey; Electrical Condensers* Dielectric * ^zCJULerr ` SOLIDS M Eased ... . Resistivity in ohm-cm* ^` - _ Vr H rw ; (f *f$r t 10000 x Mica, Madras or Bengal 10 to 130 x 1012 Mica* Canada Glass (ordinary teop*) 0*44 to 22 x 1012 10 to 10000 x 1012 Rubber' i Bake lite Unglazed Porcelain (ordinary temp*) 100 x 10000 X 101* V- ' . 0*5 to 3 x 1012 100 to 1000 x 1012 Marble . 0*1 to 10 x 109 [QUIDS ,. Transformer Oil A 490 x 10? V. V . r Transformer Oil in L 3100 x 109 i Pratts Astral (kerosene) 470000 x 10* Castor Oil Ethyl Alcohol 30000 x 109 3.3 x 1C? Linseed Oil 50 x 10?, 1\ nf "V^-iV-'x Mr)** $ OlivnOU'; 1000 x 109 **4 Tatar* Distilled { _ _ f .'1,. '* .70 x M. rr/ A -'; vvv Aroclor 1254 (100*0*, 500 Y.) -Va-# <Si f>* 100 to 000 X 109 ABG-p 9/30/41 DSW 330731 STLCOPCB4077375