US 1706158 A
Description (OCR text may contain errors)
March`l9, 1929. A. B. HENDRlcKs, JR 1,706,158
ELECTRICAL TESTING APPARATUS Filed Nov. "7, 1921 AI Ian B.Her1dr`ickS,Jrr,
, Hi sAttovhey.
ALLAN' IB. HENDRICKS, JR., 0F PITTSFIELD, MASSACHUSETTS, ASSIGNOB, T GENERAL ELECTRIC GOMPANY, .A CORPUEATIN 0F NEW YGRK.
ELECTRICAL TESTING- APPARATUS.
Application flledr November 7, i921.
My invention relates to electrical testing apparatus and more particularly to testing apparatus adapted tor use in applying a source ot high potential current tor test pure poses to parts ot electrical devices such as across the terminals of transformer coils, across t-he insulation between conductors, and so forth.
The general object of the invention is to provide a portable testing device of the nature mentioned above which shall be efficient and convenient to use. Another object oit Vthe invention is to provide a portable high potential testing 'device which may loe, safely talren directly in the hands and applied to the apparatus to be tested Without the necessity out making permanent connections. A tun ther object of the invention is to provide a portable testing device so constructed that all exposed conducting surfaces are automatically disconnectedY from the source of cui'- rent except during snchtirnes as they are deliloerately connected therewith by pressure upon a contact actuating portion ot the de vice. By reason of ALhis latter feature ot the invention, the device cannot be left inadvertently with any portion of its exposed snr#- ace connected `with the source oi current so as to he dangerous to handle.
@ne embodiment ot the invention is illus trat/ed in. the accompanying drawing in which Fig. l is a view oi a pair of high potential test handles or electrodes equipped Withinsnlated conductors adapted to connect them 'with suitable source ont high potential cnrn rent, lig. 2 is sectional vievv of one ot the handles and Fig. 3 is an enlarged sectional view of a portion ot one ont the handles.
iin the torni oit invention shown in the drawing, a pair o' test handles l and 2 are adapted to he connected with the two termio't the source oit" current, although it is olovions that cases may arise Where only one terminal ci the sonrce ot current need he need, in which case the use oi a single handle will vhe suiiicient.
As shown in the section views ng, the handle inc-indes an n i niay to lli ,cont act "r serial No. 513,218.
sha-pe irorn a piece of hard Wood. Fitted into one end of this insulating; sleeve is a stud et secured in position by the pin 5. A terrule 6 is placed over the outer end ot the stud d and a contact point 7 is threaded to the stud t outside the terrule '6. 'lhe inner or rear end of the stud 4i is recessed to snrronnd a spiral spring 8. Fitting the opening 1n the handle is a series ot conductingI contact rings 9 which are secured in definitely spaced relation by insulating` spacers l0, these rings "1 9 and spacers l() forming a lining,- for the handle and providing, a central space in which a contact carrier ll of insulating material may slide. Along the contact carrier ll is a series ot recesses, each recess acconfirnodatingI a contact spring 12 formed and arranged to present two outwardly pressed contact snrtaces, one at each end of the spring. The length of each spring l2 is such that the dis tance between its tvvo contact surfaces corre4 spends with the spacing of the contact rings 9. Each spring l2 is thus adapted to loe moved by the carrier il to bridge and conu dnctively connect two successive contact rings 9 as shown in Fig. 3. rthe recesses for the contact springs l2 are relatively so disposed ythat successive springs are angnlarly dicplaced,- preferably 180 degrees apart, about the carrier il and also overlap a short dis'- tance longitudinally et the carrier. sTins arrangement permits the adjacent ends oit successive contact springs i9 to rnalre sinonitaneous Contact with one ot the contact rings 9, the two springs extending in opposite directions to maire Contact also with tivo other rings disposed on opposite sides o the iirst ring.. The tiret or torn/'ard spring` l2 is aiu ranged to bridge the space 1between connect the recessed inner end the stro and iirst or forward one ot the Contact rings Q. in the handle shown in 'the drawing, the contact carrier ll is'providedwith tive het handle may he designed "wi i fewer i "l l ou? ii desired. the contact carrier 'il is provi extending; inside the spiih adapted to strilre bottoni oi Sti the stud 4 to arrest forward motion of the contact carrier when the contact springs 12 have been moved into position to connect together the rings 9 and stud 4.
From near the rear end of the contact carrier 11, an opening or passage extends rearwardly and outwardly at an acute angle' to the axis of the handle and a plunger 14 slides in this opening. The adjacent ends of the plunger 14 and the contact carrier 11 are formed with opposing recesses between which is fitted a pin 15, there being thus formed between the plunger and carrier a flexible compression joint. The plunger 14 is formed with an inner beveled shoulder 16 and an outer beveled shoulder 17, these beveled shoulders being arranged to engage a stop 18 in the form -ofa ring surrounding the plunger and secured in place by a screw 19. Pressure upon the plunger 14 will be communicated through the pin 15 to the contact carrier 11 and move this carrier forward against the' spiral spring 8 until the stop 13 strikes the bottom of the recess in the stud 4, the spring contacts 12 being moved by the carrier into position to connect together in series the rings 9 and the stud 4 as shown in Fig. 3. Just beyond the outer shoulder 17, the plunger is smaller than the opening in the stop 18 so that in the contact making position of the plunger it may be moved laterally to bring one side of the shoulder 17 into engagement with the stop 18, a very slight lateral pressure on the plunger being then suflicient 'to maintain this engagement and keep the contacts between the contact springs 12 and the rings 9 and stud 4 closed against the pressure of the spiral s' ring 8. Upon removing this lateral pressure rom the plunger 14, however, the pressure of the s iia spring 8 will cause the beveled shouldr 17 of the plunger to become disengaged from the stop 18, the parts then moving under the pressure of the spring into the position shown in 2 with the inner beveled shoulder 16 in engagement with the stop 18. The distance between the two beveled shoulders l@ and 17 of the plunger is preferably one halt of the distance between the two contact surfaces at the opposite ends of one of the contact springs. Consequently, while the spring 8 is holding the contact parts away from the stud with the shoulder 16 in en sagement with the stop 18, the Contact surraces olf the Contact springs 12 are midway between and out of engagement with the con tact rings 9. its the trailing contact surface each centact spring 12-leaves the contact ring 9, it is immediately t'ollowed by a portion of the insulating contact carrier 11 which covers 'the portion of the Contact ring where contact was broken and which also serves as an insulating body interposed between the contact spring and the contact ring while the contacts are broken. Thus, by pressi-ng and releasing the contact making plunger 14, the contact point 7 of the test handle is connected with and disconnected from the rear contact ring 9, there being twice as many make and break series contacts in this path as there are contact springs, the handle shown in Fig. 2 having live contact springs and therefore ten make and break contacts. The number of springs and contacts may be more or less if desired depending on the characteristics of the current which is to be interrupted when the contacts are broken. The mechanism which has been described for making and breaking the circuit in the test handle constitutes a multiple break plunger switch adapted for use in high potential circuits.
The end of the test handle just behind the plunger 14 forms a grip so as to be conveniently held in the hand with the thumb in position to operate the plunger 14. This rear portion of the handle surrounds one end ot the insulated cable 20. A set screw 2l secures in place a tube 22 of any suitable material which surrounds and retains the end of the cable inside the handle. The cable includes a central conductor 28 of fine copper strands covered by suitable layers of insulation. Thel outside layer is preferably of heavy cotton covering a layer of fine copper Wire braid 24. Inside the handle, this outer cotton braid is removed to expose the copper braid'24 which is connected by a link 25 with the ring or step 18. A sti'll helical spring 26 protects the cable at the point where it enters the handle. The conductor 23 is ei;- tended inside the handle and connected to the rear contact ring 9 so as to furnish testing current for the Contact point 7 at such times as the contacts of the switch are closed by depressing the plunger 14.
These test handles are preferably used in pairs as indicated in Fig. 1, the ends of the cablesA opposite the two handles of a pair being provided with lugs 27 for attachment to the source ot high potential current such as a transformer. The wire braid covering and any coverings outside this one are removed f rom each cable for a suiiicient distance from the lugs 27 to prevent short circuiting them. The outer covering above is then removed from each cable to expose the wire braid covering 24 for a short distance and the two cables secured together at this point by a metal clamp 28 provided with a ebain 29 which may be attached by a hook at its 'free end to some suitable ground, the length ot the chain being adjusted to relieve the cables of strain. It will be seen that ground connection is furnished through the chain 29 to the clamp 28, the braided copper covering 24 oi the cables, and through the links 25 to the plunger 14. Grounded protection is therefore provided 'for the operator against shock under normal conditions attending the use ot the handle andl also in the event ot' failure of momes the insulation at any oint as it lies between the operator and the ive conductors practically throughout the circuit. J ust in front of the plunger 14, the test handle is abruptly enlarged to form a protecting collar or guard 30 which prevents the operators hand from sliding forward on the handle toward the contact point 7.
The switch contacts are held normally open by the spiral spring 8. In testing a piece of electrical apparatus, such as a high tension winding of a transformer, the handles are connected by means of the cables 20 with a source of current ofthe proper potential for testing and the chain 29 is properly grounded. The contact points 7 are then touched to the terminals of the device under test, the sharp ends of these contact points assuring good electrical connection. The plungers 14 are then depressed to close the switch contacts, thus connecting the high potential source of current to the device under test. Slight lateral pressure on the plungers lliholds the beveled shoulders 17 in engagement with the stops 18 to keep the contacts of the switch closed as long as it is desired to subject the transformer or other device to test. At the end of the test, the lateral pressure on the plungers is removed and the spiral springs 8 cause the beveled shoulders 17 to disengage from the stops 18 and the movable switch parts to disconnect the switch contacts, the shoulders 16 coming into engagement with the stops 18 to cooperate with the spiral springs 8 in maintaining the switches in normal open condition. The opening of the switch is entirely automatic so that it is impossible to leave the switch contacts closed and the exposed points 7 of the handles alive while the plungers 14 are not being deliberately and wilfully depressed by the operator. When the high tension circuit is opened by a pair of handles constructed in accordance with the showing in Fig. 2 of the drawing, the switch in each handle makes ten breaks in the circuit and insulating material is immediately interposed between the Separated contacts of half of these breaks. The precaution of using a circuit breaker in the low voltage side of the transformer which furnishes the high potential testing current is of course advisable.
What I claim as new and desire to secure by Letters Patent of the United States, is-
1. In electrical apparatus, an insulating sleeve surrounding an elongated space having a. section of uniform diameter, a conducting member at one end of said sleeve, a contact carrier having slidable fit in the uniform section of said elongated space, a series of conducting contacts on said contact carrier, a second series of contacts secured to said sleeve along the uniform section of said elongated space, an operating member beyond the end of said contact carrier opposite said conducting member, said operating member extending through one side of said sleeve at an acute angle to the direction of motion of said contact carrier, and a flexible joint between the inner end of said operating member and the adjacent end of said contact carrier, whereby said contact carrier may be moved toward said conducting member to connect said contacts in series.
2. In electrical apparatus, a switch including a movable contact operating member, a member for moving said contact operating member in one direction to complete a circuit between contacts, said latter member being movable in a direction at an acute angle to the direction of movement of said contact operating member, said two members having opposed recesses formed in adjacent portions thereof, a compression member held between said two recesses to form a universal joint, and means for moving said contact operating member in the other direction to break said circuit.
3; In electrical apparatus, a switch including a movable contact operating member, a member for moving said contact operating member in one direction to complete a circuit between contacts, said latter member being movable in a direction at an acute angle to the direction of movement of said contact operating member, said two members having opposed recesses formed in adjacent portions thereof, a compression member held between said two recesses to forma universal joint, and means for automatically moving said contact operating member in the other direction to break said circuit.
4. In electrical apparatus, a switch including a movable contact operating member, a member for moving said contact operating member in one direction to complete a circuit between contacts, said latter member being movable in a direction at an acute angle to the direction of movement of said contact operating member, a compression member held between adjacent portions 'of said two members to form a universal joint, and means for moving said contact operating member in the other direction to break said circuit.,
5. In electrical apparatus, a switch including a contact operating member, a plunger for moving said member in one direction to complete a circuit between contacts, means for automatically movin said member in the other direction to brealr said circuit, said plunger having a shoulder, and a shoulder engaging stop, said plunger being movable laterali to cause its shoulder to engage said stop w en said circuit has been completed,
said plunger having a second shoulder engageable by said stop after said circuit has been broken.
6. In electrical apparatus, a switch includino` a hollow insulating member with a plura ity of contacts on its inner surface, an insulating carrier slidable within said memwhereb the path between contacts is closed ber, and havin a luralty of contacts disby insu'ation to prevent arcing when the conplaced longituinal y thereof, and means for tacts are separated. 10 moving sald carrier to connect and dscon- In witness whereof, I have hereunto set my 5 nect'its contacts and those of said insulating hand this 4th day of Nov., 1921.
member, said insulating carrier fitting the space withinsaid hollow insulating member, ALLAN B. HENDRICKS, JR.