US1601840A - Shunt - Google Patents

Description

' Oct. 5, 1926".

D. J. ANGUS SHUNT Filed July 24. 1925 INVENTOR. DON/HDJfl/Vfl/S,

Patented Oct. 5, 1926.

UNITED STATES DONALD J. ANGUS, 0F INDIANAPOLIS, INDIANA.

SHUNT.

Application filed July 24, 1925. Serial No. 45,787.

"In the use of shunts across which the current winding of an ammcter or a wattmeter is connected, and especially shunts of the larger size, the drop in potential across the shunt is very small, so that it is essential that any source of error be eliminated; as even a small variation in potential is relatively great when considered in connection with the potenial drop being measured. For various reasons, as because of dirty contacts, inequality in pressure of the clamping bolts, etc, there may be inequalities between the currents in the different bars of which the shunt is composed, or an oblique flow of current in the individual bars, or both. This may result in innumerable variations in the distribution of current flow in the shunt, with the result that the drop in potential between any two external points on the shunt terminal-blocks may vary considerably at dill'erent times and under dilierent conditions. By actual tests, variations as high as 8% in the potential drop have been found to exist with a single set of external conens to the terminal blocks of the shunt.

It is the object of my invention to reduce this possibility of error; and to make the possible error much smaller regardless of dirt at the contact points or inequality in pressure.

In carrying out my invention, broadly speaking", I make the connection for the current winding of the ammeter or of the wattmeter to internal points on the terminal blocks; and desirably make such connection at points approximately in the axis of the shunt a whole. By taking the current oil from the terminal block or the current winding at points in the axis of the shunt as a whole, I have found by tests that the ossible range of variation in the drop in lliOiGI'lfiiltl between the two connection points is made much smaller, so much so indeed that it is negligible in practice instead of being a real and substantial source of error.

The accompanying drawing illustrates my :ion: Fig. 1 is a plan 01? a shunt em- 1 my invention, one of the terminal blocks being in section; and Fig. 2 is a front elevation of the shunt shown in Fig. 1.

The shunt as a whole may be of any desired construction. It comprises two termi nal blocks 10 and 11, between which extend a plurality of parallel resistance bars or sheets 12, the ends of which are conveniently sweated in slots in the adjacent parallel faces 01 the two terminal blocks. The resistance bars 12 are 01 suitable resistance material; and are shown arranged in pairs, with a space 13 separating the two bars or sheets 12 of a pair to promote ventilation, though this is not essential. The outer ends of the terminal blocks 10 and 11 are provided with a series of slots 14;, paralleling each other, to receive any desired number of bus-bar conductors 15, which are usually in the form of flat plates. The arrangement of the bus-bars in the slots 14: is desirably symmetrical with respect to the shunt as a whole. Clamping bolts 16 extend through the fingers separating the slots 14:, and through the bus-bars which are received in such slots; so that by the clamping of the bolts 16, the bus-bars are rigidly and firmly clamped in place in the slots 14-. to make good connections. Usually there are at least two clamping bolts 16 on each terminal block, as is illustrated in Fig. 2.

It is of course impossible to get absolute equality in the clamping action of the bolts 1.6 even on the same bus-bar; and it is even more imposible to get equality of pressure of such bolts on the different bus-bars, and uniformity of contact of the various busbars throughout their width with the terminal blocks. It is because of this that inequality of current flow among the di'lterent shunt-bars 12, and obliquity in the direction of such current flow in the individual shunt bars, occurs; which results in an inequality in the drop in the potential between the two terminal blocks 10 and 11 as measured r'rom different points on such terminal blocks.

A possible variation in the drop in potential is least, regardless of any inequalities in the clamping action of the bolts 16 on the same and on difierent bus bars, it the points between which the drop is measured are on the axis of the shunt as a whole.

To obtain this, I do not connect the wires 17 which lead to the current winding of the ammeter or wattmeter, to external points on the terminal blocks; which is the hitherto universal custom. Instead, I connect such current-winding-supplying wires 17 to the ends of rods 18, one for each terminal block 10 and 11; and these rods 18 extend in to the axis oi the shunt, and there are attached to the terminal block. lhis is clearly indi cated in'Figs. 1 and 2, particularly Fig. 1.

Each rod 18 is received in a hole 19 in its terminal block, and is spaced therefrom so that it is out of electrical contact therewith. T he outer end of the rod 18 is held in place by an insulating washer 20. The inner end of the rod is screw-threaded into the counter bored and coiuiter-tln'eaded lower end of the hole 19, by the screw-tln-eaded end 21. This threaded connection is on the axis of the shunt, or substantially so, yiewer. from either direction. The outer ends of the rod 18 are also threaded, and receive nuts by which binding posts are torn'ied tor the connection of the wires 17 which lead to the current winding ot' the ammeter or of the wattmeter.

In this way, the current for such current winding' is taken from the terminal block at the point of mean potential thereof. Because of that fact, such point is the point of minimum variation in potential. as on account ot dirty contacts or unequal pressures of the clamping bolts. As a result, the possible variation in the drop in potential which produces the current through the current winding of the meter is reduced to a small fraction of what it otherwise would he, and is made substantially negligible instead of being an important factor of error.

I claim as my intention l. A shunt, comprising terminal blocks, resistance bars connecting such terminal blocks, and means for connecting a winding directly to internal points on said connection blocks within the projected area of the resistance bars.

2. A shunt, comprising tern'iinal blocks, resistance bars connecting such terminal blocks, and connection rods electricalt connected to said terminal blocks only at points removed from the exterionot said blocks within the projected area of the resistance 3. A shunt, comprising terminal blocks, tance bars extending between said terminal hloclts and connecting them, and connection rods extending into said terminal blocks and electrically connected therewith only at points substantially on the axis of the shunt.

A shunt,

n'ovided with comprising terminal blocks slots in their outer ends for eiving' bus-bars, resistance bars extending ween and connec said terminal bloc amping bolts for c iniping said bus-bar said slots, and conneccion rods directly ect-rically' connected to hi-1r tern'linal blocks points well. inside ot the surface dred and twenty-live.

DONALD J. ANGUS.

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