US2705774A - Electrical integrating meters and indicating instruments - Google Patents

Description

p i 1955 5. J. HEWLETT ETAL 2,705,774

ELECTRICAL INTEGRATING METERS AND INDICATING INSTRUMENTS Filed May 18, 1950 2 Sheets-Sheet 1 lm 6127601 15 $.J1iewleizb lifolfsndarz/ I I l 1955 5. J. HEWLETT ETAL ELECTRICAL INTEGRATING METERS AND INDICATING INSTRUMENTS April 5,

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United States Patent ELECTRICAL INTEGRATING METERS AND INDICATING INSTRUlVIENTS Stanley James Hewlett and Ronald Harcourt Wolfenden, London, England, assignors to Measurement Limited, London, England, a British company Application May 18, 1950, Serial No. 162,622 Claims priority, application Great Britain May 23, 1949 5 Claims. (Cl. 324-137) This invention relates to polyphase integrating meters or indicating instruments of the type in which a plurality of driving elements, each comprising a series and a shunt electro-magnet, are grouped around and produce torque on a single rotor disc.

in polyphase meters of this type, errors in registration are introduced due to the eddy currents of each element interacting with each other. This effect may be reduced, particularly with respect to those errors produced by the series or current element, by constructing the centre portion of the disc of non-conducting material so as to prevent the interacting eddy currents crossing the disc. This arrangement is limited by the size of the remaining annulus and the resulting reduction in torque.

It has been found by experiment that critical dimensions of this annulus are reached, at which the remaining interaction errors emanate principally from the eddy currents produced by the potential or shunt magnets. Such errors are found to increase in proportion as the series current is reduced, and the sign of the error is reversed when the direction of phase sequence of the elements is reversed. The error is thus equivalent to a constant torque whose magnitude and direction is a function of the applied voltage and phase rotation of the potential elements.

In order that the meter may register accurately on all loads irrespective of the balance of phase loading or the order of connecting the phases it is necessary to reduce or eliminate this interaction torque and the invention describes a method of construction which provides an opposing torque sufficient to cancel out or nearly cancel out the error.

According to the invention, the rotor disc consists of concentric portions of conducting material separated by insulating or high resistance material, the driving elements being associated with the outer conducting portion only and the shunt coils being connected so as to produce a rotating field in a direction opposing the normal direction of rotation of the instrument.

The rotor disc preferably consists of a disc of metal surrounded by a narrow ring of insulating or high resistance material, which is surrounded by an outer metal annulus. It is mounted with the outer metal annulus between the poles of the series and shunt electromagnets of the driving elements, which are suitably spaced round the disc.

The driving torque is generated mainly in the outer annulus, and by restricting the width of this annulus, the eddy currents are restricted and the interaction is thereby reduced. The dimensions of the annulus are determined by a compromise between the desirability of reducing interaction as far as possible and the necessity of avoiding undue reduction of driving torque.

The rotating field due to the shunt electromagnets generates a torque in the central disc, in opposition to the normal direction of rotation, and the diameter of the central disc is selected to give a torque adequate to reduce or even entirely neutralise the interaction eifect. The dimensions of the insulating ring are determined by the dimensions selected for the disc and outer annulus.

With the arrangement described, the inaccuracy due to interaction can be reduced to a very low value while a high useful driving torque is still obtained.

An arrangement in accordance with the invention is illustrated diagrammatically in the accompanying drawing in which Figure 1 shows the arrangement of the rotor disc and driving elements in plan and Figure 2 shows the manner of connecting the driving units.

The rotor disc is constructed of two main parts: an outer annulus a of conducting material suitably dimensioned to prevent eddy currents crossing the disc and an inner concentric disc b of similar material and of optimum diameter and thickness to produce the required amount of opposition torque, the intervening space being taken up by a ring c of insulating material. The potential magnets R, Y and B co-act with the annulus a.

When used in a polyphase meter in which the connections to the potential magnets are arranged to produce a small rotating leakage field of the correct magnitude and direction so as to produce a torque sufficient to oppose the interaction error torque, the interaction errors previously referred to are substantially reduced or even eliminated.

By way of an example, when the inner diameter of the annulus a is made 62.5 mm. the meter gives a positive error of registration when the phases are connected to reach their maximum in the order RYB and on reversal of the order of phase rotation i. e. RBY the error becomes negative by an approximately equal amount with anticlockwise direction of rotation of the disc. A central disc b of 52 mm. diameter produces a torque in a clockwise direction, i. e. the direction of the order in which the potential elements reach their maximum values, of magnitude such that when the disc b is solidly attached 1%(1116 outer annulus a, it provides the necessary cancelling e ect.

Figure 2 shows the arrangement of the shunt and series elements of the three driving elements. There is a shunt or potential element connected across the phase R, associated with a series or current element connected in series between the phase R and the load, the rotor disc (which is not shown in Figure 2) moving between the two elements. Similar pairs of elements are connected to the other phases Y and B. The three series coils are connected in the appropriate sequence to obtain anti-clockwise rotation of the rotor disc. If the meter then produces a positive error, the shunt coils are connected so that the corrective torque they produce is clockwise. If however the error were negative, the shunt coil connections would require to be modified to produce an anti-clockwise torque.

The correcting torque in the meter disc is believed to be produced by the leakage fluxes from the three shunt electromagnets cutting the inner disc and setting up eddy urrents which again coact with the shunt electromagnet uxes.

The method of construction lends itself readily to plastic moulding of the insulating ring 0 for securing the two concentric portions together but the invention is not limited to this method. An alternative construction may be obtained by diecasting the two concentric conducting portions together using sorne high resistance alloy, the inner and outer portions being suitably proportioned.

What we claim is:

1. A polyphase electrical meter or indicating instrument, having a rotor comprising concentric portions of conducting material separated by insulating or high resistance material, and a plurality of driving elements grouped round the rotor disc and associated with the outer conducting portion only, each driving element having a series and a shunt electromagnet, and the shunt coils being connected so as to produce a rotating field acting on the inner portion of the rotor disc to give a torque opposing the torque due to interaction between the eddy currents generated by the driving elements.

2. An electrical meter or instrument as claimed in claim 1, in which the rotor consists of a disc of metal surrounded by a narrow ring of insulating material, which is surrounded by an outer metal annulus, and the rotor is mounted with the outer metal annulus between the poles of the series and shunt electro-magnets of the driving elements.

3. An electrical meter or instrument as claimed in claim 2, in which the conducting disc and annulus are vsecured together by a moulded plastic insulating ring.

4. An electric meter or instrument as claimed in claim 1, in which the rotor consists of a disc of metal,

an outer metal annulus and a diecast ring of high resistance material between the disc and annulus and securing them together, and thetrotor is mounted with the annulus between the poles of the series and shunt electro-magnets of the driving elements.

5. A polyphase electrical meter 01" indicating instrument, having a plurality of driving elements and a rotor disc consisting of an outer annulus of conducting material between the poles of the series and shunt electromagnets' of the driving elements, of such width as to 10 provide adequate driving torque, a ring of high resistance material inside the annulus, and a metal disc inside the high resistance ring adapted to be acted upon by the field of the shunt coils so as to give a torque in the opposite direction to the direction of rotation to neutralise the interactlon effect.

References Cited in the file of this patent UNITED STATES PATENTS 426,335 Shallenberger Apr. 22, 1890 1,913,260 Batt June 6, 1933 2,529,571 Prince et al Nov. 14, 1950 FOREIGN PATENTS 19,081 Australia Mar. 28, 1935 90,508 Switzerland Sept. 1, 1921

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