US2132179A - System for operating alternating current switchboard instruments - Google Patents

Description

0a. 4, 193s.- H. MILLIKEN 2,132,179

SYSTEM FOR OPERATING ALTERNATING CURRENT SWITCHBOARD INSTRUMENTS Filed June 27, 1934 3 Sheets-Sheet l H. MILLIKEN 2,132,179

SYSTEM FOR OPERATING ALTERNATING CURRENT SWITCHBOARD INSTRUMENTS Filed June 27, 1934 3 Sheets-Sheet 2 I IEP LINE T0 NEUT AL vo x w 7 I/)(=KEACT\VE COMPONENT LAG! soB;H\ND

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Patented Oct. 4, 1938 UNITED STATES SYSTEM FOR OPERATING ALTERNA'I'ING CUB-BENT INSTRUMENTS Humphrey: lliliiken, Montreal, Quebec, Canada Application June 27, 1.34. Suial No. 732,738

s Claims. (01. 111-95) This invention relates to the transformation of alternating current and its utilization for the purpose of actuating instruments such as relays. ammeters, wattmeters,.power-factor meters, etc.

My invention will be more. clearly described with the aid of the accompanying drawings forming part of the specification, wherein Fig. i represents schematically one form of my current. transformer;

Fig. 2 represents structurally the arrangement of coils in my current transformer;

Fig. 3 shows schematically the arrangement of the primary winding of the current transformer and a short-circuited additional winding to increase the linkage flux;

Fig.4 shows schematically an arrangement of current transformers for use in connection with a age and current in the secondary circuitof my current transformer.

Apparatus heretofore used for this purpose, designated as current-transformers or seriestransiormers, have a magnetic circuit composed of laminated steel which completely encircles one or more turns of the primary circuit, and a secondary winding having a much greater number of turns of smaller wire wound around the steel core, evenly distributed over the core, so

as to minimize the leakage of magnetic flux, which leakage introduces error in the current measurement. The load connected to the secondary winding must have minimum impedance which limits the distance between. the currenttransformer and the switchboard instruments, limits the number of such instruments on one transformer, and requires relativelyheavy wires. Such transformer design requirements necessiate very close proximity of the primary windin (usually of high voltage) to the steel core and secondary winding which must be grounded for protection of operators. Such close proximity subjects the insulation to high unit stresses and there have been many insulation failures of such current-transformers. transformers for the higher commercial voltages is also quite costly.

This invention provides means for overcoming the above described limitations and objectionable features. The cost of insulation and danger of The insulation of such breakdown are'practically eliminated by sepamum primary current flowing. The instruments 3, C, D, E, G, H, and J connected in circuit with the secondary coils l have coils of high impedance (several thousand ohms) in place of the usual "current" coils having impedance as low as possible. Such high impedance coils draw very small currents (a few hundredths of an ampere) from the secondary winding and therefore do not reduce the terminal voltage of the secondary winding to an objectionable extent. Condensers 1" may be connected in multiple with said instrument coils to neutralize the lagging component of current and minimize the voltage loss in said secondary circuits, or the condenser 25 may be connected in series with the instrument coil and thereby raise the voltage across the instrument coil. The secondary I therefore delivers to the instrument a voltage which is closely proportional to the primary current. With this system the instrument B used for measuring the current in the primary circuit is an alternating current voltmeter having the usual potential" coil of high impedance, but with a scale graduated in amperes, and properly calibrated. Distances of one thousand feet or two thousand feet from the switchboard to the instrument transformer oil'er no obstacle with this system, since the current transmitted is so extremely small. This is advantageous in the design of 0 large hydro-electric generating stations. 1 There is a phase angle of almost exactly between the primary current I and the voltage Es induced in the secondary. With this system, therefore, an instrument C constructed like an ordinary wattmeter (substituting a "potential" coil in place of the usual "current" coil) will be the means of measuring the wattless component, and an instrument D construc ed like an ordinary wattless component meter will measure the watts w in the circuit. Directional relays (reverse-power relays) E ordinarily used to open circuit-breakers when a'short circuit occurs on one side of a station but not to open the breaker if the short circuit is on the other side, can be advantageously 2 operated with this system short-circuit currents I usually lag nearly {20 behind the line-to-neutral voltage Eb; the" voltage Es induced in the secondary 5 lags another 90, making it lag nearly 180 behind the line-to-neutral voltage Ep, and by simply reversing the two wires at the relay E, the potentials on the two coils are brought in phase and the two relay coils are made to exert a maximum attraction to close the relay contacts when they should be closed and a maximum repulsion to hold the contacts open when they should be held open. Pilot-Wire relays Gare operated more readily with this system than with the current-transformer system heretofore used, because it is a simpler matter to balance two potentials (in two stations several miles apart) than to balance two currents in secondary circuits in the two stations.

With this system it is a comparatively simple matter to operate selective relays of the well known impedance type (or distance type) H in'which a current coil exerts a pull to close the relay contacts (and open the circuit breaker) and the potential coil opposes and delays the closing of the contacts. The peculiar function of distance relays is to operate and open first the circuit breakers which are nearest to the fault and thus clear only the faulted section of the system, leaving other sections in operation. With this system it is feasible to simplify such relays by combining the two coils into one, since it is now simply a matter of balancing one voltage against another (one voltage representing the line current and the other voltage representing the line voltage) and the two secondary voltages are almost in phase (when there is a short circuit on the line). r

The structural arrangement of my current transformer A takes different forms suitable to the equipment with which it is associated. Where reactor coils are used for limiting the short-circuit current in a circuit (which is common practice) the reactor coil 4' (having no iron in its magnetic circuit) may be used as the primary coil of the'current transformer; the secondary coil 5 may be located in-any position where a sufilcient portion of the primary flux will pass through it and far enough for safety with no insulation other than air between the two coils. Fig. 1 shows the secondary coil 5 near one end of the reactor coil 4' and co-axial with it.

Fig. 2 is an elevation (partly in section) of the transformer A as it is applied to any apparatus having two or more stacks of pin-type insulators I for supporting the apparatus, for instance a power circuit-breaker. The porcelain insulators I are of a type commonly used, having iron pins and iron caps, which are therefore magnetic. A

structural steel member 2 supported by cast iron pedestals 1a joins the two stacks at the top and another steel member 3 at the lower ends. These iron and steel parts, which may support other apparatus, also serve to carry a portion of the magnetic field from the primary coils 4 at the top, through the secondary coils 5 around the bottom of the stacks, thereby increasing the voltage induced in coils 5 with a given current in the primary. The primary coils 4 shown in section in Fig. 2 and in plan (diagrammatically) in Fig. 3, are preferably made of thin wide copper bars bent into spirals and insulated from the adjacent parts supporting the coils. The two coils 4 are connected in series with the main high-tension line, with such polarity of connection as to produce magnetic flux in the same direction around the magnetic circuit asshown. The greater part of the magnetic flux induced by coils I does not reach the bottom steel member 3 and secondary coils 5, but follows shorter paths,

through the air as shown by the arrows. A sufficient portion of the flux, however, passes through the secondary coils 5 to induce a, voltage suitable for the purposes described. The secondary coils are preferably placed in the inclined position shown for the purpose of enclosing a portion of the leakage flux which would otherwise not pass through them.

While I have referred to the device shown in Fig. 2 as a transformer, it isin fact a low voltage producing means interposed in the main line conductors. The primary coils are in effect transmitting coils and the secondary coils are in effect receiving coils so spaced from the primary coils as to receive only a selected portion of the magnetic flux induced by the primary coils. It is only 1 this selected portion of the magnetic flux which is effective to produce the low voltage in the receiving or secondary coils.

The two coils 6 are for the purpose of opposing a portion of the leakage flux thereby increasing somewhat the useful portion of the flux, in cases where this is desirabledue to wide separation between the primary andsecondary coils for the higher commercial voltages. Each of the coils 6 is short-circuited on itself and bent into the peculiar shape as shown; the only current in coils 6 is that induced by the leakage flux which they oppose. V

Bundles of transformer steel laminations I may be secured to the structural steel members 2 and 3 respectively'as shown in order to increase the total magnetic flux.

Fig. 4 shows diagrammatically current transformers arranged in another form for voltages above 154,000 volts. In this form, the stacks of insulators are much longer on account of the higher voltage, and are placed in diagonal relation to act as braces and eliminate bending stresses on the stacks. This diagonal arrangement is advantageous magnetically. The three primary coils 8, 9 and I are connected in series with their polarity such as to induce flux in the direction shown by the arrows. There are six stacks of insulators numbered I I to IS. The arrangement is shown diagrammatically developed into one vertical plane. Actually the three top junctions of the three pairs of stacks are located at the corners of a triangle inithe steel plate 2, and the three bottom junctions of the stacks are likewise located at the corners of another triangle on steel structure 3. Stack II thus joins stack I6 at the top. Coil 8 encircles stacks I 2 and I3 inducing flux downward in them. Coil 9 encircles stacks I4 and I inducing flux upward in them. Coil I 0 encircles stack I6 only inducing flux downward in it. No coil encircles stack II and the flux in it is only that returning upward from the downward flux in stack I2. The flux in stacks II and I2 is not utilized. Secondary coil I'I utilizes the flux in. stacks I3 and I4 and coil I8 utilizes the flux in stacks I5 and I6.

I claim:

1. In a high-potential alternating-current system, main-line conductors; a low voltage-producing means interposed in the main line and comprising a primary or transmitting coil of a small number of coils in series with the main-line conductors, a secondary or receiving coil of a large number of coils, means for spacing and insulating 1 said secondary coil from the primary coil to locate of magnetic iiux induced by the primary coil and to form an air gap oi substantial area between the said two coils, whereby a substantial portion 01 the magnetic flux induced by the primary coil will be ineiIective and will flow through the air gap between the two coils and only a selected portion of said flux will pass through the secondary coil to induce a low voltage therein, and an instrument in circuit with said secondary coil.

2. In a high-potential alternating-current system, main-line conductors; a low voltage-producing means interposed in the main line and comprising a primary or transmitting coil of a small number of coils in series with the main-line conductors, a secondary or receiving coil of a large number of coils, means for spacing and insulating said secondary coil from the primary coil to locate said secondary coil in the outer portion of the fleld of magnetic flux induced by the primary coil and to form an air gap of substantial area between the said two coils whereby a substantial portion of the magnetic flux induced by the primary coil will be ineilective and will flow through the air gap between the two coils and only a selected portion of said flux will pass through the secondary coil to induce a low voltage therein, and an instrument in circuit with said secondary coil and provided with an instrument coil having a high impedance, and a condenser shunted across the instrument coil.

3. In a high-potential alternating-current system, main-line conductors; a low voltage-producing means interposed.in the main line and comprising a primary or transmitting coil of a small number of coils in series with the mainline conductors, a secondary or receiving coil of a large number oi. coils, means for spacing and insulating said secondary coil from the primary coil to locate said secondary coil in the outer portion of the field of magnetic flux induced by the primary coil and to form an air gap of substantial area between the said two coils, whereby a substantial portion of the magnetic flux induced by the primary coil will be ineffective and will flow through the air gap between the two coils and only a selected portion of said flux will pass through the secondary coil to induce a low voltage therein, an additional winding for each primary coil insulated and closed on itself and so positioned in relation to its associated primary winding as to increase the linkage flux between the primary and secondary windings, and an instrument in circuit with said secondary coil.

, HUMPHREYS MILLIKEN.

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