US2403637A - Rectifier regulating system - Google Patents

Description

Patented July 9, 1946 UNITED SETAT ES EN Q'F F lC E RECTIFIER REGULATING SYSTEM Soren 1L. Christie, Los-Ang elcs, .Calif:

ApplicationDecember 16, 1944; Serial No. 568,463

3 Elaims.

invention" relates to rectifiers, that is, de-

variation: inpotentialbetweenfull load and'no loadonthe; direct current supply lines leading fromthe rectifier; or-to improve-the 'voltageregulation of;the system.-

Fig.1 1 ofthedrawingshows'a circuit diagram of an installation emb'odying'my' invention; and Fig; 2" shows an alternative relay circuit.

The apparatus which I use to accomplish the purpose of-my-inventi'on may be readily-supplied by a man skilled in the art with the information supplied ,by the accompanyingspecification and the. drawin which shows simple diagrams: of"

connections: In'the drawing-l designates'transformers, 2 rectifiercolumns; and 3 and'4regulatingassemblies.- used, each having aprimary connected to an alternating current supply source. The trans Threetransformers may be formers areshown Y-connected to a three-phase source. is. connected, as shown in- Fig. l, tothe center'of one: of' the rectifiers- 2. rectifiers '2, which are preferably of "the-metal lic'disc type, is connected-to onewire-z'l of adirect-currenti load line, the other side "being con- The secondary [2 of each transformer-- One end of' each of'the nectedto theother wire 220i that line. Various.

loads 23; may be connected across these lines; as shown.

I have found that, using metallic disc rectifiers of..the form now in commonuse, the voltagebetweenthe wires2l and 22, with the load'23 drawing 100% of the-full loadratedcapacityof the rectifi'ers, may'be'only 70% of the voltage at no.

load: The loa'd23'may: be variable, andit' is;

highly desirable that the voltage between the wires or direct-"current busses-Zl and22 bekept moreuniform.

If'renderthisvoltage'more uniform or constant inpot'ential by'one or moreregulating assemblies; each ofsuch assembliesconsistingofa shunt 3| through which the current-flowing in the load 23 Connected to the ends of the shunt 3'l is the-coil of a'pil0trelay'32; The voltage impressed on'this coil'is the potential dropin the shunt 31: caused bythecurrentsfiowing through it. The

passes.

coil 32 l of the relay 32 attracts a: pivoted armature-322, but'this armature-is held in its closed position; agshown-in the drawing, by a tension spring 323. In thisclosed position the armature 322-closes the circuit through thecoil33l ofa contactor 33. The-coil 33I attracts an armature 332, which is held away from the 0011331 by aspring 333. As long asthe current flows in the coil-33!; the armature 332 holds contacts closed through which currentflows through a. ballast resistor 3'43 This-ballastresistor M is in parallel with theload 23'andis, in effect, an artificial load:

The'voltage dropin the rectifiers 2 is not a direct straight line-function of the current flowing therethrough, butabout of the total variationof*30%"voltagedrop between full load and no load occurs in the first-one-third of the, increase -in'load: If 'we consider no load voltage as 100%; the voltage at one-third load will have dropped to- Using only one regulatingassembly; I"tl'ierefore=may'make the ballasting resistance-takeone-third fullload current so that initially with no load 23- I still have-an artificial loadequal' to one-thirdfull load, this artificial load or ballast beingimposed by the'ballasting resistor 34'. The voltagebetween the wires 2| and 22 cannot rise above 85% of'no loadivoltage:

aslong' as theballast resistor 34 isin circuit.

The pilot relay is; however, so adjustedthat whenever the'current taken by the l0ad23 is more thantwo-thirds-fullload current, the relay. 32 actuates the contactor 33 and cuts the resistor 34 out of circuit. In otherwords, the pilot relay acts to cut the resistor 34 out of circuit whenever two-thirds load is taken by the-load 23; Before the relay32"so operates, the voltagebetween the:

wires-2| and'22 will have-fallen, to full load voltage; or-'70% of noload' voltage. Using a regulating-assembly, the voltage can neverexceed 85% ofno load voltageand will fall to' 70%; With noregulating'assembly; the voltage may fluctuatefrom% to70%'.

Ittv 'o regulating are used, each ballast-resistancetakes about one-third full'loa-d current, or atotal of two-thirds full'loadcurrent. may then-be about--73% of* no. load-voltage. the load draws morecurrentgup; to one-third load: the voltageldecreasesyto, say, 70%. The

1 pilotz'relay of.:th e;regnlating-:assembly -3 then ope.

The 1 voltage between the Wires 2| and 22'" erates, and the resistor 34 is cut out, and the voltage again rises to 78%. As the load 23 increases to two-thirds full load, the voltage drops to 70%, the pilot relay of the assembly I cuts out the ballast resistance, and the voltage again rises to 78%, falling gradually to 70% as the load imposed by the load 23 increases to full load. Using two assemblies, the voltage then fluctuates from 70% to 78% of no load voltage; that is, when no load 23 is imposed, the voltage is 78% of no load voltage without the regulating assemblies, and it never falls below 70% of this value. It is to be noted in Fig. 1 that the current feeding the resistor 34 passes through part of the shunt 3|, which also carries the current to the load 23, and that the relay 32 is so adjusted that after it opens and the ballast resistor 34 is disconnected, the relay will not close if the load current persists at its previous value. This current will increase slightly due to the rise in voltage due to the disconnection of the ballast resistor 34, and the relay can be, and should be, so set that it will again close if the load current falls substantially below the value it had at the time the relay opened. Practically all commercial relays will remain closed on a considerabl lower current in their coil than is needed to cause them to close. It is, however, easy to make a relay which will close with 100 millivolts at the terminal of its coils and will open when this value falls to 45 millivolts. Assuming that, using a single regulator 4, the relay 32 opens when the load is one-third of maximum rated load and that the voltage across the shunt is 100 millivolts with the resistor connected, when the resistor is disconnected, the potential across the shunt will be slightly more than 50 millivolts. If, now, the load decreases a little more than the potential across the shunt will be about 45 millivolts, and the relay 32 will then close. This provides a very sensitive control using a conventional and easily obtained pilot relay.

An even more sensitive relay circuit is shown in Fig, 2. In this arrangement I supply the relay 32 with a contact 334 which is connected to a primary resistor 335 and a secondary resistor 336, one terminal of the coil 32| being connected between the resistors 335 and 336, as shown in the drawing, and one terminal 331 of the resistor 336 being connected to the shunt 3 I, as shown. When the armature 322 is pulled out of its closed or primary position shown in full lines in the drawing into its open or secondary position, as shown in dotted lines, it completes a circuit from the wire 2| to the wire 22 through the resistors 335 and 336. Prior to this, the circuit through the resistor 335 is open, but the coil 32| is at all times energized by current flowing through the resistor 336. With no current flowing in the resistor 335, the voltage drop across the resistor 336 is merely that produced by the current flowing to the coil 32|. Nearly every relay of the type I prefer to use as the relay 32 will hold in its secondary position on less current than it will need to pull into that position, so that with the armature 322 in the position shown in dotted lines in the drawing, or in its secondary position, this armature will not be pulled back to its primary position shown in full lines until the current falls considerably below that needed to pull the armature from its full line or primary position to its dotted line or secondary position. When, however, the circuit is established through the resistors 335 and 336, the current in the resistor 336 is increased, being the sum of the currents in the re- 4 sistor 335 and the coil 32|. This results in a voltage drop in the resistor 336 greater than existed when only the coil 32| was in circuit. The voltage across the shunt 3| being unchanged, this reduce the voltage on the terminals of the coil 32| and reduces the current flowing through the coil 32|. The resistor 335 is so proportioned that with the voltage across the shunt 3| just sufficient to cause the coil 32| to pull the armature 322 from its full line or primary position to its dotted line or secondary position, the voltage across the coil 32 I, after the circuit is established through the resistors 335 and 336, is only very slightly more than that necessary to cause enough current to flow in the coil 32| to hold the armature 322 in its dotted line or secondary position. A slight decrease in the current taken by the load 23 will cause a slight decrease in the voltage across the shunt 3|, and the current in the coil 32| will decrease to a sufficient degree to allow the spring 323 to pull the armature 322 back into its full line or primary position, which will cut the ballast resistor 34 back into circuit.

One important feature common to both the al ternatives illustrated is the method of accomplishing the immediate change in relay coil voltage upon operation of the relay. Usually such a change is accomplished by a switching arrangement within the relay coil circuit, changing the resistance of that circuit. Because in a low voltage circuit any switch contact resistance may greatly affect the current flow, such a method will sometimes result in erratic and unreliable operation. In my system, the resistance in the low voltage relay coil circuit remains substantially constant, and no switching is performed in series or parallel with this low voltage circuit.

To accomplish the desired immediate change in relay coil voltage, I utilize a potential external to the relay coil circuit and in the order of times its magnitude. This follows from the fact that, while the potential operating the relay is derived from a shunt connected in series with the load, the circuit which causes the immediate change in relay coil voltage is connected in parallel with the load.

In other words, by employing the methods shown I utilize an external potential source of a magnitude of at least ten times the potential which feeds the relay coil circuit, which causes, upon operation of the relay, an immediate change in the relay magnetic flux. Due to the relatively high voltage, the eflfect of variations in contact resistance in the circuit is practically eliminated.

Furthermore, by arranging the external potential to cause a flux subtractive to the flux caused by the shunt potential, a small percentage increment in the shunt potential will cause a larger percentage increment in the resultant coil potential. This is seen from the fact that the external potential can be considered as substantially constant for small variations of the shunt potential.

I claim as my invention:

1. In an electrical system, the combination of: two supply conductors; a load connected directly to the first of said supply conductors; a shunt through which current passes to said load from the second of said supply conductors; a relay having an actuating coil connected at its first end to one terminal of said shunt; a secondary resistor connected at one end to the other terminal of said shunt and at its other end to the second end of said actuating coil; a primaryresistor connected at one end to the junction of said secondary resistor and said coil and connected at its other end to a secondary contact of said relay; a primary contact; means by which said relay connects said first conductor to said primary contact whenever the coil in said relay is actuated by a current below a predetermined value and connects said first conductor to said secondary contact whenever said current exceeds this value; a ballast resistor connected at one end to said first conductor; and means for connecting the other end of said ballast resistor to said second conductor whenever said first conductor is connected by said relay to said primary contact.

2. In an electrical system, the combination of a first and a second supply conductor; a load connected at one end directly to said first conductor; a shunt, one terminal of which is connected to said second conductor and the other terminal of which is connected to the other end of said load; a relay coil, one end of which is connected to one terminal of said shunt and the other end of which is connected to the other terminal of said shunt; a ballast resistor, one end of which is connected to said first conductor; a pair of ballast contacts, one of which is connected to the other end of said ballast resistor and the other of which is connected to an intermediate point in said shunt; and means for closing the circuit between said ballast con- 6 V tacts whenever the current in said coil exceeds a predetermined value, and opening said circuit when the current in said coil falls below a predetermined value.

3. In an electrical system, the combination of: two supply conductors; a load connected to the first of said supply conductors; a shunt through which current passes to said load from the second of said supply conductors; a relay having an actuating coil connected at its first end to one terminal of said shunt; a secondary resistor connected at one end to the other terminal of said shunt and at its other end to the second end of said actuating coil; a primary resistor; means by which said relay causes current to flow from said first conductor through said primary and said secondary resistors to said second conductor whenever the current in said shunt rises above a predetermined value, and causes a reduction in said current through said primary and said secondary resistors whenever the current in said shunt falls below said predetermined value; a ballast resistor connected at one end to one of said conductors; and means actuated by said relay for connecting the other end of; said ballast resistor to the other conductor whenever the current through said shunt falls below said predetermined value, and for reducing said current through said ballast resistor when said current through said shunt exceeds said value.

SOREN L. CHRISTIE.

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