473,276

PATENT SPECIFICATION

Application Date: March 10, 1936. No. 7206/36.

Complete Specification Left: Feb. 9, 1937.

Complete Specification Accepted: Oct. 11, 1937.

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PROVISIONAL SPECIFICATION

Improvements in or relating to Rectifiers for Alternating Current

I, ALAN DOWER BLUMLEIN, a British Subject, of 32, Audley Road, Ealing, London, W.5, do hereby declare the nature of this invention to be as follows:-

This invention relates to rectifiers used for providing D.C. from A.C. power supply and refers in particular to rectifiers having two or more rectifying units or valves operating in turn.

It is usual in such rectifiers, as for example a biphase rectifier, to feed the rectifying units from an alternating current transformer of low leakage reactance and to put a large choke impedance in series with the rectifier on the D.C. side.

The choke impedance is so large that it maintains a substantially constant current flowing from the rectifier tubes. The voltage across the transformer secondary is sinusoidal voltage and the output voltage across, say, a condenser, is supplied by the inductance of the choke. Each valve operates in turn, the output current to the choke being constant and made up of "rectangular current pulses" from the rectifying valves.

The waveform obtained in the A.C. circuit, assuming a perfect rectifying conduction and zero regulation impedance is square topped. In practice if the leakage reactance of the transformer or the reactance of the supply feeding is appreciable, it is impossible to pass the square topped current through the alternating current circuit, with the result that there is appreciable hand-over between the two rectifiers, that is to say both rectifiers are operating at the same time. This leads to poor regulation from the device and inefficient working.

The main object of the present invention is to eliminate such troubles due to leakage reactance in the alternating current circuit, and to provide a rectifier having better regulation and operating more efficiently.

The invention consists in an A.C. rectifier, having two or more rectifying units or valves operating in turn, connected to an A.C. circuit which has a high impedance for all frequencies except the fundamental frequency of the A.C. and having a shunt capacity across the rectifier output leads.

The invention further consists in an A.C. rectifier having two more rectifying units or valves operating in turn, wherein the current taken by each rectifying unit or valve is in form substantially a portion of a sine wave, and the voltage across the secondary winding of a transformer connected to the rectifying units or valves, is flat-topped in form, at least during the operation of the rectifier connected thereto.

The nature of the invention will become apparent from the following description of one form which it may assumed, which form is, however, described merely by way of example.

In carrying the invention into effect in one convenient manner as applied to a biphase rectifier, the A.C. to be rectified is fed through a series inductance and capacity to the primary winding of a transformer, while the cathodes of two rectifying valves are connected one each to the two extremities of the secondary winding of said transformer. The anodes of the rectifying valves are connected together and to one of the D.C. leads, while the other lead is centre tapped on the secondary winding of the transformer, and across these two D.C. leads is connected a shunt condenser. The series inductance and capacity in the input circuit are of such valves that the circuit is in resonance to the A.C. supply frequency. In this arrangement the rectifiers operate with sinusoidal-like currents and with square-topped applied voltage. The condenser in series with the primary transformer winding may be adjusted so that, together with the added inductance, it will tune out the leakage inductance of the transformer, and if desired the leakage inductance of the A.C. supply may also be tuned out in this way. Similarly, the transformer may be wound with very high leakage inductance so that additional inductance is not required.

When the invention is employed in a polyphase rectifier a tune circuit is connected in each phase.

The invention appears particularly suitable for operation with hot cathode mercury rectifiers, since no sudden increase or stoppage of current is required, but it is not limited to such use, and may be employed, for example, with rectifiers of the oxide type, or of the mercury pool type in which the various rectifier units are usually contained in the same envelope and share a common cathode. Furthermore, it should be understood that the invention is not limited solely to the details of the arrangement described above since various modifications may be introduced as they become desirable or necessary in order to carry the invention into effect under different conditions and requirements which have to be fulfilled, without departing in any way from the scope of the invention.

Dated this 10th day of March, 1936.

F. W. CACKETT,

Chartered Patent Agent.

COMPLETE SPECIFICATION

Improvements in and relating to Rectifiers for Alternating Current

I, ALAN DOWER BLUMLEIN, a British subject, of 32, Audley Road, Ealing, London, W.5, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:

This invention relates to rectifiers used for providing direct current from and alternating current power supply and is concerned with rectifiers employing two or more rectifying units or valves operating sequentially.

It is usual in such rectifiers, as, for example, a full wave rectifier, to feed the rectifying units from a transformer of low leakage reactance and to insert a large choke impedance in series with the rectifier on the output or direct current side. The magnitude of the choke impedance is such that it maintains a substantially constant current flowing from the rectifying units or valves. The voltage across the secondary winding of the transformer is sinuosoidal and the difference between the sinusoidal voltage and the output voltage across for example a shunt condenser in the direct current leads is supplied by the inductance of the choke. Each unit or valve operates in turn, the output current to the choke being constant and composed of "rectangular current pulses" from the rectifying valves.

The current wave form obtained in the alternating current circuit assuming a perfect rectifying conduction and zero regulation impedance is square topped. In practice it is found that if the leakage reactance of the transformer or the reactance of the supply feeding the rectifier is appreciable it is impossible to pass the square topped current impulses through the alternating current circuit with the result that distortion of the current wave form occurs, and there is consequently appreciable overlapping between the operation of the two rectifiers, that is to say, during certain periods both rectifiers operate simultaneously. This leads to poor regulation from the rectifier and inefficient working.

In addition, where the rectifying units or valves are of the kind which depend for their operation on the ionisation of a gas it is found that owing to the form of the current impulses, particularly at high frequencies, that the rectifying units or valves do not ionise sufficiently quickly to pass the rapidly rising current with the result that in the hot cathode type, heavy electron currents flow causing disintegration of the cathode.

The chief object of the present invention is to provide an improved rectifier with a view to overcoming or reducing these defects.

According to one aspect of the invention, an alternating current rectifier is provided having two or more rectifying units or valves adapted to operate in turn and connected to the secondary winding of a transformer to the primary winding of which the alternating current to be rectified is applied and a storage condenser of condensers is or are, connected across the output leads of the rectifier and the arrangement is such that the alternating current circuit presents a high impedance to all frequencies present in such circuit during operation of the rectifier except to the fundamental frequency of the supply so that substantially only the fundamental frequency flows through said primary winding.

According to a further aspect of the invention, there is provided a method of obtaining direct current from an alternating supply which consists in employing two or more rectifying units connected to the secondary winding of a transformer and adapted to operate in turn, the primary winding of which is connected to the alternating current supply, and in arranging that the current taken by each rectifying unit or valve is in form substantially a portion of a sine wave, and in arranging that the voltage across the secondary winding of the transformer and as applied to each rectifier is substantially flat topped in form at least during the operation of each rectifier.

According to a further feature of the invention, an alternating current rectifier is provided comprising two or more rectifying units or valves connected to the secondary winding of a transformer, and a storage condenser or condensers connected across the direct current supply leads from the rectifying units or valves, the primary winding of the transformer being adapted to be connected to the alternating current supply and either the primary or secondary winding having in series therewith an inductance and condenser adapted to be tuned to the frequency of the alternating current applied to said primary winding whereby substantially only the fundamental frequency of the supply flows through said primary winding.

The invention may be employed for the purpose of obtaining direct current from a single phase supply or it may be employed as hereinafter referred to for the purpose of obtaining direct current from a polyphase supply.

The invention may also be employed in connection with rectifiers which are arranged to operate as voltage doublers.

In order that the said invention may be clearly understood and readily carried into effect, the same will now be more fully described with reference to the accompanying drawings, in which:-

Figure 1 is a circuit diagram of a rectifier constructed in accordance with the invention,

Figure 2 illustrates the wave forms of the current in the rectifying units of Figure 1 and the voltage across the secondary winding of the transformer, and

Figure 3 is a circuit diagram of a rectifier constructed in accordance with the invention and adapted to operate as a voltage doubler.

The rectifier shown in Figure 1 is a full-wave rectifier and employs a pair of gaseous hot cathode discharge valves indicated by the reference numerals 4 and 5 respectively, the cathodes of the two valves are connected together and to one of the direct current leads 7, the other direct current lead 8 being centre tapped to the secondary winding 6 as shown. The cathode heating means are not shown. The storage condenser 9 is connected across the direct current leads 7 and 8. Alternating current to be rectified is obtained from any suitable source conventionally represented in Figure 1 at 10, the source being connected to the primary winding 11 of the transformer. In series with the source 10 and the primary winding 11 is an inductance 12 and a condenser 13 which are adapted to be tuned to the resonant frequency of the supply so that the alternating current circuit presents a high impedance to all frequencies obtained in the alternating current circuit except the frequency of the supply. With such an arrangement it is found that the rectifiers operated with sinusoidal-like currents as shown in Figure 2, the current impulses through the valve 4 being indicated at A in Figure 2 and the current impulses through the valve 5 being indicated by B. It is also found that the voltage across the secondary winding of the transformer is substantially flat topped as diagrammatically represented at C in Figure 2 and with current wave forms and voltage impulses as shown the disadvantages herein before referred to are substantially overcome. The condenser 13 may be adjusted so that together with the inductance 12 it will tune out the leakage inductance of the transformer, and if desired the leakage inductance of the alternating current supply may also be tuned out in this manner.

Figure 3 of the drawings illustrates a single phase full wave rectifier in accordance with the invention adapted to operate as a voltage double. Two hot cathode (cathode heating means not shown) gaseous discharge valves 14 and 15 are employed, the anode of valve 14 and the cathode of the valve 15 being connected to one end of the secondary winding 16 of a transformer. The cathode of the valve 14 is connected to one output lead 17, and the anode of valve 15 is connected to another lead 18 whilst shunted across the two leads 17 and 18 are two storage condensers 19 and 20 in series and to the junction between which the other end of the secondary winding 16 of the transformer is connected as shown.

The primary winding 21 is connected to the alternating current source indicated conventionally at 22 and in series with the sources of primary winding 21 is an inductance 23 and a condenser 24 for the purpose aforesaid.

In some cases the inductances 12 and 23 in Figures 1 and 3 may be omitted and the transformer may be so wound as to present a leakage inductance of such magnitude as to tune with the condenser 13 or 24 for the purpose aforesaid. Similarly the storage condenser of condensers provide a certain amount of negative reactance which can be allowed for when tuning the series resonate circuit.

The invention may also be employed for obtaining direct current from a polyphase supply and in such an application a tune circuit will be provided in each phase of the supply.

If desired, both in the example of the invention shown in Figure 1 and also the example shown in Figure 3 a condenser may be inserted in series with the secondary winding of the transformer so as to tune out the effect of the leakage inductance of the transformer, or part or all of the tune circuit may be put in the secondary winding.

The invention may also be applied to circuits in which a ladder of rectifiers is employed feeding into a number of condensers.

The invention has been described by way of example with the use of hot cathode gaseous rectifiers, but the invention is also particularly suitable for use with other types of rectifiers such as thermionic, cold cathode, electrolytic etc.

Reference has been made in the above description to "two rectifying units or valves," and it is to be understood that this term includes the case in which the anodes of the two units are contained in the same envelope and are associated with a common cathode.

The storage condenser or condensers shown may be followed by further stages of smoothing.

Having now particularly described and ascertained the nature of my said invention, and in what manner the same is to be performed, I declare that what I claim is:-

  1. An alternating current rectifier comprising two or more rectifying units or valves adapted to operate in turn and connected to the secondary winding of a transformer to the primary winding of which the alternating current to be rectified is applied and a storage condenser or condensers is or are connected across the output leads of the rectifier, the arrangement being such that the alternating current circuit presents a high impedance to all frequencies present in such circuit during operation of the rectifier, except to the fundamental frequency of the supply so that substantially only the fundamental frequency flows through said primary winding.
  2. A method of obtaining direct current from an alternating current supply which consists in employing two or more rectifying units connected to the secondary winding of a transformer and adapted to operate in turn, the primary winding of which is connected to the alternating current supply and in arranging that the current taken by each rectifying unit or valve is in form substantially a portion of a sine wave and arranged that the voltage across the secondary winding of the transformer and as applied to each rectifier is substantially flat topped in form at least during operation of each rectifier.
  3. An alternating current rectifier comprising two or more rectifying units or valves connected to the secondary winding of a transformer and a storage condenser or condensers connected across the direct current supply leads from the rectifying units or valves, the primary winding of the transformer being adapted to be connected to the alternating current supply and either the primary or secondary winding having in series therewith an inductance and a condenser adapted to be tuned to the frequency of the alternating current applied to said primary winding whereby substantially only the fundamental frequency of the supply flows through said primary winding.
  4. An alternating current rectifier as in Claim 3, wherein the capacity of the condenser in the alternating current circuit is such as to tune out both any added inductance and the leakage inductance of the transformer and/or the leakage inductance of the alternating current supply.
  5. An alternating current rectifier as in Claim 3, wherein the transformer is so constructed as to present a leakage inductance of such a magnitude that it will tune with the said condenser to the frequency of the alternating current supply.
  6. An alternating current rectifier as in any of the preceding Claims 1 or 3 to 5, wherein the rectifying units and the transformer are so arranged in conjunction with a pair of shunt condensers as to function as a voltage doubler.
  7. An alternating current rectifier substantially as described with reference to Figures 1 and 2 or 2 and 3 of the accompanying drawings.
  8. A method of obtaining direct current from an alternating current supply substantially as described with reference to the accompany drawings.

Dated this 9th day of February, 1937.

F. W. CACKETT,

Chartered Patent Agent.

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Leamington Spa: Printed for His Majesty’s Stationery Office, by the Courier Press. – 1937.