US 3652923 A
An electrical circuit for coupling flashing light equipment to the series lighting circuit of an airport runway so as to obtain power for the operation of the flashing light. The circuit utilizes a series lighting ferro-resonant autotransformer of suitable power rating and having three windings to provide the desired power transfer.
Claims available in
Description (OCR text may contain errors)
United States Patent Knudson [451 Mar. 28', 1972  TRANSFORMER-COUPLING CIRCUIT  inventor: Clarence B. Knudsen, Inglewood, Calif.  Assignee: l-lughey & Phillips, Inc.
221 Filed: on. 12, 197 0  Appl. No.: 80,061
 US. Cl ..323/6, 323/45, 323/61,
336/ 148  Int. Cl ..G05f 3/06  Field ofSearch ..323/2,43.5,45,48,49, 60, 323/61, 92, 6; 336/148  References Cited UNITED STATES PATENTS 2,605,457 7/1952 Peterson 3 23/2 Blume ..336/148 X 3,344,341 9/1967 Bolton ..323/45 3,389,329 6/1968 Quirk et al ..'..323/48 X 1 Primary Examiner-Gerald Goldberg Attorney-Marvin Jabin [5 7] ABSTRACT An electrical circuit for coupling flashing light equipment to the series lighting circuit of an airport runway so as to obtain power for the operation of the flashing light. The circuit utilizes a series lighting ferro-resonant autotransformer of suitable power rating and having three windings to provide the desired power transfer.
5 Clai ns, 2 Drawing Figures TRANSFORMER-COUPLING CIRCUIT BACKGROUND OF THE INVENTION lating transformer.
There are two general types of series circuits in use: (a) a 6.6-ampere current for either medium or high intensity operation, with current variations down to 2.8 amperes for intensity control, and (b) a -ampere current for high intensity operation with current variations down to 8.5 amperes for intensity control.
At times it is desirable, mainly for economic reasons, to operate electrical devices which are not normally operable from a series circuit, from the series runway circuit. Such devices are Condenser Discharge Flashing Lights, Taxiway a normal lamp load, provides an essentially sinusoidal-output waveform, because the core does not become saturated. This is not true, however, when the series transformer is utilized to supply power to another transformer, because the load is no longer resistive. Under such operating conditions the series transformer core will be saturated, because a higher than normal voltage will appear across its primary, as a result of inductive effects. The voltage waveform at the secondary will appear highly distorted, principally because ofa high percentage of third and higher order harmonics in the transformer output. Such a waveform ordinarily cannot effectively be utilized to convey power in a transformer coupled circuit. Furthermore, it is customary in the series lighting arrangement to set the primary (series) current at various regulated values (constant current), which results in a substantial variation in amplitude of the third harmonic output.
SUMMARY OF THE INVENTION According to the preferred embodiment of the present in- BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:
FIG. 1 is a schematic diagram of a circuit according to the present invention.
FIG. 2 is a graph of voltage waveforms helpful in understanding the circuit of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the drawings, FIG. 1 shows a ferro-resonant type auto-transformer 11 having windings 13, 15 and 17 arranged as shown and wound on two sections of what is commonly referred to as a cruciform core 19. Winding 13 is a center-tapped winding wound on the short center leg of the core 19 and electrically connected in series with winding 15, which is a center-tapped winding wound on the long center leg of the core 19. Winding 17 is a few turns wound over winding 15 and connected in opposition thereto.
Capacitor 21 is connected across windings I5 and 17 so as to form a ferro-resonant circuit. All of the turns in winding 13 and one-half of the turns in winding 15 form the primary or input circuit, while one-half of the'turns in winding 13 and all of the turns in winding 15 opposed by the few turns in winding 17 form the secondary or output circuit.
The turns of the windings l3, l5 and 17 are so proportioned that ferro-resonance occurs at an input below the lowest primary current in the series isolation lighting transformer, which might be 2.8 amperes in a 6.6-ampere runway circuit. The regulating effect is not as pronounced at this low input as it is at higher input currents. The section of the core 19 associated with winding 13 also becomes partially saturated at the higher input current levels which enhances the regulation to a certain degree.
FIG. 2 shows waveform 31, which represents the distorted voltage at the secondary of a series isolation lighting transformer which ordinarily is used to supply power to another transformer. The series transformer core is saturated because a voltage which is higher than normal appears across its primary as a result of inductive effects. The voltage waveform at the secondary is highly distorted because of the high percentage of third and higher order harmonics in the transformer output, and ordinarily cannot effectively be used to convey power in a transformer-coupled circuit.
Waveform 33 shows the approximate waveform of the voltage appearing across the series-connected windings 15 and 17 which form the ferro-resonant circuit of FIG. 1.
Waveform 35 shows the approximate waveform of the voltage appearing across the section of winding 13 which is connected in series with the output circuit. The output of this winding consists mainly of third and fifth order harmonics of the fundamental frequency.
Waveform 37 showsthe approximate waveform of the voltage across the output terminals which results from in-phase addition of the voltages produced by the various windings.
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and that the intention is to cover all such changes and modifications as fall within the true spirit and scope of this invention.
1. A ferro-resonant transformer of the autotransformer type adapted for coupling a series isolation transformer to a utilization circuit, comprising:
a. a first tapped winding,
b. a second tapped winding connected in series with said first winding,
c. a third winding connected in series with and wound over said second winding and connected in opposition thereto,
d. a capacitor coupled across said second and third windings so as to form a ferro-resonant circuit therewith, input terminals coupled to said first winding and the tap of said second winding, and
f. output terminals coupled to the tap of said first winding and to said third winding.
2. A circuit as defined in claim 1 in which said firstwinding is wound on the short center leg of a cruciform core, and said second winding is wound on the long center leg of said cruciform core.
3. A circuit as defined in claim 2 in which said third winding has only a few turns.
4. A circuit as defined in claim 3 in which said first and second windings are center tapped.
5. A circuit as defined in claim 4 in which said first, second and third windings are so proportioned that ferro-resonance occurs at an input below the lowest primary current in said series isolation lighting transformer.