GB1597665A - Voltage regulating transformer - Google Patents

Description

(54) VOLTAGE REGULATING TRANSFORMER (71) We, FREQUENCY TECHNOLOGY, INC., a corporation of the State of Massachusetts, United States of America, of Whitcomb Avenue, Littleton, Massachusetts, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates generally to voltage-regulating transformers and more specifically to voltage-regulating transformers of the ferro-resonant type.

Voltage-regulating ferro-resonant transformers are well known. These transformers comprise a primary winding, a tuned secondary circuit including the secondary winding, and an electro-magnetic shunt. The output of the tuned secondary circuit is essentially constant. Within a normal-range of input voltages, the secondary circuit resonates and drives the core into saturation. Thus, the secondary voltage remains substantially constant notwithstanding changes in the input voltage.

Such prior voltage regulating transformers are bulky. Furthermore, magnetic circuits in which flux transfers between a closed core and an abutting or integral shunt are characterized by eddy current losses which reduce the overall transformer efficiency.

Therefore, it is an object of this invention to provide ferro-resonant voltage regulating transformer which can be made in a compact form.

Accordingly the present invention consists in a ferro-resonant voltage regulating transformer, comprising: first and second separate permeable magnetic cores spaced by an air gap, said first core comprising a closed magnetic core and said second core having an air gap, a primary winding for connection to a source of alternating current of fluctuating voltage and arranged around portions of said cores for inducing magnetic flux therein, a secondary winding having first and second terminals, said secondary winding being arranged around a portion of said first core, so that a voltage is induced in said secondary winding in response to the magnetic flux in said first core, means for regulating the level of the magnetic flux in the first core comprising a capacitor connected across the secondary winding to provide a resonant circuit, whereby a substantial flux flows in said second core when the flux in said first core increases beyond a preselected level, a direct coupling secondary winding arranged around said primary winding, said primary winding inducing a voltage in said direct coupling secondary winding proportional to the primary voltage, a secondary correction winding around a portion of said second core, said correction winding being connected in series with said secondary winding and said direct coupling secondary winding so that the regulated output voltage is the sum of the voltages across said secondary winding, said direct transfer secondary winding and the correction winding, and whereby the flux in said second core induces a voltage in said correction winding to compensate for fluctuations in the voltage across said direct transfer winding.

Thr transformer may also include a gap partially through said first core for decreasing the saturation flux of that core.

In order that the present invention may be more readily understood, one embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which Figure 1 is a schematic diagram of a voltage regulating transformer constructed in accordance with the invention; Figure 2 is a vector diagram showing the amplitude and phase relationships of the voltages and magnetic flux in the transformer, and Figure 3 is a vector diagram showing the components of the regulated output voltage.

Figure 1 shows a regulating transformer 12 connected to receive an unregulated voltage from an ac power source 10 and energizes an electrical load 14. Typically, the voltage from the power source 10 is subject to variations of + 15%.

In Figure 1, the source 10 connects to input terminals 16 and 18 for the regulating transformer. The transformer 12 comprises laminated magnetic cores 20 and 22, each of which comprises a plurality of magnetically permeable laminations 24. The core 20 constitutes a closed magnetic circuit having vertical legs 20a and 20b connected by horizontal legs 20c. Core 22 comprises horizontal legs 22a and 22b, a vertical leg 22c close to but spaced from the leg 20a and another vertical leg 22d which includes an air gap 26. Legs 20a and 22b are separated by an air gap 27.

A primary winding 28 is wrapped around core legs 20a and 22c. A secondary winding 30, on the leg 20b, is connected in parallel with a capacitor 32 to form a resonant circuit.

A voltage Vin applied to terminals 16 and 18 induces a flux in in cores 20 and 22. The flux #in has components #a in core 20 and #b in core 22.

The voltage VR across the winding 30 is a function of the saturation flux of core 20, #as, the frequency, F, of the input voltage and the number of turns, N of the winding 32, i.e., to a rough approximation: VR = 4Nas F.

VR provides a regulated output voltage at terminals A and B of transformer 12.

The reluctance of the magnetic circuit comprising core 22 and gap 28 is considerably higher than the reluctance of the closed magnetic circuit 20. Thus, as in changes, #a tends to lead b in time. After winding 20 saturates, however, flux b accounts for substantially all further increases in #in. Since #in = #a + #b, #b varies in amplitude and phase with relation to so so as to assist in maintaining the magnitude of #a constant with variations in #in.

Within normal primary voltage variations, only core 20 saturates. Core 22 functions as a reactance in series with transformer core 20, which reactance increases as the input voltage increases. This core normally operates at substantially less than its saturation level and consequently there is less total loss in the system over a range of varying load conditions than in prior voltage regulating transformers wherein the entire core structure saturates.

Figures 2A and 2B show the amplitude and phase relationships of various voltages and fluxes in core 12 of Figure 1. Figure 2A shows V10 at its normal line level and the resultant flux #in . #in comprises, in part, #a which induces voltage VR. Figure 2B shows Vin increased to the high line condition and in correspondingly increased. #a and VR remain constant for the reasons noted above and #b is shown to vary in phase and amplitude from Figure 2A so that: = = Qua + b A direct-coupling secondary winding 34 is arranged around core legs 20a and 22c, e.g.

around primary winding 28. A voltage V/jn, induced in winding 34, is proportional to Vjn.

The windings 30 and 34 are connected in series to form a partially regulated output voltage between terminals A and C. If V'in is less than Vf0, the output voltage (V'in + VR) varies less than Vin and thus this circuit provides a degree of regulation of V10 which is adequate for many purposes. The use of the direct-coupling winding 34 is desirable since it reduces the proportion of the load power which is regulated by the transformer 12 and thereby reduces the losses in the core structure.

Furthermore, as shown in Figure 1, a correction winding 36 is arranged around leg 22d. A voltage Vc is induced in windmg 36 by flux b- Windings 30, 34 and 36 are connected in series to produce an output voltage V0 between terminals A and D. In this embodiment the capacitor 32 is across only a portion of the output voltage and can, therefore, have a lower voltage rating.

Since VR is essentially constant, winding 36 can be arranged so that (V'10 - Vc) is constant thereby eliminating the voltage variations in Vljn. Actually, VR increases somewhat with V10 and I therefore prefer to arrange the winding 36 to make changes sufficiently to compensate for changes in VR as well as V'10. More specifically, winding 36 has a sufficient number of turns with respect to windings 30 and 34 so that Vc compensates for changes in VR and V'10.

Figure 3A is a vector diagram of Vin, VR, V'in, VC and V0 for normal line voltage. The diagram expresses the vector relation: VR + V in + Ve = VO- Figure 3B is a vector diagram showing the same quantities as Figure 3A with V10 in a high voltage condition and V'jn increased proportionately. Vc has varied in amplitude and phase so that V0 remains essentially constant.

Since the cores 20 and 22 are magnetically independant the winding 28 shown in Figure 1 may comprise two series windings, one on the leg 20a and the other on the leg 22c. The input voltage Vjn is distributed between the windings so that the Q and b vary as described above.

WHAT WE CLAIM IS: 1. A ferro-resonant voltage regulating transformer, comprising: first and second separate permeable magnetic cores spaced by an air gap, said first core comprising a closed magnetic core and said second core having an air gap, a primary winding for connection to a source of alternating current of fluctuating voltage and arranged around portions of said cores for inducing magnetic flux therein, a secondary winding having first and second terminals, said secondary winding being arranged around a portion of said first core, so that a voltage is induced in said secondary winding in response to the magnetic flux in said first core, means for regulating the level of the magnetic flux in the first core comprising a capacitor connected across the secondary winding to provide a resonant circuit, whereby a substantial flux flows in said second core when the flux in said first core increases beyond a preselected level, a direct coupling secondary winding arranged around said primary winding, said primary winding inducing a voltage in said direct coupling secondary winding proportional to the primary voltage, a secondary correction winding around a portion of said second core, said correction winding being connected in series with said secondary winding and said direct coupling secondary winding so that the regulated output voltage is the sum of the voltages across said secondary winding, said direct transfer secondary winding and the correction winding, and whereby flux in said second core induces a voltage in said correction winding to compensate for fluctuations in the voltage across said direct transfer winding.

2. A voltage regulating transformer as claimed in Claim 1 and further comprising a gap partially through said first core for decreasing the saturation flux of that core.

3. A ferro-resonant voltage regulating transformer substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. Figure 3B is a vector diagram showing the same quantities as Figure 3A with V10 in a high voltage condition and V'jn increased proportionately. Vc has varied in amplitude and phase so that V0 remains essentially constant. Since the cores 20 and 22 are magnetically independant the winding 28 shown in Figure 1 may comprise two series windings, one on the leg 20a and the other on the leg 22c. The input voltage Vjn is distributed between the windings so that the Q and b vary as described above. WHAT WE CLAIM IS:

1. A ferro-resonant voltage regulating transformer, comprising: first and second separate permeable magnetic cores spaced by an air gap, said first core comprising a closed magnetic core and said second core having an air gap, a primary winding for connection to a source of alternating current of fluctuating voltage and arranged around portions of said cores for inducing magnetic flux therein, a secondary winding having first and second terminals, said secondary winding being arranged around a portion of said first core, so that a voltage is induced in said secondary winding in response to the magnetic flux in said first core, means for regulating the level of the magnetic flux in the first core comprising a capacitor connected across the secondary winding to provide a resonant circuit, whereby a substantial flux flows in said second core when the flux in said first core increases beyond a preselected level, a direct coupling secondary winding arranged around said primary winding, said primary winding inducing a voltage in said direct coupling secondary winding proportional to the primary voltage, a secondary correction winding around a portion of said second core, said correction winding being connected in series with said secondary winding and said direct coupling secondary winding so that the regulated output voltage is the sum of the voltages across said secondary winding, said direct transfer secondary winding and the correction winding, and whereby flux in said second core induces a voltage in said correction winding to compensate for fluctuations in the voltage across said direct transfer winding.

2. A voltage regulating transformer as claimed in Claim 1 and further comprising a gap partially through said first core for decreasing the saturation flux of that core.

3. A ferro-resonant voltage regulating transformer substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.