ON-LOAD TAP CHANGING TRANSFORMER

Abstract: An on-load tap changing trnsformer having a preselect­ ing switch which connects taps No.1, No.2, No.3, ... No.N to corresponding fixed contacts No.1, No.2, No.3, ... No.N during a standard connecting operation of a movable contact and connects additional taps No.N+1, No.N+2, No.N+3, .... No.N+M to corresponding fixed contacts during an additional connecting operation of a movable contact.

Description: 1. FIELD OF THE INVENTION This invention relates to an on-load tap changing transformer, and more particularly to an improvement in its tap changing. 2. DESCRIPTION OF THE RELATED ART From document DE-C-902 656, from which the preamble of present Claim 1 has been derived, an on-load tap changing transformer is known, which comprises a main winding, a tap winding having N standard taps, fixed contacts, movable contacts and selecting switches used as polarity switches. By means of the pre-selecting switches changing the polarity of the main winding more than N tap positions can be provided. In this prior art tap changing transformer no additional taps are provided. FIG.1A shows an on-load tap changing transformer of the prior art. Reference numeral 1 denotes a main winding of the transformer, reference numeral 2 denotes a tap winding, reference marks T₁, T₂, T₃ ,... T N denote taps provided on the tap winding 2, and reference numeral 4 denotes a tap selector (or a selector switch) having fixed contacts P₁, P₂, P3 ,... P N , each connected to the corresponding taps T₁ to T N . In case the numeral 4 is a tap selector, a diverter switch is used together therewith, as well-known. Its denotation is, however, intentionally omitted in the FIG. to avoid complicating explanation. Unless otherwise mentioned, the tap selector and the selector switch are hereinafter generically called "tap selector". The tap selector 4 has fixed contacts P₁ to P N arranged, for example, in uniform intervals on a circumference of a circle and has a movable contact 41, movable on the circumference of the circle. The tap selector 4 is an ordinary rotary type tap selector. As shown in FIG.1B, by rotating the movable contact 41, one of the fixed contacts P₁ to P N is selected in such an order as contacts P₁, P₂, P₃ .... P N . By further rotating the movable contact 41, one of the fixed contacts P₁ to P N is again selected in the order of contacts P₁ , P₂ , P₃ ... P N . By a reverse rotation of the movable contact 41, one of the fixed contacts P N to P₁ is selected in such order as contacts P N , P N-1 , P N-2 .... P₁. In this conventional on-load tap changing transformer, N tap positions are produced. FIG. 2A shows another prior art on-load tap changing transformer. Reference numeral 5 denotes an ordinary pre-selecting switch. The pre-selecting switch 5 is used as polarity switch. As shown in FIG.2B, by rotating the movable contact 41, one of the fixed contacts P₁ to P N is selected in such order as contacts P₁, P₂, P₃ .... P N . By further rotating the movable contact 41, the pre-selecting switch 5 is changed to a tap designated by (-) in FIG.2A. By further rotating the movable contact 41, one of the fixed contacts P₁ to P N is again selected in the order of contacts P₁, P₂, P₃.... P N . By a reverse rotation of the movable contact 41, one of the fixed contacts P N to P₁ is selected in such order as contacts P N , P N-1 , P N-2 .... P₁. In this conventional on-load tap changing transformer, 2N-1 tap positions are produced. FIG.3A shows still another prior art on-load tap changing transformer. Reference numeral 3 denotes a coarse tap winding. The pre-selecting switch 5 is used as coarse step switch. As shown in FIG.3B, by rotating the movable contact 41, one of the fixed contacts P₁ to P N is selected in such order as contacts P₁, P₂, P₃ .... P N . By further rotating the movable contact 41, the pre-selecting switch 5 is changed to a tap designated by (-). By further rotating the movable contact 41, one of the fixed contacts P₁ to P N is again selected in the order of the contacts P₁, P₂, P₃ .... P N . By a reverse rotation of the movable contact 41, one of the fixed contacts P N to P₁ is selected in such order as contacts P N , P N-1 , P N-2 .... P₁. In this prior art on-load tap changing transformer, 2N-1 tap positions are produced. In the prior art on-load tap changing transformers, only N of tap positions can be provided in case neither polarity switch nor coarse step switch (hereinafter called linear changing) are used. And, if more tap positions are necessary, the polarity switch or the coarse step switch must be provided. But the polarity switch or the coarse step switch cannot be used by limitation due to impedance of transformer. Therefore, in such a case, even if only 1 tap position is desired to be provided as additional one, a newly designed on-load tap changing transformer having N+1 contacts must be provided and used. OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to provide an improved on-load tap changing transformer having N+M taps using N contacts without using the polarity switch or the coarse step switch as in the prior art. This object is achieved by an apparatus in accordance with claim 1. In accordance with the present invention there is provided an on-load tap changing transformer comprising N fixed contacts No. 1 to No. N; a movable contact which contacts one fixed contact at a time; a main winding; a tap winding having N standard taps No. 1 to No. N, each of the respective standard taps being during a standard connecting operation of the movable contact in connection with its associated fixed contact; and preselecting switch means. The invention is constituted by the fact that the on-load tap changing transformer furthermore comprises M additional taps No. N+1 to No. N+M, each respective additional tap being associated with one of said fixed contacts No. 1 to No. N; and that the pre-selecting switch means is adapted to provide either said connecting of the standard taps No. 1 to N during the standard connecting operation of the movable contact or the connection of at least one of the additional taps No. N+1 to No. N+M to its/their associated fixed contact(/s) during an additional connecting operation of the movable contact. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1A shows a connection of a prior art on-load tap changing transformer. FIG.1B is a diagram for showing connecting condition of the on-load tap changing transformer of FIG.1A. FIG.2A shows a connection of another prior art on-load tap changing transformer. FIG.2B is a diagram for showing connecting condition of the on-load tap changing transformer of FIG.2A. FIG.3A shows a connection of still another prior art on-load tap changing transformer. FIG.3B is a diagram for showing connecting condition of the on-load tap changing transformer of FIG.3A. FIG.4A shows a preferred embodiment of an on-load tap changing transformer embodying the present invention in selecting a tap position No. 1. FIG.4B shows the preferred embodiment of the on-load tap changing transformer embodying the present invention in selecting a tap position No. N. FIG.4C shows the preferred embodiment of the on-load tap changing transformer embodying the present invention in selecting a tap position No. N+1. FIG.4D is a diagram for showing connecting condition of the on-load tap changing transformer of FIG.4A, 4B and 4C. FIG.5A shows another embodiment of the on-load tap changing transformer embodying the present invention. FIG.5B is a diagram for showing connecting condition of the on-load tap changing transformer of FIG.5A. FIG.6A shows still another embodiment of the on-load tap changing transformer embodying the present invention. FIG.6B is a diagram for showing connecting condition of the on-load tap changing transformer of FIG.6A. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The constitution of a preferred embodiment of an on-load tap changing transformer embodying the present invention is described in detail with reference to FIGs.4A, 4B and 4C. Reference numeral 1 denotes a main winding of transformer, reference numeral 11 denotes a tap winding having taps T₁, T₂, T₃ ... T N and an additional tap T N+1 , reference numeral 4 denotes a tap selector (or a selector switch) having fixed contacts P₁, P₂, P₃ ... P N , each connected to the corresponding taps T₁ to T N , and reference numeral 5 denotes a pre-selecting switch. One of fixed contacting points of the pre-selecting switch (point designated by (-) in FIG.4A) is connected to the tap T N+1 , another fixed contact point of the pre-selecting switch (point designated by (+) in FIG.4A) is connected to the tap T₁, and a movable contacting point 0 is connected to the fixed contact P₁. In FIG.4A, the pre-selecting switch 5 selects the point designated by (+), and the tap selector 4 selects the fixed contact P₁. As shown in Fig.4D, by rotating the movable contact 41, one of the fixed contacts P₁ to P N is selected in such order as contacts P₁, P₂, P₃ .... P N (hereinafter referred to as standard connecting operation). The state of selecting the contact P N is shown in FIG.4B. By further rotating the movable contact 41, the pre-selecting switch 5 is selected to the point designated by (-) (hereinafter referred to as additional connecting operation). Then the fixed contact P₁ is selected, as shown in FIG.4C. Thus, the fixed contact P₁ is connected to the tap T N+1 . In this embodiment, the N+1 tap positions can be selected in case that N fixed contacts are provided in a row of taps for the standard operation. FIG.5A shows another embodiment of the on-load tap changing transformer embodying the present invention. In FIG.5A, the tap winding 12 has the taps T₁, T₂, T₃ ... T N+2 , standard taps T₁, T₂, T₃ ... T N and additional taps T N+1 and T N+2 . Reference numeral 5 denotes a pre-selecting switch having a switch 5a and a switch 5b. In FIG.5A, the switches 5a and 5b select the point designated by (+), and the tap selector 4 selects the fixed contact P₁. As shown in FIG.5B, by rotating the movable contact 41, one of the fixed contacts P₁ to P N is selected in the order as contacts P₁, P₂, P₃ .... P N (standard connecting operation). By further rotating the movable contact 41, both the switches 5a and 5b are connected to the point designated by (-). Then the fixed contact P₁ is selected. Thus, the fixed contact P₁ is connected to the tap T N+1 . By further rotating the movable contact 41, the fixed contact P₂ is selected. Thus, the fixed contact P₂ is connected to the tap T N+2 . In this embodiment, the N+2 tap positions can be selected in case that N fixed contacts are provided. Although in the above embodiments the movable contact is successively contacted in such order as contacts P₁, P₂, P₃ .... P N , P₁, P₂ ...., in other modified embodiments the movable contacts may be successively contacted in such order as contacts P₁, P₂, P₃ .... P N , P N-1 , P N-2 .... , as shown in FIG.6A. In FIG.6A, one of the fixed contacting points of the switch 5a (point designated by (-)) is connected to the tap T N+1 , and another fixed contacting point of the switch 5a (point designated by (+)) is connected to the tap T N-1 . One of the fixed contacting points of the switch 5b (point designated by (-)) is connected to the tap T N+2 , and another fixed contacting point of the switch 5a (point designated by (+)) is connected to the tap T N-2 . As shown in FIG.6B, by rotating the movable contact 41, one of the fixed contacts P₁ to P N is selected in such order as contacts P₁, P₂, P₃ .... P N (the standard connecting operation). By reversely rotating the movable contact 41, both the switches 5a and 5b are connected to the point designated by (-). Then the fixed contact P N-1 is selected. Thus, the fixed contact P N-1 is connected to the tap T N+1 . By further reversely rotating the movable contact 41, the fixed contact P N-2 is selected. Thus, the fixed contact P N-2 is connected to the tap T N+2 . In other modified embodiments, the tap selector having fixed contacts P₁ to P N arranged in a line and endlessly and successively changing the fixed contacts may be used. As has been described in detail for various embodiments, in the present invention by using only N contacts and without the necessity of using the polarity switch or the coarse step switch, N+M tap positions can be obtained. Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form may be changed in the details of construction, and the combination and arrangement of parts may be resorted to without departing from the scope of the invention as hereinafter claimed.

Claims: An on-load tap changing transformer comprising: N fixed contacts No. 1, No. 2, No. 3 ... No. N (P₁ to P N ), a movable contact (41) which contacts one fixed contact (P₁ to P N ) at a time, a main winding (1), a tap winding (11, 12) having N standard taps No. 1, No. 2, No. 3 ... No. N (T₁ to T N ), each of said respective standard taps being during a standard connecting operation of the movable contact (41) in connection with its associated fixed contact (P₁ to P N ), and pre-selecting switch means (5), characterized in that M additional taps No. N+1, No. N+2, No. N+3 ... No. N+M (T N+1 to T N+M ), each respective additional tap being associated with one of said fixed contacts No. 1, No. 2, No. 3 ... No. N (P₁ to P N ), are provided, said pre-selecting switch means (5) is adapted to provide either said connecting of the standard taps No. 1 to N (T₁ to T N ) during the standard connecting operation of the movable contact (41) or the connection of at least one of said additional taps No. N+1, No. N+2, No. N+3 ... No. N+M (T N+1 to T N+M ) to its/their associated fixed contact(/s) (P₁ to P N ) during an additional connecting operation of the movable contact (41). The on-load tap changing transformer in accordance with claim 1, wherein said pre-selecting switch means (5) has at least one switch having two fixed connecting points and a movable connecting point, one of said fixed connecting points being connected to the associated one of said standard taps No. 1, No. 2, No. 3 ... No. N (T₁ to T N ), the other fixed connecting point being connected to the associated one of said additional taps No. N+1, No. N+2 ... No. N+M (T N+1 to T N+M ) and the movable connecting point being connected to the associated one of said fixed contacts No. 1, No. 2, No. 3 ... No. N (P₁ to P N ). The on-load tap changing transformer in accordance with claim 1, wherein said pre-selecting switch means (5) has at least one switch having two fixed connecting points and a movable connecting point, one of said fixed connecting points being connected to the associated one of said standard taps No. 1, No. 2, No. 3 ... No. N-1 (T₁ to T N-1 ), the other fixed connecting point being connected to the associated one of said additional taps No. N+1, No. N+2 ... No. N+M (T N+1 to T N+M ) and the movable connecting point being connected to the associated one of said fixed contacts No. 1, No. 2, No. 3 ... No. N-1 (P₁ to P N-1 ). The on-load tap changing transformer in accordance with claim 2 or 3, wherein said pre-selecting switch (5) is switched over when the position of said movable contact (41) is switched from the fixed contact No. N (P N ) to the fixed contact No. 1 (P₁) and when the position of the movable contact (41) is switched from the fixed contact No. N (P N ) to the fixed contact No. N-1 (P N-1 ). The on-load tap changing transformer in accordance with claim 2 or 3, wherein said pre-selecting switch (5) is switched over when the position of said movable contact (41) is switched from the fixed contact No. N (P N ) to the fixed contact No. N-1 (P N-1 ).

Inventors: YOSHIDA, KAZUO ITAMI SEISAKUSHO
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1986
Main classification: H01F29
IPC codes: H01F29