About 35kV48-level line-end voltage regulating combined on-load tap-changer

1 Introduction

Since Dr. Bernhard Jansen of Germany invented the proprietary technology of on-load voltage-regulating tap-changer with resistance transition and fast switching in 1926, on-load tap-changer has been widely used in countries around the world. SYXZ-200 switch is a Soviet-style product in my country in the 1950s and 1960s, and has accumulated decades of manufacturing and operating experience.

Most of the existing SYXZ-200 switches on the market have neutral point voltage regulation and the number of levels does not exceed 27. However, with the development of electrochemical industrial production, the demand for switches with line-end voltage regulation and a large number of levels continues to increase.

However, if the 48-level line-end voltage-regulating on-load tap-changer is designed and manufactured according to the SYXZ-400 switch structure model, its outer diameter and height dimensions will increase, which will relatively increase the cost.

So is it possible to achieve 48-level line-end voltage regulation without increasing the outer diameter and height dimensions?

2 Existing combined on-load tap-changer status

In the early 1980s, Wujiang Switch Factory (Wujiang Yuanyang Electric Co., Ltd.) introduced SYXZ-400 and SYXZ-200 switches from Shenyang and Changzhou transformer factories for large-scale production. The main transmission systems of these two switches adopt the middle shaft structure, and they are divided into two structures from the transformer installation: box top type (with box cover) and bell type (without box cover). Their installation structures must rely on the raised seat welded on the transformer box cover for sealing, and the sealing effect of their sealing structure is not very ideal. The box top type SYXZ-400 and SYXZ-200 switches are hoisted on the lower plane of the raised seat with a φ660*60/φ510*48 (the following dimensions are all in millimeters, mm) flange respectively. Their plane seal and radial seal are not convenient for actual use and it is not easy to observe the specific leakage location.

SYXZ-400 switch belongs to the embedded type four-resistance transition combined on-load tap-changer, and SYXZ-200 switch belongs to the embedded type double-resistance transition combined on-load tap-changer. Both switches are composed of a transfer switch and a tap selector, and are operated by an electric mechanism installed on the transformer box. The conversion operation is that the single and double moving contacts of the tap selector alternately select the taps and combine with the transfer switch. The tap selector and the transfer switch can be used together to achieve the purpose of voltage regulation, and this on-load voltage regulation method of selecting the tap voltage first and then switching the current is the most ideal, safest and reliable.

The quick mechanism of the switching switch of these two switches is located below the flange at the bottom of the oil chamber - in the middle of the entire switch, and the main transmission shaft system depends on the position of the quick switching mechanism, so the original design structure is a middle shaft output because it is natural. The switching switch core uses three copper flanges, and the neutral point is naturally conductive, so these two switches are neutral point voltage regulation. For the realization of D connection, please refer to a paper published by me in the third issue of "Transformer" magazine in 2003. In simple terms, the three copper flanges are made into insulating flanges. Therefore, it is not difficult to design and manufacture these two switches into line-end voltage regulation.

3 Comparison of two structural mode design and manufacturing schemes

In actual use and related test data, it is proved that the effect of four-resistance transition is not as good as that of two-resistance transition, and the working environment of 48-level switch is relatively poor, and the gear adjustment is quite frequent, so the 48-level switch designed and manufactured by Shenyang Transformer Factory in accordance with the SYXZ-400 switch structure model follows this rule. Its special 48-level voltage regulation circuit is different from the voltage regulation circuit used by foreign multi-level regulating switches. It can realize the combination of coarse and fine regulation, positive and negative regulation, and is a power-saving and energy-saving 48-level switch worthy of promotion.

The following rules should be followed when designing a switch with 48 levels of coarse and fine adjustment and forward and reverse adjustment:

(1) The oil chamber of the SYXZ-400 switch structure is φ500/φ524*900, the tap selector with a left and right parallel double-axis structure has an energized outer diameter of φ785 and an installation height of 2140.

(2) The oil chamber of the SYXZ-200 switch structure model is φ400/φ420*610, the tap selector with a left and right parallel double-axis structure has an energized outer diameter of φ680 and an installation height of 1887.

(3) The fine-tuning selector (fine-tuning winding) has 8 levels, and its sheave mechanism adopts a standard sheave mechanism divided into 8 equal parts.

(4) The coarse adjustment selector (coarse adjustment winding) is 6-stage, and its sheave mechanism adopts an 8-equal-division standard sheave mechanism or a 10-equal-division standard sheave mechanism.

(5) The main transmission shaft system is a welded head flange designed for the 48-level switch box top installation structure with a top-out shaft structure. Attention should be paid to the positional relationship between the head flange and the bottom flange of the oil chamber. A position indication mechanism can also be conveniently added next to the angle ruler gear box on the head flange to solve the long-standing problem of no position indication on the switch body, while also improving the safe operation of the switch.

(6) The main transmission shaft system is a 48-level switch box top installation structure with a central shaft structure and the old structure can still be used.

(7) The transfer switch adopts double resistance transition. The rated current is 200A for one set of working contacts, the rated current is 400A for two sets of working contacts, and the rated current is 600A for three sets of working contacts.

(8) When using a line-end voltage regulator, pay attention to the insulation technology and measures used.

(9) The electric mechanism must be able to adjust gears step by step without gear slippage, so as to facilitate maintenance.

4. Implementation and discussion of the two structural mode design and manufacturing solutions

At present, there are two switches with 48 levels of coarse and fine adjustment and positive and negative adjustment on the market: SYTZ15/600-48 produced in Shenyang and SYTZ35/400-48 produced in Wujiang. Among them, SYTZ35/400-48 produced in Wujiang is designed by me according to the structural mode of SYXZ-200 switch, and the designed switch does not use planetary gears but uses ball slider mechanism to complete rolling switching. The switch uses several groups of working contacts in parallel to make the switch rated current reach 400A, 600A, and 800A respectively. The contact system of the tap selector adopts ear plate type or wide plate type fixed contact combined with several groups of strip moving contacts to make the rated current reach 800A. In terms of voltage regulation level, not only the linear adjustment can reach 40 levels, but also the coarse and fine adjustment can reach 108 levels, which completely broadens its application field. These products are used in special transformers of many transformer factories, including Xiangtan Huaxia Special Transformer Company, Zhangjiagang Wuzhou Transformer Company, Handan Transformer Factory, Baoding North China Power Transformer Factory, etc. At the same time, since the main transmission shaft system is a top-exit shaft structure, and the UCGRN series switches produced by ABB and the G-type switches produced by MR are all top-exit shaft structures, they have received a certain degree of praise from users.

The SYTZ15/600-48 produced in Shenyang was the first one produced in China at that time. It was designed according to the SYXZ-400 switch structure mode. Since the main transmission shaft system is still a central shaft structure, the structure is relatively mature. Figure 1 shows the distribution diagram of the SYTZ15/600-48 tap selector produced in Shenyang, and Figure 2 shows the distribution diagram of the SYTZ35/400-48 tap selector produced in Wujiang. Both are based on the 8-position standard selector structure, adopting a left and right parallel double-axis structure, the coarse adjustment selector (coarse adjustment winding) is 6 levels, the fine adjustment selector (fine adjustment winding) is 8 levels, and the groove wheel mechanism adopts an 8-equal standard groove wheel mechanism. In order to prevent the fixed contacts between the coarse adjustment selector and the fine adjustment selector from interfering with each other, the fixed contacts of the fine adjustment selector must be designed as a wide plate type, that is, the fine adjustment selector is designed as a five-insulating strip frame and the coarse adjustment selector is designed as a seven-insulating strip frame.

Figure 1 shows the distribution diagram of the 48-level tap selector produced in Shenyang

Figure 2 shows the distribution diagram of the 48-level tap selector 8 produced in Wujiang

5 Features of SYTZ35/400-48

SYTZ35/400-48 produced in Wujiang is a product with independent intellectual property rights developed by me based on user needs and on the basis of a structure that has been tested for long-term operational reliability. It has unique innovation and practicality. Figure 3 is a photo of SYTZ35/400-48 with 35KV neutral point voltage regulation, and its installation height is 1827.

(1) SYTZ35/400-48 is evolved from SYXZ-200 switch. The outstanding effect of this evolution is that only some drawings are slightly changed, and very few parts are lengthened or strengthened. Without major changes in all other production processes, outsourcing purchases, and tooling equipment, the entire manufacturing process of a new product can be completed, so the price is reasonably low.

(2) A square gear box is installed on the shaft outlet hole on one side of the head flange of SYTZ35/400-48. One end of the square gear box is vertically introduced into the middle of the switch body through an insulating shaft, and the other end is designed with a position indicator mechanism to ensure that the gear position is correct, which is very convenient for maintenance and inspection.

(3) The maximum live external dimension of the outlet pile head on the oil chamber of SYTZ35/400-48 transfer switch is φ520. Considering the interchangeability with the V-type switch, the opening of the transformer box cover is determined to be φ570 and the outer diameter of the head flange is φ660.

(4) The coarse adjustment selector of SYTZ35/400-48 tap selector has 6 levels. Its grooved wheel mechanism can adopt a 10-level standard grooved wheel mechanism instead of an 8-level standard grooved wheel mechanism, so as to avoid interference with the fixed contacts of the fine adjustment selector in the plane distribution position, thereby increasing the insulation distance between the two.

(5) A mechanical limit can be set on the SYTZ35/400-48 coarse adjustment selector. This mechanical limit is the mechanical limit of the switch body, thus ensuring safe operation.

(6) SYTZ35/400-48 can be derived into a multi-level coarse and fine adjustment switch with more than 48 levels, and currently it can reach about 108 levels.

(7) The gear position indicator of the electric mechanism of SYTZ35/400-48 adopts pointer type. The two electrical limit switches are easy to adjust. The two cams that control the lifting process do not need to be adjusted or maintained. Manual operation can be achieved by turning the handle twice, which is very convenient.

(8) SYTZ35/400-48 is a product that is packaged and transported separately. The diverter switch is first fixed to the transformer cover by the head flange, and then the tap selector is connected to the diverter switch. Therefore, the maximum live outer diameter of the tap selector will not affect the opening φ570 of the transformer cover, and the outer diameter of the head flange is still φ660.