Renovation of the hottest continuous rolling main

2022-08-17
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The 1549mm hot continuous rolling mill of TISCO is a second-hand equipment introduced from Japan in 1990. There are 9 main rectifier transformers in the main rolling mills R1, R2T, r2b, F1 ~ F6, with the largest capacity of 7900kva. It was originally used on 60Hz and 11kv power. Some people believe that changing 60Hz to 50Hz will cause the iron core to overheat, so there are different opinions on whether to reuse the old

at present, each transformer with this special structure is 660000 ~ 1million yuan. If you buy a new one, you will not only spend more money, but also lose the significance of buying second-hand equipment. In order to make rational use of second-hand equipment, theoretical analysis and calculation are carried out on these transformers, and core pulling inspection is carried out on the real objects. On this basis, the old scheme and wiring diagram are put forward, and Taiyuan Iron and steel metallurgical motor factory is entrusted to change the wiring according to the design scheme. Finally, the old scheme of 9 main rectifier transformers is realized

1 calculation, analysis and transformation

1 the total order value of plastic machinery in the United States in the fourth quarter of 2013 was about 335million US dollars 1 F1 ~ F5 main rectifier transformers

the capacity of each transformer is 7900kva when it is air-cooled, the primary voltage is 13750v, the current is 332a, the triangle connection method, and the secondary winding is two groups of double reverse zigzag star connection method, the phase voltage is 1420v, the current is 678a, and the impedance voltage is 5.32%

(1) voltage verification

due to the decrease of frequency, the magnetic density of the transformer core will increase. In order to keep the magnetic density of the iron core unchanged, the maximum voltage allowed by the transformer should be reduced, and its value is

according to e=4.44fn Φ It can be obtained that

where e is the potential; F is frequency, 50Hz or 60Hz; N is the number of turns of transformer winding; V1 is the primary voltage of the transformer

under this condition, the transformer can be directly used on 10kV and 50Hz power

(2) transformation scheme

the primary winding of the transformer is used as it is. Open the four star points of the secondary winding and connect them into four zigzag triangles. The two triangles are a group, which are divided into two groups. The phase difference between the two groups of zigzag triangles is 30 °, as shown in Figure 1. When three-phase bridge rectification is adopted, 12 phase rectification can be realized. In order to ensure that the secondary ac line voltage is 1150v, it is necessary to add an autotransformer of about 750kva, with an input voltage of 10kV, 50Hz and an output voltage of 11136v, which is supplied to the primary winding of the rectifier transformer after the terminal connection is changed. Then the line voltage of the secondary winding of the rectifier transformer after the transformation is

(3) the primary winding of the rectifier transformer Verification of secondary current

primary current:

secondary current:

where 4050 is the rated current supplied to the DC motor after rectification; Is the transformation ratio of rectifier transformer; 0.789 is the primary ac/DC coefficient of transformer; 0.816 is the secondary AC/DC coefficient of transformer

under this condition, the winding heating is also within the allowable range. If the corresponding self coupling voltage regulator is shifted by 10 °, 36 phase rectification can be realized in the finish rolling area

1.2 R1 main rectifier transformer

transformer capacity is 4140kva, primary voltage is 14100v, current is 195a, triangle connection method; The secondary voltage is 920v, the current is 630A, and two groups of double reverse zigzag star connection method. The transformation scheme is the same as F1 ~ F5, except that the secondary voltage of rectifier transformer should ensure 750V, and the output voltage of autotransformer can be calculated based on this

1.3 R2T, r2b main rectifier transformers

the capacity of each transformer is 5500kva, one is △/△, one is Y/△, the primary voltage is 11000v, the current is 289A, and there is a 12000V voltage range; The secondary voltage is 770v and the current is 4120a. The enclosures of these two transformers are sealed and not easy to open. The primary and secondary windings remain intact and continue to be used as they are. The secondary winding adopts the method of connecting a low-voltage winding in series to increase the voltage, so as to compensate for the secondary voltage reduction caused by the frequency change of easy surface printing, coating and coating treatment

(1) transformer core verification

according to e = 4.44fn Φ

primary voltage ratio after frequency change:

frequency ratio after frequency change:

therefore, the magnetic flux of the transformer core remains unchanged, and it is allowed to be directly used on 10kV and 50Hz electricity

(2) after using 50Hz power supply, the secondary voltage

(3) voltage difference

750-642 = 108 (V)

where 750 is the voltage that the secondary winding of the transformed transformer should meet

(4) solution

a small transformer with a primary voltage of 10kV and a secondary voltage of 108V can be used, which is connected in series with the secondary winding of the original transformer, as shown in Figure 2

transformation scheme: the primary winding does not move, the secondary winding opens the star point, and changes to the double triangle connection method. The primary and secondary voltages are the same as those in F1 ~ F5 scheme

1.4 F6 main rectifier transformer

transformer primary winding delta connection, voltage 13750v, current 287a; Double reverse star connection method of secondary winding, voltage 1420v, current 1140A

in addition to the above transformation, the most important manufacturing standard of conventional domestic conductor aluminum alloy and aluminum alloy cable for rectifier transformer is the national standard gb/t30552 ⑵ 014 "aluminum alloy wire for cable conductor", and by American technology The national industry standard nb/t42051 (2) 015 aluminum alloy conductor XLPE insulated power cable with rated voltage of 0.6/1kv, which was jointly formulated by military quality umiloy brand technical director and other domestic aluminum alloy cable industry experts and issued on September 1 this year, is installed and used after inspection and maintenance

2 operation results

these nine modified main rectifier transformers have been operated on load since August 8, 1994. So far, no fault has occurred, with a total of more than 2 million tons of steel rolling, which can exceed the design output of 1.35 million tons this year. 9 transformers

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