C transformation of the hottest power transformer

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C transformation of power transformer

at present, the new large power transformers in the power system adopt on load voltage regulators, and are equipped with perfect low-voltage distribution network structure and sufficient reactive power compensation capacity, so as to make the power operate safely and meet the requirements of users for power quality. However, due to historical reasons, the main transformers of most local and county-level 110kV substations in China mostly use non excitation voltage regulating transformers. This method has several disadvantages; First, a certain power outage time is needed for adjustment, which interferes with normal production and supplies less power; Second, the number of adjustments is limited, and it can only be adjusted periodically or seasonally, not often. It is helpless for the voltage fluctuation caused by the peak and valley changes of daily electricity; Third, often operate the off excitation tap changer, and the seal is easy to be damaged, resulting in oil leakage; Fourth, it is common for the tap changer of agricultural distribution transformer to adjust itself, which is very easy to cause high voltage of low-voltage users or damage electrical equipment after the main transformer changes the tap position. The only way is to transform the transformer to realize on load voltage regulation

(1) booting transformation method:

booting is to open the neutral point of the high-voltage three-phase coil of the main transformer, connect the voltage regulating coil of the compensator (i.e. szz7 neutral point on load voltage regulating transformer) in series, and connect the low-voltage side of the main transformer in parallel with the excitation coil of the compensation transformer. There is still a certain corresponding relationship between the tolerance grade and the surface roughness value to realize on load voltage regulation. The voltage regulation is based on the principle of voltage superposition, and the voltage regulator compensator maintains the voltage of the coil at the high voltage side of the main transformer within the rated voltage range with the help of the on load voltage regulation switch

in this voltage regulation mode, the compensator only bears neutral point or N-level voltage regulation during operation Σ △ the voltage and insulation level of U1 are required to be low. When the neutral point of the transformer operates in high current grounding mode, its insulation level is only 35kV (we design and manufacture it according to 40kV), or higher insulation level can be designed according to the operation mode. In this method, as long as a neutral point voltage regulating transformer is manufactured separately, the transformation cost is low, and the on-site transformation of the neutral point of the main transformer can be completed in only one working day. If it is carried out simultaneously with the overhaul of the main transformer, the overhaul period is basically not increased

the booting method is applicable to the voltage fluctuation range that has exceeded the range of non excitation voltage regulation, that is, the non excitation voltage regulation switch gear can not meet the voltage requirements when it is in the highest or lowest gear. The neutral on load voltage regulation transformer we use can realize a wide range of voltage regulation of ± 12% u1n. If it is matched with the original non excitation switch of the main transformer, the voltage regulation section (non excitation voltage regulation range) can be moved up and down more conveniently to meet the actual voltage regulation needs and improve the output of the main transformer. At the same time, the voltage regulation range is determined according to the actual situation to configure the neutral on load voltage regulation transformer. Its capacity configuration is shown in Table 1. Transformers of various voltage levels are suitable for transformation. We have completed the transformation of four main transformers, and all items listed in Table 1 have been transformed. However, this method needs to increase the floor area of a transformer, and the primary wiring is slightly more complex, but from the perspective of the whole transformation period and saving investment, it is a relatively economic and reasonable transformation scheme

Table 1 capacity configuration of neutral point voltage regulating transformer and main transformer

transformer capacity (kVA) distribution voltage regulating transformer capacity (kVA) voltage regulating range (V)

10000 1250

16000 2000 u1n+8 × 1.5%

20000 2500

31500 4000

(2) knapsack transformation method:

the so-called knapsack is a more economical and applicable transformation method when the non excitation voltage regulation range of the transformer can meet the needs of 60% of the local foam materials for vehicles and the supply voltage fluctuation in the polyurethane area. That is, remove the tap lead on the original off-line tap changer, remove the switch, install a jumper or linear on load voltage regulating switch, and lead the original tap lead to the on load voltage regulating switch to realize on load voltage regulation. This transformation method also requires only one overhaul cycle, and the body transformation (cover removal or core lifting) takes only one day, With the industry's search for lighter renewable materials, bell jar (barrel shell) Or the oil tank is also transformed at the same time. The key to its transformation is to complete the transformation work within one day to ensure that the core is not affected by moisture, otherwise the power outage will be extended and the transformation cost will be increased. At the same time, since it is impossible for the original transformer to leave the lead channel during transformation, corresponding measures should be taken to ensure that the insulation distance of various types of transformers meets the requirements, and attention should be paid to facilitate future maintenance work (that is, the way of hanging cover and core remains unchanged). In this regard, we have done a lot of work, equipped with corresponding equipment, studied each link of the transformation, and formulated a set of practical and feasible construction schemes. We have transformed 5 sets with this method, which has achieved the expected purpose. It is indeed an economic and simple transformation method

(3) conclusion:

the above are two methods in our transformation plan for the main transformer over the years. We have also carried out more than 10 times of transformation, such as aluminum to copper, thin insulation to thick insulation, and the installation of voltage regulating coil on the body, but the cost is higher and the cycle is longer. For rural power transformers, the above two transformation methods have their own uniqueness. At the same time, they are also suitable for the transformation of special transformers for industrial and mining enterprises. With the continuous development of the material industry, they are effective in ensuring the quality of power operation and improving the voltage qualification rate

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