Currently, the new large-scale power system power transformer on-load voltage regulators are used, and well-equipped low-voltage distribution network and sufficient reactive power compensation capacity, so that the safe operation of power grids, power quality to meet user requirements, but most of our land, county 110kV substation main transformer due to historical reasons, the use of non-excitation voltage regulating transformer. This approach has several drawbacks; one will take some time to make power adjustments, interferes with the normal production and less for the electricity; Second, adjusting the number of restricted, only for periodic or seasonal adjustment, not regular, of daily peak power voltage fluctuations caused by changes, in the helpless state; third is often operating without circuit tap switch, easy to damage caused by seal leakage; Fourth, distribution transformer tap-agricultural self-adjustment of the is common, easily changed in the main transformer tap voltage stalls resulting from high or low users of electrical equipment damage incidents. The only way is to transform the realization of the transformer load tap changer.

(1) booted type transformation method:

Booted is the so-called high-voltage three-phase coil of the main transformer neutral point on, respectively, the series compensator (ie SZZ7 type neutral point OLTC) of the regulator coil, and the main transformer voltage regulator excitation and compensation coils in parallel, to achieve on-load tap. The voltage regulator is based on the superposition principle, the regulator compensator by means of on-load tap switch, the main transformer high-voltage side of the coil to maintain the voltage within the rated voltage.

In this way the regulator, the compensator run only under neutral or N-level regulator Σ △ U1 voltage, insulation level required is low, when the transformer neutral grounding in high-current operation, the insulation level only enough to 35kV (40kV according to our design and manufacturing), operating mode can also design a higher insulation level. This method of just a single point of making a medium-voltage regulating transformer, transforming low-cost, leads to the main transformer neutral-site transformation can be completed in just a day, if combined with the main transformer overhaul at the same time, basically do not increase the overhaul period .

Booted way for voltage fluctuation range is beyond the scope of non-excitation regulator, which is no excitation regulator switch gear in the most high-end or when they can not achieve the most low voltage qualification requirements. We use the neutral on-load tap, can achieve ± 12% U1N wide range of voltage regulator, with the main change if the original switch with no excitation can more easily move up and down regulator range (no range of excitation voltage regulator) to meet the actual needs of the regulator, and improve the main transformer output. Meanwhile, according to the actual situation to determine the pressure range to configure the neutral point OLTC, its capacity configuration as shown in Table 1, all kinds of ​voltage transformer​s​ are suitable for transformation. We completed four main transformer of the transformation task, the items listed in Table 1 have been transformed. But this method to increase the area of a transformer, a slightly more complicated wiring, but the duration of the entire transformation and conservation investment point of view, be regarded as a more economical and reasonable rehabilitation programs.

(2) backpack-style transformation method:

The so-called backpack is no excitation of the transformer voltage regulation range to meet the needs of the region, supply voltage fluctuations in the case, a more economical method of transformation. That the lifting of the original non-circuit tap points on the line of escorts, removal switch, install a jumper style or linear-load tap changer, the original sub-escorts-line lead to on-load tap changer, to achieve OLTC this transformation method is also only one overhaul cycle, body transformation (exposing the cover or hanging core) only 1 day in parallel with core body checks, Bell (drums shell) or tank also the transformation is completed. The key is to transform the day time, to ensure that the body does not damp the core to complete the transformation of the case, otherwise it will extend the outage time, increase the transformation costs. At the same time as the original renovation of the transformer can not stay out of the lead channel, so we will take appropriate measures to ensure that all types of transformer insulation distance to meet the requirements, and also to pay attention to facilitate future maintenance work (that is hanging hood, hanging manner that is not core change). We have done a lot of work, with the appropriate equipment, the transformation of every aspect of the study, and work out a set of practical construction programs. With this method we have transformed five times, and are intended purpose, is indeed a simple transformation of the economic approach.

(3) Conclusion:

These are our main transformer over the years to transform the program in two ways, we also conducted a change of aluminum copper, change the thickness of thin insulating insulation, installation of the regulator body coil, etc., more than 10 times the transformation, but the cost is high and cycle is longer. For rural power transformer, the above two methods has its unique transformation, but also for the transformation of industrial and mining enterprises dedicated transformer, the power grid to ensure quality, increase the voltage passing rate is effective.