1.Overviwe
Jiangsu stainless steel Technology Development Co., Ltd. mainly produces stainless steel medium plate, rolling mill operation generates a large amount of reactive power, resulting in the company line end power factor reduction, while the rapid instantaneous active power, reactive power changes also caused the power grid voltage flicker phenomenon. The power motor of rolling mill is DC motor, and its front end is an uncontrolled rectifier circuit composed of power electronic devices, which produces a large amount of harmonic pollution. Therefore, the whole site needs to carry out a full range of power quality control, including reactive power compensation, power grid voltage flicker suppression and harmonic control. This project originally designed a reactive power compensation and harmonic control device. The original device used the comprehensive compensation scheme of MCR+FC filter branch to compensate the on-site load. However, due to the limited MCR response speed, the fast reactive power demand generated by the rolling mill could not be compensated quickly, so the voltage flicker suppression of the on-site power grid was not ideal. Finally, the static var generator is introduced to meet the compensation requirements of the site.
2.Static Var Generator Features
Static Var Generator(SVG) is the most advanced reactive power compensation device at home and abroad. This compensation device based on voltage PWM converter realizes a qualitative leap in reactive power compensation. It no longer uses large-capacity capacitors and inductors, but realizes the transformation of non-functional quantities through high-frequency switches of power electronic devices. It can operate according to the set reactive power nature and size, power factor, grid voltage, etc. as the control target, dynamically track the change of power quality of the grid to adjust reactive power output, and realize the curve setting operation to improve the grid quality.
3.Effect
The original distribution compensation system is a combination compensation scheme of MCR+FC filter branch, and the total power factor of this compensation device is increased to more than 0.85 after the input. After testing, the response time of common MCR on site is at least more than 200ms, there is an instantaneous reactive power shortage phenomenon, and the maximum voltage fluctuation of the grid voltage reaches 1000V. It has affected the production efficiency and the quality of the products in the factory.
FGSVG's response time is less than 5ms, and the final compensation effect is excellent, and the grid voltage flicker becomes effectively controlled. As shown in Figure 8, the grid voltage is obviously stable compared with Figure 2, and the maximum and minimum voltage fluctuation does not exceed 400V. Compared with the uncompensated voltage difference of 1000V, the obvious voltage flicker suppression effect has been obtained.
4.Advantages
(1)Faster response
Response time of static var generator(SVG) series products: ≤5ms. Response time of traditional reactive power compensation device: ≥40ms. SVG products can complete the conversion from rated capacitive reactive power to rated inductive reactive power in a very short time, and this unmatched response speed is fully capable of compensating impact loads.
(2)harmonic suppression
SVG not only does not produce harmonics, but also has harmonic control function, and can filter harmonics while dynamic reactive power compensation. In SVC, TCR produces a large number of harmonics while compensating reactive power, so TCR must be used simultaneously with large-capacity filters.
(3)The voltage flicker suppression ability is stronger
SVC is limited by response speed, and its ability to suppress voltage flicker does not increase with the increase of compensation capacity, while SVG can continue to improve its ability to suppress voltage flicker due to its extremely fast response speed.
(4)Wider operating range
SVG can operate in the range of rated inductive reactive power to rated capacitive reactive power, so the operating range is much wider than SVC. More importantly, when the system voltage is low, SVG can also output reactive current close to the rated working condition.
(5)Diversification of compensation functions
SVG not only has the function of quickly compensating the reactive power of the system, but also can compensate the harmonic current, negative sequence current and comprehensive compensation of the load according to the actual needs of users.