Abstract: This paper introduces the application of a high-voltage dynamic reactive power compensation device produced by Shandong Xinfengguang Electronic Technology Development Co., Ltd. in a rural power grid in a town in Santai County, Sichuan Province. Through the upgrade, the power quality of the grid was improved, line losses were reduced, and electricity costs were decreased.
Keywords: FGSVG, reactive power compensation, harmonic control, rural power grid
Abstract: This paper describes Shandong WindSun Electronics Science &Technology Co., Ltd. production of high-voltage dynamic reactive power compensation device in a certain town in rural network in Santai County, Sichuan. Transformation improves power quality, reduces line losses, reduces electricity costs.
Keywords: FGSVG Reactive power compensation Harmonic control Rural power grid
1. Introduction
With the successive introduction of national policies supporting agriculture and benefiting farmers, the rural economy has developed rapidly, and farmers' lives have improved year by year. Regarding electricity, with the full implementation of unified grid pricing in urban and rural areas, and the gradual promotion of mechanized production and electrified living in rural areas, household appliances such as televisions, refrigerators, washing machines, induction cookers, rice cookers, and air conditioners have become rapidly popular, leading to a continuous increase in rural electricity consumption at a rate of approximately 10% to 15% annually. This increase in electrical equipment has caused significant pollution to power quality. This is mainly manifested in severely excessive harmonics, leading to increased losses in transformers, motors, capacitor banks, and lines, and even endangering equipment safety; the negative sequence current generated produces additional torque on rotating machinery such as motors, reducing working efficiency and increasing energy consumption; and the impact of reactive power causes severe voltage fluctuations and flicker, reducing production efficiency, increasing unit energy consumption, and simultaneously causing a decline in product quality. For these high-impact nonlinear loads or asymmetrical loads, on-site reactive power compensation and power pollution control should be implemented, that is, addressing this type of pollution at its source to achieve the goals of power quality improvement, energy conservation and consumption reduction, increased output, and improved product quality.
Therefore, using reactive power generator technology is one of the most effective measures to solve these problems. On the one hand, it can suppress voltage fluctuations and improve power quality; on the other hand, it can also improve the damping characteristics of the system to a certain extent. It can improve the dynamic reactive power reserve level of the receiving-end power grid and enhance the power receiving capacity.
The development of reactive power compensation technology has progressed from synchronous condensers to switched-on fixed capacitors to static var compensators (SVCs) and finally to static synchronous compensators (SVGs). Static var compensators (STATCOMs, also known as SVGs) utilize fully controlled switching devices (such as IGBTs), resulting in dynamic compensation effects unmatched by earlier reactive power compensation devices like synchronous condensers and capacitors. Static var generators, with their lower harmonics, higher efficiency, and faster dynamic response, will become crucial equipment in power transmission systems. Rural economic development and the improvement of farmers' living standards are inseparable from the support of electricity as a fundamental industry; rural power grids are of vital importance to the construction of a new socialist countryside.
2. Comparison between Wind-Solar STATCOM (hereinafter referred to as FGSVG) and traditional compensation devices
The Wind-Solar STATCOM (hereinafter referred to as FGSVG) is a high-voltage dynamic reactive power compensation device independently developed by Shandong Xinfengguang Electronic Technology Development Co., Ltd. It employs modern power electronics, automation, microelectronics, and network communication technologies, utilizing advanced instantaneous reactive power theory and a power decoupling algorithm based on synchronous coordinate transformation. Using power factor, grid voltage, or both over time periods as control targets, it dynamically tracks changes in grid power quality to adjust reactive power output, achieving high-quality grid operation. FGSVG possesses independent intellectual property rights and multiple invention patents. With its low harmonics, high efficiency, and rapid dynamic response, it has become an important piece of equipment in power transmission systems.
Compared with synchronous condensers and SVC devices, FGSVG has the following advantages:
(1) The system adopts digital control technology, which has high reliability and requires almost no maintenance, thus saving a lot of maintenance costs;
(2) Its performance in improving the transient stability of the system and damping system oscillations is far superior to that of traditional synchronous condensers;
(3) It is flexible in control, faster in adjustment speed, and wider in adjustment speed. It can be continuously and quickly adjusted under both inductive and capacitive operating conditions, and the response speed can reach the millisecond level.
(4) It operates statically, safely and stably, without large rotating equipment like a synchronous condenser, with no wear and no mechanical noise, which will greatly improve the lifespan of the device and reduce environmental impact.
(5) The capacitance requirement of the capacitor is not high, which can eliminate the large inductor and capacitor and the huge switching mechanism in conventional devices, making the FGSVG small in size and low in loss.
(6) Small connection reactance. The connection reactance of FGSVG connected to the power grid is used to filter out higher harmonics in the current and to connect the converter to the power grid. Therefore, its inductance is much smaller than that required by SVC devices such as TCR with the same compensation capacity.
(7) The output current of FGSVG is independent of voltage, exhibiting constant current source characteristics and having a wider operating range. In contrast, SVC is essentially an impedance-type compensation, with a linear relationship between output current and voltage. Therefore, when the system voltage drops, FGSVG of the same capacity can provide a larger compensation capacity than SVC. If FGSVG is combined with a fixed capacitor of the same capacity, it can form a dynamic capacitive reactive power compensator with 0 to 2 times the capacity, which is more cost-effective.
(8) FGSVG has a faster response speed than SVC, and is therefore more suitable for suppressing voltage flicker. The response time of FGSVG is within 10ms, while the response time of SVC is generally greater than 40ms. FGSVG can change from rated capacitive reactive power to rated inductive reactive power (or vice versa) within 1ms, and this response speed is fully capable of compensating for impulsive loads;
(9) The bridge circuit of FGSVG uses multiplexing technology, multilevel technology or PWM technology to eliminate lower-order harmonics and reduce higher-order harmonics such as the 7th and 11th to an acceptable level. However, SVC itself generates a certain amount of harmonics. For example, the 5th and 7th characteristic harmonics of TCR type are relatively large, accounting for 5% to 8% of the fundamental value; other types such as SR and TCT also generate higher-order harmonics such as the 3rd, 5th, 7th and 11th, which brings many difficulties to the filter design of SVC system.
(10) Under fault conditions, FGSVG has better control stability than SVC. SVC uses a large number of capacitors and reactors, and SVC will become unstable when the capacity of the external system is comparable to the capacity of the compensation device. FGSVG is not sensitive to changes in the operating conditions and structure of the external system;
(11) FGSVG has a smaller footprint and lower cost than SVC of the same capacity. Because FGSVG uses DC capacitors for energy storage, the capacitor volume can be reduced, and reactive power can be smoothly controlled without the need for parallel reactors, thus greatly reducing the installation size;
(12) FGSVG can provide active power within a certain range and reduce active power surges. SVC can only provide reactive power and does not have the function of providing active power.
3. Introduction to FGSVG Product System
3.1 FGSVG Product Principle
The schematic diagram of the FGSVG product is shown in Figure 1. The basic principle is to connect the self-commutated bridge circuit in parallel with the power grid through a transformer or reactor. By appropriately adjusting the amplitude and phase of the AC output voltage of the bridge circuit, or by directly controlling its AC current, the circuit can absorb or generate reactive current that meets the requirements, thereby achieving the purpose of dynamic reactive compensation.
3.2 FGSVG Product Structure
The main circuit structure of the FGSVG product system is shown in Figure 2:
The FGSVG product mainly consists of three parts: the incoming line cabinet, the power cabinet, and the control cabinet. Figure 3 is a schematic diagram of the electrical principle.
The incoming line cabinet is the hub connecting the power grid and the equipment, controlling the grid connection and disconnection of the equipment, and reserving an interface with the original reactive power compensation equipment (FC) for easy on-site connection.
The power cabinet adopts a modular design, with the power units having completely identical structures and electrical performance. The units are interchangeable, facilitating inspection and maintenance.
The control cabinet features an optimized human-machine interface with a user-friendly design and fully digital control. It can dynamically track and compensate for reactive power, harmonics, and negative sequence current required by the power grid in real time, control auxiliary equipment in real time, maintain communication with the host computer, and has good observability.
3.3 FGSVG Electrical Principles
The main circuit of the FGSVG product adopts a chain inverter topology with Y-type connection. The 10kV device consists of 12 units connected in series per phase, and the 6kV device consists of 8 units connected in series per phase. The operation mode is N+1.
This structure allows for independent phase control, which helps solve phase balance problems and provides better voltage support when the system is disturbed. All links have the same structure, enabling modular design and facilitating capacity expansion. Each phase link can be equipped with a redundant link, allowing the system to continue operating at full load even if one unit fails, ensuring reliability. The elimination of the connecting transformer reduces equipment cost and losses.
The power unit circuit is shown in Figure 4. To ensure the reliability of the power unit, components from the same batch were selected during the design process to guarantee the consistency of component performance. Each power unit has comprehensive protection measures, and all operating states are reported back to the main control unit. The signal connections between the main control unit and each unit are made of optical fiber.
The FGSVG device control core is implemented through collaborative computation using a high-speed 32-bit digital signal processor (DSP), a large-scale programmable logic device (CPLD/FPGA), and an integrated human-machine interface. Carefully designed algorithms ensure optimal operating performance of the FGSVG. It provides a user-friendly, fully Chinese monitoring and operation interface, while also enabling remote monitoring and networked control. The PLC controller handles the logic processing of switch signals within the cabinet and coordinates with various field operation and status signals, enhancing system flexibility. The controller employs large-scale integrated circuits and surface-mount technology, resulting in extremely high system reliability.
Furthermore, the controller and power unit employ multi-channel fiber optic communication technology, ensuring complete and reliable isolation between the low-voltage and high-voltage sections. This provides the system with extremely high safety and excellent resistance to electromagnetic interference. The controller has a power supply system independent of the high-voltage power supply, and the power unit's control power supply also uses a separate power supply, facilitating debugging and maintenance and enhancing system reliability. Without high voltage, the waveforms at various points on the equipment are essentially similar to those under high voltage, greatly simplifying the overall debugging process.
4. A typical application case in Sichuan
Tashan Power Supply Station is located in Tashan Town, Donglu, Santai County. It currently has two 6300kVA main transformers, supplying over 20 million kWh annually. The station serves one 18.6km 35kV Liuta line and six 10kV lines totaling 312.3km, serving 27,905 users. A 2000kvar SVG is currently installed on the 10kV busbar. The power supply system structure is shown in Figure 5.
During peak electricity consumption periods, the power factor at the user's site is very low, while the grid power factor remains below 0.2, indicating an "under-compensation" phenomenon. Conversely, during off-peak periods, there is an "over-compensation" phenomenon. The significant fluctuations in reactive power cause fluctuations in the 10kV grid bus voltage, impacting user electricity safety. The power supply station originally configured two sets of 0.6MVAR reactive power compensation capacitors, but one set is damaged, and the reactive power cannot be steplessly adjusted during switching of a single set of capacitors.
After extensive evaluation, the power company leadership ultimately selected the FGSVG (Fuel Gauge Switch) manufactured by Shandong Xinfengguang Electronic Technology Development Co., Ltd., with specifications of ±2000kvar/6kV, for reactive power compensation and harmonic mitigation of the power grid. Installation, including the laying of main cables and control lines, relay protection system settings and commissioning, cable withstand voltage testing, and performance testing and inspection of the device itself, commenced on September 25, 2011. Following rigorous approval procedures, the device was officially connected to the Tashan Power Supply Station on September 30, 2011. During the commissioning period, the device did not cause any adverse effects on the normal operation of the power grid.
FGSVG can operate in parallel with the original capacitor bank or independently. Because FGSVG has continuous capacitive-inductive adjustment capabilities, installing an FGSVG not only improves the power factor of the grid from below 0.2 to above 0.98, but also solves the problem of overcompensation in existing capacitor compensation devices. FGSVG is reliable, fully functional, highly automated, and easy to operate. It can record various operating parameters and faults in real time and automatically protect against various faults, demonstrating significant advantages over existing reactive power compensation equipment.
Figure 6 shows the user's site, Figure 7 shows the power factor curve before commissioning, and Figure 8 shows the power factor curve after commissioning. Figure 9 shows the FGSVG installation site.
5. Benefit Analysis
Installing FGSVG in the power grid not only reduces power consumption and improves the power factor, but also fully taps the potential of equipment power transmission. From the perspective of power users, the benefits of adding FGSVG to the distribution network mainly focus on the following aspects:
(1) It can greatly improve the quality of power.
(2) Effectively reduce power loss.
(3) Reduce users’ electricity expenses.
The benefits of FGSVG reactive power compensation are very significant. Calculations show that this user saves over one million yuan in electricity costs annually. The user's compensation also reduces grid losses and improves voltage quality.
6. Conclusion
Using reactive power compensation in rural power grids to improve the power grid quality of the power supply system can not only increase the active power output capacity and make full use of equipment capacity, but also increase the transmission capacity, reduce power loss and energy loss, and reduce voltage drop and voltage fluctuation in the lines. This achieves the goal of saving energy and improving power supply quality, creating considerable economic benefits for users. It is a good thing that benefits the country and the people and deserves to be vigorously promoted in the rural power grid system.
References
1. User Manual for FGSVG Series High-Voltage Dynamic Reactive Power Compensation Device (V1.0), Shandong Xinfengguang Electronic Technology Development Co., Ltd.
2. Static Var Compensation Technology, edited by Li Shiping and Liu Guiying, China Electric Power Press, 2006.
About the author:
Cheng Xudong, male, engineer, works in sales and other positions at Shandong Xinfengguang Electronic Technology Development Co., Ltd.
