1. Introduction The capacitive current of a transmission line is directly proportional to the line voltage and line length. The voltage at the end of a long-distance unloaded line will increase due to the increased capacitance. Therefore, to control the rise in line voltage within a certain range, it is necessary to add an appropriate number of switching stations and configure reactors of appropriate capacity in the middle of long-distance transmission lines to consume capacitive reactive power, thereby reducing the voltage at the end of the line. However, if the switching station is located in a remote area without reliable power supply and far from the load center, how to ensure the reliability of the power supply to the switching station becomes a problem worthy of study. The Ertan Hydropower Station, located on the Yalong River near Panzhihua, Sichuan Province, has an installed capacity of 3300 MW. It transmits power to Zigong via three 470 km 500 kV lines, and then to Chengdu and Chongqing via two 500 kV lines respectively. To control the voltage level, a switching station was set up in the middle of the 470 km line from Ertan to Zigong. The switching station is located in Puti Village, Zhaojue County, in the hinterland of the Liangshan Yi Autonomous Prefecture. There are no other reliable power sources in this area besides small hydropower, and the annual precipitation is very uneven and highly seasonal. The reliability of the regional power grid is extremely low. If only the regional power grid is used to supply power to the switch station, the reliability will be very poor. [b]2 Solution[/b] Under these circumstances, in order to ensure the reliability of the power supply for the Zhaojue (Puti) switch station, the relevant units have proposed the following power supply configuration schemes after a comprehensive investigation of the location of the station: (1) Introduce an external power source from the regional power grid through a 35 kV line as the main and backup power source for the station. The capacity of the station transformer is 630 kVA. (2) Install a diesel generator set with a manual start capacity of 40 kVA as an auxiliary backup power source. (3) Extract power from two 550 kV 60 Mvar high-voltage parallel reactors with pumping windings, each with a capacity of 500 kVA, as the main power source for the station. 2.1 The main structure, principle wiring diagram and technical parameters of the reactor were approved by relevant departments and through international bidding, the Sichuan Provincial Power Bureau introduced 4 sets of 12 (phase) 550 kV high-voltage parallel reactors from ELIN Company of Austria and installed them at the Puti (Zhaojue) switch station. The capacity of each (phase) unit is 60 Mvar. Among them, 2 sets are ordinary high-voltage parallel reactors and the other 2 sets are high-voltage parallel reactors with energy extraction windings. The energy extraction windings of the reactors provide station power to the switch station. (1) Structure of the reactor The reactor is a 3-column structure consisting of 1 main iron core column with an air gap and 2 auxiliary iron core columns. The 550 kV winding is located on the main column and consists of 2 parallel winding modules with a tap in the middle of the winding axis. The energy extraction winding is formed by the parallel connection of windings located on the two auxiliary iron cores. The voltage of this winding depends not only on the transformation ratio between the main winding and this winding, but also on the magnetic flux through the auxiliary winding. The three-phase energy extraction windings are led out of the bushings from the reactors and then connected to the three phases A, B, and C of the intermediate transformer via three independent cables and a load switch. The schematic diagram is shown in Figure 1. [img=312,254]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/dwjs/2001-11/78-0.jpg[/img] (2) Station Distribution Box The station distribution box is supplied as a whole by ELIN Company. Its switches, grounding switches, fuses, one 6.5 kV intermediate (distribution) transformer, load switch, surge arrester, and all protection, control, and measurement equipment are all installed in a closed cement component box. To avoid phase-to-phase short circuit faults, the energy extraction windings of the three high-voltage reactors and the high-voltage leads of the distribution box are connected by three cables. After the extracted electrical energy enters the distribution box, it is connected to the intermediate transformer via the surge arrester, grounding switch, SF6 switch, and fuse. The voltage is transformed from 6.5 kV to 400/231V by an intermediate transformer, then connected to the low-voltage busbar of the distribution box via the main load switch, and then connected to the distribution room of the switchyard control building via three separate lines. To ensure the quality of the secondary voltage of the intermediate transformer, an on-load tap-changing transformer with a voltage regulation range of ±2×2.5% is selected. The main wiring diagram is shown in Figure 2. [img=320,169]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/dwjs/2001-11/78-2.jpg[/img] (3) Main technical parameters: Reactor rated capacity 60 Mvar; Pumping winding rated capacity 167 kVA; High voltage winding rated voltage 550 kV; Pumping winding rated voltage 6.5 kV; High voltage winding rated current 189 A; Pumping winding rated current 44.5 A; Pumping intermediate transformer capacity 500 kVA; Pumping intermediate transformer primary side voltage 6.5 kV; Reactor 1681Ω, cooling method ONAN; Reactor weight 78000 kg. Test voltage is shown in Table 1. On-site photos are shown in Figure 3. [img=269,158]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/dwjs/2001-11/78-3.jpg[/img] [img=200,238]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/dwjs/2001-11/78-4.jpg[/img] 2.2 Safety Protection Measures Since the high-voltage parallel reactor is directly connected to the 500kV line, when the reactor fails, it can only be taken out of operation by tripping the switches at both ends of the line. Therefore, it may affect the safe operation of the power grid. Thus, ensuring the safe operation of the reactor is extremely important. Reactors with a pumping winding system, in addition to the structure of ordinary reactors, also have a pumping winding system, thus increasing the reactor's safety risks, namely the impact of failures in the winding system and its connected external equipment. To ensure the safe operation of this special reactor, on the one hand, manufacturers are required to take effective measures during design and manufacturing to prevent internal reactor failures, especially to prevent a fault in the winding system from spreading to the high-voltage winding system; on the other hand, the fault range of the external equipment connected to the winding should be limited to outside the reactor. Therefore, three independent cables are used to connect the external part of the winding system to each reactor, and the cables are spaced far apart to prevent short-circuit faults between the leads before the SF6 switch. To prevent the impact of equipment failures downstream of the switch on the reactor, overcurrent and grounding protection devices were configured, and a high-voltage fuse was installed on the load switch as another overcurrent protection device. Overheat and overcurrent trip protection devices were installed on the main switch of the secondary circuit of the intermediate transformer, and fuses were installed on the 400V feeder circuit to disconnect faults in the distribution circuit. Simultaneously, to prevent overvoltage from the primary side of the high-voltage reactor from entering the pumped power distribution system, surge arresters were installed on the lead-out circuit of this winding system. 2.3 Operating Status Since its official commissioning in June 1998, the high-voltage reactors with pumped winding systems at the Zhaojue (Puti) substation have operated well, and the pumped power supply has been reliable. During operation, there was only one instance where a failure of the station water pump motor caused the low-voltage side feeder circuit switch of the intermediate transformer to trip. The two sets of pumped winding systems draw power from the 500kV system, ensuring the reliability of the station's power supply. **3 Conclusions** Due to the low reliability of the regional power grid, the substation power supply introduced through the 35 kV system frequently experiences power outages. Supplying power to the substation solely from the regional power grid cannot guarantee the reliability of the substation's power supply. In remote areas without a reliable power grid, substations can utilize reactors with pumping winding systems to provide reliable substation power. Increasing the pumping capacity can provide appropriate power to areas near the substation. The system design must ensure that faults in the pumping system and its distribution system do not compromise the safe operation of the high-voltage power grid. Therefore, on the one hand, manufacturers must ensure the internal reliability of the reactor during design and manufacturing, preventing faults in the pumping winding system and its distribution system from affecting the high-voltage portion of the reactor; on the other hand, phase-separated cables should be used to ensure that short-circuit faults do not occur on the pumping leads, and switches and appropriate protection should be configured to limit faults in the distribution section to after the switches.