Achieving unmanned substations is not only a requirement for reducing power system operating costs and improving the economic benefits of power companies, but also an important benchmark for measuring the degree of automation in the power system. Currently, Zengcheng Power Bureau is carrying out unmanned substation upgrades, and has completed the construction and upgrades of six 110 kV terminal substations—Sanjiang, Shajiao, Chengxi, Nan'an, Gangling, and Yonghe—which are now operational. The following is an analysis of specific issues related to the upgrade of unmanned substations for reference by power industry workers. [b]1 Basic Components of Unmanned Substations[/b] There are two conditions for achieving unmanned substations: first, reliable relay protection; only with reliable protection can the safe operation of a substation be meaningful; second, the presence of "three-remote" functions (remote monitoring, remote control, and remote telemetry), which is a strong guarantee for remote monitoring. The upgrade of unmanned substations is achieved by adding "three-remote" equipment to the existing substation relay protection system. The "three-remote" equipment adopted by Zengcheng Bureau includes: FJY-2 type distributed AC sampling remote control device, remote control execution cabinet, operating relay cabinet, transmitter, and microwave communication equipment (or power line carrier equipment), etc. The FJY-2 type distributed AC sampling remote control device is the core of the entire system. It is a new type of remote control device that integrates microcomputer transmitter and RTU. The microwave communication equipment is the equipment for communication between the station-end remote control device and the dispatch center. Zengcheng Bureau adopts small microwave products from SRT Corporation of Canada, which have two channels and can transmit two signals simultaneously. [b]2 Experience in the transformation of unmanned substations[/b] 2.1 Acquisition of remote signaling quantities Remote signaling quantities can be divided into two types according to the relay protection in the station: one is the one-to-one contact quantity connection method; the other is to realize the communication between microcomputer protection and remote control device through serial bus. The one-to-one contact quantity connection method is the method used by traditional electromagnetic relay protection devices and early microcomputer relay protection devices. The protection signals from the relay protection device are sent to the remote signaling terminals of the remote control device via pairs of mechanical contacts. This method involves a large amount of engineering work, consumes a lot of materials, and is difficult to construct. Furthermore, problems arise when the relay protection device has no spare contacts (the remote control device requires unpotentialed contacts), necessitating the addition of intermediate relays to expand the number of contacts, thus significantly increasing the workload. The serial bus connection method involves connecting the serial interfaces of the relay protection device's communication unit in parallel with a cable, and then connecting it to the communication port of the remote control device to achieve communication. This method requires less engineering work, is convenient to construct, saves materials, and is safe and reliable. This method is generally used in substations with new microcomputer relay protection devices. Upgrading older substations still requires the use of a one-to-one contact connection method. When the number of unpotential contacts is insufficient, intermediate relays are generally added to expand the number of contacts. For electrical contacts such as those on illuminated signs, there are generally two methods to obtain remote signaling contacts, as shown in Figure 1 and Figure 2 respectively. However, Figure 1 has a potential problem. Since 709L and 710L are connected to the pre-announcement audible circuit, they must pass through a resistor of several hundred ohms in the subsequent circuit before reaching the impulse relay. When there are more illuminated signs, more bulbs light up, the current through the resistor increases, and the voltage drop across the resistor increases, inevitably causing the potential of 709L and 710L to rise. When a certain potential is reached, it will cause other intermediate relays KC to trip, resulting in false signals. The method in Figure 2 does not have this problem and has high reliability, so it is recommended, although it is more difficult to implement. [img=260,151]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gddl/gddl2000/0001/image1/t55-1.gif[/img] Figure 1 Electrical contact expansion method 1 [img=285,179]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gddl/gddl2000/0001/image1/t55-2.gif[/img] Figure 2 Electrical contact expansion method 2 For the measurement of electrical energy, there are generally two methods: one is to calculate the active power and reactive power based on the load current, and then perform time integration on the active power and reactive power to obtain the active and reactive energy; the other is to use a pulse energy meter for measurement, and the remote control device calculates the electrical energy based on the pulse quantity provided by the pulse meter. Generally, integral calculations are only approximate and lack precision; while pulse measurement methods are highly accurate, so pulse measurement is recommended. Another point to note is that when using pulse energy meters, it is recommended to use active pulse energy meters rather than passive pulse energy meters. Active pulse energy meters can output pulse quantities without an external DC voltage; while passive pulse energy meters require an external DC voltage to output pulse quantities. Since the voltage value provided by the remote control device may not meet the voltage requirements of the pulse meter, it can easily damage the pulse meter. Several pulse meters have been damaged due to this during construction, commissioning, and after operation. 2.2 Remote Measurement Acquisition Remote measurement acquisition is of two types: one is measuring the AC analog quantities of voltage and current in each protection interval; the other is measuring DC analog quantities. Here, DC analog quantities do not simply refer to DC voltage and current, but rather to some electrical quantities with high voltage values ​​such as AC and DC voltage within the station, and non-electrical quantities such as transformer temperature and transformer on-load tap changer positions, which are converted into linear 0-5V DC voltage analog quantities by the transmitter. The AC analog signal acquisition uses PT voltage and CT current for each protection interval. When calculating the active and reactive power and energy of the protection interval, it is necessary to provide the three-phase voltages of L1, L2, and L3, as well as the two-phase currents of L1 and L3. However, this would require a considerable number of measurement units, potentially leading to a shortage. In such cases, less critical protection intervals (e.g., 10 kV feeders) can be excluded from active and reactive power and energy calculations; instead, only one phase current is used to monitor the load. This approach provides sufficient measurement units while meeting practical application requirements. In actual construction, engineers only use transformers and capacitor banks for active and reactive power and energy calculations. DC analog signal acquisition requires different types of transmitters. Based on the actual situation, engineers used four types of transmitters (DC voltage transmitter, AC power transmitter, temperature transmitter, and transformer on-load tap changer position transmitter) to measure the station's DC voltage, three-phase AC voltage, transformer temperature, and transformer on-load tap changer position. The following two points are noteworthy: a) The three pins of the platinum resistance temperature probe for transformers must be connected to the transmitter in the correct order for temperature measurement. Simultaneously, the platinum resistance probe must be used as a remote/near-field temperature sensor via a switch. It is crucial to avoid using the same probe in parallel for two temperature sensors simultaneously, as this will only introduce measurement errors and may even cause the temperature sensor to malfunction. b) Some transformer on-load tap changer boxes may only have one set of contacts, while the transmitter requires unused contacts. To meet the needs of both remote and near-field measurements, an intermediate relay must be installed to expand the number of contacts. 2.3 Remote Control and Remote Operation: After receiving remote control commands from the dispatch center, the remote control device sends the commands to the remote control execution cabinet, operating the corresponding intermediate relay. The relay's contacts control the switching mechanism, thus achieving remote control functionality. It is important to note that the substation must retain near-field operation functionality while eliminating the influence of the near-field switch operating handle on the relay protection device during remote control. Therefore, a remote/near-field operation switch must be installed. Special attention must be paid to ensuring that the number of contacts on the changeover switch is sufficient. Changeover switch contacts must be added before the operating contacts of the switch operating handle (e.g., switch open/close contacts, switch pre-open/pre-close contacts, alarm activation contacts, and reclosing activation/discharge contacts). Only in this way can the remote and local operating states be completely independent and prevented from interfering with each other (e.g., the flashing power supply cannot be switched, remote tripping triggers an alarm signal, protection tripping prevents reclosing, etc.). During actual construction, careful inspection and avoidance of design errors in this regard are crucial. The reason for using an operating relay cabinet is that, in remote operation mode, the switch state must be memorized to coordinate with the alarm and reclosing circuits of the relay protection system, ensuring the correct operation of the relay protection device. The operating relay cabinet uses a dual-position relay with magnetic memory performance, which maintains its position after being triggered by open/close voltage and remains unchanged even when power is off. This relay enables the activation of the relay protection system's alarm circuit and the blocking of the reclosing circuit in remote operation mode. To achieve unmanned operation of substations, the signal reset within the station must be remotely controlled by the dispatch center. The old-style signal relays (KS) do not have a motorized reset function; therefore, all signal relays in the substation must be replaced with those capable of motorized reset. The reset circuit of microprocessor-based relay protection devices requires open contacts, necessitating the installation of intermediate relays to expand the number of open contacts available for each protection device. It is important to note that some microprocessor-based protection devices, such as the WBZ-81C type 10 kV line microprocessor protection device, require normally open open contacts connected to the reset circuit, as shown in Figure 3(a), while some microprocessor-based protection devices, such as the WBZ-01 type 110 kV transformer microprocessor protection device, require normally closed contacts connected in series to the reset circuit (as shown in Figure 3(b)). During construction, the protection drawings should be consulted, and appropriate adjustments made based on the specific circumstances. [img=128,169]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gddl/gddl2000/0001/image1/t56-1.gif[/img] [img=131,175]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gddl/gddl2000/0001/image1/t56-2.gif[/img] Figure 3. Parallel Reset Signal Circuit with Normally Open and Normally Closed Contacts 2.4 Due to the lack of remote control functionality in some remote control devices, achieving voltage quality control (such as remote adjustment of on-load tap changers and the dispatch center's switching on and off of capacitor banks based on load flow) remains challenging. To address this, Zengcheng Power Supply Bureau engineers installed the DWK-ⅢA type voltage and reactive power microcomputer integrated control device in unmanned substations. This device utilizes microcomputer technology and digital signal processing to automatically and comprehensively control the on-load tap changers of transformers and the switching of capacitor banks based on real-time grid parameters. The DWK-ⅢA device features a modular structure and can control 1-3 on-load tap-changing transformers and 3×4 capacitor banks. This device eliminates the arduous task of manual remote operation of capacitor banks by the dispatch center and effectively improves voltage quality. Regarding power supply, the FJY-2 type remote control device and remote control execution cabinet contain AC transformer rectifier circuits and DC voltage inverter circuits, allowing for both AC and DC power supply, and automatic switching to DC power supply after AC voltage loss. During construction, the DC voltage inside the station must be connected to the aforementioned devices, or simply powered solely by the station's DC power supply. In the event of an AC voltage loss across the entire station due to an accident, the remote control unit can still be powered by the station's batteries, ensuring normal operation. Furthermore, lightning protection is crucial. An opto-isolation driver should be installed between the remote control unit and the microwave communication equipment to prevent lightning strikes through the microwave communication equipment. Of course, the opto-isolation driver should also be DC-powered. [b]3 Conclusion[/b] In actual operation, the renovated unmanned substation effectively achieves the "three remote" functions (remote control, remote monitoring, and remote telemetry), exhibits high voltage quality, and maintains good and stable operation, basically achieving the expected goals. However, there are still areas for improvement. For example, installing a closed-circuit television system in the substation to transmit video signals to the dispatch center for monitoring of the equipment within the station could be considered. With the development of the power industry, substations must adapt to the requirements of integrated automation. It is believed that unmanned substations will soon be replaced by integrated automated substations. In any case, the reconstruction of unmanned substations has accumulated valuable experience for engineers and laid a solid foundation for the development of integrated automation of substations.