"Feeder Automation" Improves Active Intelligent Diagnosis Capabilities of Power Grids

Feeder automation refers to the automation of feeder lines between substation outlets and user electrical equipment. Its content can be summarized into two aspects: one is user detection, data measurement and operation optimization under normal conditions; the other is faults under accident conditions Detection, fault isolation, transfer and restoration of power control.

1. System introduction of feeder automation

This system is based on DEP-900 feeder terminal unit (FTU) to realize feeder automation.

Feeder automation is an important part of distribution network automation. To realize feeder automation, a reasonable distribution network structure is required, and the conditions for ring network power supply are required; the operating mechanism of each ring network switch, load switch, and switch in the street distribution station must have remote operation functions; the ring network switch cabinet must have reliable The switching operation power supply and the working power supply for FTU and communication equipment; it has a reliable communication system that is not affected by the external environment.

The realization principle of feeder automation is that the network reconfiguration after a fault should adopt the combination of centralized control and distributed control, and the principle of distributed control should be used first to improve the response speed; realize the closed-loop operation of the distribution network, and cut off the power distribution network instantaneously in case of a fault. Faulty section and maintain uninterrupted power supply to non-faulty areas; compatible with open-loop operation mode.

According to the above operation mode, realization principle, protection mode and communication mode, the configuration of the feeder automation device:

FTU is basically configured according to the line in the substation room as a unit. For the load-side outlet with less collection parameters, several FTUs can be configured according to the collection quantity. The dotted lines indicate the communication connection, and the realized functions include: collecting the voltage, current and other required electrical parameters and equipment status of the line and actively sending them through the RTU, executing remote control commands to perform switch opening and closing and parameter adjustment, and realizing according to the setting conditions Fault state differential protection.

The combination of distributed control and centralized control is the principle of 10/35kV line fault handling. Distributed control is used as the main means, adopting the fault state differential protection method, identifying the fault location through mutual communication between FTUs, disconnecting the switch on both sides of the fault point, isolating the fault, and ensuring the power supply of the healthy section of the line. Centralized control is used as a backup method. In the case of protection refusal, the master station system performs fault identification and isolation. Since the ring network is a cable network, the fault is generally a permanent fault, so the reclosing mode is not considered, but the FTU itself has the reclosing function.

The system operation mode is mainly closed-loop operation, and the open-loop operation mode is also taken into consideration. When a fault occurs in the closed-loop operation, the device will make a judgment within 5 cycles. In order to ensure the accuracy of the fault status of the opposite side and the adjacent side, a time limit is also required. Therefore, the time between when a fault occurs and when the command is issued is about 0.15-0.2 seconds. Single-phase ground faults, phase-to-phase short-circuit faults, and three-phase short-circuit faults can all be resolved according to the above scheme. When a fault occurs in open-loop operation, the time from fault occurrence to fault isolation is about 0.5 seconds, and the recovery of power supply in the healthy segment is about 5 seconds.

Closed-loop and open-loop operation are judged by the master station system according to the primary side wiring mode and switch status of the system. When the state of a certain switch changes, the displacement information is sent, and the master station system judges the operating state of the ring at this time. If the operation mode changes, all FTUs on the ring are notified to modify their protection action criteria.

The above schemes are all based on the small resistance grounding system. In the ungrounded system, when a single-phase ground fault occurs, the faulty line is first identified by the small current grounding line selection device, and then the distribution automation software controls and operates the line switch in groups to identify the faulty section, disconnects the corresponding circuit breaker, and Restore power to loads in non-faulty segments. The discrimination of other fault forms is similar to that of the small resistance grounding system. 4.5 Distribution Automation Terminal Unit (FTU)

The distribution network monitoring remote terminal (FTU) is responsible for receiving the real-time position signal and measurement value of the control object and remote control of the control object. For different control objects, such as substations, switching stations, pole transformers, pole cutters, and large-capacity high-voltage users, it is necessary to select an appropriate FTU.

The DEP-900 type FTU supporting this system has a capacity of 8 channels of telemetry (YC), 16 channels of remote signal (YX), 2 channels of remote control (YK), and 4 channels of RS-232/485 interfaces. Its main functions are: data acquisition, feeder monitoring, fault detection, switch opening and closing control, automatic fault isolation and self-recovery of fault line power supply, automatic load transfer, storage and reporting of load values, acceptance of remote operation instructions and forwarding of collected data and information , with the appropriate communication interface, sampling interface and output interface, to meet the requirements of indoor and outdoor environments. DEP-900 also has the function of fault current state differential protection. It is based on the fault current state differential principle and acts as feeder protection for each circuit breaker. The feeder circuit breaker is not used for equipment and backup protection. When the main protection refuses to operate, the outlet switch of the substation will trip, and then the distribution network management software will judge and isolate the fault by remote control.

The distribution network in this area adopts a ring network structure, and the power is taken from different buses on the 10KV side of the 110KV substation, which operates in a closed-loop manner. Most of the community users are high-tech enterprises with high requirements for power consumption. They hope that when the system fails, the fault can be removed instantaneously to ensure uninterrupted power supply in the fault-free area. Therefore, a higher level of electrical backup and protection methods for the distribution network is proposed Only the DEP-900 series FTU with strong performance can be selected.

2. System realization of feeder automation

The communication system is the link between the main station system and the terminal equipment of the distribution network. The information exchange between the main station and the terminal equipment can use reliable communication means to issue the control commands of the control center to each executive agency or remote terminal, and at the same time All kinds of information collected by remote monitoring units (RTU, FTU, TTU, etc.) are uploaded to the control center. Communication methods include: optical fiber communication, distribution line carrier, wired cable, wireless spread spectrum, and public communication network. The communication method should be reasonably selected according to the application occasion and the principles of safety, reliability, practicality and economy.

2.1 Substation to master station layer communication
The communication from the substation to the master station of distribution automation uses the dispatching single-mode optical cable channel that has been laid.

2.2 Substation and FTU communication
Since the distance between each communication node in the communication network formed by substations and FTUs does not exceed 3 km, multimode optical fiber can be used to form a self-healing double-ring network between substations and FTUs.

2.3 Communication between master and slave FTU
It can be seen from Figure 1 that the urban power grid of our county adopts the ring power distribution mode of the ring main unit, and the bus mode of the master-slave FTU can be selected to realize the communication between the FTUs, and the communication adopts the RS485 field bus.

2.4 Communication between FTU and distribution transformer concentrator
The standard RS232 interface is adopted from the FTU to the distribution transformer main concentrator, the shielded twisted pair RS485 bus is used from the general concentrator to the distribution transformers and meter reading concentrators on each distribution transformer table, and the shielded twisted pair RS485 bus is used from the meter reading concentrator to the acquisition device Adopt low-voltage carrier communication mode.

3. Automation function of feeder automation

In the 10 kV ring cable distribution network, the installation of FTU in the ring network cabinet and the installation of the distribution automation system are a way to realize the automation of the feeder. The FTU communication channel on each ring network cabinet is connected with the distribution automation main station or substation system. When the network fails, the main station or sub-station locates the fault through software calculation according to the information sent by the FTU, and automatically sends a remote control command to the load switch of the ring network cabinet to achieve the purpose of isolating the fault and restoring power supply. Under normal circumstances, remote measurement of operating electrical parameters (including parameters such as current, voltage, and power of equipment such as feeders and box transformers), remote monitoring of equipment status, remote control of switchgear and remote switching of related settings can be realized. . According to the voltage and reactive power of the monitoring point, the operating state of the capacitor is controlled to achieve reactive power local balance and reduce line loss.

Broadly speaking, feeder automation should include line automation within the three voltage levels of high voltage, medium voltage and low voltage of the distribution network. For high-voltage distribution lines, the load is generally the secondary step-down substation; for medium-voltage distribution lines, the load may be large power users or distribution transformers; for low-voltage distribution lines, the load is the majority of users. Each voltage level has its own characteristics, especially the low-voltage feeder, which is very different from the high-voltage and medium-voltage lines. Therefore, when discussing feeder automation, it mainly refers to high-voltage and medium-voltage feeder automation, and especially refers to medium-voltage feeder automation, especially 10kV feeder in my country.

Under normal conditions, feeder automation monitors the status of feeder section switches and tie switches, feeder current and voltage in real time, and realizes remote or local closing and opening operations of line switches. Obtain fault records in case of faults, and can automatically identify and isolate the faulty section of the feeder, and quickly restore power to the non-faulty area. Among them, fault location, isolation and automatic recovery are of great significance to improve the reliability of power supply and shorten the power outage time in non-fault areas, which is also a main function of feed automation.

3.1 Feeder operation status monitoring: divided into normal status and accident status monitoring. The quantity of normal state monitoring mainly includes voltage amplitude, current, active power, reactive power, power factor, etc., and the operating state of switchgear. The monitoring quantity is real-time, and the monitoring equipment is generally called a feeder terminal unit (FTU). When there is communication equipment, these quantities can be sent to a certain level of power distribution SCADA system; when there is no communication equipment, some quantities that can be stored or indicated can be selected for monitoring. There are many monitoring points in the distribution network, and the necessary monitoring points should be selected for monitoring to save investment.

The distribution network equipped with FTU can also complete the monitoring under the accident state. Fault indicators can be installed in places where no FTU is installed. Usually, they are installed at the entrance of branch lines and large users, and have certain anti-interference ability and timing reset function. If the fault indicator has contacts, the fault information can also be sent to a certain level of power distribution SCADA system through the communication equipment.

3.2 Feeder control: use the controllable equipment (mainly switchgear) in the distribution network to control the feeder under the accident state and normal operation.

3.3 Fault location, isolation and automatic restoration of power supply for feeders: This is a unique function of feeder automation. The system composed of circuit breakers and sectionalizers can automatically locate the fault when a permanent fault occurs in the feeder. The sequential action of the equipment realizes fault isolation; realizes load transfer and restores power supply in the distribution network with ring network operation or ring network structure but open-loop operation. When a transient fault occurs, usually after the fault current is cut off, the fault disappears automatically, and the power supply to the load can be restored by the automatic reclosing of the circuit breaker.