Intelligent switchgear for medium voltage systems

The progress of medium voltage smart grid equipment. As an important part of the smart grid, medium voltage distribution has a huge number of substations and distribution equipment. After nearly 20 years of development, medium voltage equipment has matured in technology. Smart devices are a product of the development of modern control technology, sensing technology, and communication technology. They are the fusion of primary and secondary devices and represent a revolutionary change. Building a smart grid, so that there is no clear boundary between "primary equipment" and "secondary equipment", and integrated and integrated smart devices are the inevitable trend of development. By installing sensors and intelligent components to monitor the operating mechanism, key components, and characteristics, real-time monitoring of the circuit breaker status can be achieved. However, increasing the monitoring system will inevitably lead to a decrease in the reliability of the circuit breaker. Some key characteristics, such as vacuum degree and partial discharge, do not have accurate and reliable monitoring technologies, and immature technologies can cause false alarms and other problems. For example, environmental noise has a significant impact on partial discharge. Comparing the research and development directions of medium voltage smart grid equipment among major domestic companies, it can be found from Table 1 that most companies pay more attention to the monitoring of institutions and key components, while there is less research on real system integration.

The GE Industrial Systems R&D team has been developing medium voltage intelligent circuit breakers since 2008. Based on the concept of integrated design, GE's iVB vacuum circuit breaker hopes to achieve equipment intelligence by highly integrating electronic sensing units and protection systems. The primary equipment, secondary signals, and protection are perfectly integrated to achieve maximum functional integration and create maximum value for customers. The iVB circuit breaker has a "brain" self tripping function. The iVB intelligent circuit breaker is a fully integrated product that replaces traditional switchgear discrete components such as current transformers, comprehensive protection relays, secondary wiring, etc. The total cost of the circuit breaker is lower than the total price of traditional discrete components. A circuit breaker is like an outgoing cabinet. The iVB intelligent circuit breaker adopts a new compact spring operating mechanism with high reliability, high-quality vacuum arc extinguishing chamber and contact elements, maintenance free, and no monitoring required. It can achieve four sets of conventional opening and closing, undervoltage, overcurrent coil configurations, as well as network interlocking coils to achieve interlocking between circuit breakers. The quick release device can achieve rapid opening of circuit breakers when needed. The current signal is collected from a sensor based on the Roche coil principle, with an air frame to avoid magnetic saturation, no risk of secondary open circuit, a wide measurement range, and good linearity. One specification enables full range measurement. Due to the fact that sensors are low-voltage components installed on high-voltage contact arms, electrical insulation is an important issue. iVB has excellent electric field analysis and insulation design to ensure that it meets the withstand voltage level of circuit breakers.

EntelliGuard integrated into the circuit breaker mechanism box ™ TU electronic protection unit. Responsible for monitoring current and voltage signals in a primary circuit, and providing measurement, protection, diagnosis, and communication functions for current, voltage, frequency, power, etc. in the primary circuit. Realize the intelligence of circuit breakers. The main features are as follows: a. LCD display and drop-down menu, touch buttons, easy to display parameters and parameter settings b. Fault recording and waveform capture, data recording c. Modbus communication protocol, optional HMI communication manager, can achieve IEC61850 communication with superiors, meeting the requirements of intelligent power grid communication protocol d. Complete protection curve, can achieve protection of lines, cables, transformers, capacitors, etc.

The iVB intelligent circuit breaker is still a circuit breaker designed as a whole, avoiding the installation of sensing units and protection units on ordinary circuit breakers, which makes the structure complex, and can greatly simplify the engineering technical preparation and order processing process, achieving fast delivery; The engineering design work is simplified, and the main circuit of the switchgear has been integrated with circuit breakers, requiring only a small amount of auxiliary and signal circuits to be added; The wiring of the switchgear is significantly reduced, eliminating the risk and consequences of misconnection, and the installation work of the substation will also be carried out quickly; Factory system integration, complete inspection of circuit breakers to ensure high-quality quality, safety, and operational reliability are verified. By using a power box design with integrated circuit breaker and grounding switch functions, equipped with complete mechanical interlocking, it can be used for 550mm wide compact switchgear, reducing the footprint. Due to the integration of main functions, the cabinet height and depth can also be reduced. For cooperative panel factories, only the back cabinet and instrument room need to be made, connected to copper bars, and easily assembled into cabinets. Modular design is easier to achieve, quick replacement, perfect design and tooling ensure precise coordination between switches and cabinets. In addition to completing the type test of ordinary circuit breakers, iVB has also passed electromagnetic compatibility tests, including impulse voltage tests, electrical fast transient pulse group tests, and oscillation wave immunity tests; And the sensor collects current signals, and the circuit breaker trip test is driven by electronic trip, as well as the 1000 mechanical life test of the circuit breaker driven by electronic trip.

GE's medium voltage intelligent switch counter iPV Dual aims to further leverage the characteristics of the intelligent circuit breaker iVB; GE has developed the iPV Dual, a medium voltage metal enclosed intelligent double-layer switchgear. Based on the characteristics of iVB, iPV Dual is the next generation switchgear that meets the requirements of the power grid, with minimal wiring and maintenance free. The main features of the iPV Dual intelligent switchgear are as follows:

The measured values of voltage transformers, zero sequence transformers, etc. inside each switchgear can be connected to the protection unit on the circuit breaker through aviation plugs, and the positions of the circuit breaker and grounding switch are also connected to the protection unit. The intelligent human-machine interaction interface can use twisted pair cables or optical fibers to collect data from 10 circuit breaker protection units through Modbus. One twisted pair cable can achieve local data communication and status query. The HMI can be connected to the main station system through Ethernet IEC61850 protocol. The system functions of iPV Dual are shown in the following figure.

The intelligent human-machine interaction interface (HMI) serves as the hub of the switchgear and needs to be used as the main control substation and front-end processor of the integrated automation system, forming the middle layer of the automation system. It can communicate with various systems such as the main station via computer IEC61850/MODBUS upwards, and communicate with the terminal equipment MTU in the substation via MODBUS downwards, completing the MTU collection and forwarding of terminal equipment data.

At the same time, HMI serves as an on-site data acquisition device, displaying real-time system diagram switch status. Through the touch screen human-machine interaction interface, it is easy to view real-time data such as voltage, current, power, switch status, etc. of terminal equipment in the substation, and can also view current, accident curves, etc., eliminating potential accidents.

PV Dual is designed with a small and compact size, only 550mm wide, double-layer circuit, low cost. One switchgear has two outgoing circuits, saving costs by 35%. The high-performance 12kV main busbar reaches 2500A/31.5kA, with an outgoing line of 1250A. The test meets national standards, the front panel is easy to operate, ergonomic design, and low maintenance costs. Equipped with a low-voltage side cabinet to facilitate the integration of secondary control equipment signals. Provide a complete interlocking system to prevent misoperation and improve safety. Indoor metal enclosed switchgear is easy to manufacture and maintain. The internal compartment adopts a fully metal partition design, leaving sufficient space for cable rooms to facilitate cable maintenance and installation

Conclusion: As important equipment in the power grid, medium voltage switchgear has a large quantity and is directly related to residential electricity consumption. The technology of medium voltage circuit breakers and switchgear is mature and relatively reliable. Through further design and improvement of process quality, it is possible to truly achieve maintenance free operation. As a trend in power development, the smart grid requires the correct direction to truly integrate control, protection, monitoring, communication, and other aspects through the primary and secondary integration of system equipment. The iVB vacuum circuit breaker and iPV switchgear are innovative designs by GE in the switch industry, achieving revolutionary changes in switch technology and maximizing user benefits.