Protecting and Monitoring the Low-Voltage Grid

This article is published by EEPower as part of an exclusive digital content partnership with Bodo’s Power Systems.

The power grid is changing fundamentally due to the energy transition. In the future, instead of a few large power plants, electricity will come from numerous small renewable energy sources, and new types of electric loads, such as EV charging stations and heat pumps, will pull energy from the low-voltage network. Operating companies face the enormous challenge of ensuring the smoothest possible grid operation, avoiding power outages, and maintaining high power quality. A smart NH fuse switch disconnector allows monitoring and control of this ever more complex energy flow while protecting switchgear against surge currents.

Figure 1. Smart fuse switch disconnectors monitor the current flow in building distribution systems. Image used courtesy of Adobe Stock

Protecting the Low-Voltage Grid

ProGrid, a smart solution from Mersen, a French company, was developed especially for use in grid and transformer stations, cable distribution cabinets, and low-voltage distributors. It represents a new modular generation of fuse switch disconnectors, which not only protect local low-voltage grids against surge currents but also measure energy flows and other parameters.

The solution is available in three versions: ProGrid, ProGrid Smart, and ProGrid SmartStation. ProGrid standalone fuse switch disconnectors protect substations, transformer stations, or switchgear in buildings against surge currents and short circuits. This version embeds a safer patented switching mechanism and can be upgraded for monitoring with a smart module if required. The module and sensors are already included in the second offer variant, ProGrid Smart. The latter features extended functionality and efficiently measures the energy flow at the low-voltage outlets of the switchgear, transformation station, or substation.

Figure 2. The ProGrid Smart fuse switch disconnectors monitor the energy flow from PV systems to transformer stations. Image used courtesy of Adobe Stock

Protection and Monitoring of Complete Switchgear Systems

ProGrid SmartStation makes it possible to combine ProGrid Smart with additional modular measuring instruments and sensors. The result is a complete energy and environment monitoring system for medium-voltage/low-voltage substations. ProGrid SmartStation combines the ProGrid fuse switch disconnector with additional modular measuring instruments, such as sensors for smoke detection, indoor and outdoor temperature, relative humidity, or the status of the switchgear doors. Flood detectors or ozone sensors can also be integrated with the ProGrid SmartStation monitoring system.

In 2022, Mersen presented a smart module for its current fuse switch disconnectors to enable real-time monitoring of the energy flow in low-voltage applications. ProGrid is an advancement of these smart modules. The modular fuse switch disconnectors of the latest generation protect the low-voltage grid against surge currents and also enable digitalization of the grid. This is the main requirement for intelligent and flexible electricity distribution generated by renewable energy sources. The ProGrid solutions offer numerous advantages for building automation and electrical installation specialists, as well as switchgear manufacturers. They not only protect the in-house power grid against surge currents due to fluctuations in the general power grid, but the smart ProGrid fuse switch disconnectors also measure PV system energy flow, supported on the roof or integrated directly in the building like an element of the roof or facade.

Measuring Energy Flow in Local Grids

The Renewable Energy Act (EnWG §14a) requires measuring energy flows by the distribution management system. The purpose of the distribution management system is to prevent overloads to the public power grid. If capacities are insufficient to accommodate the power generated by the PV system, the grid operator can limit various stages of the system. However, this requires measuring the energy flow from the PV systems to the grid. This is where ProGrid solutions are useful since real-time measurement of the energy flow allows efficient adaptation of the distribution networks.

ProGrid fuse switch disconnectors were developed closely with grid operators in Germany and across Europe. The development was pursued in agile mode with early user tests for the main functionalities at each stage of the project. This immediate and direct feedback allowed the development team to integrate improvements early in the process. Valuable user experiences were taken into account to deliver this final product. As a result, the fuse switch disconnectors are optimally adapted to the requirements of the substation or building automation switchgear. The degree to which Mersen tailored the ProGrid solutions to the requirements of power companies and electricians is already obvious in the patented switching/opening mechanism. It ensures the highest user safety, fast installation, and ergonomic servicing and replacement of the modules.

Opening Mechanism Facilitates Installation

The mechanism executes two-step motions: parallel and rotating. The first parallel step is safer than other solutions, as it ensures IP20 protection against electric shock for the operator. IP20 protection lasts during the complete operation of the device, with no finger access to the electrical contacts. The second rotary motion allows easy access to the fuse.

Figure 3. The patented opening and switching mechanism allows fast and safe handling of the fuse switch disconnectors. Image used courtesy of Bodo’s Power Systems [PDF]

With a suitable tool, the fuse switch disconnectors can be mounted securely on current-carrying bus bars or installed on non-threaded bus bars using hook elements–even with current transformers.

Designed for Easy Retrofitting on Switchgear

The ProGrid fuse switch disconnectors come standalone or as ProGrid Smart with factory-integrated sensors and a smart module on the top or bottom of the device. The top version is especially suitable for installation in new switch panels or transformer stations/substations. To retrofit an existing cabinet, the bottom smart solution enables one-to-one replacement of the already installed standard fuse switch disconnectors with ProGrid Smart Bottom. This is currently the most compact smart version of a fuse switch disconnector on the market and the footprint of the device matches the market standard, limiting the impact on existing installation.

Up to 24 ProGrid smart modules can be connected per master in sequence through daisy-chaining. Mounting involves only minimal wiring: the sensors’ cables are inside the fuse switch disconnector and are not in contact with the bus bar system. With only one Modbus cable distributing the communication between the modules and the gateway, the ProGrid Smart module offers direct access to real-time energy and status data.

In addition, the design of the ProGrid fuse switch disconnectors enables the upgrade from standard to smart, thanks to pre-wired accessory kits and easy-to-install sensors cabling through the inside of the device. This product concept even convinced the jury of the German Design Council, which honored ProGrid with the 2024 German Innovation Award.

Figure 4. ProGrid fuse switch disconnectors are available with a smart module mounted on the top or bottom. The smart modules can also be retrofitted on existing fuse switch disconnectors. Image used courtesy of Bodo’s Power Systems [PDF]

Worldwide Access to All Sensor Data

ProGrid Smart modules are compatible with all devices that communicate using the Modbus RTU, and ProGrid SmartStation measuring modules can also communicate using Modbus TCP/IP and MQTT protocols. Grid operators can use these interfaces for real-time access via the internet to all data measured by the sensors in the switchgear and its environment (via a light control system provided by Mersen or other partners). The Modbus RTU cable in the Mersen ProGrid Smart fuse switch disconnectors is not only used for data transfer but also supplies the modules with power. This eliminates cables and reduces installation space.

Figure 5. The ProGrid SmartStation solution not only protects transformer stations against surge currents but also monitors the current flow and measures other important parameters. Image used courtesy of Bodo’s Power Systems [PDF]

Highly compatible with any Modbus RTU or TCP/IP gateway and controllers, the ProGrid solution allows LV network data collection and analysis through all market-renown software solutions for improved and efficient maintenance by DSOs with the ultimate goal of high service availability and lower operation costs for the end consumer.

Ready for the Power Grid Transformation

The smart ProGrid NH fuse switch disconnectors offer a tool for complete monitoring and control of medium/low-voltage switchgear. The smart ProGrid solutions allow switchgear manufacturers, electrical installation, and building automation specialists to prepare for the challenges of low-voltage grids.

This article originally appeared in Bodo’s Power Systems [PDF] magazine.