Pilz has provided safety products and consultancy services to help EMB develop innovative electric generators based on fuel cells, ensuring the prototype and initial production batch are safe to operate and maintain.
Soon fuel cell systems could take over the power supply in off-grid areas or provide temporary power in the event of a mains failure - reliably, with minimum impact on the environment and low maintenance requirements. EMB Elektromotoren und Gerätebau Barleben GmbH manufactures innovative electric generators based on fuel cells and is relying on products and software components from Pilz To ensure their safe operation. Pilz is providing tailored assistance including comprehensive advice for the risk assessment process and for the forthcoming CE certification process.
The weatherproof box looks pretty innocuous: with a footprint of less than one square metre, it is roughly the size of the telephone distribution cabinets typically seen on the street. There is nothing on the outside to indicate that the housing contains high-tech equipment. However, inside the cabinet a generator based on a modern fuel cell is at work.
In autumn 2011 EMB decided to establish a new business unit focusing on renewable energy. The company had by then gained more than 45 years of experience in the construction of Buchholz relays for transformers, monitoring relays for stepping switches and other protective devices for liquid cooled and isolated devices. Working in close cooperation with the Otto von Guericke University of Magdeburg, EMB developed the prototype for an uninterruptible power supply (UPS) based on fuel cell technology. As a series model, it is intended to supply power to signalling systems, lighting equipment, radio masts, telecommunications distributors and other off-grid energy consumers. Depending on the required output, the device can also serve as a redundant emergency power unit that responds immediately in the event of a power failure. In contrast to solar-based systems, the electric generator does not need an expensive battery backup and can be used practically all the time. In the higher output segment it can replace high-maintenance, environmentally unfriendly diesel generators.
The compact energy supply unit consists of two parts: the main chamber accommodates the fuel cell module, the process control system and all the electronics, while the second, spatially separate chamber houses four pressure vessels containing hydrogen. The current model delivers 1-2kW at a freely selectable output voltage for up to 10 hours, making the prototype suitable for supply duties in the low load range.
It was clear as early as the development phase that even this innovative product is subject to the German Product Safety Act and the associated European standards and directives. The first step was to determine the risks in accordance with EN ISO 12100 in order to minimise the potential hazards for people and the environment. EMB sought the advice of proven experts: Sascha Hanf, project developer at EMB, explains: "We already knew Pilz to be an experienced provider of automation and safety solutions with applications that also extend beyond traditional mechanical engineering. In addition to technical aspects, the package of services they offer, their expertise in machine and plant safety and the resulting harmonising standards were crucial factors that led us to choose them."
After an initial consultation, EMB and Pilz were able to define the areas requiring action in terms of safety aspects. Precautions had to be taken to prevent the two doors being opened inadvertently or wilfully, for instance. Authorised persons must not be exposed to any hazards when changing the gas tanks or carrying out essential maintenance. The programmable safety system used is intended not only to monitor safe signals, but also to have an interface for the process control system, external sensors and remote maintenance. Since the housing will occasionally be all on its own, a vandal-proof version is required.
Martin Mielke, an applications engineer with Pilz, comments: "We got together with EMB to analyse the potential risks and propose possible solutions and suitable hardware and software components. The important thing was always to have a clear, easy-to-use solution that precluded attempted manipulation right from the start."
The doors are monitored by two Pilz PSENmag magnetic door switches. If they are opened without access authorisation, the system goes into a safe operating mode. Pilz's PSENslock non-contact safety gate system offers even more protection, combining secure safety gate monitoring with a strong, non-contact magnetic interlock in one unit. That enables it to meet high safety requirements while also being conditionally able to withstand vandalism.
The Pilz PITmode operating mode selector switch (pictured right) is used to ensure that service staff can change gas bottles or carry out maintenance work easily and without risk: the intelligent RFID access key defines the safe status into which the system is to go after it is inserted, what rights the key owner has and what action he is permitted or not permitted to perform on the device. The service company employee must first authorise himself with his own personal key before he can change the gas bottles. The system goes into a safe mode that enables the bottles to be changed without any risk. Once the door is closed, the system returns automatically to the operating mode.
The same applies for the service engineer: with an installed emergency stop button ensuring fast shutdown in an emergency, he can perform maintenance tasks at no risk. In EMB's current prototype, the PITmode defines two operating modes (normal and service mode). Up to five different modes can be realised if necessary. There are also plans to introduce a remote maintenance function that registers the staff on the system prior to maintenance.
Sascha Hanf adds: "What swung it for us was that everything is so straightforward and no one need have any concerns about their health when working on the module."
Safe control system
The safe signals from the doors and emergency stop button are monitored by a PNOZmulti 2 configurable control system (pictured right). The device can handle up to 20 safe inputs, eight of which can be configured as signal outputs and four as safe semiconductor outputs. Configuration is easily done with drag-and-drop actions using the PNOZmulti Configurator. Only 45mm in width, the base unit can be flexibly and economically expanded from three safety functions at any time. Furthermore, the CANopen interface enables the PNOZmulti 2 to connect to the plant control system and external sensors such as those monitoring interiors or the temperature.
Using the Pilz PAScal Safety Calculator, an EN ISO 13849 Performance Level (PL) d was calculated, and all components used by Pilz meet or exceed the requirements for this level. Sascha Hanf concludes: "Pilz has done an excellent job with its safety components and consulting services. The solution implemented is safe and easy for our staff to use. Pilz has given us enormous support on the way to developing the series product and in the upcoming CE certification process."
EMB is initially manufacturing a small batch of its fuel cell generators in 2016. Among the tasks on the to-do list for product optimisation are extending the runtime, simplifying the visualisation and remote maintenance - in the latter case using the new PASvisu web-based visualisation software from Pilz. EMB is also keen to develop systems with a much higher output power. It is likely that Pilz will again be asked to provide the safety components as well as technical advice.