2021-04-08 HVAC/R, Products
Control cabinets play a central role in most applications. When power supply issues from the grid are the cause of problems, troubleshooting can be difficult. It is better to prevent these errors through network monitoring. In addition to grid voltage, temperature inside the control cabinet also plays a crucial role in its reliability.
Components inside the control cabinet such as controllers or actuators have a power supply unit that converts grid voltage into direct current. Microprocessors, memory, and other components in the electronic device are thus supplied with energy. Undervoltage, overvoltage, phase loss, or other network problems can affect the functioning of the microelectronics. Even very short disturbances in the grid (so-called grid flickers) can lead to significant problems in the control cabinet. Since the supply network is usually beyond the direct control of the operator, the following approach is often pursued: a phase monitor monitors the three phases L1, L2, and L3, and in critical conditions (e.g., undershoot of the permissible undervoltage limit), a reset is performed in the control cabinet. The central reset brings the entire cabinet back to a safe and defined state. This avoids the possibility of individual components possibly performing resets staggered in time and, in the case of a design flaw in the watchdog (automatic reset), even remaining in an undefined state. Modern phase monitors go even further by documenting the temporal course of the grid voltage and errors or problems with a timestamp. This information can then be used in discussions with the utility company to demonstrate problems in the grid voltage. The following sections describe applications and backgrounds.
Errors Due to Regions with Unstable Supply Networks
In Western Europe, the quality of the electrical grid is usually very high. The Federal Network Agency in Germany provides detailed evaluations of the low and medium voltage grids on its website. However, internationally operating manufacturers often export their products to regions of the world that have significantly more unstable supply networks. For example, a manufacturer of ice machines in Tunisia exports to the entire North African region and uses phase monitoring relays due to the widespread network disturbances there.
Errors Due to Regional Network Problems (Microregion)
However, sometimes it is not entire countries or regions that are known for difficulties in the networks. Even in usually stable regions, there are microregions where problems occur locally. A refrigeration system in such an environment is maintained by the company Schiessl in Bergheim near Salzburg. The system is supplied by a transformer located about 100 m away, which also serves a ski lift. Due to this large consumer, there are locally significant voltage fluctuations in the network. Various controllers have repeatedly failed. A VFD operation of the system could not be implemented because the input voltage fluctuates too much. Here, a "KRIWAN INT69UY" phase monitor was found to be an easy-to-install monitoring solution. With the measured and documented data in the PDF protocol from the "INT69," discussions with the energy provider and demands for an upgrade of the supply with data and facts can now be substantiated. In this case, the additional temperature input of the phase monitor in the control cabinet is not used to measure the cabinet temperature, but rather the hot gas temperature is monitored with a PT1000 sensor. By additionally using a compressor protection device "INT69I2" with current and temperature monitoring, complete monitoring of the system for various critical errors could be achieved. Since all modules have the same diagnostic interface for data exchange with a smartphone or laptop, communication is very easy.
Aging Components
Many components in the control cabinet are used for years and sometimes even decades. Even if the function is still given under normal conditions, individual components on the board, especially capacitors, can age. In individual cases, this can lead to such relays, controllers, or PLCs becoming more susceptible to voltage fluctuations in the network or temperature variations. Such errors can occur unsystematically in individual control cabinets and increase over time. This makes them difficult for the service technician to find. Here too, the principle applies: if the control cabinet is monitored (temperature and grid voltage) and a reset is performed when limits are violated, undefined states and possibly damage to components can be avoided.
Avoid Expensive Service Calls
Clade Engineering Systems in England had recurring voltage problems with systems in the field. These were monitored by conventional voltage monitors, but these could not be adapted flexibly enough to the respective situation on-site. Due to the simple adaptability of the "KRIWAN INT69UY" phase monitors, this problem could be solved, and systems could be even better adapted to the requirements of the respective customers. A simple USB connection between the phase monitor and a laptop or mobile device allows very comfortable adjustment of parameters and behavior to the respective customer-specific system.
Dr. Christian Ellwein, KRIWAN Industrie-Elektronik GmbH, Forchtenberg
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