elcome, dear friends of protection, control and electrical engineering. In an industrial plant, powerful magnetic stirrer reactors, with a capacity of up to 25,000 liters, shut down irregularly for several weeks. In our exciting technical article, you can now find out what a magnetic stirrer is, who caused the shutdowns and how the problem was pragmatically solved.
Introduction
In petrochemicals, as in many other areas of chemistry and biotechnology, magnetic stirrers are indispensable tools for ensuring the homogeneous mixing of solutions in hermetically sealed systems and for allowing chemical processes to run in a controlled manner. Magnetic stirrers generate a rotating magnetic field inside that sets the stirring bar or mixer in the vessel in motion and can even provide magnetic storage. The animation in the following video shows an example of a side-mounted magnetic stirrer.
What happened?
At the customer's plant, several stirred reactors with capacities of up to 25,000 liters inexplicably shut down at irregular intervals of several days to several weeks. The three-phase drives were controlled by a 690 V low-voltage network via a frequency converter. Since several agitators always shut down within a few seconds of each other during each incident, it was suspected that the supply voltage could play a role.
Therefore, a standard-compliant PQ measurement was first installed in the supply line of the stirred reactors and the power consumption of the drives was also monitored. Since no failure occurred during the following days, the evaluation of the measurement data of this first measurement did not show any abnormalities.
However, it became interesting when some stirrers again stopped working for no apparent reason. Here, the evaluation of the standard-compliant measurement of the voltage characteristics at the time of the failure again showed no abnormalities. In addition, no typical power quality events were registered.
The power consumption of the drives, on the other hand, which was also recorded, showed a significant fluctuation that began well before the shutdown and continued to build up, ultimately leading to the shutdown.
Analysis of the supply voltage at the beginning of the power fluctuation showed a brief voltage dip of approx. 4% for a duration of <= 40 ms.
Subsequent measurements verified that the brief and perfectly standard-compliant voltage dip marked the beginning of an oscillatory vibration in the stirrers that had been set up by the interaction of the mass inertia of the highly viscous liquid in the stirrer and the magnetic drive.
To identify the cause of the voltage dips, further measurements were taken at the 10 kV medium voltage and at the 110 kV level. The results showed that switching operations in the upstream 110 kV high-voltage grid were responsible for the short voltage dips and could be held responsible for the shutdowns. Fortunately, the problem was solved pragmatically by switching the supply to a different source.
What can we learn from this story?
The bottom line is that despite strict compliance with all the limit values defined in the power quality, system failures can occur in production. Even small and usually permissible fluctuations in the power supply can have a significant impact on electrical equipment.
It is therefore advisable to use measuring devices that can evaluate the power quality in accordance with the standards and simultaneously carry out further high-resolution measurements that are necessary for a targeted fault analysis.
An excellent device for this purpose is the EPPE RX, which can be DIN rail mounted and used as both a power quality measuring device and a fault recorder.
With its 8-channel measurement function, it measures 4 voltages up to 1000 V and 4 currents up to 100 A, with a fast sampling rate of 200 kHz and outstanding precision of 0.05 %, making it ideal for small and medium-sized systems.
What can you do with the EPPE RX?
• Power quality monitoring in accordance with EN 50160
• Recording energy data and load profiles
• Optimizing energy consumption
• Transient recorder for detailed fault analysis
• Detecting and recording network swings
• Recording switch-on and switch-off operations
• Measuring flicker and harmonics
• Monitoring and analysis of renewable energy generation systems
• Grid optimization
• Fault location
• Monitoring critical consumers
In particular, EPPE RX makes a perfect impression as a fault recorder. With two internally separate fault recorder units, the automatic analysis of network faults and the identification of transient fault sources can be achieved simultaneously.
If you are interested in this topic and the EPPE RX, then take a look at the manufacturer's page.
Kind regards, thank you for stopping by and see you soon!
Your EEA-Team
