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Avoiding Risks of High-Voltage Motors

First temperature transmitter for motors up to 11 kV

A large German company in the process industry that equips its plants with the best available technology has become aware of a previously little-noticed risk:

Insulation defects of slot temperature sensors in high-voltage motors after years of use can present serious hazards to downstream systems and to the persons working on them. Knick has taken on the problem and closed this vulnerability with a temperature transmitter suitable for use in high-voltage motors up to 6.6 kV or 11 kV due to its extremely high isolation.

High-Voltage Motors in Continuous Operation
High-voltage motors as used in the process industry for fan, pump and compressor applications often carry out their service for years and decades without complaint. The motors are thermally monitored according to EN 60034‑1. The temperature sensors used for this purpose – so-called slot thermometers – are insulated in the stator slots together with the windings of each motor phase and are used to detect increased temperatures due to insufficient cooling or overload.  Their proper isolation is confirmed by a high-voltage test.

But the isolation is subject to influences in the course of many years of motor operation, which can lead to wear and at worst, to failure. Also carefully implemented isolation can be heavily burdened by transient overvoltages from the power supply, voltage spikes from converters, overvoltages by reflection, continuous mechanical and thermal loads and other effects. If the isolation breaks down, there is a risk of the temperature sensors becoming stressed by the high potential in a phase. The downstream systems and persons working on these systems are at risk.

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