When Siemens AG’s enormous ring motors with their 14 megawatts of power are in motion, crushing mined ores in the highlands of Bolivia, not one of the stones remains untouched. The aim is to crush ores, silver, lead and zinc ready for further processing. This tricky task is being tackled by gearless ring motors with a drum diameter of up to 40 feet. The external dimensions of a 36-foot machine are around 20 m wide and an impressive 17 m high. For comparison, the new EPHYMESS building is 20 m wide, 20 m high and 90 m long.
Generating a speed of around 10 rotations per minute when grinding the stones means that currents flow into the machine that cause the windings to heat up. In order to prevent the continuously running motors from overheating, Siemens chose to use double slot resistance thermometers from EPHYMESS GmbH. The bifilar wound sensors are installed in the slot of the ring motors and measure the temperature of the synchronous machine across the entire installation length. Continuously monitoring the temperature curve allows an excessive rise in temperature to be prevented in good time.
Redundant sensors for safety
For safety reasons, instead of a single slot resistance thermometer, a double slot resistance thermometer is used to provide redundancy. This would also ensure that full protection for the machine was maintained in the unlikely scenario of one of the sensors per phase failing. After all, despite the slot resistance thermometers’ high quality and precise craftsmanship, damage to one of the delicate components is possible if they are installed incorrectly or due to the tough conditions. It is therefore a good idea to ask the EPHYMESS engineers about the precise installation situation and correct handling.
The rigid double slot resistance thermometers used for this application have the following technical properties:
- Bifilar coiled platinum wire
- Insulation material: Mica insulation
- Resistance value: 100 Ohm at 0°C, as per DIN EN 60751
- Dimensions: 3x18x250mm
- Operating current: 0.3 to 2 mA
- Electrical strength: 2.5 kV
- Temperature range: -40°C to +180°C, insulation material class H
- Measuring accuracy: Class B as per DIN EN 60751
- Strain relief: >200N/mm 2 (in relation to conductor cross section)
- Twined Teflon line to compensate induction voltages
- VPI impregnation-proof
Explosive environment – no problem
EPHYMESS produces all its sensors in line with the specific customer’s preferences and requirements. With regard to the construction and specifications above, modifications are possible within the respective standard, allowing different installation situations to be taken into account. Slot resistance thermometers are also available in IECEx / ATEX designs for explosion-protected areas.
