For a customer from the drive application sector, Isabellenhütte developed a 1-µOhm shunt that is capable of consistently measuring 30,000 amperes on an inverter for high-performance drive control units. With its massive Cu connections, the new, compact 1-µOhm shunt is suited for direct installation to the busbar system. The resistor inside the shunt is made of the electron-beam-welded composite material Cu-Manganin-Cu. Side-mounted steel plates guarantee mechanical stability and prevent external momenta from being transmitted to the manganin strips during installation.
Because internal thermal resistance is less than 5 mK/W, the peak power loss (900 Watts) at 30,000 amperes only increases the resistor material’s hot spot temperature by approximately 4.5 kelvin.
The electric properties are comparable with those of the best mOhm shunts:
•Resistance: 1 µOhm
•Temperature coefficient: TC < 20 ppm/K
•Thermal EMF against Cu (20-60 °C): Uth < 0.2 µV/K
•Long term stability (140 °C, 2000 h): dR/R < 0.2 %
A measurement system inside the shunt with precision converters and microcontrollers takes care of 16-bit data acquisition, recording, calibration and processing.
The internal sampling rate of 4 kHz measures even rapid signal changes. Thanks to its directly assembled measurement system, the shunt provides a high level of EMC stability (electromagnetic compatibility) and noise suppression. Temperature recording of the internal shunt and measurement system helps largely eliminate the temperature coefficient. Rapid switching between areas even makes it possible to measure short-term overcurrents of up to 300,000 amperes.
An analogue low-pass filter plus an additional configurable digital filter limit the measuring channel’s bandwidth to approximately 500 Hz to avoid aliasing while still allowing DC and 50/60-HZ AC measurements. The high-current measuring module only needs a few Watts, even including data transfer. A high voltage cable with an external, electrically isolated mains adaptor supplies the IMV with power. The module also has an insulation stability of 20 kV.
Rapid, bidirectional data transfer is provided by a serial interface via optic fibre (glass or plastic). Data can also be transmitted via CAN, ethernet or other types of interface. Standard secure data transfer contains a status byte, a 16-bit CRC check word, the temperature, as well as current measurements in the 30 kA and 300 kA ranges.
A remote station is available upon request, which provides insulated power and converts the proprietary internal protocol to any external protocol, such as standardised industrial bus systems.