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Measuring currents in ac motors

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article image Block diagram of the measuring installation.

IN process industries, large centrifuges with three-phase motors are often used in hazardous locations.

Enormous forces are produced here which, when exceeding the highest permissible values which, according to Alvi Technologies , can lead to significant damage.

This damage may result in the destruction of a boiler, or the centrifuge, and the loss of filling goods due to production stop, etc.

Therefore, the current consumption of centrifuges is monitored.

By measuring the current consumption of the individual ac motor phases, an unbalance (non-symmetrical load) can be detected. Exceeding the permissible filling level, or agglomerating the processed goods, can also lead to an overload.

In automation/control, the current of the individual phases (for example, 100A per phase) is therefore transformed by a current transformer and an ac/dc transducer into a 4-20mA signal.

The transformed signal is displayed by digital loop indicators in the control room as well as on site in the hazardous locations. The digital indicators indicate the current in amperes.

The transformation of a non-intrinsically safe 4-20mA signal into an intrinsically safe signal is achieved with loop-powered IS isolators.

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