Current sensors for measuring very high currents

Paul Boughton
A range of current sensors is now available that allows the Yokogawa family of precision power meters to be used for measuring very high currents. Developed and manufactured by Hitec Power Protection of Almelo, The Netherlands, the new Zero-Flux current sensors allow the precise measurement of currents up to several thousands of amperes - including simultaneous measurement of AC and DC currents - while also providing accurate phase-shift information.
Other key features of these sensors include isolation from the primary circuits, very high stability and accuracy, high bandwidth, saturation detection with automatic reset after overcurrent, and the ability to switch on the devices with current already present when connected.
There are three types of current sensor in the Zero-Flux range: the Macc Plus external current sensor; the SC1000 split-core sensor; and the Curacc current-measuring system.
The Macc Plus external current sensor offers a 1000:1 current transfer ratio for maximum 850A peak current (600A RMS). For DC currents, a maximum of 600A DC can be measured continuously. Versions with voltage outputs are also available. With an overload capacity of 20 per cent, sinusoidal currents of 85A RMS, 170A RMS and 430A RMS can be measured. Maximum continuous DC currents are the same as the AC peak limits.
The SC1000 split-core Zero-Flux current measuring system is designed for applications where it is not possible (or permitted) to switch off a motor in a production facility or in a critical safety environment such as a nuclear power plant. It can also be used in situations where it is inconvenient or costly to remove and replace the glands on thick power cables in order to run them through the sensor hole. The SC1000 measures primary currents up to 1000A peak (700A RMS), with a transfer ratio of 1000A peak/0.5A peak or 1000A peak/10V peak for a voltage output.
If a measurement range of 1000A peak (700A RMS) is not enough, the Curacc series offers up to 6000A peak (4240A RMS) for 'current-in/current-out' applications. For currents up to and including 2000A peak (1400A RMS), a robust resin-encapsulated head is available. For DC currents, a maximum of 6000A DC (model E) can be measured continuously.
A range of junction units is available to minimise wiring.
Yokogawa products with which these current sensors can be used include the WT3000 precision power analyser, WT500 compact power analyser, WT210 (single-phase) and WT320 (2/3-phase) power meters, WT1600 and WT1600S digital power meters, and PZ4000 single-shot power analyser.
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