Current sensors can retrofit for ‘smart city’ measurements

Current sensors can retrofit for ‘smart city’ measurements

New Products |
Swiss sensor maker LEM recently added a range of devices it is calling the LEM City range of products, aiming to support the measurements that will be needed for Smart City concepts. Current measuring sensors can be applied to existing circuits and include split-core compact current transformers (ATO models) and split core thin, light, flexible Rogowski coils (ART models) for easy installation.
By Peter Clarke


The sensors offer Class accuracy 1 & 3 according to IEC 61869, and measure AC primary currents from 0 to 125A (ATO models). They offer high ratings of insulation voltage (1000 V Cat III PD2 reinforced) for ART models.

LEM has developed the “ART” Rogowski current sensor to measure current of up to 10000A AC and beyond. The ART achieves IEC 61869 Class 1 accuracy without the need for additional components such resistors or potentiometers, which can drift over time. In addition, the ART uses LEM’s “Perfect Loop” technology; this is a design of closure or clasp that locks the measuring coil around the primary conductor is a highly stable and repeatable fashion. The result is to produce not only consistent and accurate readings, but also to eliminate any sensitivity to the positioning of the primary conductor within the detecting loop. Operators only have activate a robust and fast “Twist and Click” closure. The product can provide metering functions, or monitoring of instantaneous currents for grid-regulation, and can be retrofitted to monitor currents on the output conductors of substation transformers. The sensor provides an analogue voltage output, without saturation effects, to Class 1 (fiscal) standards with a maximum inaccuracy of 0.65%. No external compensating components are required.

An internal shield is provided as standard to guard against external fields, improving accuracy and optimising performance for small current measurements. The ART series provides the same ease of installation as existing split-core transformers, but with the benefits of being thinner and more flexible.

Whatever the chosen dimension – 70, 125 and 175 mm diameter for the aperture – the ART can be mounted very quickly by simply clipping on to the cable to be measured. Contact with the cable is not necessary, and the ART ensures a high level of safety as well as providing a high rated insulation voltage (1000 V Cat III PD2 – reinforced). The ART also allows disconnection of the coil to be detected through the use of a security seal passed through a specially designed slot. It can be used in applications requiring a protection degree up to IP 67.

For AC current measurement up to 125A, LEM has also designed the ATO series of split-core current transformers in 2 mechanical designs, one with a 10 mm diameter aperture and one with 16 mm for the primary conductor. 32 models are available to accommodate different current ranges, and types of output (current or voltage).

Current output ATO models supply a ratio of 1 mA/A with a class accuracy 3 whilst the voltage output ATO models are available either with a ratio of 225 or 333 mV @ IPR (rated primary current), with a class accuracy 1 according to IEC 61869 standard.

There is no need to disconnect the primary conductor carrying the current to be measured when installing the ATO as it can simply be clipped on. It is easy to fix it to the primary conductor thanks to a cable tie system integrated into the case. ATO models can also be DIN Rail mounted.



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