Transducers measure traction energy with unprecedented accuracy
23 September 2010
LEM has created a measurement technology that enables unprecedented levels of accuracy in the monitoring of rail transport power consumption. The matched and optimised devices comprise transducers for current and voltage, and a new energy meter. All three units provide levels of accuracy not previously seen in the sector, and come with the specific certification recognised in the electric rail traction industry. Used together, they enable designers to meet or exceed existing and planned specifications; they also offer the same levels of accuracy to system designers working in other areas of high-power electrical supply.
Current, in the high-accuracy power transducer suite, is monitored by new introductions to LEM’s ITC 4000 or ITC 2000/1000 ranges. Certified to Class 0.5R, the ITC 4000 employs an advanced closed-loop (compensated) current measurement design based on the Fluxgate principle. Nominally rated at 4000A, the ITC 4000 will measure +/-6000A, consuming less than 80 mA (at zero primary current) to under +/-340 mA (at 4000A primary current) from a supply voltage of +/-24V to its measurement (secondary) circuit.
Fluxgate technology is noted for its high levels of both accuracy and linearity; the ITC 4000’s linearity error is under 0.05%. The device’s offset current is less than +/- 10A and it also exhibits extremely very low temperature drift. The ITC 4000 operates over –40 to +85 deg oC, and meets or exceeds all relevant standards for safety and operating environment.
For voltage measurement to the same standards or precision, LEM offers a development of its DV series voltage transducer that spans 1200-4200V RMS. Introduced with an accuracy performance of Class 1, further development has taken the DV Series to Class 0.75 accuracy. The DV offers (as an active device) current consumption of 19-23 mA, measurement frequency bandwidth of 12 kHz, and an insulation voltage of 18.5 kV.
A more compact device than any competing transducer, The DV series measures just 134 x 54.22 x 147.25 mm; like its current-measurement transducer counterpart, it meets all of the requirements of the rail industry in terms of EMC performance, partial discharge extinction voltage and safety, while featuring low weight, and flexible mechanical mounting and electrical output characteristics.
Completing the measurement technology package is LEM’s EM4T II single-phase energy meter, also rated to Class 0.5R accuracy: this form of accuracy specification is according to the proposed EN 50463 standard that will unify measurement practices for trans-border train operation across Europe. The EM4T II is a four-channel device that records data such as load profile, and train data and location (from GPS inputs) at regular intervals. Used in conjunction with the capabilities of the ITC 4000 current transducer, the EM4T II accurately logs bi-directional power flow, enabling accurate monitoring of energy usage even under regenerative braking.
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