Power-Monitoring Current Transformers

The new CTRC AC Current Transformers monitor circuits up to 2,000 amps and produce a safe, low voltage output proportional to the RMS current value. This output is designed as an input to a power monitor or transducer, replicating the AC wave shape with phase angle resolution better than 2 degrees. The flexible coil design allows the cable to surround multiple conductors or bus assemblies regardless of shape and eliminates the magnetically permeable core of standard current transformers while providing excellent isolation, sensing only the magnetic field of the phase inside the loop. The CTRC can be used in any power monitoring application.

CTRC Current Transformers use the Rogowski coil as the first step in power monitoring. Each coil is matched with a signal integrator, and the output is calibrated for the highest degree of accuracy possible. The resulting 1/3 volt at full range current mirrors the primary circuit wave shape with less than a 2-degree difference in the phase angle and overall linearity of better than 1 percent of the full scale output. When matched with the circuit voltage wave shapes, a highly accurate representation of the system power, measured in watts, can be derived.

The signal integrator is housed in a compact, DIN-compatible enclosure, with 1.5 meter (59 inches) of lead cable from the sensing loop to the integrator. The signal integrator is powered with 24 volts, AC or DC, consuming less than 1 watt each. The narrow dimension of the lead cable (0.87 inches) allows for installation in very close quarters, easily possible between the monitored conductor and the adjacent phase. The coils are rated to 600 VAC and do not require shorting blocks between the integrator and the connected load. Even when the current through the loop exceeds the design range, the low voltage output remains at non-hazardous levels. — NK Technologies, 800/959-4014; www.nktechnologies.com