The US Navy’s all-electric fleet will require tens of thousands of electrical sensors.  A large percentage of these sensors are required to monitor and regulate power flow. Because power systems generally have fixed or stepped voltage outputs, current is often a variable parameter.  As a result, current sensing is critical.  The following tips list important advantages of several current sensor types in order to facilitate choosing the best current sensor for a particular application. 

Sense Resistor current sensors
Sense resistors heat up in proportion to the resistance applied while conducting current.  Therefore, sense resistors with lower resistance values are more likely to measure higher current levels without overheating.  The response time for sense resistor current sensors is defined and limited by the instrument that measures the voltage drop across the resistor.  The sense resistor tolerance determines the accuracy of the current reported by the system. The primary disadvantage of sense resistors is that they are direct measurement devices. This means that the sensor must be part of the high voltage circuit in order to measure current.

Hall Effect current sensors
Hall Effect sensors are advantageous because they can eliminate errors such as offset drift, sensitivity drift, and saturation of the magnetic core.  Therefore, select Hall Effect current sensors when utilizing small tolerances for current measurements.

Current Transformers
Current transformers (CT) are simple devices that do not require driving circuitry to operate and utilize a sense resistor for current measurement.  Current transformers are generally of two classes: protection relay CTs and instrument CTs. The protection CT must saturate sufficiently high to allow a relatively accurate measurement of the fault current. Conversely, an instrument CT requires good accuracy around the nominal current. Instrument CTs by design cannot withstand currents as high as the protection CTs. Some CTs have secondary windings dedicated to protection and metering.

Rogowski Coil current sensors
Rogowski coil current sensors are advantageous because they do not suffer from voltage saturation. This makes the technology useful over a wide current range (30 amps – 300 amps) which results in a reduction of the number of sensors needed to cover a given application.

Interferometric Sensors
Interferometric sensors are not susceptible to external magnetic fields unless the sensor is encompassed by the fiber loop.  Therefore, such sensors can be employed in areas where external magnetic fields may otherwise influence current measurements.

Polarimetric Sensors
Polarimetric sensors have the potential to be influenced by other magnetic fields residing nearby.  This sensor is also sensitive to temperature. However, if the temperature is known, the sensor’s response to magnetic fields can be removed from the current measurement by electronic means.  Polarimetric sensors are advantageous because they may serve dual purposes as both a temperature sensor and a current sensor.  Table 6-1 summarizes the advantages and disadvantages of each current sensor type.