Voltage sensors

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General information and description

The development of microprocessor technology has led to changes in the requirements for the transformers used for measurement and protection in substations, due to self-powered relays based on microprocessors.

FMT has developed a series of low-power sensors, compatible with modern microprocessor-controlled relays and secondary equipment with high input impedance. The sensors meet the requirements of the IEC 61869-10 and IEC 61869-11 standards.

Installation and mounting

Voltage sensors are mounted inside the cable compartment of the main unit, in T-connectors (type C connectors).

No subsequent field adjustment of the sensor is required, as they are factory-calibrated to deliver an accurate signal in accordance with the applicable IEC standard.

Key advantages of FMT sensors
Passive technology
Completely free of active components inside, with no need for any additional power supply.
Accuracy classes
High precision and accuracy classes fully tailored to all customer needs.
Temperature range
Stable operation and safe storage under extreme conditions from -40°C to +80°C.
Compact design
Reduced dimensions and minimal weight make installation in switchgear cells easier.
Maximum cost-effectiveness
Low device cost combined with maximum installation flexibility in the field.
Increased safety
High level of protection for personnel working in substations and minimisation of human error.
Voltage sensors

Voltage sensors 12-24 kV (NSC and NSK series)

Voltage: 12 - 24 kV | Type: Resistive divider | Output: mV / V | Material: Epoxy resin

Low-power sensors designed for measurement and protection in medium-voltage substations.

Operating principle of voltage sensors

The operation of the voltage sensor is based on the resistive-divider principle, factory-adjusted to the guaranteed accuracy class. It is only necessary to know the resistive value of the input impedance of the measuring device, since the sensor is insensitive to changes in capacitance. Voltage sensors are designed for protection in medium-voltage networks and for measuring systems in accordance with the IEC 61869-11 standard, and are type- and routine-tested.

Operating principle diagram
Electrical wiring diagram and resistive divider
Voltage sensor
NSCxx-xx
NSCxx-xx
12-24 kV voltage sensor for type C cone according to EN 50181 and EN 50180 standards
Voltage sensor
NSKxx-xx
NSKxx-xx
12-24 kV voltage sensor for asymmetric T-connectors
Technical data for NSCxx-xx and NSKxx-xx:
TECHNICAL DATAVALUES AND CHARACTERISTICS
Isolation levelmax. 24 / 50 / 125kV
Nominal voltagemax. 24/√3 kV
Nominal frequency50Hz
Secondary output3,25/√3 V or customer defined
Overvoltage factor1,9 Un for 8h
Accuracy classes0,2 / 0,5 / 1 / 3 & 3P / 6P
StandardIEC 61869-11
Input impedances of measurement devices200kΩ¹; Capacitance max. 5nF
Connection2 pole, open wires inclusive screen, cable length in 2m, 10m and 20m²
Temperature rangeOperating and storage: -40 to +80°C
T-Connector for NSCxx-xxPlanned: Südkabel, Nexans, Prysmian, 3M
T-Connector for NSKxx-xxPlanned: Südkabel, Nexans, nkt, Raychem, Cellpack, 3M³

¹ Accuracy of input impedance of measurement device influences the accuracy of the entire measurement system
Rule of thumb: +/-1% means an additional error of 0.1% in the amplitude

² Cable length could be cut by the customer, if it is necessary

³ A multicompatible sensor for the short cone is used