7/30/2019 Siemens Power Engineering Guide 7E 511

1/1511Siemens Energy Sectort Power Engineering Guide tEdition 7.0

Glossary

1

Power-line carrier A device for producing radio-frequency powerfor transmission on power lines.

Potentialtransformer (PT)

A device required to provide accurate voltagesfor meters used for billing industrial customersor utility companies.

Python A dynamic object-oriented programming

language.

Q

R

Rated breakingcapacity

Value of the short-circuit current a switchingdevice is c apable of breaking at the ratedoperating voltage, rated frequency andspecified power factor (or specified timeconstant).

Rated breakingcurrent

The load breaking current in normal operation.

Rated current The current that an electrical device can carry,under specified conditions, without resulting inoverheating or mechanical overstress.

Rated insulationlevel

The > dielectric strength from phase to earth,between phases and across the open contactgap, or across the isolating distance. Thedielectric strength is verified by a lightningimpulse withstand voltage test with thestandard impulse wave of 1.2 / 50 s and apower-frequency withstand voltage test(50 Hz/1 min).

Rated peakwithstand current

The peak value of the major loop of the short-circuit current during a compensation processafter the beginning of the current flow, whichthe device can carry in closed state.

Rated short-circuitbreaking current

The root-mean-square value of the breakingcurrent in case of short-circuit at the terminalsof the switching device.

Rated short-circuitmaking current

The peak value of the making current in case ofshort-circuit at the terminals of the switchingdevice.

Rated voltage The maximum voltage at which an electr iccomponent can operate for extended periodswithout undue degradation or safety hazard.

Release (of amechanicalswitching device)

A device, mechanically connected to amechanical switching device, which releasesthe holding means and permits the opening orthe closing of the switching device.

Residual current The sum of the instantaneous values of allcurrents that flow through all the activeconductors of an electrical system at one point.

Residual current

device (RCB)

A mechanical switching device designed to

make, carry and break currents under normalservice conditions and to cause the opening ofthe contacts when the residual current attains agiven value under specified conditions.

Ring main unit(RMU)

Switchgear in distribution systems comprisingof switches for switching power cable rings andof switches in series with fuses for theprotection of distribution transformers.

Rapid spanning treeprotocol (RSTP)

Networking protocol according to IEEE 802.1wto deactivate redundant paths in a local net orto activate them if required (e.g. in case of afailure of a switch, brigde etc.).

Resistancetemperatur device/detector (RTD)

Device for temperature detection based on theresistance change in a metal, with theresistance rising more or less linearly withtemperature.

Remote terminalunit (RTU)

An electronic device to transmit data to adistributed control system or a SCADA-systemand to alter the state of connected objectsbased on control messages received from thesystem.

S

Switch-disconnector A switch which, in the open position, satisfiesthe isolating requirements specified for adisconnector.

Switch-disconnector-fuse (SDF)

A switch-disconnector comprising a > switch-disconnector and (connected in series zo this)fusebases for insertign fuse-links.

SDH A multiplexing protocol for transferringmultiple bit streams over the same optical fiber.

Selectivity Combined operation of overcurrent protectivedevices connnected in series to provide graded

disconnection.

Series reactor A reactor intended for series connect ion in anetwork, either for limiting the current underfault conditions or for load-sharing in parallelcircuits.

SFC A graphical programming language used forPLCs. It is one of the five languages defined byIEC 61131-3 standard. The SFC standard isdefined in IEC 848, Preparation of functioncharts for control systems.

Short-circuit Connection of two or more points of anelectrical circuit that are meant to be atdifferent voltages across a nebligible smallresistance or impedance.

Short-circuit current Overcurrent which flows through the > short-circuit which may result in thermal ormechanical overloading of the electricalequipment.

Short-circuitstrength

The mechanical resistance of switching devicesto short-circuit stress, particularily of busbars inswitchgear stations and distrivution boards.

Shunt release A release energized by a source of voltage.

Shunt reactor A reactor intended for shunt connect ion in anetwork to compensate for capacitive current.

Single-line diagram(SLD)

A simplified notation for representing a three-phase power system in which the polyphaselinks are represented by their equivalent singleline.

Smart grid Evolving intelligent power distribution networkusing communication, advanced sensors, anddistributed computers to improve theefficiency, reliability and safety of powerdelivery and use. It includes the possibility fordemand side management, facilitating gridconnection of distributed generation power(with photovoltaic arrays, small wind turbines,micro hydro, or even combined heat powergenerators in buildings), grid energy storagefor distributed generation load balancing, andimproved reliability against many dif ferentcomponent failure scenarios.