Cahier technique n 167 - studiecd.dk

1 Collection TechniqueCahier technique n 167 Energy-based discrimination forlow-voltage protective devicesM. SerpinetR. Moreln Merlin Gerin n Modicon n Square D n Telemecanique Cahiers Techniques are a collection of documents intended for engineersand technicians people in the industry who are looking for information ingreater depth in order to complement that given in display Cahiers Techniques go beyond this stage and constitute praticaltraining contain data allowing to design and implement electrical equipement,industrial electronics and electrical transmission and Cahier technique provides an in-depth study of a precise subject inthe fields of electrical networks, protection devices.

2 Monitoring and controland industrial automation latest publications can be downloaded on Internet from theSchneider : :mastering electrical powerPlease contact your Schneider representative if you want either a CahierTechnique or the list of available Cahiers Techniques collection is part of the Groupe Schneider s Collection technique .ForewordThe author disclaims all responsibility further to incorrect use of informationor diagrams reproduced in this document, and cannot be held responsiblefor any errors or oversights, or for the consequences of using informationand diagrams contained in this of all or part of a Cahier technique is authorised with theprior consent of the Scientific and Technical Division.

3 The statement Extracted from Schneider Cahier technique (please specify) MORELG raduated with an engineering degree from ENSMM in Besan on andjoined Merlin Gerin in 1971. Specialised in designing low voltageswitchgear and participated in designing the Sellim 1980, took over development of Compact circuit -breakers andInterpact 1985, became manager of the Low-Voltage Current Interruptiondesign office in the Low-voltage Power Components 167 Energy-based discriminationfor low-voltage protectivedevicesECT167 first issued, march 1998 Marc SERPINETJ oined Merlin Gerin in 1972 and worked until 1975 in the low-voltageequipment design offices, in charge of designing electrical cabinetsfor various installation layouts.

4 Since 1975, he has managed researchand development testing for low-voltage circuit -breakers. Graduatedin 1981 from the ENSIEG engineering school in 1991, after managing a Compact circuit -breaker project from thepreliminary studies on through to production, he was appointed headof the electromechanical design office in charge of anticipating future technique Schneider n 167/ let through by the protective deviceduring breaking. This energy is characterised byidttbb22 IibLimited short - circuit current actually flowingthrough the circuit -breaker (the break current isless than Ip).IpProspective short - circuit current that woulddevelop in the absence of protective devices(rms value).IrCorresponds to the overload protection actual breaking time (arc extinction).

5 UTElectronic processing capable of producing a ratingCorresponds to the models of the range(ex. 160 A, 250 A, 630 A, 800 A, etc.).Current-limiting circuit -breakerCircuit-breaker which, when interrupting a short - circuit current, limits the current to a valueconsiderably less than the prospective current (Ip).High-set instantaneous release (HIN)Instantaneous release used to limit thermalstress during a release (INS)Release without an intentional time delaysystem. It trips at a low multiple of In to ensureshort- circuit release (LT)Release with an intentional time delay system(several seconds) for overload discriminationDiscrimination is said to be partial when it isensured only up to a certain level of theprospective current (Ip).

6 Selective circuit -breakerCircuit-breaker with an intentional time delaysystem (time discrimination). short -time release (ST)Release with an intentional time delay systemranging from ten to several hundredmilliseconds. If the time delay is reduced as Ipincreases, the system is referred to asdependent short -time (DST).Total discriminationDiscrimination is said to be total when it is ensuredfor all values of the prospective fault ratingCorresponds to the maximum current setting ofthe trip technique Schneider n 167 / discrimination forlow-voltage protective devicesThe purpose of this Cahier technique publication is to present the newenergy-based discrimination technique that ensures tripping discriminationbetween protective devices during a short - circuit .

7 Both simpler and moreeffective than standard discrimination techniques, it has been implementedon the Compact NS range of circuit -breakers used in low-voltage powerdistribution networks. Discrimination is ensured for all prospective faultcurrents on the condition that upstream and downstream circuit -breakershave different current ratings (ratio u ) with a trip-unit rating ratio u a brief review of standard discrimination techniques, the authorsexamine the behaviour of circuit -breakers and various trip units from theenergy then demonstrate that total discrimination is possible up to thecircuit-breaker breaking capacity, over several levels, without using timediscrimination Discrimination in Definitionp.

8 Enhanced safety and availabilityp. Discrimination zonesp. 52. Discrimination techniques for Current discriminationp. Time discriminationp. SELLIM discriminationp. Zone selective interlockingp. Combining the different types of discriminationp. 93. Energy-based Choice of operating curvesp. Characterisation of a Compact NS circuit -breakerp. Characterisation of the trip unitsp. 134. Advantages and implementation Current-limiting circuit -breaker fitted with a pressure trip systemp. Discrimination with Compact NS circuit -breakersp. Combination with traditional protective devicesp. 195. Conclusionp. 216. Appendix - indications concerning breaking with current limitingp. 22energy-based discriminationprotective devicesCahier technique Schneider n 167 / Discrimination in low-voltage protective DefinitionIn an electrical installation, loads are connectedto sources via a succession of protection,isolation and control devices.

9 This CahierTechnique publication deals essentially with theprotection function using a radial feeder layout (see fig. 1 ), the purposeof discrimination is to disconnect only the faultyload or feeder from the network and no others,thus ensuring maximum continuity of discrimination studies are not or are incorrectlycarried out, an electrical fault may cause severalprotective devices to trip, thus provoking aninterruption in the supply of power to a large partof the network. That constitutes an abnormal lossin the availability of electrical power for thoseparts of the network where no fault 1: several circuit -breakers are concerned by the fault types of overcurrents may beencountered in an installation:c overloads,c short -circuits,c inrush currents,as well as:c earth faults,c transient currents due to voltage dips ormomentary loss of ensure maximum continuity of service, theremust be coordination between that voltage dips may provoke unnecessaryopening of circuit -breakers by actuatingundervoltage passes through CB1, CB2, CB3, technique Schneider n 167 / 2.

10 circuit -breaker behaviour during a Enhanced safety and availabilityA specific type of protective device exists foreach type of fault (overloads, short -circuits, earthfaults, undervoltages, etc.). However, a fault maysimultaneously bring several types of protectivedevices into play, either directly or A high short - circuit current creates anundervoltage and may trip the undervoltageprotective An insulation fault may be interpreted as azero-phase sequence fault by an earth-leakageprotective device and as an overcurrent by theshort- circuit protective device (applicable for TNand IT earthing systems).c A high short - circuit current may trip the earth-leakage protective device (in TT earthingsystems) due to local saturation of thesummation toroid which creates a false zero-phase sequence a given network, discrimination studies andthe evaluation of the protection system in generalare based on the protective devicecharacteristics published by the begin with an analysis of requirementsconcerning protective devices needed foreach type of fault.