Siemens SENTRON Configuration Manual
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Siemens SENTRON Configuration Manual

Protective devices selectivity for 3va molded case circuit breakers
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Summary of Contents for Siemens SENTRON

  • Page 3 ___________________ Introduction Selectivity - terms and ___________________ definitions Methods of implementing selectivity using circuit SENTRON breakers Selectivity implemented by Protective devices combinations of protective Selectivity for 3VA molded case devices circuit breakers ___________________ Selectivity with parallel incoming feeders Configuration Manual...
  • Page 4 Note the following: WARNING Siemens products may only be used for the applications described in the catalog and in the relevant technical documentation. If products and components from other manufacturers are used, these must be recommended or approved by Siemens. Proper transport, storage, installation, assembly, commissioning, operation and maintenance are required to ensure that the products operate safely and without any problems.

  • Page 5: Table Of Contents

    Table of contents Introduction ..............................7 Selectivity - terms and definitions ......................9 Methods of implementing selectivity using circuit breakers ..............13 Starting point ........................... 15 Selectivity in the overload zone ....................15 3.2.1 Example ..........................16 3.2.2 Circuit breaker parameters ..................... 17 3.2.3 Tripping characteristics of circuit breakers ................
  • Page 6 Table of contents Selectivity and undervoltage protection ....................69 3VA selectivity tables ..........................71 List of abbreviations ..........................73 List of abbreviations ....................... 73 Glossary ..............................75 Selectivity for 3VA molded case circuit breakers Configuration Manual, 08/2016, A5E03603181010-01...

  • Page 7: Introduction

    Introduction There are growing demands in many sectors for more reliable, secure electricity supplies for installations, whether these are data centers, airports, industrial production facilities, power plants, etc. (Over-current) selectivity can make an important contribution to fulfilling these demands. It is capable of minimizing the effects of a fault in terms of its duration and the area it affects, thereby ensuring that plant sections that are not affected by the fault will remain in operation.
  • Page 8 Introduction Navigation around the manual The following guides to accessing information are provided: ● Table of contents ● Section "Structure of the manual" ● Index Selectivity for 3VA molded case circuit breakers Configuration Manual, 08/2016, A5E03603181010-01...

  • Page 9: Selectivity - Terms And Definitions

    Selectivity - terms and definitions This chapter introduces you to the subject of "selectivity" on the basis of the key terms associated with the concept. For additional information, especially in relation to selectivity methods, please refer to chapter "Methods of implementing selectivity using circuit breakers (Page 13)". Selectivity Selectivity exists in a low-voltage network if only the protective device connected directly upstream of the fault location (as viewed in the direction of current flow) trips in response to...
  • Page 10 Selectivity - terms and definitions Over-current selectivity Excerpt from EN 60947-1, 2.5.23: Over-current selectivity (discrimination) is the "co-ordination of the operating characteristics of two or more over-current protective devices such that, on the incidence of over-currents within stated limits, the device intended to operate within these limits does so, while the other(s) does (do) not".
  • Page 11 Selectivity - terms and definitions Selectivity limit current I The selectivity limit current corresponds exactly to the over-current value at which an upstream protective device operates in addition to the protective device situated immediately upstream of the fault source. In other words, the operating characteristics of the protective devices touch or intersect at a specific current magnitude.

  • Page 13: Methods Of Implementing Selectivity Using Circuit Breakers

    Methods of implementing selectivity using circuit breakers Using the example of a fault scenario in a power distribution system, this chapter explores the potential methods for implementing selectivity. The description in this chapter focuses on the implementation of selectivity between circuit breakers. The subject of implementing a selectivity concept using combinations of different protective devices is discussed in chapter "Selectivity implemented by combinations of protective devices (Page 47)".
  • Page 14 Methods of implementing selectivity using circuit breakers Overload zone and short-circuit zone for a circuit breaker The boundary between the overload and short-circuit zones (definition I and I ) is kmin kmax described in chapter "Setting of circuit breakers (Page 36)". For further information, please see chapter "Zone selective interlocking (Page 30)".

  • Page 15: Starting Point

    Methods of implementing selectivity using circuit breakers 3.1 Starting point Starting point The starting point is a fault scenario in a low-voltage power distribution system that is protected by circuit breakers. Incoming feeder circuit breaker S2.1 - S2.3 Main distribution board circuit breaker S3.1 - S3.3 Subdistribution board circuit breaker Figure 3-1...

  • Page 16: Example

    Methods of implementing selectivity using circuit breakers 3.2 Selectivity in the overload zone breaker, both of which are equipped with an electronic trip unit with adjustable LI/LSI protective function. To make the examples shown below in chapters 3.2 - 3.4 easier to understand, the tolerances of the tripping characteristics are not shown.

  • Page 17: Circuit Breaker Parameters

    Methods of implementing selectivity using circuit breakers 3.2 Selectivity in the overload zone 3.2.2 Circuit breaker parameters In order to ensure selectivity, the protection parameters of the LI protective function must be set appropriately for the given situation. The following parameters are important for the overload zone: ●...

  • Page 18: Tripping Characteristics Of Circuit Breakers

    Methods of implementing selectivity using circuit breakers 3.3 Current selectivity 3.2.3 Tripping characteristics of circuit breakers Figure 3-3 Current-time diagram: tripping characteristics of 100 A and 250 A circuit breakers with selectivity in the overload zone In order to achieve successful selectivity in the overload zone, the overload tripping characteristics of the two circuit breakers must meet the following criteria: ●...

  • Page 19: Current Selectivity

    Methods of implementing selectivity using circuit breakers 3.3 Current selectivity Current selectivity Current selectivity is a form of selectivity in which the (instantaneous) protective devices trip at different over-current values. In the event of a fault, the following currents flow: ●...

  • Page 20: Circuit Breaker Parameters

    Methods of implementing selectivity using circuit breakers 3.3 Current selectivity 3.3.1 Circuit breaker parameters The following parameters are important for current selectivity: ● Setting of the instantaneous I release (I The parameters of the L release (I and t ) remain unchanged from the example given in chapter "Selectivity in the overload zone (Page 15)".

  • Page 21: Tripping Characteristics Of Circuit Breakers

    Methods of implementing selectivity using circuit breakers 3.3 Current selectivity 3.3.2 Tripping characteristics of circuit breakers Figure 3-4 Current-time diagram: Tripping characteristics in current selectivity applications In order to achieve successful current selectivity, the characteristics of the two circuit breakers must meet the following criteria: ●...

  • Page 22: Different Short-Circuit Currents At Different Fault Locations

    Methods of implementing selectivity using circuit breakers 3.3 Current selectivity 3.3.3 Different short-circuit currents at different fault locations In order to demonstrate the principle of current selectivity, three further scenarios with different fault locations and short-circuit currents are presented below. Figure 3-5 Examples of short-circuit currents at different fault locations Fault location within protection zone of circuit breaker S2...

  • Page 23: Time Selectivity

    Methods of implementing selectivity using circuit breakers 3.4 Time selectivity Time selectivity Time selectivity is a form of selectivity in which the (time-delay) protective devices trip at different times in response to over-currents of the same magnitude. Starting at the lowest level of an electrical power distribution system, the time delay increases with each circuit breaker in the infeed direction.
  • Page 24 Methods of implementing selectivity using circuit breakers 3.4 Time selectivity Advantages and limitations Advantages of time selectivity: ● Simple to implement ● High selectivity limit current values (I ) or total selectivity can be achieved if the short- circuit current strength of the upstream circuit breakers is sufficiently high. Total selectivity can be achieved if the instantaneous short-circuit release of the upstream protective device can be disabled.
  • Page 25 Methods of implementing selectivity using circuit breakers 3.4 Time selectivity Excerpt from IEC 60947-2, 4.4: "Selectivity category B comprises circuit breakers providing selectivity by having a short-time withstand current rating and an associated short-time delay according to 4.3.6.4. Selectivity of circuit breakers of selectivity category B is not necessarily ensured up to the ultimate short-circuit breaking capacity (e.g.

  • Page 26: Circuit Breaker Parameters

    Methods of implementing selectivity using circuit breakers 3.4 Time selectivity 3.4.1 Circuit breaker parameters The following parameters are important for time selectivity: ● Settings of the short-time delay S release (I ● Delay time of the short-time delay S release (t The parameters of the L release (I and t ) remain unchanged from the fictitious example...

  • Page 27: Tripping Characteristics Of Circuit Breakers

    Methods of implementing selectivity using circuit breakers 3.4 Time selectivity 3.4.2 Tripping characteristics of circuit breakers Figure 3-7 Current-time diagram: Tripping characteristics in time selectivity applications In order to achieve successful time selectivity, the characteristics of the two circuit breakers must meet the following criteria: ●...

  • Page 28: Implementation Of Total Selectivity

    I release can also be disabled or if the breaker features an instantaneous short-circuit release with a sufficiently high setting. The following Siemens circuit breakers are used to implement total selectivity in the following example: ● Q1, Q2, Q3: SENTRON 3WL air circuit breakers with rated short-time withstand current (I –...
  • Page 29 Methods of implementing selectivity using circuit breakers 3.4 Time selectivity Figure 3-8 Example of total time selectivity (area marked orange) and total current selectivity (area marked blue) for one branch with four circuit breakers connected in series The definitions for I and I , and the resultant settings for the circuit breakers can be kmin...

  • Page 30: Zone Selective Interlocking

    Methods of implementing selectivity using circuit breakers 3.5 Zone selective interlocking Zone selective interlocking With zone selective interlocking (ZSI), the protective devices are interconnected via separate control wires. Two communication systems that use different communication channels are provided: ● Central system: The circuit breakers communicate via a central monitoring and control unit.
  • Page 31 Methods of implementing selectivity using circuit breakers 3.5 Zone selective interlocking Signal output Signal input - - - Control wires Delay time setting for the short-circuit release Delay time (defined non-operation time) of all breakers that detect the short-circuit and/or ground fault current and do not receive a "block"...
  • Page 32 ● The maximum permissible length of control wires limits zone selective interlocking to a specific zone of an electrical power distribution network. The maximum permissible length of control wires for Siemens 3VA2 molded case circuit breakers is as follows: – < 600 m / 0.75 mm (AWG 18) –...

  • Page 33: Zone Selective Interlocking And Time Selectivity

    Methods of implementing selectivity using circuit breakers 3.5 Zone selective interlocking 3.5.1 Zone selective interlocking and time selectivity If a circuit breaker detects a fault in a combined ZSI/time selectivity system, the following applies: ● A "block" signal is present: The original delay time t remains valid.
  • Page 34 Methods of implementing selectivity using circuit breakers 3.5 Zone selective interlocking Example Signal output Delay time of the I release Signal input Delay time setting of the short-time delay short- circuit release - - Control wires Shortened delay time (defined non-operation time) Figure 3-10 Zone selective interlocking combined with time selectivity...
  • Page 35 Methods of implementing selectivity using circuit breakers 3.5 Zone selective interlocking Fault scenario F1 A fault occurs within the protection zone of circuit breaker Q11. ● If the short-circuit current is high enough, it is detected by the trip unit of circuit breaker Q11.

  • Page 36: Setting Of Circuit Breakers

    3.5 Zone selective interlocking 3.5.2 Setting of circuit breakers Simaris design, a software program published by SIEMENS, is recommended as a tool for setting circuit breakers. One of the capabilities of this program is to calculate network short- circuit values.
  • Page 37 Methods of implementing selectivity using circuit breakers 3.5 Zone selective interlocking It is clear from this diagram that selective tripping behavior cannot be implemented using the highest possible setting of the instantaneous short-circuit release (I) of the upstream 3VA2 630A molded case circuit breaker. While the tripping characteristics in the short-circuit zone of the two circuit breakers only touch with short-circuits of 5 kA or higher so that partial selectivity up to 5 kA is afforded, the required protective functions are not provided.
  • Page 38 Methods of implementing selectivity using circuit breakers 3.5 Zone selective interlocking Setting the 3RV circuit breaker for motor protection (motor starter protector): ● The value of I has been calculated as 7.0 kA at the installation point B. kmaxB The 3RV motor starter protector with a rated operational current I = 45 A has a rated rated ultimate short-circuit breaking capacity I...
  • Page 39 Using the selectivity tables (see "FAQs (https://support.industry.siemens.com/cs/de/en/view/97493202)" in Siemens Industry Online Support (SIOS)), chapter 3.2, it is possible to implement total selectivity with the upstream 3VA2 630 A molded case circuit breaker and the downstream 3RV1 circuit breaker, size S2 for motor protection up to their rated ultimate short-circuit breaking capacity = 50 kA at 400 V AC.

  • Page 40: Dynamic Selectivity

    Methods of implementing selectivity using circuit breakers 3.6 Dynamic selectivity Dynamic selectivity Dynamic selectivity is fundamentally different to current and time selectivity. Circuit breakers suitable for this application Molded case circuit breakers are used to implement dynamic selectivity because it is a concept that utilizes the current-limiting properties of these devices (see chapter "Implementation of dynamic selectivity (Page 41)").

  • Page 41: Implementation Of Dynamic Selectivity

    This ensures that the circuit breaker will not be irreparably damaged by the short-circuit current. The resulting "dual tripping principle" is a feature of the new Siemens 3VA2 molded case circuit breakers for "Selectivity Applications". In the high short-circuit current range, an additional mechanical tripping mechanism (energy release) within the switching pole trips the circuit breaker.
  • Page 42 Further information about the mutual selective behavior of 3VA2 molded case circuit breakers as a function of the prospective current can be found in the FAQs (https://support.industry.siemens.com/cs/de/de/view/97493202) in the Siemens Industry Online Support (SIOS). Note...

  • Page 43: Let-Through Energy Diagram

    Methods of implementing selectivity using circuit breakers 3.6 Dynamic selectivity 3.6.2 Let-through energy diagram The current-limiting capabilities of molded case circuit breakers are a feature that is particularly utilized in dynamic selectivity systems. According to IEC 60947-2, 2.3, the term "current-limiting circuit breaker" refers to a circuit breaker "with a break-time short enough to prevent short-circuit current reaching its otherwise attainable peak value".

  • Page 44: Example

    Methods of implementing selectivity using circuit breakers 3.6 Dynamic selectivity Note Calculation of let-through energy The let-through energy is not only determined by the magnitude of the prospective current, but also by the line voltage, line frequency and type of short-circuit (one-pole, two-pole or three-pole).
  • Page 45 Methods of implementing selectivity using circuit breakers 3.6 Dynamic selectivity The characteristic curves shown in the diagram indicate the let-through energy of the relevant circuit breaker if it is limiting and interrupting the short-circuit current on its own. If the 630 A circuit breaker is located upstream of the 250 A circuit breaker, however, the current-limiting capabilities of both circuit breakers act cumulatively in the event of a short- circuit.
  • Page 46 (I ) is reached. You can find the selectivity tables as "FAQs (https://support.industry.siemens.com/cs/de/de/view/97493202)" in the Siemens Industry Online Support (SIOS). According to chapter 2 of these tables, the total selectivity in this example is listed, i.e. the selectivity limit current I...

  • Page 47: Selectivity Implemented By Combinations Of Protective Devices

    ±10 % must be applied to the current- time tripping characteristics of the circuit breakers. The tolerance range is reduced to ±6 % if Siemens type 3NA LV HRC fuses are used. Circuit breakers with LI or LSI releases behave selectively in the overload zone with respect...
  • Page 48 ≥ 1000 A. Instead, the 3VA2 molded case circuit breaker is designed to afford dynamic selectivity. The selectivity limit current I is determined according to the selectivity table (see FAQs (https://support.industry.siemens.com/cs/de/de/view/97493202) in the Siemens Industry Online Support (SIOS)). Total selectivity in the event of a short-circuit is afforded by circuit breakers without a time-...
  • Page 49 Dynamic selectivity zone ② Tripping characteristic ③ Time-current characteristic Further information The characteristics for Siemens 3NA LV HRC fuses can be found in the Configuration Manual "Fuse Systems", order number 3ZW1012-3NW10-0AB1. Selectivity for 3VA molded case circuit breakers Configuration Manual, 08/2016, A5E03603181010-01...

  • Page 50: Fuse And Downstream Molded Case Circuit Breaker

    ±10 % must be applied to the current-time tripping characteristics of the circuit breaker. The tolerance range is reduced to ±6 % if Siemens type 3NA LV HRC fuses are used. Overload...
  • Page 51 ) is approximately 2200 A. According to the selectivity table, the selectivity limit value (I ) is 7.9 kA (see "FAQs (https://support.industry.siemens.com/cs/de/de/view/97493202) chapter 7" in the Siemens Industry Online Support (SIOS)). Selectivity for 3VA molded case circuit breakers Configuration Manual, 08/2016, A5E03603181010-01...
  • Page 52 This value is approximately 7300 A in the above example. Further information The pre-arcing time-current characteristics for Siemens 3NA LV HRC fuses can be found in the Configuration Manual "Fuse Systems", order number 3ZW1012-3NW10-0AB1. Selectivity for 3VA molded case circuit breakers...

  • Page 53: Fuse And Downstream Miniature Circuit Breaker

    Note Siemens fuses Siemens fuses have a tolerance band of only ±6 %, a positive feature which is also beneficial with respect to selectivity. For 400 V applications, Siemens fuses are even selective in the 1:1.25 ratio between rated currents.
  • Page 54 Siemens has now succeeded in developing a tripping characteristic for the ETU 340 of the 3VA2 molded case circuit breaker that has a similar characteristic curve to LV HRC fuses over the entire over-current zone.
  • Page 55 Selectivity implemented by combinations of protective devices 4.4 Fuse and downstream fuse the rated current of the fuse and the rated current I of the molded case circuit breaker rated and it is within this margin that selectivity is implemented. Previous selectivity assessments indicated that an upstream molded case circuit breaker with a rated current I of at least 250 A would be required if a 100 A LV HRC fuse were...

  • Page 57: Selectivity With Parallel Incoming Feeders

    Selectivity with parallel incoming feeders Selectivity with parallel incoming feeders can be implemented in various different scenarios. The following scenarios are presented in this chapter: ● Selectivity with two identical incoming feeders ● Selectivity with three identical incoming feeders ● Selectivity with incoming feeders connected in parallel via bus-couplers Total short-circuit current and current scale If multiple transformers are operated on a common busbar, the following applies: The partial short-circuit currents I...

  • Page 58: Selectivity With Two Identical Incoming Feeders

    Selectivity with parallel incoming feeders 5.1 Selectivity with two identical incoming feeders Selectivity with two identical incoming feeders The figure below shows an example of the distribution of short-circuit currents in a faulty outgoing feeder that is supplied by two parallel-connected transformers with the same power rating.

  • Page 59: Symmetrical Distribution (Ideal Scenario)

    Selectivity with parallel incoming feeders 5.1 Selectivity with two identical incoming feeders 5.1.1 Symmetrical distribution (ideal scenario) Symmetrical distribution of the short-circuit current occurs when the following conditions are fulfilled: ● The load feeder is positioned exactly in the center. ●...

  • Page 60: Selectivity With Three Identical Incoming Feeders

    Selectivity with parallel incoming feeders 5.2 Selectivity with three identical incoming feeders Selectivity with three identical incoming feeders 5.2.1 Fault within the protection zone of the downstream protective device With three parallel-connected transformers, effective current selectivity can be achieved because the characteristic displacement factor for the incoming feeder circuit breakers Q1, Q2 and Q3 is within the range 2 <...

  • Page 61: Fault Between Transformer Terminals And Incoming Feeder Circuit Breaker

    Selectivity with parallel incoming feeders 5.2 Selectivity with three identical incoming feeders 5.2.2 Fault between transformer terminals and incoming feeder circuit breaker Symmetrical fault current distribution The instantaneous short-circuit release (I release) must be set in such a way that its value is higher than the partial short-circuit currents I of a transformer.
  • Page 62 Selectivity with parallel incoming feeders 5.2 Selectivity with three identical incoming feeders Asymmetrical fault current distribution Asymmetrical fault current distribution is the norm as a result of variations in fault impedance among multiple incoming feeders. With sufficient damping by the fault impedance, the total short-circuit current I can be kept so small that instantaneous short-circuit tripping of the kΣ...

  • Page 63: Selectivity With Bus-Couplers

    Selectivity with parallel incoming feeders 5.3 Selectivity with bus-couplers Selectivity with bus-couplers If circuit breakers with over-current releases are installed in bus-couplers, the following can be achieved: ● Fastest possible clearance of busbar faults ● Fault restriction to the respective busbar section ●...
  • Page 64 Selectivity with parallel incoming feeders 5.3 Selectivity with bus-couplers The following diagrams show the protective response of the transformer and bus-couplers in reaction to feeder faults in the outer and center sections of the busbar: ① Total short-circuit current Figure 5-3 Selectivity with an outgoing feeder short-circuit in the outer busbar section The displacement factor of the tripping characteristics K is as follows: With a total short-circuit current = 45 kA and...
  • Page 65 Selectivity with parallel incoming feeders 5.3 Selectivity with bus-couplers ① Total short-circuit current Figure 5-4 Selectivity with an outgoing feeder short-circuit in the center busbar section The displacement factor of the tripping characteristics K is as follows: With a total short-circuit current = 45 kA and the partial short-circuit currents of all of the circuit breakers Q1 - Q5 = 15 kA, the displacement factor K The tripping characteristics of all of the instantaneous releases are far to the right of the total...
  • Page 66 Selectivity with parallel incoming feeders 5.3 Selectivity with bus-couplers The following diagrams show the protective response in reaction to incoming feeder faults in the outer and center sections of the busbar: ① Total short-circuit current Figure 5-5 Selectivity with an incoming feeder short-circuit in the outer busbar section The displacement factor of the tripping characteristics K is as follows: With a total short-circuit current = 30 kA and...
  • Page 67 Selectivity with parallel incoming feeders 5.3 Selectivity with bus-couplers ① Total short-circuit current Figure 5-6 Selectivity with an incoming feeder short-circuit in the center busbar section The displacement factor of the tripping characteristics K is as follows: With a total short-circuit current = 30 kA and the partial short-circuit currents of the circuit breakers Q1, Q4, Q3 and Q5 = 15 kA, the displacement factor K The displacement factor K...

  • Page 68: Sources Of Information And Other Documentation

    Selectivity with parallel incoming feeders 5.4 Sources of information and other documentation The transformer and bus-couplers in the multiple incoming feeder configurations of industrial networks are normally connected in series with other over-current protective devices. As a result, the inclusion of bus-couplers in the selective time grading system may unduly extend the clearance time for near-to-infeed short-circuits.

  • Page 69: Selectivity And Undervoltage Protection

    Selectivity and undervoltage protection In the event of a short-circuit, the line voltage at the short-circuit location collapses to a residual voltage that is dependent on the fault impedance. If the short-circuit is dead, the voltage at the short-circuit location drops to virtually zero. Short-circuits normally generate arcs with a peak arc voltage U within the range of 30 V ≤...
  • Page 70 Selectivity and undervoltage protection Implementation of selectivity Assuming that the operating time of the undervoltage releases t = 20 ms, instantaneous Δu’ over-current protective tripping must be implemented in t ≤ 20 ms. This applies both to near- to-infeed and far-from-infeed short-circuits. This instantaneous protective tripping ensures that the fault location is selectively disconnected from the network before the undervoltage releases can respond.

  • Page 71: 3Va Selectivity Tables

    More information The selectivity limit currents for these combinations can also be found in SIMARIS design, the software tool from Siemens for the sizing and protection coordination of low-voltage radial networks: (www.siemens.com/simaris) For users who only require the tripping characteristics, Siemens offers the software tool SIMARIS curves: (www.siemens.com/simariscurves)

  • Page 73: List Of Abbreviations

    List of abbreviations List of abbreviations Overview Table A- 1 Meaning of abbreviations used in this document Abbreviation Meaning Alternating voltage American Wire Gauge: standardized wire gauge system used in North America Direct voltage Deutsches Institut für Normierung e. V. (German Institute for Standardization) European Standard Electronic Trip Unit FTFM...
  • Page 74 List of abbreviations A.1 List of abbreviations Table A- 2 Meaning of symbols and abbreviations Sym- Meaning bol/abbreviation Let-through energy Rated breaking capacity; rated short-circuit breaking capacity Maximum short-circuit breaking capacity (total selectivity); rated ultimate short- circuit breaking capacity Rated short-time withstand current; rated short-time current Let-through current Instantaneous tripping current;...

  • Page 75: Glossary

    Glossary Coupler circuit breaker Current-limiting circuit breaker According to EN 60947-2, a current-limiting circuit breaker is a "circuit-breaker with a break- time short enough to prevent the short-circuit current reaching its otherwise attainable peak value". Delay time t Defined non-operation time of all circuit breakers that detect a short-circuit current and/or a ground fault current and do not receive a "block"...
  • Page 76 Glossary L release Inverse-time delay over-current release as overload current protective device LSI protective function The LSI protective function is a combination of multiple release types. Circuit breakers with LSI protective function have the following releases: ● Inverse-time delay over-current release (L release) as overload current protection ●...
  • Page 77 Glossary Rated operational voltage U Voltage value to which the making capacity, the breaking capacity and the utilization categories of a circuit breaker are referred. A circuit breaker can have more than one rated operational voltage. Rated short-circuit breaking capacity I A short-circuit current specified by the manufacturer that a circuit breaker can safely interrupt at the rated operational voltage U , the rated frequency and a defined power factor (or...
  • Page 78 Glossary Response current, short-time delay When this current limit is exceeded, the circuit breaker trips after a predefined time delay. S release Electronic short-time delay over-current release for delayed short-circuit protection Short-circuit Accidental or intentional conductive path between two or more conductive parts forcing the electric potential differences between these conductive parts to be equal to or close to zero as defined by IEC / DIN EN 60947-1, 2.1.5 Short-circuit current...

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