Circuit-Breakers with Protective Functions

Protective functions of LV circuit-breakers

Circuit-breakers are used, first and foremost, for overload and short-cir- cuit protection. In order to increase their protective functions, they can also be equipped with additional releases, e.g. for clearance with undervoltage, or with supplementary modules for detecting fault/residual currents (also see Chapter 6).

The circuit-breakers are distinguished according to their protective function: C Circuit-breakers for system protec-

tion acc. to EN 60947-2/ IEC 60947- 2/DIN VDE 0660-101

C Circuit-breakers for motor protec tion acc. to EN 60947-2/

IEC 60947-2 / DIN VDE 0660-101

C Circuit-breakers used in motor star ters acc. to EN 60947-4-2/ IEC 60947-4-2 / DIN VDE 0660-102 C Miniature circuit-breakers for cable

and line protection acc. to EN 60898/ IEC 60898 / DIN VDE 0641-11

Zero-current interrupters / current limiters

Depending on their method of opera- tion, circuit-breakers are available as: C Zero-current interrupters or C Current limiters (fuse-type

current limiting).

When configuring selective distribu- tion boards, zero-current interrupters are more suitable as upstream pro- tection devices and current limiters as downstream protection devices.

Overcurrent protection devices Standard Overload Short-circuit See Section

protection protection

Fuses gL EN 60 269/IEC 60 269/DIN VDE 0636 × × Section 6.2.2

Miniature circuit-breakers EN 60 898/IEC 60 898/DIN VDE 0641-11 × × Section 6.2.4

Circuit-breakers with overload EN 60 947-2/IEC 60 947-2/DIN VDE 0660-101 × × Section 6.2.1

and overcurrent releases

Switchgear EN 60 269/IEC 60 269/DIN VDE 0636 – × Section 6.2.2

fuses aM

Switchgear assemblies

with back-up fuse, utilization EN 60 269/IEC 60 269/DIN VDE 0636 – ×

category gL or aM, and

contactor with overload relay EN 60 947-4-1/IEC 60 947-4-1/DIN VDE 0660-102 × –

or

starter circuit-breaker and EN 60 947-2/IEC 60 947-2/DIN VDE 0660-101 – ×

contactor with overload relay EN 60 947-4-1/IEC 60 947-4-1/DIN VDE 0660-102 × –

×Protection provided – No protection provided.

Protection devices MV Switch-disconnectors, Circuit-breakers, Switch-disconnectors,

HV HRC fuses transducer, time- HV HRC fuses

overcurrent protection

LV Circuit-breakers or Tie breaker Circuit-breakers Network circuit-breakers

LV HRC fuses and network master relays

Cost Low Justifiable High Low

Medium-voltage side

Transformers with thermal release or full thermal protection

Low-voltage side with various series-connected protection devices in radial systems, and parallel-connected LV HRC fuses in interconnected systems Individual and parallel operating customary Optional HV HRC MV LV ≤ 630 A LV HRC ≤ 50 A, ≤ 100 A Individual and parallel operating customary MV LV I > I >> Only parallel operation customary HV HRC MV LV (interconnected system) S HV or LV HRC fuses I > I >>

Definite-time-overcurrent protection, two- level I> and I>>, via current transformer S Network master relay (directional power relay)_{via current transformer and system voltage}

Power-factor correction controller

Switch-disconnector

Circuit-breaker

Drawout circuit-breaker (with safe clearance)

Contactor

Overload relay

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Overload and overcurrent protection

Tables 3/3 and 3/4 provide an overview of releases and relays in LV circuit-breakers. Table 3/5 contains the operating ranges of the overcur- rent releases. According to the stan- dards specified in Table 3/1, the oper- ating value at which the releases trig- ger may deviate by ± 20% from the set value.

Overcurrent releases

The instantaneous electromagnetic overcurrent releases have either fixed or variable settings, whereas the electronic overcurrent releases used in Siemens circuit-breakers all have variable settings.

Modules

The overcurrent releases can be inte- grated in the circuit-breaker or sup- plied as separate modules for retro- fitting or replacement. Possible ex- ceptions are indicated in the manufacturer specifications.

Overload releases

Mechanical (thermal) inverse-time-de- lay overload releases (L-releases) are not always suitable for networks with a high harmonic content. Circuit- breakers with electronic overload re- leases must be used in such cases.

Short-circuit protection with S-releases

In the case of circuit-breakers with definite (short-)time-delay overcur- rent releases (S) used for time-grad- ing short-circuit protection, it should be noted that the circuit-breakers are designed for a specific maximum per- missible thermal and dynamic load. If, in the event of a short circuit, the time delay results in this load to be exceeded, an I-release must also be used to ensure that the circuit- breaker is opened instantaneously with very high short-circuit currents.

The information supplied by the Table 3/4 Circuit-breaker releases and relays with protective functions

Function Release Relay

Overload Overload release Overload relay

protection Inverse-time delay or Thermal delay or

electronic delay electronic delay

Thermistor protection release devices

Short-circuit Overcurrent release Overcurrent relay

protection Instantaneous electromagnetic Instantaneous electromagnetic

or electronic release

Selective Overcurrent release –

short-circuit Instantaneous electromagnetic

protection or electronic

Protective Siemens Time-delay Graphical symbol acc. to

function symbol characteristics EN 60 617/DIN 40 713

of release

Circuit diagram Block

or diagram

Overload L Inverse-time

protection delay

Selective S1) _{Definite-time}

short-circuit delay by

protection timing element

or

inverse-time delay

Fault current/ G1) _{Definite-time}

residual current/ delay

earth fault or

protection inverse-time

delay

Short-circuit I Instantaneous

protection

1)_{For SENTRON 3WL and SENTRON 3VL circuit-breakers, protection also includes}

“zone-selective interlocking” (ZSI)

In the following, combinations of releases will be referred to by their code letters

only (L-, S- and I-releases).

I >I >

I

I > I >>

manufacturer should be consulted when the release type is selected.

Reclosing lockout after short-circuit tripping

A number of circuit-breakers can be fitted with a mechanical and/or elec- trical reclosing lockout which pre- vents reclosing to the short-circuit after short-circuit tripping.

The circuit-breaker can only be closed again after the fault has been elimi- nated and the lockout has been reset manually.

Fault-current/residual-current protection

The global importance of fault-current protection devices has grown in the field of protection technology due to the high level of protection they pro- vide (protection of human life and property) and their extended scope of protection (alternating and pulsat- ing current sensitivity).

Apart from residual-current-operated circuit-breakers, miniature circuit- breaker assemblies, e. g. miniature circuit-breakers with fault-current trip- ping, are being used to an increasing extent for commercial and industrial applications.

MCBs with fault-current tripping

These circuit-breaker assemblies are available as compact factory-built de- vices or may be assembled from a miniature circuit-breaker as the basic device and an add-on module.

Circuit-breakers with fault-current/ residual-current tripping

The assembly comprising a circuit- breaker and add-on module has es- tablished itself for circuit-breakers with rated currents Inof up to 400 A

and fault-current/residual-current trip- ping.

Technical features

The add-on module for residual-cur- rent tripping used in system protec- tion applications includes such tech- nical features as:

C Rated residual current I_∆n, ad-

justable in steps, e.g. 30 mA/ 100 mA/300 mA/500 mA/1,000 mA/3,000 mA

C Tripping time ta, adjustable in

steps,

e. g. instantaneous/60 ms/ 100 ms/250 ms/500 ms/1,000 ms C Operation depends on system

voltage

C Sensitivity: tripping with alternating and pulsating DC fault currents C Reset button ”R” for resetting after residual-current tripping

C Test button ”T” for testing the circuit-breaker assembly

C Status display for the current leak- age / residual current I_∆in the downstream circuit, e. g. by means of colored LEDs: – green: I_∆≤0.,5 I_∆n – yellow: 0,25 I_∆n< v∆≤0.5 v∆n – red: cA> I∆> 0.5 I∆n I_A = Tripping current of additional residual- current module C Disconnection of the electronics

overvoltage protection prior to insu- lation measurement in the installa- tion

C ”Remote tripping” C ”Auxiliary switch (AS)”

Interface to bus systems

With appropriate interfaces, the circuit-breaker assemblies can be equipped to bus systems to enable the exchange of information and in- teraction with other components in the electrical installation.

AC/DC sensitive circuit-breaker assemblies

In industrial applications, circuit- breaker assemblies which are sensi- tive to AC/DC currents are required for electrical installations in which smooth DC fault currents or currents with a low residual ripple occur in the event of a fault.

Applications Time-delay Operating ranges of

(primarily for characteristic inverse-time-dealy overcurrent

short-circuit release as multiple of set

current clearance) value Ir

Circuit-breaker Instantaneous or Approx. 3 to 6 · Ir

for generator short-time delay

protection

Circuit-breaker for Instantaneous Approx. 6 to 12 · Ir

line protection

Circuit-breaker for Instantaneous or Approx. 8 to 15 · Ir

motor protection short-time delay1)

1) _{Poss. short-time delay for rush current shunting}

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Standards

The standards EN 60947-2/ IEC 60947-2 / DIN VDE 0660-101 apply for circuit-breakers with add- on fault-current or residual-current modules.

Selection criteria for circuit- breakers

When selecting the appropriate cir- cuit-breaker for system protection, special attention must be paid to the following characteristics:

C Type of circuit-breaker and its re- leases according to the respective protective function and tasks C Rated voltages

C Short-circuit strength I_cu/ Icsand

rated short-circuit making (Icm)and

breaking capacity (Icn)

C Rated and maximum load currents The system voltage and system frequency are crucial factors for selecting the circuit-breakers according to

C Rated insulation voltage Ui

and

C Rated operating voltage Ue.

Rated insulation voltage Ui

The rated insulation voltage Uiis the

standardized voltage value for which the insulation of the circuit-breakers and their associated components is rated in accordance with HD 625 / IEC 60664 / DIN VDE 0110, Insulation Group C.

Rated operating voltage Ue

The rated operating voltage Ueof a

circuit-breaker is the voltage value to which the rated short-circuit making and breaking capacities and the short- circuit performance category refer.

Short-circuit current

The maximum short-circuit current at the installation location is a crucial factor for selecting the circuit-breakers according to

C Short-circuit strength Icu/ Ics, as well

as

C Rated short-circuit making Icmand

breaking capacities Icn.

Dynamic short-circuit strength

The permissible dynamic short-circuit strength is indicated as the peak short- circuit current. It is the highest permis- sible instantaneous value of the prospective short-circuit current along the conducting path with the highest load.

Thermal fault withstand capability (1-s current)

The permissible thermal short-circuit strength is referred to as the rated short-time current Icw. It is the maxi-

mum current which the breaker is ca- pable of withstanding for X s without any damage occurring. Generally, the

I_cwcurrent refers to 1 s. Other time values can be converted assuming

Icn= constant.

Rated switching capacity

The rated switching capacity of the circuit-breakers is specified as the rated short-circuit making capacity and rated short-circuit breaking capacity. Table 3/6 Correlation n between rated short-circuit making and breaking capacity

and the respective power factor (for AC circuit-breakers)

Rated short-circuit Power factor Minimum value n

breaking capacityIcn cos ϕ _{n =}short-circuit making capacity

(r.m.s. value) kA short-circuit breaking capacity

4.5 < I≤ 6 0.7 1.5

6 < I≤ 10 0.5 1.7

10 < I≤ 20 0.3 2.0

20 < I≤ 50 0.25 2.1

50 < I 0.2 2.2

Table 3/7 Switching performance categories acc. to EN 60947 / IEC 60947 / DIN VDE 0660 and IEC 157-1

The rated short-circuit breaking capacity is indicated using two values:

Switching capacity Icu Ics

Rated ultimate Rated service

short-circuit short-circuit

breaking capacity breaking capacity

Test sequence O-t-CO O-t-CO-t-CO

Test of • ultimate short-circuit • service short-circuit

breaking capacity breaking capacity

Testing Testing

• the overload tripping • the overload tripping

• the insulation resistance • the insulation resistance

• the overheating • the overheating

O Opening (O = Open)

CO Opening and closing (C = Close)

Circuit-breaker type Rated current Application example Tripping characteristic

Air Protection of distribution systems, motors,

circuit-breaker (ACB) 630A to 6,300 A transformers and generators

SENTRON 3WL1 – High rated short-time current for time selectivity

– Two series, SENTRON WL1 and SENTRON WL6 with high and medium rated switching capacity – Electronic, microprocessor-based overcurrent

releases independent of external voltages – Zone-selective interlocking (ZSI) with total delay

time of 50 ms

Current-limiting Designed and tested in compliance with

circuit-breaker EN 60947 / IEC 60947 / DIN VDE 0660

(MCCB) Possible applications:

SENTRON 3VL

TM release: For system protection up to 1,600 A

16 A to 630 A Optional adjustable overload and overcurrent release:

ETU release: Precise adaptation to protection requirements

63 A to 1,600 A

ETU release: For motor protection up to 500 A

63 A to 500 A Electronic overload release with adjustable time-lag class:

Effective protection when motor is under full load

M release: For starter combinations up to 500 A

63 A to 500 A Unsusceptible to inrush currents:

Breaker not tripped by direct-on-line motor starting

M release: As isolating circuit-breaker (load interrupter) up to 2,000 A

100 A to 1,600 A with integrated overcurrent releases,

no back-up fuse required

Circuit-breaker 0.16 to 100 A 3 RV1 circuit-breaker for motor protection

3RV1 with overload and overcurrent protection

L Overload tripping S Short-time delay overcurrent tripping I Instantaneous overcurrent tripping G Ground fault tripping

L S I G L S I L I L I I I L I I

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In document 53534403 Siemens Switchboard and Protection Manual (Page 50-56)