iec standards & power factor correction

ABB Group March 10, 2015 | Slide 1

Lionel Ng, LPBS - Low Voltage Products

Welcome To ABB Technical Sharing Session

Circuit BreakersStandards Guidelines IEC 60947-2


IEC 60947-2

Circuit Breaker Standard, for industrial application

Definitions for MCCBs and ACBs

Choice criteria based on rated and limit values

Agenda


International Standard IEC 60947

European Standard EN 60947

IEC 60947-1 Part 1: General rules

IEC 60947-2 Part 2: Circuit breakers

IEC 60947-3 Part 3: Switch disconnectors

IEC 60947-4-1 Part 4: Contactors

IEC 60947-5-1 Part 5: Control circuit devices

IEC 60947-6-1 Part 6: Multifunction devices

IEC 60947-7-1 Part 7: Auxiliary materials

Standard for LV apparatus

IEC 60947 Standard for industrial application


A mechanical switching device capable of breaking, carrying and

making currents under normal circuit conditions and also making,

carrying, for a specified time, and breaking currents under specified

abnormal circuit conditions such as those of short-circuit.

BREAKING Breaking Capacity

WITHSTAND Short time withstand

MAKING Making Capacity

IEC Standard definitions

Circuit Breaker - IEC 60947-2


A mechanical switching device capable of breaking, making and

carrying currents under normal circuit conditions but only making and

carrying, for a specified time, currents under specified abnormal circuit

conditions such as those of short-circuit.

BREAKING Breaking Capacity

WITHSTAND Short time withstand

MAKING Making Capacity


Switch Disconnector - IEC 60947-3


Moulded case circuit breaker (MCCB): a circuit breaker having a supporting housing of moulding insulating material, forming an integral part of the circuit breaker (Tmax-XT).




Air circuit breaker (ACB): a circuit breaker having a supporting housing of moulding insulating material and a metallic frame, forming an integral part of the circuit breaker (Emax & Emax 2).


A circuit breaker with a break-time short enough to prevent the short-circuit

current from reaching its peak value.

Current limiting circuit breaker

Current limiting circuit breaker (IEC 60947-2 def. 2.3)

A current-limiting circuit

breaker is able to reduce the

stress, both thermal and

dynamic, because it has been

designed to start the opening

operation before the short-

circuit current has reached its

first peak, and to quickly

extinguish the arc between the

contacts.



A = Direction of arc due to the magnetic field

R= Repulsion of moving contacts due to the short circuit current

A

I

A

R

R


Time

Current


Energy limitation


Value of the limited peak

of the short circuit current

according to the value of

the symmetrical short

circuit current Irms.


Peak limitation curves


Value of the let-through

energy according to the

value of the symmetrical

short circuit current Irms.


I2t curves


Protection against short-circuit (IEC 60364)

To protect a cable against short-circuit, the specific let-through energy of

the protective device must be lower or equal to the withstanding energy of

the cable:

where

I2 t is the specific let-through energy of

the protective device which can be read on

the curves supplied by the manufacturer;

S is the cable cross section [mm2]; in the

case of conductors in parallel it is the

cross section of the single conductor;

k is a factor that depends on the cable

insulating and conducting material.

0.1kA 1kA 10kA 100kA

1E-2MAs

0.1MAs

1MAs

10MAs

100MAs

1E3MAs

Specific let through energy curve LLL


Energy limitation


Rated values (Iu, Ue)

Limit values (Icu, Ics, Icw, Icm)

Insulation values (Ui, Uimp)

Choice criteria



the rated uninterrupted current of an equipment is a value of

current, stated by the manufacturer, that the equipment can carry

in uninterrupted duty (at 40 C)

IEC 60947-1 def. 4.3.2.4

Rated value Iu

Rated uninterrupted current Iu


Rated value Iu

The rated uninterrupted current Iu is different from the rated

current In, which is the rated current of the thermomagnetic or

electronic trip unit and is lower or equal to Iu.

A new concept

for setting the

current In: the

rating plug


XT1 160

XT4 250

Rated uninterrupted current Iu

Some factors may reduce the Iu of a circuit breaker

like temperature, altitude or frequency.

Rated value Iu


the rated operational voltage of an equipment is a value of voltage

which, combined with a rated operational current, determines the

application of the equipment and to which the relevant tests and

the utilization categories are referred.

IEC 60947-1 def. 4.3.1.1

Rated value Ue

Rated operational voltage Ue


Breaking capacity is always referred to the operational voltage; the

breaking capacity decreases when the voltage increases.

Rated value Ue

Rated operational voltage Ue


Some factors may reduce the Ue of a circuit breaker

Rated value Ue





Choice criteria



Breaking capacity according to a specified test sequence.

Do not include after the short circuit test, the capability of the

circuit breaker to carry its rated current continuously.

- test sequence: O - 3 min - CO

- dielectric withstand at 2 x Ue- verification of overload release at 2.5 x I1

Limit value Icu

Icu = RATED ULTIMATE SHORT

CIRCUIT BREAKING CAPACITY

IEC 60947-2

def. 4.3.5.2.1


Breaking capacity according to a specified test sequence.

Include after the short circuit test, the capability of the circuit

breaker to carry its rated current continuously

- test sequence: O - 3 min - CO - 3 min CO

- dielectric withstand at 2 x Ue- verification of temperature rise at Iu- verification of overload release at 1.45 x I1- verification of the electrical life

Ics = RATED SERVICE SHORT

CIRCUIT BREAKING CAPACITY

IEC 60947-2

def. 4.3.5.2.2

Limit value Ics


Limit values Icu and Ics

The service breaking capacity Ics can be expressed as

a value of breaking current, in kA;

Standard ratios between Ics and Icu

Relation between Ics and IcuThis relation is always true!!!

Ics Icu

a percentage of Icu, rounded up

to the lowest whole number,

in accordance with the table (for

example Ics = 25% Icu).

When is Icu required?

Where continuity of service is not a fundamental requirement.

For protection of single terminal load.

For motor protection.

Where maintenance work is easily carried out without much

disruption.

Generally for circuit breaker installed on terminals part of

plant.

When is Ics required?

Where continuity of service is a fundamental requirement.

For installation in power center.

Where is more difficult to make maintenance.

When is difficult to manage spare breakers.

Generally for installation in main distribution board

immediately downstream transformer or generator.


Main circuit breakers or circuit breakers for which

a long out-of-service period can not be accepted

(for example naval installation)

CB selection

based on

Ics

Icu

circuit breakers tor termlnal circuits or

circuit breakers for economic application

Limit values Icu and Ics

Icu and Ics: selection criteria

Icu or Ics ?

Application of Icu / Ics circuit breakers

When Isc = 100 % of Icu is not necessary ?

When the real short circuit current in the point of

installation is lower than the maximum Ics breaking

capacity.

U LOAD

B

A

Breaker A:

Icu =100 kA

with Ics = 100 % of Icu

Breaker B:

Icu = 100 kA

with Ics = 75 % of Icu

70 kA

50 kA !!!Please also consider

that short circuit current

at the end of the line is

still lower

When Isc = 100 % of Icu is not necessary ?

Motor Protection according to IEC 60947- 4-1

Duty cycle:

O - 3mins - CO at Iq current (maximum short circuit current)

O - 3mins - CO at r current (critical short circuit current depending from the contactor size)

Where:

O: Tripping of the circuit breaker under short circuit condition.

CO: Closing by the contactor under short circuit condition and tripping of the

circuit breaker.

Icu or Ics ? Conclusion

Consider that not always Ics = 100% of Icu for all the employ

voltage range, i.e. (from 220 V a.c. to 690 V a.c.duty, and 250

V d.c.).

Selection of circuit breaker with breaking capacity Icu or Ics

must be done according to the real technical installation

requirement.

Independently from the duty cycle selected the safety of the

plant is strictly dependent from the maximum circuit breaking

capacity (in most of cases Icu).


Limit value Icw

Icw = RATED SHORT-TIME

WITHSTAND CURRENT

IEC 60947-2

def. 4.3.5.4

Example of use of category B circuit breakers

in electrical plant

Trafo 630kVA

Ucc%=4%

400V

ACB E1B12

MCCB XT4

22.7kA

MCCB XT3

The upstream circuit

breaker can withstand

the fault current up to 1

sec, thus guaranteeing

an excellent selectivity

with downstream

apparatus


Circuit breakers specifically intended for selectivity in short

circuit conditions in relation to other protection devices in

load-side series, that is with an intentional delay (adjustable)

applicable in short circuit conditions.

These circuit breakers have a specified rated short-time

withstand current Icw.

IEC 60947-2

Table 4CATEGORY BCIRCUIT BREAKER

Limit value Icw


Circuit-breakers not specifically intended for selectivity under

short circuit conditions with respect to other protection devices

in series on the load side, that is without intentional short-time

delay provided for selectivity under short-circuit conditions.

These circuit-breakers have not a specified rated short-time

withstand current value Icw.

Limit value Icw

IEC 60947-2

Table 4CATEGORY ACIRCUIT BREAKER


It is the value of short-time withstand current assigned to the

circuit-breaker by the manufacturer under specified test

conditions. This value is referred to a specified time (usually 1s or 3s).

It must be stated when the circuit-breaker is classified in

category B and its value must be greater than:

The highest value between 12 Iu and 5 kA for CBs with Iu 2500A

30 kA for CBs with Iu > 2500A

Circuit breakers without Icw value are classified in category A

Limit value Icw

IEC 60947-2

Table 3Icw = RATED SHORT-TIME

WITHSTAND CURRENT

Selectivity Categories


IEC 60947-2

def. 4.3.5.1Icm = RATED SHORT-CIRCUIT

MAKING CAPACITY

Making capacity for which the prescribed conditions according

to a specified test sequence include the capability of the circuit

breaker to make the peak current corresponding to that rated

capacity at the appropriate applied voltage.

Limit value Icm

It is always necessary to verify that:

Icm Ipeak


Limit value Icm

Icm n x Icu

For a.c. the rated short-circuit making

capacity of a circuit-breaker shall be not

less than its rated ultimate short-circuit

breaking capacity, multiplied by the factor

n of the table.

IEC 60947-2

Table 2


16,8kA

50kA

54kA

Peak

Irms

105kA

10kA 100kA

10kA

100kA

T6L800 In800

XT2L 160 In160

Example



If the cos of the plant is higher than the standard prescribed

value, it is not necessary to take into account the rated short-

circuit making capacity of the circuit-breakers (Icm).

If the cos of the plant is lower than the standard

prescribed value, usually near to the transformer and/or

generator, it is necessary to verify Icm Ipeak.

Limit value Icm


If the cosk of the plant is equal to 0.16 (lower than the standard

prescribed value) the evaluated Ip = 175 kA.

Short circuit current of the plant is Icc = 75kA ;

The used circuit breaker has an Icu = 75 kA;

According to the table 2, cosk=0.2 and n=2,2 so Icm = n x Icu = 165 kA.

Since Ip > Icm the CB selected is not correct. I will use a CB with a greater

value of Icu in order to have an Icm value suitable to the peak current of the

plant.

Sometimes it can happen

Limit value Icm


Limit value Icm





Choice criteria



IEC 60947-1

def. 4.3.1.2Ui = RATED INSULATION

VOLTAGE

The rated insulation voltage of an equipment is the value

of voltage to which dielectric tests and creepage

distances are referred.

It shall be always verified that:

Ue < Ui

Limit value Ui


IEC 60947-1

def. 4.3.1.3Uimp = RATED IMPULSE

WITHSTAND VOLTAGE

The peak value of an impulse voltage of prescribed form and

polarity (1,2/50ms) which the equipment is capable of

withstanding without failure under specified conditions of test

and to which the values of the clearances are referred.

It shall be always verified that:

Uimp > transient overvoltage in the plant

Limit value Uimp

Temperature-rise for terminals and accessible parts


IEC 60947- 2

Table 7

Overload protection

ABB Group March 10, 2015 | Slide 48 i

t

IEC 60947- 2

Table 6

Short circuit protection


i

S

I

t

IEC 60947- 2

8.3.3.1.2

Type Tests

The tests to verify the characteristics of

circuit breakers are:

type tests carried out on samples:

IEC 60947- 2

8.3

Type Tests


Routine Tests


routine tests carried out on

all circuit breakers and

including the following tests:

IEC 60947- 2

8.4

Tests of EMC for circuit breakers with electronic overcurrent protection

Immunity

Emission

Electrostatic discharges

Radiated radio-frequency electromagnetic fields

Electrical fast transients/bursts

Surges

Conducted disturbances induced by radio-frequency fields

Harmonics

Voltage fluctuations

Conducted disturbances

Radiated disturbances

Climatic testsDry heat test Damp heat test

Temperature variation cycles at a specified rate of change

Annex F - J

CE Marking


According to european directives:

Low Voltage Directive 73/23 EEC

Electromagnetic Compatibility 89/336 EEC

Annex H

Test sequence for circuit-breakers for IT systems

This test is intended to cover the case of a second fault to earth in presence of a first

fault on the opposite side of a circuit breaker when installed in IT systems.

In this test at each pole the applied voltage shall be the phase-to-phase voltage

corresponding to the maximum rated operational voltage of the circuit breaker at which it

is suitable for applications on IT systems.

Circuit BreakersStandards Guidelines IEC 60898


International Standard References

IEC 60898

Applicable to circuit-breakers for protection of wiring installation

in buildings and similar applications, and designed for use by

uninstructed persons, and for not being maintained.

Part 1: Circuit-breakers for a.c. operation

Part 2: Circuit-breakers for a.c. and d.c. operation (additional requirements)

Miniature Circuit Breakers MCB

Rated values (In, Ue)

Limit values (Icn, Ics)


Choice criteria

Rated uninterrupted current (In):

the rated uninterrupted current of an equipment is a value

of current, stated by the manufacturer, which the equipment

can carry in uninterrupted duty, at a specified reference

ambient air temperature (30 C).

The rated current doesnt exceed the 125A.

IEC 60898-1 def. 5.2.2

Rated value In

Rated operational voltage (Ue):

The rated operational voltage of a circuit-breaker is the

value of voltage, assigned by the manufacturer, to which

its performances (particularly the short-circuit

performance) are referred.

The rated operational voltage doesnt exceed the 440Vac

220Vdc.

IEC 60898-1 def. 5.2.1.1

Rated value Ue


Limit values (Icn, Ics) Limit values (Icn, Ics)

Choice criteria

The rated short-circuit capacity is the value of the ultimate

short-circuit breaking capacity for which the prescribed

conditions, according to a specified test sequence, do not

include the capability of the circuit-breaker to carry 0.85 times

its non-tripping current for the conventional time.

The rated short circuit capacity doesnt exceed the

25kA in ac and 10kA in dc

test sequence: O - 3 min - CO

- leakage current at 1.1 Ue (< 2 mA)

- dielectric strength test at 900 V

- verification of overload release at 2.8 x In

IEC 60898-1

def. 5.2.4Icn = RATED SHORT CIRCUIT

CAPACITY

Limit value Icn

The service short-circuit capacity of a circuit-breaker is the

value of the breaking capacity for which the prescribed

conditions according to a specified test sequence include the

capability of the circuit-breaker to carry 0.85 times its non-

tripping current for the conventional time.

IEC 60898-1

def. 3.5.5.2Ics = RATED SERVICE SHORT

CIRCUIT CAPACITY

Limit value Ics

Service Short Circuit capacity (Ics):

- test seq. : O - 3 min - O - 3 min CO (for one or two poles cb)

O - 3 min - CO - 3 min CO (for three or four poles cb)

- leakage current at 1.1 Ue (< 2 mA)

- dielectric strength test

- verification of no tripping at 0,85 x In

A circuit-breaker with a rated short-circuit capacity (Icn) has a corresponding service short-

circuit capacity (Ics) as from this table:

The circuit breaker with

Icn < 6000A Ics is equal to 1xIcn

6000A < Icn < 10000A Ics is equal to 0,75xIcn Minimum value of Ics is 6000A.

Icn > 10000A Ics is equal to 0,5xIcn Minimum value of Ics is 7500A.

Limit value Ics

Ics Test

The main difference between the overload protection curve of the CBs responding to

IEC 60947 or IEC 60898 are referred to the conventional non tripping current.

The prescibed conditions are given in this table:

Overload characteristics

Tripping Curves

The CBs according to IEC 60947 usually have the instantaneous threshold at 5 or 10 times

the rated current with a tolerance of + 20%.

The CBs according to IEC 60898-1 (ac applications) have different instantaneous

threshold referred to the type B , C , D as indicated in the table below:

Magnetic characteristics

Tripping Curves

Tripping Curves

In some cases, the conditions IB < In < IZand I2 < 1.45 IZ do not guarantee complete

protection, e.g. when overcurrents are

present for long periods which are smaller

than I2. They also do not necessarily lead

to an economical solution. It is therefore

assumed that the circuit is designed so

that minor overloads of a long duration will

not occur regularly.

IEC 60364-4-43

Tripping Curves

Tripping Curves

IEC 60947-2 IEC 60898-1

People Instructed Uninstructed

Maintenance Possible Not possible

Rated Voltage (Ue)< 1000 Vac

< 1500 Vdc

< 440 Vac

< 220 Vdc

Ambient

Temperature40 C 30 C

Rated CurrentNo limits

(Iu < 6300 A)In = 125 A

Short circuit

breaking currentNo limits for Icu

Icn = 25 kA (ac)

Icn = 10 kA (dc)

Comparison IEC 60947-2 vs IEC 60898

Generalities about the main electrical parameters Dont forget

Ue Un Icu or Ics Ik Icm Ip

Ue, Icu, Ics, Icm?

Selection of protective Devices

Protection of feeders against overload

Ib In or I1 Iz

against short-circuit

I2t k2S2

In

Iz S

Ib


The correct circuit breaker must be selected to satisfy the following

conditions:

It must own short circuit breaking power (lcu or eventually lcs) greater or

equal to the short circuit current lcc

It must use a protection release so that its overload setting current ln (l1)

satisfies the relation lB < ln < lZ

The let through energy (l2t) that flows through the circuit breaker must be

lesser or equal to the maximal one allowed by the cable (KS)


As far as the verification required by IEC 60364, according to which the

overload protection must have an intervention current lf that assures the

operation for a value lesser than 1,45 lz (lf < 1,45 lz), we must state that it

is always verified for ABB Circuit breakers, since according to IEC 60947-2

the required value is less than 1,3 ln.


Protection of generators Ingen I1 I3 or I2 2.5-4 x Ingen

G


Protection of transformers InT I1 Upstream CB

I3 or I2 Iinrush


Steps determining the short-circuit

currents

choosing the CB

setting of the MV overcurrent

protection

setting of the LV overcurrent

protection

20kV

400V


20kV

400V


As to be able to protect LV/MV transformers LV side, we must mainly

take into account:

Rated current of the protected transformer, LV side, from which

the rated current of the circuit breaker and the setting depend on

(In);

The maximum estimated short circuit current in the installation

point which defines the minimal breaking power of the protection

circuit breaker (Isc).

Protection of Transformers

Sn

In

Isc

U20

Protection of TransformersSwitchboards with one transformer

The rated current of the transformers LV side is defined by the

following expression

where

Sn = rated power of the transformer [kVA]

U20 = rated secondary voltage (no load) of the transformer [V]

ln = rated current of the transformer, LV side [A]

In =Sn x 103

3 x U20

The full voltage three-phase short circuit current immediately after the LV

side of the transformer can be expressed by the following relation once we

suppose infinite power at the primary:

where

Ucc %= short circuit voltage of the transformer [%]

ln = rated current, LV side, [A]

lsc = three-phase rated short circuit current, LV side, [A]

Isc =In x 100

Ucc %


The short circuit current is normally lesser than the preceding deduced

value if the circuit breaker is installed at a certain distance by means of

a cable or bar connection, according to the connection impedance.


The following table shows some possible choices within the SACE Emax

ACB range according to the characteristics of the CB to protect.

Attention

Those indications are valid at the conditions that we declare in the table;

different conditions will lead us to repeat calculations and modify the

choices.


(1) For values of the percent short circuit voltage Ucc% different from the Ucc% values as per table, the rated three-phase short

circuit current Icn becomes:

(2) The calculated values refer to a U20 voltage of 400 V. for different U20 values, do multiply In and Isc the following k times:

Isc =Ucc %

Ucc %

Isc

U20 [V] 220 380 400 415 440 480 500 660 690

k 1.82 1.05 1 0.96 0.91 0.83 0.8 0.606 0.580


Sn [kVA] 500 630 800 1000 1250 1600 2000 2500 3150

Ucc (1) % 4 4 5 5 5 6,25 6,25 6,25 6,25

In (2) [A] 722 909 1154 1443 1804 2309 2887 3608 4547

Isc (2) [kA] 18 22.7 23.1 28.9 36.1 37 46.2 57.7 72.7

SACE Emax E1B08 E1B12 E1B12 E2B16 E2B20 E3B25 E3B32 E4S40 E6H50

Protection of TransformersSwitchboards with more than 1 transformer in Parallel

Circ

uit b

reaker B

I1 I2 I3

1 2 3

Isc2 + Isc3

Isc1 + Isc2 + Isc3

I4 I5

Circ

uit b

reaker A

Isc1

As far as the calculation of the rated current of the transformer is

concerned, the rules beforehand indicated are completely valid.

The minimum breaking capacity of each circuit breaker LV side must be

greater than the highest of the following values: (the example refers to

machine 1 of the figure and it is valid for the three machines in parallel):

lsc 1 (short circuit current of transformer 1) in case of fault

immediately downstream circuit breaker 1;

lsc2 + lsc3 (short circuit currents of transformer 2 and 3) in case of

fault immediately upstream circuit breaker 1;


Circuit breakers l4 and l5 on the load side must have a short circuit

capacity greater than lsc1 + lsc2 + lsc3; naturally every transformer

contribution in the short circuit current calculation is to be lessened by the

connection line transformer - circuit breaker (to be defined case by case).



Low voltage selectivitywith ABB circuit breakersSelectivity definitions and Standards

Definitions and Standards

Selectivity techniques


Back-up protection

AgendaLow voltage selectivity with ABB circuit breakers

Selectivity (or discrimination)

is a type of coordination of two or

more protective devices in series.

Selectivity is done between

one circuit breaker on the supply side

and one circuit breaker, or more than

one, on the load side.

A is the supply side circuit

breaker (or upstream)

B and C are the load side circuit

breakers (or downstream)

IntroductionWhat is selectivity?

Better selectivity

FAULT CONTINUITY OF SERVICEDAMAGE REDUCTION

Fast fault elimination

Reduce the stress and prevent damage

Minimize the area and the duration of power loss

IntroductionProtection system philosophy

Selective coordination among devices

is fundamental for economical and technical reasons

It is studied in order to:

rapidly identify the area involved in the problem;

bound the effects of a fault by excluding just the affected zone of the network;

preserve the continuity of service and good power quality to the sound parts of the network;

provide a quick and precise identification of the fault to the personnel in charge of maintenance or to management system, in order to restore the service as rapidly as possible;

achieve a valid compromise between reliability, simplicity and cost effectiveness.

Main purposes of coordinationSelectivity purpose

The definition of selectivity

Trip selectivity (for overcurrent) is a coordination between the

operating characteristics of two or more overcurrent protection

devices, so that, when an overcurrent within established limits

occurs, the device destined to operate within those limits trips

whereas the others do not trip

IEC 60947-1 Standard: Low voltage equipment

Part 1: General rules for low voltage equipment

Standards definitionSelectivity

IEC 60947-1

def. 2.5.23

In occurrence of a fault

(an overload or a short circuit)

if selectivity is provided

only the downstream circuit

breaker opens.

Overcurrent selectivityExample

All the system is out of service!

In occurrence of a fault

(an overload or a short circuit)

if selectivity is not provided

both the upstream and the

downstream circuit breakers

could open

Overcurrent selectivityExample

A and B connected in series:

partial selectivity and total selectivity.

Standards definitionPartial and total selectivity

IEC 60947-2

def. 2.17.2 - 2.17.3

Partial selectivity is an overcurrent selectivity where, in the

presence of two protection devices against overcurrent in series,

the load side protection device carries out the protection up to a

given level of overcurrent, without making the other device trip.

B opens only according to fault current

lower than a certain current value;

values equal or greater than Iswill give the trip of both A and B.

Is is the ultimate

selectivity

value!

Is = ImA

Standards definition Partial selectivity

Only B trips for every current value

lower or equal to the maximum

short-circuit current.

Total selectivity is an overcurrent selectivity where, in the

presence of two protection devices against overcurrent in series,

the load side protection device carries out the protection without

making the other device trip.

B A

Is = Ik

Standards definitionTotal selectivity

Upstream circuit breaker A

T4N 250 PR221DS In = 250 (Icu = 36kA)

Downstream circuit breaker B

S 294 C100 (Icu = 15kA)

Standards definitionPartial and total selectivity

Overload zone

Thermal protection

L protection

Short-circuit zone

Magnetic protection

S, D, I and EF protections

Time-current selectivity

Current, time, energy, zone,

directional, zone directional selectivity

Selectivity analysisTime-current curves

Real currents circulating through the circuit breakers

I>A

B I> I> I>

A

B

I>

I>

I>

I> I>

A

B

I>

I>

IA = IB

IA IB

tA

tB

tA

tB

IAIBIA=IB

tA

tB

IA = IB + Iloads IA = (IB + Iloads) / 2

Selectivity analysisReal currents

ABB Group, BU Breakers and Switches March 10, 2015 | Slide 106


Selectivity techniques Selectivity techniques

Back-up protection


ABB Group, BU Breakers and Switches March 10, 2015 | Slide 107

Current selectivity

Time selectivity

Energy selectivity

Zone (logical) selectivity

IntroductionSelectivity techniques

The ultimate selectivity value

is equal to the instantaneous trip threshold

of the upstream protection device

Other methods are needed to have a total

selectivity

AB

ImB ImA

Current selectivity: closer to the power supply

the fault point is, higher the fault current is

In order to guarantee selectivity,

the protections must be set to different

values of current thresholds

Ultimate

selectivity

value

1kA

3kA

tB

tA

tA

Current selectivityBase concept

A

B

Here the selectivity is a total selectivity,

because it is guaranteed up to the maximum

value of the short-circuit current, 1kA.

Circuit breaker A will be set to a value which does not

trip for faults which occur on the load side of B.

(I3Amin >1kA)

Circuit breaker B will be set to trip for faults which

occur on its load side (I3Bmax < 1kA)

0.1kA 1kA 10kA

10-2s

10-1s

1s

10s

102s

103s

104s

3kA

Is Is = I3Amin

Current selectivityExample

Plus

Easy to be realized

Economic

Instantaneous

Minus

Selectivity is often only partial

Current thresholds rise very quickly

CURRENT SELECTIVITY

Current selectivity Plus and minus

Time selectivity is based on a trip delay of the upstream

circuit breaker, so to let to the downstream protection the

time suitable to trip

B A

Setting strategy:

progressively increase the

trip delays getting closer to

the power supply source

On the supply side

the S function is required

Time selectivityBase concept

0.1kA 10kA 100kA

10-2s

10-1s

1s

10s

102s

103s

104s

1kA

The ultimate selectivity value is:

Is = IcwA (if function I = OFF)

Is = I3minA (if function I = ON)

Ik

A will be set with the current threshold I2adjusted so as not to create trip overlapping

and with a trip time t2 adjusted so that

B always clears the fault before A

B will be set with an instantaneous trip

against short-circuit

BI2

t2

Is

Time selectivityExample

0.1kA 10kA 100kA

10-2s

10-1s

1s

10s

102s

103s

104s

1kA

The network must withstand high values of

let-through energy!

If there are many hierarchical levels, the

progressive delays could be significant!

Ik

Which is the problem of time selectivity?

In the case of fault occurring at the busbars,

circuit breaker A takes a delayed trip time t2

B

t2

Time selectivity Example

Plus

Economic solution

Easy to be realized

Minus

TIME SELECTIVITY

Time selectivityPlus and minus

Quick rise of setting levels

High values of let-through energy

Energy selectivity is based on the current-

limiting characteristics of some circuit breakers

A

B

0.1kA 1kA 10kA

10-2s

10-1s

1s

10s

102s

103s

104s

Current-limiting circuit breaker

has an extremely fast trip time,

short enough to prevent the

current from reaching its peak The ultimate current

selectivity values

is given by the

manufacturer

(Coordination tables)

Energy selectivityBase concept

1kA 10kA0.1kA10-2s

10-1s

1s

10s

102s

103s

104s

Circuit breaker A conditions:

I3=OFF

S as for time selectivity

A

B

Is = 20kA

Energy selectivityExample

PLUS

MINUS

ENERGY SELECTIVITY

Energy selectivityPlus and minus

High selectivity values

Reduced tripping times

Low stress and network disturbance

Increasing of circuit breakers size

Zone selectivity is an evolution of the time

selectivity, obtained by means of a electrical

interlock between devices

The circuit breaker which detects a fault

communicates this to the one on the supply side,

sending a locking signal

Fault

locking

signal

Only the downstream circuit breaker opens,

with no need to increase the intentional time

delay

Zone selectivityBase concept

A Does Not Open

B Does Not Open

C Opens

A

B

C

Zo

ne 1

Zo

ne 2

Zo

ne 3

Zone selectivityExample

Is up to 100kA for Tmax

Is up to Icw for Emax

It is possible to obtain zone selectivity between Tmax and Emax

Zo

ne 1

Zo

ne 2

Zo

ne 3

Zone selectivity needs:

a shielded twisted pair cable

an external source of 24V

dedicated trip units

PR223EF for Tmax T4, T5 and T6

PR332/P for Tmax T7 and T8

PR122/P and PR123/P for Emax

PR332/P and PR333/P for X1

Zone selectivitySpecifications

PLUS

MINUS

ZONE SELECTIVITY

Zone selectivityPlus and minus

Trip times reduced

Low thermal and dynamic stress

High number of hierarchical levels

Can be made between same size circuit breakers

Cost and complexity of the installation

Additional wiring and components

ABB Group, BU Breakers and SwitchesMarch 10, 2015 | Slide 122


Selectivity techniques

Back-up protection Back-up protection


Back-up protection (or cascading)

is a type of coordination of two protective

devices in series which is done in electrical

installations where continuous operation is

not an essential requirement.

Back-up protectionWhat is back-up protection?

Back-up protection

excludes the use

of selectivity!!!

The definition of back-up is given by the

Back-up is a coordination of two overcurrent protective

devices in series, where the protective device on the supply

side, with or without the assistance of the other protective

device, trips first in order to prevents any excessive stress on

downstream devices.

IEC 60947-1 Standard: Low voltage equipment

Part 1: General rules for low voltage equipment

Back-up protectionStandards definition

IEC 60947-1

def. 2.5.24

Back-up is used by those who need

to contain the plant costs

The use of a current-limiting circuit

breaker on the supply side

permits the installation of lower performance

circuit breakers on the load side

Both the continuity of service and the selectivity are sacrificed

Back-up protectionBase concept

T4L 250

T1N 160 T1N 160 T1N 160

Ik = 100 kA

T4L 250 T4L 250 T4L 250 Icu = 120kA

Icu = 36kA

Icu (T4L+T1N) = 100kA

Back-up protection Application example

Back-up protection tables

T4L 250

T1N 160 T1N 160 T1N 160

Ik = 100kA

Icu (T4L+T1N) = 100kA

Ik = 100kA

A

B C D

Back-up protection Application example

General power supply

is always lost

Plus

Economic solution

Quick tripping times

Minus

No selectivity

Low power quality

BACK-UP PROTECTION

Back-up protectionPlus and minus

Incoming = T5H 630A (70kA

rating) Outgoing = T3N 160A

(36kA rating)

Results: The co-ordination

resulted in a conditional short-

circuit of 65kA for the T3 mccb!

The discrimination is up to 20kA.

Example of Selectivity

Iz

T5H 630A 70kA

T3N 160A 36kA

65kA

~


Discrimination


Back-Up

T5H 70kA

T3N 36kA

Example of Selectivity Meaning of Selectivity Value

T3N 36kA

T5H 70kA

Y is 20kA

Fault level at Y is 20kA

T3N 36kA

T5H 70kA

T5H

T3N 20kA


5kA

T5H T3N

5kA fault ON Trip

T3N 36kA

T5H 70kA


T5H T3N

5kA fault ON Trip

10kA fault ON Trip

10kA

T3N 36kA

T5H 70kA


T3N 36kA

20kA

T5H 70kA T5H T3N

5kA fault ON Trip

10kA fault ON Trip

20kA fault Trip Trip


T3N 36kA36kA

T5H 70kA T5H T3N

5kA fault ON Trip

10kA fault ON Trip




T3N65kA

T5H 70kA T5H T3N

5kA fault ON Trip

10kA fault ON Trip




36kA


Motor co-ordination ABB offers co-ordination tables

MV/LV Transformer SubstationsSelection of Protective & Control Devices

Co-ordination between CBs and switch-disconnectors

T2S160

T1D160

400V

MV/LV Transformer SubstationsSelection of Protective & Control Devices


Power Factor Correction

ABB Group

March 10, 2015 | Slide 143

Power Factor CorrectionGeneralities on Power Factor Correction

In alternating current circuits, current is absorbed by a load which can be represented by two components:

The Active component

In phase with the supply voltage

Directly related to the output

The Reactive component

Quadrature to the voltage

Used to generate the flow necessary for the conversion of powers through the electric or magnetic field

In most installations the presence of inductive type loads, the current lags the active component (IR).

Generalities

ABB Group

March 10, 2015 | Slide 144

In order to generate and transmit active power (P) a certain reactive power (Q) is essential for the conversion of the electrical energy but is not available to the load.

The power generated and transmitted make up the apparent power (S).

Power factor (cos ) is defined as the ratio between the active component (IR) and the total value of current (I).

is the phase angle between the voltage and the current.

Generalities on Power Factor CorrectionPower Factor CorrectionGeneralities

ABB Group

March 10, 2015 | Slide 145

Generalities on Power Factor CorrectionPower Factor CorrectionGeneralities

ABB Group

March 10, 2015 | Slide 146

Typical Power Factors of some electrical equipmentPower Factor CorrectionGeneralities

ABB Group

March 10, 2015 | Slide 147

Advantages of Power Factor Correction Power Factor CorrectionGeneralities

ABB Group

March 10, 2015 | Slide 148

Advantages of Power Factor Correction

Better utilization of electrical machines

Generators & transformers are sized according to the

apparent power (S). With the same active power (P),

the smaller the reactive power (Q) delivered, the

apparent power will be smaller.

Better utilization of cables

The reduction in current allows the use of smaller

cables in the installation.

Power Factor CorrectionGeneralities

ABB Group

March 10, 2015 | Slide 149

Reduction in losses

By improving the power factor, power losses is reduced

in all parts of the installation.

Reduction in voltage drop

The higher the power factor the Voltage drop will be

lower at the same level of Active power.


ABB Group

March 10, 2015 | Slide 150

Economical savings

Power supply utilities apply penalties for energy used

with poor factor. An improved power factor will reduce

such penalties from the utilities.


ABB Group

March 10, 2015 | Slide 151

Advantages of Power Factor Correction

Improve capacity of transformers and cables

By improving the power factor, you reduce the kVA load on the transformer and the current carried by the cables

Thus additional transformer capacity is available if upgrade or expansion is required in the future

Or new cables might not be needed if new loads are connected to an existing switchboard

Apparent Power (VA)

e.g 2MVA Transformer

At 100% capacity

Real Power (W)

eg. 500kW Load

Reactive Power (VAR)

e.g Motors (inductive)

100kW at 0.7pf = 102kVAR

Reactive Power (VAR)

eg. 50kVAR Capacitors


ABB Group

March 10, 2015 | Slide 152

Distributed power factor correction

It is achieved by connecting a capacitor bank properly

sized according to the load and is connected directly to

the terminals of the load.

Power Factor CorrectionDifferent Methods

ABB Group

March 10, 2015 | Slide 153

Group power factor correction

It is achieved by connecting a capacitor bank properly

sized according to a group of loads and is connected to

the upstream of the loads to be corrected.


ABB Group

March 10, 2015 | Slide 154

Types of Power Factor correction

Centralized power factor correction

It is achieved by installing an automatic power factor

correction bank capacitor bank directly to the main

distribution boards.


ABB Group

March 10, 2015 | Slide 155

Types of Power Factor correction

Combined power factor correction

This solution is derived from a compromise between a

distributed & centralized power factor correction.

Distributed power factor correction is used mainly

for higher loads and a smaller centralized power

factor correction is used for the small loads.


ABB Group

March 10, 2015 | Slide 156

Switching and Protection

Electrical switching phenomena

The switching of a capacitor bank causes an electric

transient due to the phenomena of electric charging of

the bank.

The overcurrents at the moment of switching depends

greatly on both the inductance of the upstream network

as well as from the number of connected capacitor

banks.

Power Factor CorrectionCapacitor Switching

ABB Group

March 10, 2015 | Slide 157

Switching and Protection

Choice of protective device


In

Resistance

In

Motor

In

Capacitor

AC-1 AC-3 AC-6b


Single step capacitor

In

30 times In


Multi steps capacitor bank

In

> 100 times In


Ith = 1.3 x 1.15 x Inc = 1.5 Inc

Thermal current

Up to 30% for harmonics and voltage fluctuations on main

Up to 15% for tolerances on capacitor power

Contactor have to support Ith

Contactor sizing: Thermal current + peak current

Power Factor CorrectionContactor Sizing

ABB Group

March 10, 2015 | Slide 162

Example Power Factor CorrectionExample

kVARh is billed if it is higher than the contracted level.

Apparent power (kVA) is significantly higher than the Active power (kW)

The excess current causes losses (kWh) which is billed.

The design of the installation has to be over-dimensioned.

The installation requires 850kW at power factor of 0.75.

The transformer will have to be overloaded to 850k / 0.75 = 1.133MVA.

Current taken by the system is

Losses in the cables

P = I2R

The Transformer, Circuit breaker & Cable has to be increased.

PI =

3 * U * Cos = 1636A

I = 1636A

Cos = 0.75

kVA

kW kVar

Cos = 0.75

850kW Load

1MVA

400V

ABB Group

March 10, 2015 | Slide 163

Example Power Factor CorrectionExample

kVARh is reduced to lower than the contracted level or eliminated.

Apparent power (kVA) is significantly higher than the Active power (kW)

The charges based on the contracted kVA demand is close to the active

power.

The installation requires 850kW at a power factor of 0.9.

The transformer will not be overloaded to 850k / 0.90 = 945 kVA.

Current taken by the system is

Losses in the cables

P = I2R

There is not need to increase the Transformer, Circuit breaker & Cable.

PI =

3 * U * Cos = 1364A

I = 1364A

Cos = 0.90

kVA

kW kVar

Cos = 0.90

850kW Load

1MVA

400V

ABB Group

March 10, 2015 | Slide 164

Technical Application Paper Power Factor Correction

iec standards & power factor correction

Documents

circuit breaker standard

circuit breakers iec

circuit breaker emax

control circuit devices

air circuit breaker

international standard

contactors iec

limit valuesagenda abb