IEC电气装置蓝色安全保护防止过流保护(外文文献翻译)

IEC 60364.4.43-2008

LOW-VOLTAGE ELECTRICAL INSTALLATIONS-3

Part 4-43: Protection for safety Protection against overcurrent

434.2.2

A

protective

device

may

be

placed

on

the

supply

side

of

the

reduced

cross-sectional area or another change made, provided that it possesses an operating

characteristic

such

that

it

protects

the

wiring

situated

on

the

load

side

against

short-circuit, in accordance with 434.5.2.

NOTE The requirements of 434.2.2 may be met by the method given in Annex D.

434.3 Omission of devices for protection against short-circuit

Provided that both of the following conditions are simultaneously fulfilled:

?

the

wiring

is

installed

in

such

a

way

as

to

reduce

the

risk

of

a

short

-circuit

to

a

minimum (see item b) of 434.2.1), and

? the wiring is not

placed close to combustible material, devices for protection against

short-circuit need not be provided for applications such as:

a) conductors connecting generators, transformers, rectifiers, accumulator batteries to

the associated control panels, the protective devices being placed in these panels;

b)

circuits

where

disconnection

could

cause

danger

for

the

operation

of

the

installations concerned, such as those cited in 433.3.3;

c) certain measuring circuits;

d) at

the origin

of an installation where the

distributor installs

one or more devices

providing

protection

against

short-circuit

and

agrees

that

such

a

device

affords

protection to the part of the installation between the origin and the main distribution

point of the installation where further short-circuit protection is provided.

434.4 Short- circuit protection of conductors in parallel

A

single

protective

device

may

protect

conductors

in

parallel

against

the

effects

of

shortcircuit

provided

that

the

operating

characteristics

of

that

device

ensures

its

effective

operation

should

a

fault

occur

at

the

most

onerous

position

in

one

of

the

parallel conductors. Account shall be taken of the sharing of the short-circuit currents

between

the

parallel

conductors.

A

fault

can

be

fed

from

both

ends

of

a

parallel

1

conductor.

If

operation

of

a

single

protective

device

is

not

effective,

then

one

or

more

of

the

following measures shall be taken:

a) The wiring shall be carried out in such a way as to reduce to a minimum the risk of

a short-circuit in any parallel conductor, for example by protection against mechanical

damage, and conductors shall be installed in such a manner as to reduce to a minimum

the risk of fire or danger to persons.

b) For two conductors in parallel, a short-circuit protective device shall be provided at

the supply end of each parallel conductor.

c) For more than two conductors in parallel, short- circuit protective devices shall be

provided at the supply and load ends of each parallel conductor. Guidance is given in

Clause A.3.

434.5 Characteristics of short-circuit protective devices

Each short-circuit protective device shall meet the requirements given in 434.5.1.

434.5.1

The rated breaking capacity shall be not less than the prospective maximum

shortcircuit

current

at

the

place

of

its

installation,

except

where

the

following

paragraph applies.

A lower rated breaking capacity is permitted if another protective device having the

necessary

breaking

capacity

is

installed

on

the

supply

side.

In

that

case,

the

characteristics of the devices shall

be coordinated so that the energy let

through by

these two devices does not exceed that which can be withstood without damage by the

device on the load side and the conductors protected by these devices.

NOTE In certain cases other characteristics may need to be taken into account such as

dynamic

stresses

and

arcing

energy

for

the

device

on

the

load

side.

Details

of

the

characteristics needing coordination should be obtained from the manufacturers of the

devices concerned.

434.5.2

For

cables

and

insulated

conductors,

all

current

caused

by

a

short-circuit

occurring at any point of the circuit shall be interrupted in a time not exceeding that

which brings the insulation of the conductors to the permitted limit temperature.

For operating times of protective devices <0,1 s where asymmetry of the current is of

2

importance and for current-limiting devices

k

2

S

2

shall be greater than the value of the

letthrough energy (

I

2

t

) quoted by the manufacturer of the protective device.

For

short-circuits

of

duration

up

to

5

s,

the

time

t

,

in

which

a

given

short-circuit

current

will

raise

the

insulation

of

the

conductors

from

the

highest

permissible

temperature

in

normal

duty

to

the

limit

temperature

can,

as

an

approximation,

be

calculated from the formula:

t

= (

k * S / I)

2

(3)

where

t

is the duration, in s;

S

is the cross- sectional area, in mm

2

;

I

is the effective short-circuit current, in A, expressed as an r.m.s. value;

k

is

a

factor

taking

account

of

the

resistivity,

temperature

coefficient

and

heat

capacity of the conductor material, and the appropriate initial and final temperatures.

For common conductor

insulation, the values of

k

for line conductors are shown in

Table 43A.

434.5.3

For

busbar

trunking

systems

complying

with

IEC

60439-2

and

powertrack

complying with the IEC 61534 series, one of the following requirements shall apply:

? The rated short

-time withstand current (

I

CW) and the rated peak withstand current

of

a

busbar

trunking

or

powertrack

system

shall

not

be

lower

than

the

prospective

short-circuit current r.m.s. value and the prospective short-circuit peak current value,

respectively. The maximum time for which the

I

CW is defined for the busbar trunking

or

powertrack

system

shall

not

be

less

than

the

maximum

operating

time

of

the

protective device.

?

The

rated

conditional

short

-circuit

current

of

the

busbar

trunking

or

powertrack

system

associated

with

a

specific

protective

device,

shall

not

be

lower

than

the

prospective shortcircuit current.

435 Coordination of overload and short- circuit protection

435.1 Protection afforded by one device

A

protective

device

providing

protection

against

overload

and

short-circuit

currents

shall fulfil the applicable requirements of Clauses of 433 and 434.

3