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-k2級(jí)
是并聯(lián)導(dǎo)體的校正系數(shù)，可通過(guò)
以下公式：
式中，n是每相并聯(lián)的導(dǎo)體數(shù)量；
-1.2是標(biāo)準(zhǔn)允許的磁閾值公差。
TN系統(tǒng)
小短路電流的計(jì)算公式為：
因此：
IT系統(tǒng)
當(dāng)?shù)诙€(gè)故障將IT系統(tǒng)變成
TN系統(tǒng)。
有必要單獨(dú)檢查中性點(diǎn)未分布的裝置
中性分布。
ABB |電氣設(shè)備461
4保護(hù)人類
4.8保護(hù)人類的大保護(hù)長(zhǎng)度
1SDC010044F0001
Dy L1
L2級(jí)
L3級(jí)
體育課
體育課
體育課
任
我
k L3 L2 L1 Z
體育課
我
k L3 L2 L1
中性點(diǎn)未分配
當(dāng)發(fā)生第二個(gè)故障時(shí)，公式為：
因此：
中性分布
案例A：中性點(diǎn)分布式IT系統(tǒng)中的三相電路
公式為：
因此：
案例B：IT系統(tǒng)中的三相+中性電路，中性點(diǎn)分布
公式為：
因此：
462電氣設(shè)備| ABB
4保護(hù)人類
4.8保護(hù)人類的大保護(hù)長(zhǎng)度
1SDC010045F0001
Dy L1
L2級(jí)
L3級(jí)
N
體育課
體育課
體育課
任
我
k L3 L2 L1 N Z
體育課
我
k L3 L2 L1
A、B
表格使用說(shuō)明
已定義顯示大保護(hù)長(zhǎng)度（MPL）的表格
考慮以下條件：
-每相一根電纜；
-額定電壓等于400 V（三相系統(tǒng)）；
-銅電纜；
-中性非分布式，僅適用于IT系統(tǒng)；
-保護(hù)導(dǎo)體橫截面符合表1：
表1：保護(hù)導(dǎo)體橫截面
相導(dǎo)體截面S保護(hù)導(dǎo)體截面SPE
[平方毫米
][平方毫米
]
s≤ 16秒
16<秒≤ 35 16
S>35秒/秒
注：相導(dǎo)體和保護(hù)導(dǎo)體具有相同的絕緣和導(dǎo)電材料
每當(dāng)使用電子脫扣器的S功能（延遲短路）時(shí)
對(duì)于大保護(hù)長(zhǎng)度的定義，有必要驗(yàn)證
跳閘時(shí)間低于第4.5章表1中報(bào)告的時(shí)間值
對(duì)于TN系統(tǒng)和第4.6章表1中的IT系統(tǒng)。
對(duì)于與參考條件不同的條件，以下修正系數(shù)
應(yīng)適用。
- k2
is the correction factor for conductors in parallel, obtainable by the
following formula:
where n is the number of conductor in parallel per phase;
- 1.2 is the magnetic threshold tolerance allowed by the Standard.
TN system
The formula for the evaluation of the minimum short circuit current is:
and consequently:
IT system
The formulas below are valid when a second fault turns the IT system into a
TN system.
It is necessary to separately examine installations with neutral not distributed
and neutral distributed.
ABB | Electrical devices 461
4 Protection of human beings
4.8 Maximum protected length for the protection of human beings
1SDC010044F0001
Dy L1
L2
L3
PE
PE
PE
REN
I
k L3 L2 L1 Z
PE
I
k L3 L2 L1
Neutral not distributed
When a second fault occurs, the formula becomes:
and consequently:
Neutral distributed
Case A: three-phase circuits in IT system with neutral distributed
The formula is:
and consequently:
Case B: three-phase + neutral circuits in IT system with neutral distributed
The formula is:
and consequently:
462 Electrical devices | ABB
4 Protection of human beings
4.8 Maximum protected length for the protection of human beings
1SDC010045F0001
Dy L1
L2
L3
N
PE
PE
PE
REN
I
k L3 L2 L1 N Z
PE
I
k L3 L2 L1
A B
Note for the use of the tables
The tables showing the maximum protected length (MPL) have been defined
considering the following conditions:
- one cable per phase;
- rated voltage equal to 400 V (three-phase system);
- copper cables;
- neutral not distributed, for IT system only;
- protective conductor cross section according to Table 1:
Table 1: Protective conductor cross section
Phase conductor cross section S Protective conductor cross section SPE
[mm2
] [mm2
]
S ≤ 16 S
16 < S ≤ 35 16
S > 35 S/2
Note: phase and protective conductors having the same isolation and conductive materials
Whenever the S function (delayed short-circuit) of electronic releases is used
for the definition of the maximum protected length, it is necessary to verify that
the tripping time is lower than the time value reported in Chapter 4.5 Table 1
for TN systems and in Chapter 4.6 Table 1 for IT systems.
For conditions different from the reference ones, the following correction factors
shall be applied.
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