AN TOAN DIEN

Chơng 1
Khái niệm chung về an toàn điện
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1.1. Những nguy hiểm dẫn đến tai nạn do dòng điện gây ra
1.1.1. Điện giật
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1.2. Tác dụng của dòng điện đối với cơ thể ngời
1.2.1. Tác dụng của dòng điện đối với cơ thể ngời
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1.2.2. Những yếu tố xác định tình trạng nguy hiểm khi bị điện giật
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2. §êng ®i cña dßng ®iÖn qua ngêi
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3. TÇn sè dßng ®iÖn

jT 0:FT0,vW:")E.8T,
* Nguyªn nh©n:
BTc0)F:r(9";LArA49'/)0Q"!8(9
AJL=!!P#W:P,
BT 0)F:rA)0Q"!8(9#T]0 :
8rZ]0#:A,j@!!A#W:Y,BE.P
r:!)E.4T]0=r: !=W:P,
h:4c|rAQE908(9,
[CL4C#E.UbdRidV}:4,E.2L:34!,hR
L.9E.AE7F#W:)0F,
4. Tr¹ng th¸i søc khoÎ cña ngêi
B9'3#(F:%9'P2A24a )2
UT7.V,)2A)"5)+<F,1%9'O
F:9'4A@TA6F:,
1.3. ®iÖn ¸p tiÕp xóc vµ ®iÖn ¸p bíc
1.3.1. Dßng ®iÖn ®i vµo trong ®Êt
B8(9'P#()P(9'.4H@T)4)A= 6
L.4c)*@TT)"";9.4,
zMT)L29EO4@!4E4)4ρ#T
H";9.04<7W3TA5:0:A4,
v3TA:;9Ec K
2
d
x.2
I
J
π
=
@Kr


T)4,
zMc"4@E #<2OE9! 2=@@c"K
Trường ĐH KTCN Thái Nguyên
n

dx.
x.2
I
dx.Jdu
2
d
ρ
π
=ρ=
I(A:eLc !(Ae): )$*Uϕ
∞
~dVK
x
1
.k
x.2
.I
.
x.2
I
dx.
x.2
I
duU
d

x
d
x
2
d
x
AA
=
π
ρ
=ρ
π
−=ρ
π
==ϕ−ϕ=
∞
∞∞
∞
∫∫
@K
π
ρ
=
2
.I
k
d
&9:W=#@:9:a"Ag:6L.4U2cRQV# :.4
",
[CL#@K

Rio{"F"A)c,
RQ`{"FUcRcdV,
RG FQd#"9Cd,
j@@#.4!8.49E@9!Qd,
h(@"O=(9'.4p

•

2T)4r

 'K
d
d
d
I
U
R =
→



p
•
r =
1.3.2. §iÖn ¸p tiÕp xóc
B(9'@.49'P#@)P(9'"K
•

~r


,p

h(%(" /)(9'.(L)W;=4#2TA6 
L("4HA="(" /U2cRQVK

••• −=
@KRr

T)4#p

.4,
R•

"A:L.4c ,
&9:W4K"(" /%W L("4,h(%W )3Qd2•

~d#@"(" /9C)"8L("4•

,
1.3.3. §iÖn ¸p bíc
B%W=O4%Q;Q)'!#=%H"'L=5(
•

)•
t
U2cRQV,-L=()37"9K


,
Q

,r

c

c
,
Q
,r
•••

 9
+
=






+
−=−=
+
π
ρ
π
ρ
@K
R89;Ud#`÷d#oV,
R (gA4,
I"99CdW FQdOQ;W=)TT€(,

Trường ĐH KTCN Thái Nguyên
o
H×nh 1-2:\;9."(" /)"9x
TL.A)4,
R
d
U
b
=U
x
-U
x+a
U
x
U
x+a
r
d
U
d
U
x
U
tx
=U
d
-U
x
U
tx

=U
d
x
dx
20m

Ch¬ng 2
c¸c biÖn ph¸p b¶o vÖ an toµn ®iÖn khi
tiÕp xóc trùc tiÕp víi m¹ng ®iÖn
2.1. m¹ng ®iÖn mét pha
2.1.1. M¹ng ®iÖn 1 pha cã trung tÝnh c¸ch ®iÖn ®èi víi ®Êt
1. Khi ngêi tiÕp xóc víi hai cùc cña m¹ng ®iÖn (h×nh 2-1)
a) Dßng ®iÖn qua ngêi
A#$:@.4$#%":4(" /"L8
A@"•,
jT6%H@'.4)9CK
ng
ng
R
U
I =
UQRcV
@Kp

8%,
b) C¸c biÖn ph¸p an toµn
L(#(" /"L)34!D )$;)=",v
)=L#UOE##),,,VA"L,B@#* %@W=(#
#8#,,,Z$@T6%,
12)3#:9@:"F""K

R9'$;E8(W)0,
R]W$))L&9$)$ A,
Rj*"4")'4"Uw`d1V,
2. Khi ngêi tiÕp xóc víi mét cùc cña m¹ng ®iÖn, ®iÖn dung ®èi víi ®Êt nhá (h×nh 2-2)
BA@"4"2.)4P#)2)3z

4@:9P6A
,
a) Dßng ®iÖn qua ngêi
Gs=FSK
R•K"5L8A,
Rp
c
#p
Q
K8;J.)4,
Rz
c
#z
Q
K8;J.)4,
Rr

KT6F:%,
Rp

K8F:%,
Rp

K"..(")%U8#0%W=@#8

,,,V,

Trường ĐH KTCN Thái Nguyên
q
1
2
U
R
ng
r
ng
H×nh 2-1:hx%(" /)L8A

l%W4)A";Jc,I:!FS(U2QRQ9V9P6
8A4),jT6%K
QcQc
c
c
c
c
c
Q

pV,ppUpp
p
,•
p
c
V,
pp

p,p
,U
V
pp
p,p
Up
•
r
++
=
+
+
+
=
UQRQV
h(p
c
~p
Q
~p

K
cdng
ng
RR2
U
I
+
=
 UQRmV

h(%W@4'%Y.)49C"F9
#A@"p

>.(")p

@TA6%,
tBp
c
≠p
Q
#TA6%HK
2cd1cd2cd1cdsng
1cd
ng
R.R)RR)(RR(
R.U
I
+++
=
UQR`V
tBp
c
~p
Q
~p

#TA6%HK
cdsng
ng
R)RR(2

U
I
++
=
UQRbV
t%"94Kp

~d#/@T6%HK
sng
ng
RR
U
I
+
=
UQRiV
b) C¸c biÖn ph¸p an toµn
Rl")38A,
R&9:W=4#Yp

8@:Tr

(W,
B9(T6%"M"r
"
#@: ''.8:
9K
ng
ngcp
at.cd

R2
I
U
R −≥
UQRnV
@Kp
,
,
B!%4K
p

~Uodd÷cdddVΩ
r
"
~Uo÷cdVeUE.•~bd}V,
130:9K
p

≥p
,
%":4(" /";Jc/;JQ9'A4Up
Q
~dV,jT6%UR
%"V@'.4<9:WK
Trường ĐH KTCN Thái Nguyên
cd
H×nh 2-2:hx%(" /)cL8A
,-FSx,
9, -F S  ( 8 A  x% A " ;
Jc,

1
2
U
0
I
ng
a)
C
R
c®
C
R
c®
1
2
I
ng
U
ng
R
s
b)
R
cd1
X
c1
R
cd2
X
c2

U
R
ng

ng
max.ng
R
U
I =
R&9:W=#(Yp

2T6%,j@:)EY=
p

9C(9'9K#)3,,,
VÝ dô: h(4Kp

~cdddΩ‚ r
"
~cde,
!p

:9.)K
tvA"•~cQn12p

≥cd,nddΩ
tvA"•~QQd12p

≥Qd,dddΩ
3. Khi ngêi tiÕp xóc víi mét cùc cña m¹ng ®iÖn, ®iÖn dung ®èi víi ®Êt lín (h×nh 2-3)

B"8A#9P6.)4F40),
a) Dßng ®iÖn qua ngêi
&FS@K
Q
c
Q

c
Q

Q
c
Q


Q
c
cc
cc
c
c

zp
z,p
ƒ
zp
p,z
VƒzpV,UƒzpU
Vƒzp,Uƒz,p
ƒzp

ƒz,p
ƒzp„
+
−
+
=
−+
−
=
+
=−=
13#@K
Q
c
Q


Q
c

zp
p,z
p
+
=
)
Q
c
Q


c
Q


zp
z,p
z
+
=
UQRoV
l'8] '9CK
Q
c
Q

c
Q
Q
c
Q

c
Q

Q
Q
c
Q



Q
c
Q

Q

zp
z,p
zp
z,p
zp
p,z
zp„
+
=








+
+









+
=+=
UQRqV
jT]AK
Trường ĐH KTCN Thái Nguyên
cc
H×nh 2-3:-FS(8Ax%A";J
)x@,
1
2
I
ng
U
ng
X
c1
X
c2
U
R
dt
X
c2
U
X
dt
R

ng
R
s

QQ
c
Q

Q
Q
`
c
Q
Q
Q
c
Q

Q
m
c
Q

Q
Q
`
Qc
`

Q

c
`

Q

`
c
QQ
c
Q

Q
Q
cQc
Q

Q

`
c
Q
Q
Q
c
Q

c
Q

QQ

c
Q

Q

`
c
Q
Q
Q

VzpU
z,zz,z,p,Q
z,z,p,Qz,pz,z,p,Qz,pp,z
•
VzpU
z,zVzz,Up…p,z
•
z
zp
z,p
VzpU
p,z
•
VzzUp
•
„
•
r
+

++
+++++
=
=
+
+++
=








+
+
+
+
=
++
==
Σ
Σ
Q
c
Q

Q
Q

Q
c
Q
Qc
Q

Q
c
Q

Q
Q
Q
c
Q
Q
Q
Qc
Q

Q
c
Q

QQ
c
Q

Q
c

Q

Q
Q
Q
c
Q
c
Q

Q
Q
Q

Q
c
Q
Qc
Q

Q
c
Q

Q
c
Q

Σ
zp

z,zVzzUp
•
zp
z,zz,pz,z,p,Qz,p
•
VzpU
VzpUz,z
VzpUz,pVzpUz,z,p,QVzpUz,p
•
r
+
++
=
+
+++
=
+
++
++++++
=
I"O=%K
Q
Q
Q
c
Q
Qc
Q

c

Q
c
Q

c
Q
c
Q

Q
Q
Q
c
Q
Qc
Q


z,zVzzUp
z,p,•
zp
z,p
,
zp
z,zVzzUp
•
„,r•
++
=
+

+
++
==
Σ
jT6%K
Q
Q
Q
c
Q
Qc
Q

c



z,zVzzUp
z,•
p
•
r
++
==
UQRcdV
h(z
c
~z
Q
~

C
XX
cc
.
1
21
ω
==
2@T6%9:WK
1 4

).(ω
1
)
.ω
2
(
.
1
.
222
4
22
+
=
+
=
CR
CU
C

C
R
C
U
I
ng
ng
ng
ω
ω
ω
UQRccV
B%)49p

2T6%K
Trường ĐH KTCN Thái Nguyên
cQ

1.ω.)(4
.ω.
222
++
=
CRR
CU
I
sng
ng
UQRcQV
†h(!TA6%r


%"!TA68.
)4Usr
,
V)TA6.)4Usr
,
V2*6K
2
c.ng
2
r.ngng
III +=
b) C¸c biÖn ph¸p an toµn
&9:WUQRcQV#4:T6%@9C9""K
Rl"0,
RY%p

,
2.1.2. M¹ng ®iÖn 1 pha cã trung tÝnh trùc tiÕp nèi ®Êt
1. Khi ngêi tiÕp xóc víi mét cùc cña m¹ng ®iÖn cã mét d©y dÉn
a) Dßng ®iÖn qua ngêi
vA;JU2QR`VAD*;J:J(F=#T;J)0 
%#4,,,%@"4"#@@:9P68%;)4,
B%W4)A";Jc#FS(:!U2QR`V,
jT6F:%K
dd



d




p,pVppUp
p,•
p
c
,
pp
pp
,
p
pp
pp
•
r
++
=
+
+
+
=
UQRcmV
@K
Rp
d
K.48A,
Rp

K8;Jc.)4,

Rp

K8%.)4,
R•K"8;Jc.)4,
h(5%)4@p

2T6%K
dd


p,pVppVUppU
p,•
r
+++
=
UQRc`V
%"AL.4.2p
d
≈d#H@K
sng
ng
RR
U
I
+
=
h)3#T6%Y=,
h:4.4.Up
d
≈dV#Au#$@#EUp


≈dV,
B@#T6%K
ng
max.ng
R
U
I =
b) C¸c biÖn ph¸p an toµn
&9:WUQRc`V4#:T6%@:*9""K
Trường ĐH KTCN Thái Nguyên
cm
U
R
s
R
cd
R
0
R
ng
r
ng
1
1
U
H×nh 2-4:-FSA)(x%A);Jc,
R
cd
r

ng
R
ng
r
0
R
s
R
0

Rl"4"8,
RY,
RY.48#THP4(!8.)4,
2. Khi ngêi tiÕp xóc víi mét cùc cña m¹ng ®iÖn cã 2 d©y dÉn.
vAJJ@.490a=U2QRbV,vAZ%O"
#A*_#9("%",,,%"d#`1,[P68;
J,
a) Dßng ®iÖn qua ngêi
- Khi tiÕp xóc víi d©y dÉn 1.
tB)92%#=;J@T)r
)
)"";9.=;J@AK
axlvx.lv
R.IU =
@K
Rp

K8A;J!&(: M ,
R•
),

K"A: M ,
13@K
•
),
~d
•
),9
~r
)
,p
9
h)3•
),9
@'.4#%K•
),9
~Ud#dc÷d#dcbV•

1K•

K"'W8A,
j @#  ( ("  / )  ; J  c     )  92  %Z D  '   "   4  9CK•
),
 ~
Ud#dc÷d#dcbV•

#
%"(" /):H'"PF#A":€A#@K
ab
ac
max.nglvaclvc.lvnglv

l
l
.UR.IUU ===
tB>A A:9,
@K
2
U
R.IU
abNbN
≈=
1K•K"8A,
jT6% 'K


p,Q
•
r =
UQRcbV
h(%)49p

2T6%K
Vpp,UQ
•
r


+
=
UQRciV
h)3))92%#"O=%>A)2)3T6%4

:,12(A"OE2#e":@>A>A,
- Khi tiÕp xóc víi d©y dÉn 2.
%"W:Z.%" M%"A;J,hX
T6%4#!<9:WK
Trường ĐH KTCN Thái Nguyên
c`
H×nh 2-5:vA;J
VGA";JQ,
9V-L";9."=;J)0c)92x%,
V-L";9."=;J)0c>AA9,
2
U
Z
pt
1
a)
2
r
lv
Z
pt
1
b)
ba c
U
b.lv
2
1
c)
ba c

U
b.N

ng
max.ng
R
U
I =
b) C¸c biÖn ph¸p an toµn
&9:WUQRciV4T6%$"8AD"
"8S4"),j@:T6%*"F""K
Rl"8A,
RY,
2.2. m¹ng ®iÖn ba pha
Am"#L:(" /""E")40(.K
"8A#2A)8:!#'.8"#8".) 
4,,,
2.2.1. M¹ng ®iÖn ba pha cã trung tÝnh c¸ch ®iÖn víi ®Êt
1. Khi ngêi tiÕp xóc víi 1 pha cña m¹ng ®iÖn
a) Dßng qua ngêi khi líi ®iÖn cã c¶ ®iÖn dung vµ ®iÖn trë c¸ch ®iÖn
B(" /)c"8m"!.)4#H@T6F: %,jT
H@!6)U2QRiV,
B(" /)c;JU;cV#<'3B<••r@K
0
dt
dU
C
dt
dU
C

dt
dU
CUgUgU).gg(
3
3
2
2
1
133221ng1
=++++++
@KR•
c
#•
Q
#•
m
'.W%8"")4,
RG
c
#G
Q
#G
m
8")4,
 R
c
#
Q
#
m

J8")4FW)p
c
#p
Q
#p
m
,
l"F2=#@T6%K

2
321
22
ng321
2
3232
2
2323
ng
ng
)CCC()gggg(
)]CC.(3)gg.(3[)]CC(.3)gg(3[
.
2
g.U
I
++ω++++
+ω+−+−ω++
=
UQRcnV
h(p

c
~p
Q
~p
m
~p

)G
c
~G
Q
~G
m
~G#()"F2UQRcnV@T6%K
2
cd
22
2
cdcdng
2
cd
222
ng
2
cdcdng
2
cd
222
ng
2

cd
22
2
cd
2
ng
222
cdng
2
cd
22
222
ngcd
22
cd
ng
ng
R.C1
RR.R6)RC1(R9
U3
RR.R6)RC1(R9
R.C1
.U.3
R.R.C9)RR3(
R.C1
.U.3
)C3.()
R
1
R

3
(
)C6()
R
6
(
.
R.2
U
I
ω+
++ω+
=
++ω+
ω+
=
ω++
ω+
=
ω++
ω+
=
Vp,GcUpq
VppiUp
c,p
•
p,Gc
pp,pi
pq
•m

r
Q

QQQ



Q

QQ
Q

Q


ω
ω
+
+
+
=
+
+
+
=
UQRcoV
Trường ĐH KTCN Thái Nguyên
cb
H×nh 2-6:-FSx(8Ax%A""c
U

I
ng
R
c®
1
2
3
C R
c®
C R
c®
C
U
1
2
3
U
R
ng
R
c®1
1
Cω
R
c®2
1
Cω
r
ng
R

c®3
1
Cω

b) Khi m¹ng ®iÖn cã ®iÖn dung nhá
Rh(9"89"!$9C,p
c
≠p
Q
≠p
m
)
G
c
~G
Q
~G
m
~d)9:WUQRcnV,jTA6%%(" /);JK
321133221
2
332
2
21
321133221
2
332
2
21
321133221

2
23
2
221
321123132
2
23
23
2
23
32
321
2
321
2
32
2
23
) (
3
) (.2
12.1212.
) (.2
)(3)(9.
.) (
)(3)(9
.
.2
)
1111

(
)]
11
(3[)]
11
(3[
.
.2
cdcdcdcdcdcdcdcdcdng
cdcdcdcdcdf
cdcdcdcdcdcdcdcdcdng
cdcdcdcdcd
cdcdcdcdcdcdcdcdcdng
cdcdcdcdcdf
cdcdcdcdcdcdcdcdcdng
cdcd
cdcd
cdcd
cdcd
cdcdcdng
ng
f
ngcdcdcd
cdcdcdcd
ng
f
ng
RRRRRRRRRR
RRRRRU
RRRRRRRRRR

RRRRRU
RRRRRRRRRR
RRRRRU
RRRRRRRRRR
RR
RR
RR
RR
RRRR
R
U
RRRR
RRRR
R
U
I
+++
++
=
+++
++
=
+++
−++
=
+++
−
+
+
=

+++
−++
=
UQRcqV
Rh(9"89"!9C,p
c
~p
Q
~p
m
~p

)G
c
~
G
Q
~G
m
~d)9:WUQRcnV,jTA6%%(" /)A9'PK
cdng
f
cdng
ngcd
cdng
f
ngcd
cd
ng
f

ng
RR
U
RR
RR
RR
U
RR
R
R
U
I
+
=
+
=
+
=
.3
.3
3
.
.
.
.3
)
13
(
)
1

.6(
.
.2
2
2
UQRQdV
Rh(%)49p

,
cdsng
f
ng
RRR
U
I
++
=
).(3
.3
UQRQcV
c) Khi m¹ng ®iÖn cã ®iÖn dung lín
'.p
c
~p
Q
~p
m
~d)G
c
~G

Q
~G
m
~G)9:WUQRcnV@K
222
222
2
.ω91(
ω.3
ω9)
1
(
)ω6(
.
2
ng
f
ng
ng
f
ng
RC
CU
C
R
C
R
U
I
+

=
+
=
UQRQQV
VÝ dô: h("•~mod1#p

~cdddΩ#p

~cd,dddΩ)G~cd
Rcd
‡UF.PV2TA
6%@'K
140,0
10)10.314.101(9
)10.610(10
1.3
1
.
1000
380
I
61228
344
ng
=
+
+
+
=
−

UeV
d) C¸c biÖn ph¸p an toµn
&9:WUQRcoV#UQRcqV#UQRQdV#UQRQcV)UQRQQV4#:T6%@:*9
""K
Rl"8A4",
RY%8AUT6%PV,
Rl8)4U82T6%HV,
RYp

,
Trường ĐH KTCN Thái Nguyên
ci

2. Dßng ®iÖn qua ngêi khi tiÕp xóc víi 2 hoÆc 3 pha
a) Dßng ®iÖn qua ngêi
B%(" /)QOm"#"O=%";=4:#T6%K


p
•
r =
UQRQmV
b) C¸c biÖn ph¸p an toµn
%"(" /L(")QOm;J4! #%D )$;)=,12)3
@:9""K
R9'$;E8(W)0,
R]W$))L&9$)$ A,
Rj*"4")'4"Uw`d1V,
2.2.2. M¹ng ®iÖn ba pha cã trung tÝnh nèi ®Êt
1. Dßng ®iÖn qua ngêi khi tiÕp xóc víi 1 pha

a) TiÕp xóc víi mét pha
B(" /)c"8Am"@!L(".4U2QRoV#T6% 'K
d
•

pp
•
r
+
=
UQRQ`V
h(%)49p

#T6%K
d
•

ppp
•
r
++
=
UQRQbV
b) C¸c biÖn ph¸p an toµn
&9:W=4#:T6%@:*9""K
Rl"84",
RYp

,
RYp

d
,
2. TiÕp xóc víi mét pha vµ pha kia ch¹m ®Êt
a) Dßng ®iÖn qua ngêi
zMA@!L(".4U2QRqV,
Trường ĐH KTCN Thái Nguyên
cn
H×nh 2-8: hx%(" /);JA
m"!L(".4
3
2
1
R
ng
r
ng
R
0
R
s
U
f
H×nh 2-9: vA9"L(".4,
U
1
U
2
U
3
U

0
U
ng
3
2
1
R
ng
r
ng
R
0
R
d
R
ng
r
ng
3
2
1
U
0
R
0
U'
1
R'
d
U

ng
O
O'
U'
1
2
1
3
H×nh 2-7:-FSxx%(" /Q"
U
I
ng
1
2
3

l(;Jc9'A4#%W4)A";JQ,
I"A:A4.)4K
•ˆ
c
~r

,pˆ

I"A:!9(".)4K
•
d
~r

,p

d
B@#"O=%K
•

~•
Q
R•
d

'..@: '&‰ˆ‰Q<9:WK
20
2
2
2
0
0
20
2
2
2
0
.120cos 2 UUUUUUUUU
ng
++=−+=
UQRQiV
jT6%K



p

•
r =
B%)4p

#T6%K



pp
•
r
+
=
UQRQnV
h(.4p
d
~d#@•
d
~d#)3•

~•
Q
~•
•
,
b) C¸c biÖn ph¸p an toµn
R&9:W=4#(" /)Am"@!L(".4#"O=%H
F"")PF";")p
d
,h(p

d
P2T6%P)
A#)2)3:T6%"p
d
,
RI:T6%@:Yp

,
h(AT≤cde#2"0K
ng
f
s
R
01,0
U
R −>
VÝ dô:z'T6%%(" /)A@"mod1!.4L("K
@K
22010.
1000.3
380
R.3
U
R
U
I
3
ng
ng
f

ng
====
UeV
4'F'"M"cde,1394|00@:;(%,
3. Dßng ®iÖn qua ngêi khi tiÕp xóc víi 2 hoÆc 3 pha
B(" /)QOm"#FL@!L(".4,
2.3. ChÕ ®é trung tÝnh cña líi ®iÖn
2.3.1. NhËn xÐt
&";!=4K
vA@!L(".4@O:K
tBA4c"@!.4TA4T>A#9)F<> 
AL.# 4(" /";J2A,GTA@!29)F< 
$:,
tBA4@!.4#L.&="O=8(9'D
""#8DE(A)"",GT@!2"A4
";=(9'"(A)";,
tI8".)48@!.4$@A(T6%,GT
@!#p

T6%P,
tB%(" /)c")$@"A4@!.4#(p
d
P2T
6%4:,
2.3.2. ChÕ ®é trung tÝnh cña m¹ng ®iÖn cao ¸p
Trường ĐH KTCN Thái Nguyên
co

Ry@"≥ccd1!.4L(",10O2.4L("@@L
.A4"#9)F<H>AL.P,h%)3%SA8

" 6gA4)g.4#@ 4:%)E@,
h@:T>AA4"=.4,
Ry@"
kV35≤
#:!!.4L("#%O.463"
S6,B.463"S6#)0O@@T6gA4#@
"6gA4,
10#!)4F)2)8;JP#(" /
)"!:F,
I.)"#(!T"0)D=(,
2.3.3. ChÕ ®é trung tÝnh cña m¹ng ®iÖn h¹ ¸p
I.)A"# 4%(" /)c" 4,12)32A)8:!
E"9(" /""#T6%P4,
y@!TA4c"PF@!.4,B9'P#
" ;3"))P)"EJ8@!SA4;;:,h(@
!.49)H>:L.,j@L(AA"%.4L(":
!,
2.4. c¸c ph¬ng tiÖn b¶o vÖ c¸ nh©n
I";b@K
RG"F9)K@)9)%#9CY%)"E@"
)4U#2#@E#Y#8#,,,V,
R-T73D'"99(@$@",
R9'>A).4,
RpA%UVC!9)%$(" /)"E@"OE
g,
RG9$9C$9:%@WE"E@"@L/sE(O$
94.@:J(A,,,
Ch¬ng 3
c¸c biÖn ph¸p b¶o vÖ an toµn ®iÖn khi
tiÕp xóc gi¸n tiÕp víi m¹ng ®iÖn

3.1. Dßng ®iÖn qua ngêi khi tiÕp xóc gi¸n tiÕp
B@L.P(9'#="EA)P(9'#>#J @: 4… 
",|<AL.P#"=)P(9'@:4PO9C""FW)L.P
AE)8(9',
B$;)"% =(" /)(9',h()P(9'@"#%H'"8)P
(9'7"(" /•

,
BY 4"(" /$;)U2mRcV,
%"Y04L.PAE)8(9'#T6%HFW("
/L(",
Trường ĐH KTCN Thái Nguyên
cq
a) b) c) d)
U
f
U
H×nh 3-1:h5Y 4"(" /,
,l5)P(9')4,
9,l5"E(" /))P(9')4,
,l5)P(9')"E(" /)4UxV,
,l5)P(9'9'L.",

RI.)@!.4#"(" //9C""8U2mRQ#9#V#TT
6%HK
ng
f
ng
tx
ng

R
U
R
U
I ==
RI"(" /@:9C"5"8U2mRQV#TT6%HK
ng
d
ng
tx
ng
R
U
R
U
I ==
3.2. b¶o vÖ b»ng c¸ch nèi vá thiÕt bÞ ®iÖn
®Õn hÖ thèng nèi ®Êt
3.2.1. Nguyªn t¾c thùc hiÖn
h($@59""9.#2T6F:%(" /("@:@'
(" /L(",I:T6%X"(" /#@:L9C.)P(9'(
..4,
B@.4)P(9'TL.HM"A6K
- Líi ®iÖn trung tÝnh nèi ®Êt:TL.HM"A6..4)38S4" 
U2mRQV,
- Líi cã trung tÝnh c¸ch ®iÖn ®èi víi ®Êt:TL.HM"A6p

)G.)
46"8U2mRQ9V,
B@L.P#(%(" /))P(9'.42TL.HA)46

%)(9'.4U2mRmV,
@K
RIL.p

,
RI.9).4p

,
RI8%p

,
R•
•
"5" L.)4,
I8..4)8%.),h(%(" /))P8(9'
9'P2%"'"8.9'.4•

,
jTL.K
Trường ĐH KTCN Thái Nguyên
Qd
H×nh 3-2:jTL.(9'.4,
Vy@!.4,
9Vy@!.
a)
U
f
R
0
R

d
U
f
R
d
C C C
R
c®
R
c®
R
c®
b)
H×nh 3-3: Ix%8TL.(9'A)P
R
d
r
sc
r
d
R
sc
r
ng
R
ng
U
f
1
2

3
U
f
r
d
R
d
r
ng
R
ng
r
sc
U
tx
R
sc
R
s










p,pp,pp,p

Vpp,U
pp
p,p
p

p

r
++
+
=
+
+
==
B%(" /))P(9'"(" /%"'HK





p,pp,pp,p
p,p,
pp
p,p
,r
++
=
+
=
UmRcV

I8..4PF40)8%@9P6p

#@K



pp
p,

+
=
UmRQV
jT6..4K





pp

p

r
+
==
h(L.9Cd#T6..4K



p

r =
UmRmV
jT6%K





pV,ppU
p,
p

r
+
==
h(%)49p

2T6%K
VppV,UppU
p,
r



++
=
UmR`V
* Nhận xét:
&";!=4K

RI"(" / '9""8A)8..4#(p

P2

PJ(T6%P,13"(" /@:('()P(9'4)
'P:TL.A6a#T6%P,
[)9C.(..459""9)4.*::
3(" /(",[""9)*"]9()2@4F)+0,
RjT6..4FW)T6%(" /L("#Dp

9Cp

,
3.2.2. Tính toán điện trở nối đất bảo vệ an toàn
A8.("49)"4)()8!,
R.("4)3K.("4L<=ETP8(9':@:
),
R.("49)K.L<=E:0"TA)P(9'@
",
1. Lới điện có trung tính cách điện đối với đất
a) Lới điện 1 pha 2 dây
*Điện trở nối đất an toàn khi lới có điện dung nhỏ. (bỏ qua điện dung C)
RBp
c
p
Q
K
tjTA46..4HK
QcQc
c

p,pVppUp
p,
r
++
=
UmRbV
tI"(" /HK
QcQc
c

p,pVppUp
p,p,
p,r
++
==
UmRiV
tl'A8.("4K
Trng H KTCN Thỏi Nguyờn
Qc

)RR(UR.U
R.R.U
R
2cd1cdcp.tx1cd
2cd1cdcp.tx
cp.d
+−
≤
UmRnV

@K•"8U1V,•
 ,"
"8%"M"%4`d1,
RBp
c
~p
Q
~p

K
tjTA46..4HK
cdd
d
RR2
U
I
+
=
UmRoV
tI"(" /HK
cdd
d
ddtx
RR2
R.U
R.IU
+
==
UmRqV
@K•"8#U1V,p


8.)4#UΩV,
tI8.("4K
cp.tx
cdcp.tx
cp.d
U2U
R.U
R
−
≤
h)34K"(" /Z8.("4")8
.)4Up

V,
VÝ dô 1:I"(" /"M"•
 ,"
~`d1‚8.)4p

~cd,ddd
Ω
#
"•~cQn1U%"O"PETV,B@#.9).4"K
8510
40.2127
10000.40
R
cp.d
=
−

≤
Ω
VÝ dô 2:I"(" /"M"•
 ,"
~`d1‚p
Q
~bdddd
Ω
,•~mod1‚p
c
~cd,ddd
Ω
,B@8
.9).4HK
625
)500010000.(4010000.380
5000.10000.40
R
cp.d
=
+−
≤
Ω
*§iÖn trë nèi ®Êt an toµn khi líi cã ®iÖn dung lín. (bá qua ®iÖn trë R
cd
)
RjT6.A4K
222
d
d

CR41
C U
I
ω+
ω
=
UmRcdV
RI"(" /K
222
d
d
ddtx
CR41
R.C U
R.IU
ω+
ω
==
UmRccV
RI8.("4K
)U4U(C.
U
R
2
cp.tx
222
2
cp.tx
cp.d
−ω

≤
UmRcQV
VÝ dô 3: IKp

~bddd
Ω
‚G~cd
Ri
‡‚
ω
~Q
π
•~Q
π
,bd‚•~mod1‚•
 ,"
~`d1,
)(342
)40.4380()10.(314
40
)U4U(C.
U
R
22262
2
2
cp.tx
222
2
cp.tx

cp.d
Ω=
−
=
−ω
≤
−
&    )!
=4#".)4#(8 9% =
'F.2.4$E'P,
b) Líi ®iÖn 3 pha
*§iÖn trë nèi ®Êt an toµn khi líi cã ®iÖn dung nhá. (bá qua ®iÖn trë C)
RB.4p
c
≠
p
Q
≠

p
m
,
tjT6..4K
Trường ĐH KTCN Thái Nguyên
QQ

321133221
2
332
2

21
)(
3
cdcdcdcdcdcdcdcdcdd
cdcdcdcdcdf
d
RRRRRRRRRR
RRRRRU
I
+++
++
=
UmRcmV
tI"(" /K
321133221
2
332
2
21
)(
3
.
cdcdcdcdcdcdcdcdcdd
cdcdcdcdcddf
ddtx
RRRRRRRRRR
RRRRRRU
RIU
+++
++

==
UmRc`V
tI8.("4K
)].( 3[
.
133221.
2
332
2
21
321.
.
cdcdcdcdcdcdcptxcdcdcdcdcdf
cdcdcdcptx
cpd
RRRRRRURRRRRU
RRRU
R
++++

UmRcbV
RB.4p
c
~p
Q
~p
m
~p

,

tjT6..4K
cdd
f
d
RR
U
I
+
=
3
.3
UmRciV
tI"(" /K
cdd
df
ddtx
RR
RU
RIU
+
==
3
3
.
UmRcnV
tI8.("4K
cptxf
cdcptx
cpd
UU

RU
R
.
.
.
3.3
.


UmRcoV
*Điện trở nối đất an toàn khi lới có điện dung lớn. (bỏ qua điện trở R
cd
)
RjTA4@'K
cGpq
G,,m
r
QQQ


+
=


UmRcqV
RI"(" /K
cGpq
p,G,,m
p,r
QQQ

+
==


UmRQdV
RI8.("4K
Q

QQQQQQ

Q

Q

QQQQQQ

Q
",
QQQ
",
VG,,,mGqUp
p,G,,,mVcGpq,Up,G,,,mcGpq,
=
=+=+


2

txcp
2
cp.tx
cp.d
UUC.3.
U
R


UmRQcV
&";!=4#.)9".)4(8
2% ='F.2"(" /',
c) Khi xảy ra sự cố hỏng cách điện ở hai thiết bị trong cùng một lới điện
h( A4S%AQ(9'#=Q"7A4M"24:
U2mR`V,
vg(9'0.(.("4=@FWp
c
)p
Q
,jTL.HM"!
6"@9'P)p
c
)p
Q
8.("4,
Trng H KTCN Thỏi Nguyờn
Qm
1
3
2

R
cđ1s
c1
r
P
r
d
R
c1
R
cđ2s
c2
R
c2
R
P2
R
d2
R
P1
R
d1
R
c
U
c
a)
R
cd1
R

sc1
R
cd2
R
sc2
r
sc
R
c
1
3
2
U
R
P1
R
d1
R
ng
R
ng
R
P2
R
d2
r
P
r
d
b)

U
C
U
tx
U
tx
r
R
c1
R
c2

v. '"%"'(" /))P(9'9'L.#2" 'TA
6.("4,
* NÕu R
c1
= R
c2
= 0)%W=04#p

~d#p

ŠŠp

,jTL.@A4M"K
2d1dc
2d1dc
2sc1sc
sc
RRR

)RR.(R
RR
U
I
++
+
++
=
UmRQQV
@K
t•K"5"8,
tp
c
#p
Q
K9'"‹8(9'c)Q,
tp
c
#p
Q
K8.("4.()P(9'c)Q,
tp

K8;J.5)P(9',
Rh(p
c
~p
Q
~dUA)PL("V#H@K
)RR.(R

)RRR.(U
RRR
)RR.(R
U
I
2d1dc
2d1dc
2d1dc
2d1dc
sc
+
++
=
++
+
=
jTA6.("4K
Qc
Qc
pp
•
rr
+
==
UmRQmV
jTA6;J.Q(9'K


p
•

r =
13#r

~r

tr

,
RBp

~∞#W$@%;.0)P#2TA4A5(9'("4K
Qc
Qc
pp
•
rrr
+
===
UmRQ`V
I"(" /=)P8(9'#@'LAK
1d
2d1d
1d1d1tx
R.
RR
U
R.IU
+
==
UmRQbV

2d
2d1d
2d2d2tx
R.
RR
U
R.IU
+
==
UmRQiV
]"(" /H$])9C")8#•
 c
t•
 Q
~•$")p
c
)p
Q
,13#H@!4cQ(9' 4"(" /:,
Trường ĐH KTCN Thái Nguyên
Q`
H×nh 3-4:.7
vAL.P(9'*
@!.)4,

4# 4A4M"#($@;J.)P(9').).(" 
42"(" /$")5'.8.("4D")6
5/#W")K
k
R

R
2d
1d
=
,
h(D)9:W!•
 c
)•
 Q
@K
k1
k
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RR
U
U
1p
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+
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+
=
k1
1
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RR
U
U
2d

2d1d
2tx
+
=
+
=
4#"(" /$")p
c
)p
Q
,
h(Kp
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2
U
UU
2tx1tx
==
UmRQnV
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VÝ dô 4:Gp
c
~c
Ω
#p
Q

~co
Ω
#•~mod1
!K
20
181
380
I
d
=
+
=
UeV
•
 c
~Qd,c~Qd U1V
•
 Q
~Qd,co~mid U1V
(9'WQ@:(A:,
* NÕu R
c1

≠
R
c2

≠
0,%W=04p
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~d#;JA)Pp
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~d#p

ŠŠp

,jTL.@A
4M"K
2d1dc
2d1dc
2c1c
sc
RRR
)RR(R
RR
U
I
++
+
++
=
@Kp
c
)p
Q
58;J"c)QATL.,
RjTA6.("4K
)RR.(R)RRR)(RR(
R.U
II

2d1dc2d1dc2c1c
c
2d1d
+++++
==
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RI"(" /FWK
)RR.(R)RRR)(RR(
R.R.U
R.IU
2d1dc2d1dc2c1c
1dc
1dd1tx
+++++
==
UmRQqV
)RR.(R)RRR)(RR(
R.R.U
U
2d1dc2d1dc2c1c
2dc
2tx
+++++
=
UmRmdV
VÝ dô 5:G•~mod1‚p
c
~p
Q
~c

Ω
‚p

~d#Qb
Ω
‚p
c
~p
Q
~Qd
Ω

21
)2020(25,0)202025,0)(11(
20.25,0.380
UU
2tx1tx
=
+++++
==
U1V
170
202025,0
)2020(25,0
11
380
I
c.s
=
++

+
++
=
UeV
&";!=4#TL.=T@:9),h(L.$
A2"(" /ZH4P,
d) KÕt luËn
[)%(" /)(9'9'P9C.("4(50
K
RG@%;.)P8(9')4@P,
Trường ĐH KTCN Thái Nguyên
Qb

RI8.("4"F.P:9"(" /PF'"M",
R\9'9))%;.Q(9'@8P:TA48#9)H@
A4M",
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UeV
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tK0%;#UV,
2. Lới điện có trung tính trực tiếp nối đất.
!8S4".46.("4)3#.("4)3
p
d
,
h((9'@)P("4#2L.9'P#THA6p

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("49)p

S%68%p

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6S4"U2mRbV,
%D Ac")2)3T6%.)m")c"R
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a) Khi ngời tiếp xúc với thiết bị bị h hỏng cách điện
RjT6..4HK
dd


p,pVppUpp
p,
r
+++

=
UmRmcV
RI"%"'(" /))P8(9'L.HK
dd


p,pVppUpp
p,p,
p,r
+++
===
UmRmQV
h(A)P)p

~d)p

F40)p

)p
d
2K
d


pp
p,

+
=
UmRmmV

RjT6%,
d




p
c
,
pp
p,
p

r
+
==
UmRm`V
b) Dòng điện và điện áp khi ngời tiếp xúc với phần tử dẫn điện, đồng thời lại tiếp xúc với hệ thống tiếp đất vận hành
(hình 3-5)
RI"(" /A..4)3K
0
0d
f
0d0.tx
R.
RR
U
R.IU
+
==

UmRmbV
Rh%@:'"(" /]8"(" /H9C)"",


t
,d
~

13# A4"!("4#(9'L.@.("4,v.
("4H@"(" /A(':,
c) Điện trở nối đất và điện trở nối đất vận hành
Trng H KTCN Thỏi Nguyờn
Qi
Hình 3-5:,o
vA L.P(9'
a)
R
cd
R
sc
r
P
r
d
R
P
R
d
R
ng

r
ng
U
f
R
0
K k
=
R
P
R
d
R
0
R
0
R
ng
U
tx
R
P
R
d
R
ng
U
tx
r
P

r
d
r
sc
R
cd
R
sc
U
f
b)

IOK
k
R
R
0
d
=
[:W"(" /K
k1
k
.UU
ftx
+
=
UmRmiV
k1
1
.UU

f0tx
+
=
UmRmnV
- Khi chỉ tiếp xúc với thiết bị bị sự cố.
4#"(" /$")'.8("4")8/,
I;5946789)9C("4!("4,
I:95p

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d
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tW)

~QQd1modQQd1@K
b#`
c
`dQQd

`d


=


tW)

~ccd1Qddccd1@K
nb#c
c
`dccd
`d


=


13:92p
d
~`#bp

)p
d
~c#nbp

.)QQd)ccd1,
I.)@!L(".4#94|L:A0@:A9(9'
9)#(5.("4)3).("49)@P#TL.
T>A,

Ví dụ 6:h(8.("49)p

~`

#:"(" /
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~`d1#2
.:8.("4)3"K
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d
~`#b,`~co

tI.)Qddccd1p
d
~c#nb,`~n

I"(" /.("4)3%"=HK
tI.)modQQd1
,d
~
183
5,4
1
1
1
.220 =
+
U1V
tI.)Qddccd1
,d

~
64
75,1
1
1
1
.110 =
+
U1V
h5"@:;AE7,
- Khi tiếp xúc với phần tử dẫn điện, đồng thời lại tiếp xúc với hệ thống tiếp đất vận hành.
@K

t
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,12)3$@"(" /:,%""9'(9'9
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3.2.3. Giá trị điện trở an toàn và yêu cầu của hệ thống nối đất
1. Điện trở an toàn
a) Lới điện áp thấp, trung tính cách điện với đất
%*(9'*P#'4"M"K
RI.)(9'92%p

`,
Rh($4SPcdd1e#(9'8A$$#$ 2p

cd,
B.(9'#%..("4,B@8.("4

"@'Q

,
b) Lới điện áp thấp, trung tính trực tiếp nối đất
.("4@:! 4"&"(" /O.4"M",
- Điện áp tiếp xúc:"(" /$"M")6`d1%Wd#o.)(9'
A4#(" /S%)3("4):(9C$,
Trng H KTCN Thỏi Nguyờn
Qn

13K
d
d
I
40
R
#@Kr

TA4,
12Tr

4@ '= '9CTELT
@E2FW8(9'@$44#WK
CD.m
d
I
40
R
UmRmqV
jTr

,Gj
'!44"9ET'W8E2,
- Điện trở của hệ thống tiếp đất bảo vệ:1""M"`d1#8..4$"M"
@'F`

,
c) Lới điện cao áp
(9'"#94|(9'"Z"L.9)("4:.45)P
(9'@:@"L.,j%(" /)%$;)3)9'
K#Y# =.4=E K
- Lới điện cao áp trung tính cách điện với đất.
I.)(9'#"c1@!O.)49=$#
M"@9'.M,
tB.49)D=(9'c1#'.p

'<9:WK
)(10
I
250
R
d
d
=
UmR`dV
tB.49)(9'wc1#'.p

'<9:WK
)(10
I
125

R
d
d
=
UmR`cV
@Kr

'.!8T>AA4,
tB..49)*AA")A"@!)42
'<9:WUmR`cV):A<0Kp

c`,
- Lới điện cao áp có trung tính trực tiếp nối đất.
A#TA4T>Ac"@:*9)=KI8
.("49)d#b,
2. Yêu cầu của hệ thống tiếp đất.
.("4%.)2@:KL=(@: 45)P
8(9'*.("49)=+#S%).("4=(F#
$/6F)2@:@.4PF,
1.49)8"EAA"8AA"#8A";".,,,!8
A".(.("4#2.("4"9).("4"E(,IO9
(9'9)6"==U.MV,
$%#.("4)3@:.).("49)(62)3
"(" /)"9$)65'"M",
3.3. bảo vệ bằng cách nối vỏ thiết bị
đến dây trung tính
3.3.1. Khái niệm chung
1. Nguyên tắc thực hiện bảo vệ
B.)P(9'(;!9)#79);!,'P
2HAT>Ac"#9)>"E9'L.PU2mRiV,

j@(%(" /)(9'Z$9':%SAT6 %P,I:
99)")%>d#Q,
jT>A!9C9:WK
TTf
f
sc
RR
U
I
+
=
@K
t

K""9'L.#U1V,
tp

K]8;J"L.#&S()'!L.#UV,
tp

K]8;J!#UV,
Trng H KTCN Thỏi Nguyờn
Qo