Turkish Chamber of Electrical Engineers (TMMOB) Grounding Measurements in Electrical Installations and Evaluation of Measurement Results Note: This study was prepared by Electrical Engineer Taner İRİZ and Electrical and Electronics Engineer Ali Fuat AYDIN for use in the trainings of the Chamber of Electrical Engineers. Permission must be obtained from the authors if this work is used outside of the Chamber or if the text is modified. 1. When measuring both soil resistivity and radiating resistance in electrical installations, all electrodes are conceptually considered to be hemispheres. Hemispherical electrodes, which are not used in practice, facilitate calculations in grounding measurement theory. In the case of homogeneous soil resistivity (ρ constant), the resistance of a hemispherical electrode with radius r to the ground can be simply calculated using the relation ρ r2 π, R yk = R. The potential at a location at a distance x from the center of this electrode is calculated using the relation yk = IRφ yk = ρI x2 π, where I is the current flowing through the electrode. In principle, we will use the resistance and potential formulas from the previous slide, creating the appropriate conditions for all calculations. Example: For a vertical rod, ETTY gives the relation Rç ρ= L2 π ln L4 D. Here L is the length of the rod and D is its diameter. To calculate the hemispherical equivalent of the rod, the equality ρ r2 π = ρ L2 π ln L4 D is considered. r = L L4 D ln L=20 cm, D=1 cm. For a stake, r=4.6 cm is found. 3 • SOIL RESISTIVITY MEASUREMENTS • SOIL SPREAD RESISTANCE MEASUREMENTS • EVALUATION OF MEASUREMENTS 4 SOIL RESISTIVITY MEASUREMENTS 5 Until recently, soil resistivity measurement concerned a limited group of electrical engineers. 1. Those involved in cathodic protection (the description in TS 4363 is related to cathodic protection.) 2. Those involved in the grounding design of large substations. With the new regulations published in recent years, soil resistivity measurement has begun to concern a wider segment of the population. 6 Article 10/c-5.i.1 of the Regulation on the Preparation of Electrical Internal Installation Projects dated December 3, 2003, requires the determination of soil resistivity before starting projects. Furthermore, the draft Lightning Protection Regulation also recommends measuring soil resistivity during the design phase of lightning protection systems. Article 16 of the Draft Lightning Protection Regulation states that "in most geographical regions, and especially in areas where temperature and precipitation show unusual seasonal variations, changes in soil resistivity should be taken into account by measuring the depth profile of specific resistivity under different weather conditions." 7 P2 C1 P1 C2 8 φ 1P = ρI 2 π 1 C1P1 1 C2P1 C1 P2 φ 2P = ρI 2 π 1 C1P2 1 C2P2 C2 P1 = φU P1 φ P2 = ρI 2 π 1 C1P1 1 C2P1 1 C1P2 + 1 C2P2 9 (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - - - (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - = R = U I ρ 2 π 1 C1P1 1 C2P1 1 C1P2 + 1 C2P2 = k 2 π 1 C1P1 1 C2P1 1 C1P2 + 1 C2P2 kρ = U I Here ρ (Ω.m) is the resistivity of the soil, I (A) is the current applied to the ground, U (V) is the voltage between the P1 and P2 terminals, and k is a geometric factor. The k factor depends on the distances between the measurement stakes. 10 (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - - (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - - 1 C1P1 + 1 C2P2 1 C2P1 + 1 C1P2 Measurement stakes can be placed as desired, provided that each created measurement system has its own unique geometric factor. Example x x C1 x P1 P2 x C2 0U = In this case, ρ cannot be measured. 11 (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) ’ Various classical methods such as Wenner, Schlumberger, dipole-dipole, single electrode-dipole, half Wenner and half Schlumberger can be used in soil resistivity measurement. All the traditional methods mentioned above are applied by driving 4 measurement stakes into the ground at different intervals along a straight line. While specially developed measuring devices are used for measurements made at small intervals, the voltmeter-ammeter method is used for measurements made at large intervals. A +I current with a frequency of 100-150 Hz is sent to the ground from the C1 terminal of the measuring device. This current returns as -I from the C2 terminal. These currents create a potential difference of U at the P1 and P2 terminals. Measuring devices directly give the U/I ratio in Ω. New generation measuring devices determine the k factor in addition to the U/I ratio and directly display it. It can also give a resistivity of 12. WENNER METHOD 13 Rö C1 P1 P2 C2 I I a a a 14 Rö C1 P1 P2 C2 I a a a φ 1P = ρI 2 π 1 a 1 a2 φ 2P = ρI 2 π 1 a2 = φU P1 φ P2 = ρI 2 π 1 a 1 a2 + 1 a2 1 a 1 a 15 (cid:247) ł (cid:246) (cid:231) Ł (cid:230) - (cid:247) ł (cid:246) (cid:231) Ł (cid:230) - (cid:247) ł (cid:246) (cid:231) Ł (cid:230) - - - = R = U I ρ 2 π 1 a 1 a2 + 1 a2 1 a =(cid:247) ρ 2 π 1 a π= aR2ρ 16 ł (cid:246) (cid:231) Ł (cid:230) - - SCHLUMBERGER METHOD 17 Rö C1 P1 P2 C2 I I r O Δr 18 Rö C1 P1 P2 C2 r Δr φ 1P = ρI 2 π 1 r Δ 2 r 1 r Δ 2 + r φ 2P = ρI 2 π 1 r Δ 2 + r 1 r Δ 2 r = φU 1P φ 2P = ρI 2 π r 1 r Δ 2 1 r Δ 2 + r 1 r Δ 2 + r + r 1 r Δ 2 19 (cid:247) (cid:247) (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) (cid:231) (cid:231) Ł (cid:230) - - (cid:247) (cid:247) (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) (cid:231) (cid:231) Ł (cid:230) - - - - - (cid:247) (cid:247) (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) (cid:231) (cid:231) Ł (cid:230) - - = R ρ 2 π P1P2 £ C1C2 10 rΔ = R ρ 2 r2 π 1 r2 Δ 2 r Δ 2 r4 + r2 Δ r Δ + r2r 2 r 2 Δ 4 r r 5, provided that ρ π= 2 r r Δ R 20 (cid:247) (cid:247) (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) (cid:231) (cid:231) Ł (cid:230) - - (cid:247) (cid:247) (cid:247) (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) (cid:231) (cid:231) (cid:231) Ł (cid:230) - (cid:247) ł (cid:246) (cid:231) Ł (cid:230) £ DIPOLE-DIPOLE METHOD 21 Rö C1 P1 P2 C2 I nx x I x C1 C2 P1 P2 22 Rö C1 P1 P2 C2 I x I nx 1 nx 1 + x)2n( + 1 + (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - - - 2 n + = R ρ 2 π 2 nn2 2 n2n3 + x)2n)(1n(n + 2 + nn + n2 ρ = π xR)2n)(1n(n + + 24 (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - - - - - SINGLE ELECTRODE-DIPOL METHOD 25 Rö C1 P1 P2 C2 I I nx x 26 ¥ φ 1P = ρI 2 π 0 1 nx φ 2P = ρI 2 π 0 1 + x)1n( = φU 1P φ 2P = ρI 2 π 1 nx + 1 + x)1n( = R ρ 2 π + n1n + x)1n(n xR)1n(n2ρ = π + 27 (cid:247) ł (cid:246) (cid:231) Ł (cid:230) - (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - - (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) Ł (cid:230) - - The expressions in the previous slides were derived by assuming the medium has a homogeneous character (r is constant) and the measurement stakes are hemispheres. However, in reality, the earth is not homogeneous. In this respect, the calculated resistivity is called apparent resistivity (AP). AP depends on the geological structure within the earth and the resistivity of this structure. Based on this definition, AP and medium resistivity can only be related if the medium is homogeneous and semi-infinite. They can be equal. In layered cases (which is often the case), the resistivity of each layer is different. 28 Various problems are encountered depending on the number of layers. The semi-infinite single-layer problem is the simplest form, but it often does not meet our needs. The 2-layer model can be a good choice for finding the soil resistivity of locations where MV substations are located. In large substations, the 3-layer model should be preferred. Although the n-layer problem was solved by Stefanescu, it is not often used in electrical engineering practice. The n-layer problem is generally a subject of interest to geophysicists. 29 Air Earth ρ constant h 8 ρ1 ρ2 Air Earth Air Earth h1 h2 8 ρ1 ρ2 ρ3 h1 h2 h3 hn ρ1 ρ2 ρ3 . . . . . ρn Air Earth 30 2-LAYER MODEL The difference in resistivities of two layers The ratio of the total to the reflection factor is defined as the reflection factor and is denoted by K. If K = 2ρρ + 2ρ1ρ1ρ2=ρ1, then K=0; if the lower layer is a perfect insulator, K=1, and if the upper layer is a perfect insulator, K=-1. In this case, -1<K<Condition 1 is met. -1<K<ρ2 when 0<ρ1 (the top layer is more resistant than the bottom layer) 0<K<1 when ρ1<ρ2 (the lower layer is more resistant than the upper layer) 31 - Air I Earth ρ 32 Air I Earth h ρ1 ρ2 33 IMAGE METHOD h h I KI hρ Air Earth ρ1 ρ1 ρ2 34 ¥ fi 2h h 2h KI I KI Air Earth ρ1 ρ1 ρ1 ρ2 35 KI I KI K2I 2h h 2h 2h Air Earth ρ1 ρ1 ρ1 ρ1 ρ2 36 K2I 2h KI Earth I KI K2I a P 2h C 2h 2h = φ P Iρ 1 2 π 1 a + 2 =1n 2 a n K ( + ) 2 nh2 ρ1 Rö C1 P1 P2 C2 I a I a a ρ g ρ 1 += 41 = 1n + 1 n K 2 nh2 a 4 = 1n n K + 4 2 nh2 a ρ g = ρ 1 ,K(f a h ) 37 ¥ ¥ (cid:247) (cid:247) (cid:247) ł (cid:246) (cid:231) (cid:231) (cid:231) Ł (cid:230) (cid:229) ¥ (cid:229) (cid:229) ¥ ¥ (cid:247) ł (cid:246) (cid:231) Ł (cid:230) - (cid:247) ł (cid:246) (cid:231) Ł (cid:230) ρg/ρ1 ordinate, By assigning values to K from -1 to +1 with a difference of 0.1, where a/h is the abscissa, and using a logarithmic scale, families of curves f(K, a/h) can be drawn. These curves are called theoretical resistivity curves for two layers in the Wenner array. K, ρ1, and h are calculated by superimposing the ρg=f(a) curve obtained in the field with the theoretical ρg/ρ1=f(K, a/h) curve. ρ2 can be determined from the expression K1 = ρ2 + K1. 38-39 The radius of the circle whose area is equal to the area of the grounding network is defined as the equivalent radius. The effect of the soil beyond the equivalent radius depth on the grounding resistance can be ignored. To determine whether the soil is homogeneous at the location where the grounding project will be carried out, it is necessary to increase the electrode spacing in the Wenner array to the equivalent radius size. The relation 40 ρ=2πaR is valid if the electrode length L is very small compared to the electrode spacing a (L>r kabulü ile
rx
x
φ 1P
=
φ 2P
=
ρI
2
π
ρI
2
π
1
r
1
y
1
x
1
z
=
φU
1P
φ
2P
=
ρI
2
π
1
r
1
x
+
1
y
1
z
62
(cid:247)
ł
(cid:246)
(cid:231)
Ł
(cid:230)
-
(cid:247)
(cid:247)
ł
(cid:246)
(cid:231)
(cid:231)
Ł
(cid:230)
-
(cid:247)
(cid:247)
ł
(cid:246)
(cid:231)
(cid:231)
Ł
(cid:230)
-
-
-
@
-
=
R
=
U
I
ρ
2
π
1
r
1
x
+
1
y
1
z
=
Rö
ρ
r2
π
1
r
x
+
r
y
r
z
=
R
ö
1R
g
r
x
+
r
y
r
z
63
(cid:247)
(cid:247)
ł
(cid:246)
(cid:231)
(cid:231)
Ł
(cid:230)
-
-
(cid:247)
(cid:247)
ł
(cid:246)
(cid:231)
(cid:231)
Ł
(cid:230)
-
-
(cid:247)
(cid:247)
ł
(cid:246)
(cid:231)
(cid:231)
Ł
(cid:230)
-
-
R
ö
=
R
g
1
r
x
+
r
y
r
z
=(cid:247)
1
r
x
1
x
+
r
y
r
z
=
0
r
+
1
y
1
z
=
0
1
x
+
1
x
+
1
y
1
z
=(cid:247)
0
=
1
y
1
z
64
(cid:247)
ł
(cid:246)
(cid:231)
(cid:231)
Ł
(cid:230)
-
-
(cid:222)
-
-
(cid:247)
ł
(cid:246)
(cid:231)
(cid:231)
Ł
(cid:230)
-
-
-
-
+
1
x
1
y
=
1
z
=
z
xy
+
yx
2
z
=
2
x
+
2
y
xy2
cos
θ
P2
z
y
C2
r
θ
x
T (C1,P1)
2
xy
+
yx
cos
θ
=
=
2
x
+
2
y
xy2
cos
θ
+
ξ
2
1
2
ξ
1
1
++
ξ
2
2
ξ
ξ=
x
y
65
-
(cid:247)
(cid:247)
ł
(cid:246)
(cid:231)
(cid:231)
Ł
(cid:230)
-
(cid:247)
(cid:247)
ł
(cid:246)
(cid:231)
(cid:231)
Ł
(cid:230)
-
cosθ
1
0,875
θ=29
º
b
a
1
£ ξ
618,1
0,618
1
1,618
ξ
a
x
0,5x
29º
0,618x
b
a’
66
£
Tekil elektrotlar ve küçük tesislerde %61,8 yöntemi
uygulanırsa da, büyük tesislerde direnç eğrisi
çıkartılarak, eğride orta bölümün eğimi saptanır,
buna bağlı olarak gerçek direnci ölçmek için
gerekli olan gerilim kazığı uzaklığı belirlenir. Bu
arada akım kazığının tesis merkezine uzaklığı
merkez çapının 5 katından az olmamalıdır.
Büyük ve simetrik olmayan tesislerde 4 nokta
yöntemi, kesişen doğrular yöntemi ve eğim
yöntemi uygulanabilir. Çok büyük şalt tesislerinde
akım ve gerilim kazıkları ters taraflara yerleştirilir.
Bu tür yerlerde voltmetre-ampermetre ya da
wattmetre-ampermetre yöntemleri yeğlenmelidir.
Çok büyük tesislerde kullanılacak kablo
bağlantılarının birbirine paralel olması nedeniyle
açı yöntemi de kullanılabilir. Bu durumda x ve y
arasındaki açı 60º’den küçük olamaz.
67
68
69
ÖLÇÜM SONUÇLARININ
DEĞERLENDİRİLMESİ
70
Yıldız noktası direnç üzerinden topraklanmış şebeke;
Z = R
I''k1
L1
L2
L3
71
Ulusal ağ şebekemizde 25 MVA’nın üzerindeki 154 / 34,5
kV trafoların yıldız noktaları;
-Havai hat çıkışlı merkezlerde 60 Ω,
-Kablo çıkışlı merkezlerde 20 Ω dirençle topraklanmıştır.
Bu durumda havai hatla beslenen 34,5 kV YG
şebekelerde faz toprak kısa devre akımı
I 1k
=
3/
34500
60
A300
Kablo çıkışlı 34,5 kV şebekelerdeki faz toprak kısa devre
akımı ise
=
I 1k
34500
20
3/
1000
A
ile sınırlıdır.
72
@
¢
¢
@
¢
¢
Örnek:
154 kV
50 MVA
34,5 kV
2000 MVA
60 Ω
3 x PIGEON
10 km
3 x SWALLOW
1 km
3 x 95 mm2 XLPE
200 m
1000 kVA
34,5 kV
0,4 kV
154/34,5 kV merkezde sekonder tarafta yıldız noktası 60Ω
dirençle topraklanmış olduğundan I''k1=300A ile
73
sınırlanmıştır.
c
b
a
V
1000
9
8
7
6
5
4
3
i
m
2UTp
1
100
9
8
7
6
5
i
l
i
r
e
g
a
m
n
u
k
o
D
4
3
3
4
5 6 7
8 9 0,1
2
3
87654
9 1
2
Akım süresi t
3
87654
9
10
s
YG` de sınırlı akım süreleri için izin verilen en yüksek dokunma gerilimleri
a) Hayvanlardaki zamana bağımlı dokunma gerilimi
b) Eski VDE 0141’deki dokunma gerilimi
c) Yeni kabul edilen eğri
74
Hata süresi
tF
Topraklama
gerilimi
UE
Tesislerin dış
duvarlarında ve
çitlerinde
Tesislerin içinde
Bina içi
(dahili tip)
tesis
Bina dışı
(harici tip)
tesis
M4.1
veya
M4.2
tF>5 s
tH
5 s
UE
4UTp
M1 veya
M2
M3
UE>4UTp
UE
4UTp
UT
UTp
olduğunun
ispatı
M1 veya
M2
M3
M4.2
M3
M4.2
UE>4UTp
UE
UTp olduğunun ispatı
75
£
£
£
£
£
76
AG HAVA HATLARINDA FAZ-TOPRAK HATASI
(FAZ KOPMASI)
RT
RB
Rh
A
L1
L2
L3
PEN (N)
RB: İşletme topraklaması direnci
RE: L3 fazının toprağa temas direnci
U0: Toprağa göre anma a.a. gerilimi etkin değeri
77
Eşdeğer devre:
0
RB
U0
RT RH
A
RE
Ih
78
RT ve RH dirençleri ihmal edilirse
U
0
+
R
U
0
+
R
IR
HB
I
h
U
R
R
=
=
B
B
=
E
B
R
R
UB
V50
Madde 3.7 gereği
R
R
B
UR
0B
U
0
50
U
0
50
U
0
+
R
R
R
R
R
50
1
+
R
+
E
E
E
B
B
E
1
B
1
50
B
B
E
R
U
0
50
50
B
R
+
R
E
B
U
0
50
R
R
E
B
50
ETTY s.17
R
R
B
E
U
0
50
79
£
£
‡
fi
‡
-
‡
fi
-
‡
fi
‡
-
£
380/220 V şebekede U0=220 V
R
R
B
E
50
220
50
R
R
B
E
50
170
R
R
B
E
294,0
R
R
E
B
1
294,0
R
R
E
B
4,3
R
E
R.4,3
B
80
£
fi
£
fi
-
£
‡
fi
‡
fi
‡
L3
0
2
X
X
L1
2
=
220
V250
X
50 V
220 V
L2
+
50
2
.2
220
.50.
cos
120
81
@
-
L uzunlukta, d çaplı silindirik topraklayıcının yayılma
direnci ETTY s.88 Şekil T-7’nin altında
R
ρ=
L
π
ln
L2
D
şeklinde verilmiştir.
d (mm)
5,58
6,60
7,41
8,34
9,36
10,50
11,79
Rose
Lily
Iris
Pansy
Popy
Aster
Pholox
ln
40.2
d
9,57
9,40
9,29
9,17
9,05
8,93
8,82
1
π
ln
40.2
d
3,05
2,99
2,95
2,92
2,88
2,84
2,81
Ort.3
82
L=1 m
=
RE
ρ
1.
π
ln
1.2
0086
,0
=
73,1
ρ
L=10 m
=
RE
ρ
10.
π
ln
10.2
0086
,0
=
25,0
ρ
L=40 m
RE
3
ρ»
L
RE
ρ075,0
83
»
L (m)
ρ (Ωm)
RE (Ω)
1
10
40
100
100
100
173
25
7,5
O halde yönetmeliğin dayattığı en küçük temas direnci
yaklaşık 40 m iletken uzunluğunda gerçekleşir.
84
R ‡
E
R4,3
B
RE
ρ075,0
R minE
ρ075,0
R.4,3ρ075,0
B
ρ
4,3
075,0
ρ ‡
R
B
BR.45
RB (Ω)
0,1
1
2
)m(Ωρ
5,4ρ ‡
ρ ‡
ρ ‡
45
90
85
@
‡
‡
(cid:222)
‡
NÖTR KOPMASI
RB1
P P P+ΔP
L1
L2
L3
PEN (N)
RB2
In
P
Δ=
U
0P =Δ
U
nötr
=
R
nh
P
Δ =
U
r
l
nh
P
Δ
U
ise
Unötr
=
0
86
RB1
L1
L2
L3
PEN (N)
RB2
87
Eşdeğer devre:
U0
RB1
I
U 2
0
P
Δ
RB2
=
I
U
0
R
1B
+
R
2B
+
2
U
0
P
Δ
=
(
R.P
Δ
U.P
Δ
0
+
R
2B
1B
)
+
2
U
0
U
2B
=
U.P.R
Δ
2B
0
)
+
+
R
2B
1B
(
R.P
Δ
fi=Δ
U0P
2B
2
U
0
=
0
88
YG-AG SİSTEMLERİNDE
TOPRAKLAMA
TESİSLERİNİN
BİRLEŞTİRİLMESİ
89
Madde 11
a) Bir yüksek gerilim tesisinde toprak hatası esnasında
alçak gerilim sisteminin nötr veya PEN iletkeni, yüksek
gerilim tesis sisteminin topraklama tesisleri ile aşağıdaki
koşullar yerine getirilmek kaydıyla bağlanabilir.
- Alçak gerilim şebekesinde veya tesis edilen tüketim
tesislerinde tehlikeli dokunma gerilimleri ortaya çıkmaz ise
(Çizelge 13)
- Tüketim tesislerinde alçak gerilim cihazlarının gerilim
dayanımının (işletme frekansındaki) yüksekliği alçak gerilim
yıldız noktasında bir potansiyel yükselmesinin sonucu
olarak Çizelge 13’te izin verilen değerleri aşmaz ise,
90
b) Bir yüksek gerilim tesisi, topraklama alanı içindeki
alçak gerilim tüketicilerini besliyorsa; YG topraklama
tesisleri içindeki tüm işletme ve koruma topraklamaları
birleştirilmelidir.
c) Yüksek gerilim topraklama tesisinin alanı dışındaki
alçak gerilimli tesislerin beslenmesi:
- Söz konusu yüksek gerilim topraklama tesisi global
topraklama sistemine bağlanmış ise,
- veya AG şebekesinde Çizelge 13’teki koşullar yerine
getirilmiş ise,
ortak topraklama tesisinin yapılması önerilir.
91
AG
Sistem
Tipi
Hata Süresi
TT
TN
t £
5 s
t > 5 s
PEN sadece
TM’de
topraklı
PEN bir çok
noktada
topraklı
Ortak topraklama koşulları
Dokunma
Gerilimi
Zorlanma
Gerilimi
Uygulanmaz
UE £
UE £
1200 V
250 V
UE £
UTp
UE £
2.UTp
Uygulanmaz
92
TEŞEKKÜR EDERİZ
93
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