High voltage underground cables

1. University of Turkish Aeronautical Association
Electric and Electronic Engineering Department
EEE 589 SPECIAL TOPICS IN ELECTRIC & ELECTRONIC ENGINEERING
Presented by:
Layth Faeq & Mahmood Natiq
Supervisor :
Dr. Ibrahim Mahariq
Fall -2016

2. Contents
Introduction
Advantages and disadvantages of cables
Construction of cables
Classification of cables
Calculation of high voltage cable parameters
Power losses and capacity amperage losses
Extension of underground cables
Types of cable faults
High voltage cables faults location methods
conclusion

3. Introduction
Underground cables is one of the means used for the
transmission and distribution of electric power in addition to the
overhead lines.

4. Where these cables are placed ?
Directly buried underground Placed inside the underground
tracks
Placed inside the
underground ducts.

5. these cables are considered more safer than overhead lines, where the
probability of touching people or birds or animals or small metal objects with
conductors carrying voltage electrode to be very rare .

6. Advantages & Disadvantages
Advantages
Better general appearance
Less liable to damage through storms or lighting
Low maintenance cost
Less chances of faults
Small voltage drops
Disadvantages
The major drawback is that they have greater installation cost and
introduce insulation problems at high voltages compared with
equivalent overhead system.

7. the general construction of a 3-conductor cable. The
various parts of cable are :
1-copper conductor
2- Inner semi-conductive
3-XLPE insulation
4-Outer semi-conductive
5-Semi-conductive tape
6-Copper tape screen
7-filling
8-PVC separation sheath
9-Galvanized double steel tape
10-PVC outer sheath

8. Classification of cables according to:-
1 - number of cores in the cable .
2 - the type of insulating materials used in their manufacturing.
.3 - the voltage for which they are manufactured

9. The number of cores in the cable.
(1)_ single core cable
(2)_multi-core cable

10. the type of insulating material used in
their manufacture
1- Paper insulated cables
It has good electrical properties .
It needs the experience and accuracy
In performance plug endings .
2-Impregnated Paper cables

11. 3-ethylene propylene Rubber
Easier to installMore flexible -
Better flame resistance
Increased thermal stability
4-Polyvinyl chloride (PVC)
It is cheap .
It considered the best choice until 3.3 kv .
It is inappropriate for high voltage .

12. 5- Cross Linked poly- ethylene (XLPE)
1-This material has temperature range beyond 70-90
2-This material good insulating properties

13. the voltage for which they are
manufactured
Low-tension (L.T.) Cables......upto 1000V
Thickness of insulating = 1.5 mm
high-tension (H.T.) Cables.... 11KV
Thickness of insulating = (4-5) mm
super-tension (S.T.) Cables.. 33KV
Thickness of insulating = (8) mm
Extra-high tension(E.H.T) Cables.. 66KV
Thickness of insulating = (16) mm
Extra-super voltage Cables.. 132KV
Thickness of insulating = (23) mm

14. Conductor resistance of A single-core cables
A ᵨ
ᵨ=Material with resistivity
L = Length
A= Cross – sectional area
R=
ᵨ L
A
(ohm)
Where
ᵨcu
(ohm ∕ m)
(m)
(m2)
= 1,724* 10-8
ᵨAl = 2,803* 10-8
Calculation of high voltage cable parameters

15. Insulation resistance of A single –core cables
Radius of conductor=r1
Radius of sheath=r2
Thickness of layer=dx
R =
ᵨ
2π L
ln
r1
r2
(ohm)
This shows that insulation resistance of a cable is inversely proportional to its length. In
other word, if the cable length increases , its insulation resistance decreases and vice-versa

16. Capacitance of single core cable
Conductor diameter=d
Inner sheath diameter=D
The charge per meter =Q coulombs
the relative permittivity of the insulation=ϵr
Permittivity=ϵ0
Vph=∫ E.dx =∫
C=
IC= ωcVph (Amper)
Where ϵ=ϵ0 ϵr2 πϵ
ln
D
d
Q
Vph
D∕2
d∕2
Q
2 πϵ x
.dx =
d∕2
D∕2
Q
2 πϵ
ln
d
D (Volt)
= (F∕m)
Where ω=2π F

17. Capacitance of 3-core cable
CcCc
Cc
Ce
CeCe
A
N
B C
Ce3Cc
3Cc
Ce 3Cc
Ce
CAN = CBN = CCN = 3Cc+Ce

18. Electrical field intensity
Vph
X.ln
r2
r1
Emax=
Vph
r1.ln
r1
r2
Emin=
Vph
r2.ln
r1
r2
E= (volt∕ m)
(volt∕ m)
E=
Q
2πϵ0ϵr X
(volt∕ m)
Q=
2πϵ0ϵr Vph
ln
r1
r2
(coulombs)

19. Wd
I2 R
T2
T3
R.λ1nl2
R.λ2nl2
T4
T1
Power losses and capacity amperage losses
Δθ = ( I2 R+0.5wd ) T1+ ( I2R (1+λ1)+ wd ) nT2 + ( I2 R (1+λ1+λ2) + wd) n( T3+T4)
I ={ Δθ – wd [ 0.5T1 + n (T2+T3+T4)
RT1 + nR ( 1+λ1) T2 + nR (1+λ1+λ2)(T3+T4)
}
1/2
where Thermal resistancesT1,T2,T3,T4 =
wd= loss in insulation
n= number of conductors
λ1= loss between conductor and metallic sheath
λ2= loss between conductor and armour

20. Extension of underground cables
20 cm20 cm
60 cm80 cm
30 cm
10 cm
20cm
5 cm
20 cm
20 cm
30cm
5 cm
110 cm
River sand
Cutting
concrete
Soft soil
Natural soil
without stones
Warning tape
Natural soil
slabbing

23. High voltage Cable Joint
1 2 3 4
5 6 7 8
9 10 11 12

24. Types of cable faults
the following are the faults most likely
to occur underground cables.
1) open circuit fault
2) short circuit fault

25. Time Domain Reflectometer (TDR) Method
TDR method is based upon the measurement of the time that it takes the pulse to reach a
fault and reflect back
The distance d of the fault can be obtained as follows
t = time of pulse to travel to the fault and back
V = propagation velocity
c = the speed of light (3*108 ms)
μr = dielectric materials
ϵr = relative permittivity of the dielectric material
Propagation
Velocity v
(m/μs)
Dielectric
Constant εr
Insulation
1982.3PE
2371.6Paper
1345PVC
1982.3XLPE
High voltage cables faults location methods

26. For fully understand the principle, the equivalent circuit of a transmission line
Characteristic Impedance of transmission line
Z o =
LR + jωL
G + jωC
=
C
ᵨr =Reflection coefficient
ZL =0 at short circuit
ᵨr =
ZL – Z0
ZL + Z0
Vr= -V
s

27. Arc Reflection Method
The arc-reflection analyzer simultaneously applies high-frequency, low-voltage pulses
to the cable to reflect from the low resistance arc .
Surge Generator provides high impulse causes the high-resistance fault to break down,
.thus causing a low- resistance arc at the fault

28. conclusion

29. Thank you for
listening