This document discusses power cables and their properties. It covers several topics: - The electrical properties of cables including conductor resistance, capacitance, inductance, and electrical field. - Insulation materials used in cables like PVC, XLPE, and EPR and their advantages and disadvantages. - Factors that influence cable breakdown voltage and how to prevent cable faults. - The effects of sheath on cable losses and how to reduce them. - Tests conducted on cables and cable fault localization.

1. Power cable
‫وترتيب‬ ‫جمع‬
‫مهندس‬
/
‫محمد‬ ‫محمود‬
Mahmoud.ali8585@gmail.com

2. Objective:
 Classification of cables
 voltage drop
 Short circuit current
 Some of Cables problems
 Protection on cables
 Fuses and circuit breaker
 Cable Fault Localization
 Tests on cables
 Ring Main Unit , RMU
 Types of earthing

3.  Cables electrical properties:
1- conductor resistance
2- insulator resistance
3- cable capacitance
4- inductance
5- electrical field inside cable

4. 1- conductor resistance
R=(ΡL/A) L=1m A=1mm
Resistivity
material
.018
CU
.028
AL
65
Carbon
20000000
glass
1000000000
mica

5.  The relation between (R and L):
- Ac current resistance differ about dc current for same
material for two reasons :
1- skin effect
2- proximity effect

7.  Cable capacitance:
C=(q/v)
- Produce capacitance charges between core and sheath
(earth) or between cores and earth
- Must discharge the cable after the disconnection
- Occurs some losses caused by these charges but it is
useful for power factor correction

9. 3- electrical field:
V=K (q/d) E= v/d v/m
- Max electrical field at conductor surface
- Min electrical field at inner sheath surface
-

10.  E = V / [x ln (R/r)] v/m
- Max (E) at (x=r)
- Min (E) at (x=R)
- Max (E) at conductor surface so that use
semiconducting material on core for field regulating

11. 4- insulation resistance :
- (not Rins = ∞ )
- use insulator has high resistance to reduce (tan δ )

12.  Cable electrical stresses:

13. - To connect cable shield must cut part of shield of cable
end to prevent cable fault
- This causes un continuous of electrical field and
concentration on shield surface lead to insulation
failure
- Use tube to reduce pressure

15.  Wires Scheduled causes increasing in electrical field
on conductor surface about (20%)
 so that semiconducting on conductor reduce
electrical field on surface

16.  conductor shield is made of plastic with black carbon
to give semiconducting
 Where semiconducting resistance higher than
conductor resistance

17. cable without semiconducting
cable with semiconducting cable without semiconducting

18.  advantages of semiconducting material:
1- regulate the electrical field
2- plastic property make adequateness (expansion
and shrinkage) with insulator in periods (loading
and unloading )
- This to prevent bubbles between conductor
insulator

19.  sheath effect :
 when flow current in conductor produce field and
causes emf in cable sheath and behind cables
sheath
 These emf causes (eddy current )

20.  1- eddy current losses in sheath :
 It about (2% of conductor losses ) where appear in metallic
sheath cables

21.  2- sheath losses :
 when connect cable sheath to earth or other cable sheath
produce (closed loop ) “emf” where current flow in sheath
in single core cables causes losses
 These losses reduce current capacity for cable
 Solution : use cross bonded

23.  Metal tap shield and semiconductor:

24.  Breakdown voltage for cable:
1- voltage effect time
2- conductor shape
3-temperature
4- spaces quantity in cable
Cable (A) Void between the Conductor and the Insulation
(B) Tracking In Cable

25.  At testing:
- Used voltage in old cable is less than Used voltage in
new cable ‽
Solution:
- At loading and unloading increase and decrease
temperature
- lead to expansion and shrinkage in cable causes
spaces and ionization causes faliure

26.  polymeric material insulated:
1- PVC 2- XLPE 3- EPR

27. 
‫والميكانيكية‬ ‫والفيزيائية‬ ‫الكهربائية‬ ‫البوليمرات‬ ‫خواص‬
:

‫للبوليمرات‬ ‫الكهربائية‬ ‫الخواص‬ ‫التالي‬ ‫الجدول‬ ‫ويبين‬
0

29.  1- PVC:
 Advantages:
1- used in voltages (3.3kv)
2-used at low temperature
3- high hardness
4- moisture resistance
5- resistance to ozone gas, acids
6- resistance to flame

30.  disadvantages:
1-In high temperature reduce the insulation resistance
2-not exposed to continuous temperature exceeds about
(105 c) or reduce to zero
3- not exceeds conductor temperature about (150c -160c)
4- at high temperature (insulator cracking),
At low temperature (insulator stiffen)

31.  2- XLPE:
 Advantages:
1-used in high voltages (up to 275kv)
2- carry high temperature during continuous loading
“90c” or S.C at “250c”
3- tan δ is small
4- breakdown voltage (50-70kv/mm)
5-high resistance moisture

32. 6-high resistance for ozone gas
7- high rigid material

33.  Curing processing:
 Used water steam or (inert gas “nitrogen”) to prevent
impurities and gap or moisture

34.  Must be subject to the following when using cables
XLPE:
1- not exceeds max continuous loading temperature (90c
) for conductor
2- not exceeds max over loading temperature (130c for
conductor )
3- not exceed max temperature about (250 c ) for
conductor during short circuit
 disadvantages:
1- not used at Bending because it has rigid

35. 3- EPR:
1- used at voltages (5-35kv )
2- carry high temperature at (90c )
3- good elastic properties
4- ozone resistance