This document discusses the construction, testing, and standards for underground power cables. It describes the typical components of cables including conductors, insulation materials like XLPE and PVC, sheathing and armor. Key tests for cables are outlined, including partial discharge testing to check for insulation defects and high voltage testing. Standards for cables from organizations like IEC and BIS are also referenced.

1. Tests on Cables, Transformers
and Standby Generators
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2. 2

3. CONTENTS
■ INTRODUCTION
■ CONSTRUCTION OF CABLES
■ CLASSIFICATION OF CABLES
■ TESTING OF CABLES
■ HANDLING OF CABLES
■ LAYING PROCEDURE
■ CABLE TERMINATION
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4. INTRODUCTION
• AN UNDERGROUND CABLE ESSENTIALLY CONSISTS OF ONE OR MORE
CONDUCTORS COVERED WITH SUITABLE INSULATION AND
SURROUNDED BY A PROTECTING COVER.
• WHERE THESE CABLES ARE PLACED
• PLACED INSIDE THE UNDERGROUND
• DIRECTLY BURIED UNDERGROUND TRACKS
• PLACED INSIDE THE UNDERGROUND DUCTS
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5. 6
CONSTRUCTION OF CABLES
The general construction of a 3-conductor cable consists of
• Cores or Conductors
• Insulation
• Metallic sheath
• Bedding
• Armouring
• Serving

6. 7
CONSTRUCTION OF CABLES-INSULATION
Properties of Insulating Material
• High resistivity.
• High dielectric strength.
• Low thermal co-efficient.
• Low water absorption.
• Low permittivity.
• Non – inflammable.
• Chemical stability.
• High mechanical strength.
• High viscosity at impregnation temperature.
• Capability to with stand high rupturing
voltage.
• High tensile strength and plasticity.
Different Insulating Materials
• PVC (Polyvinyl Chloride)
• PE (Polyethylene)
• XLPE (Cross-Linked Polyethylene)
• EPR (Ethylene Propylene Rubber)
• Polytetrafluoroethylene (PTFE)
• Thermoplastic Rubber (TPR)
• Neoprene (Polychloroprene)
• Styrene Butadiene Rubber (SBR)
• Chlorosulfonated Polyethylene (CSPE)

7. 9
CONSTRUCTION OF SINGLE CORE XLPE
CABLES (CROSS LINKED POLY-ETHYLENE)
• This material has temperature range beyond 250 – 300 C
• This material gives good insulating properties
• It is light in weight, high mechanical strength, low water
absorption.
• These cables permit conductor temperature of 90 C and 250 C
under normal and short circuit conditions.
• These cables are suitable up to voltages of 800 kV.

8. 10
CONSTRUCTION OF SINGLE CORE XLPE
CABLES (CROSS LINKED POLY-ETHYLENE)

9. 11
CONSTRUCTION OF THREE CORE XLPE
CABLES (CROSS LINKED POLY-ETHYLENE)

10. 14
CABLES FOR DIFFERENT VOLTAGE LEVELS
• For L.V. distribution cable may be selected on the basis of continuous load current.
• In case of MV/HV distribution it is always safer to select the cable on the basis of ability of conductor
to carry expected short circuit current.
Short circuit current rating of cable should be in line with short circuit capacity of damping apparatus
such as circuit breakers, Transformers & reactor etc. beside its capacity to carry desired load current.
Short circuit ratings of cables each size are calculated on the basis of IEC-949 & IEC-986 &
considering the following factors
• a) Temperature of conductor just prior to short circuit
i) With XLPE insulation - 90 Deg. C ii) With PVC insulation - 70 Deg. C
• b) Maximum permissible conductor temperature during short circuit
i) With XLPE insulation - 250 Deg. C ii) With PVC insulation - 160 Deg. C

11. 15
CABLES FOR DIFFERENT VOLTAGE LEVELS

12. 16
STANDARDS FOR CABLES
The various Indian standards associated with cables are
1. IS 10810 part (1- 63) Testing of cables
2. IS 7098 Specification for crosslinked polyethylene insulated PVC sheathed cables
p1for working voltages up to and including 1100 volts
p2 for working voltages from 3.3 kV up to and including 33 kV
p3 for working voltages from 66 kV up to and including 220 kV
The various International Standards for cables are
1. IEC 986 – Guide to Short Circuit Temperature Limits of Electric Cables
2. IEC 949 – Calculation of Thermally permissible Short Circuit Currents, taking into account non adiabatic
heating.
3. IEC 60502 -

13. 17
TESTING OF CABLES
• CLASSIFICATION OF TESTS
• Type Tests
• Acceptance Tests
• Routine Tests
• Pre – Commissioning Tests
• Routine Tests
The following shall constitute routine tests:
• a) Conductor resistance test,
• b) Partial discharge test (for screened cables only),
• c) High voltage test, and
• d) Resistance test for armour (for mining cables)

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CONDUCTOR RESISTANCE TEST
• Methods of test for cables “I.S 10810 part 5 conductor resistance test
• Apparatus
• Kelvin double bridge of accuracy 0.2 percent having current and potential
terminals;
or
wheatstone bridge of accuracy 0.5 percent.
• Sensitive galvanometer.
• DC Source
• Thermometer
• The measured resistance is converted to the standard temperature and standard length.

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PARTIAL DISCHARGE TEST
• Partial discharge is a small localized dielectric breakdown of an electrical insulation system under high
voltage stress.
• Each discrete partial discharge is the result of an electrical breakdown of an air pocket within the
insulation.
• These discharges erode insulation and eventually result in insulation failure.
• This test is performed on such extruded dielectrics in order to ensure that the insulation is free from
partial discharges in excess of certain limits.
• PD occurs if the electric field strength applied to a dielectric exceeds the dielectric withstand strength of
an insulation system locally

16. 21
PARTIAL DISCHARGE TEST
• Equipment Required
• Coupling Capacitor
• High Voltage Voltmeter
• Calibration Pulse Generator
• Screened Enclosure
• The partial discharge magnitude at test voltage equal to 1.73 Uo shall not exceed 10 pC for routine
tests/ acceptance tests and 5pC for Type Tests.

17. 22
PARTIAL DISCHARGE TEST
• Failures in the test
• Manufacturing Defects
• Ageing & Environmental
• Improper Installation

18. 23
HIGH VOLTAGE TEST

19. 24
RESISTANCE TEST FOR ARMOUR (FOR MINING
CABLES)
• Methods of test for cables “I.S 10810 part 5 conductor resistance test
• Apparatus
• Kelvin double bridge of accuracy 0.2 percent having current and potential
terminals;
or
wheatstone bridge of accuracy 0.5 percent.
• Sensitive galvanometer.
• DC Source
• Thermometer
• The measured resistance is converted to the standard temperature and standard length.