CABLES
• What are the purposes of cable trays?
a. Avoid sagging of cables
b. Give mechanical support
• What are the disadvantages of paper insulation?
a. Absorbs moisture.
b. Cable termination/sealing problems.
• What are the advantages of XLPE?
a. Easy routing at heights
b. Easy maintenance
c. Large current (90 ºC)
d. No sheath (no fatigue)
e. No paper tape wrapping technique
f. High dielectric strength
g. Very little deformation even at high temp,
h. More rated current, overload, short ckt capacity
i. Low tan delta and hence suits long routes
j. Very light
k. Good mechanical properties.
• What is the specified cable life?
50 years.
• How armours /sheaths grounded?
1 core cables -- sheaths/shields/armours grounded at one end only, other end
insulated to prevent the circulating current through sheaths.
3 core cables -- grounded at both ends but not including core balance CT’s, since
even small induced current causes 50N operation.
• Why armouring done?
For mechanical strength, protect against damage by impact of an object.
• How the required conductor size can be reduced by use of HRC fuses?
HRC fuse limits the peak amplitude of fault current. HRC fuse melts at prospective
current but not allows circuit to pass their high rupturing capacity that is it’s kA.
• What are the types of cables used in 6.6 kV and 415 V system voltages?
In 6.6 kV system AC (unearthed) grade having stranded aluminium conductors
cables are used. Their insulation’s are as follows.
1. XLPE – Crossed linked polyethylene insulation.
2. FRLS PVC – Fire retardant low smoke insulation with PVC inner and outer
insulation. In RB copper conductor stranded cables are used.
3. FS – fire survival insulation.
4. HR PVC – heat resistant insulation.
In 415 V system 1100 V grade copper or aluminium stranded cables are used. Their
insulations are HR PVC and FS type.
• At what temperature cables are rated?
Normally cables are rated for 40°C
Maximum temp in °C Short time temp in °C
PVC 70 160
HRPVC 85 160
Fire survival 90 250
Silicon rubber 90 250
XLPE cable 90 250
• Why 1.1 kV grade cables used for 415V?
To take care of the both earthed / unearthed systems.
• While carrying out cable joints, why should we ensure the continuity of 1) metallised
paper for PILC, 2) sheath and armour.
Continuity of metallised paper ensures less voltage gradient, hence preventing
puncture of insulation.
Continuity of sheath / armour ensures that grounding is maintained, so no over
voltage is induced, and easy to detect earthfault in cables.
• Why bimetallic washers provided in aluminium copper transition joints?
To avoid galvanic corrosion failure.
• What is the type cable used in radiation areas?
Mineral insulated (MI) cables.
https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg RRB JE, SSC AE/JE UPSSSC JE, SSC JE, CIVIL ENGINEERING MCQs, ELECTICAL ENGINEERING MCQs, preavious year quesion papers, dmrc, lmrc, drdo,rrb ntpc, ntpc, pgcil, dsssb, states board, GATE IES EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA
• What are the purposes of cable trays?
a. Avoid sagging of cables
b. Give mechanical support
• What are the disadvantages of paper insulation?
a. Absorbs moisture.
b. Cable termination/sealing problems.
• What are the advantages of XLPE?
a. Easy routing at heights
b. Easy maintenance
c. Large current (90 ºC)
d. No sheath (no fatigue)
e. No paper tape wrapping technique
f. High dielectric strength
g. Very little deformation even at high temp,
h. More rated current, overload, short ckt capacity
i. Low tan delta and hence suits long routes
j. Very light
k. Good mechanical properties.
• What is the specified cable life?
50 years.
• How armours /sheaths grounded?
1 core cables -- sheaths/shields/armours grounded at one end only, other end
insulated to prevent the circulating current through sheaths.
3 core cables -- grounded at both ends but not including core balance CT’s, since
even small induced current causes 50N operation.
• Why armouring done?
For mechanical strength, protect against damage by impact of an object.
• How the required conductor size can be reduced by use of HRC fuses?
HRC fuse limits the peak amplitude of fault current. HRC fuse melts at prospective
current but not allows circuit to pass their high rupturing capacity that is it’s kA.
• What are the types of cables used in 6.6 kV and 415 V system voltages?
In 6.6 kV system AC (unearthed) grade having stranded aluminium conductors
cables are used. Their insulation’s are as follows.
1. XLPE – Crossed linked polyethylene insulation.
2. FRLS PVC – Fire retardant low smoke insulation with PVC inner and outer
insulation. In RB copper conductor stranded cables are used.
3. FS – fire survival insulation.
4. HR PVC – heat resistant insulation.
In 415 V system 1100 V grade copper or aluminium stranded cables are used. Their
insulations are HR PVC and FS type.
• At what temperature cables are rated?
Normally cables are rated for 40°C
Maximum temp in °C Short time temp in °C
PVC 70 160
HRPVC 85 160
Fire survival 90 250
Silicon rubber 90 250
XLPE cable 90 250
• Why 1.1 kV grade cables used for 415V?
To take care of the both earthed / unearthed systems.
• While carrying out cable joints, why should we ensure the continuity of 1) metallised
paper for PILC, 2) sheath and armour.
Continuity of metallised paper ensures less voltage gradient, hence preventing
puncture of insulation.
Continuity of sheath / armour ensures that grounding is maintained, so no over
voltage is induced, and easy to detect earthfault in cables.
• Why bimetallic washers provided in aluminium copper transition joints?
To avoid galvanic corrosion failure.
• What is the type cable used in radiation areas?
Mineral insulated (MI) cables.
https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg RRB JE, SSC AE/JE UPSSSC JE, SSC JE, CIVIL ENGINEERING MCQs, ELECTICAL ENGINEERING MCQs, preavious year quesion papers, dmrc, lmrc, drdo,rrb ntpc, ntpc, pgcil, dsssb, states board, GATE IES EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA
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