Cable Voltage Grade

DDo your own homework.

Not even disguised.

Key info is absent, such as what voltage of system.

System voltage is 11kV eathed system

As explained before you missed the standard .Is it manufactured according to BS or IEC 60502-2 ?

According to IEC 60502-2 4.1 Rated voltages:

"The rated voltage of the cable for a given application shall be suitable for the operating

conditions in the system in which the cable is used. To facilitate the selection of the cable,

systems are divided into three categories":

A-ground fault clearance up to 1 min.

B-ground fault clearance up to 1 hour

C-more than 1 hour.

That means since a grounded neutral system short-circuit current has to be cleared in seconds your cable enter A category: 6/10 kV

I do not know what is your level of education in Electrical Engineering or your experience. The question appears to be from an interview or a test paper for which you are supposed to know the answer and members of this forum are not expected to answer it. How ever I would like give a hint . the examiner wants to know weather you know the range of LV , MV , HV, and EHV ( LT, MT , HT , EHT ) Once you study it you will get the answer.

I raised this question because we know that in 11kV unearthed system voltagde grade is 11/11kV the logic is during ph-E fault healthy phase voltage raised by root3 times ph-earth voltage this stress created due to high resistence in ground path which resist the flow of fault current to earth.On this basis cable using high insulating material & its grade is 11/11kV i.e. In case of fault ph to armour voltage stress is 11 & ph to ph voltage stress is 11kV (which is in denominator). At this same logic I can say that if the system is 11kV earthed then the voltage grade for XLPE could be 6.35/11kV . As per my understanding during ph-e fault the voltage of healthy phase should not raise above system voltage/root3. Then why we select 12.7/22kV?

I think you've all answered your own question, Mildreds. Anyway, as an individual you could always ask someone else in the we. If no-one there knows, then your outfit would be best not meddling in these voltages and cables. Don't you have any selection protocols to work to? That's appalling!

The answer to your original post is (2) as 12.7/22kV is HV and answer (1) is MV

6.35/11 kv is MV grade and when you specify it as High Voltage Cable then the cable has to be graded as HV and not MV

Dear Sir, In india MV range is 1-50kV.

As per IE Rules 1956 HV is only up to 33 kV . I think IE rules are applicable in India. IE rules specify MV only up to 660 Volts Quote from IE rules reproduced below.

"(av) "Voltage" means the difference of electric potential measured in volts between any two conductors or between any part of either conductor and the earth as measured by a suitable voltmeter and is said to be; "Low" where the voltage does not exceed 250 volts under normal conditions subject, however, to the percentage variation allowed by these rules; "Medium" where the voltage does not exceed 650 volts under normal conditions subject, however, to the percentage variation allowed by these rules; "High" where the voltage does not exceed 33,000 volts under normal conditions subject, however, to the percentage variation allowed by these rules; "Extra high" where the voltage exceeds 33,000 volts under normal conditions subject, however, to the percentage variation allowed by these rules. "

Your system rated voltage of 11 kV [according to BS6622-may be-or IEC60502-2] category A-[grounded], the maximum operation voltage-continuously-could be 12 kV [6/10 kV rated].

If the system will operate in a ground fault case more then 1 hour until clearing it is 8.7 kV -phase-to ground -rated insulation recommended to use [15/8.7 kV].No requirement of higher insulation level-according to IEC 60502.

In certain situation IEEE [USA] may recommend a higher level. [See IEEE 141/1993 ch.12.4:

" 100% insulation level cables are applicable to grounded systems provided the protection

devices will clear ground faults within 1 min. On ungrounded systems where the clearing time of the 100% level category cannot be met, and yet there is adequate assurance that the faulted section will be cleared within 1 h, 133% insulation level cables are required.

On systems where the time required to de-energize a grounded section is indefinite, a 173% insulation level is used."

In a rough approximation 100% 6/10 kV ,133% 8.7/15 kV 173% 12/20 kV.

As per my experience 6.35/11kV (E) grade will be OK for 11kV (Earthed ) system.However,11/11kV (E) grade is advisable to be on safe side.