What Is the Application of a System That Does Not Clear Ground Faults?

F

FEstanol

Member
Location
Toronto
Occupation
Electrical Engineer
Asking out of professional curiosity

I've reviewed the Ontario Electrical Safety Authority (ESA) bulletin 36-16-* and they state

(1) Application of cable insulation levels
The cable voltage rating to be used in a particular installation shall be selected on the basis of the applicable phase-to-phase voltage. In addition to the cable voltage rating, the insulation level shall be suitable for the application in accordance with CSA C68.10. Below is a brief description for the applicability of each insulation level as defined in the Standard.
- Cables with 100% insulation level are applicable to grounded systems provided with protection that will clear ground faults within 1 minute.
- Cables with 133% insulation level may be applied where the clearing time requirements of the 100% level category cannot be met, but there is adequate assurance that the faulted section will be deenergized in a time not exceeding 1 h. This insulation level corresponds to that formerly designatedfor ungrounded systems.
- Cables with 173% insulation level are applicable to systems where the time required to de-energize a grounded section is indefinite.

What sorts of systems would have protection systems that would clear ground faults over 1 min to indefinite time periods?
 
FEstanol said:
What sorts of systems would have protection systems that would clear ground faults over 1 min to indefinite time periods?
Click to expand...
Typically continuous process industries.
Although I would bet most of these types of systems are leftover from the mid-20th century. Cable insulation is not the only concern with with these power systems.
 
jim dungar said:
Typically continuous process industries.
Although I would bet most of these types of systems are leftover from the mid-20th century. Cable insulation is not the only concern with with these power systems.
Click to expand...
Would you mean something like an old oil and gas refinery or other continuous chemical process?
 
FEstanol said:
Would you mean something like an old oil and gas refinery or other continuous chemical process?
Click to expand...
jim dungar said:
Typically continuous process industries.
Although I would bet most of these types of systems are leftover from the mid-20th century. Cable insulation is not the only concern with with these power systems.
Click to expand...
Would the logic in this scenario be "Cant stop the process, dont trip a breaker. Alarm, trouble shoot and fix without stopping the process"?
 
The standard we have had for many years in order to manufacture medium voltage cables
of 5-35 kV was UL 1072/1995. This standard presents only 100% and 133% insulations.
100 PERCENT LEVEL - Cables in this category are intended for use where the system is provided with relay protection such that ground faults clear as rapidly as possible but, in any case, within 1 min.
133 PERCENT LEVEL - This insulation level corresponds to that formerly designated for undergrounded systems. Cables in this category are intended for use in situations in which the clearing-time requirements of the 100 percent level category cannot be met, and yet there is reason to expect that the faulted section is de-energized in a time not exceeding 1 h.
NEMA WC 74-2000/ICEA S-93-639 5-46KV SHIELDED POWER CABLE FOR USE IN THE TRANSMISSION AND DISTRIBUTION OF ELECTRIC ENERGY
in Table 4-4 CONDUCTOR SIZES, INSULATION THICKNESSES AND TEST VOLTAGES
presents also 173% insulation.
100 Percent Level - Cables in this category may be applied where the system is provided with relay protection such that ground faults will be cleared as rapidly as possible, but in any case, within 1 minute. Where additional insulation thickness is desired, it shall be the same as for the 133 percent insulation level.
4.2.1.2 For Delta Systems Where One Phase May Be Grounded for Periods Over One Hour
Use the 173 percent thickness values given in Table 4-4. Also, see the 173 percent level note following Table 4-4.
173 Percent Level - Cables in this category should be applied on systems where the time required to de-energize a grounded section is indefinite. Their use is recommended also for
resonant grounded systems. Also they may be used when additional insulation strength over the 133 percent level category is desirable.
 
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