Ground(earth) continuity conductor (ECC) within substation

[Theelectricalengineer]

We need to connect 33kV 630sqmm CWS cables from Power transformer(132/33kV) to switchgear. The consultant proposed solidly bonded system at first stage and then changed to bonding at single end without ECC. The distance between transformer and switchgear is 50meters and part of same earth mesh within substation. From what I understand, in a substation yard with same earth grid, the grid itself carries ground fault current and there’s no need to run a separate ground conductor within the substation since the ground grid is designed for that purpose. CCan anyone provide some insight into this? Could we do a single end bonding without ECC within substation equipment?

 

[waross]

There will be an induced potential in the Copper Wire Screen.
If the screen is bonded at both ends, the induced potential will cause a current to flow.
This will add heat and the resulting losses.
Due to the added heat generated, the ampacity of the cable should be de-rated.

 

[Theelectricalengineer]

There will be an induced potential in the Copper Wire Screen.
If the screen is bonded at both ends, the induced potential will cause a current to flow.
This will add heat and the resulting losses.
Due to the added heat generated, the ampacity of the cable should be de-rated.

Thanks for the comment. Could we use single point system w/o an ECC?

 

[waross]

Thanks for the comment. Could we use single point system w/o an ECC?

It depends;
Local codes
Local practice
Local engineering standards; Design firm or customer standards.
The distance between the transformer and the switchgear. as the distance between thee transformer and the switchgear increases the impedance of an ECC may increase more than the impedance of the grounding grid and running without an ECC may be seen as more feasible, subject to other concerns.
Design firm or customer preference.
Consider;
The withstand ability of the buried ground grid re: fault currents.
Possible undetected degradation of the buried ground grid versus a visible ECC on the surface accompanying the power conductors.

 

[RRaghunath]

When the copper shield / armour of the HT cable is earthed at only one end, it becomes necessary to use SVLs (Surge Voltage Limiters) at the other end.
The voltage rise at the unearthed end at the time of fault current flowing in the power cable (due to an external fault) will be safely discharged by the SVLs.

 

[Theelectricalengineer]

When the copper shield / armour of the HT cable is earthed at only one end, it becomes necessary to use SVLs (Surge Voltage Limiters) at the other end.
The voltage rise at the unearthed end at the time of fault current flowing in the power cable (due to an external fault) will be safely discharged by the SVLs.

Thanks RRaghunath, will that be same case if the terminations are at smaller distance and sharing the same earth mesh? Our one is just 50m separation.

 

[7anoter4]

If the cable run in trefoil formation -as per IEEE 575-for a rated load -up 1000 A the built-up voltage it will be less than 3 V .
In case of short-circuit up to 90 kA- the voltage will be 250-300 V
In flat formation-one feet distance, not cross bonding-for rated load may be 10 V, but for 90 kA short-circuit it could be 850- 900 V.