Modelling and Analysis - Protection Co-ordination & Equipment Withstand

Protection Co-ordination Analysis
Along with a periodic review of system fault levels in order to ensure that equipment remains fit for service under fault conditions, a protection review needs to be completed in order to ensure that minimum fault levels still provide sufficient current to operate the protective devices sufficiently quickly and also to ensure that maximum fault levels do not create discrimination problems between protection stages.

The software we use allows us to create bespoke time/current curves for any device and this is an important advantage over most other software packages for protection modelling. Whereas most other packages use 'generic' models to allow modelling of un-supported devices, our software enables us to accurately simulate the exact tripping curve of the device, either based on manufacturer's documentation (hence requiring no downtime) or based on actual measured response through secndary injection. We have the ability to use the software's own supplied models of protection devices if available, but this bespoke time/current characteristic modelling ensure we will always have the right curve for your protection.

The examples below show some time/current curves we recently produced. Note that these are for example only and may not reflect the eventual findings of the analysis. They do however show the principles behind the time/current curves and the level of detail that can be included. most of the presented curves were generated specifically for this project.

Protection Arrangement across 11kV:415V 2500kVA transformer LV switchboard outgoing circuit discrimination with Main Incomer LV switchboard outgoing circuits showing discrimination with Main Incomer

Equipment Withstand Assessment
The energy that passes through an electrical component due to a fault is the critical parameter in determining whether a piece of equipment will remain fit for further service following the fault. The two aspects of this, the current level and the duration for which the fault current flows, are derived by the fault level analysis and the protection co-ordination study in order to be able to pin-point the required equipment rating for any point in the system under consideration. Hence the switchgear rating (typically 50kA 1 second for LV equipment) can be assessed against the actual current level and the duration for which it passes through the equipment. If the equipment current-time relationship is higher than the system fault level and duration then the equipment should remain fit for further service without significant detrimental impact from either thermal or magnetic effects. However there may need to be maintenance carried out before returning to service. This will be stated in the manufacturer's documentation.




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Director: Stuart Shaw


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Last Modified 8th October 2018