50 Shades Darker - CDEGS Myths Busted!

CDEGS Modelling Software demystified!

It's interesting how the psychology of the car has found a place in our daily lives.  How many times have you asked or been asked ‘what car do you drive?’

If you’re one of the lucky few that own a Ferrari (unfortunately, I am not one of those!) – you might receive a different response than if you own a Nissan Micra.  The common thread is that there are both ‘cars’ aimed to transport you from A to B – but each one has been designed, developed and delivered to fit two very different budgets and to two very different purposes.

When to ask for black or white – not all CDEGS Modelling Software are the same!


CDEGS Modelling Software Demystified

In the land of cars, we measure performance in terms of acceleration (0-60 MPH), top speed, economy (MPG), ecology (g/CO2) or lap times if you’re a Top Gear fan …

In Earthing – the key performance measures (for EN 50522, 50122-1) are a function of accuracy % error, complexity, and/or correlation to reality.  The trouble is, one of the best-kept secrets is that different versions of “CDEGS Modelling Software” also exist - From the £7,000 Nissan Micra to the £200,000 Ferrari 488.

So, next time you receive a fee proposal for an Earthing Study that claims to be CDEGS compliant – ask the provider ‘what version/module of the CDEGS Modelling Software are you intending to use?’ Why (you might ask)?

The chief reason boils down to the engine that powers the modules – some modules, like MALT and MALZ rely on ‘Circuit Theory’.  Others, such as HI-FREQ are based in ‘Electromagnetic Field Theory’.

Why does this matter?

Two words … ERROR RATE.   If your application is on the simpler, smaller end of the earth design spectrum, with lower fault energisation levels; then the more budget sensitive versions of the CDEGS  Modelling Software which are based in Circuit Theory may be sufficient… but as the complexity and/or the size increases, so will the rate of error increases – sometimes as much as 50%.

Think about it – let’s say there’s a 6 kA fault with a 50% split factor.  This means there’s 3 kA going through the Main Earth System to earth.  For ease of calculation, let’s assume the Earth is 1 Ω impedance, which means the basic Earth Potential Rise (EPR) for the system should be around the 3 kV mark.

But what if the software module selected has underestimated the EPR by 50%?  This would lead to a 1.5 kV difference in predicted verses actual – is this significant??

I accept in this scenario mentioned, it’s not possible to be definitive without understanding a bit more about the circumstances but taking this at face value, an underestimate of 1.5 kV could have a significant impact on the touch/step safety – without putting too fine a point on it, enough to kill.

So, an upgrade in the computational engine is required for the larger, longer, more commonly encountered earth designs or studies for ‘power systems’, which can take account of mutual coupling effects, inductance, capacitance, e.g. the calculations are not limited to just the conductive/resistive effects.

Armed with an Electromagnetic Field Theory engine, the risk of error is mitigated – typically by an order of magnitude lower, which means we can all sleep at night because the design is using robust, accurate, low levels of error, based in the latest accepted science for its calculations.

If you have a ‘critical’ asset or infrastructure project – then the standard requirement has to be the elimination (or reduction at least) of error that can be easily avoided.  In most cases, this can be achieved by simply being more aware of the choices available and the residual risk in the modules used.  Knowingly or otherwise, no-one wants to be haunted by easily avoidable errors.

There’s a bewildering quantity of CDEGS modelling software modules – so if you’re not sure whether what is being used on your project is fit for purpose - drop us a line on our live chat facility below ... for a super quick response.

Featured Image:  LaFerrari

Ian Griffiths SelfieIan Griffiths

Ian is a Principal Consultant at GreyMatters, with 26 years experience solving HV earthing, EMC, and lightning problems for clients worldwide.  When he’s not busy studying problems and designing solutions, you can find him mountain biking, sailing and racing motorbikes in the summer.  In the winter he tends to head off to the mountains chasing the snow with friends and family.  Ian holds a Master’s Degree, and Degrees in both Mechanical and Electrical disciplines, and is one of the top 1% accredited CDEGS consultants and advisor to international utility companies, data-centre and infrastructure developers globally.

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