4.2.2 German Guide DGUV-I 203-078 Arc Flash Calculations
Unlike the IEEE 1584 Guide described previously, the German guide DGUV-I 203-078 (Thermal Hazards from Electric Fault Arc) is very different in approach and the two standards cannot be compared with each other. The calculations used by DGUV-I 203-078 are derived from the box test method for PPE which is detailed in the standard IEC 61482-1-2:2014 Live Working – Protective Clothing against the thermal hazards of an electric arc. This test standard is discussed in detail in Chapter 7: Protection, but in summary, it is a simple pass/fail against just two fixed parameters of fault current, 4kA and 7kA. In other words when tested according to box test, a sample of the material that the protective clothing is made of is assigned one of two arc protection classes (APC). This will either be APC 1 which is subjected to a prospective short circuit current of 4 kA for 500ms or APC 2 at a prospective short circuit current of 7 kA for 500ms. The test is fairly simple and can be replicated on many industrial sites unlike the open arc method that requires serious decoupled motor/generator supplies.
The PPE box test method predates the calculations and more recent refinements of the mathematical models that have been achieved from work at Ilmenau Technical University in Germany. In other words, the results of the box test output have been reverse engineered to provide a quantitative method of matching site conditions to the test method. The tests to produce the IEEE 1584 calculations is discrete from the open arc tests to assess the thermal performance of PPE whereas, the DGUV-I 203-078 calculations are integral to the box test. As of 2021, the time of writing, a 2020 edition of this guide had been published in German and an English translation is expected shortly.
4.2.2.1 Merits and Drawbacks of the DGUV-I 203-078 method
Whilst the DGUV guide is used in parts of Europe for low voltage utility applications, I would recommend the use of IEEE 1584 for industrial and commercial applications. That said, the calculations are fairly simple bearing in mind that IEEE 1584 has a total of 25 formulae some of which have six variables and thirteen coefficients.
DGUV-I 203-078 considers the reactive power component for the power transferred into the arc whereas IEEE 1584 does not. It also highlights the use of arc voltage and resistance.
Unlike IEEE 1584 which is based on empirically derived data, DGUV-I 203-078 is a theoretical model. The voltage range is from 50 volts right up to 110 kV, but it is mainly applied to low voltage applications. The test rig resembles a low voltage utility service point or cut out at a voltage of 400 volts and has an aluminium and a copper electrode. The mixture of aluminium and copper outside of utility distribution termination equipment is relatively rare nowadays.
There is just one electrode configuration in DGUV whereby IEEE 1584 considers five configurations. Some may see that as an advantage but there is considerable variance of arcing current results because of the additional electrode configurations. I would trust the IEEE 1584 results as they emulate real conditions particularly circuit parameters. This is an important consideration when calculating arcing current as the two methods will produce differing results. If the arcing current is incorrect then this will have a huge impact when predicting the severity of the arc hazard.
One of the drawbacks of the DGUV-I 203-078 method is that the algorithm is reverse engineered from a test method which does not emulate field conditions in commercial and industrial setting. It is after all, a single phase 400-volt test whereas the IEEE 1584 formulae are based on real world conditions and are divorced from the PPE open arc tests. In other words, they are independent.
The following table gives a comparison between the two methods.
Comparison between the DGUV-I 203-078 and IEEE 1584 Guides | |
DGUV Guide | IEEE 1584 Guide |
Theoretically derived from the box test method of testing protective clothing against the thermal hazards of an electric arc to IEC 61482-1-2: Live working. | Empirically derived from actual high power laboratory tests for the full range of the guide. |
Linked to the box testing of PPE. | Independent of PPE testing. |
The R/X ratio required. | No requirement for R/X ratio. |
Requires maximum and minimum fault currents to IEC 60909. | Calculates a minimum arcing current to account for variations in system parameters. |
Note: that in all cases when obtaining fault levels, the discovery phase should account for system configuration and of utility variations as a prerequisite for using both methods. | |
Arcing current theoretically derived from a single-phase low power source which cannot be matched to site conditions. | 3 phase arcing current based upon 5 different electrode configurations which are based upon actual site conditions. |
No allowance for enclosure dimensions. | Correction factors calculated for different height, width and depth of enclosures. |
Aluminium and copper electrodes used in the box test. | No requirement for aluminium electrodes. |
Calculates arc energy. | Calculates incident energy level at a working distance. |
PPE restricted to standard protection APC1 or enhanced protection APC2 only. | No restriction on PPE range (except for an upper limit 100 cal/cm^{2} -see IEC 61482-2) |
Application of correction factors for transmission factor KT (enclosed, semi open and open arc) plus actual distance to the APC1 and APC2 creates an equivalent PPE protection level. This equivalent protection level must be greater than the arc energy. | PPE matched directly to the calculated incident energy. |
Does not provide an arc flash protection boundary. | Calculates an arc flash protection boundary. |
Gives a maximum cut off disconnection time of 1 second for reaction time. | Gives a maximum cut off disconnection time of 2 seconds for reaction time. |
Starts the risk assessment with PPE in mind rather than a last resort. Does not give a meaningful severity calculation. | Gives a measure of the severity of the hazard. PPE recommendations are excluded from the guide. |