Aug 22, 2010  I have used SKM Ground Mat software to calculate the touch and step voltages for two earthing configurations of the transformer kiosk assuming: 1. Kiosk occupies an area of 5m x 3m, Kiosk occupies an area of 5m x 3m. Earthing Calculator Products & Services Lightning Protection International Australia LPI. All calculation use formulas taken directly from recognised IEEE and.

1. Earthing Pdf

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Three O/H line leave the station with a ground underneath the three wires and no neutral. Dont you think in that case if a fault occurs 1 KM down the line on secondary side, fault current would return through the ground connection and then the grid, the neutral connection and then the transformer back to the line faulted feeding the fault.

The boundary for thesafe area is defined by the yellow plane and includes all the area inside the earthgrid and a small area outside the grid. All step voltages are below the 'tolerable step voltage'of 351V. • RE: Earthing resistance and calculations (Electrical) 19 Aug 10 03:16. The data on rows 54 to 91 of the spreadsheet Eng-Tips_Thread238-279051-01.xlsx is incorrect and should be removed. Rows 54 to 91 had incorrect data on the prospective single phase to earth fault current on the 415V side of the 11 / 0.415kV, 1.0 MVA transformer. Only the 11kV system should be considered when determining the touch and step voltages.

Whilst the formulas used cover a range of common simple arrangements, the design of an earth system (including the input parameters) requires engineering judgement and all results should be verified by an appropriately qualified engineer taking into account such things as step and touch potential, site layout, materials, fault current, and so on. If in doubt, contact the below to make use of LPI's design service.

From the equation giving the voltage at a distance r away from the electrode or the grid: Vr = Icc * rho / (2 * pi * r) if the short circuit current Icc alone is 25kA, the Vr will be in the order of 3-4 kV, which is way above the acceptable level of a step voltage (should be not more than 100V if the protection trips in 0.1s to my understanding, maybe IEEE 80 allows a bit more). So if this calculation is correct, has it been 'always wrong' to use only a couple of rods, and indeed a grid that covers and extends beyond the area where people might be standing near the substation?

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Can anyone please return a 'corrected' excel sheet? RE: Earthing resistance and calculations. [quote]Three O/H line leave the station with a ground underneath the three wires and no neutral. Dont you think in that case if a fault occurs 1 KM down the line on secondary side, fault current would return through the ground connection and then the grid, the neutral connection and then the transformer back to the line faulted feeding the fault.[/wuote] By 'ground underneath' do you mean a ground wire? If so, this will be the same as a multigrounded neutral and will be a path for return current.

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I assume the above could read 'Three O/H line leave the station with an underslung earth wire'. Assuming uniform wooden pole spacing and earth resistivity at each pole electrode, could the Garrett method - described in IEEE 80 Section 15.9 - be used to calculate the division of current between the earth and earth wire? AS3835.2 - 2006 section 5.9.2 shows a simplified method of determining the impedance of the O/H earthwire in parallel with pole earth electrode resistance.

Jghrist, It looks like my grounding concepts are messed up again, I need to go back and read all your posts again. Anyways I would appreciate your word on this. Thanks RE: Earthing resistance and calculations (Electrical) 19 Aug 10 03:12. If the 11kV is not earthed ( transformer secondary delta ) then in the event of an earthfalt on the 11kV system, only a very low capacitive current will flow in the earth. Most 11kV systems will be earthed ( transformer secondary star point earthed – or zig-zag transformer ). If the O/H line includes an earth wire ( OHEW ) then in the event of an earth fault on the 11kV system, the total earthfault current ( 3Io ) will split between the earthgrid and the OHEW. An approximate method to determine this split is shown in AS 3835.2:2005 Section 5.9.2.

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Is there any free software to do these calcs? And what about the 'value' of taking a decent soil resistivity using a vertical probe vs the 4 point method and coming up with just 1 value? Especially if the software will just ask for the soil resistivity as 1 value input and calculate the voltage gradients from the short circuit current and the grid layout.

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System z1 = z2 = zo, 4. Standard IEEE 80, person weight 70kg barefeet, fault duration 0.2 sec, No Decrement factor used, soil resistivity 100 Ohm-m, No surface blue-metal, Earth Electrode L = 4.5m, DIA = 8 mm, equal current flows in earth and OHEW, Depth to top of Electrode /Grid = 0.5m. Calculated total current 3Io for an earth fault of the 11kV system at the transformer Kiosk = 443A. Current flowing into the ground = 222A The results of both the following configurations are shown on the attached spreadsheet. Configuration 1.

See attached file Eng-Tips_Thread238-279051-02.xlsx The earthing grid comprises of a rectangle 5m x 3m with horizontal earth conductors 1.0m apart. At each corner of the grid is a 4.5m long, 8mm DIA electrode. The total earthfault current ( 3Io ) from the source of 443A splits equally between the earthgrid and the overhead earthwire ( OHEW ). The SKM Ground Mat study results shows the area where the touch voltages are below the 'tolerable touch voltage'of 351V w.r.t remote earth. The boundary for thesafe area is defined by the yellow plane and includes all the area inside the earthgrid and a small area outside the grid. All step voltages are below the 'tolerable step voltage'of 351V.

(For interest rows 54 to 77 of tab 1_Input Data of attached spreadsheet Eng-Tips_Thread238-279051-03.xlsx shows calculated bolted earthfault on 415V terminals of 26425A I have used SKM Ground Mat software to calculate the touch and step voltages for two earthing configurations of the transformer kiosk assuming: 1. Kiosk occupies an area of 5m x 3m, 2. 11kV system prospective short-circuit current is 250 MVA, 3. System z1 = z2 = zo, 4.

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Some of the fault current will flow through the earth for a line fault and cause step- and touch-voltages at the substation. Usually, a fault on the HV side of the substation is a worse condition, however. If there is no metallic return, then there may be step- and touch-voltage problems at the substation, but there will be a worse problem at the location of the fault unless there is a large ground grid system there. You may also have problems detecting and tripping for a fault with no metallic return path. RE: Earthing resistance and calculations.

It seems on that post they say IEEE 80 notes that only the HV side of the fault is to be considered. I would like to question this a bit, in the ETA Power Station document i'm reviewing, you do a short circuit calculation on the network, you say which buses to include in the fault, and it will pass on to the earthing module the highest kA value, which obviously would be from the LV side of the transformer. Maybe the LV bus should not be selected in the first place to be included in the short-circuit calculation? If so, ok, lesson learnt.

The all expressions for the calculation are presented as the text. The representation of expressions as text is very comfortable at the big and difficult calculations.

Maybe the LV bus should not be selected in the first place to be included in the short-circuit calculation? If so, ok, lesson learnt. Regarding the 3-4kV from 400V, ok, let's consider it's the HV side, if the utility has a fault level of 250MVA, then at 11kV primary, the fault level is 13kA.

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If there is an OHEW the total earthfault current would be larger and some of this current would return to the source via the OHEW. Tab 4_Ig=1193A shows a third configuration where 4.5m earth electrodes are installed at the intersection of each earth grid mesh. The earthgrid resistance is 4.84 Ohm resulting in a total earthfault current of 1193A flowing only in the earthgrid. Touch and step voltages exceed the tolerable levels. If the overhead line includes an earthwire ( OHEW ) connected to earth electrode(s) at each pole, then detailed information on the overhead line, earth wire, span, earth electrode details, earth resistivity would be required to determine the current split. Is star point of the source transformer solidly earthed?

In this situation, we will always have to design a grid with secondary fault in consideration. My concepts are rusted for now so there is a possibility that I might be missing something in here. Thanks RE: Earthing resistance and calculations (Electrical).

Is star point of the source transformer solidly earthed? Current split between ground and earthwire is required to calculate touch and step voltages.

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And written a mail on same day and awaiting your reply till now i.e., 13/6/2016. While going through the attached sheet for D. Sizing found lots of discrepancies. Hence you are requested to explain and elaborate for better understanding of myself as follows: In practical all DG sets above 10-15 KVA are available in 3ph 4 wire system, hence single phase calculation is irrelevant in my case.

I understand that IEEE 80 and the rest of the stuff is more towards 'zone substations'/'outdoor switch yards' with sizeable area. What about a 1 MVA kiosk substation? Historically, i think all that is required was two deep driven electrodes, one at the HV and one at the LV sides. As i'm trying to understand this better, the fault level of this substation at the LV side is around 25kA. From the equation giving the voltage at a distance r away from the electrode or the grid: Vr = Icc * rho / (2 * pi * r) if the short circuit current Icc alone is 25kA, the Vr will be in the order of 3-4 kV, which is way above the acceptable level of a step voltage (should be not more than 100V if the protection trips in 0.1s to my understanding, maybe IEEE 80 allows a bit more). So if this calculation is correct, has it been 'always wrong' to use only a couple of rods, and indeed a grid that covers and extends beyond the area where people might be standing near the substation?

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Earthing Pdf

This impedance in parallel with the earth grid resistance would then be used to calculate total earhtfault current 3Io. The current division between O/H earth wire current and current in the earth could then be calculated. I have attached a sketch similar to the O/H line 'equivalent ladder network' shown in AS3835.2 Section 5.9.2.

It seems on that post they say IEEE 80 notes that only the HV side of the fault is to be considered. I would like to question this a bit, in the ETA Power Station document i'm reviewing, you do a short circuit calculation on the network, you say which buses to include in the fault, and it will pass on to the earthing module the highest kA value, which obviously would be from the LV side of the transformer. Maybe the LV bus should not be selected in the first place to be included in the short-circuit calculation? If so, ok, lesson learnt. Regarding the 3-4kV from 400V, ok, let's consider it's the HV side, if the utility has a fault level of 250MVA, then at 11kV primary, the fault level is 13kA. Vr = 13 kA * rho / (2 * pi * 3 meters) is still in the 2kV level, much higher than an acceptable step voltage, so again, aren't / haven't every 2 rods only been sufficient for a kiosk substation?

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The charts functionality allows: • Graphical comparison of deduced soil model with field measurements, for model acceptance • Color-coding of the surface potential gradients based on user-defined thresholds for touch or surface potentials. Any area of the grid can be selected with the mouse for detailed calculations and danger point evaluation • Equipotential contours for surface potentials in either 2-D or 3-D plots, with facilities to examine the graphs from any desired viewing angle • Graphics of touch and step voltage variation along any straight line, with comparison to the safe values computed by the safety assessment module • Graphic indications on the 2-D grid layout of the area being analyzed for touch and step voltages, for easy identification of hazardous locations.