Retrofitting and Upgrade of an old 3 Phase Installation to become compliant with SANS 10142 - Part 1
I have taken on a project to retrofit an old installation and have a couple of questions that I would appreciate some help with.
Background Information:
1) The Supply is being upgraded from a 300 Amps to 600 Amps.
2) Council transformer is rated at 800 kVA, 420 Volt, Impedance Volts Ratio 4.65%.
3) Manual calculations as per SANS show that I have a phases to phase fault level of 23.66 kA at the transformer, 8.56 kA at the Point of Control (before upgrade) and 12.57 kA at the POC (after upgrade)
4) The supply is a TN-C-S with the supply cable armouring earthed on both the supply and load sides.
5) Earth Electrode is encased in a concrete slab and is looped back to the board.
6) The main board supplies a meter room (owned by the body corporate) which then distributes power to 12 factories.
7) The load is very diverse and includes lots of welding equipment, huge metal bending and cutting machinery, large printing machines etc.
8) A typical snapshot of the load is R = 252 Amps, W = 218 Amps, B = 195 Amps, Power factor 0.75, THD (Voltage) = 1.3 %, THD (Current) = 4.6 %
Questions:
1) I used my multi function tester to confirm the calculated current fault level at the POC before the upgrade and was surprised to find that the measured readings varied significantly from my calculated readings as shown in the table below. The tests were performed with the
load connected. I suspect that the readings might be affected by the harmonics and the power factor of the system but would appreciate your comments on this. I am planning on redoing the tests on a weekend with the majority of the load off and comparing the results.
PSC Measurements 08 June 2018 PSC (Phase - Phase) Test 1 Test 2 kA Loop Impedance kA Loop Impedance R - B 19.7 Ka 20 mΩ 13.2 Ka 26 mΩ B - W 20.0 Ka 23 mΩ 19.9 Ka 21 mΩ W - R 19.9 Ka 22 mΩ 13.3 Ka 26 mΩ PSC (Phase - Neutral) Test 1 Test 2 kA Loop Impedance kA Loop Impedance R - N 7.8 Ka 31 mΩ 7.6 Ka 29 mΩ B - N 7.8 Ka 33 mΩ 11.6 Ka 24 mΩ W - N 7.8 Ka 33 mΩ 7.7 Ka 27 mΩ PEFC (Phase - Earth) Test 1 Test 2 kA Earth Loop Impedance kA Earth Loop Impedance R - E 11.7 Ka 19 mΩ 11.4 Ka 17 mΩ B - E 11.8 Ka 21 mΩ 11.4 Ka 21 mΩ W - E 11.7 Ka 22 mΩ 11.4 Ka 22 mΩ The calculated Prospective phase to phase fault current = 8.562 kA
Q2) I have measured the earth electrode resistance using the stake less method and found that the reading varied between 0.5 - 1.5 ohms. The COC will require a reading of less than 1 ohms as the supply is greater than 150 Amps. Once again I assume that it may be some harmonic current flowing in the earth electrode that is impacting this measurement. I plan to switch off the supply before council upgrades the cable in order to do the more traditional 3 pole fall of potential test. Would it be acceptable to also include the cold water piping and fire fighting water supply pipework in this measurement? Any comments on this would be highly appreciated.
Q3) Has any members used the following board manufacturers and if so what has been your experience with these companies: (I hope that I am allowed to ask this question on the forum)
EDS Switchboards, Switchboard Manufacturers Cape, Nedlog, J2D. Alternatively could you recommend some additional board manufacturers.
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