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Thread: Retrofitting & Upgrade to an Old 3 Phase Installation - Part 1

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    Retrofitting & Upgrade to an Old 3 Phase Installation - Part 1

    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 m 13.2 Ka 26 m
    B - W 20.0 Ka 23 m 19.9 Ka 21 m
    W - R 19.9 Ka 22 m 13.3 Ka 26 m
    PSC (Phase - Neutral) Test 1 Test 2
    kA Loop Impedance kA Loop Impedance
    R - N 7.8 Ka 31 m 7.6 Ka 29 m
    B - N 7.8 Ka 33 m 11.6 Ka 24 m
    W - N 7.8 Ka 33 m 7.7 Ka 27 m
    PEFC (Phase - Earth) Test 1 Test 2
    kA Earth Loop Impedance kA Earth Loop Impedance
    R - E 11.7 Ka 19 m 11.4 Ka 17 m
    B - E 11.8 Ka 21 m 11.4 Ka 21 m
    W - E 11.7 Ka 22 m 11.4 Ka 22 m
    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.

    Last edited by Dave A; 22-Jun-18 at 01:26 PM. Reason: fixed table layout

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    Hi Carli

    Looking at your loop impedance readings I would safely say that your earth is not connected to the star point of the transformer ( maybe I am misreading , have assume Mega ohm) - I would first check the transformer neutral earth connection and then ensure that the earth from the transformer to the meter room is continuous.Also check that the neutral is continuous

    With the earth neutral connection missing it could play around with all the other readings .

    If you can check it with another meter - Maybe your meter is playing up - Had a contractor during the week getting strange readings and it was a meter problem.

    Is your tester rated to test PSCC for 3 phase and above 100Amp . What size cable and length is installed , what make and size of C/Breaker is at the point of control.

    With regards to EDS - We were instructed by a client to use EDS and felt that they were nominated suppliers , placed the order in that way and then argued when the DB was ready over payment methods.The client would not certify the DB for payment until on site due to the risk of transport and EDS would not release the DB until full payment even though they were doing the transporting.Like normal the DB was already late and there was no time to arrange credit facilities. It annoy me to no end that they accepted the order , built the DB and only then decided to let me know that they would not release the DB.We had no part in the design or accepting the DB at factory testing level.
    We ended up paying for the DB and the client taking 90 Days to pay.
    Bearing in mind that the client would not pay our transport to witness the DB in the factory and preferred to do it himself - We are based in PE- The DB arrived on site , 650 Amp main switch , with din rail mounted wago 20 Amp neutral connections , the neutral connections where not connected to the incoming neutral bar.Client ended up having to pay us to correct the neutrals since they had accepted the DB.
    All in all the DB was good , prices where good - took a bit of time to get workshop drawings. If we had to use them again I would insist on inspecting the DB before it leaves and make sure that we understand each other over the payment terms.

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    Morning All

    My understanding is that the PSC and loop tests should be done with the loads switched off, the variance in your readings compared to your calculated values could well be the result of having the load connected while performing these tests (harmonics interfering and hence these test are done with out the loads connected)

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    Hi Sean & GCE with regards to your comments above:
    1) The loop impedances are in milli ohm.
    2) Have checked my meter on another installation, and the calculated and actual PSC and PEFC correlate very well, with the load isolated. (Thanks Sean)
    3) So looks like the harmonics and power factor significantly impacts the kA readings.

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    SeanM (03-Jul-18)

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    Hi Carli

    Thank you for the feedback it is always good to get closure as such.

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