C
ck_shekel
Hi all.
First time on the forum, but have enjoyed reading many ofthe threads, thanks. I am looking for some advice on a fault from a TT systemand would greatly appreciate any input.
History, my wife and I are volunteering in Africa for a fewyears. The charity I am helping does not have an electrician and we have been askedus to stay for as long as possible. The support I have here for this type ofproblem is limited. Our site is fed from our own 2 X 200KVA Transformers with abackup 265KVA Generator (With load shedding). We have 2 apartments off site,but within 60 to 80 Meters, which is fed by a separate Transformer owned by thesupply authority. This Transformer feeds around 40 other homes within thecomplex.
When I arrive a cable had been ran from our site to the apartmentsand 2 auto change over units installed with Over & Under Voltage Relays togive the apartments a supply via us when the city power goes down. They used a4 Core Cable.
First thing I did when we arrived was to undertake anInspection of all our properties. These apartments had no earth, none, no earthrod and only RCD protection on the Fridge Sockets. We replaced the DB’s withinthe apartments (4 of including 300m Amp Time Delay & 30m Amp RCD’s) andinstalled 4 of 2.4 Meter earth rods per apartment. When supplied via ourTransformer the reading of Ze is 2.24 Ohms, which is the best reading I havehad on a TT system (I am using my Meggar Multi Tester which I bought in the UK,this does not have the Earth Rod option on it so readings are taken using theEarth Loop Function). When supplied via the Supply Authority the reading fluctuatesbetween 90 and 100 Ohms at the time of installation. I contact them and askedthem to check their earthly arrangements, not sure if they did this though. Iam checking the earth rods every 3 months and on Friday the following voltages weretaken on the system: -
Supply Authority=
L1-L2=404, L1-L3=403, L2-L3=404
L1-N=237, L2-N=235, L3-N=235
L1-E=394, L2-E=398, L3-E=8
N-E=225
Our Transformers=
L1-L2=406, L1-L3=407, L2-L3=411
L1-N=231, L2-N=233, L3-N=234
L1-E=233, L2-E=233, L3-E=232
N-E=1
Ze=
L1= 2.24 Ohms
L2= 1.93 Ohms
L3= 1.91 Ohms
Could the supply neutral maybe burnt out within thetransformer or their Main Panel and the fact that the loads maybe be close to balancedacross the 40 to 50 homes fed from the Transformer has stop anyone noticing thefault? I am sure that the other homes do not have earth rods.
This still does not explain the readings from Line to Earth,unless they have an earth rod connected to the star point in the Transformer?
Any ideas would be greatly appreciated. Thank you.
First time on the forum, but have enjoyed reading many ofthe threads, thanks. I am looking for some advice on a fault from a TT systemand would greatly appreciate any input.
History, my wife and I are volunteering in Africa for a fewyears. The charity I am helping does not have an electrician and we have been askedus to stay for as long as possible. The support I have here for this type ofproblem is limited. Our site is fed from our own 2 X 200KVA Transformers with abackup 265KVA Generator (With load shedding). We have 2 apartments off site,but within 60 to 80 Meters, which is fed by a separate Transformer owned by thesupply authority. This Transformer feeds around 40 other homes within thecomplex.
When I arrive a cable had been ran from our site to the apartmentsand 2 auto change over units installed with Over & Under Voltage Relays togive the apartments a supply via us when the city power goes down. They used a4 Core Cable.
First thing I did when we arrived was to undertake anInspection of all our properties. These apartments had no earth, none, no earthrod and only RCD protection on the Fridge Sockets. We replaced the DB’s withinthe apartments (4 of including 300m Amp Time Delay & 30m Amp RCD’s) andinstalled 4 of 2.4 Meter earth rods per apartment. When supplied via ourTransformer the reading of Ze is 2.24 Ohms, which is the best reading I havehad on a TT system (I am using my Meggar Multi Tester which I bought in the UK,this does not have the Earth Rod option on it so readings are taken using theEarth Loop Function). When supplied via the Supply Authority the reading fluctuatesbetween 90 and 100 Ohms at the time of installation. I contact them and askedthem to check their earthly arrangements, not sure if they did this though. Iam checking the earth rods every 3 months and on Friday the following voltages weretaken on the system: -
Supply Authority=
L1-L2=404, L1-L3=403, L2-L3=404
L1-N=237, L2-N=235, L3-N=235
L1-E=394, L2-E=398, L3-E=8
N-E=225
Our Transformers=
L1-L2=406, L1-L3=407, L2-L3=411
L1-N=231, L2-N=233, L3-N=234
L1-E=233, L2-E=233, L3-E=232
N-E=1
Ze=
L1= 2.24 Ohms
L2= 1.93 Ohms
L3= 1.91 Ohms
Could the supply neutral maybe burnt out within thetransformer or their Main Panel and the fact that the loads maybe be close to balancedacross the 40 to 50 homes fed from the Transformer has stop anyone noticing thefault? I am sure that the other homes do not have earth rods.
This still does not explain the readings from Line to Earth,unless they have an earth rod connected to the star point in the Transformer?
Any ideas would be greatly appreciated. Thank you.