Earth loop impedance calculations In this assignment we are attempting to calculate earth loop impedance values of a distribution system of a factory the diagram of which is shown below. We were asked to calculate calculate the values values of earth loop impedance impedance at the motor, socket and sub distribution board in order to this we must add the values of impedance from other parts of the circuit also and other calculat ions must also be undertaking which can be seen below also. For the purpose of our calculations the value of circuit breakers and bus-bars are negligible.
1-Oct-2010
Brendan Stack
Page 1
Transformer
impedance:
For the transformer from the information I acquired from the diagram the values of resistance and reactance which were got from our tables are as follows: R = 2.12m and X =11.61m. Please note for the sake of calculations we are using complex notation thus impedance for the transformer is 2.12m + j11.61m
Feeder cables impedance: For the feeder cables from the information I acquired from the diagram the values of resistance and reactance which were got from our tables are as follows: R = 0.446m and X = 0.356mthus for a 20 metre run in length we get
As there are three conductors in each phase we must apply the following formula
1st level distribution impedance: For the 1st level distribution from the information I acquired from the diagram the values of resistance and reactance which were got from our tables are as follows: R = 0.446m and X = 0.167m thus for a 90 metre run in length we get
For ease of future calculation I shall now add the three series impedances together to give us the value of resistance at point A which is shown in our diagram above.
1-Oct-2010
Brendan Stack
Page 2
(a) Earth loop impedance at the motor For the impedance at the motor from the information I acquired from the diagram the values of resistance and reactance which were got from our tables are as follows: R = 16.86m and X = 0.22m thus for a 50 metre run in length we get
We shall now add the impedances from our earlier calculations to get a total value therefore total earth loop impedance at the socket is equal to.
Z = 888.233m + j40.013m or 0.889133 @ 2.57 degrees
(b) Earth loop impedance at the socket For the impedance at the socket from the information I acquired from the diagram the values of resistance and reactance which were got from our tables are as follows: R = 27.53m and X = 0.23m thus for a 60 metre run in length we get
We shall now add the impedances from our earlier calculations to get a total value therefore total earth loop impedance at the socket is equal to.
Z = 1.697033 + j0.042813 or 1.69757 @ 1.445 degrees
1-Oct-2010
Brendan Stack
Page 3
(c) Earth loop impedance at the sub-distribution board For the impedance at the sub-distribution board from the information I acquired from the diagram the values of resistance and reactance which were got fro m our tables are as follows: R = 2.135m and X = 0.182m thus for a 35 metre run in length we get
We shall now add the impedances from our earlier calculations to get a total value therefore total earth loop impedance at the socket is equal to.
Z = 119.958m + j0.035383 or 1.2506 @ 16.434 degrees
