HW3-2016

BSE515 HW #3

Due on 10 Nov. 2016

A 70m-long 4/c XLPE/SWA/PVC cable is installed on a tray in an electrical duct to supply balanced loads in a computer centre. The cable is protected by fuses to BS88 Part 2/6, and fed from a main LV switchboard at the ground level. The ambient temperature in the duct is 35o C. It is noted from a previous survey that the harmonic current was very rich. Fig. Q1 shows the harmonic content of the current in one phase with the fundamental current 120A and the displacement power factor 0.95.

1.Estimate phase current, neutral current, and their total harmonic distortion;

2.Determine the size of the cable

3.Check whether the cable is subject to overheating problems or not.

Fig. Q1

Circuit Type Voltage drop Conditions Loss (%) Limit

Main Circuit -- Alternative requirement is

available

0.5%

Feeder Circuit 2.5% Not for PFC circuit 2.5%

Sub-main Circuit 1.5%

Non-residential building – circuit

length <100m

1.5%

1.5%

Non-residential building – circuit

length >100m

2.5%

(sub-main circuit

+ 32A –above

final circuit) 1.5% Residential building 2.5%

Final Circuit 2.5% Circuit rating>32A 1%