Q$1$ a$)$ A $440$ V distribution board from which the cable is fed has a fault level of

$(15$ marks$)$

SMVA. Calculate the size of

$($i$)$ XLPE copper cable for $1$ serond fault clearance time $(3$ marks$)$

$($ii$)$ PVC copper cable for $1$ second fault clearance time $(3$ marks$)$

b$)$ Verify that the two $($XLPE and PVC copper cable$)$ sizes $($in $m{m}^2)$ selected in question a$)$ can supply a $3$ phase, $400$ volt, $75$ kW motor over a distance of $50$ m when the cable is directly buried in the ground. The motor has a power factor of $0\mathrm{.}85$ lagging and will be started with a star$-$delta starter $($assume $3$ times starting current$).$ The voltage drop should not exceed $5\%.$ Ignore all derating factors as it is assumed cable is installed under standard conditions with no derating. $(9$ marks$)$

Show all calculations.

Tip:

Isc$=\frac{\text{A}\text{x}\text{K}}{\sqrt[\phantom{2}]{t}}$

Where:

$K=115$ for $PV\frac{C}{?}$ copper cables of $1000$ V rating

$K=143$ for XLPE$/$copper cables of $1000$ V rating

and where:

the conductor cross sectional area in mm

the duration of the fault in seconds

$A=$ the conductor cross sectional area in mm

$t=$ the duration of the fault in seconds

Use data sheets below for XLPE and PVC cables