Question $1$

A $30-kW,3-$phase,$400-V$ resistance oven is to employ nickel$-$chrome strip for the three star$-$connected heating elements. If the wire temperature is to be $1,100C$ and that of the charge to be $700C,$ estimate a suitable length of the strip. Assume emissivity $=0\mathrm{.}9$ and radiating efficiency to be $0\mathrm{.}5$ and resistivity of the strip material is $101\mathrm{.}6{10}^{-8}-m.$