E2: Ohm’s Law — A level

An engineer is choosing a cable for a high voltage transmission line. Here are some parameters for the design.

• Current rating: 500A. This is the largest current it will carry.
• Length: 100km
• Maximum voltage drop allowed: 1000V
• Maximum mass that the pylons can hold: 8,000kg / km

The copper cable sizes to choose from are:

• 630mm², mass 5,670kg / km
• 800mm², mass 7,200kg / km
• 1000mm², mass 9,000kg / km
• 1200mm², mass 10,800kg / km
• 1400mm², mass 12,600kg / km

The aluminium cable sizes to choose from are:

• 800mm², mass 2,240kg / km
• 1000mm², mass 2,800kg / km
• 1200mm², mass 3,360kg / km
• 1400mm², mass 3,920kg / km
• 1600mm², mass 4,480kg / km

Your task is to select one of the cables for this transmission line. You also need to give reasons to justify your selection.

1. Calculate the highest resistance allowed for the cable.
2. Use this resistance calculator to help you work out which cables are usable for the resistance you calculated.
3. Select one of the cables that will meet the requirements of the job.

Write out all calculations and working, and your reasons for your final selection.