Ohm’s Law for Power Stations: The Formula, Table and Worked Examples
Ohm’s Law states that voltage across a circuit is directly proportional to the current flowing through it, with resistance as the constant of proportionality. The formula is V = I x R, rearranged as I = V / R or R = V / I. On a power station it is the calculation behind cable sizing, voltage drop on long feeders, transmission loss, and the thermography inspection that finds a hot joint before it fails. Combined with the power relationship P = V x I, it yields twelve usable forms.
Ohm’s Law and Power Formula Reference Table
| Quantity | Ohm’s Law Form | Power Form | Derived Form |
| Voltage (V) | V = I x R | V = P / I | V = square root of (P x R) |
| Current (I) | I = V / R | I = P / V | I = square root of (P / R) |
| Resistance (R) | R = V / I | R = V squared / P | R = P / I squared |
| Power (P) | P = V x I | P = V squared / R | P = I squared x R |
Voltage is in volts, current in amperes, resistance in ohms, and power in watts. For AC circuits, multiply the power expressions by the power factor to obtain real power, and by 1.732 as well for three phase systems.
Why This Decides Your Transmission Voltage
The I squared R term is the reason power is transmitted at medium and high voltage. Delivering 1 MW at 400 V and 0.8 power factor draws 1,804 amperes. The same 1 MW at 11 kV draws 65.6 amperes. Because losses rise with the square of current, the low voltage option wastes roughly 756 times more energy in the conductor.
The same logic governs site cabling. A 500 ampere feeder with 0.02 ohms of total loop resistance drops 10 volts and dissipates 5 kW as heat, continuously. Undersized cable is not a one time saving, it is a permanent parasitic load on the plant, which is why power plant engineering treats conductor sizing as an economic calculation rather than a code minimum.
Resistance also creates the failure mode. A loose or corroded termination adds milliohms that dissipate as heat at the joint, which is why infrared thermography surveys belong in every preventive maintenance schedule. A connection running hotter than its neighbours is Ohm’s Law announcing a fault before the protection does.
Frequently Asked Questions
What is the formula for Ohm’s Law?
V = I x R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. Rearranged, I = V / R and R = V / I.
How do I calculate power loss in a cable?
Use P = I squared x R. Multiply the square of the current by the total loop resistance of the conductor. A 500 ampere circuit through 0.02 ohms loses 5 kW.
Does Ohm’s Law apply to AC systems?
Yes, but with impedance in place of pure resistance, and with power factor applied to any power calculation. Ignoring the power factor term overstates real power on motor driven sites.
Ohm’s Law is where every load study starts, and where most sizing errors begin. USP&E Global has applied it across 150+ projects in 35+ countries, from EPC construction through the generating equipment in our live inventory, and the outcomes are documented in our client references. Transmission and distribution loss data by country is published by the World Bank, the African Development Bank, and the U.S. Energy Information Administration.
Ready to Power Your Project? Talk to USP&E’s Engineers Free.
USP&E Global offers a complimentary 4-hour engineering consultation for qualified power station, EPC, and O&M projects. Whether you are in early feasibility or ready to mobilize, our team of 350+ engineers across 35+ countries is ready to guide your project to success with speed and without excuses.
USP&E Global. Powering Possibility. Built for the Frontier.
ISO 9001:2015 | ISO 45001:2018 | 150+ Projects | 35+ Countries | Zero Lawsuits