Formula Used
Temperature corrected resistance: RT = Rref × [1 + α × (T - Tref)] × L
Three phase loss: Ploss = 3 × I² × RT
Single phase or DC loss: Ploss = 2 × I² × RT
Three phase voltage drop: VD = √3 × I × (RT × PF ± XT × sinφ)
Single phase voltage drop: VD = 2 × I × (RT × PF ± XT × sinφ)
Efficiency: Efficiency = Load kW ÷ (Load kW + Loss kW) × 100
How to Use This Calculator
- Select the line system.
- Enter one way route length in kilometers.
- Enter current, voltage, resistance, and reactance.
- Set the power factor and its type.
- Adjust temperature values when conductor heating matters.
- Leave load power blank unless you know the exact delivered kW.
- Enter annual hours and energy cost for yearly loss cost.
- Press calculate, then download CSV or PDF when needed.
Example Data Table
| System |
Length |
Current |
Voltage |
R/km |
X/km |
PF |
Estimated Loss |
| Three phase |
10 km |
120 A |
11000 V |
0.18 ohm |
0.35 ohm |
0.85 lagging |
About 94.57 kW |
| Single phase |
2 km |
45 A |
240 V |
0.42 ohm |
0.08 ohm |
0.95 lagging |
About 4.25 kW |
| Direct current |
1.5 km |
30 A |
120 V |
0.25 ohm |
0 |
1.00 |
About 0.68 kW |
Transmission Line Losses Guide
Transmission line losses matter in every power study. A line carries current through real conductor resistance. That resistance turns useful energy into heat. The result is lower efficiency and higher operating cost. This calculator helps you study that effect with practical inputs. It also estimates voltage drop, annual energy waste, and loss cost.
What the calculator measures
The main result is copper loss. It is also called I squared R loss. For a three phase line, the loss appears in three conductors. For a single phase or direct current line, it appears in the outgoing and return paths. The tool corrects resistance for conductor temperature. This is useful because warm metal has higher resistance. You can keep the default copper coefficient. You can also enter another value for aluminum or another conductor.
Why voltage drop is included
Loss is not the only concern. Long feeders can lose useful voltage along the route. The voltage drop estimate uses resistance, reactance, current, and power factor. Lagging loads usually increase the reactive part of drop. Leading loads may reduce it. The result is an engineering estimate. It is not a replacement for a full load flow model.
Practical use
Use measured current when possible. Use conductor data from a cable table or project drawing. Enter resistance per kilometer for one conductor. Enter reactance per kilometer if it is known. Set length as one way route length. Then choose the phase system. For three phase circuits, enter line to line voltage. For single phase circuits, enter the service voltage. For direct current circuits, enter the DC voltage.
Reading the results
High loss percentage means wasted energy. It can suggest undersized conductors. It may also show a route that is too long. A low efficiency result can justify a larger conductor. A high voltage drop can affect motors, drives, and electronics. Use the annual cost field for planning. It turns technical loss into money. That makes comparison easier. Always check local standards before final design.
Common checks
Compare several conductor sizes. Keep the same current and route length. Review the loss percentage first. Then review voltage drop. A larger conductor often lowers both values. It costs more upfront. It may save more over service life.
FAQs
What is transmission line loss?
It is the power lost as heat when current flows through conductor resistance. The common copper loss formula is based on current squared times resistance.
Why does the calculator ask for one way length?
Conductor tables usually give resistance per conductor per kilometer. The calculator applies the correct conductor count for three phase, single phase, or direct current systems.
What voltage should I enter for three phase?
Enter the line to line voltage. The calculator uses the square root of three in the three phase power and voltage drop equations.
Does power factor change line loss?
Power factor does not change I squared R loss when current is already known. It does affect estimated load power and voltage drop.
Why is temperature correction included?
Conductor resistance rises as temperature increases. Temperature correction gives a more realistic resistance when the line operates hotter than the reference condition.
Can this calculator be used for cable sizing?
It can support early checks. Final cable sizing should also consider ampacity, insulation rating, installation method, protection, short circuit limits, and local rules.
What does negative voltage drop mean?
It can occur with leading power factor. In that case, the reactive component may act like voltage rise in this simplified estimate.
Why enter known load power?
Known load power improves efficiency and loss percentage results. Leave it blank when you want the calculator to estimate load power from voltage, current, and power factor.