Home » Calculations » Voltage Drop Calculator

Voltage Drop Calculator

Below voltage drop calculator tool will help to quickly check voltage drop on a cable run. The input required is voltage level, load rating, and cable parameters. The type of cable used for calculation is 50Hz XLPE/SWA in accordance with IEC 60502 or IEC 60092. The result of voltage drop calculator for 3 cores cable data (i.e. resistance and reactance) can be applied on 4 cores cable. Also, note that cable resistance implemented in the calculation has been converted to XLPE operating temperature viz. 90oC.

INPUT:
RESULT
Fulll Load Current: A
Cable Resistance: Ohm/km
Cable Reactance: Ohm/km
Voltage Drop: %

Voltage Drop Calculator Input

  • Select System: Choose from dropdown list AC MV 3 Phase, AC LV 1 Phase, AC LV 3 Phases or DC
  • System Voltage: Choose from dropdown list voltage with respect to system AC 6kV, AC 3kV, AC 400V, AC 380V, AC 230V, AC 220V, DC 110V, DC 24V or DC 12V
  • Load Rating: Input load rating in kW or kVA. Should kVA is used, power factor is 1 (unity) in next step
  • Power factor: Power factor of AC load, use 1 (unity) for DC load
  • Number of Cable Run: How many cable in parallel
  • Select Cable Size (sqmm): Choose cable size (i.e. 3C x 90) in sq mm
  • Cable Length: Input cable length in meter

Voltage Drop Formula

The voltage drop will be calculated using the following formulas:

Thee-phase circuit voltage drop formula:

AC-three-phase-voltage-drop-formulas

Single phase circuit voltage drop formula:

AC-single-phase-voltage-drop-formulas

DC circuit voltage drop formula:

DC-voltage-drop-formulas
where:
VD:Voltage drop, in volts
cosΦ:Load power factor
R:Resistance of cable, in ohms per phase per 1000m
X:Reactance of cable, in ohms per phase per 1000m
I:Load current, in amperes
L:Total length of cable, in meter

Cable resistance and reactance

Following cable resistance and reactance is applied to calculation:

  • Low voltage AC cable and DC cable
No.Cable SizeResistance (ohm/km)Reactance (ohm/km)
12.59.450.0932
245.880.0875
363.930.0837
4102.330.0785
5161.470.0761
6250.9270.0768
7350.6690.0743
8500.4940.0739
9700.3420.0726
10950.2470.0708
111200.1960.0705
121500.160.0709
131850.1280.0712
142400.09870.0703
  • AC Medium Voltage 3kV cable
No.Cable SizeResistance (ohm/km)Reactance (ohm/km)
1102.330.107
2161.470.102
3250.9270.0949
4350.6680.0905
5500.4940.0878
6700.3420.0836
7950.2470.0806
81200.1960.0786
91500.160.0768
101850.1280.0753
112400.09860.0733
  • AC Medium Voltage 6kV cable
No.Cable SizeResistance (ohm/km)Reactance (ohm/km)
1102.330.115
2161.470.11
3250.9270.102
4350.6680.0972
5500.4940.094
6700.3420.0891
7950.2470.0855
81200.1960.0831
91500.1590.081
101850.1280.0792
112400.09840.0773

How to calculate voltage drop ?

Example 1 - MV motor feeder during normal operation

A 1100 kW induction motor is connected to a 6 kV 3-phase 50 Hz supply. The motor has the following performance data:

  • Power factor is reading from manufacturer motor nameplate: 0.83
  • Cable length from electrical SWG/MCC to motor: 350 m
  • Cable size: 3C x 120 sqmm in 1 run

Step 1: Full load current, IFL = 1100 / 1.73 / 6 / 0.83 = 127.67 A

Step 2: Derive 3C x 120 sqmm 6kV cable resistance and reactance from table:

R = 0.196 (Ω/km)

X = 0.0831 (Ω/km)

Step 3: Voltage drop of 3 phase motor feeder using above formula

VD = 1.73 * 127.67 * (0.196 * 0.83 + 0.0831 * 0.56) * 350 / 1000 = 16.17 V

VD (%) = 16.11 / 6000 *100 = 0.269%

Example 2 - MV motor feeder during startup

Using the same motor as example 1, we will calculate voltage drop during motor starting.

  • Power factor during starting: 0.2
  • Starting current factor: 5.5 for MV motor

Step No. 1: Starting current, Is = 5.5 * IFL = 5.5 * 127.67 = 702.23 A

Step No. 2: Using same data as example 1

Step No. 3: Voltage drop of 3 phase motor feeder using above formula

VD = 1.73 * 702.23 * (0.196 * 0.2 + 0.0831 * 0.98) * 350 / 1000 = 51.29 V

VD (%) = 51.29 / 6000 *100 = 0.85%