Voltage Drop Calculator - Electrical Engineering

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. 90^oC.

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:

Single phase circuit voltage drop formula:

DC circuit voltage drop formula:

where:
	V_D	:	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 Size	Resistance (ohm/km)	Reactance (ohm/km)
1	2.5	9.45	0.0932
2	4	5.88	0.0875
3	6	3.93	0.0837
4	10	2.33	0.0785
5	16	1.47	0.0761
6	25	0.927	0.0768
7	35	0.669	0.0743
8	50	0.494	0.0739
9	70	0.342	0.0726
10	95	0.247	0.0708
11	120	0.196	0.0705
12	150	0.16	0.0709
13	185	0.128	0.0712
14	240	0.0987	0.0703

AC Medium Voltage 3kV cable

No.	Cable Size	Resistance (ohm/km)	Reactance (ohm/km)
1	10	2.33	0.107
2	16	1.47	0.102
3	25	0.927	0.0949
4	35	0.668	0.0905
5	50	0.494	0.0878
6	70	0.342	0.0836
7	95	0.247	0.0806
8	120	0.196	0.0786
9	150	0.16	0.0768
10	185	0.128	0.0753
11	240	0.0986	0.0733

AC Medium Voltage 6kV cable

No.	Cable Size	Resistance (ohm/km)	Reactance (ohm/km)
1	10	2.33	0.115
2	16	1.47	0.11
3	25	0.927	0.102
4	35	0.668	0.0972
5	50	0.494	0.094
6	70	0.342	0.0891
7	95	0.247	0.0855
8	120	0.196	0.0831
9	150	0.159	0.081
10	185	0.128	0.0792
11	240	0.0984	0.0773

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, I_FL = 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

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

V_D (%) = 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, I_s = 5.5 * I_FL = 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

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

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