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3 Phase Motor Control Unit https://forumelectrical.com/vfd-control-circuit-testing-step-by-step-procedure-for-reliable-drive-operation/

Forward-reverse control circuit of a three-phase motor using contactors KM1 and KM2, fuses, overload relay, and push buttons, featuring electrical interlocking to prevent simultaneous operation and ensure safe, reliable motor direction control.
#motor #motors #electricalmotor #electricalmotors #electricmotor #forwardcontrol #reversecontrol #feedbackcontrol
1. Cable Design https://forumelectrical.com/cable-size-calculator/

Cable design means selecting the correct cable size and type so it can safely carry current without overheating, excessive voltage drop, or damage during faults.

Main factors in cable design:

Load current

Voltage drop

Short circuit capacity

Derating factors

Installation method

Ambient temperature

Type of insulation

2. Load Current (Current Carrying Capacity) Load current is the maximum current a cable must carry continuously without overheating.

Formula

I=PVI = \frac{P}{V}I=VPWhere

I = Current (A)

P = Power (W)

V = Voltage (V)

For Single Phase

I=PVXPFI = \frac{P}{V \times PF}I=VxPFPFor Three

Phase

I=P3×V×PFI = \frac{P}{\sqrt{3} \times V \times PF}I=3

×V×PFPWhere PF = Power Factor

Example

Power = 10 kW

Voltage = 400 V

PF = 0.8

I=100001.732×400×0.81 = \frac{10000}{1.732 \times 400 \times 0.8}I=1.732×400×0.8100001=18AI = 18

AI=18ASo cable must carry at least 18 A.

3. Voltage Drop

Voltage drop is the reduction in voltage along the cable due to resistance and reactance.

Formula (Single Phase)

Vd=2×I×L×RV_d = 2 \times I \times L \times RVd

=2×I×L×RWhere

I = Current (A)

L = Length (m)

R = Resistance (Ω)

Formula (Three Phase)

Vd=3×I×L×(Rcos+Xsin)V_d = \sqrt{3} \times I

\times L \times (R\cos\phi + X\sin\phi)Vd=3

×I×L×(Rcos+Xsino) Acceptable Voltage Drop

Typical limits:

Lighting circuits → 3%

Power circuits 5%

4. Short Circuit Capacity

Short circuit capacity is the ability of a cable to withstand fault current without damage.

Formula

Isc=kxStl_{sc} = \frac{k \times S}{\sqrt{t}}Isc=tkxS Where

Isc = Short circuit current (A)

S = Conductor area (mm²)

t = Fault duration (seconds)

k = Material constant

Typical k values:

Materialk valueCopper143Aluminium94

Example

Copper cable = 25 mm²

Fault time = 1 s

Isc=143×2511_{sc} = \frac{143 \times 25}{\sqrt{1}}Isc =1143×25lsc=3575AI_{sc} = 3575 Alsc=3575A5.

Derating Factors

Derating factors reduce cable capacity when conditions are not ideal.

Reasons for derating:
High ambient temperature

Cables grouped together

Underground installation

Soil thermal resistivity

Cable insulation type

Example

Cable rating = 100 A

Ambient temperature factor = 0.9

Grouping factor = 0.8

Adjusted Current=100×0.9×0.8Adjusted\ Current =

100 \times 0.9 \times

0.8Adjusted Current = 100 * 0.9 * 0.8 = 72A =

72A-72AActual allowable current = 72 A

6. Installation Methods

7. Types of Power Cables

8. Cable Selection Steps

#CableSelection #Cable #cables #wire #Voltage #VoltageDrop
https://forumelectrical.com/cable-size-calculator/