## 27/03/2021

### Capacitance of Three Core Cable

• Let us consider the three core belted cable.
• As there is potential difference exists between core to core of cable and core to sheath of cable, electrostatic field set up between them.
• There is core to core capacitance Cc and core to sheath capacitance Ce exists in the three core cable.
• The core to core capacitance is delta connected whereas core to sheath capacitance is star connected.

Core to core capacitance = Cc

Core to sheath capacitance = Ce

• The three core to core delta connected capacitance is converted into equivalent star connection.

Ceq = 3Cc

Where

Ceq = Equivalent star connection of delta connected core to core

Capacitance

• There, the total capacitance is equal to parallel combination of core to sheath capacitance and equivalent star connection of core to core capacitance of cable.
• The capacitance between core to neutral

CN = Ce + Ceq

= Ce + 3Cc

### ( 1 ) Three cores bunched together

• The three cores of cable are bunched together and capacitance is measured between cores and sheath of cable.
• As the three cores are bunched together, there is no capacitance between cores. There exists capacitance between core and sheath Ce which are in parallel.
• Let us consider that this capacitor is C1 therefore

C1 = 3Ce

Ce = C1 / 3…….. ( 1 )

### ( 2 ) Capacitance between two cores is measured with third core connected to the sheath

• The capacitance between two cores is measured with the third core connected to the sheath.
• This eliminated one core to sheath capacitance. Let us consider that this capacitance is C2.

C2 = Cc + Cc / 2 + Cs / 2

= ( Cc + Cc / 2 ) + Cs / 2

= ( 3Cc / 2 ) + Cs / 2

= ½ ( 3Cc + Cs )

= ½ CN

### ( 3 ) Capacitance between two cores shorted with the sheath and third core

Let us consider that this capacitor is equal to C3.

C3 = 2Cc + Cs

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