## 27/03/2021

### Capacitance of Three Core Cable

In this theory, formula for capacitance of three core to core cable and core to sheath is given.

# Capacitance of Three Core Belted 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 = Cand Core to sheath capacitance = Ce

• The three cores 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
• Therefore, 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

## Measurement of capacitance of cable

### 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 )

### 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

### 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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