- 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 C
_{c}and core to sheath capacitance C_{e}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 = C _{c}**

**Core to sheath capacitance = C _{e}**

_{}

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

C_{eq} = 3C_{c}

Where

C_{eq} = 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

C_{N} = C_{e} + C_{eq}

= C_{e}
+ 3C_{c}

_{}

_{}

### Measurement of capacitance of cable

### ( 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 C
_{e}which are in parallel. - Let us
consider that this capacitor is C
_{1}therefore

C_{1} = 3C_{e}

C_{e} = C_{1} / 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 C
_{2}.

C_{2} = C_{c} + C_{c} / 2 + C_{s}
/ 2

= ( C_{c} + C_{c} / 2 ) + C_{s}
/ 2

= ( 3C_{c}
/ 2 ) + C_{s} / 2

= ½ ( 3C_{c}
+ C_{s} )

= ½ C_{N}

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

Let us consider that this capacitor is equal to C_{3}.

C_{3 }= 2C_{c} + C_{s}

_{}

_{}

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