Electric field distribution and insulators, Distribution systems

1. Electric Field Distribution

Electric field is the force experienced by unit positive charge.

Electric field distribution is important in transmission lines and insulators.

Non-uniform electric field causes insulation failure.

Electric Field Formula

E = V / d

Where:
E = Electric field (V/m)
V = Voltage
d = Distance

Electric Field Around Conductor

E = (V / r ln(D/r))

Where:
r = conductor radius
D = distance between conductors

Electric field is maximum at conductor surface.

Maximum electric stress occurs at conductor surface.

2. String Insulators and Voltage Distribution

Suspension insulators are used in high voltage transmission lines.

Voltage distribution across insulator string is non-uniform due to shunt capacitance.

Disc nearest to conductor has highest voltage.

String Efficiency

String Efficiency (%) = (Total voltage across string) / (n × voltage across lowest unit) × 100

Where:
n = number of insulator discs

Maximum efficiency = 100%
Practical efficiency = 70% to 90%

Methods to Improve String Efficiency

Use guard ring
Increase distance from tower
Reduce shunt capacitance

3. Types of Insulators

Type	Voltage Level	Application
Pin Insulator	Up to 33 kV	Distribution lines
Suspension Insulator	Above 33 kV	Transmission lines
Strain Insulator	High voltage	Dead end towers
Shackle Insulator	Low voltage	Distribution lines

Insulator Materials

Porcelain
Glass
Polymer

Insulator Failure Types

Flashover → discharge over surface
Puncture → breakdown through material

Flashover is less dangerous than puncture.

4. Distribution Systems

Distribution system delivers power from substation to consumers.

Primary distribution → 11 kV
Secondary distribution → 415 V
Domestic supply → 230 V

Components of Distribution System

Feeder → carries power from substation
Distributor → supplies consumers
Service mains → connects consumer

Feeder Characteristics

Current is constant
Voltage drop varies

Distributor Characteristics

Current varies
Voltage drop is important

5. Types of Distribution Systems

Type	Reliability	Cost
Radial	Low	Low
Ring Main	High	Medium
Interconnected	Very High	High

6. Comparison: Overhead vs Underground

Parameter	Overhead	Underground
Cost	Low	High
Maintenance	Easy	Difficult
Reliability	Low	High
Fault detection	Easy	Difficult

7. Important GATE Exam Points

Electric field is maximum at conductor surface
Voltage distribution across insulator string is non-uniform
String efficiency is less than 100%
Disc nearest conductor has highest voltage
Radial distribution has lowest reliability
Interconnected system has highest reliability
Pin insulator used up to 33 kV
Suspension insulator used above 33 kV

8. Quick Revision Summary

Electric field causes insulation stress
Insulators prevent leakage current
Voltage distribution in string is non-uniform
Distribution system delivers power to consumers
Radial system is cheapest
Interconnected system is most reliable