Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
IImmppoorrttaanntt ppooiinnttss
 Fig. shows tthhee eeqquuiivvaalleenntt cciirrccuuiitt ooff ssttrriinngg 
iinnssuullaattoorrss.. 
 LLeett VV11,, VV22 aa...
PPrroobblleemm 22 
AA 33--pphhaassee ttrraannssmmiissssiioonn lliinnee iiss bbeeiinngg 
ssuuppppoorrtteedd bbyy tthhrreeee...
SSOOLLUUTTIIOONN 
• The equivalent circuit of string insulators is the 
same as shown in Fig. It is given that V1 = 8 kV 
...
Problem 3 
• Each line of a 3-phase system is 
suspended by a string of 3 similar 
insulators. If the voltage across the l...
SSoolluuttiioonn 
Fig. shows the equivalent circuit of string 
insulators. If C is the self capacitance of each 
unit, the...
Problem 4 
Each line of a 3-phase system is suspended by 
a string of 3 identical insulators of self-capacitance 
C farad....
The capacitance between each unit 
and line is artificially increased by 
using a guard ring as shown in Fig. 
This arrang...
Insulator problems
Insulator problems
Insulator problems
Insulator problems
Insulator problems
Insulator problems
Insulator problems
Insulator problems
Upcoming SlideShare
Loading in …5
×

Insulator problems

965 views

Published on

transmission and distribution

Published in: Engineering
  • Be the first to comment

Insulator problems

  1. 1. IImmppoorrttaanntt ppooiinnttss
  2. 2.  Fig. shows tthhee eeqquuiivvaalleenntt cciirrccuuiitt ooff ssttrriinngg iinnssuullaattoorrss..  LLeett VV11,, VV22 aanndd VV33 bbee tthhee vvoollttaaggee aaccrroossss ttoopp,, mmiiddddllee aanndd bboottttoomm uunniitt rreessppeeccttiivveellyy.. IIff CC iiss tthhee sseellff--ccaappaacciittaannccee ooff eeaacchh uunniitt,, tthheenn KKCC wwiillll bbee tthhee sshhuunntt ccaappaacciittaannccee..
  3. 3. PPrroobblleemm 22 AA 33--pphhaassee ttrraannssmmiissssiioonn lliinnee iiss bbeeiinngg ssuuppppoorrtteedd bbyy tthhrreeee ddiisscc iinnssuullaattoorrss.. TThhee ppootteennttiiaallss aaccrroossss ttoopp uunniitt ((ii..ee..,, nneeaarr ttoo tthhee ttoowweerr)) aanndd mmiiddddllee uunniitt aarree 88 kkVV aanndd 1111 kkVV rreessppeeccttiivveellyy.. CCaallccuullaattee ((ii)) tthhee rraattiioo ooff ccaappaacciittaannccee bbeettwweeeenn ppiinn aanndd eeaarrtthh ttoo tthhee sseellff--ccaappaacciittaannccee ooff eeaacchh uunniitt ((iiii)) tthhee lliinnee vvoollttaaggee aanndd ((iiiiii)) ssttrriinngg eeffffiicciieennccyy..
  4. 4. SSOOLLUUTTIIOONN • The equivalent circuit of string insulators is the same as shown in Fig. It is given that V1 = 8 kV and V2 = 11 kV. • (i) Let K be the ratio of capacitance between pin and earth to self capacitance. If C farad is the self capacitance of each unit, then capacitance between pin and earth = KC. • Applying Kirchoff’s current law to Junction A,
  5. 5. Problem 3 • Each line of a 3-phase system is suspended by a string of 3 similar insulators. If the voltage across the line unit is 17·5 kV, calculate the line to neutral voltage. Assume that the shunt capacitance between each insulator and earth is 1/8th of the capacitance of the insulator itself. Also find the string efficiency.
  6. 6. SSoolluuttiioonn Fig. shows the equivalent circuit of string insulators. If C is the self capacitance of each unit, then KC will be the shunt capacitance where K = 1/8 = 0·125. Voltage across line unit,V3= 17·5 kV
  7. 7. Problem 4 Each line of a 3-phase system is suspended by a string of 3 identical insulators of self-capacitance C farad. The shunt capacitance of connecting metal work of each insulator is 0·2C to earth and 0·1 C to line. Calculate the string efficiency of the system if a guard ring increases the capacitance to the line of metal work of the lowest insulator to 0·3 C.
  8. 8. The capacitance between each unit and line is artificially increased by using a guard ring as shown in Fig. This arrangement tends to equalize the potential across various units and hence leads to improved string efficiency. It is given that with the use of guard ring, capacitance of the insulator link-pin to the line of the lowest unit is increased from 0·1C to 0·3 C.

×