Calculate Dielectric Strength Breakdown Voltage

[theman408]

I know it has to do something with the Breakdown voltage but I've looked everywhere on my book and i have no idea how to calculate it.

 

[theman408]

i would reallly like to know, without this i can't do my problem.

this is all i need.

 

[rock.freak667]

i would reallly like to know, without this i can't do my problem.

this is all i need.

What is the problem exactly?

 

[theman408]

It's two parallell plates which 12 volts are applied, i already calculated the capacitance with the Area and distance between the plates. Now i must calculate it's dielectric strength.

 

[rock.freak667]

already calculated the capacitance with the Area and distance between the plates. Now i must calculate it's dielectric strength.

The capacitance depends on the area, dielectric strength and distance. How did you find C with only two?

 

[theman408]

Sorry, forgot to specify. i used the formula of

C= eoerS/D

where Eo is the permitivity constant, Er is the relative permitivity which was given in the exercise, S is the area of the surface and D is the distance between the plates.

The Problem is which is the min. dielectric strength that it has.

 

[rock.freak667]

Sorry, forgot to specify. i used the formula of

C= eoerS/D

where Eo is the permitivity constant, Er is the relative permitivity which was given in the exercise, S is the area of the surface and D is the distance between the plates.

The Problem is which is the min. dielectric strength that it has.

but the dielectric strength depends on the fluid between the plates. The dielectric strength which is given by e_0er

 

[theman408]

What would the min. value?

would i have to calculate a new er?

 

[theman408]

and it doesn't specify the fluid, which is kinda of the point, for us to calculate it without looking at the table.

 

[rock.freak667]

and it doesn't specify the fluid, which is kinda of the point, for us to calculate it without looking at the table.

What you are doing sort of looks counter-intuitive to me.

$$C=\frac{\epsilon_0 \epsilon_r A}{d}$$

you used that to get C, yes I get that. You know, A,d,ε₀ and ε_r. You find C.


What you are asking is to get ε (or ε₀ε_r) for the same C, A and d. You will just get back what you used above. Am I missing something ? Does A,d or A change?

 

[theman408]

Exactly that's the formula but what I am asked to calculate is the min. dielectric strength V/M.

They give us Er which i looked up on a table and it's the Dielectric constant of Barium titanate.

 

[rock.freak667]

Exactly that's the formula but what I am asked to calculate is the min. dielectric strength V/M.

V/M ? as in volt per metre as units? If that is the case then those units mean you need to find the electric field strength. Which is simply E=V/d

 

[theman408]

Yep, it's positive right?

 

[rock.freak667]

Yep, it's positive right?

I would think so.

 

[theman408]

The table in the back of my book that gives the different dielectric strengths it's unit is expressed x10^6 V/M and with that formula it only gives me kv/m.

 

[rock.freak667]

The table in the back of my book that gives the different dielectric strengths it's unit is expressed x10^6 V/M and with that formula it only gives me kv/m.

What is the distance between the plates?

 

[theman408]

2x10^-3 m

 

[rock.freak667]

2x10^-3 m

Well the dielectric strength gives the maximum electric field that can be applied before breakdown occurs. I doubt 12V is the maximum voltage, but that would be how to find it.

 

[theman408]

Im in the crossroads in using this formula E= Q/EoArea that yields 7.2 x10^6 V/M or E= V/D that yields 6 kv/M

A= 1m^2
Q= 63.72 uC
D= 2mm
V= 12 V

all the dielectric strength values in the table appear in x10^6 V/M