Method and system of non-intrusively monitoring the mixture ratio of a gas mixture having at least two components

1. A method of monitoring the proportion X of a component in a gaseous mixture, said gaseous mixture having two components, a first component which is SF 6 and a second component selected from the group consisting of N 2 and CF 4 , and being contained in an electrical switchgear enclosure, said method comprising the steps of:

a) measuring the pressure P, the temperature T, and the density ρ of the gas mixture contained in the electrical switchgear enclosure by means of sensors mounted on said enclosure,

b) determining said proportion X by processing the measured values of pressure P, temperature T and density ρ in a data-processing unit which delivers as output the proportion X determined by solving the following equations:

P (SF 6 ) =A 1.ρ(SF 6 ) +A 2. (ρ(SF 6 )) 2 +A 3.(ρ(SF 6 )) 3

and

P (N 2 )= A 4.ρ(N 2 ),

P=X.P (N 2 )+(1− X ). P (SF 6 ),

ρ=ρ(N 2 )+ρ(SF 6 ),

or

P (CF 4 )= A 4. ρ(CF 4 ),

P=X.P (CF 4 )+(1− X ). P (SF 6 ),

ρ=ρ(CF 4 )+ρ(SF 6 )

where A 1 , A 2 , A 3 and A 4 are functions of T,

P(SF 6 ) and P(N 2 or CF 4 )are the partial pressures of SF 6 and (N 2 or CF 4 ),

ρ(N 2 ), ρ(CF 4 ) and ρ(SF 6 ) are the densities of N 2 , CF 4 and SF 6 ,

and wherein step a) is carried out without tapping said gas mixture.

2. The method according to claim 1 , in which said electrical switchgear enclosure is a high-voltage switchgear.

3. The method according to claim 1 , in which said electrical switchgear enclosure is a gastight enclosure.

4. The method according to claim 1 , in which said proportion X of a component in the mixture is determined by the data-processing unit which stores a data table in a memory, said data table containing a plurality of data items representative of various proportions of said component in correspondence with data items representative of various measurements of the pressure P, of the temperature T, and of the density ρ of the gas mixture containing said component.

5. The method according to claim 1 , wherein the density is measured by means of a vibrating-blade sensor.

6. The method according to claim 1 , wherein the density is measured by means of a capacitor whose capacitance is a function of the permittivity of the gas mixture.

7. The method according to claim 1 , wherein the density is measured by means of an interferometer.

8. A method according to claim 1 , in which the data-processing unit is a microcomputer.

9. A method according to claim 1 , in which the data-processing unit is formed by microprocessors or microcontrollers.

10. Electrical switchgear provided with an enclosure containing a mixture of two dielectric gases under pressure, a first component which is SF 6 and a second component selected from the group consisting of N 2 or DF 4 , wherein the proportions of the dielectric gases in the mixture are determined by implementing a method according to claim 1 .

11. Electrical switchgear according to claim 10 , wherein the electrical switchgear enclosure is a high-voltage switchgear.

12. Electrical switchgear according to claim 10 , wherein electrical switchgear enclosure is a gastight enclosure.

13. A method according to claim 1 , in which said gaseous mixture acts as an insulation gas in the electrical switchgear.

14. Electrical switchgear provided with an enclosure containing a gaseous mixture of two dielectric gases under pressure, a first component which is SF 6 and a second component selected from the group consisting of N 2 or DF 4 , wherein the proportion X of one of these dielectric gases in the mixture is determined by implementing a method comprising the steps of:

a) measuring the pressure P, the temperature T, and the density ρ of the gas mixture contained in the electrical switchgear enclosure by means of sensors mounted on said enclosure,

b) determining said proportion X by processing the measured values of pressure P, temperature T and density ρ in a data-processing unit which delivers as output the proportion X determined by solving the following equations:

P (SF 6 ) =A 1.ρ(SF 6 ) +A 2. (ρ(SF 6 )) 2 +A 3. (ρ(SF 6 )) 3

and

P (N 2 )= A 4.ρ(N 2 ),

P=X.P (N 2 )+(1− X ). P (SF 6 ),

ρ=ρ(N 2 )+ρ(SF 6 ),

or

P (CF 4 ) =A 4.ρ(CF 4 ),

P=X.P (CF 4 )+(1− X ). P (SF 6 ),

ρ=ρ(CF 4 )+ρ(SF 6 )

where A 1 , A 2 , A 3 and A 4 are functions of T,

P(SF 6 ) and P(N 2 or CF 4 ) are the partial pressures of SF 6 and (N 2 or CF 4 ),

ρ(N 2 ), ρ(CF 4 ) and ρ(SF 6 ) are the densities of N 2 , CF 4 and SF 6 ,

wherein step a) is carried out without tapping said gas mixture.

15. A method of monitoring the proportion X of a component in a gaseous mixture, said gaseous mixture having at least two components, a first component which is SF 6 and a second component selected from the group consisting of N 2 or DF 4 , and being contained in an electrical switchgear enclosure, said method comprising the steps of:

a) measuring the pressure P, the temperature T, and the density ρ of the gas mixture contained in the electrical switchgear enclosure by means of sensors mounted on said enclosure,

b) determining said proportion by processing the measured values of pressure P, temperature T and density ρ in a data-processing unit, which delivers as output the proportion X determined by solving the following equations:

P (SF 6 ) =A 1.ρ(SF 6 )+ A 2.ρ(ρ(SF 6 )) 2 +A 3.(ρ(SF 6 )) 3

and

P (N 2 )= A 4.ρ(N 2 ),

P=X.P (N 2 )+(1− X ). P (SF 6 ),

ρ=ρ(N 2 )+ρ(SF 6 ),

or

P (CF 4 )= A 4.ρ(CF 4 ),

P=X.P (CF 4 )+(1− X ). P (SF 6 ),

ρ=ρ(CF 4 )+ρ(SF 6 )

where A 1 , A 2 , A 3 and A 4 are functions of T,

P(SF 6 )and P(N 2 or CF 4 ) are the partial pressures of SF 6 and (N 2 or CF 4 ),

ρ(N 2 ), ρ(CF 4 ) and ρ(SF 6 ) are the densities of N 2 , CF 4 and SF 6 , and

c) running algorithms in the data-processing unit for correcting errors and drift specific to said sensors,

wherein step a) is carried out without tapping said gas mixture.

16. A system for monitoring the proportion X of a component in a gaseous mixture, said gaseous mixture having two components, a first component which is SF 6 and a second component selected from the group consisting of N 2 or DF 4 , and being contained in an electrical switchgear enclosure, said system comprising:

at least one sensor mounted on said enclosure for measuring the pressure P, the temperature T, and the density ρ of the gas mixture contained in the electrical switchgear enclosure, said sensor measuring without tapping the said gas mixture, and

a data processing unit for processing the measured values of pressure, temperature and density, the data processing delivering as output the proportion X determined by solving the following equations:

P (SF 6 ) =A 1.ρ(SF 6 ) +A 2.(ρ(SF 6 )) 2 +A 3.(ρ(SF 6 )) 3

and

P (N 2 )= A 4.ρ(N 2 ),

P=X.P (N 2 )+(1− X ). P (SF 6 ),

ρ=ρ(N 2 )+ρ(SF 6 ),

or

P (CF 4 )= A 4.ρ(CF 4 ),

P=X.P (CF 4 )+(1− X ). P (SF 6 ),

ρ=ρ(CF 4 )+ρ(SF 6 )

where A 1 , A 2 , A 3 and A 4 are functions of T,

P(SF 6 ) and P(N 2 or CF 4 ) are the partial pressures of SF 6 and (N 2 or CF 4 ),

ρ(N 2 ), ρ(CF 4 ) and ρ(SF 6 ) are the densities of N 2 , CF 4 and SF 6 .

17. A system for monitoring the proportion X of a component in a gaseous mixture, said gaseous mixture having two components, a first component which is SF 6 and a second component selected from the group consisting of N 2 or DF 4 , and being contained in an electrical switchgear enclosure, said system comprising:

first means mounted on said enclosure for measuring the pressure P, the temperature T, and the density ρ of the gas mixture contained in the electrical switchgear enclosure, said first means measuring without tapping said gas mixture, and

second means for processing the measured values of pressure, temperature and density and delivering as output the proportion X determined by solving the following equations:

P (SF 6 )= A 1.ρ(SF 6 ) +A 2.(ρ(SF 6 )) 2 +A 3.(ρ(SF 6 )) 3

and

P (N 2 )= A 4.ρ(N 2 ),

P=X.P (N 2 )+(1− X ). P (SF 6 ),

ρ=ρ(N 2 )+ρ(SF 6 ),

or

P (CF 4 )= A 4.ρ(CF 4 ),

P=X.P (CF 4 )+(1− X ). P (SF 6 ),

ρ=ρ(CF 4 )+ρ(SF 6 )

where A 1 , A 2 , A 3 and A 4 are functions of T,

P(SF 6 ) and P(N 2 or CF 4 ) are the partial pressures of SF 6 and (N 2 or CF 4 ),

ρ(N 2 ), ρ(CF 4 ) and ρ(SF 6 ) are the densities of N 2 , CF 4 and SF 6 .