Measuring array

Abstract

The measuring array with an earth connection point ( 5 ) for determining the insulation resistance (R iso ) of an energized electrical apparatus or of an installation with a supply voltage U B with a positive pole ( 6 ) and a negative pole ( 7 ), two switches (S 1 , S 2 ) or a corresponding two-way switch being provided for creating a current path between one of the two poles and said earth connection point ( 5 ) in order to determine the insulation resistance (R iso ) generally obtained when one or a plurality of insulation faults occur at any potential reference, two measurements being performed one after the other for determining the insulation resistance, the first switch (S 1 ) being closed and the second switch (S 2 ) open during the first of these two measurements and the first switch (S 1 ) being open and the second switch (S 2 ) closed during the second of these measurements.

I claim: 
     
       1. A measuring array with an earth connection point for determining an insulation resistance (R iso ) of an energized electrical apparatus or of an installation including a supply voltage U B  with a positive pole and a negative pole, the measuring array comprising:
 two switches (S 1 , S 2 ) or a corresponding two-way switch being provided for creating a current path between one of the two poles and said earth connection point in order to determine the insulation resistance (R iso ) generally obtained when one or a plurality of insulation faults occur at any potential reference; 
 a current measuring system connected between the connection point of the two switches (S 1 , S 2 ) and the earth connection point; 
 a microcontroller configured for determining the insulation resistance by performing two measurements one after the other, in which during the first of these two measurements, the first switch (S 1 ) is closed whilst the second switch (S 2 ) is open, and during the second of these measurements, the first switch (S 1 ) is open whilst the second switch (S 2 ) is closed; and 
 said microcontroller is further configured for measuring a current between the connection point of the two switches (S 1 , S 2 ) and the earth connection point so that the currents measured at that point during the two measurements are used to calculate the insulation resistance (R iso ), wherein the insulation resistance (R iso ) is calculated from R iso =U B / (I PE -I PE ′)wherein I PE  is the current measured with the current measuring system with switch S 1  Being closed and switch S 2  being open, and I PE ′ is the current measured with the current measuring system with switch S 2  being closed and switch S 1  being open. 
 
     
     
       2. The measuring array as set forth in  claim 1 , wherein a microcontroller or a microprocessor is provided for calculating the insulation resistance (R iso ). 
     
     
       3. Use of a measuring array as set forth in  claim 1  for measuring the insulation resistance in photovoltaic installations for producing electric energy. 
     
     
       4. Use of a measuring array as set forth in  claim 1  for measuring the insulation resistance in inverters, in solar inverters in particular. 
     
     
       5. Use of a measuring array as set forth in  claim 1  for measuring the insulation resistance in transformerless inverters. 
     
     
       6. A measuring array with an earth connection point for determining an insulation resistance (R iso ) of an energized electrical apparatus or of an installation including a supply voltage U B  with a positive pole and a negative pole, the measuring array comprising:
 two switches (S 1 , S 2 ) or a corresponding two-way switch being provided for creating a current path between one of the two poles and said earth connection point in order to determine the insulation resistance (R iso ) generally obtained when one or a plurality of insulation faults occur at any reference; 
 a current measuring system connected between the connection of one of the two switches (S 1 , S 2 ) that is not connected to the earth connection point and one of the two poles, and the connection of the other switch that is not connected to the earth connection point is connected to the other one of the two poles through a constant current source; 
 a transistor mounted in parallel to the two switches in such a manner that its emitter or source connection is connected to the current source whilst its collector or drain connection is connected to the current measuring system; 
 a microcontroller configured for determining the insulation resistance by performing two measurements one after the other, in which during the first of these two measurements, the first switch (S 1 ) is closed whilst the second switch (S 2 ) is open, and during the second of these measurements, the first switch (S 1 ) is open whilst the second switch (S 2 ) is closed; and 
 said microcontroller is further configured for calculating the insulation resistance (R iso ) based on the currents measured with the current measuring system during the two measurements. 
 
     
     
       7. The measuring array as set forth in  claim 6 , wherein the insulation resistance R iso  is calculated from R iso= U B /(I pos -I pos ′), wherein I pos  is the current measured with the current measuring system with switch S 1  being closed and switch S 2  being open and I pos ′ is the current measured with the current measuring system with switch S 2  being closed and switch S 1  being open. 
     
     
       8. The measuring array as set forth in  claim 7 , wherein the current I PE  or I pos  is measured via a shunt. 
     
     
       9. The measuring array as set forth in  claim 6  wherein the switches (S 1 , S 2 ) are relay switches or semi-conductor switches. 
     
     
       10. Use of a measuring array as set forth in  claim 6  for measuring the insulation resistance in photovoltaic installations for producing electric energy. 
     
     
       11. Use of a measuring array as set forth in  claim 6  for measuring the insulation resistance in inverters, in solar inverters in particular. 
     
     
       12. Use of a measuring array as set forth in  claim 6  for measuring the insulation resistance in transformerless inverters. 
     
     
       13. A method for determining an insulating resistance (R iso ) of a circuit, the circuit having a first switch between a positive node and an earth connection point and a second switch between a negative node and the earth connection point, the circuit further comprising a current measuring element connected between a connection node between the first switch and the second switch and the earth connection point, the method comprising:
 providing a supply voltage (U B ) between the positive node and the negative node;   measuring a first current (I PE ) with the current measuring element, wherein the first current is measured when the first switch is closed and the second switch is open;   measuring a second current (I PE′ ) with the current measuring element, wherein the second current is measured when first switch is open and second switch is closed; and   calculating the insulating resistance (R iso ) according to R iso =U B /(I PE -I PE′ ) by a microcontroller or microprocessor.    
     
     
       14. The method according to claim 13, wherein the first switch and the second switch are embodied in a two way switch.  
     
     
       15. The method according to claim 13, wherein the first switch is a relay or a semiconductor switch, and wherein the second switch is a relay or a semiconductor switch.  
     
     
       16. The method according to claim 13, wherein the current measuring element is a shunt.  
     
     
       17. A circuit having a positive node, a negative node and an earth connection point, the circuit comprising:
 a first switch between the positive node and the earth connection point;   a second switch between the negative node and the earth connection point;   a current measuring element connected between the earth connection point and a connection node between the first switch and the second switch; and   a microcontroller configured to perform a first current measurement when the first switch is closed and the second switch is open, and a second current measurement when the first switch is open and the second switch is closed,   wherein the microcontroller is further configured to calculate an insulation resistance (R iso ), wherein the insulation resistance (R iso ) is calculated according to R iso =U B / (I PE -I PE ), wherein I PE  is a current measured in the first current measurement, and I PE′  is a current measured in the second current measurement, and wherein U B  is a supply voltage over the positive node and the negative node.    
     
     
       18. The circuit according to claim 17, wherein the first switch and the second switch are embodied in a two way switch.  
     
     
       19. The circuit according to claim 17 wherein first switch or the second switch is a relay or a semiconductor switch.  
     
     
       20. A method for determining an insulating resistance (R iso ) of a circuit, the circuit having a first switch between a first node and an earth connection point and a second switch between a second node and the earth connection point, the circuit further comprising a current measuring element between the first node and the first switch, a constant current source between the second node and the second switch and a transistor disposed parallel to the first switch and the second switch, wherein an emitter or a source of the transistor is connected to the constant current source, and wherein a collector or a drain connection is connected to the current measuring element, the method comprising:
 providing a supply voltage (U B ) between the first node and the second node;   measuring a first current including a current of the constant current source with the current measuring element, wherein the first current is measured when the first switch is closed and the second switch is open;   measuring a second current including the current of the constant current source with the current measuring element, wherein the second current is measured when the first switch is open and the second switch is closed; and   calculating the insulating resistance (R iso ) by a microcontroller or microprocessor based on the first current, the second current and the supply voltage (U B ).    
     
     
       21. The method according to claim 20, wherein the first switch and the second switch are embodied in a two way switch.  
     
     
       22. The method according to claim 20, wherein the first switch or the second switch is a relay or a semiconductor switch.  
     
     
       23. The method according to claim 20, wherein the first node is a positive node and the second node is a negative node.  
     
     
       24. The method according to claim 20, further comprising applying a constant current source supply voltage to the constant current source by the transistor, wherein the constant current source supply voltage is substantially smaller than the supply voltage (U B ).  
     
     
       25. A circuit having an earth connection point, a first node and a second node, the circuit comprising:
 a first switch between the first node and the earth connection point;   a second switch between the second node and the earth connection point;   a current measuring element connected between the first node and the first switch and a constant current source connected between the second node and the second switch;   a transistor disposed parallel to the first switch and the second switch, wherein an emitter or a source of the transistor is connected to the constant current source, and wherein a collector or a drain connection is connected to the current measuring element; and   a microcontroller configured to perform a first current measurement when the first switch is closed and the second switch is open, and a second current measurement when the first switch is open and the second switch is closed, and the microcontroller further configured to calculate an insulation resistance (R iso ) based on the first current measurement and the second current measurement.    
     
     
       26. The circuit according to claim 25, wherein the first switch and the second switch are embodied in a two way switch.  
     
     
       27. The circuit according to claim 25, wherein the first switch or the second switch is a relay or a semiconductor switch.  
     
     
       28. The circuit according to claim 25, wherein the current measuring element is a shunt.  
     
     
       29. The circuit according to claim 25, wherein the first node is a positive node and the second node is a negative node.  
     
     
       30. A system comprising:
 an inverter, the inverter having an earth connection point, a first node and a second node, the inverter comprising
 a first switch between the first node and the earth connection point; 
 a second switch between the second node and the earth connection point; 
 a current measuring element connected between the first node and the first switch and a constant current source connected between the second node and the second switch; 
 a transistor disposed parallel to the first switch and the second switch, wherein an emitter or a source of the transistor is connected to the constant current source, and wherein a collector or a drain connection is connected to the current measuring element; 
 a microcontroller configured to perform a first current measurement when the first switch is closed and the second switch is open, and a second current measurement when the first switch is open and the second switch is closed, and the microcontroller further configured to calculate an insulation resistance (R iso ) based on the first current measurement and the second current measurement; and 
   a photovoltaic generator having a first generator terminal and a second generator terminal, wherein the first generator terminal is electrically connected to the first node, and wherein the second generator terminal is electrically connected to the second node.    
     
     
       31. The system according to claim 30, wherein the first switch and the second switch are embodied in a two way switch.  
     
     
       32. The system according to claim 30, wherein the first switch or the second switch is a relay or a semiconductor switch.  
     
     
       33. The system according to claim 30, wherein the first generator terminal and the first node are positive, and wherein the second generator terminal and the second node are negative.  
     
     
       34. The system according to claim 30, wherein the inverter is a transformerless inverter.