Ground scheme identification method

Abstract

The present techniques include methods and systems for detecting the grounding condition of an electrical system to automatically determine a suitable electrical drive configuration. The drive includes a test resistor which may be connected or disconnected from the drive to measure different drive voltages. The measured drive voltages are analyzed to determine a type of grounding configuration of the electrical system in which the drive is to be installed. Embodiments also include determining ground resistance condition such as a high resistance ground (HRG) fault or a ground resistance fault when the drive is in operation.

1 . A method, comprising:
 connecting or disconnecting a test resistor in a drive, wherein the drive comprises a power converter configured to convert AC power to DC power applied to the DC bus and an inverter configured to convert DC power from the DC bus to output AC power, and wherein the test resistor is connected either between the DC bus and a ground potential or between a load of the drive and the ground potential;   measuring a voltage at a node while the test resistor is connected or disconnected and while the drive is coupled to an electrical system, wherein the node is between a low side of the DC bus and a ground potential in the drive; and   determining one or more of a ground condition of the electrical system and a ground resistance condition of the drive based on the voltage.   
     
     
         2 . The method of  claim 1 , further comprising disconnecting the test resistor from the drive and determining the ground condition of the electrical drive to be a solid grounded Δ when the voltage is substantially similar to a phase voltage of the drive. 
     
     
         3 . The method of  claim 1 , further comprising connecting the test resistor to the drive and determining the ground condition of the electrical drive to be a solid grounded Y configuration when the voltage is substantially smaller than a DC voltage on the DC bus. 
     
     
         4 . The method of  claim 1 , further comprising connecting the test resistor to the drive and determining the ground condition of the electrical drive to be ungrounded when the voltage is greater than or equal to approximately one half of a DC voltage on the DC bus. 
     
     
         5 . The method of  claim 1 , further comprising connecting the test resistor to the drive and determining the ground condition of the electrical drive to be a high resistance ground (HRG) configuration when the voltage is smaller than approximately one half of a DC voltage on the DC bus. 
     
     
         6 . The method of  claim 1 , further comprising:
 connecting the test resistor to the drive during a test duration, wherein the test duration occurs in regular time intervals while the drive is operating;   measuring the voltage at the node during the test duration; and   determining the ground resistance condition based on the voltage measured during the test duration.   
     
     
         7 . The method of  claim 6 , wherein determining the ground resistance condition comprises determining one or more of a shorted HRG resistor, an open HRG resistor, a normally operating HRG resistor, a shorted ground resistor, an open ground resistor, and a normally operating ground resistor. 
     
     
         8 . The method of  claim 6 , wherein the test interval is approximately 2-5 hours. 
     
     
         9 . A drive, comprising:
 a power converter configured to convert AC power to DC power;   a DC bus configured to receive the DC power from the power converter;   an inverter configured to receive the DC power from the DC bus and output AC power;   a node between a low side of the DC bus and a ground potential in the drive, wherein the node is configured to be measured for a voltage indicative of one or more of a grounding condition of an electrical system coupled to the drive and a ground resistance condition of the drive; and   a test resistor coupled between the DC bus and a ground potential or coupled between a load of the drive and the ground potential.   
     
     
         10 . The drive of  claim 9 , further comprising a switch configured to open to disconnect the test resistor from the drive and close to connect the test resistor to the drive. 
     
     
         11 . The drive of  claim 9 , further comprising a contactor configured to open to disconnect the test resistor from the drive and close to connect the test resistor to the drive.