System and method for monitoring a dc power system

Abstract

The present application discloses an integrated direct current (DC) subsystem monitoring system for monitoring and reporting status of a utility substation, the DC subsystem monitoring system having the ability to actively monitor and report on changes in the float current and current capacity of the system, as well as to monitor for ground faults.

1 . An apparatus for testing a battery bank comprising at least one battery, the battery bank being part of a load circuit in which the battery bank, a charger, and a system load are arranged in parallel, the apparatus comprising:
 a controller;   a main contactor located on a first leg of the load circuit between the battery bank and the charger, so that the battery bank is electrically disconnected from the charger when the main contactor is open and the battery bank is electrically connected to the charger when the main contactor is closed, the first leg of the load circuit having a battery side extending between the main contactor and the battery bank and a system load;   a float current test circuit arranged in parallel with the main contactor;   a first voltage sensor having a first connection point that is in electrical contact with the the first leg; and   a fail-safe circuit having first and second ends electrically connected to the first leg and first and second fail-safe devices, each of the first and second fail-safe devices having an active mode in which electrical current is permitted to flow in a forward direction through the fail safe device and electrical current is prevented from flowing in a backward direction through the fail-safe device and an inactive mode in which electrical current is prevented from flowing in both the forward and backward directions through the fail safe device, each of the fail-safe devices being operationally configured to change between active and inactive modes based on a mode signal, the first fail-safe device and the second fail-safe device being installed in the fail-safe circuit in opposite orientations, so that the forward direction of the first fail-safe device corresponds to the backward direction of the second fail-safe device;   wherein the controller is electrically connected to the main contactor, the float current contactor, the first fail-safe device, and the second fail-safe device and the controller is operationally configured to (a) close the float current contactor when the main contactor is open, (b) open the float current contactor when the main contactor is closed, and (c) cause the first and second fail-safe devices to enter active mode if the controller detects a failure of the main contactor.   
     
     
         2 . The apparatus of  claim 1 , wherein the first and second fail-safe devices each comprise a semiconductor-controlled rectifier. 
     
     
         3 . The apparatus of  claim 1 , wherein the float current test circuit includes first and second end points in electrical contact with the first leg at a first connection point that is located between the main contactor and the battery bank and a second connection point located between the main contactor and the system load. 
     
     
         4 . The apparatus of  claim 1 , wherein the first leg is a negative leg of the load circuit. 
     
     
         5 . The apparatus of  claim 1 , wherein the float current test circuit comprises a shunt, a float current contactor, and a fuse arranged in series. 
     
     
         6 . The apparatus of  claim 5 , wherein the float current circuit further comprises a diode arranged in series with the shunt, the float current contactor, and the fuse. 
     
     
         7 . The apparatus of  claim 5 , wherein the fuse comprises a resettable fuse. 
     
     
         8 . An apparatus for testing a battery bank comprising at least one battery, the battery bank being part of a load circuit in which the battery bank, a charger, and a system load are arranged in parallel, the apparatus comprising:
 a controller;   a main contactor located on a first leg of the load circuit between the battery bank and the charger, so that the battery bank is electrically disconnected from the charger when the main contactor is open and the battery bank is electrically connected to the charger when he main contactor is closed, the first leg of the load circuit having a battery side extending between the main contactor and the battery bank and a system load;   a float current test circuit arranged in parallel with the main contactor, the float current test circuit comprising a shunt, a float current contactor, and a fuse arranged in series;   a first voltage sensor having a first connection point that is in electrical contact with the first leg; and   a fail-safe circuit having first and second ends electrically connected to the first leg and arranged in parallel with the main contactor, the fail-safe circuit having an active mode in which electrical current can flow in at least one direction through the fail-safe circuit and an inactive mode in which the fail-safe circuit is open, which prevents electrical current from flowing in either direction through the fail-safe circuit;   wherein the controller is electrically connected to the main contactor, the float current contactor, the first fail-safe circuit and the controller is operationally configured to (a) close the float current contactor when the main contactor is open, (b) open the float current contactor when the main contactor is closed, and (c) cause the fail-safe circuit to enter active mode if the controller detects a failure of the main contactor.   
     
     
         9 . An apparatus for testing a battery bank comprising at least one battery, the battery bank being part of a load circuit in which the battery bank, a charger, and a system load are arranged in parallel, the apparatus comprising:
 a controller;   a main contactor located on a first leg of the load circuit between the battery bank and the charger, so that the battery bank is electrically disconnected from the charger when the main contactor is open and the battery bank is electrically connected to the charger when he main contactor is closed, the first leg of the load circuit having a battery side extending between the main contactor and the battery bank and a system load;   a float current test circuit arranged in parallel with the main contactor;   a first voltage sensor having a first connection point that is in electrical contact with the battery side of the first leg and a second connection point in electrical contact with the system load side of the first leg;   a remote sense contactor in electrical contact with the first voltage sensor, the remote sense contactor operationally configured to selectively electrically connect the first voltage sensor to one of the first connection point and the second connection point;   a fail-safe circuit having first and second ends electrically connected to the first leg and arranged in parallel with the main contactor, the fail-safe circuit having an active mode in which electrical current can flow in at least one direction through the fail-safe circuit and an inactive mode in which the fail-safe circuit is open, which prevents electrical current from flowing in either direction through the fail-safe circuit; and   wherein the controller is electrically connected to the main contactor, the float current contactor, the fail-safe circuit, and the controller is operationally configured to (a) close the float current contactor, cause the remote sense contractor to connect the first voltage sensor to the first connection point when the main contactor is open and (b) open the float current contactor, cause the remote sense contractor to connect the second voltage sensor to the second connection point when the main contactor is closed.   
     
     
         10 . A method of performing a float current test on a bank of batteries comprising at least one battery, the battery bank being part of a load circuit in which the battery bank, a charger, and a system load are arranged in parallel, the method comprising:
 (a) determining if all of a set of test start conditions are met; and   (b) initiating a float current test when all of a set of test start conditions are determined to be met, the float current test comprising:
 (i) starting a timer; 
 (ii) recording a battery start voltage when the timer reaches a first predetermined time period has elapsed; 
 (iii) disconnecting the battery bank from the charger by opening a main contactor, enabling a float current circuit, and changing a location of a remote voltage sense from a first location to a second location when a second predetermined time period has elapsed, the first location being between the main contactor and the charger and the second location being between the main contactor and the battery bank; 
 (iv) determining if record conditions are met; 
 (v) measuring and storing a float current value for the battery bank if the record conditions are determined to have been met in step (iv); and 
 (vi) repeating steps (iv) and (v) until a predetermined number of float current values are recorded; and 
 (viii) providing a constant voltage to the battery bank during the performance of step (b). 
   
     
     
         11 . The method of  claim 10 , further comprising:
 (c) terminating step (b) if, during the performance of step (b), any test end conditions are met, the test end conditions comprising (a) a total float current test time exceeds a predetermined amount of time, (b) the charger begins to charge the battery bank, (c) the battery bank begins to discharge, (d) a predetermined number of data points have been collected.   
     
     
         12 . The method of  claim 10 , wherein step (a) further comprises determining if all of a set of test start conditions are met, the test start conditions comprising (a) the charger is not currently charging the battery bank, (b) the charger has not charged the battery bank within a predetermined period of time, (c) a voltage of the battery bank is within a predetermined range, (d) no other tests are currently running, (e) no failures have been detected. 
     
     
         13 . The method of  claim 12 , wherein step (c) further comprises terminating the float current test if any test end conditions are met, the test end conditions comprising (a) a total float current test time exceeds a predetermined amount of time, (b) the charger begins to charge the battery bank, (c) the battery bank begins to discharge, (d) a predetermined number of data points have been collected. 
     
     
         14 . The method of  claim 10 , wherein step (b)(v) comprises measuring and storing a float current value and a temperature value for the battery bank if the record conditions are determined to have been met in step (iv). 
     
     
         15 . The method of  claim 14 , further comprising:
 (c) calculating and storing a temperature-corrected float voltage for each float current value stored in step (b)(v) based on the measured temperature value.   
     
     
         16 . A method for performing a capacity test on testing a battery bank comprising at least one battery, the battery bank being part of a load circuit in which the battery bank, a charger, and a system load are arranged in parallel, the battery bank having a nominal capacity and a set of capacity factors, the set of capacity factors including first and second capacity factors K t1  and K t2 , the method comprising:
 (a) electrically disconnecting the battery bank from the charger and the system load;   (b) placing the battery in electrical contact with a capacity test circuit operationally configured to apply a constant resistance across the battery bank;   (c) maintaining the battery bank in electrical contact with the capacity test circuit until the battery bank reaches a predetermined end voltage;   (d) measuring a time to end voltage TD 2  comprising a period from the start of step (b) to the end of step (c);   (e) measuring a temperature that is indicative of a temperature of the battery bank and calculating a temperature correction factor T cf  based on the measured temperature;   (f) calculating an average current I avg  consisting of the mean of a first set of measurements of a current flowing through the capacity test circuit, each of the measurements of the first set of measurements being taken at first frequency during the performance of step (c);   (g) calculating an average capacity factor K t  that is equal to the nominal capacity divided by the average current I avg ;   (h) calculating a rated discharge time t for the capacity test performed in steps (a) through (d) as a function comprising a linear interpolation between first and second capacity factors K t1  and K t2 ; and   (i) calculating a percentage C of the nominal capacity as a function of the rated discharge time t, the measured time to end of-voltage TD 2 , and the temperature correction factor T cf .   
     
     
         17 . The method of  claim 16 , wherein step (h) further comprises calculating a rated discharge time t for the capacity test performed in steps (a) through (d) based on the following formula: 
       
         
           
             
               t 
               = 
               
                 
                   t 
                   1 
                 
                 + 
                 
                   
                     
                       ( 
                       
                         
                           t 
                           2 
                         
                         - 
                         
                           t 
                           1 
                         
                       
                       ) 
                     
                      
                     
                       ( 
                       
                         
                           K 
                           t 
                         
                         - 
                         
                           K 
                           
                             t 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                       ) 
                     
                   
                   
                     ( 
                     
                       
                         K 
                         
                           t 
                            
                           
                               
                           
                            
                           2 
                         
                       
                       - 
                       
                         K 
                         
                           t 
                            
                           
                               
                           
                            
                           1 
                         
                       
                     
                     ) 
                   
                 
               
             
           
         
       
       where: t 1  is a rated discharge time associated K t1  and t 2  is a rated discharge time associated K t2 . 
     
     
         18 . The method of  claim 16 , wherein step (i) comprises:
 (j) calculating a percentage C of the nominal capacity based on the following formula:   
       
         
           
             
               C 
               = 
               
                 
                   
                     TD 
                     2 
                   
                   
                     t 
                     × 
                     
                       T 
                       cf 
                     
                   
                 
                 × 
                 100.