Patent Publication Number: US-2022221495-A1

Title: Test system for an intelligent electronic device in an electric sub-station

Description:
TECHNICAL FIELD 
     The present subject matter relates, in general, to test systems for intelligent electronic devices, and in particular, to test switches of such tests systems. 
     BACKGROUND 
     Electrical power generation and distribution systems include a number of components and electrical circuitry. Such components and circuitry may be generally controlled through Intelligent Electronic Devices (referred to as IEDs). In operation, such components and circuits are coupled to one or more sensors. The sensors may detect the appropriate operational parameters which may be communicated to the IED. The IED, on receiving the information from sensors may generate a number of control signals for controlling the components and the electrical circuitry. The IEDs may be periodically tested during which the IEDs may be isolated from the main current paths of the electrical power generation and distribution systems using appropriate test devices. The current modular test switch assemblies such as US 2011/0056819 A1, US 2014/0253146 A1 and WO2016/161522A1 disclose a switch for each test unit which may increase the human error in usage procedure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The features, aspects, and advantages of the present subject matter will be better understood with regard to the following description and accompanying figures. The use of the same reference number in different figures indicate similar or identical features and components. 
         FIGS. 1-2  illustrates a cross-sectional view of a test switch unit in various stages of operation, in accordance with one implementation of the present subject matter; 
         FIGS. 3-5  illustrates a cross-sectional view of a test switch unit in various stages of operation, in accordance with another implementation of the present subject matter; 
         FIGS. 6-7  illustrates a cross-sectional view of a test switch unit in various stages of operation, in accordance with another implementation of the present subject matter; and 
         FIG. 8  illustrates an isometric view of the test switch unit, in accordance with one implementation of the present subject matter. 
         FIG. 9-11  illustrates a cross-sectional view of a test switch unit for opening a trip circuit, in various stages. 
         FIG. 12-14  illustrates a cross-sectional view of a test switch unit, for isolation of a Current Transformer (CT) circuit, in various stages as per another example of the present subject matter. 
         FIG. 15-17  illustrates a cross-sectional view of a test switch unit, for shorting of a Voltage Transformer (VT) circuit, in various stages as per yet another example of the present subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     Electrical power generation and distribution systems are adapted to generate, transmit, and distribute electrical energy to loads. Such systems may further include electrical substations that may include equipment, such as electrical generators, power transformers, power transmission/distribution lines, circuit breakers, and voltage regulators. Such equipment may be protected, monitored, and controlled through intelligent electronic devices or IEDs. Through various sensors, the IED may receive operational information pertaining to the various components, in response to which the IED may generate one or more control signals for controlling the operation of such equipment. 
     Of the components mentioned above, the IED may also be coupled to trip circuits, current transformer (CT) circuits, and voltage transformer (VT) circuits. As is generally understood, trip circuits respond to overload conditions by opening the circuit in through which electrical power is passed. Further, both the CT circuit and the VT circuits transform the electrical current to levels which can be then utilized or measured. 
     The IEDs may be routinely subject to maintenance, or in certain cases may have to be repaired. The testing and maintenance of the IEDs is implemented through test switch units. The test switch units, generally, may be coupled to the IED which is to be tested. Before testing commences, the testing switches may isolate the IED and the trip, CT and the VT circuits. Once the relevant circuits and the IED are isolated, the test switch unit may provide the IED with one or more test inputs for testing the functioning of the IED. The IED may generate certain responses corresponding to the test inputs, which may then be assessed for determining whether the IED is operating in the desired manner. 
     Generally, multiple test switches are utilized as part of a test system. In certain cases, the test systems may be composed of disparate and separate parts which may have to be used for performing the testing operations. For example, such conventional test systems may include a main unit (which is coupled to the IED) in which an insertable unit may be inserted. The insertable unit may then either open or isolate the appropriate circuits in order to isolate the IED for testing. However, in such test switch units, the main unit and the insertable unit are separate components that are both required for testing the intelligent electronic device. For using the test system, test personnel may have to manually insert and adjust the plugs of the insertable unit into the contacts of the main unit. In cases where multiple IEDs are to be tested, the insertable unit has to be serially removed from one main unit and inserted into the main unit of the other IED which is to be tested. The continuous insertion and removal of the insertable unit entails tremendous manual efforts. 
     Furthermore, the insertable unit while being inserted may also have to be properly aligned with each contact of the main unit, since improper alignment may lead to a loose connection and therefore may not result in a proper isolation of the IED for testing. In certain cases, where the main unit is positioned at a height, further efforts may have to be made by the testing personnel for properly aligning and securing the insertable unit inside the main unit. 
     Approaches and example of a test switch unit for a test system are described. In one example, the test systems as described are a singular unit. To that end, at least the test systems may be installed and operated using less efforts. Furthermore, since no separate insertable unit is present, the issues pertaining to alignment and loose connection also are avoided. The test systems as described include one or more test switches which may be used for testing the IED. In one example, a test switch unit for a test system for an intelligent electronic device may include a relay lead and a field lead. In one example, the test switch unit may be either for a trip circuit or for a CT/VT circuit. In either case, the test switch unit may further include at least one contact element. The relay lead is any terminal which may be electrically connected with the IED. On the other hand, the field lead is the terminal which is to receive the input current. The contact element enables, in one example, opening of the trip circuit. In another example, for a CT circuit, the test switch unit may include at least two contact elements. In such cases, the contact element may enable isolation of the CT circuit coupled to the IED, so that the IED under consideration may be tested. 
     The test switch unit may further include a rotatable cam. The cam is provided with one or more profiled elements, such as a cam lobe, provided at its circumference. It may be noted that the profiled elements may be considered as any structural protrusion or protrusions provided on the circumference of the cam. Such elements during operations engages with the contact elements upon rotation of the cam, which pushes the contact elements in a downward direction away from the cam. The rotation of the cam, in one example, may be affected manually through the action of a lever coupled to a shaft on which the cam is mounted. Manually moving the lever affects the rotation of the shaft and in turn, the rotation of the cam. As the cam rotates, the profiled element provided on the cam also moves and engages with the one or more contact elements to move from its initial position. As the contact elements move, one of the opening of the trip circuit, the shorting of the CT and subsequently isolation of the VT circuits may occur, depending on whether the test switch unit being used is for a trip circuit or for the CT/VT circuits. Once the trip circuits have been opened, and the CT/VT circuits have been shorted and isolated, respectively, the IED may be tested by providing the appropriate test signals. In one example, the test switch unit coupled to a trip circuit comprises a trip contact element. In another example, the test switch unit coupled to one of the CT/VT circuits includes a primary contact element and a secondary contact element. 
     Approaches and example of a method for operating a test system are described. In one example, the test system may include a first test switch unit, a second test switch unit, and a third test switch unit. A lever may be engaged to rotate a cam about its axis (A). The lever is coupled to the cam. Upon rotation, the cam opens a trip circuit coupled to the first test switch unit when the cam engages with a trip contact element of the first test switch unit. Upon further rotation, the cam shorts a CT circuit coupled to the second test switch unit. In one example, the cam may include a leading profiled element and a secondary profiled element. The leading profiled element engages with a secondary contact element of the second test switch unit and the trailing profiled element engages with a primary contact element of the second test switch unit. Upon further rotation, the cam isolates a VT circuit coupled to the third test switch unit when the cam engages with a VT contact element of the third test switch unit. 
     The approaches described eliminates the need for a test handle as a separate component and overcomes any issues that may arise from locating such a test handle for the purposes of testing. The installation of the test switch unit is also easier to install and does not require to be skillfully guided into the appropriate and desired slots. As is described in the following paragraphs, the test switch unit provides for an efficient mechanism for isolating various types of circuits with minimal efforts. Furthermore, the test switch units as described are also less complex, and hence, would be cost effective and economical. 
     The operation of the test switch units is further described in conjunction with the accompanying figures. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar parts. 
       FIG. 1  illustrates a cross-sectional view of a test switch unit  100 , as per one example of the present subject matter. Units such as the test switch unit  100  may be further installed in a test system, wherein such test system may be utilized for testing intelligent electronic devices (IEDs) installed within power generation and distribution systems. As noted above, the present illustration depicts the test switch unit  100  in one example. Other examples may also be possible without deviating from the scope of the subject matter of the claims. 
     Returning to  FIG. 1 , the test switch unit  100  includes a rectangular shaped enclosure in which various components may be present. In one example, the test switch unit  100  includes a relay lead  102  and the field lead  104 . The relay lead  102  is adapted such that it may be coupled to the intelligent electronic device and the corresponding trip circuit. As would be generally understood, trip circuits may include circuit breakers that open the circuit in situations where there may be certain overload conditions, such as thermal overload, short-circuit, and a ground fault. The field lead  104  on the other hand is adapted to be coupled to a field supply current. The test switch unit  100  may further include a test signal lead  106 . The test signal lead  106  is electrically coupled to the relay lead  102  through a conducting element  108 . The conducting element  108  may be in the form of a wired connector or may be a solid metallic plate, which provides electric coupling between the relay lead  102  and the test signal lead  106 . 
     Coupled to the field lead  104 , the test switch unit  100  also includes a trip contact element  110 . The trip contact element  110  may be manufactured from an electrically conducting and flexible material. One end of the trip contact element  110  is fixed with the field lead  104 . Owing to the flexible material of the trip contact element  110 , the other end of the trip contact element  110 , i.e., the end  112  is moveable. In the present example, the end  112  of the trip contact element  110  abuts against the conducting element  108 . In normal operation, the test signal lead  106  is not utilized and is open, the trip contact element  110  provides an electrically conducting path for the field supply current from the field lead  104  to the trip circuits which may be coupled to the relay lead  102 . 
     The test switch unit  100  may further include a cam  114  mounted on a shaft  116 . The shaft  116  is further coupled to a lever  118 . The lever  118  is adapted to move in a notional plane which is perpendicular to an axis A about which the cam  114  is adapted to rotate. The cam  114  is provided with a profiled element  120  which also moves in a circular path, as the cam  114  rotates. In one example, the lever  118  may be actuated manually or may be coupled, either directly or indirectly, through mechanically driven means. In case of the latter, such mechanically driven means may be actuated based on one or more control signals. 
     As described previously, the relay lead  102  may be coupled to an IED and a trip circuit. The testing of the IED would involve the test signal lead  106  to be used for providing one or more test signals. Since the conducting element  108  provides an electrically conducting path for the field supply current between the field lead  104  (to which the and the relay lead  102 , utilizing the test signal lead  106  during normal operation may result in the field supply current to pass through the test signal lead  106  as well. To this end, the trip circuit is opened so that no field supply current passes through the lever  118  using the test switch unit  100 . The manner in which the test switch unit  100  operates is further described in conjunction with  FIG. 2   
       FIG. 2  illustrates a cross-sectional view of the test switch unit  100  in different stages of its working. As described previously, test switch units such as the test switch unit  100 , are installed within the electrical power generation and distribution systems. Furthermore, test switch units, such as the test switch unit  100  may be coupled to the trip circuit and the IED. Under normal operating conditions, the field supply current (interchangeably referred to as the “field current”) generated from the appropriate generating components is provided to the field lead  104 . The field current passes through the field lead  104  and through the trip contact element  110 . Since the end  112  of the trip contact element  110  was previously in contact (as depicted in  FIG. 1 ) with the conducting element  108  and because the test signal lead  106  is open, the field current travels through the trip contact element  110  and the conducting element  108 , to the relay lead  102  and eventually through the trip circuit which may be coupled to relay lead  102 . 
     For isolating the IED for testing, the lever  118  is moved in the direction depicted as direction B. The movement of the lever  118  in the direction B, affects the rotation of the shaft  116 , which in turn causes the rotation of the cam  114 . As the cam  114  rotates, the profiled element  120  of the cam  114  also moves in circular path approaching the trip contact element  110 . As the profiled element  120  moves closer, it engages with the trip contact element  110 . As the profiled element  120  moves further, it pushes the trip contact element  110  such that the end  112  moves in the direction depicted as direction C. As the end  112  moves away from the conducting element  108 , it electrically decouples and opens the connection of the field lead  104  from the conducting element  108 . Since the conducting element  108  is also connected to relay lead  102  and the test signal lead  106 , the movement of the end  112  also decouples the field lead  104  from the relay lead  102  and the test signal lead  106 . As the end  112  decouples from the conducting element  108 , the trip circuit which may be coupled to the relay lead  102  is in an open state. The stage may then commence for shorting and isolating the CT circuit coupled with the IED. This is explained in conjunction with  FIGS. 3-5 . 
       FIG. 3  illustrates a cross-sectional view of a test switch unit  300 , as per one example of the present subject matter. Units such as the test switch unit  300  may be further installed in a test system, wherein such test system may be utilized for testing intelligent electronic devices (IEDs) installed within power generation and distribution systems. As noted above, the present illustration depicts the test switch unit  300  in one example. Other examples may also be possible without deviating from the scope of the subject matter of the claims. The test switch unit  300  as described is such that it may be coupled to the CT circuits and the IED. 
     Returning to  FIG. 3 , the test switch unit  300  includes a rectangular shaped enclosure in which various components may be present. In one example, the test switch unit  300  includes a relay lead  302  and a field lead  304 . The relay lead  302  is so adapted such that it may be coupled to the intelligent electronic device and corresponding CT circuit. As would be generally understood, the CT circuits are circuits which allow the transformation of the high current supplies to lower current supplies. Such transformations enable measurement of the current values, which otherwise may not be possible considering their high magnitude. 
     The field lead  304  is adapted to be coupled to the field current. The test switch unit  300  may further include a test signal lead  306  and another connecter port  308 . The test signal lead  306  is electrically coupled to the relay lead  302  through a conducting element  310 . The conducting element  310  may be in the form of a wired connector or may be a solid metallic plate which provides electric coupling between the relay lead  302  and the test signal lead  306 . 
     Coupled to the field lead  304 , the test switch unit  300  also includes a primary contact element  312  and a secondary contact element  314 . One end of each of the primary contact element  312  and the secondary contact element  314  are connected with the field lead  304 . The other ends of the primary contact element  312  and the secondary contact element  314 , namely, the end  316  and end  318 , respectively, are moveable by the cam  320 . Each of the primary contact element  312  and the secondary contact element  314  may be manufactured from an electrically conducting and flexible material. In the present example, the end  316  of the primary contact element  312  abuts against the conducting element  310 . In normal operation, when the test signal lead  306  is not utilized and is open, the primary contact element  312  provides an electrically conducting path for the field supply current from the field lead  304  to the CT circuit which may be coupled to the relay lead  302 . 
     The secondary contact element  314 , in the manner similar to the primary contact element  312 , extends linearly away from the point where it is attached to the field lead  304 . The end  318  of the secondary contact element  314  is, however, not in contact with any of the other components of the test switch unit  300 . In one example, both the primary contact element  312  and the secondary contact element  314  are moveable. In one example, the movement of the primary contact element  312  and the secondary contact element  314  is affected through the cam  320 . 
     The cam  320  is mounted on a shaft  322  which in turn is coupled to a lever  324 . Similar to lever  118 , the lever  324  is such that it is adapted to move in a notional plane which is perpendicular to the axis A about which the cam  320  is adapted to rotate. In one example, the lever  324  may be actuated manually or may be coupled, either directly or indirectly, through mechanically driven means. In case of the latter, such mechanically driven means may be actuated based on one or more control signals. The cam  320  is provided with a leading profiled element  326  and a trailing profiled element  328  (collectively referred to as the profiled elements  326 ,  328 ). The leading profiled element  326  is such that its leading edge extends beyond the leading edge of the trailing profiled element  328 . As the cam  320  rotates, the profiled elements  326 ,  328  also moves on a circular path. The profiled elements  326 ,  328  may be cam lobes provided on the outer surface of the cam  320 . 
     In one example, the length of the secondary contact element  314  may be greater than the length of the primary contact element  312 , with the secondary contact element  314  being positioned just marginally beneath the primary contact element  312 . In one example, both the primary contact element  312  and the secondary contact element  314  are shaped in the form of linearly extending sheets. In another example, the primary contact element  312  may be provided with a slot (not shown in  FIG. 3 ) so shaped which allows the leading profiled element  326  to pass through and engage with the secondary contact element  314  (as explained later in conjunction with  FIGS. 4-5 ), but without engaging with the primary contact element  312 . In one example, the cross-sectional width of the trailing profiled element  328  is greater than width of the slot provided in the primary contact element  312 . The test switch unit  300  may further include a short-circuit element  330  connected with the connecter port  308 . The short-circuit element  330  may be a metallic plate having a surface to allow the end  318  of the secondary contact element  314  to come into contact with the short-circuit element  330 . 
     As explained previously, a test system may include a plurality of test switch units, such as test switch unit  300 , which may be arranged adjacent to each other (as depicted in and explained in conjunction with  FIG. 8 ). Each of the test switch units may be connected with each other. In one example, the connecter port  308  of one test switch unit  300  may be adapted to be electrically coupled to the connecter port  308  of an adjacently positioned test switch unit. 
     Returning to  FIG. 3 , in one example the relay lead  302  is coupled to an IED and CT circuit. The testing of the IED would involve the test signal lead  306  to be used for providing one or more test signals. Since the conducting element  310  provides an electrically conducting path for the field supply current between the field lead  304  to which the and the relay lead  302 , utilizing the test signal lead  306  during normal operation may result in the electric supply current to pass through the test signal lead  306  as well. In order to ensure that the IED may be tested, the CT circuit is to be isolated. Isolation of the CT circuit requires that the conductive path for the field current is routed through the connecter port  308 . To this end, the CT circuit is to be shorted. The manner in which the CT circuit is shorted is described further in conjunction with  FIGS. 4-5 . As would be explained, in the paragraphs that follow, the path for the field current is to be established prior to breaking the conductive path (i.e., the path established between the field lead  304  and the relay lead  302 , through the conducting element  310 ). 
       FIGS. 4-5  illustrates cross-sectional views of the test switch unit  300  in different stages of its working. As opposed to the trip circuit, which may be in an open state, i.e., non-conducting, the CT circuit cannot be opened in order to ensure that the field current is not disrupted. As described previously, test switch units such as the test switch unit  300 , are installed within the electrical power generation and distribution systems. Furthermore, test switch units, such as the test switch unit  300  may be coupled to the trip circuit and the IED. Under normal operating conditions, the field current generated from the appropriate generating components is provided to the field lead  304 . The field current passes through the field lead  304  and through the primary contact element  312 . Since the end  316  of the trip contact element  312  is contact with the conducting element  308  and because the test signal lead  306  is open, the field current travels through the trip contact element  306  and the conducting element  308 , to the relay lead  302  and eventually through the CT circuit which may be coupled to relay lead  302 . 
     For isolating the CT circuit, the lever  324  is moved in the direction depicted as direction M. The movement of the lever  324  in the direction M, affects the rotation of the shaft  322 , which in turn causes the rotation of the cam  320 . As the cam  320  rotates, the leading profiled element  326  and the trailing profiled element  328  also moves in a circular path in the direction which is aligned with the direction M. As the leading profiled element  326  moves it passes through the slot present in the primary contact element  312 . Without engaging with the primary contact element  312 , the leading profiled element  326  proceeds and engages with the secondary contact element  314 . As the cam  320  further rotates, the leading profiled element  326  pushes the secondary contact element  314  in the direction as shown (direction N). As the secondary contact element  314  continues to move in the direction N, it proceeds and abuts against the short-circuit element  330 . Once the secondary contact element  314  is in contact with the short-circuit element  330 , an alternate path for the field current is established between the field lead  304  and the connecter port  308  ( FIG. 4 ). 
     Since the rotation of the lever  324  continues further down along the direction M, the cam  320  too continues to rotate. At this stage, the trailing profiled element  328  continues to move till it begins pushing the primary contact element  312  along direction N. The trailing profiled element  328  may now engage with the primary contact element  312 . With the contact between the secondary contact element  314  and the short-circuit element  330  already established, the primary contact element  312  loses contact with the conducting element  310  thereby breaking the electrically conductive path, i.e., path between the field lead  304  and the relay lead  302 , provided through the conducting element  310  ( FIG. 5 ). At this stage, field lead  304  and the short-circuit element  330  (and hence in turn the connecter port  308 ) are connected to each other through the secondary contact element  314 . The field current traversing through the field lead  304  and the secondary contact element  314  is then routed to the connecter port  308 . In one example, the connecter port  308  may be further connected with a similar connector port in a test switch unit positioned to the adjacent to the test switch unit  300  within a test system. With the field current being routed through the connecter port  308  (as opposed to the relay lead  302 ), the CT circuit is shorted and the IED is isolated. 
     As has been described previously for testing the IED, the trip circuit has to be opened. Along with the opening of the trip circuit, the CT circuit is to be shorted and isolated, with VT circuits to be isolated. To such an end, with the trip circuit opened (as described in conjunction with  FIGS. 1-2 ), and the CT circuit being shorted and isolated (as described in conjunction with  FIGS. 3-5 ), the next steps involve isolation of the VT circuits. The isolation of the VT circuits is now described in conjunction with  FIGS. 6-7 . 
       FIG. 6  illustrates a cross-sectional view of a test switch unit  600  for isolating a VT circuit, as per one example of the present subject matter. Units such as the test switch unit  600  may be further installed in a test system, wherein such test system may be utilized for testing intelligent electronic devices (IEDs) installed within power generation and distribution systems. As noted above, the present illustration depicts the test switch unit  600  in one example. Other examples may also be possible without deviating from the scope of the subject matter of the claims. 
     The test switch unit  600  includes a relay lead  602  and a field lead  604 . The relay lead  602  is so adapted such that it may be coupled to the intelligent electronic device and corresponding trip circuit. The field lead  604  on the other hand is adapted to be coupled to a field current. The test switch unit  600  may further include a test signal lead  606 . The test signal lead  606  is electrically coupled to the relay lead  602  through a conducting element  608 . The conducting element  608  may be in the form of a wired connector or may be a solid metallic plate which provides electric coupling between the relay lead  602  and the test signal lead  606 . 
     Coupled to the field lead  604 , the test switch unit  600  also includes a VT contact element  610 . The VT contact element  610  may be manufactured from an electrically conducting and flexible material. One end of the VT contact element  610  is fixed with the field lead  604 . In one example, the other end of the VT contact element  610 , i.e., the end  612  is moveable. In the present example, the end  612  of the VT contact element  610  abuts against the conducting element  608 . In normal operation, the test signal lead  606  is not utilized and is open, and the VT contact element  610  provides an electrically conducting path for the field current from the field lead  604  to the trip circuits which may be coupled to the relay lead  602 . 
     The test switch unit  600  may further include a cam  614  mounted on a shaft  616 . The shaft  616  is further coupled to a lever  618 . The lever  618  is such that it is adapted to move in a notional plane which is perpendicular to the axis about which the cam  614  is adapted to rotate. The cam  614  is provided with a profiled element  622  which also moves in a circular path, as the cam  614  rotates. In one example, the lever  618  may be actuated manually or may be coupled, either directly or indirectly, through mechanically driven means. In case of the latter, such mechanically driven means may be actuated based on one or more control signals. 
     As described previously, the relay lead  602  may be coupled to an IED and a VT circuit. The testing of the IED would involve the test signal lead  606  to be used for providing one or more test signals. Since the conducting element  608  provides an electrically conducting path for the field current between the field lead  604  (to which the and the relay lead  602 , utilizing the test signal lead  606  during normal operation may result in the field current to pass through the test signal lead  606  as well. To this end, the VT circuit is opened so that no field current passes through test signal lead  606  using the test switch unit  600 . The manner in which the test switch unit  600  operates is further described in conjunction with  FIG. 7 . 
       FIG. 7  illustrates a cross-sectional view of the test switch unit  600  in different stages of its working. Under normal operating conditions, the field current generated from the appropriate generating components is provided to the field lead  604 . The field current passes through the field lead  604  and through the VT contact element  610 . Initially the end  612  of the VT contact element  610  is in contact with the conducting element  608  and because the test signal lead  606  is open, the field current travels through the VT contact element  610  and the conducting element  608 , to the relay lead  602  and eventually through the trip circuit which may be coupled to relay lead  602 . 
     For isolating the IED for testing, the lever  618  is moved in the direction depicted as direction X. The movement of the lever  618  in the direction X, affects the rotation of the shaft  616 , which in turn causes the rotation of the cam  614 . As the cam  614  rotates, the profiled element  622  of the cam  614  also moves in circular path approaching the VT contact element  610 . As the profiled element  622  moves closer, it engages with the VT contact element  610 . As the profiled element  622  moves further, it pushes the VT contact element  610  such that the end  612  moves in the direction depicted as direction Y. As the end  612  moves away from the conducting element  608 , it electrically decouples and opens the connection of the field lead  604  from the conducting element  608 . Since the conducting element  608  is also connected to relay lead  602  and the test signal lead  606 , the movement of the end  612  also decouples the field lead  604  from the relay lead  602  and the test signal lead  606 , thereby completely isolating the VT circuit. 
     With the trip circuit isolated (as explained in conjunction with  FIGS. 1-2 ), the CT circuit shorted and isolated (as explained in conjunction with  FIGS. 3-5 ), and the VT circuit isolated (as explained in conjunction with  FIGS. 6-7 ), the testing of the IED may be initiated. In such cases, the one or more test signals may be provided to the test signal lead  606  for testing the IED coupled to the relay lead  602 .  FIG. 8  illustrates isometric views of the different stages of two test switch units  800 - 1  and  800 - 2 , similar to the test switch unit  300 , provided within a test system  800  for testing an intelligent electronic device installed in an electric substation, as per one example. In an example, the test system  800  may have a plurality of test switch units, in addition to test switch units  800 - 1  and  800 - 2 . It should be noted that the type of test switch unit would be dependent on the type of circuit, i.e., any one of the trip, CT and the VT circuit is to be isolated. As would be observed, the lever  324  is coupled to the shaft  322  (depicted through a dotted line for sake of clarity), which extends through the test switch units  800 - 1  and  800 - 2 . 
     In the present example, the connecter port  308  of the adjacent test switch units  800 - 1 - 800 - 2  are connected through a contact  806 .  FIG. 8  depicts the stages as explained in conjunction with  FIG. 3-5  for isolating the CT circuit for testing the IED. In operation, the lever  324  is moved in the direction depicted as direction M, which in turn causes the rotation of the cam  320 . As the cam  320  rotates, the leading profiled element  326  and the trailing profiled element  328  moves in a circular path. As the leading profiled element  326  moves it passes through the slot present in the primary contact element  312 . Without engaging with the primary contact element  312 , the leading profiled element  326  proceeds and engages with the secondary contact element  314 . As the cam  320  further rotates, the leading profiled element  326  pushes the secondary contact element  314  in the direction as shown (direction N). As the secondary contact element  314  continues to move in the direction N, it proceeds and abuts against the short-circuit element  330 . Once the secondary contact element  314  is in contact with the short-circuit element  330 , an alternate path for the field current is established between the field lead  304  and the connecter port  308 . 
     The trailing profiled element  328  continues till it begins pushing the primary contact element  312  along direction N. The trailing profiled element  328  may now engage with the primary contact element  312 . With the contact between the secondary contact element  314  and the short-circuit element  330  already established, the primary contact element  312  loses contact with the conducting element  310  thereby breaking the electrically conductive path, i.e., path between the field lead  304  and the relay lead  302 , provided through the conducting element  310  (as is depicted in  FIG. 8 ). At this stage, field lead  304  and the short-circuit element  330  (and hence in turn the connecter port  308 ) are connected to each other through the secondary contact element  314 . The field current traversing through the field lead  304  and the secondary contact element  314  is then routed to the connecter port  308 . 
     The connecter ports  308  of both the test switch units  800 - 1  and  800 - 2  may be further connected through a connector  806 , with each other. In this manner, the field current is routed through from the field lead  304  to the connecter ports  308  of the test switch units  802 - 1  and  802 - 2 . It may be noted that the present example has been explained depicting only two test switch units, namely, units  800 - 1  and  800 - 2 . Additional number of test switch units, such as test switch units  100 ,  600  may also be used without deviating from the scope of the present subject matter. For example, the test system  800  may include test switch units  100 ,  300 , and  600 . In such a case, actuation of the lever  324  will result in the movement of the cam (e.g., cams  114 ,  320 ,  614 ) in each of the test switch units (e.g., test switch units  100 ,  300 ,  600 ) and accordingly isolate the appropriate circuits. In such instances, the test switch units  100 ,  300  and  600  would operate in the manner as described in conjunction with the preceding figures. 
     Methods for operating test system  800  comprising first test switch unit (e.g., test switch unit  100 ), a second test switch unit (e.g., test switch unit  300 ) and the third test switch unit (e.g., test switch unit  600 ), are described. In one example, the method involves engaging a lever, such as the lever  324 . The lever  324  is, in turn, coupled to cams, i.e., cam  114 , cam  320  and cam  614  of the respective test switch units  100 ,  300 ,  600 . The movement of the lever  324  affects the rotation of cam  114 , cam  320  and cam  614 . As each of the cam  114 , cam  320  and cam  614  rotates, it results in the opening of the trip circuit coupled to the first test switch unit  100  upon the cam  114  engaging with the trip contact element  112  of the test switch unit  100 . Along with the movement of cam  114 , the cam  320  also moves. The cam  320  includes a leading profiled element  326  and a trailing profiled element  328 . As the cam  320  moves, the leading profiled element  326  of the cam  320  engages with the secondary contact element  314  and the trailing profiled element  328  of the cam  320  engages with the primary contact element  312 . In a similar manner, rotation of the cam  614  affects isolation of the VT circuit when the cam  614  engages with the VT contact element  610 . 
     It may be noted that the various examples of the test switches described in conjunction with the previous figures, may be implemented by way of other examples, which too, would fall within the scope of the present subject matter. Such examples are further described in conjunction with  FIGS. 9-17 . 
       FIG. 9  illustrates a cross-sectional view of a test switch unit  900  for opening a trip circuit, as per another the present subject matter. In one example, the test switch unit  900  includes relay lead  902  and field lead  904 . The relay lead  902  is adapted such that it may be coupled to the IED and the corresponding trip circuit. On the other hand, the field lead  904  is adapted to be coupled to a field supply current. The test switch unit  900  also includes a first primary contact element  906 , a second primary contact element  908  (collectively referred to as primary contact elements  906  and  908 ) and a secondary contact element  910 . In one case, the primary contact elements  906  and  908  and the secondary contact element  910  may be manufactured from an electrically conducting and flexible material. It may be noted that the primary contact element  908  may be similar to the trip contact element  110  (as explained in conjunction with  FIGS. 1-2 ). 
     Within the test switch unit  900 , one end of both the first primary contact element  906  and the secondary contact element  910  are connected with the relay lead  902  with the other respective ends, i.e., the ends  912 ,  914  being free. Similarly, one end of the second primary contact element  908  is connected with the field lead  904  with the other end of the second primary contact element  908 , i.e., end  916  also not affixed to any portion of the test switch unit  900 . As a result, each of the contact elements  906 ,  908 ,  910  are affixed at one end and moveable at the other. The test switch unit  900  further comprises cam  918 . In one example, portions of the cam  918  may engage with the contact elements  906 ,  908 ,  910  as a result of which each contact element  906 ,  908 ,  910  moves about the point to which the respective points where they are fixed. 
     The cam  918  is mounted on a shaft  920  which in turn is coupled to a lever  922 . Similar to lever  118 , the lever  922  is such that it is adapted to move in a notional plane which is perpendicular to the axis A about which the cam  918  is adapted to rotate. In one example, the lever  922  may be actuated manually or may be coupled, either directly or indirectly, through mechanically driven means. In case of the latter, such mechanically driven means may be actuated based on one or more control signals. The cam  918  is provided with set of inner profiled elements  924 ,  926  and an outer profiled element  928 . The inner profiled elements  924 ,  926  are so defined on the cam  918  such that the inner profiled elements  924 ,  926  are disposed nearly diametrically with respect to each other. As the cam  918  rotates, the inner profiled elements  924 ,  926  are to contact and move the primary contact elements  906 ,  908 , whereas the outer profiled element  928  is to contact and move the secondary contact element  910 . 
     Continuing with the present example, the test switch unit  900  further includes a test signal lead  930  connected to a conducting element  932 . The conducting element  932  may be a metallic plate having a surface to allow the end  914  of the secondary contact element  910  to come into contact with the conducting element  932 . As described previously, the relay lead  902  may be coupled to an IED and a trip circuit. The testing of the IED would involve the test signal lead  930  to be used for providing one or more test signals. As explained in conjunction with  FIG. 1 , for testing, the trip circuit is opened by moving the lever  922  so that no field supply current passes through the lever  922  using the test switch unit  900 . The manner in which the test switch unit  900  operates is further described in conjunction with  FIG. 10-11 . 
       FIG. 10-11  illustrates the example test switch unit  900  coupled to the trip circuit and the IED, in various stages of operation. Under normal operating conditions, the field supply current (interchangeably referred to as the “field current”) generated from the appropriate generating components is provided to the field lead  904 . The field current passes through the field lead  904  and through the second primary contact element  908 . Since the first end  912  of the first primary contact element  906  were previously in contact, with the end  916  of the second primary contact element  908  (as depicted in  FIG. 9 ) and because the test signal lead  930  is open, the field current travels through the pair of primary contact elements  906 ,  908 , to the relay lead  902  and eventually through the trip circuit which may be coupled to relay lead  902 . 
     For isolating the IED for testing, the lever  922  is moved downwards direction B, as depicted in  FIGS. 10-11 . The movement of the lever  922  affects the rotation of the shaft  920 , which in turn causes the rotation of the cam  918 . As the cam  918  rotates, the inner profiled elements  924 ,  926  also move in circular path. As the inner profiled elements  924 ,  926  moves it pushes against the primary contact elements  906 ,  908 . As the opposing inner profiled elements  924 ,  926  pushes against the primary contact elements  906 ,  908 , the primary contact elements  906 ,  908  are pushed apart thereby breaking the contact between them ( FIG. 10 ). 
     As the lever  922  is further pushed in the downward direction, the cam  918  rotates further such that the outer profiled element  928  moves towards the secondary contact element  910 . As the lever  922  is pushed further down, the outer profiled element  928  continues to move towards the secondary contact element  910 . The outer profiled element  928  may subsequently push against the secondary contact element  910  thereby resulting in the secondary contact element  910  to move towards and eventually contacts the conducting element  932  ( FIG. 11 ). 
     With the contact between the secondary contact element  910  and the conducting element  932  already established and with the primary contact elements  906 ,  908  no longer in electrical contact, the electrically conductive path, i.e., path between the field lead  904  and the relay lead  902 , provided through the pair of primary contact elements  906  and  908  is disrupted. At this stage, field lead  904  and the conducting element  932  (and hence in turn the test signal lead  930 ) are connected to each other through the secondary contact element  910 . As the end  914  couples with the conducting element  932 , the trip circuit which may be coupled to the relay lead  902  is in an open state. The stage may then commence for shorting and isolating the CT circuit coupled with the IED. This is explained in conjunction with  FIGS. 12-14 . 
       FIG. 12  illustrates a cross-sectional view of a test switch unit  1200 , as per another example of the present subject matter, wherein the test switch unit  1200  is coupled to an IED and CT circuit. The test switch unit  1200  as described is such that it may be coupled to the CT circuits and the IED. The test switch unit  1200  includes a relay lead  1202  and a field lead  1204 . The relay lead  1202  is so adapted such that it may be coupled to the intelligent electronic device and corresponding CT circuit. 
     The field lead  1204  is adapted to be coupled to the field current. The test switch unit  1200  may further include a test signal lead  1206  and a connecter port  1208 . The test switch unit  1200  also includes a first primary contact element  1210 , a second primary contact element  1212 , (collectively referred as primary contact elements  1210 ,  1212 ), and a first secondary contact element  1214 , and a second secondary contact element  1216  (collectively referred as secondary contact elements  1214 ,  1216 ). One end of each of the first primary contact element  1210  and the first secondary contact element  1214  are connected with the relay lead  1202 . Similarly, one end of each of the second primary contact element  1212  and the other secondary contact element  1216  are connected with the field lead  1204 . The other ends  1218 ,  1220  of the primary contact elements  1210 ,  1212  and the end  1222 ,  1224  of the secondary contact elements  1214 ,  1216  are free and not affixed to any portion of the test switch unit  1200 . The primary contact elements  1210 ,  1212  and the secondary contact elements  1214 ,  1216  may be manufactured from an electrically conducting and flexible material. In normal operation, when the test signal lead  1206  is not utilized and is open, the pair of primary contact element  1212  and  1214  provides an electrically conducting path for the field supply current from the field lead  1204  to the CT circuit which may be coupled to the relay lead  1202 . It may be noted that the primary contact element  1212  and the secondary contact element  1216  may be similar to the primary contact element  312  and the secondary contact element  314  (described in  FIGS. 3-5 ), respectively. 
     The test switch unit  1200  further includes a cam  1226  is mounted on a shaft  1228 , which in turn is coupled to a lever  1230 . Similar to lever  118 , the lever  1230  is such that it is adapted to move in a notional plane which is perpendicular to the axis A about which the cam  1226  is adapted to rotate. The cam  1226  is provided with set of inner profiled elements  1232 ,  1234  and the outer profiled elements  1236 ,  1238 . The inner profiled elements  1232 ,  1234  are so defined on the cam  1226  such that the inner profiled elements  1232 ,  1234  are disposed nearly diametrically with respect to each other. In a similar manner, the outer profiled elements  1236 ,  1238  are disposed nearly diametrically with respect to each other. The outer profiled elements  1236 ,  1238  are such that they traverse a circular path having a larger radius when compared with the inner profiled elements  1232 ,  1234 . 
     In operation, as the cam  1226  rotates, the inner profiled elements  1232 ,  1234  are to contact and move the primary contact elements  1210 ,  1212 , whereas the outer profiled elements  1236 ,  1238  is to contact and move the secondary contact elements  1214 ,  1216 . The test switch unit  1200  may further include conducting elements  1240 ,  1242 , each connected with the connecter port  1208  and the test signal lead  1206 , respectively. The conducting elements  1240 ,  1242  may be a metallic plate having a surface to allow the ends  1222 ,  1224  of the secondary contact elements  1214 ,  1216  to come into contact with the conducting elements  1240 ,  1242 . 
     In order to ensure that the IED may be tested, the CT circuit is to be isolated. Isolation of the CT circuit requires that the conductive path for the field current is routed through the connecter port  308 . To this end, the CT circuit is to be shorted. The manner in which the CT circuit is shorted is described further in conjunction with  FIGS. 13-14 . As would be explained, in the paragraphs that follow, the path for the field current is to be established prior to breaking the conductive path (i.e., the path established between the field lead  1204  and the relay lead  1202 , through the conducting elements  1240 ,  1242 ). 
     Initially, the ends  1218 ,  1220  of the primary contact elements  1210 ,  1212  are in contact, with neither of the secondary contact elements  1214 ,  1216  being in contact with the conducting elements  1240 ,  1242  ( FIG. 12 ). As a result, the field current travels through the pair of primary contact elements  1210  and  1212 , to the relay lead  1202  and eventually through the CT circuit which may be coupled to relay lead  1202 . 
     For isolating the CT circuit, the lever  1230  is moved in the direction M. The movement of the lever  1230  in the direction M, affects the rotation of the shaft  1228 , which in turn causes the rotation of the cam  1226 . As the cam  1226  rotates, the inner profiled elements  1232 ,  1234  also move in circular path and push against the primary contact elements  1210 ,  1212 . As the opposing inner profiled elements  1232 ,  1234  pushes against the primary contact elements  1210 ,  1212 , the primary contact elements  1210 ,  1212  are pushed apart thereby breaking the contact between them. In a similar manner, the outer profiled elements  1236 ,  1238  moves towards the secondary contact elements  1214 ,  1216 . As the lever  1230  is pushed further down, the outer profiled elements  1236 ,  1238  continue to move towards the respective secondary contact elements  1214 ,  1216 . The outer profiled elements  1236 ,  1238  may subsequently push against the secondary contact elements  1214 ,  1216  to move towards and eventually contact the conducting elements  1240 ,  1242  ( FIG. 13 ). 
     With the contact between the secondary contact elements  1214 ,  1216  and the conducting elements  1240 ,  1242  already established, the primary contact elements  1210 ,  1212  loses contact with each other, thereby breaking the electrically conductive path, i.e., path between the field lead  1204  and the relay lead  1202  ( FIG. 14 ). At this stage, the relay lead  1202  and the field lead  1204  are in electrical connection with the conducting elements  1240 ,  1242 . The field current traversing through the field lead  1204  and the secondary contact element  1216  may then be routed to the connecter port  1208 . In one example, the connecter port  1208  may be further connected with a similar connector port in a test switch unit positioned to the adjacent to the test switch unit  1200  within a test system. With the field current being routed through the connecter port  1208  (as opposed to the relay lead  1202 ), the CT circuit is shorted and the IED is isolated. 
     As has been described previously for testing the IED, the VT circuit has to be opened. Along with the opening of the trip circuit, the CT circuit is to be shorted and isolated, with VT circuits to be isolated. To such an end, with the trip circuit opened (as described in conjunction with  FIGS. 9-11 ), and the CT circuit being shorted and isolated (as described in conjunction with  FIGS. 12-14 ), the next steps involve isolation of the VT circuits. The isolation for the VT circuits is now described in conjunction with  FIGS. 15-17 . 
     Within the test switch unit  1500 , one end of both the first primary contact element  1506  and the secondary contact element  1510  are connected with the relay lead  1502  with the other respective ends, i.e., the ends  1512 ,  1514  being free. Similarly, one end of the second primary contact element  1508  is connected with the field lead  1504  with the other end of the second primary contact element  1508 , i.e., end  1516  also not affixed to any portion of the test switch unit  1500 . As a result, each of the contact elements  1506 ,  1508 ,  1510  are affixed at one end and moveable at the other. The test switch unit  1500  further comprises cam  1518 . In one example, portions of the cam  1518  may engage with the contact elements  1506 ,  1508 ,  1510  as a result of which each contact element  1506 ,  1508 ,  1510  move about the point to which the respective points where they are fixed. It may be noted that the primary contact element  1508  may be similar to the VT contact element  610  (described in  FIGS. 6-8 ), respectively. 
     The cam  1518  is mounted on a shaft  1520  which in turn is coupled to a lever  1522 . The lever  1522  is such that it is adapted to move in a notional plane which is perpendicular to the axis A about which the cam  1518  is adapted to rotate. The cam  1518  is provided with set of inner profiled elements  1524 ,  1526  and an outer profiled element  1528 . The inner profiled elements  1524 ,  1526  are so defined on the cam  1518  such that the inner profiled elements  1524 ,  1526  are disposed nearly diametrically with respect to each other. As the cam  1518  rotates, the inner profiled elements  1524 ,  1526  are to contact and move the primary contact elements  1506 ,  1508 , whereas the outer profiled element  1528  is to contact and move the secondary contact element  1510 . 
     Continuing with the present example, the test switch unit  1500  further includes a test signal lead  1530  connected to a conducting element  1532 . The conducting element  1532  may be a metallic plate having a surface to allow the end  1514  of the secondary contact element  1510  to come into contact with the conducting element  1532 . The manner in which the test switch unit  1500  operates is further described in conjunction with  FIGS. 16-17 . 
       FIGS. 16-17  illustrates the example test switch unit  1500  in various stages of operation. Under normal operating conditions, the field supply current (interchangeably referred to as the “field current”) generated from the appropriate generating components is provided to the field lead  1504 . The field current passes through the field lead  1504  and through the second primary contact element  1508 . Since the first end  1512  of the first primary contact element  1506  were previously in contact, with the end  1516  of the second primary contact element  1508  (as depicted in  FIG. 15 ) and because the test signal lead  1530  is open, the field current travels through the pair of primary contact elements  1506 ,  1508 , to the relay lead  1502  and eventually through the trip circuit which may be coupled to relay lead  1502 . 
     For isolating the IED for testing, the lever  1522  is moved downwards direction B, as depicted in  FIGS. 16-17 . The movement of the lever  1522  affects the rotation of the shaft  1520 , which in turn causes the rotation of the cam  1518 . As the cam  1518  rotates, the inner profiled elements  1524 ,  1526  moves and pushes against the primary contact elements  1506 ,  1508 . As the opposing inner profiled elements  1524 ,  1526  pushes against the primary contact elements  1506 ,  1508 , the primary contact elements  1506 ,  1508  are pushed apart thereby breaking the contact between them ( FIG. 16 ). 
     As the lever  1522  is further pushed in the downward direction, the cam  1518  rotates further such that the outer profiled element  1528  moves towards the secondary contact element  1510  and may subsequently push against the secondary contact element  1510  thereby resulting in the secondary contact element  1510  to move towards and eventually contacts the conducting element  1532  ( FIG. 17 ). At this stage, field lead  1504  and the conducting element  1532  (and hence in turn the test signal lead  1530 ) are connected to each other through the secondary contact element  1510 . 
     Although implementations of present subject matter have been described in language specific to structural features and/or methods, it is to be noted that the present subject matter is not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed and explained in the context of a few implementations for the present subject matter.