System and method for shared hybrid transfer switch system with integrated relay self test
The present disclosure relates to a shared transfer switching system with built in relay testing ability, for transferring power received by a load from a preferred AC power source to an alternate AC power source, or transferring power being received by the load from the alternate AC power source to the preferred AC power source. The system selectively controls various ones of the relays used to apply power from either the preferred or alternate power sources to the load, such that the relays are switched from open to closed states at controlled times, while voltage measurements are made at select locations between the relays. The system can identify which specific ones of a plurality of relays associated with each of the preferred and alternate power sources has properly opened and closed, and thus verify that all of the relays needed to switch between the preferred and alternate power sources are operating properly.
1. A shared transfer switching system with built in relay testing ability, for transferring power received by a load from a preferred AC power source to an alternate AC power source, or transferring power being received by the load from the alternate AC power source to the preferred AC power source, the shared transfer switching system comprising:
one first primary relay and one first secondary relay coupled in series, and in series with the preferred power source and the load, to enable the load to be powered by the preferred power source;
one second primary relay and one second secondary relay coupled in series, and also in series with the alternate power source and with the load, for providing power from the alternate power source to the load when the preferred power source is not available to power the load;
a voltage sensing resistor string (VSRS) coupled across the second secondary relay;
a controller for controlling operation of the second primary relay and the second secondary relay;
a switching subsystem in communication with the controller and the first primary relay, the first secondary relay, the second primary relay, and the second secondary relay, and the load, the switching subsystem configured to be controlled by the controller to control a switch over from one or the other of the preferred or alternate power sources to the load; and
a relay test subsystem including a relay test software module and a voltage detection subsystem operably controlled by the controller for carrying out a relay test process including performing a plurality of voltage tests by;
while the first primary relay and the first secondary relay are closed, and while the second primary relay is open, opening the second secondary relay, and using power from the alternate power supply to help verify, through a first voltage measurement taken using the VSRS, that the second secondary relay has opened, without causing an interruption of power to the load;
opening the second secondary relay without interrupting power to the load;
closing the second primary relay while the second secondary relay remains open, and while the first primary relay and the first secondary relay both remain closed, and using the VSRS to obtain a second voltage measurement, while using the power from the preferred power source and without interrupting power to the load, to verify that the second primary relay has successfully closed.
2. The system of claim 1 , wherein the voltage sensing resistor string of the voltage detection subsystem is configured to help make a voltage measurement at a node which is between the second primary relay and the second secondary relay, and in series with the second primary relay and the second secondary relay.
3. The system of claim 2 , further comprising a user interface having a control for enabling the relay test process.
4. The system of claim 1 , wherein the relay test software module carries out the relay test process by opening the second secondary relay while the second primary relay is open and making a voltage test at a node representing an intermediate point therebetween, and then closing the second primary relay while the second secondary relay is open and making a voltage test at the node.
5. The system of claim 4 , wherein the relay test module is configured to carry out the relay test process by opening the first secondary relay while the first primary relay is open, and making a voltage test at the node, and then closing the first primary relay while the first secondary relay is open and making a voltage test at the node.
6. The system of claim 1 , further comprising a load voltage sensing resistor string in communication with the controller, for monitoring a voltage across the load to help in evaluating a condition of one or more of the first primary relay or the second primary relay.
7. The system of claim 1 , wherein the switching subsystem includes an additional relay and a solid-state switching device, configured to work in series to provide a temporary current path between the alternate power source and the Load, when the additional relay is in a closed condition and the solid-state switching device is turned on, during a switchover operation when a switchover is made from the preferred power source to the alternate power source; and
wherein the additional relay is opened when initiating the relay test process.
8. A shared transfer switching system with built in relay testing ability, for transferring power received by a load from a preferred AC power source to an alternate AC power source, or transferring power being received by the load from the alternate AC power source to the preferred AC power source, the shared transfer switching system comprising:
one first primary relay and one first secondary relay coupled in series, and also in series with the preferred power source and the load, to enable the load to be powered by the preferred power source;
one second primary relay and one second secondary relay coupled in series, and also in series with the alternate power source and with the load, for providing power from the alternate power source to the load when the preferred power source is not available to power the load;
a voltage sensing resistor string (VSRS) coupled across the second secondary relay;
a controller for controlling operation of the first and second primary relays and the first and second secondary relays;
a switching subsystem in communication with the controller and the first and second primary relays and the first and second secondary relays, the switching subsystem configured to be controlled by the controller to control a switch over from one or the other of the preferred or alternate power sources to the load; and
a relay test subsystem including a software module and a voltage detection subsystem, both controlled by the controller, for carrying out a relay test process including performing a plurality of voltage tests by:
while the first primary relay and the first secondary relay are closed, and while the second primary relay is open, selectively opening the second secondary relay, and using the alternate power source to help perform a first voltage test to obtain a first voltage measurement using the VSRS, without an interruption of power to the load, to verify that the second secondary relay has opened;
opening the second secondary relay without interrupting power to the load;
closing the second primary relay while the second secondary relay remains open, and while the first primary relay and the first secondary relay both remain closed, and using the VSRS to obtain a second voltage measurement, while using the power from the preferred power source and without interrupting power to the load, to verify that the second primary relay has successfully closed.
9. The system of claim 8 , wherein the second primary relay and the second secondary relay are tested by the controller while the system is being powered by the preferred power source.
10. The system of claim 8 , wherein the first primary relay and the first secondary relay are tested while the system is being powered by the alternate power source.
11. The system of claim 8 ,
wherein the controller uses the relay test software module to close the second primary relay while the second secondary relay is opened, and uses the voltage detection subsystem to measure a voltage at a node representing an intermediate series connection point between the second primary relay and the second secondary relay, while power is being provided by the preferred power source, to verify proper operation of the second primary relay.
12. The system of claim 8 ,
wherein the controller uses the relay test software module to close the first primary relay while the first secondary relay is open, and uses the voltage detection subsystem to measure a voltage at a node representing an intermediate series connection point between the first primary relay and the first secondary relay, while power is being provided by the alternate power source, to verify proper operation of the first primary relay.
13. The system of claim 8 , further comprising a user accessible control for initiating the relay test process.
14. The system of claim 13 , further comprising a user interface subsystem, and wherein the user accessible control includes a button operably associated with the user interface subsystem, for enabling user initiation of the relay test process.
15. A method for testing a plurality of relays associated with a system for transferring power from one or the other of a preferred AC power source or an alternate power source to a load, the method comprising:
using one first primary relay and one first secondary relay coupled in series, and in series with the preferred power source and the load, to enable the load to be powered by the preferred power source;
using one second primary relay and one second secondary relay coupled in series, and also in series with the alternate power source and with the load, for providing power from the alternate power source to the load when the preferred power source is not available to power the load;
a voltage sensing resistor string (VSRS) coupled across the second secondary relay;
using a switching subsystem in communication with the first primary relay, the first secondary relay, the second primary relay, and the second secondary relay, and the load, the switching subsystem configured to be controlled to switch over from one or the other of the preferred or alternate power sources to the load; and
carrying out a relay test process controlled by the controller, the relay test process including performing a plurality of voltage tests by:
while the first primary relay and the first secondary relay are both closed, and the second primary relay is open, selectively opening the second secondary relay and using the alternate power source, along with the VSRS, to perform a first voltage measurement to verify that the second secondary relay has moved into an open position, and without an interruption of power to the load;
opening the second secondary relay without interrupting power to the load;
closing the second primary relay while the second secondary relay remains open, and while the first primary relay and the first secondary relay both remain closed, and using the VSRS to obtain a second voltage measurement, while using the power from the preferred power source and without interrupting power to the load, to verify that the second primary relay has successfully closed.
16. The method of claim 15 , further comprising performing the first voltage measurement at a node defining an intermediate point between a series connection of the second primary relay and the second secondary relay; and
subsequently performing the second voltage measurement at the node after the second primary relay has been opened and the second secondary relay has been closed.