On-line testable solid state reversing DC motor starter
View Patent ↗A solid state reversing DC motor starter that is testable on-line and satisfies the requirements for nuclear safety grade equipment. The motor starter employs a bridge of solid state switches which connect the polarity of the motor winding to conform to the desired direction of travel. The reversing switch bridge is in series with the main switch that is coupled in parallel with a reduced current by-pass flow path.
1. A solid state DC motor starter configured to have a test capability that will test a plurality of components of the solid state DC motor starter while the motor starter is connected between a power source and a motor that the motor starter actuates, without actuating the motor or taking the motor out of service, comprising:
a main switch for turning the solid state DC motor starter and the motor on and off;
a test circuit in parallel with the main switch, the test circuit comprising;
a current reducing component;
a test switch in series with the current reducing component, wherein when current is supplied to the parallel arrangement of the test circuit and the main switch with the main switch off the current reducing component maintains the current to the motor windings below a value that will actuate the motor when the test switch is turned on; and
means for monitoring the voltage at an output of the respective plurality of components.
2. The solid state DC motor starter of claim 1 wherein the current reducing component maintains the current to the motor winding to approximately 50 mA or less.
3. The solid state DC motor starter of claim 1 wherein the current reducing component is a resistor of approximately 2,500 ohms.
4. The solid state DC motor starter of claim 1 including a reversing circuit connected between the main switch and the motor, the reversing circuit being responsive to an open input to connect a winding of the motor to the main switch with a first polarity and responsive to a closed input to connect the motor winding to the main switch with a second polarity wherein the reversing circuit cannot be energized unless the main switch is turned on and a signal is received at either the open input or the closed input.
5. The solid state DC motor starter of claim 4 wherein the open input and closed input are interlocked so that a signal cannot be communicated through the open input and the closed input at the same time.
6. The solid state DC motor starter of claim 5 wherein a signal communicated to either the open input or the closed input that is not blocked by the interlock, is latched in an on condition for a predetermined period of time.
7. The solid state DC motor starter of claim 4 wherein if the signal is received at either the open input or the closed input and the main switch is turned on while the test switch is on, the motor will actuate.
8. The solid state DC motor starter of claim 4 including a control logic circuit wherein the control logic circuit assures the signal is received at either the open input or the closed input before the main switch is turned on.
9. The solid state DC motor starter of claim 8 wherein the control logic circuit will turn off the main switch, the open input and the closed input for a predetermined period of time if the signal is received at either the open input or the closed input at a time when the other of the open input or the closed input is on.
10. The solid state DC motor starter of claim 9 wherein the predetermined period of time is substantially equal to the time required to allow the motor to stop and transients to subside.
11. The solid state DC motor starter of claim 10 wherein following the predetermined period of time the control logic circuit will issue the signal to a one of the open input or the closed input that will cause the motor to reverse its direction from a last actuation and turn on the main switch.
12. The solid state DC motor starter of claim 11 wherein the predetermined period of time is approximately 1 second or longer.
13. A solid state DC motor starter having a test capability that will test a plurality of components of the solid state DC motor starter while the motor starter is connected between a power source and a motor that the motor starter actuates, without actuating the motor, comprising:
a main switch for turning the solid state DC motor starter and the motor on and off;
a test circuit in parallel with the main switch, the test circuit comprising;
a current reducing component;
a test switch in series with the current reducing component, wherein the current reducing component maintains the current to the motor windings below a value that will actuate the motor when the test switch is turned on; and
means for monitoring the voltage at an output of the respective plurality of components; and
a reversing circuit connected between the main switch and the motor, the reversing circuit being responsive to an open input to connect a winding of the motor to the main switch with a first polarity and responsive to a closed input to connect the motor winding to the main switch with a second polarity wherein the reversing circuit cannot be energized unless the main switch is turned on and a signal is received at either the open input or the closed input, wherein the reversing circuit comprises a plurality of reversing polarity switches and the solid state DC motor starter further includes a control logic circuit wherein the control logic circuit turns off the reversing polarity switches a predetermined interval after the main switch is turned off.
14. The solid state DC motor starter of claim 13 wherein during a test of the main switch the reversing polarity switches are turned off so that current only flows through a shunt winding of the motor so that no motor motion occurs.
15. The solid state DC motor starter of claim 13 wherein the predetermined interval is long enough to allow transients due to inductive current switching to subside before the reversing polarity switches are turned off.
16. A solid state DC motor starter having a test capability that will test a plurality of components of the solid state DC motor starter while the motor starter is connected between a power source and a motor that the motor starter actuates, without actuating the motor, comprising:
a main switch for turning the solid state DC motor starter and the motor on and off;
a test circuit in parallel with the main switch, the test circuit comprising;
a current reducing component;
a test switch in series with the current reducing component, wherein the current reducing component maintains the current to the motor windings below a value that will actuate the motor when the test switch is turned on; and
means for monitoring the voltage at an output of the respective plurality of components; and
a delay switch in series with the main switch and in parallel with the test circuit, the delay switch remaining open for a pre-selected period of time when the main switch is first opened; and
a resistor in parallel with the delay switch and in series with the main switch for reducing the current through the motor on initial start up of the motor during the pre-selected time the delay switch remains open.
17. The solid state DC motor starter of claim 1 including a snubber circuit in parallel with the main switch.