Grounded isolation system

• US 20020136161A1
• Filed: 05/22/2002
• Published: 09/26/2002
• Est. Priority Date: 09/28/1999
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Mayer, William J., Fisher, David S., Cleereman, Douglas P.
• Granted Patent: US 7,212,391 B2
• Time in Patent Office: Days
• US Class Current: 370/216
• CPC Class Codes: B23Q 5/58 Safety devices protecting the operator B23Q11/0089

Abstract

An system and method are disclosed for isolating and grounding a load device, where grounding only occurs after the voltage(s) on the load device have been reduced to acceptable levels. The system includes power and grounding contacts, a sensing device, and a control device. The power contact determines whether a power line is coupled to a terminal of the load. The grounding contact determines whether the terminal is coupled to ground. The sensing device is coupled to the terminal, and the control device communicates with the contacts and sensing device. Upon a signal being provided to the control device, the control device causes the power contact to decouple the terminal from the power line and, upon the sensing device determining that a condition has been met concerning the terminal, the control device causes the grounding contact to couple the terminal with ground and a system indication light to be illuminated.

Claims

1. A system for coupling a load to a ground, the system comprising:

a first power contact that determines whether a first power line is coupled to a first terminal of the load;

a first grounding contact that determines whether the first terminal of the load is coupled to the ground;

a first sensing device coupled to the first terminal; and

a control device in communication with the first power and grounding contacts and the first sensing device;

wherein, upon a first signal being provided to the control device, the control device causes the first power contact to decouple the first terminal from the first power line; and

wherein, upon the first sensing device determining that a first condition has been met with respect to at least the first terminal, the control device causes the first grounding contact to couple the first terminal with the ground.

2. The system of claim 1, wherein the first sensing device includes a first sensing coil.

3. The system of claim 2, wherein each of the first power contact and the first grounding contact are normally open.

4. The system of claim 3, wherein the control device includes:

a first switch;

a first power coil that controls the first power contact so that, when the first power coil is energized, the first power contact is closed;

a second grounding contact that is normally closed and is coupled in series with the first switch and the first power coil between a power source and the ground;

a first grounding coil that controls the first and second grounding contacts so that, when the first grounding coil is energized, the first grounding contact is closed and the second grounding contact is opened;

a first sensing contact that is normally closed and is controlled by the first sensing coil and wherein, when the first condition is not met, the first sensing coil is energized and the first sensing contact is opened;

a second power contact that is normally closed and is coupled in series with the first sensing contact and the first grounding coil between the power source and the ground, wherein the second power contact is also controlled by the first power coil so that, when the first power coil is energized, the second power contact is opened.

5. The system of claim 4,

wherein the first signal is provided to the control device when the first switch changes from being closed to being open;

wherein the opening of the first switch causes the first power coil to turn off, which in turn causes the first power contact to decouple the first terminal from the first power line and further causes the second power contact to close; and

wherein upon sensing that the first condition has been met, the first sensing coil is turned off so that the first sensing contact closes and the first grounding coil is energized, which in turn causes the first grounding contact to couple the first terminal to the ground.

6. The system of claim 5, further comprising a second switch coupled in series with the second power contact, the first grounding coil and the first sensing contact between the power source and the ground, wherein the second switch is mechanically coupled to the first switch so that, upon the first switch being opened, the second switch closes, and vice-versa.

7. The system of claim 4, further comprising:

a third power contact that is normally open and determines whether a second power line is coupled to a second terminal of the load, wherein the third power contact is closed when the first power coil is energized; and

a third grounding contact that is normally open and determines whether the second terminal of the load is coupled to the ground, wherein the third grounding contact is closed when the first grounding coil is energized.

8. The system of claim 7, wherein the first sensing coil is coupled between the first and second terminals of the load, and further comprising:

a second sensing coil comprised within the first sensing device and coupled between the second terminal and a third terminal of the load, and

a second sensing contact that is normally closed, is controlled by the second sensing coil, and is coupled in series with the first sensing contact, the second power contact, and the first grounding coil between the power source and the ground,

wherein the first condition is determined to have been met when both the first and second coils turn off, which respectively cause the first and second sensing contacts to close, so that the first grounding coil is turned on and consequently the first and third grounding contacts are closed.

9. The system of claim 4, further comprising:

a third power contact coupled in series with the first power contact between the first power line and the first terminal,

wherein the control device further includes

a second switch;

a second power coil that controls the third power contact so that, when the second power coil is energized, the third power contact is closed;

a third grounding contact that is normally closed and is coupled in series with the second switch and the second power coil between the power source and the ground;

a fourth power contact that is normally closed and is coupled in series with the first sensing contact, the second power contact, and the first grounding coil;

wherein the second switch is mechanically coupled to the first switch so that the first and second switches open and close in unison.

10. The system of claim 9, wherein upon the opening of the first and second switches, the first and second power coils are turned off, which in turn causes the first, second, third, and fourth power contacts to be opened;

wherein upon sensing that the first condition has been met, the first sensing coil is turned off so that the first sensing contact closes and the first grounding coil is energized, which in turn causes the first grounding contact to couple the first terminal to the ground; and

wherein the first grounding coil is mechanically coupled to each of the first and second power coils.

11. The system of claim 10, wherein an indication of load isolation is provided when the first and second power coils are turned off and the first grounding coil is energized.

12. The system of claim 11, further comprising an additional grounding contact that is normally open, two additional power contacts that are normally closed, an indicator lamp and an additional switch, all of which are coupled between the power source and the ground,

wherein the additional switch is coupled to the first and second switches and opens when the first and second switches are closed, and vice-versa;

and

wherein the two additional power contacts are closed when the first and second power coils are respectively deenergized, and the additional grounding contact is closed when the grounding coil is energized, so that the indicator lamp turns on to provide the indication when the first and second power coils are turned off and the first grounding coil is energized.

13. The system of claim 2, wherein the first sensing coil is coupled between the first terminal and a second terminal of the load, and wherein the first condition is met when a voltage between the first and second terminals falls below a threshold voltage such that the first sensing coil turns off.

14. The system of claim 13, wherein the threshold voltage is approximately 33% of a voltage between the first and second power lines.

15. The system of claim 14, where a delay occurs between the decoupling of the power supply from the first terminal and the coupling of the first terminal to the ground due to the operation of the first sensing coil and the control unit.

16. The system of claim 1, wherein the first sensing device is arectifier circuit including first, second, third and fourth diodes and a first coil, wherein the first and second diodes are coupled between the first terminal and first and second ports of the first coil, respectively, and the third and fourth diodes are coupled between an additional terminal and the first and second ports of the first coil, respectively.

19. The method of claim 18, further comprising:

deenergizing a first power coil in response to the command, wherein the deenergizing of the first power coil causes the opening of the first contact and also causes the closing of a third contact; and

closing a fourth contact upon determining that the first condition has been met, wherein the third and fourth contacts are coupled in series with a first grounding coil and a switch between a power source and the ground, and wherein the switch is closed upon receiving the command, so that the closing of the third and fourth contacts causes the first grounding coil to be energized, so that the second contact is closed.

20. The method of claim 19, wherein the first condition is met when a sensing coil coupled to the load is deenergized, which in turn causes the second contact to close.

17. A system for decoupling first, second, and third terminals of a load from first, second and third power lines and then coupling the first, second and third terminals to a ground, wherein the coupling of the first, second and third terminals to the ground is delayed until voltage levels at those terminals meet a predetermined condition, the system comprising:

first, second and third power contacts coupling the first, second and third terminals of the load with the first, second and third power lines, respectively;

first, second and third grounding contacts coupling the first, second and third terminals of the load with the ground;

sensing means for sensing the predetermined condition;

control means for controlling the status of the power contacts and the grounding contacts, wherein the control means is coupled to the sensing means, the power contact and the grounding contacts;

wherein the control means causes the power contacts to decouple the first, second and third terminals of the load from the first, second and third power lines, respectively, in response to receiving a first signal at a first time; and

wherein the control means causes the grounding contacts to couple the first, second and third terminals of the load with the ground at a second time following the first time in response to the sensing means sensing the predetermined condition.

18. A method of controlling the decoupling of a power line from a load and coupling that load to a ground in order to isolate and ground the load, the method comprising:

receiving a command to decouple the load from the power line;

opening a first contact between the power line and the load so that the power line is decoupled from the load;

determining that a first condition concerning a status of the load is met; and

upon determining that the first condition has been met, closing a second contact between the load and the ground so as to ground the load.