GROUND FAULT DETECTOR AND METHOD FOR DETECTING GROUND FAULTS

• US 20170261541A1
• Filed: 09/12/2014
• Published: 09/14/2017
• Est. Priority Date: 09/12/2014
• Status: Abandoned Application

• Current Assignee: Otis Elevator Company (Otis Worldwide Corp.)
• Original Assignee: Otis Elevator Company (Otis Worldwide Corp.)
• Inventors: Herkel, Peter
• Application Number:
  US15/509,708
• Publication Number:
  US 20170261541A1
• Time in Patent Office: Days
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults

Abstract

A ground fault detector circuit (140) for a people conveyor configured to detect a ground fault in a safety chain (100) of the people conveyor, comprises a first resistor (130) connected between a first contact (P1) on the supply (126) of the safety chain (100) and a second contact (P2) on the return (122) of the safety chain (100), and a device (134) for detecting a change in voltage drop (UGFD) with respect to ground across said first resistor (130).

Claims

1. A ground fault detector circuit (140) for a people conveyor configured to detect a ground fault in a safety chain (100) of the people conveyor, comprising:

a first resistor (130) connected between a first contact (P1) on the supply (126) of the safety chain (100) and a second contact (P2) on the return (122) of the safety chain (100), and a device for detecting a change in voltage drop (UGFD) across said first resistor (130) with respect to ground (114).

2. The ground fault detector circuit (140) according to claim 1, further comprising a network including at least the first electrical resistor (130) and a second resistor (132) connected in series between the first contact (P1) on the supply (126) of the safety chain (100) and the second contact (P2) on the return(122) of the safety chain (100).

3. The ground fault detector circuit (140) according to claim 1, wherein the device (134) for detecting a change in voltage drop (UGFD) across said first resistor (130) with respect to ground (114) is a third resistor (134) that is connected in parallel to the first resistor (132) for detecting the change in voltage drop across the first resistor (130) with respect to ground (114).

4. The ground fault detector circuit (140) according to claim 3, wherein the third resistor (134) is connected between a third contact (P3) upstream of the first resistor (130) and a fourth contact (P4) at ground (114).

5. The ground fault detector circuit (140) according to claim 1, wherein the second contact (P2) is connected downstream of a safety chain relay (118).

6. The ground fault detector circuit (140) according to claim 1, wherein the return (122) of the safety chain is at an electrical potential larger than the electrical potential of ground (114), and wherein the third resistor (134) is connected in parallel to the first resistor and to a fourth resistor (136) connected between the return (122) of the safety chain (100) and ground (114).

7. The ground fault detector circuit (140) according to claim 6, wherein the fourth resistor (136) is connected between the first resistor (130) and ground (114).

8. The ground fault detector circuit (140) according to claim 1, further comprising a microprocessor for evaluation of the change in voltage drop across the first resistor (130).

9. The ground fault detector circuit (140) according to claim 1, wherein the safety chain (100) includes a safety relay (118) having a coil resistance of 100 Ohm or larger.

10. The ground fault detector circuit (140) according to claim 1, further adapted to carry out a ground fault test continuously over time.

11. The ground fault detector circuit (140) according to claim 1, further adapted to carry out a ground fault test at discrete points in time.

12. The ground fault detector circuit (140) according to claim 1, further adapted to determine a dangerous ground fault in case the change in voltage drop across the first resistor (130) is equal to, or larger, than a first threshold value and to shut-down a power supply of the people conveyor in case a dangerous ground fault is detected.

13. The ground fault detector circuit (140) according to claim 1, further adapted to determine a tolerable ground fault in case the change in voltage drop across the first resistor (130) is equal to, or lower, than a second threshold value.

14. The ground fault detector circuit (140) according to claim 1, further including a power supply unit (112) having a rated power corresponding to nominal voltage times rated current in the safety chain (100).

15. A method for detecting a ground fault (124) in a safety chain (100) of a people conveyor, comprising:

Detecting a change in voltage drop with respect to ground across a first resistor (130) connected between a first contact (P1) on the supply (126) of the safety chain (100) and a second contact (P2) on the return (122) of the safety chain (100).