Ground fault detection circuit for an ungrounded control system

Details Ground fault detection circuit for an ungrounded control system Ground fault detection circuit for an ungrounded control system

1995-04-11

1996-07-16

Gaffin, Jeffrey A.

Electricity: electrical systems and devices

Safety and protection of systems and devices

Ground fault protection

361 35, 361 38, 361 49, H02H 300

Patent

active

055372830

ABSTRACT:
A ground fault detection circuit monitors an interlock control circuit for use with a machine or process control system. The interlock control system utilizes electromechanical relays with hard contacts. The interlock control system will disable operation of the machine or process if any ground fault condition exists in the interlock control circuit. A ground condition in the machine or process control circuits is permissible. The system uses a redundant circuit path to verify the integrity of the components in the interlock control system. The control system includes an ungrounded isolation transformer for supplying power to separate monitoring relays interposed between each leg of the transformer and ground. The contacts of these relays are series connected with emergency-stop (e-stop) switches to energize interposing control relays. The outputs of the interposing relays are used to energize the final control relay that controls the operation of the machine or process. If a ground fault occurs, the particular monitoring relay will deenergize and the interposing control relays will also deenergize, causing the machine or process to be disabled. A reset circuit prevents continued operation of the control system as long as the ground fault condition exists.

REFERENCES:
patent: 3678338 (1972-09-01), Beachley
patent: 3840783 (1974-10-01), Eckart

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