Time delay device

Details Time delay device Time delay device

1999-05-11

2001-03-13

Sherry, Michael J. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Automatic reclosing

C361S075000, C361S202000

Reexamination Certificate

active

06201676

ABSTRACT:

TECHNOLOGY FIELD
This invention relates to a time delay device for a circuit recloser.
BACKGROUND
On high voltage lines, many problems, such as lightning striking the line, tree branches or wires blowing in a wind gust, or animals on the lines, are only temporary. However, even these temporary problems can cause permanent damage to electrical equipment if power is not shut off for their duration. A device such as a recloser may be used in high voltage lines to deal with such problems.
A recloser is an automatic, high-voltage electric switch that shuts off electric power in an electric distribution line when a problem, such as a short circuit, occurs. After shutting off power, and waiting for expiration of a time delay, the recloser automatically restores power and tests the distribution line to determine whether the problem has been removed. If the problem is still present, the recloser shuts off power again. The recloser may repeat the shut-off-wait-restore process several times. If the fault is permanent, the recloser may shut off the power permanently after a certain number of repetitions (for example, three or four).
SUMMARY
The invention provides a hydraulic time delay device for coupling to a fault-sensing element in a circuit recloser. To this end, the time delay device includes a piston having an external connection and operable to move through a housing in the device to cause hydraulic fluid in the housing to flow out of the housing and into a passageway. A time delay of the time delay device corresponds to a time required to move the piston.
In one general aspect, the time delay device includes a first adjustable orifice formed in the passageway to define an adjustable first fluid flow path through the passageway, and an adjustable valve positioned to provide an adjustable second fluid flow path through the passageway. A second adjustable orifice formed in the passageway provides further adjustment of the second fluid flow path. Adjustment of the first orifice, the valve, and the second orifice affect the time required to move the piston.
Embodiments may include one or more of the following features. The time delay device may further include a piston spring inside the housing. The piston moves through the housing in a first direction in response to a force on the external connection, and the piston spring asserts a force on the piston in an opposite direction. The piston may include an aperture that closes when the piston moves in the first direction to push the hydraulic fluid into the passageway, and opens when the piston moves in the opposite direction to permit the hydraulic fluid to flow through the aperture.
Adjustments to the orifices may be made by adjusting their sizes. Adjustments to the valve may be made by adjusting the position of the valve.
The time delay device may further include an adjustable screw that applies a force to the valve through a valve spring which couples the valve to the screw. The force applied to the valve may modify the second fluid flow path. A set screw positioned inside the adjustable screw may be used to adjust the second orifice.
The circuit recloser may be used to open contacts in the circuit after the time delay. The fault sensing element may be linked to the external connection of the piston.


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