Crowbar circuit verification testing system

Details Crowbar circuit verification testing system Crowbar circuit verification testing system

1999-08-16

2001-05-22

Sherry, Michael J. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Load shunting by fault responsive means

C361S057000, C361S104000, C324S424000

Reexamination Certificate

active

06236546

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the art of crowbar circuits and, more particularly, to verification of the operativeness of such a circuit.
BACKGROUND OF THE INVENTION
Crowbar circuits are known in the art and are typically employed for protecting an electrical device from damage by high currents resulting from fault conditions. For example, an inductive output tube (IOT) is frequently employed in UHF television transmitters. Such an IOT is connected to a high voltage (HV) power supply and may suffer adverse damage from a sudden high current resulting from internal tube arcing. Under such conditions, an unprotected IOT will draw excessive current from the HV power supply causing possible damage to the tube.
A crowbar circuit serves to detect a sudden rise in current drawn from the HV supply due to fault conditions. This will cause an electronic switching device, such as a deuterium thyratron, to be turned on and it serves to direct the fault current from the supply away from the IOT to prevent damage. When the crowbar switching device, thyratron, is turned on it informs an amplifier controller and the controller causes a circuit breaker to open disconnecting the HV power supply from its AC line voltage source.
The thyratron is connected directly across the HV supply and, hence, when it is turned on it provides essentially a short circuit across the IOT. An electrode, such as the anode, of the thyratron is connected to earth ground. In order to determine whether the crowbar circuit is operative, a fuse wire may be connected between the cathode of the thyratron and a point that may be shorted to ground quickly.
A crowbar circuit verification device known in the prior art is illustrated in FIG.
1
and it includes a fuse wire together with a vacuum switch, which, when closed, provides a short circuit around the thyratron to direct fault current to ground. The fuse wire together with the vacuum switch are disclosed in detail in
FIG. 2
which will be described in greater detail hereinbelow. This vacuum shorting switch of the prior art has several shortcomings including the fact that it requires an external power source to operate the switch. Additionally, this form of a shorting switch cannot normally be installed inside a typical HV compartment because it requires transmitter interlocks to be defeated. The shorting switch does not provide positive provision for connecting the fuse wire. The switch is bulky and difficult to transport and is relatively expensive.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide means for verifying the operativeness of a crowbar circuit which does not require an external power source to operate the crowbar shorting switch.
In accordance with the present invention, a system is provided for verifying the operativeness of a crowbar circuit that normally protects an electrical device located in a series circuit with a power supply. The crowbar circuit includes means for sensing fault current in the series circuit and a crowbar switch that responds to the sensing means for protecting the electrical device by directing the fault current away from the electrical device. The system includes verification testing means having a fuse and actuatable pneumatic shorting switch connected together in series so that when the pneumatic switch is actuated it provides a short circuit across the crowbar shorting switch to verify the operativeness of the crowbar circuit which, if not operative, will cause the fault current to flow through and blow out the fuse.


REFERENCES:
patent: 4156264 (1979-05-01), Hoover
patent: 4864286 (1989-09-01), Ohshita et al.
patent: 4926281 (1990-05-01), Murphy
patent: 39 23 474 A1 (1991-01-01), None
patent: 196 24 517 C1 (1997-11-01), None
XP-000972519 Test Wire for High Voltage Power Supply Crowbar System, by Joseph T. Bradley III and Michael Collins, Los Alamos National Laboratory, LANSCE-5, M.S. H827, P.O. Box 1663, Los Alamos, NM 87545, John M. Gahl, University of New Mexico, Albuquerque, NM 87131, Mar. 1997.
PCT International Search Report.

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