Circuit protects technical personnel and test equipment from hazardous currents conducted through safety barriers and into data acquisition equipment. Network isolates energy source, restricts arcing to remote area, and dissipates harmlessly residual energy transient

Cambra, J. M.

English

NASA Technical Reports Server

1 
Data 
Recorder 
-----J 
Thermocouple	 I	 Spark Gap 
FT
	 Transducer)
L__	
\j 
High Voltage Protection 
Long Twiste 
Shielded-Pal 
Cable 
1972	 B72-10119 
NASA TECH BRIEF 
Ames Research Center 	 - 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
High Voltage Protection Network 
A circuit has been designed to protect technical 
personnel and test equipment from the hazardous 
currents that can be conducted through safety bar-
riers and into data acquisition equipment by instru-
mentation wiring in the event that electrical failures 
occur on high-voltage, high-energy apparatus. The 
I -
verted from a step function to a pulse by the action 
of the high-voltage fuse. The first spark gap will con-
duct when its firing voltage is exceeded, drawing 
sufficient current to blow the fuse, quickly separating 
the rest of the network from the fault. Succeeding 
elements constitute a nonlinear filter, further attenu-
--
circuit will act to isolate the energy source, restrict 
arcing to a remote area, and dissipate harmlessly the 
residual energy transient. Each conductor is protected 
individually. 
The circuit shown in the figure consists of a high-
voltage fuse shunted by a spark gap, an RLC network 
formed by the remaining shunt spark gaps, a small 
resistance, and a long, twisted shielded-pair cable. 
In the event that a high-energy, high-voltage source 
is accidentally connected to the transducer, the 
energy propagated down each conductor will be con-
.
This documetct was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
ating the remaining pulse. The spark gaps behave like 
capacitive elements except during the time their fir-
ing voltage is exceeded, when they are resistive and 
dissipate energy. 
The long cable provides shunt capacitance for the 
filter network, and its low-voltage breakdown charac-
teristic offers an additional element of protection 
against high voltages. It also provides protection by 
ensuring that there is a long distance between per-
sonnel, the data equipment room, and the area where 
high-energy arcing will occur.
(continued overleaf) 
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned.rights.
https://ntrs.nasa.gov/search.jsp?R=19720000119 2020-03-17T03:31:16+00:00Z
For the demonstration test, a 9.1-kV, 15-megawatt 
energy source was connected directly to a representa-
tive circuit, which was terminated with an oscillo-
scope probe having a 12-megohm, 5-pf input imped-
ance. Spark-gap breakdown voltage was 280 volts. 
Energy reaching the termination measured less than 
6 x 10 watt-seconds with a peak voltage of 600 volts. 
Notes: 
1. The concept has been shown by test to be suffi-
ciently effective, yet avoids the expense and com-
plication of systems that circumvent hard wiring. 
2. Care is taken to maintain the cases of the data 
acquisition equipment and all associated equip-
ment as well as the environment of operating per-
sonnel at the ground potential. Operators cannot 
reach equipment without standing on grounded 
copper sheets.
8. Requests for additional information may be di-
rected to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP72-101 19 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code 200-1A 
Ames Research Center 
Moffett Field, California 94085 
Source: Joseph M. Cambra 
Ames Research Center 
(ARC-10197)
. 
. 
. 
B72-10119	 Category 02


High voltage protection network

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