How SensorGuard works

SensorGuard is a multi-function power quality monitor for electronic equipment. A control board continuously monitors the quality of the power grid. As abnormal voltage conditions are detected, the control board turns off a definite purpose power contactor, which in turn provides the isolation for the electronic equipment from the power service. Should a power problem be detected, SensorGuard shuts ‘off’ power and then automatically restores it after a user defined period, only if no additional electrical threats are detected. While the timer is holding the circuit in ‘protect’ mode, if additional problems are detected, it will reset and only allow the equipment to be reconnected to AC if an “all clear” condition is determined.

To detect and assess risk of lightning induced surge damage, SensorGuard employs an external lightning sensor. The lightning sensor continuously monitors the earth surface for approaching lightning ground strikes and will isolate equipment from the AC power when these strikes are within the present factory setting of approximately ten kilometers from the sensor’s location.

The detection distance can be adjusted by the user to become more or less sensitive as required by the application. For protection of pipeline systems, the sensitivity is usually adjusted to the highest setting to detect storms up to and in excess of 30 kilometers away, thus assuring maximum protection. In addition, the sensor is unique in its ability to sense the build-up to a near or actual lightning strike through detection of the “stepped leader event,” enabling SensorGuard to isolate equipment from the AC power in advance of a damaging lightning event. The following illustration shows a typical installation:

Guards Against Poor Power Quality

In today’s electrical environment, power stability has become a serious if not critical issue. As the power distribution grid becomes more stressed due to the demand for power, saturation occurs. Power quality is not always assured. Such conditions as brownouts, momentary blackouts, line bumps, voltage sags and swells, over voltage conditions and repeated inductive switching events can all lead to serious problems for sensitive electronic equipment. Repeated exposure to any of these conditions can seriously shorten the life expectancy of connected equipment, if not destroy it outright. SensorGuard’s ability to detect these events and isolate your electronic equipment protects your operations against these unpredictable issues. While detection and protection against these events is less critical for cathodic protection systems, such events do reduce the life of rectifier systems due to the cumulative damage caused.

Guards Against Lightning Induced GPR Conditions

Ground potential rise (GPR), describes those conditions produced in the earth's surface where abnormally elevated voltage charges result from downed power line phase conductors that come into contact with soil. A lightning ground strike also produces, for the same instant in time, a GPR condition. As the GPR voltage encounters grounded metallic objects, charges are transferred into them and fault currents will flow through all interconnecting conducting mediums during the dissipation of the energy.

For example, a cathodic protection system ground rod is connected via the AC Power connection neutral to the very well grounded power Sub Station. A potential difference will exist between the two upon a Lightning strike at or near the site. As the potential difference or imbalance that exists between these two ground sources equalizes, the resulting fault current flow can and often will damage sensitive circuits in the path.