Gas Hourly And Daily Trend Alarm Conditions - GE Hydran M2-X Instruction Manual

Hydran* M2-X Instruction Manual
Hydran M2-X Maximum Reading
Obtained During the Monitoring Period
Below 70 ppm
From 70 to 400 ppm
Above 400 ppm
Table 6-2: Suggested Guidelines for Setting the Gas Level High Alarm Condition

6.2.5 Gas Hourly and Daily Trend Alarm Conditions

6.2.5.1 Purpose of Gas Hourly and Daily Trends
Detection of hourly and daily trend alarm conditions is a unique feature of the
Hydran M2-X that provides early warning of slowly increasing gas levels.
For example, let us consider a transformer with a 50-ppm gas level and a gas
level High alarm set point of 150 ppm.
Note: An increase of 25 ppm or more per month requires investigation.
• If no trend alarm condition is used and if the gas level reading starts
increasing at the rate of 50 ppm per month (twice the concern rate), it will
take two months before the gas level High alarm condition is detected
and the investigation of the possible causes of the increase begins.
• If the daily trend High alarm condition is used and its alarm set point
adjusted to 25 ppm, its period to 30 days and its alarm delay to 33 % of
the period (10 days), the alarm would occur approximately 23 days after
the beginning of the gas level increase. Investigation of the possible
causes could thus start five weeks earlier.
computations, see Section 6.2.5.2.
6.2.5.2 Gas Hourly and Daily Trend Computations
A unique computation method is used for both the hourly and daily trends. In
these computations, the gas level reading is processed through a first- order, digital,
low -pass filter; the trend reading (slope) is then extracted using a first-order, digital,
high-pass filter. The time constants for both filters are set to 33 % of the trend
period for optimum results.
Table 6-3 and Table 6-4 below show two examples of trend computations.
MA-029 Rev. 1.0, 30-Jul-18
Minimum Suggested Alarm Set Point
to Reduce the Risks of Unnecessary
Alarms
100 ppm
1.5 times the highest Hydran M2-X
reading
200 ppm above the highest Hydran M2-X
reading
For details on trend
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