10.1.2 Purpose Of Hourly And Daily Trends; Table 10-1 - Alarm Conditions Monitored By The Hydran 201Ti - GE Hydran 201 i Instruction Manual
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in the oil during a period of time measured in days. The daily trend is updated every five
minutes.
The complete list of fail alarm conditions is shown in Section 10.5.1 on page 10-14.
Table 10-1 on page 10-3 lists the alarm conditions monitored by the Hydran 201Ti.
Source
Gas level
Hourly trend
Daily trend
Sensor temperature
Battery voltage
Sensor and connections
a.
Either one of the following cables (or connectors in the connection link): Sensor, sensor
thermistor, or heating plate thermistor.
10.1.2 Purpose of Hourly and Daily Trends
Detection of hourly and daily trend alarm conditions is a unique feature of the
Hydran 201i System that provides early warning of slowly increasing gas level. For
example, let us consider a transformer with a 50-ppm gas level and a typical gas High alarm
set point of 150 ppm.
• If no trend alarm is used and if the gas level reading starts increasing at the rate of 50 ppm
per month, it takes two months before the gas High alarm condition is detected and the
investigation of the possible causes of the increase begins (unless the gas reading was
already closely monitored).
• If the daily trend High alarm is used and its alarm set point is 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. For details on trend computa-
tions, see Section 10.4.3 on page 10-12.
Part 17997
Table 10-1 - Alarm Conditions Monitored by the Hydran 201Ti
Low-Low
a
Cable
short
Rev. 6, March 2011
Possible States
High
Low
—
Replace
Replace
sensor soon
sensor now
Alarm Levels
High-High
—
a
Cable
open
10-3
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