6.2.5.4 Guidelines for Setting Alarm Conditions of Gas Trends
Hourly and daily trend High and High-High alarm condition settings cannot be
described in terms of absolute criteria. They are related to the user’s field experience
and the utility’s standard practice. This Section provides a few guidelines to optimize
both the hourly and daily trend alarm conditions.
1. The readings of the Hydran M2-X should be monitored over a minimum
period of two to three times the trend period before setting these parameters.
Follow the same rules as for the gas level High alarm condition listed in
Section 6.2.4.
2. If a fast response to a sudden gas level increase is needed, it is best to rely on
the gas level alarm conditions rather than on trend alarm conditions. Trend
alarm conditions are ideal to detect slow and steady changes from
fluctuating readings, but are not as good to detect abrupt changes.
3. The transformer (or other equipment) past history and the user’s field
experience are the most important criteria for alarm condition settings. If
existing, records of previous dissolved gas analysis (DGA) for the equipment
monitored should be used to help determine alarm condition settings in
general and especially for the daily trend.
4. Trend alarm delays should be set according to each trend period (see
guidelines in Section 3.2.8.1). For example:
• If the hourly trend period is set to four hours, the hourly trend reading may
show quite large, but short, positive and negative peaks during a day. In
this case, an hourly trend alarm delay of 50 to 75 % of the period could
avoid unnecessary alarms.
• However, if the hourly trend period is set to 48 hours, daily fluctuations
would not affect the trend reading significantly. In this case, the alarm
delay could be set to 10 to 20 % of the period.
6.3 System Fault Conditions
An alarm due to system fault conditions warns the operator that the Hydran M2-
X is not functioning properly. Such an alarm must therefore be verified and solved
rapidly because it indicates that the monitoring system (the Hydran M2-X) of the
transformer is faulty.
Note: An alarm due to system fault conditions does not concern the transformer.
To Next Page
Loading...
