Stale Data Detection

Stale Data Defined

Stale data is defined as non-zero inter-site analog values which have good data quality, but are not fluctuating in the expected manner.

In General, “good” data quality means that the remote has reported the value as “good”.

More precisely, good data quality means that none of the following flags are set on ISDID Quality:

If none of the above conditions are present, the Intersite analog data source is “Potentially” stale (i.e. the analog’s quality appears to be “good” for the purposes of state data detection).

Zero values are excluded because they are typically not expected to fluctuate. Rather than only exclude values which are exactly zero, the analog’s Stale Zero Deadband parameter may be used to specify a band, centered about zero, within which values “sufficiently close to zero” will be considered non-stale.

Fluctuating in the “expected manner” is defined by specifying the analog’s Stale Deadband parameter, along with its Stale Period parameter. The Stale Deadband is the minimum change in amplitude that must occur over the user specified number of seconds defined by the analog’s Stale Period.

Stale Data Detection Features

Stale data detection may be enabled, disabled and parameterized on a per analog basis. Stale data detection may also be enabled or disabled on a system-wide basis.

Analogs enabled for stale data detection may optionally specify that an alarm be issued whenever the stale quality of the analog, or any of its Intersite sources, changes.

The values and data qualities which are received from the analog’s Intersite data sources are monitored for staleness independently of one another. Whenever a good quality ISDID value fluctuation in excess of the analog’s stale Deadband is detected, the value and the system time are stored with the ISDID. The timestamp marks the beginning of the ISDID’s Stale Detection “sliding time window”. The duration of the time window is equal to the analog’s Stale Period. If the time window expires before a subsequent fluctuation in excess of the stale Deadband is detected, the ISDID is marked stale.

Each ISDID has its own “stale” data quality flag, as does the analog itself. If the analog has a single Intersite data source, the stale quality of the analog will follow the stale quality of the ISDID. Because the stale data quality contributes to the composite “suspect” data quality, an alternate, good quality, non-stale ISDID will be used for the analog if one is available for analogs with secondary sources.

Counts are maintained of the number of stale analogs, Intersite data sources within each substation. Alarms associated with the transitions of the stale counts to and from zero may be enabled or disabled on a per substation basis.

Disabling the stale count alarms for a substation also disables stale alarms on the individual analogs within that substation. This mechanism is provided as a means of avoiding distractions caused by stale alarms from a problematic site while corrective measures are underway to resolve the root cause of the problem.

Stale alarms on a per-analog basis are also suppressed if the operator overrides the analog by placing it into any of the following conditions, which also prevent the analog from being marked stale.

1. Not In Service.

Manually replaced value.

Calculation replaced.

State Estimator replaced.

Uncommission.

Three displays are provided to support the monitoring of stale data. The (1) Substation Stale List (Stale Station Directory) displays a list of all substations containing stale analogs or Intersite data sources. The (2) Substation Stale Data Summary displays the currently stale analogs and Intersite data sources within a given substation. The (3) Substation Stale Data Tuning Display shows all of the stale-enabled analogs within a substation, regardless of whether or not they are currently stale.

Enabling/Disabling Stale Detection Globally

During the initial setup of Stale Data Detection on your system, a certain degree of trial and error may be expected in the selection and fine-tuning of the Stale Dead-bands and Stale Periods for the analogs to be monitored. Setting these values incorrectly may result in analogs being prematurely marked stale, resulting in suspect data qualities being assigned to healthy analogs. If the adversely affected analogs are critical, and/or their volume is large, your ability to utilize the EMS to perform non-Stale Data related functions could become problematic.

An additional scenario is that a malfunctioning Intersite data source could, under extreme cases, generate alternating bursts of stale and non-stale data reports, resulting in nuisance alarms.

In either situation, it may be advisable to temporarily turn off Stale Data Detection for the entire system and re-enable the function after the problem(s) have been corrected.

The following procedure describes how to enable or disable Stale Data Detection on a system-wide basis.

1. Call up the SCADA Parameters page within SCADA Online Editor.

Check or clear the “Global Stale data detection enable” checkbox.

Enabling/Disabling Stale Detection for an Analog

The following procedure describes how to enable or disable Stale Data Detection for a specific analog.

1. Call up the Analog Definition page within SCADA Online Editor.

Check or clear the Stale Data Detection “Detect” checkbox.

Enabling/Disabling Stale Alarms for an Analog

Disabling Stale Data Detection also disables Stale Data Alarms for a given analog. Refer to the previous section for how to disable Stale Detection for a specific analog.

Provided that Stale Data Detection is enabled for the analog, the following procedure describes how to enable or disable Stale Data Alarms for that analog.

1. Call up the Analog Definition page within SCADA Online Editor.

Check or clear the Stale Data Detection “Alarm” checkbox.

Note that an upper limit is placed on the number of analogs within the system for which stale data alarms may be generated. By default, the limit is set to 500. This enables a modest number of high priority analogs to generate individual Stale Data alarms, while preventing the volume of alarms from overwhelming the operator.

For example, if all of the data received from a misbehaving remote ICCP partner were to turn stale in a sudden burst, the operator could be tasked with acknowledging 10’s of thousands of stale data alarms.

The preferred strategy is to use the ability to enable stale alarms on individual analogs very sparingly, and use substation stale counter alarms as the means to be notified that stale data has been detected.

Enabling/Disabling Stale Alarms for a Substation

For each substation, counts are maintained of the number of analogs, Intersite data sources which are currently stale within that substation.

Note that because the analog’s quality may get good quality InterSite quality from a secondary source, if only one source is stale, the counters may provide early warning of stale data prior to it being propagated to the analog.

Zero value is the desired, normal, state for the 3 substation stale counters. When any of the counters change from zero to non-zero, an operator alert (alarm) is typically desired. An alarm exception is also issued when the counter(s) return to zero, but this is typically configured as an event, rather than an alarm.

When a substation stale alarm occurs, the recommended procedure for managing the situation is to monitor the stale analogs within problematic substations and correct the source of the stale data. The substation stale counts returning to zero provide confirmation that the problem has been resolved.

While corrective measures are underway to resolve the root cause of stale data, it is sometimes useful to suppress the generation of stale data alarms within a given substation. Disabling stale data alarms at the substation level suppresses stale alarms for the substation’s counters, as well as stale alarms for any analogs which have stale alarming individually enabled.

The following procedure describes how to enable/disable stale data alarms for a particular substation:

1. Call up the SCADA Online Editor.

Select the substation of interest, calling up the SCADA Substation Topology display.

Check or clear the “Stale Alarms” checkbox.

Identifying which Substations Contain Stale Data

Stale data alarms, at the substation or individual analog level, specify the substation within which the stale data has been detected. However, it is useful to have a quick indication of the locations of stale data across the entire system as an aide in executing corrective measures.

The following procedure describes how to call up the Stale Station Directory, which presents a list of all substations containing stale data:

While SCADA Station Directory is on display:

1. Select Related Displays (displays dropdown menu)

Select Substation Ordered Summaries (displays fly-out menu)

Select Substation Stale List

Identifying the Stale Analogs within a Substation

The Substation Stale Data Summary Display presents a tabular list of all analogs within a given substation whose Intersite data sources are currently stale.

The display may be called up by either of the following 2 methods:

1. Left-clicking a Substation identifier on the Stale Station Directory (see previous section).

Right-clicking on a substation in the Station Directory and selecting the ”Station Stale Summary” option.

Monitoring the Stale Detection of Problematic Analogs

The Substation Stale Data Summary Display (see preceding section) shows all the analogs within a substation which are currently stale. As soon as an analog becomes non-stale, it is removed from that display.

During the setup and tuning of stale data parameters, it is often useful to be able to monitor the behavior of analogs as they transition between stale and non-stale, without having them disappear. The Substation Stale Data Tuning Display provides this capability, showing all analogs which are enabled for Stale Data Detection, whether they are stale or not.

The Substation Stale Data Tuning Display may be invoked via the following procedure:

1. Right-click the substation via the Station Directory.

Select “Station Stale Tuning”.