Contingency Options: Advanced Limit Monitoring

 

These options are all available on the Contingency Analysis dialog under the Contingency Options tab under the Limit Monitoring grouping.

The Advanced Limit Monitoring page allows you to shape how limit violations are detected and reported.

Many of these settings can also be specified on a Limit Group-specific basis. See the Limit Group Dialog for more information. If specified for a limit group, those settings will supersede those specified here with the contingency options.

 

Never report violations if…

This section controls the reporting of violations that should NEVER be reported. Minimum changes in branch flows, voltages, and interface flows which must be met before a device is reported as violating a limit can be specified. These options will only be used if the checkbox is checked at the beginning of this section. The minimum change values may be specified for:

Increase in line/transformer flows – This is the minimum change in percentage points that the loading on a line/transformer must increase before the line/transformer gets reported as a violation. For example, if this value is set to 2%, line limits are being monitored at 100%, and a line has a base case loading of 99% and a post-contingency loading of 100%, the line will not get reported as a violation.

Decrease in low bus voltage – This is the minimum change in a bus voltage that must occur for a bus low voltage violation to be reported. For example, if this value is set to 0.05 pu, the low voltage limit on a bus is 0.90 pu, the base case voltage at the bus is 0.91 pu, and the post-contingency voltage at the bus is 0.89 pu, this bus will not be reported as a low voltage violation.

Increase in high bus voltage – This is the minimum change in a bus voltage that must occur for bus high voltage violation to be reported. For example, if this value is set to 0.05 pu, the high voltage limit on a bus is 1.1 pu, the base case voltage at the bus is 1.09 pu, and the post-contingency voltage at the bus is 1.11 pu, this bus will not be reported as a high voltage violation.

Increase in interface flows – This is the minimum change in percentage points that the loading on an interface must increase before the interface gets reported as a violation. For example, if this value is set to 2%, interfaces are being monitored at 100%, and an interface has a base case loading of 99% and a post-contingency loading of 100%, the interface will not get reported as a violation.

Always report as a violation if…

This section allows you to specify the minimum change in flow or voltage at which point any device meeting the minimum change requirement will ALWAYS be reported, EVEN if the actual device limit (flow or voltage) is NOT violated. In other words, these options allow the reporting of large changes in flow or voltage, even if the device's actual limit is NOT itself violated. These options will only be used if the checkbox is checked at the beginning of this section. The minimum change values may be specified for:

Increase in line/transformer flows – This is the minimum change in line/transformer flow in percentage points that the loading on a line/transformer must increase so that the line/transformer gets reported as a violation even if the loading does not exceed the element’s limit. For example, if this value is set to 2%, line limits are being monitored at 100%, and a line has a base case loading of 50% and a post-contingency loading of 63%, this line will be reported as a violation even though the post-contingency loading does not exceed the limit.

Decrease in low bus voltage – This is the minimum amount that a bus voltage must decrease for a bus low voltage violation to be reported even if the resulting voltage is higher than the bus low voltage limit. For example, if this value is set to 0.05 pu, the low voltage limit at a bus is 0.90 pu, the base case voltage at the bus is 1.0 pu, and the post-contingency voltage at the bus is 0.95 pu, this bus will be reported as a low voltage violation.

Increase in high bus voltage – This is the minimum amount that a bus voltage must increase for a bus high voltage violation to be reported even if the resulting voltage is lower than the bus high voltage limit. For example, if this value is set to 0.05 pu, the high voltage limit at a bus is 1.10 pu, the base case voltage at the bus is 1.0 pu, and the post-contingency voltage at the bus is 1.05 pu, this bus will be reported as a high voltage violation.

Increase in interface flows – This is the minimum change in interface flow in percentage points that the loading on an interface must increase so that the interface gets reported as a violation even if the loading does not exceed the interface limit. For example, if this value is set to 2%, interface limits are being monitored at 100%, and an interface has a base case loading of 75% and a post-contingency loading of 77%, this interface will be reported as a violation even though the post-contingency loading does not exceed the limit.

Caution should be used when using the Always report… options because this may result in a very large number of reported violations.

Report changes in bus dV/dQ sensitivity

Check this option to enable reporting changes in voltage to reactive power sensitivity for buses in the post-contingency solution. Set the sensitivity multiplier to the minimum change in sensitivity for reporting the value(s) under contingency. Any sensitivity that changes by the given multiple will be reported. You can also define an advanced bus filter using the Define Filter button, and choose either the newly defined bus filter or a previously existing bus filter for reporting dV/dQ sensitivity changes at only buses that meet the defined filter.

Also, regardless of the sensitivity multiple setting, any bus that meets the filter and has a negative dV/dQ will be reported as a violation.

Caution should be used when selecting this option. Calculating the dV/dQ sensitivities requires more computation time. Define a filter so that the dV/dQ sensitivities are only calculated for those buses for which it is important to calculate these values.

Report as a violations if a bus becomes disconnected

When checked, buses that become disconnected from the system due to a contingency will be reported as violations.

Re-reporting of base case violations

This section controls the reporting of Base Case violations. Because the concern of contingency analysis often is to identify those limitations that result directly from a particular outage or event, you may desire not to report all violations that were present in the Base Case with each contingency-specific set of violations. These options allow you to specify just how much of the Base Case violation information to report for each contingency. It gives you three options:

Do not report Base Case violations

When this option is checked, any element that was violated in the Base Case is omitted from the set of violations listed for each contingency.

List all Base Case violations for all contingencies

When this option is checked, all elements that were violated in the Base Case and are still violated post-contingency are included in the set of violations listed for each contingency.

Use these criteria

When this option is checked, only those elements that were violated in the Base Case and that meet the four criteria listed below will be listed with the contingency-specific violations. The four criteria include:

Minimum % increase in line/transformer flows: Only those branches that were violated in the Base Case whose flow has increased by at least this amount as a result of the contingency will be listed as contingency violations.

Minimum per-unit decrease in low bus voltage: Only those bus voltages that were violated in the Base Case that have decreased by at least this amount as a result of the contingency will be listed as contingency violations.

Minimum per-unit increase in high bus voltage: Only those bus voltages that were violated in the Base Case that have increased by at least this amount as a result of the contingency will be listed as contingency violations.

Minimum % increase in interface flows: Only those interfaces that were violated in the Base Case whose flow has increased by at least this amount as a result of the contingency will be listed as contingency violations.

Percentage values here are expressed in reference to a limit rather than either the base case value or post-contingency flow value. When calculating the percentage for the Base Case violations used in the comparisons, the post-contingency rating sets are used. Comparisons made using percentage changes for branches are done using percentage points and not as a percentage of the actual change. For example, if the value for the minimum percent increase in line flow is 2%, lines are monitored at 100%, and a line is loaded at 100% in the base case and, the line must be loaded to at least 102% post-contingency to be reported.

How to Monitor Voltage Changes

Voltage changes can be monitored either directly on the amount of the bus per unit voltage, or based instead on a percentage change in per unit voltage from the base case per unit voltage values.