GIC Analysis Tables and Results

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This section provides a reference explanation for each of the GIC specific fields on the GIC Analysis Tables and Results:

Areas Tab

The Areas page contains the following fields:

Area Num, Area Name: Give the standard identifiers for each area.

Ignore GIC Losses: Indicates whether or not GIC related losses are calculated for the transformers in the area. In large cases when solving the power flow it may be helpful to avoid calculating the GIC related losses for transformers in distant areas.

Mvar Losses: Gives the total GIC related transformer Mvar losses for the area.

Buses Tab

The Buses page contains the following fields:

Number, Name, Area Name and Nom kV: Give the standard identifiers for each bus.

PU Volt: The AC solution per unit voltage.

GIC DC Volt: The GIC DC voltage for the bus.

GIC Neutral DC Volt: The bus’s substation neutral bus voltage.

GIC Gen Step-up Conductance Per Phase: Total of the per phase conductance for all the implicitly modeled generator step-up transformers at the bus. See the Generator Page for details.

GIC Gen Step-up Amps to Neutral: Total of the amps flowing into the neutral for all the implicitly modeled generator step-up transformers at the bus. See the Generator Page for details.

Generators Tab

The Generators page contains the following fields:

Number of Bus, Name of Bus, ID: Give the standard identifiers for each generator.

Status, Gen MW: Status and real power output of the generator.

Include Implicit GSU: Often the generator step-up transformer (GSU) is modeled explicitly in the power flow. For this situation the transformer would appear on the Transformers page and this field should be No. However, sometimes the transformer is not explicitly modeled. This may be indicated by the generator being directly connected to a high voltage bus, or it may be indicated by non-zero entries for the R and X fields in the Generator Step-up Transformer group on the Generator Dialog, Faults page. If this is the cause then the field should be Yes. If unknown then the entry should be Default, in which case an implicit GSU is assumed if either 1) the R or X fields are non-zero, or 2) the generator is connected to a bus with a nominal voltage greater than 30 kV. This implicit generator is assumed to be y-connected on the transmission side, delta on the generator side. If the R value is non-zero the associated per phase conductance is calculated from this value. Otherwise a default value is used. Currently the default value cannot be changed.

GIC Step-up Amps to Neutral: The total amps (all three phases) flowing from the implicitly modeled GSU into the substation neutral.

GIC Step-up Conductance Per Phase: Per phase conductance for the implicitly modeled GSU; zero indicates no transformer.

Implicit GSU Mvar Losses: Total of the Mvar losses associated with the implicitly modeled GSU. Currently this is not implemented, but will be added shortly.

Ignore Losses from Implicit GSU: This field is always disabled to indicate it is not set here. It tells whether the GIC related losses from the implicitly modeled GSU are ignored for the generator’s area.

GMatrix Tab

The GMatrix page shows the entries in the G (conductance) matrix. The entries are for the parallel combination of all three phases.

Lines Tab

The Lines page contains entries for all the transmission lines and transformers in the model. It contains the following fields:

From Number, From Name: Standard identifiers for the From end bus.

To Number, To Name: Standard identifiers for the To end bus.

Circuit: Line two character circuit ID.

GIC DC Volt Input: The GIC DC voltage modeled for the line. This comes from the data on the Create GMD Electric Field Input page. The polarity is the positive terminal is towards the To end.

GIC DC Amps Per Phase From: For a transmission line this is the per phase GIC current in amps flowing into the From end of the line. If this is a transformer then this is the per phase current flowing into the substation neutral unless it is an auto-transformer. For an auto-transformer it is either the series or common winding flow, depending upon whether the From or To bus has the higher nominal voltage.

GIC DC Amps Per Phase To: For a transmission line this is the per phase GIC current in amps flowing into the To end of the line. If this is a transformer then this is the per phase current flowing into the substation neutral unless it is an auto-transformer. For an auto-transformer it is either the series or common winding flow, depending upon whether the From or To bus has the higher nominal voltage.

GIC DC Amps Per Phase Max Abs Value: This is the absolute value of the maximum current flow in the previous two fields. The field is included to make it easy to sort by the maximum current.

GIC DC Volt From: The GIC DC voltage for the From bus.

GIC DC Volt To: The GIC DC voltage for the To bus.

GIC Conductance Per Phase: The per phase conductance for all the transmission lines. The field value is determined from the per unit power flow data. This field is zero for transformers since the winding values are given/entered on the Transformers page.

GIC Mvar Losses: The GIC related reactive power losses for the transformers. Field is blank for transmission lines.

Distance Between Substations: Distance between the From and To bus substations in either km or miles, depending on the value of the Units of Distance field on the Create GMD Electric Field Input page.

Compass Angle Between Substations: Compass angle in degrees pointing from the From bus substation to the To bus substation.

Substations Tab

The Substations page contains entries for all the substations in the model. It contains the following fields:

Sub Num, Sub Name, Sub ID: Standard identifiers for the substation

GIC DC Neutral Voltage: DC voltage of the substation neutral

GIC Amps to Neutral: Total amps flowing into the substation neutral; a negative number is used for current flow out of the neutral into the system.

Grounding Resistance: Substation grounding resistance in Ohms. This is a user input field and should be set if known. If the value is left zero then an approximated value will be used in the computations (see the next field).

GIC Used Grounding Resistance: This is the grounding resistance value in Ohms that was actually used in the GIC calculations. If the Grounding Resistance field is non-zero then that value is used. Otherwise the resistance is approximated, based upon the the voltage of the highest bus in the substation and the number of buses in the substation. The approximation assumes larger, higher voltage substations have a larger footprint and hence a lower resistance.

Latitude, Longitude: Latitude and longitude for the substation. Latitude values in the Northern Hemisphere are entered as positive numbers and those in the Southern Hemisphere as negative values. Longitude values in the Eastern Hemisphere are entered as positive values and those in the Western Hemisphere as negative values.

Transformers Tab

The Transformers page contains entries for all the transformers in the model. It contains the following fields:

From Number, From Name: Standard identifiers for the From end bus of the transformer.

To Number, To Name: Standard identifiers for the To end bus of the transformer.

Circuit: Line two character circuit ID for the transformer.

Manually Enter Coil Resistance: Toggle to allow the transformer’s coil resistance to be set manually (Yes) or estimated based upon the transformer’s series resistance in the power flow (No). Ideally these values should be set manually. However, in a large case this may be impractical. A reasonable approach could be to set the values for key transformers in the area of interest. When this field is set Yes the next two fields are enterable. Otherwise the next two fields are overwritten with the resistance value actually used in the GIC solution.

From Side Ohms per Phase: If the Manually Enter Coil Resistance field is Yes then this field is enterable, and should be set to the per phase coil winding resistance for the From Bus winding. Otherwise the coil resistance is estimated, and this value is overwritten. The value need not be set for coils that are not connected to ground except is should be set for the series winding on an auto-transformer.

To Side Ohms per Phase: If the Manually Enter Coil Resistance field is Yes then this field is enterable, and should be set to the per phase coil winding resistance for the To Bus winding. Otherwise the coil resistance is estimated, and this value is overwritten. The value need not be set for coils that are not connected to ground except is should be set for the series winding on an autotransformer.

Is AutoTransformer: Indicates whether the transformer should be modeled as an autotransformer. Since this is not a standard power flow model parameter, the default value is Unknown. Set to Yes if it is an autotransformer and No if it is not. When the value is Unknown the current functionality is to assume it is an autotransformer provided (1) it is not a phase shifter, (2) the From and To bus nominal voltage values differ, (3) the turns ratio is no greater than 4 to 1, and (4) the highest nominal voltage is above 100 kV. Entries (3) and (4) can be modified under the DC Current Calculation Options

Assumed to be an AutoTransformer: Indicates whether the GIC calculations treated the transformer as an autotransformer.

Transformer GIC Neutral Amps: Total amps flowing from the transformer into the substation neutral.

GIC Mvar Losses: Total GIC induced reactive power losses (in Mvar) for the transformer. The following fields describe how this value is calculated.

Ignore GIC Losses: Indicates whether the GIC losses for the transformer are being ignored. Since this is currently set on an area by area basis, the field is disabled here; it is just for informational purposes.

Core Type: Core type of the transformer. This value is only used if the next field, GIC Model Type, is Default. Since the core type is not a standard power flow field the default value is Unknown. Available core types are as follows.

  1. Unknown
  2. Single Phase
  3. Three Phase Shell
  4. 3-Legged, Three Phase,
  5. 5-Legged, Three Phase
  6. 7-Legged, Three Phase
  7. Core, Three Phase Generic

GIC Model Type: The GIC Model Type field is used to relate the GIC currents flowing into the transformer coils into reactive power losses. Currently two values are available, either Default or Linear. When the value is set to Linear, the total GIC-related Mvar losses modeled in the power flow are this value times the GIC coil current in amps. A typical range for this field is between 0.3 to 1.5. When the value is Default, a linear model is used with the reactive power losses estimated based on the core type.

GIC Model Param: When the GIC model type is linear, this field is used to determine the transformer reactive power losses based on the GIC current flowing in the transformer coils.

GIC Blocked for Transformer Neutral: When set to Yes has a GIC blocking device which will blocked dc neutral current.

GIC Model K Used: Will show the K Value actually used by the transformer. This will potentially depend on the GIC Model Type, Core Type, GIC Model Param, and the settings on the Options\AC Power Flow Model settings. See the Options description for more details.