Calculation of power system modes

Engee is an Engee application designed to calculate and analyse steady-state modes of electric power systems.

To open the application, go to the Engee workspace and in the upper left corner under Engee applications select Engee . The application runs in a separate browser tab and has the following view by default:

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Working with the application

Three tabs with tables are used to work with the application:

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Nodes

Nodes

Column

Units

Explanation

Node number, must be unique

Type

Node type (for more details see. * Node type *)

_Rn

Active load in the node

_Qn

Mvar

Reactive load in the node

_Gsh

µSm

Active conductivity of the shunt in the node

_Vsh

µSm

Reactive conductance of the shunt in the node (for details see: Vsh µSm). Reactive shunt conductivity in the node and in the branch)

Neighbourhood

District number

Node voltage modulus

Delta

Degrees

Node voltage angle

_Vnom

Nominal node voltage

_Vmax

Maximum permissible node voltage

_Vmin

Minimum permissible node voltage

_Rg

Active generation capacity in the node

_Qg

Mvar

Reactive generation capacity in the node

_Rsh

Active power released at the shunt in the node

_Qsh

Mvar

Reactive power released at the shunt in the node

_Iinject

Total generation and load current in the node

branches

Branches

Column

Units

Explanation

Branch number, must be unique

_Nnach

Node number of the start node of the branch

_Ncon

Node number of the end of the branch

Ohm

Active resistance of the branch

Ohm

Reactive resistance of the branch

µSm

Active transverse conductivity of the branch

µSm

Reactive transverse conductance of the branch (for more details, see B µSm). Reactive shunt conductivity in the node and in the branch)

kV/kV

Modulus of the transformation ratio (for details see ) *Transformation coefficient)

Status

Enabled or disabled state of the branch

_{Imax_nach}

Permissible maximum current at the beginning of the branch

_{Imax_end}

Permissible maximum current at the end of the branch

_Inach

Estimated current at the beginning of the branch

_Icon

Estimated branch end current

_Rnach

Estimated active power of the beginning of the branch

_Qnach

Mvar

Estimated reactive power at the beginning of the branch

_Rcon

Estimated active power of the end of the branch

_Qcon

Mvar

Estimated reactive power of the branch end

Active power losses in the branch

Mvar

Reactive power losses in the branch

_Rsh

Active power losses in the branch shunt

_Qsh

Mvar

Reactive power losses in the branch shunt

Generators

Generators

Column

Units

Explanation

Generator number

_Node

Generator installation node number

Type

Node type after the mode calculation (for more details, see the following table). * Node type *)

_Rg

Active power generation task

_Qg

Mvar

Reactive power generation task (ignored if node type = "Gen")

_Qmax

Mvar

Maximum permissible value of reactive power generation

_Qmin

Mvar

Minimum permissible value of reactive power generation

_Vzd

Setpoint voltage (ignored if node type = "Heating")

Status

Enabled or disabled status of the generator

* Node type *

"Load" - load (generation can be set via , );
"Gen" - generating (generation can be set via , );
"Base" - balancing;
"Gen+" - generating (generation set via , ), and reaching the maximum limit on allowable reactive power;
Gen- - generating (generation set via , ), and reached the minimum limit of permissible reactive power.

The node type can be set only in the table "Nodes", in the table "Generators" the column is not available for editing.

Reactive shunt conductivity in the node and in the branch

Inductive conductivity is negative. Capacitive conductivity is positive.

*Transformation coefficient

The following buttons are used to work with tables:

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Upload file with mode - uploads files from PC via File browser . Available formats: Matpower (.m), HDF5 (.h5).
Save mode file - saves the mode file edited in the application to File browser . In the root folder /user a folder grid_downloads is created, in which the mode file in HDF5 format is saved, with the name Grid$number of nodes in the model$.h5, for example Grid14.h5.

It is recommended to rename the file so that it is not overwritten by the next save in the application.
Add row - adds a row to the end of the current table.
Delete row - deletes the active row from the current table. To make a row active, click on it with the left mouse button.
Clear All - clears the contents of all tables.
Set visible columns - shows/hides columns of the selected table. The displayed columns are in bold, the hidden ones - in plain text:
- performs verification and validation of the entered data. After it performs the mode calculation and fills in the columns with the calculation results.
- link to this article in the documentation.

Power system model

The branches are modelled by a U-shaped substitution diagram:

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The load can be modelled by fixed power or shunt. Generation can be modelled by PV or PQ model.

Example of working with the application

In the application, you can set the initial circuit data in two ways:

Enter the data manually.
Load the data in .h5 or .m format. A test 14-node schematic can be downloaded from link.

The following rules must be adhered to in order to enter the raw schema data:

Draw the schematic diagram showing all nodes and branches.
Number all nodes in the electrical network, including all intermediate nodes.
- For example, a power station can be represented by two nodes - the generator voltage busbars and the busbars behind the transformer.
- The node in the programme source data corresponds to the electrical busbars.
- The node number must be a unique positive number; end-to-end numbering is not necessary.
- For ease of orientation in the diagram, it is advisable to give similar node numbers (3, 13, 103, 1003, etc.) to nodes belonging to the same object.
- The selected node numbers should be plotted on the network diagram.
For each node, determine its nominal voltage and plot it on the diagram.
For each load node, determine the active and reactive power consumption.
- If the initial data is given by active power and , then calculate the reactive power: .
If there are shunts to ground in the node - a battery of static capacitors (BSC) or shunt reactors (SR) - determine their conductivity (in microsiemens) and plot them on the schematic according to the rule:
- Capacitive conductance is positive.
- Inductive conductivity is negative.
For power lines (transmission lines):
- Specify a unique branch number.
- Specify the start node and end node of the branch.
- Define longitudinal resistance and conductivity to earth (conductivity is specified in microsymens, capacitive character is reflected by a plus sign).
For transformers, determine:
- Resistance: , reduced to the high voltage side.
- Shunt conductivity to earth: .
- The transformation ratio, equal to the ratio of the nominal voltage of the end of the branch to the nominal voltage of the beginning of the branch (it is assumed that the transformation ratio is less than unity). In order to obtain this, it is necessary to take the highest voltage node as the starting node of the transformer branch.
The autotransformers and three-winding transformers are designed in a star circuit with an intermediate node and three branches, two of which have transformation ratios.
Determine the number of the balancing node from those with generation and its voltage modulus.
For nodes with synchronous machines (generators, compensators):
- In the Nodes tab, set the type to Gen.
- In the Generators tab set:
  - The unique number of the generator.
  - Number of the node in which it is installed.
  - Active power of generation.
  - Reactive power control limits ( ).
  - Specified (fixed) voltage modulus (_Vzd).

The peculiarities of setting the initial data for such nodes are explained by the action of excitation regulators of synchronous machines (CM). Usually, the CM keeps the voltage modulus on the high voltage busbars (behind the transformer) or on the generator voltage busbars unchanged by regulating the reactive power provided by the CM.

The reactive power is monitored during the mode calculation and if one of the set limits is violated:

The reactive power is fixed at its value.
The voltage module is released.

It is also possible to specify a generator with fixed reactive power generation. To do this:

In the Nodes tab it is necessary to set the type Harvest.
In the Generators tab set parameters: Pg, Qg.

An example of the prepared scheme is shown below. In it:

Node 201 is the balancing node.
Nodes 201 and 204 represent the power plants.
The loads in the nodes are specified.
The generator in node 204 produces `10 MW.

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Complete the tables to prepare for the calculations as follows:

For the node table:

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For the branch table:

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For the generator table:

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This will result in a calculation:

For the node table:

calculation of the power grid modes 18 x

For the branch table:

calculation of the power grid modes 19 x

For the generator table:

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The results of the calculation are plotted:

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Next, save the calculation results using the button calculation of the power grid modes 5 Save file with mode.

In the Engee file browser a directory with the saved mode file appears:

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In order to load this file into the Engee application again, download it to a PC and upload it again via the calculation of the power grid modes 4 button Download mode file.

Calculation of power system modes

Working with the application

* Node type *

Reactive shunt conductivity in the node and in the branch

*Transformation coefficient

Power system model

Example of working with the application

Useful links