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We recommend adding components to a one-line diagram and referencing them on TCC
drawings. The one-line diagrams provide a convenient way to describe the power system
topology and component connections. The actual component names, connections, and data
are stored in the database and only referenced on the one-line diagrams and TCC drawings.
Deleting a component from the database will automatically remove it from all of the one-
line diagrams and TCC drawings where it was displayed.
Multiple One-line Diagrams
Since the database stores the entire project and system model information, all or any
selected part of the system model can be displayed on any number of different one-line
diagrams. This allows you to have an over-all system one-line as well as smaller one-lines
that display specific sub-stations, areas, processes, buildings, etc. Groups of components
can be copied from one one-line diagram and copied to other one-line diagrams. You can
also selectively hide and display project components on any of the one-line diagrams. If
you understand that the one-lines and TCC drawings simply display components and their
connections from the project database, you can understand how a component or group of
components can be displayed on multiple one-lines in the same project.
Connecting Components on the One-line
It is important to note that system studies require definition of impedance between
designated points in the power system. Traditionally, these designated points are called
“Buses” and the impedance components connecting the buses are called “Branches”.
Traditionally, each end of an impedance component must be connected to a bus.
Components that don’t have defined impedance or the negligible impedance is ignored
(such as relays, breakers, switches, etc.) can be connected in series with impedance devices
without affecting the impedance connections. A few examples will help illustrate the
allowable connections in PTW:
- You cannot place two impedance components in series without an interconnecting bus or
bus-node. (When we refer to impedance components, we mean cables, 2-winding and 3-
winding transformers, transmission lines, pi impedances, motors, generators and loads.)
If you connect two impedance components in series, PTW will automatically insert a bus
or bus-node.
Invalid
Valid
Bus
Bus
Bus
Impedance
Impedance
Impedance
Impedance
