IEEE Power & Energy Magazine - July/August 2019 - 39

eters and confirm initial conclusions. Each synchronous
condenser installation comprises a synchronous generator,
a step-up transformer, auxiliary systems, and an excitation
system. Synchronous condensers mainly provide variable
reactive power to support transmission system voltages during events that could otherwise create unacceptably high or
low voltages.
The objective of these studies was to verify the rating of
the equipment deployed with each synchronous condenser
installation. The evaluations included design requirements
on step-up transformers and how the synchronous condenser
performed in various system conditions, including auxiliary
load voltages.
A synchronous condenser's step-up transformer has two
design factors that need to be addressed. First, the transformer needs to be adequately sized to provide the required
reactive power range at the connection point. Second, the
transformer's impedance can affect winding losses, voltage
regulation, and short circuit contributions to the system and
the synchronous condenser terminal. An optimization of the
step-up transformer impedance might be needed to ensure
that the synchronous condenser provides sufficient reactive
support to the system under a wide variety of conditions.
An example resulting from such an investigation is shown
in Figure 3. The letters show grid requirements that must
be met by the synchronous condenser installation. Here, the
synchronous condenser fulfills the required reactive power
range at the 230-kV transmission connection point with

approved those projects several planning cycles later, when
the system evolved to the worst-case scenarios showing the
greatest need for improvements. SDG&E then installed synchronous condensers at four existing substations by the end
of 2018. After the synchronous condenser technology was
selected to address the system needs, various technical studies were completed to verify the designs and confirm the system performance with more detailed implementation studies. The following section describes those required studies in
detail. A close collaboration between SDG&E and Siemens
at an early stage was essential to optimizing the synchronous condenser system designs (i.e., sizing, footprint, and
so on) to meet all requirements.

Technical Studies
Technical studies included power flow, transients, grounding, insulation coordination, protection coordination, and
dynamic performance. Although these studies are based on
the synchronous condenser applications to SDG&E's system,
they are generally applicable to synchronous condensers or
other transmission equipment additions to any transmission
systems as well.

Power Flow Study
Numerous power flow studies had been performed to identify the need for reactive resources as well as their most
effective locations and capacities for ensuring system reliability. The studies described here optimize design param-

Synchronous Condenser Inductive Capability
Synchronous Condenser Capacitive Capability
Grid Requirements

265
260
255
250

245

240
VHV (kV)

235
230

225
220
215
210
205

200
195
-200 -175 -150 -125 -100 -75

-50

-25

0
25
50
QHV (Mvar)

100

125

150

175

200

225

250

figure 3. The transmission network voltage as a function of reactive power capability. The value VHV represents
the 230-kV system voltage, and QHV represents the Mvar injected/withdrawn on the high side of the synchronous
condenser transformer.
july/august 2019

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IEEE Power & Energy Magazine - July/August 2019

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