IEEE Power & Energy Magazine - July/August 2019 - 36

energy and reactive power resources, which presents a challenge to maintaining system reliability and stability.
This article illustrates how a solution technology using synchronous condensers was selected to mitigate these combined
system reliability threats and what technical studies should be
conducted for its deployment. Synchronous condenser solutions have recently been reintroduced to support transmission
systems by offering additional reactive power control, short
circuit current, and inertial kinetic energy. Because converterbased renewable power generation does not contribute material short circuit current to the transmission network, the
installation of stand-alone synchronous condensers is becoming necessary when an increase in the strength of the transmission grid is required. Modern synchronous condensers
are equipped with advanced excitation systems and have high
reliability and low losses.

Overview of System Characteristics
The San Diego Gas and Electric Company (SDG&E) serves
approximately 5,000 MW of load in the southwestern corner of the United States in the Western Interconnection. As
shown by the power flow patterns in Figure 2, the load is
concentrated along the Pacific coast. The demand in this
area was formerly supplied mainly by "in Basin" generation located within SDG&E's load center. Prior to 2009, this
area included approximately 4,500 MW of dispatchable gen-

eration and was characterized by the following generation
resource mix:
✔ two large gas-fired thermal power plants
✔ a large nuclear power plant
✔ small conventional generation facilities
✔ various peaking units totaling roughly 600 MW.
The balance of demand was supplied through a 500-kV
line from the east and five 230-kV lines from the north. During
summer peaks, SDG&E typically experienced a 1,200-MW
flow from the north and 1,600 MW from the east. Under that
prior system load and resource profile, the SDG&E transmission system reliably served 3.5 million customers.
For years, a major challenge to system planners was ensuring that the transmission system could reliably transfer the
output of the company's generating resources to serve existing and future loads. In many instances, system constraints
were transmission thermal capacities and acceptable steadystate voltage performance during peak load conditions. This
operating scenario is becoming more challenging with the
changing resource portfolio.

Problem Statement
In the last decade, some major generation portfolio changes
occurred within and around SDG&E's operating territory.
✔ Thermal generation was replaced by renewable generation. Approximately 2,000 MW of large gas-fired

Estimate

100,000

BTM Solar
Solar
Wind
Geothermal
Small Hydro
Biomass

90,000
80,000
70,000

14% BTM* Solar
13,618
Solar
31% 30,262

(GWh)

60,000
50,000
40,000

29%

Wind
27,838

30,000
20,000
10,000
0
1983

1985

1990

1995
2002
First California
RPS Established
(20% by 2017)

2000

2005

2006
RPS Increased
to 20% by 2010
CSI Initiated
Global Warming
Solutions Act
of 2006

2010

2015

2011
2015
RPS
RPS
Increased Increased
to 33%
to 50%
by 2020 by 2030

14% Geothermal
13,249
4% Small Hydro
8% 4,347
Biomass
8,044
2018
RPS
Increased
to 60%
by 2030

figure 1. California renewable generation by resource type. BTM: behind the meter; CSI: California Solar Initiative.
(Source: California Energy Commission; used with permission.)
36

ieee power & energy magazine

july/august 2019

IEEE Power & Energy Magazine - July/August 2019

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2019