The Role of Distributed Generation in Power Quality and Reliability

While the system protects from long-term outages, there is no protection from short duration
voltage disturbances. The customers that would utilize such a system have either an economic or
a health and safety need to avoid extended outages but are relatively insensitive to short-term PQ
issues. Customers that are sensitive to short-term PQ fluctuations would derive very little benefit
from this configuration.
There are a large number of standby systems in place. There have been some attempts made to
harness this large resource of "cold iron” for providing indirect electric system peak load
support. These schemes are hampered by the air pollution emissions associated with
uncontrolled diesel power generation and also by the restrictive nature of the switching, control,
and load connections. Generally, additional engine permitting, emissions clean-up often by
alternative fuel capability, and more sophisticated switch-gear are needed to support this DG
function.
Figure 2.2 shows a standby or secondary DG system that utilizes energy storage and a more
sophisticated control system to provide not only protection from long-term outages but also from
short-term and momentary disturbances as well. The on-site energy storage provides the ride
through capability until the generator can start. The static switching and controls technology
ensure that these changes from the utility source to the standby or secondary DG source are not
detected by the load.
Figure 2.2 Standby or Secondary DG System Offering PQ Support
This is a common configuration for PQ sensitive customers that utilize UPS supported by battery
energy storage system and one or more standby generators. In very sensitive applications there
are usually redundancies in some or all of the component parts of the system. The same (or very
similar) level of reliability and power quality protection can be provided by this type of system
with an upgraded generator and permitting to run for economic rather than emergency reasons.
Emissions control, dual-fuel conversion, or replacement with gas-fired technologies could be
used to make the system available for peak shaving. A customer could reduce his own peak
demands by operating 1500-3500 hours per year. However, a more mutually beneficial
application for the customer and the utility is to operate only during system-wide peak events –
generally 75-400 hours per year. This type of application requires an automatic notification or
Energy and Environmental Analysis / Pace Energy 4 The Role of DG in Power Reliability