The Electrical Engineer - Institute of Integrated Electrical Engineers ...

DISTRIBUTED GENERATION
By Engr. Jules S. Alcantara
IIEE VP Technical (2010), PEE, ASEAN Engineer, MS Energy Mngt, M. Engg (EE), CESO V
Distributed Generation (DG) is generally defined as
small scale electric power generation within distribution
networks or on the customer side of the network. Other
terms used are “embedded generation”, “dispersed
generation”, “decentralized generation”, “Distributed
Energy Resource (DER)” and “Distributed Resource
(DR)”. The terms “cogeneration”, “RE” and “small power
production” refer to types of DGs.
The Philippine Renewable Energy Act of 2008 defines DG
as up to 100 kW. The Electric Power Research Institute
(EPRI) defines the rating of DG to be up to 50 MW.
The IEEE Standard 1547-2003 covers capacities up to
10,000 KW.
There are three types of DGs: (a) solid-state or static
invertors (b) induction machines (c) synchronous
machines. The inverter type acts as current source while
the rotating machines act as voltage source. The former
type supplies lower fault current levels than the rotating
machines.
There are currently 12 million DG units installed in the
US with a total capacity of about 200,000 MW. Many
of these units are used as back-up units to provide
emergency power during shortages or unavailability of
power from the grid.
The purposes and benefits of the DG include the following:
1. DGs provide active power within the distribution
network;
2. It ensures continuity and availability of power
for critical business processes;
3. It may result in improvement of system reliability
– A study on the Pennsylvania/New Jersey/
Maryland interconnection (PJM) system by the
Oak Bridge National Laboratory indicated that
capacity expansion with ten small plants showed
a better Loss of Load Probability than an
expansion of a single large plant of the same
size;
4. DGs are highly efficient (overall efficiency
greater than 75% ) and financially attractive
when the DG industrial owner captures the heat
generated from the DG technology for use in
production processes, for hot water domestic
use and other uses.
5. DGs resolve power quality problems of voltage
sags and disruptions;
6. The use of alternative/renewable energy
resources for DG enhances environmental
conditions since it may have zero emissions. The
TECHNICAL PAPER
Philippine Renewable Energy Act formally
jumpstarts non-utility-owned small scale
distributed generation technologies of the
renewable type;
7. New fuel powered and waste-to-energy DG
technologies have low emissions that also
enhances environmental conditions;
8. New technologies in DG have made it possible
to tailor energy systems to the specific needs of
the consumer;
9. DGs may provide ancillary services including
voltage support/reactive power and back-up;
10. Peak power requirements are reduced;
11. Reduces and offsets investments in generation,
transmission or distribution facilities that would
otherwise be recovered through rates. There are
also savings in T & D losses and Congestion
costs;
12. Reduces vulnerability to terrorism and
improvements in infrastructure resilience;
13. Reduces land-use effects and Right-of-
Way acquisitions to build new power plants,
electric transmission and distribution lines;
14. Short construction times compared to central
generators;
15. Inherent system stability due to multiplicity of
inputs;
16. Weather related interruptions are more easily
predicted and of shorter duration.
The IEEE 1547-2003 Standard for Interconnecting
Distributed Resources with Electric Power Systems is
a standard developed by the Institute of Electrical and
Electronics Engineers (IEEE) meant to provide a set of
technical criteria and requirements in the interconnection
of distributed generation resources into the power grid
in the United States. It facilitates the tapping and use of
excess capacity of electricity from alternative sources.
The US Congress in its US Energy Policy Act of 2005
established the IEEE 1547 as the national standard for
the DG interconnection. Other applicable standards are
the UL and National Electrical Code of the NFPA (USA)
while the Philippines has the existing Philippine Electrical
Code (IIEE), the Philippine Grid Code and the Philippine
Distribution Code. However, technical standards for DG
interconnection differ from country to country.
Some of the technical issues to be addressed in the
interconnection of DGs to the existing power system are
the following:
1. Voltages outside an acceptable range (IEEE
1547-2003 mandates tripping in 0.16 sec for
U1.2 pu);
THE ELECTRICAL ENGINEER MAGAZINE 3RD QUARTER 2010 33