"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014)
International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA.
Importance of Reactive Power for Distributed Generation
Akash, Gaurav Shah1, Himnay Pratap Singh2, Avinas Kumar Chauhan3
Moradabad Institute of Technology, Moradabad
Abstract-- Reactive power, measured in volt-amperes
reactive or VARs, is one of a class of power system reliability
services collectively known as ancillary services. Ancillary
services are essential for the reliable operation of the bulk
power system. Reactive power flows when current leads or
lags behind the voltage; typically, the current lags because of
inductive loads like motors. Reactive power flow wastes
energy and transmission capacity, and causes voltage drop.
The role of reactive power in maintaining system reliability,
especially during unforeseen system contingencies, is the
reason for the growing interest by regulators and system
operators alike in alternative reactive power supplies.
Distributed Generation is an attractive option for solving
reactive power and distribution system voltage problems
because of its proximity to load. Distributed Generation is
very useful for the supply of MW in remote areas but since
DGs are not able to produce VAR. So we have to compensate
VAR through compensating devices to fulfill the demand of
MW in remote areas.
I. INTRODUCTION
Reactive power, measured in volt-amperes reactive or
VARs, is one of a class of power system reliability services
collectively known as ancillary services. Ancillary services
are essential for the reliable operation of the bulk power
system. Reactive power flows when current leads or lags
behind the voltage; typically, the current lags because of
inductive loads like motors. Reactive power flow wastes
energy and transmission capacity, and causes voltage
droop.
Fig. 1: A simple block diagram of supplying reactive power for DG
To correct power flow, leading reactive power (current
leading voltage) is supplied to bring the current in phase
with voltage. Reactive power can be supplied from either
static or dynamic VAR sources. Static sources are typically
transmission and distribution equipment, such as static
VAR compensators or capacitors at substations, and their
cost has historically been included in the revenue
requirement of the transmission owner (TO), and recovered
through cost-of-service rates.
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"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014)
International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA.
By contrast, dynamic sources are typically energy
producers, including generators capable of producing
both real and reactive power, and synchronous
condensers, which produce only reactive power. Thee
equipment may be owned either by tos or independent
entities. For dg to supply reactive power, the cost of
modifying these devices to provide reactive power
needs to be reduced and system operators must develop
a compensation plan for a local voltage regulation
service.
Fig. 1 shows a simple block diagram which shows the
introduction and idea behind this topic that is supplying
reactive power for distributed generation. As we know
that many of the distributed generation sources like
Solar Energy, Wind Energy, Photovoltaic can only able
to produce real power that is KW. They are not able to
produce reactive power. As we all know that reactive
power is too necessary for our system operation. It is
the imaginary part of the total power that is VA. Also
we are familiar to the situation that the condition of the
villages in terms of electricity is very bad. As India is a
developing country and the majority of this country is
villages. So the condition of the electricity in the
villages are need to be improved. As we all know that
the government of the India and many other companies
which provide electricity are only able to provide
approx. 6 to 8 hours electricity in a whole day. So
supplying reactive power is a very good concept to
provide electricity in the villages, in many of the remote
areas in India so that India can become a developed
country. Also in remote areas, if we use the concept of
distributed generation, then there will no need to install
transmission and distribution system (T & D).
II. REACTIVE P OWER
Reactive power is a concept used by engineers to
describe the background energy movement in an
Alternating Current (AC) system arising from the
production of electric and magnetic fields. These fields
store energy which changes through each AC cycle.
Devices which store energy by virtue of a magnetic field
produced by a flow of current are said to absorb reactive
power; those which store energy by virtue of electric fields
are said to generate reactive power.
Power flows, both actual and potential, must be carefully
controlled for a power system to operate within acceptable
voltage limits.
Reactive power flows can give rise to substantial voltage
changes across the system, which means that it is necessary
to maintain reactive power balances between sources of
generation and points of demand on a 'zonal basis'. Unlike
system frequency, which is consistent throughout an
interconnected system, voltages experienced at points
across the system form a "voltage profile" which is
uniquely related to local generation and demand at that
instant, and is also affected by the prevailing system
network arrangements. National Grid is obliged to secure
the transmission network to closely defined voltage and
stability criteria. This is predominantly achieved through
circuit arrangements, transformers and shunt or static
compensation.
III. SOURCES OF REACTIVE P OWER
Most equipment connected to the electricity system will
generate or absorb reactive power, but not all can be used
economically to control voltage. Principally synchronous
generators and specialized compensation equipment are
used to set the voltage at particular points in the system,
which elsewhere is determined by the reactive power flows.
Synchronous Generators- Synchronous machines can be
made to generate or absorb reactive power depending upon
the excitation (a form of generator control) applied. The
output of synchronous machines is continuously variable
over the operating range and automatic voltage regulators
can be used to control the output so as to maintain a
constant system voltage.
Synchronous Compensators-Certain smaller generators
once run up to speed and synchronized to the system, can
be declutched from their turbine and provide reactive
power without producing real power. This mode of
operation is called Synchronous Compensation.
Capacitive and Inductive Compensators - These are
devices that can be connected to the system to adjust
voltage levels. A capacitive compensator produces an
electric field thereby generating reactive power whilst an
inductive compensator produces a magnetic field to absorb
reactive power. Compensation devices are available as
either capacitive or inductive alone or as a hybrid to
provide both generation and absorption of reactive power.
Overhead Lines and Underground Cables - Overhead lines
and underground cables, when operating at the normal
system voltage, both produce strong electric fields and so
generate reactive power.
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"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014)
International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA.
When current flows through a line or cable it produces a
magnetic field which absorbs reactive power. A lightly
loaded overhead line is a net generator of reactive power
whilst a heavily loaded line is a net absorber of reactive
power. In the case of cables designed for use at 275 or
400kV the reactive power generated by the electric field is
always greater than the reactive power absorbed by the
magnetic field and so cables are always net generators of
reactive power.
Transformers - Transformers produce magnetic fields and
therefore absorb reactive power. The heavier the current
loading the higher the absorption.
Consumer Loads - Some loads such as motors produce a
magnetic field and therefore absorb reactive power but
other customer loads, such as fluorescent lighting, generate
reactive power. In addition reactive power may be
generated or absorbed by the lines and cables of
distribution systems.
IV. D ISTRIBUTED GENERATION
DG is a fairly new trend in the electricity industry,
market, and deregulated systems. Till now, there are no
consistent definitions that can describe DG terminologies.
However, there are some definitions that can be considered
common for most literatures. Some of these definitions are
discussed below.
DG names
There are several terms used to refer to distributed
generation, for example:
• ―Dispersed generation‖ used in North America.
• ―Embedded generation‖ used in South American
countries.
• ―Decentralized generation‖ used in Europe and
some Asian countries.
However, literature survey recommended the name of
―distributed generation‖ to be used all over the world.
DG purpose
Basically, it is used to provide part or all of a customer’s
real power demand and/or as a standby supply. Therefore,
according to this definition, there is no need to supply
reactive power from DG as in the case of FC for example.
DG location
A definition: ―The location of distributed generation is
defined as the installation and operation of electric power
generation modulars connected directly to the distribution
network or connected to the network on the customer site
of the meter‖.
This definition under the deregulation trend encourages
us suggest addition to the transmission and distribution
systems definition. A transmission system can be defined
as: ―The system, which is operated by an independent
company and not providing power generation or involved
in distribution or retail service‖. A distribution system can
be defined as:
―The system, which is operated by a distribution
company, can provide power generation through an electric
utility or customers and involved in distribution or retail
service‖.
The proposed addition to the transmission system,
distribution system and DG location definitions are helpful
for exceptional cases as follows:
• If a large industrial customer site is connected directly
on the transmission network and has a CHP system.
In this situation CHP can be considered as a DG
because it is connected directly on the customer side
of the meter.
• If a distribution network capacity is limited, a medium
size wind farm can be connected directly to a
transmission system. In this case the wind farm
cannot be considered as a DG.
DG rating
There are different definitions for generation size range
according to some institutes and literatures as However,
these definitions are dependent on the government
regulations as discussed below:
In the Swedish market
The DG capacity is up to 1.5MW. This value is not
enough for deciding that this generation rating is for DGs
or not, due to the cases below:
• In case of wind energy, Sweden plans offshore wind
farms having a maximum capacity of 1000MW. Each
wind turbine rating is 1.5MW, which can be
considered as a DG based on the modular rating not
the total wind farm capacity.
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
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"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014)
International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA.
• In the case of hydro modulars the capacity is
calculated as the total rating of the power station not
for each individual modular. So in most cases they are
not considered to be as a DG.
In Germany (Berlin)
The local utility BEWAG built a power generation
station in the city Centre. This power station, which feeds
into 110, 33 kV distribution lines, provides electricity and
heat (300MW each, respectively). The generated electricity
and heat are consumed locally so that this power station
can be considered as a DG.
According to the above discussion there is no common
DG rating definition because the maximum capacity of a
DG connected to the distribution network depends on the
distribution system’s capacity and its voltage level.
However, most literatures use small and medium DG sizes.
DG power delivery area
There is no specific definition for DG power delivery
area, but usually the DG produced energy is supposed to be
consumed within the distribution network. However, DGs
can feed back some of their generated electric power to the
transmission if it exceeds the distribution network load
demand where DGs are installed.
V. REACTIVE P OWER FOR D ISTRIBUTED GENERATION
To help the reader understand these benefits, a simple
two-bus system shown in Fig. 2 is used to illustrate the
benefits. In the figure there is a generation bus, a load bus,
and a line connecting the two buses. The generation bus
represents a generation center, the load bus represents a
load center, and the line represents an inter-tie or an
interface between the two areas. The generation centre is a
distributed generation centre which is able to provide VA
(the combination of real and reactive power that is KW and
KVAR respectively).Now we assume that the power
transfer is in the form of (Pm + jQm). The tie line is
congested due to the maximum transfer capability between
two areas. We assume the generation center has a cheap
unit with a cost of $20/MWh. The load center has a large
amount of load, served by a utility as a load serving entity
(LSE), and an expensive unit, owned by an independent
power producer(IPP), with a cost of $25/MWh.
The original import into the load center is (Pm + jQm).
If there is a local VAR injection (Qc in the figure), the flow
at the receiving end will be reduced to (Pm + j(Qm-Qc)).
If the same MVA transfer limit is maintained, then we
can send more real power over the tie-line since the
reactive power flow has been reduced. Therefore, more
MW can be dispatched from the cheap generation center.
Hence, the output from the expensive IPP generator may be
reduced. Thus, the total system cost will be reduced and the
LSE utility will pay less to serve the same load.
Fig. 2: A Two-Bus System
Advantages




The total system cost will be reduced.
Power can be transferred to remote area.
Power Factor will also be improved.
It is the first step for the development of any country.
Disadvantages


Most of the DG system is only able to provide
active power. So, reactive power should be
provided by compensation technique.
It can provide energy at a very small scale.
VI. CONCLUSION
Distributed generation or DG is an attractive option for
solving reactive power and distribution system voltage
problems because of its proximity to load. Providing
dynamic reactive power near the load provides significant
economic benefits such as reduced losses, increasing
availability of local generation, and improved local voltage
control, supply electricity in remote areas, improving the
power factor, reducing total system cost. Several
technology options are available to supply reactive power
for DG; these include small generators, synchronous
condensers, fuel cells, and microturbines.
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
Page 87
"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 4, Special Issue 1, February 2014)
International Conference on Advanced Developments in Engineering and Technology (ICADET-14), INDIA.
They can provide continuous variable dynamic reactive
power which can respond quickly to reactive power
demand.
Criteria need to be met for DG to become widely
integrated as a source of electricity in rural areas.
 The overall costs of retrofitting devices to absorb or
produce reactive power need to be reduced.
 There needs to be a market mechanism in place for
ISOs/RTOs/TOs to procure reactive power from the
customer side of the meter where DG resides.
 Novel compensation methods need to be introduced to
encourage the dispatch of dynamic resources close to
areas with critical voltage issues.
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