09-05-2012, 12:21 PM
COORDINATED VOLTAGE CONTROL IN DISTRIBUTED SYSTEM WITH DISTRIBUTED GENERATORS
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Abstract
The continued interest in the use of distributed
generation in recent years is leading to the growth in number of
distributed generators connected to distribution networks.
Steady state voltage rise resulting from the connection of these
generators can be a major obstacle to their connection at lower
voltage levels. The present electric distribution network is
designed to keep the customer voltage within tolerance limit.
This may require a reduction in connectable generation capacity,
under utilization of appropriate generation sites. Thus
distribution network operators need a proper voltage regulation
method to allow the significant integration of distributed
generation systems to existing network. In this work a voltage
rise problem in a typical distribution system has been studied. A
method for voltage regulation of distribution system with
multiple DG system by coordinated operation distributed
generator and OLTC has been developed. A sensitivity based
analysis has been carried out to determine the priority for
individual generators in multiple DG environment. The
effectiveness of the developed method has been evaluated under
various cases through simulation results.
Index Terms-- Distributed generation, voltage control,
sensitivity factor.
I. INTRODUCTION
he need for energy is never ending. This is certainly true
for electrical energy, which is a large part of total global
energy consumption. But growing in tandem with energy
needs are the concerns about sustainable development and
environmental issues, such as the movement to reduce
greenhouse gas emissions. The result of fulfilling energy
needs and meeting environmental, social concerns is the
growing interest in reliable distributed energy sources. Inter
connection of these generators to distribution network will
offer a number of benefits such as improved reliability, power
quality, efficiency, alleviation of system constraints along
with the environmental benefits[1,2]. With these benefits and
due to the growing momentum towards sustainable energy
developments, it is expected that a large number of DG
systems will be interconnected to the power system in the
R. Shivarudraswamy, is a research scholar in the department of Electrical
and Electronics Engineering, National Institute of Technology Karnataka
Surathkal, Mangalore-575025 Karnataka, India (e-mail: swamysrs@
nitk.ac.in).
D. N. Gaonkar is with department of Electrical and Electronics
Engineering, National Institute of Technology Karnataka Surathkal,
Mangalore-575025 Karnataka, India (e-mail: dngaonkar[at]ieee.org).
.
coming years [2, 3]. The present scenario of deregulation of
the power utilities and the competition in the energy markets
are further accelerating the growth in parallel operation of DG
systems with the utility [2,3]. In order to achieve these
benefits with large penetration of DG source in existing utility
network, several technical problems are to be fronted such as
degradation of system reliability, power quality problems,
potentially damaging over voltages, islanding and various
other safety issues[1-5].
Steady state voltage rise problem is reported as one of the
main obstacles for interconnection of large amounts of
distributed generation units to the existing radial networks [3,
4]. In [3], the results of some generic studies explaining the
voltage rise issue and how it may be overcome are presented.
Several methods like reducing primary substation voltage and
constraining the generator operation are discussed.
Distribution networks are designed to keep the customer
voltage constant within tolerance limit as dictated by statute
and has always been a top priority [5]. The range of voltage
which must be met under a number of different standards does
not exceed ±10%, with some standards being even tighter than
this [3-6].
A simple analytical expression for the voltage profile of
distribution system with DG has been presented in [6]. The
conventional voltage regulation methods such as online tap
changing transformer associated with automatic voltage
control (AVC) relay are not going to be effective in presence
of a significant number of DG systems [5]. Several methods
like network reinforcement and constraining the generator
operation to counter the voltage rise are discussed in [3, 4].
These methods are not effective due to many reasons. A new
method for determining the introduction limit, when DG unit
is introduced into distribution system of which the voltage is
generally controlled by LCT (load-tap changing transformer)
and LDC (line drop compensation) is presented in [7]. An
attempt has been made to design an AVC relay using the
artificial neural network (ANN) for voltage regulation purpose
in [8]. A novel approach, using consumer load control is
discussed for countering steady state voltage rise in
distribution system with wind generation plant [9]. Simulation
case study has been made to compare this method with the
existing methods such as system reinforcement and
connection point changes. The disadvantage of this method is
installation and use of load control for voltage regulation
alone requires a
COORDINATED VOLTAGE CONTROL IN DISTRIBUTED
SYSTEM WITH DISTRIBUTED GENERATORS
R. Shivarudraswamy, and D. N. Gaonkar, Member, IEEE
T
34th National Systems Conference, 10-12th December, 2010
National Institute of Technology Karnataka Surathkal, Mngalore-575025
significant capital. Recent developments involving mixed
voltage/power factor control have shown that by intelligently
controlling the synchronous generators, voltage variations can
be mitigated and reinforcement may be avoided [10].
Generators and tap-changing transformers can be used to
control the level of voltage throughout a network. The
transformers in the network also influence the direction and
magnitude of the reactive component of power that flows to
the loads [11, 12]. In this paper investigates the coordinated
voltage control under various conditions in distribution
system. A comprehensive approach to voltage control in a
distribution system by taking in to account of number of DG
systems and capacitors under various condition has been
presented.
Besides offering environmental benefits, integration
of modular generating units to distribution network may bring
other significant benefits such as increased reliability, loss
reduction, load management and also the possibility of
delaying the adjustment of transmission and distribution
networks [1, 4, 5]. In order to achieve these benefits with
large penetration of DG source in existing utility network,
several technical problems are to be fronted. Some of the
technical issues must be considered for successful
introduction of DG systems are steady state voltage
regulation, increased system fault level, islanding operation,
degradation of power quality and reliability, protection and
stability of the network [2 ]. These issues are further
complicated by the type of interface used for DG system to
interconnect it to the grid [3]. One of the major concern is the
rise in steady state voltage level of distribution system.