International Journal of Innovative and Emerging Research in Engineering
Volume 3, Issue 6, 2016
Available online at www.ijiere.com
International Journal of Innovative and Emerging
Research in Engineering
e-ISSN: 2394 - 3343
p-ISSN: 2394 - 5494
Power Quality Issues in Industries and Distribution systems.
a
a
Vidya.M,, bDr.P.Pramila,
Assistant Professor, Department of EEE, Dayananda Sagar College of Engineering ,Bengaluru, India.
b
Prof and Head, Department of EEE, Bangalore Institute of Technology,Bengaluru, India.
ABSTRACT:
The term power quality is defined as provision of voltages and system design of electric power which the
consumer can utilize the electric energy from the distribution system without interference on interruption and
maintain nearly sinusoidal power distribution bus voltage at rated magnitude and frequency. The main purpose
of electrical distribution system is to meet the consumer’s demands for energy after receiving the bulk electrical
energy from the transmission or sub station. Different network configurations are possible to meet the required
supply reliability. Protection, control and monitoring equipment are provided to enable effective operation of
distribution network. There are several electrical disturbances that commonly affect industrial processes. Some
of them include the voltage imbalance, harmonics, voltage sags, voltage spikes etc. This paper presents the
different issues which can be observed in industries and the distribution system.
Keywords: Power quality, distribution system, voltage sag, voltage imbalance, harmonics.
I. INTRODUCTION
An electric distribution system is part of an electric system between the bulk power sources and the consumer’s service
switches. The bulk power sources are located in or near the load area to be served by the distribution system and may be
either generating stations or power substations supplied over transmission lines[1]. 80% of all power quality problems are
attributed to inadequate electrical grounding or wiring, or due to interactions between loads within the premises. The
distribution systems can be divided into six parts namely, sub transmission circuits, distribution substations, distribution or
primary feeders, distribution transformers, secondary circuits or secondary’s and consumer’s service connections and
meters or consumer’s services. One of the most common power quality problems is the voltage sag. A voltage sag is defined
as a decrease in RMS voltage magnitude lasting from 0.5 to 30 cycles. Voltage sag is caused by a fault in the utility system,
a fault within the customer’s facility or a large increase of the load current[6]. Typical faults are single-phase or multiplephase short circuits, which leads to high currents. The high current results in a voltage drop over the network impedance.
Harmonic currents in distribution system can cause harmonic distortion, low power factor and additional losses as well as
heating in the electrical equipment. An impulsive transient is typically characterized by a sudden change in frequency not
related to the power frequency. A voltage unbalance exists when phase voltages at the point of utilization are unequal. An
unbalanced three-phase voltage causes three-phase motors to draw unbalanced current, which can cause the rotor of a motor
to overheat.
.
II. GENERAL PROBLEMS THAT OCCUR IN DISTRIBUTION SYSTEMS.
The basic design principles is essential in the operation of electric power systems. The transmission system voltage is
stepped-down to lower levels by distribution substation transformers. The primary distribution system is that portion of the
power network between the distribution substation and the utilization transformers. The primary distribution system
consists of circuits, referred to as primary or distribution feeders, that originate at the secondary bus of the distribution
substation. The distribution substation is usually the delivery point of electric power in large industrial or commercial
applications[3]. A substation consists of one or more power transformer banks together with the necessary voltage
regulating equipment, buses, and switchgear. Transformers in some circumstances inject certain harmonic or inter
harmonics to the system. Harmonics and inter harmonics of a waveform can be defined in terms of its spectral components
in the quasi-steady state over a range of frequencies. The second harmonic has a tremendous impact on peak voltage
asymmetry[1]. For single-phase and three phase rectifiers with large dc filter capacitors, these devices start injecting dc in
response to the second harmonic. The dc is biasing transformers and causes saturation. The third harmonic is mainly zero
sequence. It raises the potential of the neutral and has a much stronger effect on communication lines than the 5 th and 7th.
The third harmonic when zero-sequenced is one of the most dangerous ones. When is positive or negative sequenced, it is
not as harmful. The harmonics of order seven, eleven, thirteen are also present in supply voltages.
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III. FACTORS AFFECTING THE EFFICIENCY OF SYSTEMS.
Waveform distortion and voltage unbalance have become very important factors that essentially decrease the efficiency of
both power supply systems and the consumers connected to them. New equipments are more sensitive to power quality
variations. The advent of new power electronic equipment, such as variable speed drives and switched mode power
supplies, has brought new disturbances into the supply system. For an industry voltage sags occur more often and cause
severe problems and economical losses. Utilities often focus on disturbances from end-user equipment as the main power
quality problems. Harmonic currents in distribution system can cause harmonic distortion, low power factor and additional
losses as well as heating in the electrical equipment. Voltage sags are usually caused by a fault in the utility of transmission
or distribution system[6]. Power-line faults can be caused by animals on lines, a car striking a utility pole, or lightning
strikes to power lines. Although proper maintenance, grounding, and arresters can minimize the number of faults, faults
can never be eliminated. The voltage sag depends upon how close the customer is to the fault location, resistance at the
fault, and the available fault current.
Example of Distribution System Showing Fault Location and Affect on the Customer.[6]
Harmonic distortion of the voltage and current in an industrial facility is caused by the operation of nonlinear loads and
devices on the power system. A nonlinear load is one that does not draw sinusoidal current when a sinusoidal voltage is
applied. Examples of nonlinear loads are arcing devices such as arc furnaces, saturable devices such as transformers, and
power electronic equipment such as adjustable-speed drives and rectifiers. Harmonic currents increase the volt-amperes
required for a load without increasing the watts. Overheating of transformers is another problem associated with harmonic
currents. The overheating is caused primarily by the higher eddy-current losses inside the transformer than were anticipated
by the designer[6]. A voltage unbalance exists when phase voltages at the point of utilization are unequal. The causes of
voltage unbalance, include the malfunction of automatic power factor-correction equipment and voltage regulators in the
utility distribution lines, unevenly distributed single-phase loads in a facility, high-impedance connections, and an
unbalanced transformer bank. An unbalanced three-phase voltage causes three-phase motors to draw unbalanced current,
which can cause the rotor of a motor to overheat. Voltage fluctuations in the power system is due to result from impedance
of transmission lines, loading types, and uneven distribution of single-phase loads. The scenarios become much severer in
the low-voltage micro grid system due to reverse power flow contributed by distributed generations (DGs) in either threeor single-phase connection. Voltage fluctuations causes system losses, capacity reduction, transformer overloading, and
motor overheating, and even results in output limitation of DGs, nuisance tripping of protected devices, and malfunction
of sensitive equipment.
IV: POSSIBLE SOLUTIONS TO THE POWER QUALITY PROBLEMS IN INDUSTRIES AND DISTRIBUTION
SYSTEMS.
The adverse effects of the disturbances can be mitigated by installing power-conditioning equipment or by utilizing
different wiring or power-distribution methods. The cost of the solution must be evaluated against the losses associated
with the disturbance. Most voltage-sag solutions can be handled by ferro resonant transformers. These are also known as
constant-voltage transformers (CVTs). CVTs are ideally suited for constant, low-power loads. The CVT allows the core to
become saturated with magnetic flux, which maintains a relatively constant output voltage during input voltage variations
such as under voltages, over voltages, and harmonic distortion. CVTs are usually 1:1, single-phase transformers used with
120-V control circuits or other small loads. The CVT should be sized at least two times the load current[6].
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Volume 3, Issue 6, 2016
Output Voltage Regulation of a 1000-VA Constant-Voltage Transformer (CVT)[6]
The CVT has no significant stored energy, hence it is applicable for protection against voltage sags, not interruptions.
CVT Output Response to Input Variations[6]
Dip-Proof Inverters: The dip-proof inverters(DPI) are relatively new off-line device that is sized for the nominal load. The
device continually rectifies incoming AC voltage to charge DC bus capacitors. When it detects a voltage sag that drops
below an adjustable threshold, the line to the incoming power is opened and the DPI supplies a square-wave output to the
load for about 1 to 3 seconds. The time that the load will be supplied can be calculated based on the real power and the
energy storage of the particular DPI[6].
Dip-Proof Inverter[6]
Large-Scale Solutions: The large-Scale Written Pole Motor Generator provides low inrush current on start and
synchronous motor speed. This unit is available in sizes up to 250 kW and can supply power for up to 15 seconds during
an interruption of voltage. Superconducting Magnetic Energy Storage (SMES) consists of a superconducting coil that
carries megawatt levels of current at practically zero electrical resistance. A power electronic converter is used to divert
the current into a capacitor if energy is to be extracted from the SMES. A SMES unit is designed to protect the whole of
an industrial facility. The units can produce from 300 kW to several megawatts for several seconds. The PQ 2000 is a
high-capacity standby power system. The system topology is similar to that of a standby UPS in that energy from batteries
supplies power to the load when the normal source voltage falls outside predetermined limits but differs from the traditional
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International Journal of Innovative and Emerging Research in Engineering
Volume 3, Issue 6, 2016
UPS by its design to supply power to large loads for a short duration of time. The units are rated as high as 2 MVA for a
minimum of 15 seconds[6]. The units can be provided to supply both low-voltage and medium-voltage loads. Utility
voltage surges caused by lightning or switching can be mitigated by surge-suppression devices. Surge-suppression devices
protect equipment by diverting the energy to ground when the voltage exceeds the breakdown voltage of the device[6].
The affect of harmonic currents on facility devices can be reduced in several ways. One method is to add harmonic filters
to divert the harmonic current from the main equipment. A second method is to add reactors or isolation transformers on
the feeders connected to harmonic producing loads. A third method is to isolate the harmonic loads from other sensitive
equipment so that the harmonic level at the sensitive loads is lower due to the system impedance between the harmonic
source and the sensitive loads[6]. If the voltage unbalance cannot be eliminated, then the motor must be derated to ensure
long life. NEMA Standard MG1-14.35 recommends derating an induction motor when the voltage unbalance exceeds one
percent and recommends not operating a motor at all when the voltage unbalance exceeds five percent[6].
III. CONCLUSIONS
In this paper, the various problems that occur in an industry and in the distribution systems is presented. Also by
critical analyzing about power quality problems, issues, and their effect in life and the corrective measures using different
means has been discussed. The corrective measures which can be remedy for power quality problems generated in different
equipments has been presented in co-ordination with existing industry practices.
ACKNOWLEDGMENT
I thank Prof. Dr.P.Pramila, HOD,EEE, BIT, V.V.Pura Bengaluru, for her valuable guidance in bringing out this paper.
Also I thank the IJIERE team for the valuable suggestions given through mail in formatting this paper.
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