20-10-2012, 05:41 PM
Power Quality Problems and New Solutions
Power Quality Problems.pdf (Size: 779.61 KB / Downloads: 168)
Abstract:
In this paper, the main Power Quality (PQ)
problems are presented with their associated causes and
consequences. The economic impacts associated with PQ are
characterized. Finally, some solutions to mitigate the PQ
problems are presented.
Introduction
Power Quality (PQ) related issues are of most concern
nowadays. The widespread use of electronic equipment,
such as information technology equipment, power
electronics such as adjustable speed drives (ASD),
programmable logic controllers (PLC), energy-efficient
lighting, led to a complete change of electric loads
nature. These loads are simultaneously the major causers
and the major victims of power quality problems. Due to
their non-linearity, all these loads cause disturbances in
the voltage waveform.
Along with technology advance, the organization of the
worldwide economy has evolved towards globalisation
and the profit margins of many activities tend to
decrease. The increased sensitivity of the vast majority of
processes (industrial, services and even residential) to PQ
problems turns the availability of electric power with
quality a crucial factor for competitiveness in every
activity sector. The most critical areas are the continuous
process industry and the information technology services.
When a disturbance occurs, huge financial losses may
happen, with the consequent loss of productivity and
competitiveness.
Power Quality Characterization
Even the most advanced transmission and distribution
systems are not able to provide electrical energy with the
desired level of reliability for the proper functioning of
the loads in modern society. Modern T&D (transmission
and distribution) systems are projected for 99,9 to
99,99% availability. This value is highly dependant of
redundancy level of the network, which is different
according to the geographical location and the voltage
level (availability is higher at the HV network). In some
remote sites, availability of T&D systems may be as low
as 99%. Even with a 99,99% level there is an equivalent
interruption time of 52 minutes per year.
The most demanding processes in the modern digital
economy need electrical energy with 99.9999999%
availability (9-nines reliability) to function properly.
Distributed Resources – Distributed
Generation
Distributed Generation (DG) units can be used to provide
clean power to critical loads, isolating them from
disturbances with origin in the grid. DG units can also be
used as backup generators to assure energy supply to
critical loads during sustained outages. Additionally DG
units can be used for load management purposed to
decrease the peak demand.
At present, reciprocating engine is the prevalent
technology in DG market, but with technology
advancements, other technologies are becoming more
attractive, such as microturbines or fuel cells (Table III).
Make End-use Devices Less Sensitive
Designing the equipment to be less sensitive to
disturbances is usually the most cost effective measure to
prevent PQ problems. Some manufacturers of end-use
equipment are now recognising this problem, but the
competitive market means that manufacturers should
reduce costs and only respond to customers’
requirements. The exception is the ASD market, where
manufacturers are actively promoting products with
enhanced ride-through capabilities.
Adding a capacitor with a larger capacity to power
supplies, using cables with larger neutral conductors,
derating transformers and adjusting undervoltage relays,
are measures that could be taken by manufacturers to
reduce the sensitivity of equipment to PQ problems.
Conclusions
The availability of electric power with high quality is
crucial for the running of the modern society. If some
sectors are satisfied with the quality of the power
provided by utilities, some others are more demanding.
To avoid the huge losses related to PQ problems, the
most demanding consumers must take action to prevent
the problems. Among the various measures, selection of
less sensitive equipment can play an important role.
When even the most robust equipment is affected, then
other measures must be taken, such as installation of
restoring technologies, distributed generation or an
interface device to prevent PQ problems.