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VOLTAGE SAG ANALYSIS
Post: #1
Sad 

A voltage sag is a momentary decrease in the rms voltage, usually caused by a fault in the utility transmission line or distribution system within customer facility. It is a temporary voltage drop below 90% of the nominal voltage level. Voltage sags and momentary power interruptions are probably the most important power quality problems affecting industrial and large commercial customers. This paper describes the causes of voltage sags, their impacts on equipment operations and possible solutions. This paper focuses on system faults as the major cause of voltage sags. The sensitivity of different types of equipments including programmable logic controllers and motor contactors is analyzed. Then the range of fault locations on the power system that can cause problems is estimated (area of vulnerability).Available methods of power conditioning for these sensitive equipments are also described in this paper. The problems of voltage sags can be tackled in two ways. The customer will have to improve the ride through capability of their sensitive equipment. If system power conditioning is expensive it may be economical in the long term to improve the design of the equipment. Mitigation of voltage sags requires careful inspection of the characteristics of the process and of the nature and origin of events. The installation of mitigation devices (normally the only choice for the customers) can be seen as a short term solution. The mitigation capability of these devices is mainly limited by the energy storage capacity. Only improvement of system performance (for long deep sags) and of equipment tolerance (for short, shallow sags) can solve the problem in the long term
Post: #2
[quote='rumi' pid='1064' dateline='1233253808']
i want the details of the seminars topic voltage sag analysis
Post: #3
please send the report
Post: #4
not yet bored but need this topic as soon as possible
Post: #5
use this links
http://nalanda.nitc.acnitcresources/ee/l...ageSag.pdf
http://lib.tkk.fi/Diss/2005/isbn9512278863/article1.pdf
http://omniverterpdf/wp_voltagesag.pdf
http://linkinghub.elsevierretrieve/pii/S...9600000857
http://exit.udg.edu/articles/90.pdf
Post: #6
seminars report on voltage sag analysis
Post: #7
Hi,
visit this thread:
http://seminarprojectst-voltage-sag-analysis?pid=21220#pid21220

The full report pdf has been posted there.
Post: #8
Presented by:
Manish Sharma

[attachment=11033]
Abstract
Voltage, usually caused by a fault in a voltage sag is a momentary decrease in the rms value of the utility transmission line or distribution system within customer facility. It is a temporary voltage drop below 90% of the nominal voltage level. Voltage sags and momentary power interruptions are probably the most important PQ problem and power quality problems affecting industrial and large commercial customers. These events are usually associated with a fault at some location in the supplying power system. Interruptions occur when the fault is on the circuit supplying the customer. But voltage sags occur even if the faults happen to be far away from the customer's site. Voltage sags lasting only 4-5 cycles can cause a wide range of sensitive customer equipment to drop out. To industrial customers, a voltage sag and a momentary interruption are equivalent if both shut their process down. This paper describes the causes of voltage sags, their impacts on equipment operations and possible solutions. This paper focuses on system faults as the major cause of voltage sags. The sensitivity of different types of equipments including programmable logic controllers and motor contactors is analyzed. Then the range of fault locations on the power system that can cause problems is estimated (area of vulnerability). Available methods of power conditioning for these sensitive equipments are also described in this paper. The problems of voltage sags can be tackled in two ways. The customer will have to improve the ride through capability of their sensitive equipment. If system power conditioning is expensive it may be economical in the long term to improve the design of the equipment.
INTRODUCTION
A voltage sag isa momentary decrease in the rms voltage, usually caused by a fault in the utility transmission line or distribution system within customer facility. It is a temporary voltage drop below 90% of the nominal voltage level. Voltage sags and momentary power interruptions are probably the most important power quality problems affecting industrial and large commercial customers.
A voltage sag is a sudden reduction in the supply voltage magnitude followed by a voltage recovery after a short period of time. Voltage sags are mainly caused by short circuits, overloads and starting of large motors. The importance of voltage sags has increased due to problem sags cause to many types of equipment. To be able to estimate the damage voltage sags cause to customers also new tools and analysis programs are needed.
Network information systems are widely used in power distribution companies. These systems include tools for case-specific steady state analysis for different purposes, e.g. programs for load flow calculations, fault current analysis, load growth estimation and reliability analysis. Also voltage sag analysis could be included in this list of programs.
This paper presents typical voltage sag distributions calculated for Finnish rural and urban networks. Voltage sags propagate throughout the power system and a sag sensitive customer can experience sags caused by faults at the same, higher or lower voltage levels. In this paper the main interest is distribution companies and their possibilities in decreasing the impact of voltage sags. Thus only voltage sags caused by short circuit faults on MV radially operated networks and experienced by LV customers are studied. Network characteristics have influence on voltage sag distribution.
In this paper it is shown that while one investment may be justified e.g. in the sense of reliability the same investment may worsen the situation related to voltage sags. This is one basis to include sag analysis in network information systems. The platform used for network planning in power distribution companies and including voltage sag analysis is presented.
This paper describes the causes of voltage sags, their impacts on equipment operations and possible solutions. This paper focuses on system faults as the major cause of voltage sags. The sensitivity of different types of equipments including programmable logic controllers and motor contactors is analyzed. Then the range of fault locations on the power system that can cause problems is estimated (area of vulnerability)
The customer will have to improve the ride through capability of their sensitive equipment. If system power conditioning is expensive it may be economical in the long term to improve the design of the equipment. Mitigation of voltage sags requires careful inspection of the characteristics of the process and of the nature and origin of events.
The installation of mitigation devices (normally the only choice for the customers) can be seen as a short term solution. The mitigation capability of these devices is mainly limited by the energy storage capacity. Only improvement of system performance (for long deep sags) and of equipment tolerance (for short, shallow sags) can solve the problem in the long term
WHAT ARE VOLTAGE SAGS?
Electronic devices function properly as long as the voltage (or driving force) of the electricity feeding the device stays within a consistent range. There are several types of voltage fluctuations that can cause problems, including surges and spikes, sags, harmonic distortions, and momentary disruptions. A voltage sag is not a complete interruption of power; it is a temporary drop below 90 percent of the nominal voltage level. Most voltage sags do not go below 50 percent of the nominal voltage, and they normally last from 3 to 10 cycles—or 50 to 170 milliseconds. Voltage sags are probably the most significant power quality (PQ) problem facing industrial customers today, and they can be a significant problem for large commercial customers as well.
There are two sources of voltage sags: external (on the utility’s lines up to your facility) and internal (within your facility). Utilities continuously strive to provide the most reliable and consistent electric power possible. In the course of normal utility operations, however, many things can cause voltage sags. Storms are the most common cause of external sags and momentary interruptions in most areas of the U.S. A storm passing through an area can result in dozens of major and minor PQ variations, including sags.
For example, consider how PQ would be affected by a lightning strike on or near a power line or by wind sending tree limbs into power lines. Other common causes of external voltage sags are ice storms, animals (particularly squirrels), and the start-up of large loads at neighboring facilities. Internal causes of voltage sags can include starting major loads and grounding or wiring problems.
Whether or not a voltage sag causes a problem will depend on the magnitude and duration of the sag and on the sensitivity of your equipment. Many types of electronic equipment are sensitive to voltage sags, including variable speed drive controls, motor starter contactors, robotics, programmable logic controllers, controller power supplies, and control relays. Much of this equipment is used in applications that are critical to an overall process, which can lead tower expensive downtime when voltage sags occur.
If your facility is having frequent voltage sag problems, a good place to start is with your utility. Ask about the utility’s statistics regarding performance in your area. You should also look into possible internal causes. But whether the causes are mainly external or internal, you should consider taking charge of the problem and working toward a cost effective solution for your facility.
VOLTAGE SAG DEFINITION
Voltage Sag:

A Voltage Sag as defined by IEEE Standard 1159-1995, IEEE Recommended Practice for Monitoring Electric Power Quality, is a decrease in RMS voltage at the power frequency for durations from 0.5 cycles to 1 minute, reported as the remaining voltage.
The measurement of a Voltage Sag is stated as a percentage of the nominal voltage, it is a measurement of the remaining voltage and is stated as a sag to a percentage value. Thus a Voltage Sag to 60% is equivalent to 60% of nominal voltage, or 288 Volts for a nominal 480 Volt system.
Voltage Dip:
In North America a Voltage Dip is usually understood to mean the amount by which the nominal voltage declines - in percentage terms this is 100-Voltage Sag. Thus a voltage dip of 40% equates to a Voltage Sag to 60% . Unfortunately in practice there is confusion and the terms Voltage Sag and Voltage Dip are sometimes interchanged. It is therefore important that data is clarified.
Post: #9
Presented by-
Manish Sharma

[attachment=11044]
Voltage Sag Analysis
WHAT ARE VOLTAGE SAGS ?
WHERE DO VOLTAGE SAGS OCCUR?

Utility Systems
Inside Industrial Plants
CAUSES OF VOLTAGE SAGS
MULTI PHASE SAGS AND SINGLE PHASE SAGS
Single Phase Sags
MULTI PHASE SAGS AND SINGLE PHASE SAGS
Phase to Phase Sags
Voltage-Sag Analysis- Methodology
Load Flow
Voltage Sag Calculation
Voltage Sag Occurrence Calculations
Study of Results of Sag- Analysis
Equipment Sensitivity Studies
Process controllers
Chip Testers
DC Drives
Programmable Logic Controllers
Machine Tools
SOLUTIONS TO VOLTAGE SAG PROBLEMS
VOLTAGE SAG CORRECTION DEVICES

Motor generator sets (M-G sets)
Uninterruptible Power supply (UPS's)
Constant voltage transformers (CVT's)
Magnetic synthesizers
Super conducting storage devices (SSD's)
Electronic Voltage Regulators
Typical Voltage Sag Mitigation Technologies And Costs
Future Aspects
Conclusion
The voltage sag integration program if implemented by utilities can yield the following benefits to utility,
Existing customer satisfaction may b e enhanced by quick correction of voltage sag
Power quality disputes can be settled.
Public relations will be better.
Even current protection can be evaluated as it applies to duration of voltage sag.
 

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