07-04-2011, 01:20 PM
Can i get the report of this seminar topic in pdf n word format. plzzz
07-04-2011, 01:20 PM
Can i get the report of this seminar topic in pdf n word format. plzzz
22-04-2011, 03:40 PM
hi
you can see these pages to get the details on voltage-sag-analysis https://seminarproject.net/Thread-vo...ysis--1052 https://seminarproject.net/Thread-vo...g-analysis https://seminarproject.net/Thread-voltag...0#pid21220 https://seminarproject.net/Thread-vo...?pid=42025 http://project-seminars.com/attachment.php?aid=4067
23-09-2016, 04:50 PM
voltage sag
24-09-2016, 09:23 AM
Abstract - This paper summarizes the results from a number of different voltage sag investigations. These investigations involve characterizing the voltage sag performance at a customer facility and evaluating equipment sensitivity to different voltage sag magnitudes and durations. Possible solutions to voltage sag sensitivity problems are also described. INTRODUCTION Voltage sags and momentary power interruptions are probably the most important power quality problems affecting industrial and large commercial customers. These events are usually associated with a fault somewhere on the supplying power system. Actual interruptions occur when the fault is on the circuit supplying the customer. Voltage sags are much more common since they can be associated with faults remote from the customer. Even voltage sags lasting only 4-5 cycles can cause a wide range of sensitive customer equipment to drop out. Analysis of voltage sag concerns requires a knowledge of the voltage sag characteristics, statistical information describing the likelihood of a voltage sag occurring, and information describing the sensitivity of important loads within the facility. Developing this knowledge base requires close cooperation between the utility, the customer, and equipment manufacturers. In order to develop a better understanding in all of these areas, the Electric Power Research Institute (EPRI) and a number of individual electric utilities have been sponsoring case studies to investigate voltage sag concerns and available solutions. This paper summarizes some of the important results from these case studies. CHARACTERISTICS OF VOLTAGE SAGS Voltage sags which can cause equipment impacts are usually caused by faults on the power system. Motor starting also results in voltage sags but the magnitudes are usually not severe enough to cause equipment misoperation. The simplified one line diagram in Figure 1 can be used to explain how a fault results in a voltage sag at a customer facility. Figure 1. Example Power System Consider a customer that is supplied from the feeder designated with breaker 1 on the diagram. If there is a fault on this feeder, the customer will experience a voltage sag during the fault and then an interruption when the breaker opens to clear the fault. If the fault is temporary in nature, a reclosing operation on the breaker may be successful and the interruption will only be temporary. Regardless, sensitive equipment will almost surely trip during this interruption. A much more common event would be a fault on one of the other feeders from the substation or a fault somewhere on the transmission system (see fault locations shown on the figure). In either of these cases, the customer will experience a voltage sag during the period that the fault is 2 actually on the system. As soon as breakers open to clear the fault, normal voltage will be restored at the customer. Figure 2 is a plot of the rms voltage vs. time and the waveform characteristic at the customer location for one of these fault conditions. p Phase C-A Voltage RMS Variation Trigger 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 80 85 90 95 100 105 110 115 Time (Seconds) Voltage (%) 0 25 50 75 100 125 150 175 -150 -100 -50 0 50 100 150 Time (mSeconds) Voltage Duration 0.150 Sec Min 81.38 Ave 96.77 Max 101.4 BMI/Electrotek Figure 2. Example Voltage Sag Characteristic During a Fault on a Parallel Feeder Circuit The waveform given in Figure 2 is typical of the customer voltage during a fault on a parallel feeder circuit that is cleared quickly by the substation breaker. The total duration of the fault is 150 msec, or about nine cycles. The voltage during a fault on a parallel feeder will depend on the distance from the substation to the fault location. A fault close to the substation will result in a much more significant sag than a fault near the end of the feeder. Figure 3 shows the voltage sag magnitude at the plant bus as a function of fault location for an example system. Note that a single line-to-ground fault condition results in a much less severe voltage sag than a three phase fault condition due to a delta-wye transformer connection at the plant. Plant Service Entrance Bus Voltage vs. Fault Location Distance From Substation to Fault (Feet) 0 10 20 30 40 50 60 70 80 90 100 0 2500 5000 7500 10000 12500 15000 Normal Voltage (100%) Single-Line-To-Ground Fault 3 Phase Fault Figure 3. Plant Phase-to-Phase Bus Voltage (%) as a Function of Fault Location on a Parallel Feeder Transmission related voltage sags are normally much more consistent in duration than distribution voltage sags. Because of the large amounts of energy associated with transmission faults, they are cleared as soon as possible. This normally corresponds to 3-6 cycles, which is the total time for fault detection and breaker operation. Normally, customers do not experience an interruption for a transmission system fault. Transmission systems are looped or networked, as opposed to distribution systems which are radial. This means that if a single line trips, or is out of service, the remaining system supplies the load. If a fault occurs as shown on the 115 kV system, the protective relaying will sense the faults and breakers A and B will open to clear the fault. While the fault is on the transmission system, the entire power system, including the distribution system, will experience a voltage sag. Figure 4 shows the magnitude of measured voltage sags at an industrial plant supplied from a 115 kV system. Most of the voltage sags were 10-30% below nominal voltage, and no momentary interruptions were measured at the plant during the monitoring period (almost one year). Magnitude of Voltage Sags at Industrial Plant 0-10% Below Normal Voltage 44% 40-50% Below Normal Voltage 2% 30-40% Below Normal Voltage 10% 20-30% Below Normal Voltage 10% 10-20% Below Normal Voltage 34% >50% Below Normal Voltage 0% Figure 4. Industrial Plant Sag Magnitude Data (magnitudes are in % below nominal voltage) Figure 5 gives a three dimensional plot illustrating the number of sags experienced as a function of both the voltage sag magnitude and the duration. This is a convenient way to completely characterize the actual or expected voltage sag conditions at a site. Evaluating the impact of voltage sags at a customer plant involves estimating the number of voltage sags that can be expected as a function of the voltage sag magnitude and then comparing this with the equipment sensitivity. The estimates of voltage sag performance are developed by performing short circuit simulations to determine the plant voltage as a function of fault location throughout the power system. Total circuit miles of line exposure that can affect 3 the plant (area of vulnerability) are determined for a particular voltage sag level. Historical fault performance (faults per year per 100 miles) can then be used to estimate the number of sags per year that can be expected below that magnitude. Finally, a chart such as the one in Figure 6 can be constructed breaking down the expected voltage sags by magnitude and cause (voltage level of faulted line). This information can be used directly by the customer to determine the need for power conditioning equipment at sensitive loads in the plant. |
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