Variation of generator reactance during a fault fault calculations 12. Fundamentals and improvements for directional relays karl zimmerman and david costello, schweitzer engineering laboratories, inc. Fault calculations are one of the most common types of calculation carried out during the design and analysis of electrical systems. These calculations involve determining the current flowing through circuit elements during abnormal conditions short circuits and earth faults. The flash protection boundary is the distance at which staff without personal protective equipment ppe may suffer seco nddegree injuries that can be cured. While a fault occurs for some reason, at that time the repairing process related to that particular cable is difficult due to not knowing the exact location of the cable. The maximum distance range is dependent upon the frequency range. Lets work through another sample calculation where the electric utility fault power level is known click here to see fig. Ieee 1584 presents two formulas for calculating arc fault currents, one for use with 0.
Best for fault calculation, though in principle, drawing zbus element at a bus is done by injection of current at the node, and no current injections at all other buses injection of the current. Therefore the fault locator is an integral part of the distance protection function. With option zvlk2, distancetofault, the analyzer can locate faults and. It uses the frequency domain reflectometry fdr measurement technique. Pdf distance calculation for underground cable fault using. Ohmslaw algorithms if we know the voltages and currents during a fault, we can use these to estimate the distance to the fault.
Create a perphase perunit equivalent circuit of the power system using either subtransient reactances if subtransient currents are needed or transient reactances if transient currents are needed. Calculation of apparent impedance and distance relay. If the propagation velocity is set incorrectly, the fault location will be identified at the wrong distance. Observe that for the balance point fault, the v is exactly equal to iz. Fdr is a transmission line fault isolation method which precisely identifies signal. It is classified in four parts dc power supply part,cable part,controlling part, display part. The fault impedance is calculated by the distance protection. The equation is simple, just ohms law see figure 2. Although directional relays have been applied successfully for. Performance analysis of distance protection using different. Andrichak general electric company malvern, pa introduction the single line to ground fault is the most common typ eof fault that occurs on transmission lines, and ground distance functions are often used for the detection of these faults. For instance, if a linetoline fault occurs 50 feet from a transformer, then 100 feet of cable impedance must be included in the calculation. Dc power supply part consist of ac supply of 230v is stepdown using transformer, bridge.
As you can see, simplified short circuit fault calculations can be performed using a basic understanding of sources of fault power and current and impedance values that impede the short circuit power flow. Perunit ag apparent impedance calculation illustrates the amount of under and overreach with fault resistance and load flow figure 6. Distancetofault introduction distancetofault dtf measurements, typically expressed in units of reflection coefficient, return loss, or vswr as a function of distance, are used to find common faults in coaxial cables and connectors table 1. Distance calculation for underground cable fault international. The underground cable system is a common practice followed in many urban areas.
Pdf ground distance relay compensation based on fault. That means fault current calculations must be done so that the appropriate protective devices can be selected. Alexander general electric co malvern, pa introduction distance functions have been in use for many years and have progressed from the original electromechanical types thr ough analog types and now up to digital types of functions. Distance calculations are based on the assumption of a specific propagation velocity value for the cable or transmission line. A new compensation method based on fault resistance calculation is presented. Easy and simple methods for calculating short circuit curr. Variation of current with time during a fault fault calculations 11. To do this, fault data was collected from many sources, and various faultlocation approaches were evaluated. Now we can find the fault current using the following formula. Three phase fault in a three phase fault, all three phases l1, l2 and l3 are shorted together. Calculation of esdd02006 system fault levels issue no. To add cable into your calculation use the formula.
Arc fault current calculations are based on voltage, bolted fault current, conductor gap distance, and other factors. The value can be displayed and used to determine the fault location. Jetter, 122007 2 different cable types if the second cable is of different type, you can still correctly locate the fault on the first. Fault current versus distance classic connectors and clampstar. The most commonly used ground distance characteristic is the mho or the quadrilateral characteristic. This is proposed model of underground cable fault distance locator using microcontroller. Earth fault distance computation with fundamental frequency signals. The current that flows through an arcing fault is usually significantly less than the bolted fault current, due to greater resistance.
While distance to fault conveys a simple, generic meaning. Shortcircuit current calculations cooper industries. Relay settings calculations electrical engineering. His areas of interest are measuring transformers, power system analysis and simulation. Ground distance relay compensation based on fault resistance calculation. Analysis of different types of fault is an important and complex task in a power system. Pdf this paper deals with the postfault analysis of operation of distance protective relays from the line terminals. This allows the fault current to flow through a conductor. Calculation of distance protection settings in mutually. Thank you very much, interesting topics nevertheless, could you provide me a background for the medium voltage transformer ground fault system protection.
Another common method for detecting ground faults is to use distance based measuring elements. The fault distance is determined by assuming that the line reactance is proportional to the line length between the sending end and the fault point. These ground distance functions measure an apparent impedance to the fault, based upon the ratio of relay voltage to relay current. Pdf postfault analysis of operation of distance protective relays of. An electrical fault can either be a bolted fault or an arc fault.
Distance relays use these voltage and current phasors, obtained from pts and cts, to calculate impedance. Accurate fault analysis requires models that determine fault distances in a transmission line. Distance to fault capability is available in anritsu handheld products. See optimizing frequency range, on page 12, for further explanation.
The 480v fault current value at the secondary of the kva transformer based on a 250mva utility source at the primary of the transformer the calculated value is 18,790a when the cable and its length is added to the circuit the fault current in a 480v system will decrease to a smaller value. By convention, the faulted phases are selected for fault symmetry with respect to reference phase a. Lecture notes eee 360 michigan technological university. Abstractphase and ground directional elements are relied on for fast and secure protection throughout the power system. Copy this formula down through the bottom of this column. This can be represented with a simple equation for estimating. To find the fault current at any point in the network, a sum is made of the impedances in the network between the source of supply including the source impedance and the point at which the fault is occurs. Distance to fault dtf is a performance verification and failure analysis tool used for antenna and transmission line service and maintenance. Once the distance protection has provided a trip signal, the value of the fault impedance is displayed in ohms or in.
A singleended, impedancebased method can approximate the distance to the fault using the current and voltage of the involved phases, the zero and positive. Fundamentals and improvements for directional relays. Article calculation of distance protection settings in. Of the two, the latter is the most dangerous because it can lead to very high fault currents and these currents can have very substantial effects thermal heating and electromechanical. Distance relay fundamentals 63 fault, operation does not occur because izv and v are 180 out of phase. Various combinations of voltages and currents are possible in the power system in an event of fault. The mathematical models accurately capture behavior of different types of faults and location in a timely manner, and prevents damaging power system from fault. Symmetrical fault current calculations to determine the fault current in a large power system. A c a 5 where db distance of the boundary from the arcing point mm cf calculation factor 1.
There are two major problems that can occur in electrical systems. The overreaching problem can be minimized by restricting the reactive reach. However, the involved phases dictates which measurements to use within the to distance fault calculations. Goch march 14, 2012 click here to view and download this article in a print friendly, pdf format. For a zone 1 ground distance element, this means reducing the amount of instantaneous protective coverage. This is true for the threephase fault shown also for a phasetophase fault and for a phase distance function only. The calculations on the following pages illustrate 1o fault calculations on a singlephase transformer system. Distance relays are widely used as primary or backup. In particular, design application and calculation of a right ngr for a power transformer, 1214mva. If the linetoground voltage, v 5000 v, and the fault current, i 1500 a, the fault is at about 3.
A new compensation method based on fault resistance calculation is. Published in the sel journal of reliable power, volume 1, number 1, july 2010 previously presented at the 2006 ieee rural electric power conference, april 2006. Impedancebased fault location experience karl zimmerman and david costello schweitzer engineering laboratories, inc. Mar, 2012 degraded, high resistance splices, connectors, damaged conductors, etc. Sel311c distance protection settings distance zone nonhomogeneous correction angle load impedance and load encroachment power swing detection out of step detection switch on to fault sotf fuse failure scheme or loss of potential lop sel351a backup over current settings back up over current settings. A simple method for determining fault location on distribution lines. Distance protection elements based on quadrilateral operation characteristics, as the one shown in figure 1, are the most widely used in the protection schemes of transmission lines, given their good fault resistance coverage and higher immunity to load when compared to other operating.
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