Three phase to ground fault calculation software

Unearthed systems will have high voltage rise under fault. The calculation of the sag magnitude for a fault somewhere within a radial distribution system requires the point of common coupling pcc between the fault and the load. Linetoground faults, figure 1d, are the most common type of faults and are usually the least disturbing to the system. The current in the faulted phase can range from near zero to a value slightly greater than the bolted three phase fault current. Mike holt worked his way up through the electrical trade from apprentice electrician through electrical contractor, to become one of the most recognized experts in the world as it relates to electrical power installations. Bussmann series fc2 calculatorfault current calculation. What is the only case that makes the single lineto ground fault bigger than the 3 phase short circuit fault. In 1974, mike realized there was a need for quality electrical training and opened mike holt. Analyze the effect of balanced and unbalanced faults using etap short circuit analysis software. Circulating fault currents in twowinding and threewinding. Giving the nodes to be reduced, the program determines the boundary nodes.

A phase means r phase, b means y phase and c means b phase. The arc extinction process of the threephase fault block is the same as for the breaker block. Three phase ground fault electrical engineering stack. This module performs short circuit analysis on 3phase, 2phase and. Iec 60909 short circuit currents in threephase systems gives the accepted calculation method for threephase fault currents. Simulation results validate sag for three phase to ground fault. For example, a 75kva transformer with a 208y120 secondary and 5% impedance has a capacity of 208 amps. Similarly, the currents also have equal magnitudes and phase angles of 120 degrees apart, which.

Perform device duty calculations using etaps short circuit analysis software which allows you to determine fault currents and automatically compare these values against manufacturer short circuit current ratings. Fundamentals of calculating shortcircuit current everything you need to know about calculating fault currents, you learned in circuits 101, trigonometry, and basic math classes. The faults currents for three 3 phase unbalance faults are as follows. The software we use to calculate fault levels only gives us the 3phg option, however when the calcs are run there is no ground fault current. Short circuit calculations and symmetrical components part 1. How to calculate 3phase linetoground voltage sciencing. 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. Threephase symmetric short circuit, calculation according to iec 60909 calculation. The fault analysis calculation is a linearized calculation about the operating point. They sent me back readings for phase phase at 480v, but phase ground measured approximately 277v for each leg. Overstressed device alarms are displayed on the oneline diagram and included in short circuit analyzer and study reports. The calculation of shortcircuit currents are of two types and essential for two main purposes.

Consequences of shortcircuits the consequences are variable depending on the type and the duration of the fault, the point in. The programs take into consideration all of the key electrical parameters of power distribution system including power supply, cables, transformers, motors and generators. Sequence network connections for a three phase fault for a single phase to ground fault, the three networks are connected in series. He was a journeyman electrician, master electrician, and electrical contractor.

Lecture notes eee 360 michigan technological university. Presented program provides the calculation of threephase 3ls, single linetoground 1lg, linetoline. The voltage rise depends on how your threephase system is earthed. Figure 1 illustrates a simple singleline diagram that very well could be your basic service entrance for a.

With the advanced development of computers, there is a. The 2 kv busbar threephase fault level is equal to 100 mva0. The utility company says it is an ungrounded delta secondary at 480v 3 phase 3 wire system. On the occurrence of an unsymmetrical fault, the currents in the three. There are various methods of distributing and sharing all 3 phases in a road, street or small area to give a semblance of balance to the grid but the earth remains the same and there is no single earth fault on single phase that is somehow different on three. Any phase circuit to ground condition is called a ground fault. This type of fault often degenerates into a three phase fault c three phase only 5% of initial faults these different shortcircuit currents are presented in figure 5.

To gain a better understanding, it is worth running through the typical steps required to solve a fault calculation problem. Hand 44ka software 43ka my problem is on the single phase to ground fault scenario. Short circuit calculations and symmetrical components. But the answers i obtain from my software program and the answers from my hand calculations invinite bus are not the same somewhere i am doing something wrong. The xspider software system is a graphically oriented design system for. It is necessary that the proper impedance be used to represent the primary system. Introduction to symmetrical components shown in figure 4, the calculation of symmetrical components in a three phase balanced or symmetrical system results in only positive sequence voltages, 3v 1. You will find sheet with very nice example already fulfilled.

The threephase fault block uses three breaker blocks that can be individually switched on and off to program phase to phase faults, phase to ground faults, or a combination of phase to phase and ground faults. A fault in a threephase system can either be symmetrical balanced or unsymmetrical unbalanced. Clearly, the bus section and feeder circuitbreakers are all potentially overstressed. Electrical power and arc flash training programs four. In an electric power system, a fault or fault current is any abnormal electric current. In three phase power systems, if the system is not grounded, for all intents and purposes, there will be no current flow to ground in a phase to ground fault. This is because 3 phase systems have built in efficiencies for high power transmission systems. 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. Three phase fault in a three phase fault, all three phases l1, l2 and l3 are shorted together. Any two phases connected together and then to ground. The word 3 phase means the system has three separate lines, spaced 120 degrees apart, where each line. Insert the the kva rating power factor pf and impedance z of the transformer is not required to continue. An opencircuit condition is known as a series fault.

Insert available fault current ampere rating from your local utility step 1b. Mva method unbalance fault calculation in the mva method short circuit calculation tutorial, we have discussed how to calculate the three 3 phase and phase to ground fault currents. A mathematical theorem using symmetrical components and sequence networks was the most practical method to conduct fault studies. If 480v three phase motor control center feeds a 50hp motor 65a a 40hp motor 52a and a 10hp motor 14a the minimum feeder ampacity is 161. In actuality, there will be current flow to ground in an ungrounded system with a phase to ground fault due to the natural capacitive coupling to ground of the system. There is only positive sequence components throughout the network. John sokolik and it represents an easy way to calculate fault current by entering few values in indicated fields.

A single line to ground fault on a three phase supply causes the phasetoneutral voltage on the unfaulted phases to rise. The three fault breakers are connected in wye between terminals a, b, and c and the internal ground resistor. Shortcircuit current calculations cooper industries. The worst type of three phase faults and why it happens. Grounding transformers, also called earthing transformers have been applied to ungrounded three phase power systems to provide a source of ground fault current during lineto ground faults 1. For a three phase fault, the positivesequence network is used with the fault point connected back to the neutral bus, as shown in fig. Most three phase faults are unsymmetrical, and that makes doing the fault current calculation more difficult. Makes pointtopoint fault current calculations easy.

Presented program provides the calculation of threephase 3ls, single lineto ground 1lg, linetoline. This is basically a combination of the steps in the perunit calculation method. The comprehensive fault analysis program provides a network solution of three phase. Three phase fault example three phase fault example. Short circuit current calculations three phase short circuits basic pointtopoint calculation procedure step 1. Onephase asymmetric short circuit against the ground, calculation according to. Single line to ground fault analysis electrical concepts.

Its reactances per unit to the machines own base are x s 2 and the time constants are s4. Among all faults, a balanced 3 phase short circuit is the most critical and serious. Before starting fault current calculation, you will have to choose between step 1a and step 1b which are explained below. I asked them to take voltage readings between phase phase and phase ground just to make sure it is an ungrounded delta secondary. Using sophisticated modelling software contrelec is able to provide. In three phase systems, a fault may involve one or more phases and ground, or may occur only between phases.

Before computer software applications, the task of calculating fault currents for a three phase electrical system was a challenging task. For example, a short circuit is a fault in which current bypasses the normal load. Given the system single line diagram, construct and simplify. Ground fault current magnitudes can vary according to the grounding method used in the system.

Also, the generatortransformer breakers are overstressed for a fault on the transformer side of the. Three phase systems are prevalent in many power distribution systems. This is not necessary on transformers below 15kva, thus why ul does not require the impedance on the nameplate of transformers below 15kva. Threephasetoground fault and its impact on voltage. Calculate the fault current for a three phase solid fault at bus 3. Symmetrical components made easy part 1 manta test. Ptw uses the threephase fault data and the singlelinetoground fault data to calculate the positive, negative and zerosequence impedances. I am doing a three phase and a single phase to ground fault calculation on the secondary side of a transformer.

Short circuit current calculations cooper bussmann. However, it is one of the least likely of faults to occur. In a symmetrical fault all three phases are equally affected. If the threephase fault block is set to external control mode, a simulink input is added to the block to control the opening and closing of the three internal breakers. The transformer short circuit current is calculated as follows. Single phase to ground fault calculation electric power. With the software i obtain 56ka this is way higher than the threephase fault. The three phase fault calculation is no problem, the handcalcs and the softwarecalcs are almost the same. Fuse sizing guide assists with fuse and conductor sizing. In fact, what comes to our homes is usually one phase out of the three. Let us consider a three phase system with earthed neutral as shown below.

The entire electrical system has to be modelled in the software. Analyzers, plots and reports allow for quick determination of the worstcase fault current device duty. Theoretically speaking, a 3 phase fault and a 3 phase to ground fault are the same thing. How do you calculate the maximum possible available fault. Short circuit analytic sca software and mobile apps perform available short circuit fault current calculations in three phase electric power systems you are working with. Fc 2 mobile app quickly delivers fault current calculations in the palm of your hand. Calculation of system fault levels sp energy networks. Short circuit analysis short circuit software etap. Transformer short circuit fault current calculator jcalc. Three phase is exactly the same voltage to earth as single phase. Although the ground fault currents can reach values up to thousands of amps, the nec 2011 in the article 230. Per unit analysis can be used to calculate system three phase fault levels and the current distributions.