ContentsIntroduction ......................................................................................................2Distance Relay Modeling .................................................................................2Setting the Distance Relay...............................................................................8Creating and Editing a Path ...........................................................................11Adding More Relays.......................................................................................15Creating a New Path......................................................................................16Creating a Time-Distance Plot .......................................................................16

Distance Protection TutorialIntroductionThis tutorial demonstrates the modeling and editing of protective devicestypically found in transmission networks. The network that is used can befound, as an application example, in the 1987 edition of Protective RelaysApplication Guide (PRAG) published by GEC Measurements, paragraph11.32. Some differences from the original example in the text have beenintroduced to demonstrate specific PowerFactory applications, as well as tomodel a more realistic example.

As it is assumed that the user is familiar with basic editing of data, the networkhas been prepared for use, only requiring the editing of protection devices.Instructions to perform load flows and the observations of the results are thusleft to the students discretion. It is also assumed that the student hascompleted the overcurrent protection tutorial so that the basics of relaymodeling are familiar.

Distance Relay ModelingThe textbook example uses a Quadramho relay. In this tutorial however, aMicromho relay will be used, which is very similar. The Micromho typecharacteristics are available in the tutorial project library. The steps we followto model the relay are as follows:

Right click on the cubicle feeding Line G from Station P. Select NewDevices / Relay Model. as is shown below.

A relay element data input window opens, where the new relay isnamed Relay G.

We select the relay type using the select button and look for the relaytype in the project library. The project library should open with the relaytype filter activated.

There is only one distance relay type saved in the library, this has beenplaced there for use in this tutorial and of course this relay type is theMicromho that we want to use in this example.

We select this Micromho relay by double clicking on the relay type icon.The relay element data input window is now updated as shown below.

Select Create CT to model a CT input to the relay. The CT data inputwindow as shown below, opens.

The CT element can be given a special name such as CT G, but thisis not absolutely necessary.

Again we need to select a CT type from the project library. This is doneby pressing selecting a type from the project library once again. Thenselect the 600/1 CT Type from the project library.

The CT element data window is updated to show a 600/1 ratio. Ofcourse, had the CT type been a multi-ratio CT, we would also need toselect the CT ratio.

The Location is not specified and therefore the CT is automaticallymodeled in the same cubicle as the relay. A specific location, otherthan the local cubicle, would only be used if current measurement wasrequired from a different feeder that that in which the relay is located.

Press OK and the CT element is correctly modeled and visible in therelay element model.

Now a VT element must be created. To do this, the Create VT button ispressed. A element data input window, as shown below, opens.

The VT is given a name VT G. Note that the VT is defined in terms of a Type and Secondary Type. In

other words the VT model consists of a separate primary andsecondary. Firstly the primary type is defined by selecting the relevanttype using the selection button. A drop down menu appears and weselect the VT that is available in the project library.

Now the Secondary Type is selected from the project library using htenormal type selection procedure, this time for the Type in theSecondary section. Use the Voltage Transformer Secondary that isavailable in the project library.

Press OK and we are back to the relay element input window, but thistime with a VT modeled in the relay.

Just as with real systems, we need to be sure that the relay model typeis correct for the application. Double click on the Measurement elementin the relay, and we notice that the relay has been rated with a nominalcurrent of 1 A and a nominal voltage 110 V. These values correctlymatch the CT and VT input values. Pressing OK closes themeasurement element.

The Relay G has been modeled in place, but has not yet been set. This is ournext step.

Setting the Distance RelayThe relay elements are set individually using the same settings proposed inthe textbook, as follows:

Double click on the polarizing element. The window shown belowopens.

Note that the line k0 (described as kn, residual compensation factoradjustment in the ref. book) value is automatically calculated anddisplayed. As should be expected, the value of 0.49 at an angle of 7.8degrees matches the textbook exactly. By pressing Assume k0, the k0setting is changed to 0.48, which is the closest available setting to0.4893 for this relay. Press OK.

Double clicking the starting element opens the next setting window:

The starting element consists of earth fault and over-current elements.It is important that these elements are set sensitively enough to pick upfor all faults at the end of the setting zones. To determine thissensitivity we can use PowerFactory to calculate the 3-phase and earthfault currents at the end of zone 3 for relay on Line G. Using a faultimpedance of, say, 10 Ohms, we give us a conservative value forsetting the starting elements. For this tutorial the busbar at SubstationR/B1 at the end of Line J is faulted, using the complete calculationmethod. Respective resultant fault currents of 600 A and 410 A for 3-phase- and earth fault through Line G are calculated.

Set the Current, 3*I0 to 0.6 sec.A and Current I>> to 1 sec.A. PressOK.

Double click on the earth fault measuring element for phase 1 calledPGZ1. The window shown next opens.

The secondary ohm impedance values of the first line are automaticallycalculated and shown. Assuming we want to set this element to 80% ofthe impedance of Line G, we calculate a value of 8.78 sec.Ohms(10.981 x 80%). Set the Replica Impedance to 8.78 and the RelayAngle to 65 deg. The branch angle reach is automatically calculated as79.93% of the line impedance, confirming that the setting is correct.Press OK.

The Zone 2 reach must be set to cover the protected line plus 50% ofthe shortest adjacent line or 120% of the protected line whichever isthe greater. For the application under consideration Zone 2 is set tocover the protected line plus 50% of the shortest adjacent line. Usingthe same procedure as for setting PGZ1, we set PGZ2 ReplicaImpedance to 15.37 sec ohm and the Relay Angle to 65 deg.

Again we set PGZ3 using the same procedure as for PGZ1 and PGZ2.This time we set the PGZ3 Replica Impedance to 65.89 sec ohm andRelay Angle to 65 deg. The Character Angle is kept at 90 deg (tomaintain a circular tripping characteristic) and the Offset Impedance isset to 2.2 sec ohm.

The phase elements of PPZ1, PPZ2 and PPZ3 are all respectively setto be exactly the same as the earth fault elements of PGZ1, PGZ2 andPGZ3.

Double clicking on the Z2GD element (earth fault timer), opens thefollowing window:

Select time Z2GD Time Setting to 0.3 s. Press OK. Repeat this procedure for Z3GD, setting the Time Setting to 0.6 s. The same procedure is used to set Z2PD and Z3PD timers to 0.3 s and

0.6 s respectively. The last element to be set is the logic element. In most cases, such as

this one, it needs no setting. However, should we wish to trip a differentbreaker to the one in the same cubicle as the relay, we would need todefine this here. For this exercise, we will not set the logic unit.

Creating and Editing a PathWhen there are several relays in a system and one would like to check thesettings of some of these distance relays, in series, it is beneficial to define apath. We define a path as follows:

Multi-select the busbars and lines from Station P Busbar B3 (132 kV)to Station R Busbar B1 by clicking on each of the elements along thispath, while holding down the Control key.

Right click anywhere on this multi-selection. A drop down menuappears. Select Path / New.as shown.

The following input window appears:

The path to be created can be given a unique name for identification.Press OK.

The path selected should appear in red on the single line diagram. Right click anywhere on the path and select Path / Create R-X Plot

on the drop down menu as shown next.

An RX Plot appears showing the settings of Relay G, as well as some lineimpedances. Note that the earth fault and phase fault impedance elementsare on top of each other for each zone. This can be seen by double clickingon, say, the outer zone setting (Zone 3). The following window appears:

Relay elements can be set directly from the RX plot by double clickingon the displayed characteristic. In case of there being more than oneplot being on top of another, as we have here, a window will open inwhich we must then select the relevant relay setting to be edited.

After selecting the element to be set or changed, press the Edit Objecttool on the toolbar, and the setting sheet of the selected elementappears. Alternatively, double click on the element icon to arrive at thesetting sheet.

Double click anywhere on the diagram (but not on a plot) and the relayplot editor appears. Select Options and the window shown belowappears.

Select Zone 2 in the Branches, Z options. Press OK and OK again toreturn to the graphic.

A new line has appeared. Double click on the new vertical line and wesee that this is represents the impedance of transformer T6.

Adding More RelaysThe aim of any protection engineer is to ensure that coordination betweendifferent distance and overcurrent relays is correct. This coordination can bechecked using RX plots, Time-Distance plots and time Overcurrent plots.Defining paths for the relays to be coordinated is a tool that may be used inorder to make maximum use of these different plots. Before this can bedemonstrated, more relays must be added to our project. In the next fewsteps, we add an overcurrent relay to the source side (Station Q side) of LineK, and a distance relay at the source side of Line J, as follows:

Right click on the Station Q cubicle connected to Line K. Select NewDevices/ Relay Model.

Name the relay Line K OC. Select the Standard OC Relay type relay from the library. Select Create CT. From the library select the type to be a 400/200/1

CT and press OK. Note that the CT defaults to the lowest available ratio of 200/1. We

want to use the 400/1 ratio and must select it in the Primary Tap dropdown menu. Press OK.

Set the three-phase over-current element to 5 p.u. and the timemultiplier to 0.2 (double click on the Toc3Ph element field to accessthese setting fields). Press OK.

Right click on the Station Q cubicle connected to Line J. Select NewDevices/ Relay Model.

Name the relay Relay J. Select the Micromho type relay from the library. Select Create CT. On the window that appears, select the Type arrow

down. From the library select the 600/1 CT and press OK. Select Create VT. Define both primary and secondary VT type as

before for Relay G. Set the relay as follows:

PGZ1 = PPZ1 = 18 sec.Ohm; PGZ2 = PPZ2 = 30 sec.Ohm;PGZ3 = PPZ3 = 60 sec.Ohm; Relay Angle = 65 degrees;Z3 Offset Impedance = 0; Characteristic Angle = 90 degrees

The new distance relay Relay J is already in the defined path. The relay caneither be added to the existing RX plot, or a new RX plot could be generatedcontaining all relays in the path. The second option is chosen:

Right click on the red path in the grid and select Path / Create R-XPlot.

A new RX plot appears showing both Relay G and Relay Jimpedance plots.

Creating a New PathSay we need to check the tripping coordination between Relay G and LineK OC relays. One way to do this would be to use a time-distance plot. First anew path needs to be defined:

Multi-select the new path shown below holding down the control key.Make sure the Station Q 132 kV bussection cubicle/ breaker is alsoselected in the path, or you will receive a warning Path not complete.To do this, you may need to enlarge the area around the bussection.

Select Path / New.

A dialogue for the new path appears with the path colour as green (thiscan of course be changed). Select OK. The new path will appear ingreen.

Creating a Time-Distance Plot Right click on the newly created green path and select Path / Create

Time-Distance Diagram. Make sure that you do not right click on acombined path, but select a part of the path that is unique to the greenpath in order to create the correct diagram.

Press Execute on the window that opens. Two plots are shown, but these need to be further defined. Double click

anywhere on the plots. The screen shown will appear.

Only a forward plot is required. In the drop down menu next toDiagrams, select Forward.

For the Reference Relay, Forward select Relay G. Press OK. The curves may not appear immediately as the scale could be

incorrect. Press the Scale X-Axis Automatically and Scale Y-AxisAutomatically buttons on the second toolbar, and the curves shouldappear as shown next.

From the diagram it is noticed that the distance relay (Relay G) will operatefaster than the overcurrent relay. This would cause incorrect tripping. To setthis right, take the following steps:

Double click on the green curve of the over-current relay. Change theCurrent Setting to 1.5 p.u. and Time Dial to 0.1.

Press OK. Double click on the Zone 2 part of the red distance relay (Relay G).

The PPZ2 window opens. Select Timer. The Z2PD window opens. Setthe Time Setting to 0.5 seconds. Press OK and OK.

Double left click on the Zone 3 part of the red distance relay. The PPZ3window opens. Select Timer. The Z3PD window opens. Set the TimeSetting to 1.0 seconds. Press OK and OK.

Press the Rebuild button on the second toolbar. After the recalculation has been completed, rescaling the Y-Axis may

be required. This is done by pressing the Scale Y-Axis Automaticallybutton on the second toolbar.

The Time-Distance diagram now appears as shown below.

It is now clear that for three-phase faults without any fault impedance alongthe green path, tripping coordination will be correct.