Distance Protection

Distance Protection

Overview

The module distance protection allows the user

• to enter distance protection relays with their settings or characteristics respectively,

• to get all voltage, current and impedance values (primary or secondary) seen by a relay due to a short circuit,

• to check the relay settings, • to set the relay automatically and • to enter the tripping schedules.

All impedance values shown in the module are calculated with a short circuit calculation according to the superposition method with or without load flow (see chapter "Short Circuit").

The module distinguishes two types of relays

• user-defined or general relay (relay type given by the user) • predefined relay type (relay type predefined by the program)

The characteristic of a general relay can be entered in a R/X-diagram. The user in the dialog distance protection can enter the type of the relay.

When selecting the relay type from a predefined list, the user will be able to enter the relay dependent setting parameters in a special dialog. The program will build up the characteristic. The predefined list will be displayed, when pressing the button "…" beside “Predefined type” in the dialog distance protection.

Starter

The following starter systems can be entered: • pure over current starter

• under impedance starter (U-/I-limits) • R/X-characteristic

The starter system can be selected in the dialog “Starter” of the distance protection relay. All starter systems can be defined for line-line and line-earth faults. The selection of the fault type will be done with “Data input” (“L_L” or “L-E”) in the dialog “Parameter” of the relay.

With the starter system coupled are • the directional end time and • the non-directional end time.

The pure over current and the under impedance starter can be defined for user-defined relays as well as for preuser-defined relays. On the other hand the starter R/X-characteristic cannot be defined for predefined relays, because it is determined by the setting parameters.

Pure Over current

The input data are:

I1/Ir

I / Ir U / Ur

Starting area

The relay will start if the measured line current is larger than I1/Ir independent of the voltage. Ir is the nominal current at primary side of the current transformer. A current limit can be defined for line-line and line-earth faults.

Under Impedance

The data are entered according to fig. 10.2 and 10.3:

U2/Ur I2/Ir I1/Ir I / Ir U / Ur U1/Ur Starting area

Fig. 10.2 Phase-independent under impedance starter

U2/Ur=

U / Ur

U1/Ur

The value I3/Ir should set to zero for phase-independent under impedance starters. The input of "Phi1" and "Phi2" is then unimportant.

The value I3/Ir must be defined for a phase-dependent under impedance starter. The values U1/Ur and U2/Ur must be set equal. In case of a short circuit and if the angle between line current and line-earth voltage is between Phi1 and Phi2, the current limit I3/Ir is considered instead of I2/Ir.

R/X-Characteristic

The following characteristics can be entered

• a polygon defined by a table of R/X values or • a circle defined by a centre and a radius

If the measured impedance is inside the polygon or inside the circle the relay will start.

X

R Starting area

Fig. 10.4 Starter with R/X-characteristic

A characteristic for line-line and for line-earth faults can be defined. The characteristic for predefined relays is defined by the setting parameters.

Measurements

The following zones can be entered: • Zones 1 – 4

• Overreach zone (zone 1 ext.) • Backward zone

• Auto-reclosure zone

The zones are defined by a characteristic (polygon or circle). For predefined relays the characteristic is determined by the relay setting parameters. The characteristics can be given as primary or secondary values. A characteristic for line-line and line-earth faults can be entered. The type of input can be selected by the parameter „Data input“ in the relay dialog.

A measurement direction can be assigned to each zone. The measurement direction is normally given by the proper entry of the characteristic. The definition of the measurement direction is only necessary, if a simplified characteristic is entered, e.g. a circle around zero point (0/0) or a rectangular in all forth quadrants. With the input of a direction the circle or the rectangular will be divided through a diagonal in the 2. and 4. quadrants. The diagonal changes the characteristic.

To each zone a tripping time or time delay in seconds must be assigned. The input of the delay time is also done for line-line and line-earth faults.

Each zone can be activated or de-activated. Zones, which are not active, are not considered during the calculations.

Setting Parameters for Predefined Relays

The following relay types are predefined • ABB REL316

ABB REL316

Tripping characteristic (only for 1st stage)

X -X / 8 X R -RR / 2 -RRE / 2 RRE RR 27° 27° 7°

For each stage the compensation factor k0 and for parallel lines also the

compensation factor k0m has to be entered.

Siemens 7SA511, 7SA513

RA1 RAE RA2 RAE X+A X-A RA2 X R RA1 PHIA

Tripping characteristic (only for 1st stage)

X1 R1 RE1 RE1 X R R1 45°

AEG PD531, PD551, SD36

Beta 110° Rv L-L Xv Zr X R Zv 70° Rv L-E

Tripping characteristic polygon (only for 1st stage)

-X -135° X Alpha -RL-L X R RL-L RL-E -RL-E

-135° Delta Alpha X R Arc compensation Phi

The function to get the arc compensation circle is:

) sin( 1 delta Z Zcor + =

Delta is in the range -45° < phi < alpha: delta = alpha - phi

and in the range 135° < phi < (alpha + 180°): delta = alpha - phi + 180°

For the overreach stage the factor ku for L-L and L-E faults must be entered.

Backup Protection

The distance protection relay can also be defined as an over current relay with two definite time stages

I2/Ir t1 I1/Ir I / Ir t t2

Fig. 10.5 2 definite time stages

I1/Ir and I2/Ir are the setting values for the two stages. Ir is the nominal current of the CT at primary side. The delay times t1 and t2 are tripping time of the two stages.

When evaluating the relay settings and if the relay has not been started by the distance protection part of the relay, the values of the backup protection are checked (see relay evaluation). If there is no over current functionality in the relay no values have to be entered here.

Automatic Impedance Setting

The threshold impedance values or the characteristics of the stages 1 to 4 are automatically calculated by the program with the help of the tripping schedules, which are entered by the user.

The tripping schedules are generated in the NEPLAN menu option „Analysis-Distance protection-Tripping schedule“. A relay can belong to any number of tripping schedules. The arbitrary numbers of schedules are reduced to a single schedule with the smallest impedances. In the minimum impedance path contains only relay nodes. In the dialog “Setting” and at “Decisive nodes for relay setting” the smallest impedance path, that means the nodes and the corresponding impedances, are displayed. The displayed impedances are positive sequence impedances, which the present relay will measure, if a 3phase short circuit at the nodes takes place. The impedances are calculated according to the superposition method with or without load flow (see short circuit parameters).

There are two methods to set the relays: • Relative

• Absolute

These methods can be selected in the dialog „Setting“. The two methods are explained below. The base for both methods is the minimum impedance path. The figure below shows an example for the creation of a minimum impedance path.

Z / Ohm

1. 2. 3.

Relay location A

Zone

User defined tripping schedules

Minimum impedance path

R R R R

B C D

Fig. 10.6 Getting the minimum impedance path in meshed networks With the minimum impedance path the relay in location R will be set. Setting according to relative method

t

a b

b1

b2

Z

Fig. 10.7 Setting according to relative method The rules are:

Z1 = p1 * a

Z2 = p2 * (a + b1) Z3 = p3 * (a + b2)

Z1ext = p1ext* a (overreach zone or zone 1 ext.)

Z1, Z2, Z3 are the setting values at the relay. The parameter p1 for 1. zone, p2 for 2. zone, p3 for 3. zone, etc. are input values, which can be entered in the dialog „Zone settings”. The rule for setting zone 4 is accordingly.

Impedance corrections due to infeeds are considered in the lines b1 and b2. Setting according to absolute method

This method is used to set the last zone. For example, if the last zone has to cover 50% of the transformer impedance.

t

a b b1

Z

Fig. 10.8 Setting according to absolute method The rules are:

Z1 = p1 * a

Z2 = a + p2 * b b1 = p2*b

The zone (impedance) is calculated absolutely to the impedance of the corresponding zone.

Impedance corrections due to infeeds are considered in the line b. Setting of relay considering the minimum reach

If the parameters „Minimum zone setting“ for zone 2 and/or zone 3 are activated, the program will check after the automatic setting if a minimum impedance value for zone 2 or zone 3 is reached. If not, the set values will be corrected.

t

a / p1

The minimum reach is calculated as follows: For zone 2: Z1min = a / p1

For zone 3: Z2min = pmin * a (for parallel lines)

Z2min = (a + b lg) / p2

blg means the longest adjacent line. The user can consider the infeed factor for

calculating the impedance blg. To calculate the impedance blg it is maybe

necessary to switch off or to reduce the infeed. The calculation of impedance blg

at the present stage of the network is done by pressing the button „Get longest line for zone 3“ in dialog „Setting“. For the normal setting of the relay the infeed must be considered in full.

Considering Arc resistance

The calculated impedance values are corrected with the arc resistance and the resistance for tower footing path. These values can be entered in the relay specific parameters.

Correction for line-line faults: RR = RR + RfL-L / 2 Correction for line-earth faults:

RR = RR + RfL-E + RM with:

RfL-L: Arc resistance for line - line faults RfL-E: Arc resistance for line - earth faults

RM: Tower resistance for tower footing earth path

If no characteristic has been assigned to the relay the following rectangle will be assigned:

P1 = -RR, -XR (R, X) P2 = -RR, XR

P3 = RR, XR P4 = RR, -XR

XR and RR are the reactance and resistance calculated from the impedances Z1, Z2, Z3, etc. of each zone. If defining a direction, the characteristic will be modified by the “direction line” into the 2. and 4. quadrant.

In case that a characteristic has already been assigned to the relay, the characteristic will be reduced or enlarged proportional.

The relay setting parameters are assigned to the predefined relays directly.

Tripping schedule

The user can define any number of tripping schedules with NEPLAN menu option „Analysis-Distance protection-Tripping schedules“. After having selected this option the following items are available

• Tripping schedule

with add, delete, edit, display graph and print • View

with zoom out, zoom out all, edit, trace mouse position, trace curve, colors, etc.

The option „Tripping schedule-Edit“ allows the user to define a tripping schedule. A tripping schedule is described by the relay Z/t-characteristic and the node impedances measured from the relay. Any number of nodes can be displayed. Important is only, that the relay location nodes are displayed. The relay location nodes are starting points for the Z/t-characteristic.

The following parameters are available:

Fig. No. An arbitrary figure number can be entered. Title A description of the schedule can be entered. Relays

Insert A new relay will be inserted. The node, in which the selected relay has been built-in, will also be added to the list of displayed nodes.

Relays

Edit Parameters of the selected relay are displayed in a dialog. Characteristic or setting parameters can be changed directly. Relays

Delete

changed.

Close The dialog will be closed without regeneration of the schedule. The items „View-Zoom out“ and „View-Zoom out all“ allow changing the view of the diagram. These items are only active, if a “Zoom” has taken place. Holding the left mouse button and selecting the section to be zoomed the user can do a „Zoom“. The colors for the Z/t-characteristics and the nodes can be selected in “View-colors”. Up to six different colors are available.

The items of menu option „View“ can also be displayed by pressing the right mouse button on the diagram.

Structure of tripping schedule

Relays can measure the impedance of the same node distort, because of infeeds and parallel lines. The following example illustrates that.

t a b Z t a b1 Z A B A B K1 K2 _{K1 K2}

Fig. 10.10 a) Without infeed b) With infeed

The relay A measures the impedance of node K2 without infeed as: ZK2 = a + b;

The relay A measures the impedance of node K2 with infeed as: ZK2 = a + b1 = a + k*b; k > 1.0;

However relay B measures the impedance of node K2 always as: ZK2 = b;

Obviously relays A and B have different impedance coordinate systems caused by the infeed. It is therefore important to relate all Z/t-characteristics and node impedances to one common coordinate system. The common coordinate system is given by the first relay in the tripping schedule. The conversion factor(s) are the infeed factor(s). The infeed factor is calculated as:

Fig. 10.11 Calculation of the infeed factor

0

.

1

'

'

'

>=

+

=

I

I

I

k

The calculation of the impedance values from the R/X- to Z/t-diagram is done with the help of the complex node impedance. The distance of the intersection between the node impedance and the characteristics (polygon or circle) from the origin (0,0), represents the impedance, which is shown in the Z/t-diagram:

1 . z o n e X /O h m R /O h m N o d e im p e d a n c e 1 . z o n e t/s Z /O h m P 1 P 2 _{P 3} P 4 P h i L

Fig. 10.12 Calculation of the impedance values from the R/X- to the Z/t-diagram

Display of impedances and relay characteristics

Relay characteristics and short circuit impedances measured by the relay can be displayed in a R/X diagram. The short circuits can be defined on nodes and lines. After having selected option „Analysis-Distance protection-Protection devices“ all relays are listed at the left side of the screen. The following options are available:

• Protection devices

with Display relay characteristic, Show relay dialog, Edit parameters, Show impedance list, Show relay documentation, etc.

• View

Impedances to be displayed in the diagram can be selected with option „Edit parameters“. The dialog can also be called by a double click on the diagram. The dialog contents the following parameters:

Fault type The fault type can be selected here. The same types are available as in the SC calculation (see short circuit calculation parameters). The calculation method has to be set in the SC calculation parameters (superposition with or without load flow). Impedances The impedances to be displayed in the diagram can be chosen. The calculation of the loop impedances is explained below. The displayed impedances are secondary or primary values

according to the parameter set by the user. Faults on

nodes The buttons „Insert“ and „Delete“ allows the user to define the faulted nodes. The impedances measured by the relay are displayed in the diagram. All faulted nodes are listed. A node in the list can be activated or de-activated. Parameter “Faults on nodes-Active“ allows activating or de-activating all nodes in the list.

Faults on lines The buttons „Insert“ and „Delete“ allows the user to define the faulted lines. The impedances measured by the relay are

displayed in the diagram. All faulted lines are listed. A line in the list can be activated or de-activated. Additionally the user can define the fault location as the distance in percentage from the “From node” of the line. The parameter “scanning” indicates if the fault location will scan over the line in a given distance. In this case not only one set of impedances will be calculated, but a quantity of impedance sets (trajectory). Parameter “Faults on lines-Active“ allows activating or de-activating all lines in the list. Characteristic The relay characteristic for line-line and/or line-earth faults can

be selected here. Recalculate

and Close The dialog will be closed and the impedances recalculated. This button has to be pressed, if relay or node data has changed. Close The dialog will be closed without recalculation of impedances.

A footer or header can be displayed.

Menu item „Protection devices-Show impedance list“ lists all calculated impedances. The impedance values can be exported to a file RDS. The fields are separated by tabs.

Calculated relay impedances

The following impedances are measured by the relay: • Impedance of the positive sequence system

This impedance is only reasonable, when making 3phase faults. • Loop impedances

Loop impedances are in practice measured impedances by the relay. Loop impedances are calculated as follows:

with compensation with compensation for parallel lines 0 0 3 kI I U Z R R R = ₊ Em m R R R I k k I I U Z 0 0 0 3 + + = S R S R RS _{I I} U U Z − − = 0 0 3 kI I U Z S S S + = Em m S S S I k k I I U Z 0 0 0 3 + + = T S T S ST I I U U Z − − = 0 0 3 kI I U Z T T T + = Em m T T T I k k I I U Z 0 0 0 3 + + = R T R T TR I I U U Z − − = 1 1 0 0 _{3 Z} Z Z k ⋅ − = 1 0 0 _{3 Z} Z k m m = _⋅ with

UR, US, UT Line-earth voltage in phase R, S, T or L1, L2, L3

IR, IS, IT Line currents in phase R, S, T or L1, L2, L3

3I0 Three times zero sequence system current or earth current IE

Z1, Z0 Line impedance of positive and zero sequence system

Z0m Zero sequence coupling impedance of two parallel lines

IEm Earth current of parallel line

k0 Compensation factor for zero sequence system (input value)

k0m Compensation factor for parallel line coupling (input values).

The line, which is in parallel to the line with the present relay, can be entered in the dialog of relay.

Procedure for Entering a Relay

For the input and setting of a relay the following procedure has to be done: • Step: Insert all distance protection relay in the network. This can be done

graphic- or list-oriented. Each relay has to be named (predefined or user-defined relay). Characteristics can also be imported.

• Step: Insert to each DP-relay current (CTs) and voltage transformers (VTs). The VTs are assigned to a node. This is only necessary, if secondary values are considered. It is also possible to enter the impedance ratio directly. • Step: Define all tripping schedules, even when no relay characteristics are

entered at this point and thus the schedules not displayable. This step is very important for the automatic setting of the relays.

• Step: To each relay a starter system can be assigned and the parameter or characteristic can be entered for the zones. The relays can also be set automatically.

• Step: Sometimes it is necessary to define a node as a distance protection node, when this node is important for the automatic setting of a relay. This can be done in the dialog of the node (see remark above).

• Step: To evaluate the relay settings short circuits can be calculated in the network. The tripping time of the relays are displayed in the single line diagram.

Remark:

Although in node B there is no relay located, node B can be important for the automatic setting of the relay DP. This is the case, if for example node B is the end of a feeder or if in node B there is a over current protection.

DP

B

C

The parameter „Distance protection node“ in the node dialog indicates if the node is relevant for the automatic relay setting.

Relay Documentation

After having selected option „Analysis-Distance protection-Protection devices“ all relays are listed at the left side of the screen. A relay will be

documented by choosing “Protection devices-Relay documentation”. Beside the relay parameters the node impedances, which are important for the relay setting, are displayed. Z / Ohm 1. 2. 3. Relay location Zone Impedance zone 1 Impedance

zone 2 Impedance _{zone 3}

Fig. 10.13 Impedances of relay zones

The impedance values of stage 1 represent the line impedance or the impedance to the next relay node. The impedance values are given for the positive system. In order to get the line impedance between stage 1 and 2 a subtraction of the impedance values of stage 2 and 1 must be done.

The documentation shows the setting values for a general (user-defined) relay with consideration of the arc resistances.

The relay documentation can be exported to a file with extension DDS. The fields are separated by tabs.

Checking the Relay Settings

All relays can be checked by calculating several variants (different fault locations, faults on lines, arbitrary fault types). The program calculates the tripping times of the relays. The tripping times are displayed in the single line diagram. It is

recommended to select only one fault location and to set in return the fault distance (see SC calculation parameters) to a large number. With it all voltages and currents at the relays are calculated.