Woodward ESDR 4 Current Differential Protection Relay

ESDR 4

Current Differential Protection Relay

The ESDR 4 is a three-phase current differential protection relay for generators and motors (protected object).

The currents flowing in the individual lines are each measured using a current transformer on both sides of the

protected object. They form the protection area boundary or zone. All two or three-phase short circuits and line

to-earth faults within this protection area are detected by the ESDR 4 as fault currents which initiate tripping.The

unit does not trip if fault currents occur outside the protection zone. In this way, a selective protection is guaran

teed.

The unit monitors six (6) measured currents via isolated inputs. The unit calculates internally the restraint current

(Is) and the differential current (Id) separately for each phase. The actual values of the calculated parameters (Dif

ferential current Id und Restraint current IS) are shown on the display either as absolute values or as a percentage

of the generator rated current (selectable in locked input mode).

Theoretically the currents Ia and Ib are equal, both in fault-free operation and outside the protection zone (Figure

4-1-a).The difference is zero and the differential protection does not initiate. However, in practice current differ

entials do occur (= spurious currents), even in fault-free operation. They result, for example, from summation or

phase angle errors in the CTs, which are influenced by deviating burden values. These spurious currents remain

small inside the operating range, but increase with increasing load and are especially high when one or more CTs

become saturated (e.g. in the case of an external short circuit). In order to prevent a tripping of the relay due to

spurious currents, the trigger threshold is not held statically constant but increases in relation to the restraint cur

rent Is.  Spurious currents need to be taken into account when adjusting the trip characteristic.

When a fault occurs inside the protection area (Figure 4-1-b), unequal currents flow in the CTs, which result in a

current differential. If this exceeds the differential protection threshold, the relay will trip.

Monitoring of the Differential Current

The monitoring of the differential current is carried out in two stages..

The first monitoring level serves as a warning and can be enabled or disabled. Should the adjustable warning

characteristic be exceeded, a text appears in the display and a relay contact is enabled. The pick-up time and the

dropout delay of the relay output are adjustable. The warning stage of the monitoring is auto-resetting.

The second stage of monitoring (main stage) serves to initiate tripping. In contrast to the first stage, it offers the

possibility to monitor the overstepping of an adjustable tripping characteristic (Id < In) and additionally, a fixed

tripping-threshold of 100%, relative to the generator rated current (Id > In). The trigger-delay for each limit value

may be independently adjusted, thus allowing a shorter triggering time at higher differential currents. When one

or both tripping characteristics are exceeded, a text display is initiated and two relay contacts are energized. The

tripping characteristics possess a 2% hysterisis relative to the generator rated current. .

The signal relay is only automatically reset if the function “automatic reset relay” in the Entry field on the screen

is configured to “on”. Otherwise, the resetting is carried out by pressing the “Clear” button on the front of the

unit or via the discrete input terminal 18 “reset”.

The two monitoring levels can also be used to change the characteristics of the control function (stage 1: small

value and a long time; stage 2: high value and a short time)

Tripping Characteristic

The following figure shows the tripping and warning characteristics (with sample values for X12. Y1.and Y2). It

represents the tripping and warning thresholds (Y) relative to the restraint current (X) The positions of the corner

points are determined by the coordinates P (X12/Y2) and P (X12/Y1). The selection of these positions is depend

ent on the generator being protected. The following gives the ranges of tripping and warning thresholds:

IS / IN

IS / IN

IS / IN

0 to X12

X12 to 5 × IN

> 5 × IN

The threshold Id is independent of the restraint current..

The threshold Id is dependent on the restraint current. A change of 100% in the

restraint current causes an increase of 10% in the tripping threshold.

The threshold Id stays constant at 85%.

Different characteristics can be chosen for the first and second monitoring levels, whereby the horizontal position

(X-coordinate) is valid for both stages. The vertical position (Y-coordinate) can be chosen separately for each

monitoring level. This results in a fixed difference in thresholds of the first and second monitioring levels for

each restraint current Is.

Control Inputs

Configuration

Terminal 17

Acknowledgement

Terminal 18

Blocking

Terminal19

Relays

Tripping (relay 1)

Terminals 1/2/3

Tripping (relay 2)

Terminals 4/5/6

Warning (relay 4)

Terminals 11/12/13

Ready for operation

(relay 3)

Terminals 7/8

When this input is energized, the unit locks into Configuration mode and stays in this

mode until the terminal is de-energized.

If this input remains energized for at least 1 s, the faults detected in monitoring

level 2 are reset. This means that the relays will be de-energized and the text display

will be deleted from the screen as long as the monitored currents are not exceeding

the configured threshold level.

When this input is energized, the differential protection is disabled.This means that

the differential current is not monitored, no relay can be enabled and no text is dis

played.

This relay becomes enabled when the unit detects threshold limit 2 (main stage) has

been exceeded. The configured differential current characteristics and delay time will

determine how relay 1 functions.

This relay becomes enabled when the unit detects threshold limit 2 (main stage) has

been exceeded. The configured differential current characteristics and delay time will

determine how relay 2 functions.

This relay becomes enabled when the unit detects threshold limit 1 has been ex

ceeded. The configured differential current characteristics and delay time will deter

mine how relay 4 functions.

This relay is enabled when the unit is operational and the differential current is being

monitored. The relay becomes disabled if the monitoring is deactivated through any

of the following reasons:

• the internal self-monitoring has detected a malfunction of the unit. A correct func

tioning of the unit cannot be guaranteed and corrective action may be necessary.

• the set values for parameter “CT-ratio” or parameter “Generator Current” are out

side the permissible limits (see page 19).

• the digital input “Blocking” is energized.

• the parameter “Monitoring” is configured to “Off”.

When in configuration mode (simultaneous pressing of “Digit↑” and “Cursor→”), the configuration screen can

be advanced by pressing the “Select” button. Should there be no entry, parameter change or other action for 60

seconds, the unit will automatically revert into Automatic mode.

During the configuration mode, the monitoring function is still active. This means inevitably, that while adjusting

parameters during operation, it is possible to cause a tripping of the relay.

adjust settings

[press “SELECT”]

Configuration mode “Select” button

Pressing the “Select” key activates the configuration mode, and the following pa

rameters can be enabled or changed within the given limits. Please you note that as

you advance through the configuration screens, by configuring some parameters as

“ON”, additional screens must be configured relating to that parameter. If the pa

rameter is configured as “OFF”, the additional screens will be disabled and not dis

played.

Software version

Software version

Displays the software version.

SPRACHE/LANGUAGE —————-

Language selection english/german

The screens can be displayed in German or English.

curr. transform.

ratio     0000/x

CT-Ratio Selection 10 to 6.000/{x} A

The Ratio of the CTs being used is entered here. The CTs should be selected so that

in fault-free operation at generator rated current, at least 60 % of nominal current

flows in the CT-secondary. Failure to use properly a sized CT-Ratio leads to loss of

resolution and inaccuracies in the monitoring functions.

generator nomin.

current    0000A

Generator rated current 5 to 6.000 A

This value is used as reference value for the calculation and display of restraint cur

rent and differential current. The entered value of generator current must be at least

60% of the nominal current of the CT and must not exceed the entered value of  CT

nominal current.

Example CT-Ratio 500/5 A

Range of Generator rated current 300 A to 500 A.

If the nominal value is less than 50% of the transformer ratio, the message “Wrong

Entry” will be displayed on the screen in Automatic mode and the unit will de

activate monitoring functions (the Monitoring LED goes out).

automatic reset

relay       ON

Automatic reset of the relay ON/OFF

Applies only to monitoring level 2 (tripping).

Monitoring level 1 (warning) always Auto-resets.

ON…………….The relays de-energize automatically when the fault is no longer pre

sent. The screen input “Automatic reset of error text” determines

what happens to the Alarm-text in the display.

OFF…………..The relays remain energized until they are reset.

monitoring

ON

Monitoring ON/OFF

ON…………….Monitoring of the differential current is active and the follow

ingscreens of this option are displayed.

OFF…………..The monitoring is de-activated and the following screens are not dis

played.

release limit

Is/In     X=000%

Trigger Value IS/IN (X12) 50 to 300 %

Definition of the threshold characteristic for the monitoring of levels 1 and 2.

This value determines the horizontal position (X12-coordinates of points

P [X12/Y1] and P [X2/Y2]) of the corner points of the Warning and Tripping char

acteristics.

release limit

Id/In     Y=000%

Limit valueId

This value determines the vertical position (Y2-coordinate) of the corner point

P [X12/Y2] of the tripping characteristic (monitoring level2).

pick-up t. Id>IN

release    0.00s

Relay enable delay time for Id>IN (monitoring level 2) 0.04 to 3.00 s

If the differential current surpasses the generator rated current without interruption

over this time period, a fault condition for exceeding the threshold limit will be ini

tiated.

pick-up t. Id<in< p=””></in<>

release    0.00s

Relay enable delay time for Id

If the differential current surpasses the adjusted trigger threshold without interrup

tion over this tme period, a fault condition for exceeding the threshold limit will be

initiated.

release time

release    0.00s

Relay disable delay time (monitoring level 2) 0.10 to 3.00 s

Only visible when the screen “Automatic reset of the relay” is configured to

ON .

If the differential current value which initiated the fault condition should fall 2% or

more below the trigger threshold limit and remain uninterrupted for the period of

time configured here, the fault condition will be terminated and the relay output

and the fault text will be reset.

automatic reset

error text   ON

Automatic reset of error text ON/OFF

Only visible when the screen “Automatic reset of the relay” is configured to

ON

ON…………….The displayed fault text will be automatically deleted, when the fault

conditions are no longer detected.

OFF…………..The displayed fault text must be deleted manually, and can only be

done when fault conditions are no longer detected.

automatic reset

error text   00s

Delay for automatic reset of error text 1 to 60 s

Only visible when the screens “Automatic reset of the relay” and “Automatic

reset of error text” are configured to ON

The fault text will automatically delete, when the fault conditions are no longer de

tected for the time period set here.

warning

ON

Warning (monitoring level 1) ON/OFF

ON…………….The adjustable warning characteristic is being monitored and the fol

lowing screens of this option are displayed.

OFF…………..The adjustable warning characteristic is not being monitored and the

following screens of this option are not displayed.

warning limit

Id/IN    Y=00.0%

Trigger value Id/IN (monitoring level1. Y1) 3.0 to 40.0 %

Only visible when the screen “Warning” is configured to ON.

This value determines the vertical position of the corner point of the warning char

acteristic. The horizontal position (X12) is identical with that of the trip character

istic. Usually the warning limit is lower than the trip limit value.

pick-up time

warning    0.00s

Enable delay time of the “warning” relay (monitoring level1) 0.04 to 3.00 s

Only visible when the screen “Warning” is configured to ON.

If the differential current exceeds the warning threshold curve without interruption

over this time period, the control recognizes that the warning limit has been ex

ceeded.

release time

warning    0.00s

Relay disable delay time (monitoring level 1) 0.10 to 3.00 s

Only visible when the screen “Warning” is configured to ON

If the differential current value which initiated the warning should fall 2% or more

below the trigger threshold limit and remain uninterrupted for the period of time

configured here, the fault condition will be terminated and the relay output and

fault text will be reset.

display value

Id           [-]

Display – measured value Id in [%] / [A]

[%]……………The percentage of the rated generator current that is measured is dis

played on the screen.

[A]:……………The measured absolute values are displayed on the screen.

display value

IS           [-]

Display – measured value IS in [%] / [A]

[%]……………The percentage of the rated generator current that is measured is dis

played on the screen.

[A]:……………The absolute measured values are displayed on the screen