Areva MiCOM P521 Operator's manual

MiCOM P521
Current Differential Relay
Software Version 1.D
Update Documentation
P521/EN AD/B21

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MiCOM P521 Page 1/24
P521 UPDATE DOCUMENTATION
In the firmware version 1.D of P521, several changes on existing features have been
added. These are described with reference to the documentation listed below:
Release Version Documentation
29.01.2004 P521/EN M/B11 Technical Manual
Document Ref. Section Page No. Description
P521/EN FT/B11
3.4.2 13
Relay hardware or software alarms
DEFAULT CONFIG. : alarm message
re-written
3.5.3.7 32
Protection communication menu
Protocol - SDLC menu : “and IEEE
C37.94/2” removed from the menu
description
3.5.4.8 57 - 58
Inverting of the auxiliary output
relays
New section added
57
Inputs sub menu
Section re-numbered : was 3.5.4.8
3.5.4.9 58
AUTOMAT. CTRL menu : description
amended
3.5.4.10 59
Broken conductor sub menu
Section re-numbered : was 3.5.4.9
Cold load pick-up sub menu
Section re-numbered : was 3.5.4.10
3.5.4.11 60
AUTOMAT. CTRL menu : description
amended
Circuit breaker failure sub menu
Section re-numbered : was 3.5.4.11
3.5.4.12 62
AUTOMAT. CTRL menu : description
amended
Circuit breaker supervision sub
menu
Section re-numbered : was 3.5.4.12
3.5.4.13 62
AUTOMAT. CTRL menu : description
amended
P521/EN TD/B11
6.2 15
Logic inputs and outputs
Logic input : re-written
9.1 17
Dielectric withstand
Paragraphs 2 and 3 : amended

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Document Ref. Section Page No. Description
P521/EN AP/B11
53
MiCOM P521 trip circuit supervision
mechanism
Figure 22 : amended
54 Figure 23 : amended
3.8.1 55 Figure 24 : amended
5.8 74
Unconditional 4 wire pilot
communications for distances
greater than 1.2km (P595)
Note : amended
P521/EN CM/B11
9.3.2 32
Protection comms. fault
Figure 2 : amended
P521/EN MC/B11
2. 3
Definitions
Switch diagram : added to end of section
P521/EN AC/B11
5.1 13
Function of loopback test box
Figure 6 : amended
P521/EN VC/B11
- -
Hardware/software version history
and compatibility
Updated to reflect latest relay software

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USER GUIDE (P521/EN FT/B11)
3.4.2 Relay hardware or software alarms
Any software or hardware fault of the MiCOM relay generates a "hardware/software
alarm". If several alarms are generated they are all stored in their order of
appearance. The alarms are displayed in reverse order (the most recent first and the
oldest last). Each message is numbered and the total number of messages is
indicated below.
The user can read all the alarm messages with the aid of &,without entering the
password.
The acknowledgement of the relay alarm messages is IMPOSSIBLE if the fault is still
present. The alarm can only be acknowledged when the cause of the alarm has
disappeared.
The management of the WARNING LED is directly linked to the status of the alarms
stored in the memory.
ÞIf the fault is major (the relay cannot perform protection functions), the
WARNING LED is continuously illuminated and the watchdog contact will
operate.
ÞIf the fault is minor (no influence on the protection and automation function
e.g. SCADA communication failure), the WARNING LED flashes. This will
not cause operation of the watchdog contact.
Possible Hardware or Software alarm messages:
Major fault
SETTING ERROR: Setting error occurred due to data
memory fault
EEPROM ERROR CALIBR.: Calibration memory faulty
CT ERROR: Analogue channel faulty
PROT. COMMS FAIL: Protections comms card faulty
DEFAULT CONFIG.: Factory settings restored due to data
memory fault. This message will also be
displayed following a firmware upgrade.
Minor fault-
RAM ERROR: RAM supplied by battery faulty
BATTERY FAIL: Battery faulty (flat or not correctly fitted)
Note: The “Battery backed RAM memory” and “Battery failure” alarm
messages can be configured to display or not; YES or NO in
CONFIGURATION/Alarms menu. If NO is selected an alarm
will not be raised in the event of a Battery Fault.
COMM.ERROR: Internal communications faulty
CLOCK ERROR: Real time clock faulty
PROT. COMMS RECOVER: Recovering from transient comms fault
(back-up protection available)

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3.5.3.7 Protection communication menu
COMMUNICATION
Heading of the COMMUNICATION menu. To gain access
to the Protection Comms menu, press 2, 63 times then
2and 6. To gain access to the sub menu points, press
2.
Protection
Heading of the Protection Comms menu. To gain access
to the Protection Comms menu, press 2.
Protocol
SDLC
Displays the currently selected protocol for the protection
comms. Select from SDLC, NRZ using 8or 2and
enable your choice using 5.
Data Rate
64k
Displays the speed of protection comms transmission.
Select from: 9.6k, 19.2k, 56k, 64k and 2M bits per second
using 8or 2and enable your choice using 5.
Relay Address
A1
Displays the relays protection comms address. Select
from: A1, A2, A3, B1 etc. through to F3 using 8or 2
and enable your choice using the 5key.
Clock Source Ch1
INTERNAL
Displays the source of the protection comms clock. Select
from INTERNAL or EXTERNAL using 8or 2and enable
your choice using 5.
Comm Fail Timer
0 ms
Allows a settable delay for which a comms failure must be
present before an alarm is issued.
Comm Delay Tol
1 ms
Displays the maximum allowable propagation time
variation. Variations greater than the set value will result
in a bias characteristic modification, in order to stabilise
the relay.
Char Mod Time
1 s
Displays the duration the bias characteristic is modified
for, following a variation in the propagation delay greater
than the "Comm Delay Tol".
3.5.4.8 Inverting of the auxiliary output relays
This sub menu makes it possible to invert the state of the individual output relays
during the relay energized condition.
AUTOMAT. CTRL
Heading of the AUTOMAT. CTRL Menu. To gain access to
the Invert Output Relays menu, press 2, 6, 6 times, 2,
followed by
6
9 times.

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Invert Output
Relays
Heading of the Invert Output Relays sub menu. To gain
access to the sub menu content, press 2.
Output 2
No
Invert output relay RL2.
Select Yes or No.
Output 3
No
Invert output relay RL3.
Select Yes or No.
Output 4
No
Invert output relay RL4.
Select Yes or No.
Output 5
No
Invert output relay RL5.
Select Yes or No.
Output 6
No
Invert output relay RL6.
Select Yes or No.
Output 7
No
Invert output relay RL7.
Select Yes or No.
3.5.4.9 Inputs sub menu
This sub menu makes it possible to allocate any of the 5 logic inputs to either a label
or an automation function. The available selections are shown in the following table:
Label abstract Label signification
None No allocation
Unlatch Unlatches currently latched output contacts
52 a Status of 52a CB auxilliary contact
52 b Status of 52b CB auxilliary contact
Aux 1 Initates auxilliary timer AUX 1
Aux 2 Initates auxilliary timer AUX 2
Blk Log 1 Blocking logic 1
Blk Log 2 Blocking logic 2
Strt Dist Triggers the disturbance recorder
Cold L PU Enables cold load pick up functionality

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Label abstract Label signification
Log Sel 1 Logic select 1
Log Sel 2 Logic select 2
Change set Changes setting group (default setting group = 1)
θReset Resets the thermal state
Trip Circ Assigns an input for trip circuit supervision
Strt tBF Starts the breaker fail timer
Permis IT Initiate a permissive intertrip
Direct IT Initiate a direct intertrip
Comms RST Reset protection comms statistics
Log Trip Assigns an input to trip the circuit breaker
Log Close Assigns an input to close trip the circuit breaker
In addition to the input allocation the user can specify the required operating time for
auxiliary timers 1 and 2.
AUTOMAT. CTRL
Heading of the AUTOMAT. CTRL Menu. To gain access to
the Inputs menu, press 2, 6, 6 times, 2, followed by 6
10 times.
Inputs
Heading of the Inputs sub menu. To gain access to the
sub menu content, press 2.
Input 1
None
Allocation of logic input 1. To allocate a function to logic
input 1, press 5then use 8or 2to select the desired
function from the available list. Validate your choice using
5.
Input 2
None
Allocation of logic input 2. To allocate a function to logic
input 2, press 5then use 8or 2to select the desired
function from the available list. Validate your choice using
5.
Input 3
None
Allocation of logic input 3. To allocate a function to logic
input 3, press 5then use 8or 2to select the desired
function from the available list. Validate your choice using
5.
Input 4
None
Allocation of logic input 4. To allocate a function to logic
input 4, press 5then use 8or 2to select the desired
function from the available list. Validate your choice using
5.

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Input 5
None
Allocation of logic input 5. To allocate a function to logic
input 5, press 5then use 8or 2to select the desired
function from the available list. Validate your choice using
5.
Aux1 Time
tAux1 0 ms
Displays the time delay for auxiliary timer 1 (tAux1). To
adjust the time, press 5. The tAux1 time is adjustable
from 0 ms to 200 s in steps of 10 ms. Validate your
choice using 5.
Aux2 Time
tAux2 0 ms
Displays the time delay for auxiliary timer 2 (tAux2). To
adjust the time, press 5. The tAux1 time is adjustable
from 0 ms to 200 s in steps of 10 ms. Validate your
choice using 5.
3.5.4.10 Broken conductor sub menu
3.5.4.11 Cold load pick-up sub menu
The Cold Load PU allows the user to enable the cold load pick-up function and its
associated settings.
AUTOMAT. CTRL
Heading of the AUTOMAT. CTRL Menu. To gain access to
the Cold Load PU menu, press 2, 6, 6 times, 2,
followed by
6
12 times.
Cold Load PU
Heading of the Cold Load PU sub menu.
To gain access to the sub menu points, press 2.
Cold Load PU?
No
Enables the cold load pick-up function. Select Yes or No.
If the user selects (Yes), the following menu is displayed. If
the user selects (No), the cold load pick-up function is
disabled.
Cold Load PU
tI>? No
Associates the I> time delay threshold with the cold load
pick up function. To associate tI> with the cold load pick
up function, press 5and select (Yes). Select (No) if the
user does not wish to associate tI> with the cold load pick
up function. Validate your choice using 5.
Cold Load PU
tI>>? No
Associates the I>> time delay threshold with the cold load
pick up function. To associate tI>> with the cold load
pick up function, press 5and select (Yes). Select (No) if
the user does not wish to associate tI>> with the cold load
pick up function. Validate your choice using 5.

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Cold Load PU
tI>>>? No
Associates the I>>> time delay threshold with the cold
load pick up function. To associate tI>>> with the cold
load pick up function, press 5and select (Yes). Select
(No) if the user does not wish to associate tI>>> with the
cold load pick up function. Validate your choice using 5.
Cold Load PU
tI>>>>? No
Associates the I>>>> time delay threshold with the cold
load pick up function. To associate tI>>>> with the cold
load pick up function, press 5and select (Yes). Select
(No) if the user does not wish to associate tI>>>> with
the cold load pick up function. Validate your choice using
5.
Cold Load PU
tIe>? No
Associates the Ie> time delay threshold with the cold load
pick up function. To associate tIe> with the cold load pick
up function, press 5and select (Yes). Select (No) if the
user does not wish to associate tIe> with the cold load
pick up function. Validate your choice using 5.
Cold Load PU
tIe>>? No
Associates the Ie>> time delay threshold with the cold
load pick up function. To associate tIe>> with the cold
load pick up function, press 5and select (Yes). Select
(No) if the user does not wish to associate tIe>> with the
cold load pick up function. Validate your choice using 5.
Cold Load PU
tIe>>>? No
Associates the Ie>>> time delay threshold with the cold
load pick up function. To associate tIe>>> with the cold
load pick up function, press 5and select (Yes). Select
(No) if the user does not wish to associate tIe>>> with the
cold load pick up function. Validate your choice using 5.
Cold Load PU
tIe>>>>? No
Associates the Ie>>>> time delay threshold with the cold
load pick up function. To associate tIe>>>> with the
cold load pick up function, press 5and select (Yes).
Select (No) if the user does not wish to associate tIe>>>>
with the cold load pick up function. Validate your choice
using 5.
Cold Load PU
tI2>? No
Associates the I2> time delay threshold with the cold load
pick up function. To associate tI2> with the cold load pick
up function, press 5and select (Yes). Select (No) if the
user does not wish to associate tI2> with the cold load
pick up function. Validate your choice using 5.
Cold Load PU
tI2>>? No
Associates the I2>> time delay threshold with the cold
load pick up function. To associate tI2>> with the cold
load pick up function, press 5and select (Yes). Select
(No) if the user does not wish to associate tI2>> with the
cold load pick up function. Validate your choice using 5.

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Cold Load PU
t Therm.? Yes
Associates the thermal threshold with the cold load pick up
function. To associate the thermal threshold with the cold
load pick up function, press 5and select (Yes). Select
(No) if the user does not wish to associate the thermal
threshold with the cold load pick up function. Validate
your choice using 5.
Cold Load PU
level 200 %
Selection of the cold load pick up percentage scaling value
associated with the selected thresholds. Select from 20%
to 500% in steps of 1 % using 8or 2and validate your
choice using 5.
Cold Load PU
tCL = 400 ms
Selection of the cold load pick up time delay. Select from
100 ms to 3600 s in steps of 10 ms using 8or 2and
validate your choice using 5.
3.5.4.12 Circuit breaker failure sub menu
The CB Fail sub menu makes it possible to enable the circuit breaker failure detection
function and its associated settings.
AUTOMAT. CTRL
Heading of the AUTOMAT. CTRL Menu. To gain access to
the CB Fail menu, press 2, 6, 6 times, 2, followed by
6
13 times.
CB Fail
Heading of the CB Fail sub menu. To gain access to the
sub menu points, press 2.
CB Fail?
No
Enables / Disables the circuit breaker failure function. If
the user validates (Yes), the following menu is displayed. If
the user selects (No), the breaker failure function is
inactive.
I<=
0.1 In
Selects the under current threshold associated with the CB
failure detection function. Select from 0.02 In to 1 In in
steps of 0.01 In.
CB Fail Time
tBF 100 ms
Selects the circuit breaker failure time delay. Select from
30 ms to 10 s in steps of 10 ms using 8or 2and
validate your choice using 5.
Block I>?
No
Select the possibility to block the instantaneous signal I> in
the event of a circuit breaker failure. Select Yes or No.

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Block Ie>?
No
Select the possibility to block the instantaneous signal Ie>
in the event of a circuit breaker failure detection. Select
Yes or No.
3.5.4.13 Circuit breaker supervision sub menu
The CB Supervision sub menu makes it possible to enable the circuit breaker
supervision and monitoring function and the various settings associated with this
function.
AUTOMAT. CTRL
Heading of the AUTOMAT. CTRL Menu. To gain access to
the CB Supervision menu, press 2, 6, 6 times, 2,
followed by
6
13 times.
CB Supervision
Heading of the CB Supervision sub menu.
To gain access to the sub menu points, press 2.
TC Supervision
Yes
Enables / Disables the trip circuit supervision function.
Select Yes or No. If the user selects (Yes), the function is
active. If the user selects (No) the TC supervision is
disabled (go to CB Open Time menu).
t Trip Circuit
t SUP 200 ms
Selects the Trip circuit supervision time. Select from 0.1 s
to 10s in steps of 10 ms using 8or 2and validate your
choice using 5.
CB Open S'vision
Yes
Enables / Disables the CB operating time supervision
function. Select Yes or No. If the user selects (Yes) the
following menu is displayed. If the user selects (No) the
CB operating time supervision function is disabled (go to
CB Close menu).
CB Open Time
50 ms
Selects the maximum allowable CB operating time (tCBO).
Select from 50 ms to 1.0 s in steps of 10 ms using 8or
2and validate your choice using 5.
CB Close S'vision
Yes
Enables / Disabled the CB closing time supervision
function. Select Yes or No. If the user selects (Yes), the
following menu is displayed. If the user selects (No) the
CB closing time supervision function is disabled (go to CB
Open Alarm menu).
CB Close Time
50 ms
Selects the maximum allowable CB closing time (tCBC).
Select from 50 ms to 1.0 s in steps of 10 ms using 8or
2and validate your choice using 5.

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CB Open Alarm?
Yes
Enables / Disables the maximum CB operations function.
Select Yes or No. If the user selects (Yes), the following
menu is displayed. If the user selects (No) the CB
Operations supervision function is disabled (go to
ΣAmps(n) menu).
CB Open NB =
0
Selects the maximum number of CB operations. Select
from 0 to 50000 in steps of 1 using 8or 2and
validate your choice using 5.
ΣAmps(n)?
Yes
Enables / Disables the Summation Amps (or square Amps)
interrupted by the CB function. Select Yes or No. If the
user selects (Yes), the following menu is displayed. If the
user selects (No) the CB ΣAmps(n) function is disabled (go
to t Open Pulse menu).
ΣAmps(n)?
1000 E6
Selection of the summation Amps (or square Amps) alarm
threshold. Select from 0 to 4000 E6 A (or A2) in steps of 1
E6 using 8or 2and validate your choice using 5.
n 1
Selection of the type of summation (Amps or square
Amps). Select 1 for just Amps or 2 for Amps squared
using 8or 2and validate your choice using 5.
t Open Pulse
100 ms
Selection of the tripping pulse time. Select from 100 ms to
5 s in steps of 100 ms using 8or 2and validate your
choice using 5.
t Close Pulse
100 ms
Selection of the closing pulse time. Select from 100 ms to
5 s in steps of 100 ms using 8or 2and validate your
choice using 5.
CB Man Trip Dly
0 ms
Selects the circuit breaker manual tripping delay. Select
from 0 to 60s in steps of 0.1s using 8or 2and validate
your choice using 5.
CB Man Close Dly
Selects the circuit breaker manual closing delay. Select
from 0 to 60s in steps of 0.1s using 8or 2and validate
your choice using 5.

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TECHNICAL DATA AND CURVE CHARACTERISTICS (P521/EN TD/B11)
6.2 Logic inputs and outputs
Logic input
−Type Independent optical isolated
−Burden 10mA per input
−Recognition Times <10ms (dc applied to standard opto input)
<20ms (ac applied to standard opto input)
<20ms (dc applied to special ENA variant
input)
−Supply Options:
24 - 60Vdc range
48 - 150Vdc range
130 - 250Vdc/
100 - 250Vac range
48 - 150Vdc (Special ENA*)
130 - 250Vdc (Special ENA*)
Between 19.2Vdc and 72Vdc
Between 19.2Vdc and 180Vdc
Between 19.2Vdc and 300Vdc/25Vac and
300Vac 50/60Hz
Between 19.2Vdc and 180Vdc
Between 19.2Vdc and 300Vdc
* Special ENA variants are intended for UK applications which require compliance
with EATS PAP 48-5 Issue 2: 2000 and NGTS 3.24.15 Issue 1 Dec 2000 section
7.55. These digital inputs (dc only) provide immunity to ac coupled differential power
frequency interference. The modified software filtering increases the recognition time
to <20ms.
Logic output
−Type Dry Contact Ag CdO
−Rating:
Make
Carry
Break
30 Amps and carry for 3s
5 Amps continuous
135Vdc, 0.3 Amps (L/R=30 ms)
250Vdc, 50W resistive or 25W inductive
(L/R=40ms)
220Vac, 5 Amps (cos ϕ=0.6)
−Operation Time <7ms
−Mechanical Durability >100 000 Operations

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9.1 Dielectric withstand
IEC60255-5: 2000
2.0kVrms for one minute between all terminals and case earth (including
RS485/RS232 socket SK1).
2.0kVrms for one minute between all terminals of each independent circuit grouped
together, and all other terminals (including RS485/RS232 socket SK1).
1.0kVrms for one minute across dedicated normally open contacts of output relays.
1.0kVrms for 1 minute across normally open contacts of changeover and watchdog
output relays.

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APPLICATION GUIDE (P521/EN AP/B11)
3.8.1 MiCOM P521 trip circuit supervision mechanism
The Trip Circuit Supervision function included in the MiCOM P521 relay is performed
as follows:
A logic input can be programmed in the AUTOMAT.CTRL / Inputs/ Input #/Trip
Circ
menu. This logic input must be inserted in the trip circuit according to one of the
typical application diagrams, shown later.
When the function TC Supervision is enabled by selecting ‘Yes’ within the
AUTOMAT.CTRL/CB Supervision sub-menu, the relay continuously checks the trip
circuit continuity whatever the CB status – opened CB or closed CB. This function is
enabled when the trip output contact (relay RL1) is not energised and it is disabled as
long as the trip output contact is operating.
A “TRIP CIRCUIT” alarm signal (trip circuit failure) is generated if the opto-input
detects no voltage signal for a time longer than the settable timer tSUP
(AUTOMAT.CTRL / CB Supervision) . The “52 Fail” contact can be selectively closed
in the event of a trip coil failure.
As the TC supervision function is disabled when the trip output contact is operating,
this function is suitable for use with the product latching logic on.
The following table shows the setting associated with the trip circuit supervision
function:
Setting Range
Menu Min Max Step
TC Supervision ?Yes No
tSUP 100ms 10s 50ms
P0037ENb
Logic input
Trip Circ.
Tripping
Relay RL1
Energized
tSUP 0
&
52 FAIL
Signal
Figure 21: Trip circuit supervision logic diagram
Three application examples are shown below.
Example 1
In this example only the 52a auxiliary contact is available, the MiCOM P521 relay
monitors the trip coil whatever the CB status (CB open or CB closed ). However, in
this example the relay does not supervise the trip circuit prior to the trip contact.

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MiCOM P521
+Vdc
Trip Order
RL
52a
Opto-input
26
Trip Coil
- Vdc
P0038ENb
Figure 22: Trip coil monitoring
Example 2
In this example both the 52a and 52b auxiliary contacts are available, the MiCOM
P521 relay monitors the whole of the trip circuit when the CB is closed and part of the
trip circuit when the CB is open. When the circuit breaker is open the supervision
current bypasses the trip coil via the 52b contact, thus trip coil supervision is not
provided whilst in this condition. If the circuit breaker is open, a fault in the trip path
will only be detected on CB closing, after the tSUP delay time (typically set to 400ms).
In this example resistor R1 needs to be placed in series with the 52b contact to
prevent damage if the trip contact (RL1) is latched, stays involuntarily closed, or a
long trip pulse time is programmed.
MiCOM P521
+Vdc
Trip Order
RL
52a
Opto-input
26
Trip Coil
- Vdc
P0039ENb
52b
Resistor R
Figure 23: Trip coil and auxiliary contact monitoring

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Example 3
As with example 2, both the 52a and 52b auxiliary contacts are available. The
MiCOM P521 relay monitors the whole of the trip circuit whatever the CB status (CB
open or CB closed).
In this example resistor R1 needs to be fitted to prevent permanent trip coil
energisation, if the trip contact (RL1) is latched, stays involuntarily closed, or a long
trip pulse time is programmed.
MiCOM P521
+Vdc
Trip Order
RL
52a
Opto-input
26
Trip Coil
- Vdc
P0040ENb
52b
Resistor R
Figure 24: Trip coil and auxiliary contact monitoring regardless of CB
position
5.8 Unconditioned 4 wire pilot communications for distances greater than 1.2km
(P595)
In order to increase the transmission distance of EIA(RS)485 up to 10 kilometres it is
necessary to use the P595 (see PZ511 publication AFS.12.05940/1098EN)
interfacing device at each end of the line. To gain maximum performance of the
P521, the data rate must be set to 19.2kbps and the protocol set to “NRZ” (Non
Return to Zero).
Pilot isolation must also be considered, when connecting the P595. If the longitudinal
voltage exceeds 900V the PCM-FLU 10kV or 20kV isolating transformers must be
fitted in series with the P595. The PCM-FLU isolating transformer has “a”, “m” and
“b” taps on both primary and secondary windings. For all P521 applications,
connection must be made between taps ‘a’ and ‘m’, which has a maximum
frequency of 2MHz. Connection between ‘a’ and ‘b’ may result in unreliable
communications as the maximum frequency for this tap configuration is 6kHz.
Connection to ‘a’ and ‘m’ taps must be adhered to on both primary and secondary
so as to maintain a 1:1 ratio.
Refer to section P521/EN CO for connection diagrams.

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Note: The P595 interface device is identical to the AREVA T&D PZ511
interface except that the P595 has accessible setting switches.
The switch settings, to allow communications between P521
relays, can be found in the modem configuration document
(P521/EN MC). For all other P595 information refer to the
accessories section (P521/EN AC) or the P595 manual
(P595/EN M/A11).

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COMMISSIONING AND MAINTENANCE (P521/EN CM/B11)
9.3.2 Protection comms fault
As soon as a problem with the protection comms is detected the operation of the
main protection is stopped. All other protection elements continue to operate and
those selected as backup in the current setting group will be enabled.
Message:
“COMMS ALARM CH1”: communications channel failure detected.
Cause:
Hardware or software failure of the communications card.
Hardware failure of the communications module retained in the case when the active
part is withdrawn.
Failure of the relay at the distant end of the communications link.
Failure of a device in the communications path or break in the communications link.
Live parts exposed within the P521 case, when the P521 module is
removed.
Action:
Determine the location of the failure using the P520L loopback test box
(see Accessories section).
Initiate a loopback test on the back of each of the relays. If the protection comms
alarm resets then the fault is with the communications link not the relays. The relays
should assist with diagnosing the location of the fault by indicating the faulty path (Tx,
Rx or both). If the protection comms alarm does not reset on one relay it is likely that
the relay is faulty. To diagnose if the fault is in the active part (withdrawable part) of
the relay or the protection communications card, remove the relay and plug in the
P520L loopback test box as shown in Figure 2. It is recommended that the battery is
tested, before inserting the test box, by selecting battery test and checking that the
green LED illuminates. With the loopback tester inserted select “Loopback Test” using
the selector switch and ensure that the green LED illuminates. Initiate a loopback test
from the remote relay so that the comms signal passes through the local relay
communications card. If the comms fail alarm on the remote relay disappears, then
the protection comms card is functioning correctly, hence the problem is with only the
active part. If the comms fail alarm does not reset then the local protection comms
card is faulty.