Calculations For External Resistor; Self-Diagnostic Features; Watchdog Feature - GE P50 Agile P253 Technical Manual

8 Monitoring & Control
Figure 11: TCS Scheme
When the breaker is closed, supervision current passes through opto input 1 and the trip coil. When
the breaker is open current flows through opto input 2 and the trip coil. No supervision of the trip path
is provided whilst the breaker is open. Any fault in the trip path will only be detected on CB closing,
after the elapse of TCS timer available under CB CONTROL menu.
2.11.1

Calculations for External Resistor

As shown in the TCS scheme, optional resistors R1 and R2 can be added to prevent tripping of the
CB if either opto input is shorted.
The minimum sensing current required by opto coupler is 0.18 mA and the maximum current capacity
of opto coupler is 10 mA. For the safe operation, the current should be always between minimum
required current and maximum current capacity of opto coupler. The maximum current is limited by
internal resistor (RInt.) connected in series with opto coupler. The value of this internal resistor (RInt.)
is 82 KΩ (Ohm).
The supervision current is a lot less than the current required by the trip coil to trip a CB. The opto-
input limits this supervision current .If the opto-input were to be short-circuited however; it could be
possible for the supervision current to reach a level that could trip the CB. For this reason, optional
resistors R1 and R2 are often used to limit the current in the event of a short-circuited opto-input. It is
recommended to use 2.5 KΩ / 50 W resistor for all type of auxiliary power supply.
2.12

Self-Diagnostic Features

The P253 relay includes a self-monitoring function to check the operation of its hardware and software
while in service. If there is a problem with the hardware or software, it is able to detect and report the
problem.
The relay continuously monitors the hardware and in the event detects any hardware fault/error;
corresponding error code is displayed on the LCD. These faults/errors are stored in the 'Main't Rec
Num= "and can be viewed from Maint Record submenu. Error log is stored as 16 bit integer.
As an example if RTC error occurs, error code/error log will be as under:
Error code :
Error log on LCD: 0004
If the error is cleared during the self-diagnostic procedure the corresponding error bit will be cleared.
The P253 internal errors are also indicated by a change in status of ON and OUT OF SERVICE LEDs.
For more details refer to the Troubleshooting chapter.
2.13

Watchdog Feature

The relay continuously monitors the healthiness of hardware and detects the hardware fault/error.
As soon as an internal fault is detected, ON LED changes from green to red and contact assigned to
'Relay OK' signal will operate.
8-18
+ve
Trip Output Relay
R1 Opto-input 1
R2
Opto-input 2
V01215
0000 0000 0000 0100
52A
Trip path
52B
P50 Agile P253
Trip coil
Circuit Breaker
-ve
P253/EN M/C