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Thermal Memory
This is the cooling time constant which is user selectable. It
provides a direct relationship to the thermal content which will
be decremented when measured current is less than Ir. Time
constants available are:
Instant, 10 min, 20 min, 30 min, 45 min, 1 hour, 2 hours and 3
hours.
The time constant is the time taken for the thermal content to
drop to 36.8% of its original value.
If thermal memory is not required, set cooling time to instant.
Note: For thermal memory operation an auxiliary power
supply is required
Digital Inputs and Outputs
The M-PRO 30 and M-PRO 40 trip units have four volt free
relay outputs, which are rated at:
24/48Vdc
1A
resis
tive
0.3A
induc
tive
110Vdc
0.5A
resis
tive
0.1A
induc
tive
110/220V
ac
1A
The usage of these outputs is defined below:
M-PRO 30:
Output 1 - Maintenance output is opened if any of the
following faults occur:
• processor malfunction
• primary contact maintenance alarm
• digital input active
Note - this is a normally closed output with the M-PRO
powered up and healthy. The contacts open on power down.
Output 2 - Load monitoring output indicates that pre-trip warn
or load shedding is active
Note - this is a normally open output.
Output 3 - M-PRO initiated trip output indicates that the M-
PRO has opened the breaker due to a trip condition.
This output is reset when the trips are reset. If the
breaker is already open and a trip is initiated (e.g.
test box trips) then the output will not be activated.
The user may configure the M-PRO such that
restricted earth faults will not activate this output.
Note - this is a normally open output.
Output 4 - HV inter-trip output is closed to initiate a trip of
the HV breaker. This will be used for restricted and
standby earth fault protection. The user may disable
the inter-trip feature for standby earth faults.
Note - this is a normally open output.
M-PRO 40:
Output 1 - ACB close. This output changes state momentarily
to operate the closing coil, so that the ACB can be
closed via the serial link (the maintenance
information indicated on output 1 on the M-PRO 30
will be sent down the serial link on the M-PRO 40). It
is assumed that the breaker’s closing coil is wired
through this output.
Note - this is a normally open output.
Output 2 - As M-PRO 30
Output 3 - ACB open. The output will momentarily
operate on ‘command to open’ from the serial link.
(The trip status information conveyed by this output
on M-PRO 30 is available down the serial link on M-
PRO 40). It is assumed that the breaker’s shunt trip
coil is wired through this output.
Note - this is a normally open output.
Output 4 - As M-PRO 30
An auxiliary power supply is required for correct operation of
the digital outputs as all the outputs will be opened when the
M-PRO powers down.
The outputs are updated every 100ms.
Load Monitoring
Load monitoring gives an indication when overloading of the
circuit is imminent. M-PRO provides two alternative types of
load monitoring - (a) pre-trip warning (b) load shedding.
Pre-trip warning is initiated when M-PRO detects an overload
current greater than 1.1 x Ir and the thermal register is greater
than 60%. The thermal register within M-PRO indicates the
relative thermal state of the circuit breaker; a trip is initiated
when the thermal register reaches 115%. The pre-trip warning
is normally displayed on the LCD, the red ‘Warn/Alarm’ LED
will flash, and digital output 2 is activated (when fitted). If the
‘communications’ feature has been specified for (M-PRO 40)
the warnings can be transmitted down the serial link.
Load shedding levels start and stop shedding, are user
settable. Start shedding level is adjustable between the
following values:
25% to 100% Ir in steps of 5%.
The stop shedding level is adjustable between the following
values:
20% to 95% Ir in steps of 5%.
the result of starting and stop shedding are indicated both
locally and reflected in the switching of digital output 2.
Communications
M-PRO 40 offers communications via and RS485 serial link
connected via the PAMM. Two or 4-wire operation is
supported though 4-wire operation is preferred. Up to 100 M-
PRO units may be ‘daisy-chained’ together on one network. All
breaker information is available on the link and is
communicated using the Modbus RTU protocol at either 9600
or 19200 baud. An auxiliary power supply is required for the M-
PRO 40. Detailed information is available on request.
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