Functionality
50 USER MANUAL FPC 200 - 3/2017
Machine Thermal Overload Protection - ANSI code 49M
Machine thermal overload protection (MTOP) is designed to protect machines with different heating and cooling constant
against thermal overload. The function estimates temperature of the object according to measured phase currents its
characteristics and ambient temperature.
2.5.2.1 Functionality
The algorithm calculates the relative temperature of
protected device based on current measurement. The
temperature is calculated for each phase separately and
only highest current is displayed. The monitored value
for protection is the highest calculated temperature.
When the alarm or trip temperature value is reached,
the appropriate alarm or trip temperature warning
signal is stated. The alarm and trip temperature value
parameter can be set in percentage of machine heating.
In order to make the calculation of time to trip possible,
the heating and cooling time constant parameters must
be set. Information about the heating constant for
particular machine can be found in device tables or
acquired from the manufacturer of the protected
equipment. For passive cooling machines, the cooling
constant is equal to the heating constant.
The protection detects the overload, when the maximal
allowed permanent thermal current I
max
, which causes
the start of overheating of protected element, is
exceeded. The service factor has to be set. The constant
is defined as service factor = I
max
/ I
n_obj
, where the I
max
is
maximal thermal current and the I
n_obj
is nominal
current of the protected device.
The service factor is maximal allowed permanent
current of the machine. It is determined by materials
used, construction properties and it is defined according
to the environment where the protected device is used.
Usually it is available from property tables supplied by
the manufacturer.
Trip signal is stated when current in any phase exceeds
I
max
and temperature exceeds set trip temperature.
Hot state indicates the level above which it is
considered that machine is now at nominal operating
temperature if set correctly.
When the circuit breaker disconnects the
line because of thermal protection, the trip
signal resets, otherwise the CBFP
protection of the circuit breaker Switch
module would operate.
The closing of circuit breaker is inhibited
until the temperature fall below the set
High temperature value.
Current over temperature values are written to
Temperature Lx outputs separately for each phase. The
value is written as a relative value, where 100 %
represents that the maximal allowed over temperature
is reached. By resetting values on outputs, their start
values can be set by user interface. At the device start-
up, this outputs are reset to zero, which represents no
over temperature.
Equations below are used in protection algorithm.
2.5.2.1.1 Heating and cooling equation
Equation 7: Heating and cooling differential equation.
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