Iskra FPC 200 - Power and Machine Protections

Functionality
48 USER MANUAL FPC 200 - 3/2017
2.5 Power and machine protections
Thermal overload protection – ANSI code 49T
This protection is designed to protect power lines, power cables and passive cooling transformers against thermal
overload. The function estimates temperature of the object according to measured phase currents.
2.5.1.1 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 per cent of machine heating. In
order to make the calculation of time to trip possible,
the heating time constant must be set.
The k-factor of individual machine is similar to service
factor and is maximal allowed permanent current of the
object. K-factor is determined by materials used,
construction properties and it is defined according to
the environment where the protected device is used.
2.5.1.1.1 High temperature mode
Start on trip
High temperature signal starts with trip signal and ends
when temperature drops below high temperature value.
Start on high temperature
Signal high temperature starts as the high temperature
value is reached and ends when temperature drops
below high temperature value.
2.5.1.1.2 Heating and cooling equation

I
dt
d


 1
Equation 4: Heating and cooling differential equation.
2









n
I
I
I
Equation 5: Temperature which would be reached at
specific current.

t
II
e

 )(
0
Equation 6: temperature which would be reached at
specific current I in specific time t, started from 
0
temperature.
I – Present machine current.
Θ
I
– final temperature that would be reached in infinite
amount of time, maintaining constant current.
Θ
0
– Initial temperature.
Θ – Current temperature.
τ – Heating and cooling time constant.
t – time
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.