Technical information

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1SDC210033D0202
Glossary
Motor protection
G4.1 Protection against phase unbalance and phase loss (U)
Protection function which acts if unbalance between the current values of the individual
phases protected by the circuit-breaker is detected (according to IEC 60947 annex T).
G4.2 Rotor lock protection (R)
The function protects motor from possible damages caused by rotor stopping during func-
tioning.
G4.3 Starting current
Is the current value which, in accordance with the CEI EN 60947-4-1 Standard, is assigned
a value of about 7.2xIe. It represents the current required by the motor during the starting
phase, and which persists throughout the starting time.
G4.4 Starting time
This is the time the motor takes to reach its rated running speed. The starting time depends
on the characteristics of the load the motor must drive, and particularly on the type of motor.
G4.5 Operating class
The starting classes distinguish the thermal relays according to their trip curves. The fol-
lowing table (which refers to the most common applications) lists the classes defined in the
IEC60947-4-1 Standard.
Operating class
Trip time
Ti [s] for 7.2xIr
Trip time
Ti [s] for 7.2xIr
(banda “E”)
2–Ti ) 2
3 – 2 < Ti ) 3
5 0,5 < Ti ) 5 3 < Ti ) 5
10A 2 < Ti ) 10 –
10 4 < Ti ) 10 5 < Ti ) 10
20 6 < Ti ) 20 10 < Ti ) 20
30 9 < Ti ) 30 20 < Ti ) 30
40 – 30 < Ti ) 40
Time Ti is the cold trip time of the thermal relay at 7.2 times the set current value. It is com-
mon practice to associate class 10 with the normal starting type and class 30 with the
heavy-duty starting type.
The other trip classes and trip time indicated under band “E”, have recently been introduced
in a variant to the CEI EN 60947-4-1 Standard, and are characterised by a more restricted
trip range due to raising the minimum non-trip time.
(*)
The load characteristics which the motor must carry, the type of motor and the starting methods, are factors which affect the
starting time and therefore selection of the thermal trip unit.
G4.6 Contactor
Mechanical operating device with a single stand-by position and non-manual operation able
to make, carry and break currents under normal circuit conditions, including overload oper-
ating conditions.
G4.7 Utilisation category of the contactor
The Standard establishes different utilisation categories for the contactor. Each category de-
fines precise minimum performance values (e.g. application range or rated breaking capac-
ity) according to current, voltage, power factor or time constant values and test conditions
specified in the Standard.
G4.8 PTC
Thermostatic probe able to measure the internal temperature of an electric motor.
Consult QT7: The asynchronous three-phase motor, general information and ABB offer for coordinating the protections” for further details.