Long-Time Protection
The long-time protection function protects cables (phases and neutral) against overloads. This function is based on true rms measurements.
Thermal Memory
The thermal memory continuously accounts for the amount of heat in the cables, both before and after tripping, whatever the value of the current (presence of an overload or not). The thermal memory optimizes the long-time protection function of the circuit breaker by taking into account the temperature rise in the cables. The thermal memory assumes a cable cooling time of approximately 15 minutes.
Setting the Ir Pickup
The Ir pickup setting values depend on the long-time rating plug inserted in the MicroLogic A/E trip unit. For more information, refer to Long-Time Rating Plug.
Ir pickup = setting value x In rated current.
As standard, trip units are equipped with the standard rating plug (0.4–1 x In).
|
Rating plug |
Current setting |
||||||||
|---|---|---|---|---|---|---|---|---|---|
|
Standard |
0.4 |
0.5 |
0.6 |
0.7 |
0.8 |
0.9 |
0.95 |
0.98 |
1 |
|
Low-setting option |
0.4 |
0.45 |
0.50 |
0.55 |
0.60 |
0.65 |
0.70 |
0.75 |
0.8 |
|
High-setting option |
0.80 |
0.82 |
0.85 |
0.88 |
0.90 |
0.92 |
0.95 |
0.98 |
1 |
|
Off-plug |
No long-time overcurrent protection (Ir = In for Isd setting) | ||||||||
When the current is higher than Isd or Ii, only short-time overcurrent protection and instantaneous protection are operational.
Setting the tr Time Delay
The time delay settings indicated on the rating plugs correspond to the tripping times for an overload of 6 x Ir in cold-state conditions.
The table below gives tripping times according to tr time delay.
|
Tripping time (s) |
Accuracy |
tr time delay |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
0.5 |
1 |
2 |
4 |
8 |
12 |
16 |
20 |
24 |
||
|
at 1.5 x Ir |
0 to -30% |
12.5 |
25 |
50 |
100 |
200 |
300 |
400 |
500 |
600 |
|
at 6 x Ir |
0 to -20% |
0.5 |
1 |
2 |
4 |
8 |
12 |
16 |
20 |
24 |
|
at 7.2 x Ir |
0 to -20% |
0.34 |
0.69 |
1.38 |
2.7 |
5.5 |
8.3 |
11 |
13.8 |
16.6 |