Long-Time Protection
The long-time protection function helps to protect cables against overloads. This function is based on true rms measurements.
It is possible to select either I2t long-time protection or Idmtl long-time protection.
Idmtl long-time protection proposes tripping curves with different slopes, used to improve:
-
Discrimination with fuses positioned upstream (HV) and/or downstream
-
Protection for certain types of loads
Five types of curve are available:
-
DT: definite time curve
-
SIT: standard inverse time curve (I0.5t)
-
VIT: very inverse time curve (It)
-
EIT extremely inverse time curve (I2t)
-
HVF: compatible with high-voltage fuses (I4t)
I2t long-time protection is selected by default.
Select Idmtl long-time protection by making fine adjustments to the long-time protection on the Idmtl (A) screen.
I2t long-time protection can be selected again by making fine adjustments to the long-time protection on the I (A) screen.
For the factory settings, the setting ranges, increment steps and setting accuracies, refer to Threshold and Time-Delay Settings.
Long-Time Current Setting Ir
The Ir pickup setting values depend on the long-time rating plug inserted in the MicroLogic P trip unit. For more information, refer to Long-time Rating Plug.
Ir pickup = setting value x In rated current. Tripping between 1.05 and 1.20 Ir.
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.
I2t Tripping Time
The tr 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 for long-time protection with I2t tripping curve.
Idmtl Tripping Time
The tr 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 for long-time protection with Idmtl tripping curve.
|
Tripping curve |
Tripping time (s) |
Accuracy |
tr time delay |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
0.5 s |
1 s |
2 s |
4 s |
8 s |
12 s |
16 s |
20 s |
24 s |
|||
|
DT |
at 1.5 x Ir |
0 to –20% |
0.53 |
1 |
2 |
4 |
8 |
12 |
16 |
20 |
24 |
|
at 6 x Ir |
0 to –20% |
0.53 |
1 |
2 |
4 |
8 |
12 |
16 |
20 |
24 |
|
|
at 7.2 x Ir |
0 to –20% |
0.53 |
1 |
2 |
4 |
8 |
12 |
16 |
20 |
24 |
|
|
at 10 x Ir |
0 to –20% |
0.53 |
1 |
2 |
4 |
8 |
12 |
16 |
20 |
24 |
|
|
SIT |
at 1.5 x Ir |
0 to –30% |
1.9 |
3.8 |
7.6 |
15.2 |
30.4 |
45.5 |
60.7 |
75.8 |
91 |
|
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% |
0.7* |
0.88 |
1.77 |
3.54 |
7.08 |
10.6 |
14.16 |
17.7 |
21.2 |
|
|
at 10 x Ir |
0 to –20% |
0.7* |
0.8 |
1.43 |
2.86 |
5.73 |
8.59 |
11.46 |
14.33 |
17.19 |
|
|
VIT |
at 1.5 x Ir |
0 to –30% |
3.6 |
7.2 |
14.4 |
28.8 |
57.7 |
86.5 |
115.4 |
144.2 |
173.1 |
|
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% |
0.7* |
0.81 |
1.63 |
3.26 |
6.52 |
9.8 |
13.1 |
16.34 |
19.61 |
|
|
at 10 x Ir |
0 to –20% |
0.7* |
0.75 |
1.14 |
2.28 |
4.57 |
6.86 |
9.13 |
11.42 |
13.70 |
|
|
EIT |
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% |
0.7* |
1 |
2 |
4 |
8 |
12 |
16 |
20 |
24 |
|
|
at 7.2 x Ir |
0 to –20% |
0.7* |
0.69 |
1.38 |
2.7 |
5.5 |
8.3 |
11 |
13.8 |
16.6 |
|
|
tr at 10 x Ir |
0 to –20% |
0.7* |
0.7* |
0.7* |
1.41 |
2.82 |
4.24 |
5.45 |
7.06 |
8.48 |
|
|
HVF |
at 1.5 x Ir |
0 to –30% |
164.5 |
329 |
658 |
1316 |
2632 |
3950 |
5265 |
6581 |
7900 |
|
at 6 x Ir |
0 to –20% |
0.7* |
1 |
2 |
4 |
8 |
12 |
16 |
20 |
24 |
|
|
at 7.2 x Ir |
0 to –20% |
0.7* |
0.7* |
1.1* |
1.42 |
3.85 |
5.78 |
7.71 |
9.64 |
11.57 |
|
|
at 10 x Ir |
0 to –20% |
0.7* |
0.7* |
0.7* |
0.7* |
1.02 |
1.53 |
2.04 |
2.56 |
3.07 |
|
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.
Neutral Protection
Overload protection (long time) for the neutral is disabled if the Idmtl protection function is selected. However, the short-circuit protection (short-time and instantaneous) remains operational.
Intermittent Overloads
As long as the MicroLogic P trip unit remains supplied with power, the effects of intermittent overloads on cables are calculated. If power is cut, temperature rise in cables is not calculated.
Circuit Breaker Thermal Limit
For certain settings, the Idmtl curves may be limited by the I2t curve when the time delay tr is set to 24 seconds or by its thermal memory. The maximum I2t curve remains active for the phases and the neutral even when the Idmtl curves are activated.