NHP TemBreak PRO P - Thermal Memory; Hot-Cold Start Mode

Protection Settings
Long Time Delay (LTD) protection
28
TemBreak PRO P_BE-UM-001-EN V1.3.0
Thermal memory / Hot–Cold start mode
TemBreak PRO electronic OCRs have a thermal imaging function, which models the active heating and cooling of electrical conductors as current passes
through them. The thermal imaging function calculates a thermal value (θ) for the conductors, which trips the MCCB when its thermal threshold (θ
trip
) is
reached. This allows the MCCB to simulate the true thermal state of the conductors more accurately, and better protect against overload conditions between
successive operating cycles.
Thermal imaging cannot be disabled in the OCR, however, the P_BE model can be supplied with either a hot or cold start mode, which determines whether
the calculated thermal value θ is retained if the current drops below the LTD pick-up current threshold (between 1.05…1.20 x I
r
).
The standard P_BE OCR is supplied with Cold start mode only. If Hot start mode is required, a made-to-order P_BE can be supplied. Contact NHP for
details on the Hot start mode option.
Alternatively, the P_SE model can be configured with either a hot or cold start mode using the embedded display, or TPCM or TPED accessories.
Hot start mode
In Hot start mode, the thermal imaging continues to calculate the thermal value (θ
H
), even if the current is below the LTD pick-up threshold.
As long as the OCR is powered (self-supply or external backup power), the thermal imaging will continue to function. If power is removed from the OCR,
thermal imaging will continue to operate for at least 20 minutes or until the calculated thermal value θ
H
reaches 0.
Cold start mode
In Cold start mode, the thermal value (θ
C
) is only calculated from when the current reaches and exceeds the LTD pick-up current threshold.
If the current drops below the LTD pick-up current threshold, then the thermal value θ
C
resets to 0.
The below figure illustrates the OCR with thermal imaging in both hot and cold start modes. Where the current (I) drops below the LTD pick-up current
threshold (region in grey between 105…120% of I
r
), the Hot mode thermal value θ
H
continues to be calculated, whereas the Cold mode thermal value θ
C
resets to 0 each time. In either start mode, the MCCB trips when the respective thermal value threshold θ
trip
is reached. The differences between start
modes is made most apparent by the different tripping times after successive operations, where hot mode θ
H
reaches the tripping threshold θ
trip
earlier,
providing added safety and optimum protection of the conductors.
LTD pick-up current threshold
(105…120% of I
r)
Current (I)
Time (t)
Thermal Imaging Value (
θ)
Current (I)
Hot mode value (θ
H
)
Cold mode value (θ
C
)
Thermal trip threshold
(θ
trip
)
Hot mode tripping point