Areva MiCOM P225, Technical Manual

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User Guide P225/EN FT/B11
MiCOM P225 Page 21/52
4.10.1.1 Function inhibiting thermal tripping during a start:
θ
INHIBIT
This function permits inhibition of the thermal tripping information THERM. OV. during the
starting phase. It may be necessary to use this function for some motors with temperature
rise characteristics in a starting phase very different from those in a locked rotor condition.
If the user brings this function into service, this inhibition is activated as soon as the starting
time delay tI
start
begins (cf. submenu [48] EXCES. LONG START). On expiry of tI
start
(end of
the time allowed for starting), this inhibition is deactivated.
When this function is activated, that is during the motor starting phase, the value of the
thermal state
θ
calculated cannot exceed 90 %. This means that thermal tripping cannot take
place under any circumstances. At the end of the time allowed for starting, the value of the
thermal state is authorised to exceed 90 %.
N.B.: – This function has no influence on the thermal alarm signal
“
θ
ALARM” and thermal base blocking start function “
θ
FORBID.
START”.
– When this function is brought into service, the motor is still
thermally protected by the monitoring of the starting time.
4.10.1.2 Function of the thermal image influenced by ambient temperature (optional): RTD1
INFLUENCE
When the ambient temperature e 40°C, the admissible motor current diminishes in
relation to its rated current. A setting of the protection parameters which is suitable under
normal temperature conditions is no longer suitable when the ambient temperature rises
above +40°C.
The MiCOM P225 relay offers the possibility of taking into account this necessary derating of
motors. The thermal image can be modified by the ambient temperature measurement.
When this function is brought into service by the user, if the ambient temperature rises above
+ 40°C, the value of the thermal threshold I
θ
> is automatically modified to adapt the motor
protection to the external temperature conditions. The rule for the ambient temperature
measurement influencing the thermal image is:
For an ambient temperature lower than or equal to + 40°C, the thermal image is not
modified.
−
For an ambient temperature b 40°C and + 65°C, the thermal threshold I
θ
> is
modified by a multiplying coefficient in compliance with the following formula:
−
Multiplying coefficient = 1 - (ambient temperature in °C - 40)/100
−
For a temperature greater than or equal to + 65°C, the thermal threshold I
θ
> is
modified by a multiplying coefficient of 0.75.
The table below gives the relationship between the ambient temperature measurement and
the influence on the thermal image:
Ambient temperature
(in ° Celsius)
+40 °C +45 °C +50 °C +55 °C +60 °C +65 °C
Correction coefficient for
the thermal threshold I
θ
>
(multiplying coefficient)
1,00 0,95 0,90 0,85 0,80 0,75
N.B.: – This function can only be used if the relay has the option "10 RTD
monitoring".
– The probe used for this function is RTD 1 (terminals 2d-2b-2z). To
use this function, a RTD measuring the ambient temperature of the
place where the motor is located must be connected to terminals
2d-2b-2z.
– The operator can program the temperature thresholds of RTD 1
([49/38] RTD submenu) even if he has brought this RTD1
INFLUENCE function into service.