Areva MiCOM P225, Техническое руководство

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User Guide P225/EN FT/B11
MiCOM P225 Page 19/52
STATE OF THE PROTECTION FUNCTIONS (ACTIVE/INACTIVE) ACCORDING TO THE
OPERATION MODE OF THE MOTOR
The MiCOM P225 protection functions are automatically* activated or deactivated by the
relay itself according to the motor's operation mode (motor halted, start-up sequence, re-
acceleration phase or normal running condition). The table below indicates under which
conditions these protection functions are active or inactive.
Protective
functions
Motor halted Start-up sequence Motor running
Re-acceleration
phase
Thermal image Activated (Tr)** Activated (Te2)** Activated (Te1)** Activated (Te2)**
Short-circuit Activated Activated Activated Activated
Earth fault Activated Activated Activated Activated
Unbalance Activated Activated Activated Activated
Excessive long start Deactivated Activated Deactivated Activated
Stalled rotor whilst
running Deactivated Deactivated Activated Deactivated
Locked rotor at start Deactivated Activated Deactivated Deactivated
Undervoltage Deactivated Activated**** Activated Activated
Overvoltage Activated Activated Activated Activated
Loss of load Deactivated Activated*** Activated*** Activated***
Overtemperature Activated Activated Activated Activated
* These protection functions are activated by the relay only if they have previously been
commissioned by the user.
** The time constant used in the thermal model depends on the value of the motor load
current and on the motor's operating mode. The time constant indicated in brackets is
the one used by the relay.
*** The "loss of load" function is activated upon expiry of the Tinhib timer. This timer is
user settable, it is initiated by the relay when a motor start is detected.
**** The user can inhibit this function during the starting sequence.
4.10.1 The [49] THERMAL OVERLOAD submenu: Protection against thermal overload conditions
The MiCOM P225 relay produces a thermal image of the motor from the line current and the
negative component of the current consumed by the motor, in such a way as to take into
account the thermal effects created in the stator and in the rotor. The currents' harmonic
components contribute to the motor's heating. For this reason, the thermal replica uses the
line current
I
RMS
expressed in true rms value. The negative component currents consumed in
the stator generate in the rotor large amplitude currents which create a substantial
temperature rise in the rotor winding. The composition carried out by the MiCOM P225
results in an equivalent thermal current
I
eq
, the image of the temperature rise caused by the
current in the motor.
The current
I
eq
is calculated according to the following formula:
5 . 0
negative
RMS eq
²) I Ke ² I( I ⋅ + =
Starting from this equivalent thermal current, the thermal state of the motor
θ
is calculated
every cycle (every 20 ms for a 50Hz system) by the MiCOM P225 relay according to the
following formula:
) / t ( )] / t exp( 1 [ )² I / I(
i eq 1 i
Τ − ⋅ θ + Τ − − ⋅ > θ = θ
+