Areva MiCOM P225, Technical Manual

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User Guide P225/EN FT/B11
MiCOM P225 Page 27/52
4.10.8.2 Locked rotor at start
This function, which makes it possible to detect that the motor is locked at the start, is
activated only during the starting phase, that is during the course of the starting time delay
t
I
start
.
It uses a motor speed indication received via a logic input of the P225 relay set on SPEED
SW and the t
I
stall
time-delay: locked rotor time (a speed switch device must be connected to
this logic input: paragraph 4.11.4.2. “the INPUTS submenu: programmable inputs”).
On detection of a start, the "locked rotor at start" function is activated: the time delay tI
stall
begins. At the end of this time delay, the logic input set on SPEED SW must be in logic state
1 to indicate that the motor speed is not zero. The opposite case (zero speed) means that
the rotor is locked, so the P225 relay generates a locked rotor at start order LOCKED
ROTOR.
Internal
logic
signals
&
t I
stall
0
Motor
start-up
detection
Speed switch
open
(EL2 = 0)
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N.B.: – The speed switch device sends information to the P225 relay
indicating, by the closing of a contact, that the rotor is rotating.
– The time delay tI
stall
is common to the protection functions for "rotor
stalled while motor is running" and "rotor locked at start".
– If the motor is not fitted with a speed switch device, this function
cannot be used and must therefore be deactivated.
4.10.9 The [37]LOSS OF LOAD submenu: Protection against undercurrent/loss of load conditions
The [37] UNDERCURRENT function which makes it possible to detect a loss of load (for
example the draining of a pump or breakage of a conveyor belt), uses definite time
undercurrent protection. The user sets the following parameters:
−
undercurrent threshold I <
−
time delay tI < associated with the undercurrent threshold
−
the inhibit start time delay T
inhib
.
This function is deactivated when the motor is shut down (logic input L1 in the 0 state) and
also during the inhibit time delay T
inhib
.
When the P225 relay detects that the motor is starting, this function is activated at the end of
the inhibit time delay T
inhib
.
The time delay T
inhib
is useful for motors with no-load starting which take on load gradually at
the end of starting.
When the motor is running (and after expiry of the inhibit time delay T
inhib
), if the value of one
of the phase currents consumed by the motor is lower than the threshold I < for a period
greater than or equal to tI <, the P225 relay will generate a loss of load signal “ t I< ”.
I<
tI<
0
I
A
I
B
I
C
Internal
logic
signals
&
t
inhib
Motor
start-up
detection
Motor
shutdown
( EL1 = 0 )
>=1
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