IMM 8001/8002 – Digital Motor Protection Relay
ICE / CEE
____________________________________________________________________________________________
IMU307-1 GB Ind. B
74
5.12. MINIMUM LOAD PROTECTION (PUMP UNPRIMING) [37 P/I]
To provide the protection against minimum loads function, the user can choose (with parameter setting)
either detection of underpower [37P] if a PT is available, or detection of undercurrent [37I] (see
Reference variables chapter). Underpower protection is preferable since, in the event of loss of load,
mainly the power factor diminishes, not the current.
Underpower [37P]
Function
The IMM 8000 relays provide protection against pump unpriming by means of an active underpower
unit
P<.
This function, if put into serviced, is operational after an enabling time-delay
(tP<on)
activated on
motor starting. The underpower protection is disabled on motor stop.
Main characteristics
Adjustments
Operating level
P<
:
10 - 50 % of Sn (Un
∗
In
∗
√
3) in steps of
1 % Sn.
Time-delay
t(P<)
:
1-100 seconds in steps of 0.1 second.
Enabling time-delay
after start detection :
tP<on
1-1000 seconds in steps of 1 second
Undercurrent (37I)
Function
If the measurement voltage is not available, the IMM 8000 relays provide protection against pump
unpriming by means of a minimum positive phase sequence current unit
I<.
This function, if put into serviced, is operational after an enabling time-delay
(tI<on)
activated on motor
starting. The undercurrent protection is disabled on motor stop.