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2.11 MAXIMUM NUMBER OF STARTS (66)
2.11MAXIMUM NUMBER OF STARTS (66)
Due to the existing similarities between generators and motors, the majority of functions included in MIGII apply to both
types of machines. However, the present function is used specifically in motor protection.
Starts per hour: When a motor start occurs, one of the STARTS PER HOUR timers is loaded with 60 minutes. Once the
motor is stopped, the number of starts within the past hour is compared to the number of starts allowable. If the two are the
same, an inhibit will occur. If an inhibit occurs, the lockout time will be equal to one hour less the longest time elapsed since
a start within the past hour.
2
Restart time may be used to ensure that a certain amount of time passes between stopping a motor and restarting that
motor. This time feature may be very useful for some processes, applications or motor considerations. If a motor is on a
down-hole pump, after the motor stops, the liquid may fall back down the pipe and spin the rotor backwards. It would be
very undesirable to start the motor at this time. In another scenario, a motor may be driving a very high inertia load. Once
the supply to the motor is disconnected, the rotor may continue to turn for a long period of time as it decelerates. The motor
has now become a generator and applying supply voltage out of phase may result in catastrophic failure.
This unit operates only if the motor is stopped, in order to avoid a new start. The unit will never operate while the motor
is running.
As regards the detection of starts, two possibilities are considered depending on the Supervision by 52B setting in relay-
generated settings:
•
1.Supervision by 52B = NO. The motor is considered to be stopped when the average current of the three phases is
below 5% of the value set for FLC. A start is detected when, being the motor stopped (according to the above
definition), the average current of the three phases rises above 7% of FLC.
•
2.Supervision by 52B = YES. The motor is considered to be stopped when the unit detects that the breaker is open.
A motor startup is detected when the breaker is closed.
EVENTS
MIGII stores an historical record with the last 24 events. Each event contains the event description, date and time (4 ms
accuracy), the current values in phases and ground at that moment, and a summary of the status signals that can produce
events, and whether they were active or not in that moment.
In ENERVISTA MII SETUP there is an "EVENTS" menu, where the user can check how many events have been produced
since the last time the Events were deleted. If this number is higher than 24 (maximum number of events stored), this
means that only the last 24 will be stored.
This event record is stored in a capacitor backed up RAM memory. Events functionality in MIGII is performed via the
ENERVISTA MII SETUP software.
Inside the ADVANCED SETTINGS group, there is a sub-group called EVENT MASKS, from where the different causes that
can produce events can be masked. They are detailed in the SETPOINT – SETPOINT – ADVANCED SETTINGS – EVENT
MASK section. The following table shows a list of all possible events:
Table 2–1: LIST OF EVENTS
37 Pickup/Drop out (MIGII Q)
50P Pickup/Drop out
50G Pickup/Drop out
48 Pickup/Drop out (MIGII Q)
51P Pickup/Drop out
51G Pickup/Drop out
46 Pickup/Drop out
49 Pickup/Drop out
87R Pickup/Drop out (MIGII P)
37 Trip (MIGII Q)
50P Trip
50G Trip
48 Trip (MIGII Q)
51P Trip
51G Trip
2-14
MIGII Digital Protection for Electrical Machines
2 PRODUCT DESCRIPTION
GEK-113188A
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