Woodward MRM4, Руководство пользователя

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Protective Elements
Necessary means:
•
3-phase current source;
•
Ammeter; and
•
Timer for measuring of the tripping time.
Procedure
Testing the threshold values( single-phase )
Feed in a testing current significantly smaller than the pick-up value. For testing the threshold values and
fallback values, the test current has to be increased until the relay is energized. When comparing the displayed
values with those of the ammeter, the deviation must be within the permissible tolerances.
Testing the tripping delay
For testing the trip delay, a timer is to be connected to the contact of the associated trip relay. Feed in a testing
current significantly smaller than the pick-up value, the test current has to be increased suddenly above the
threshold value. The timer is started when the limiting value of the tripping current exceeded the threshold and
the operating time is elapsed and it is stopped when the relay trips.
Testing the fallback ratio
Enlarge the measuring quantity to less than 97% of the trip value. The relay must only fall back at 98% of the
trip value at the earliest.
Successful test result
The measured tripping delays, threshold values and fallback ratio comply with those values, specified in the
adjustment list. Permissible deviations/tolerances can be found under Technical data.
LRC - Locked Rotor During Start
Functional Description
The Locked-rotor protection function is an integral part of the thermal model and is used to protect the motor in
the event that the motor fails to start or accelerate after being energized. The heating in the motor during this
period of time can be significantly higher than the heating at rated current, ranging from 10 to 50 times the
normal rated heating. The time that a motor can remain at a standstill after being energized varies with the
applied voltage and has an I 2 T limit.
When determining the heat in the motor during this period of time, both the negative and positive sequence
currents are used in the equation that approximates the heat generated in a locked rotor condition. The heat
can be approximated by the equation:
I 2
H
= I
1
2 + K I
2
2
where :
I
1
= the per unit stator positive sequence current;
K = weighting factor for the value of I
2
resulting from the disproportionate heating caused by the
negative sequence current component due to skin effect in the rotor bar; and
I
2
= per unit stator negative sequence current.
Settings for the Locked Rotor Current can be found under the [Field Parameters]. The LRC value is a multiplier
of Ib (FLA).
Page 354 EN MRM4 01/11