Woodward MRM4, Manual

Page: 348 / 460

Protective Elements
Commissioning: Undercurrent [ANSI 37]
Object to be tested:
•
Testing the pick-up value for Undercurrent protection;
•
Testing the trip delay; and
•
Testing the fallback ratio.
Necessary means:
•
3-phase current source;
•
Ammeter; and
•
Timer for measuring of the tripping time.
Procedure
Testing the threshold values( single-phase, three phase)
Feed in a testing current significantly greater than the pick-up value. For testing the threshold values and
fallback values, the test current has to be decreased 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 trip 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 greater than the pick-up value, the test current has to be decreased suddenly below the
threshold value. The timer is started when the limiting value of the tripping current falls below 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 more than 103% of the trip value. The relay must only fall back at 103% of
the trip value at the earliest.
Successful test result
The measured tripping delays, threshold values and fallback ratio comply with those specified in the adjustment
list. Permissible deviations/tolerances can be taken from Technical Data.
JAM [51LR]
Elements
Jam[1] ,Jam[2]
Functional Description
When the motor is running, a current increase above normal load may be an indication of a malfunction in the
load. JAM protection recognizes mechanical problems, such as broken drive gears. Refer to the JAM protection
limit (the right vertical line in the “Underload and JAM Trip Function” curve example). In this curve example, the
JAM trip is set at 150% of Ib (FLA).
Page 348 EN MRM4 01/11