Page 48 I.L. 17562
PR 0.3 Effective 8/99
NOTE
This UTC setting is where the user considers the service factor rating of the motor. Never adjust
the FLA setting P1L1 according to the service factor (see subsection 9.1.3.3).
For normal use, set UTC to service factor times 100 %. The available range is 85% to 150%.
The service factor is found on the motor nameplate or in manufacturer’s data.
Note that the relay will not trip at the moment the current goes above UTC during motor running.
Instead, it models the gradual stator heating for currents above UTC, and will trip only after some
time has passed. The trip time depends on a variety of setpoint and operating factors, including
motor nameplate data contained in other setting values.
Use a conservative, or lower, value of UTC than that dictated by the service factor if motor
ambient temperatures may rise above 40ºC and the optional URTD Module is not used (see
Subsection 9.1.3.6). Also, consider lowering the UTC if the motor is suitably rated, yet additional
safety is critical for the application.
CAUTION
If UTC is set above 100 percent times the service factor, motor damage could result.
5.1.5 Setpoint P1L5, Phase Current Transformer Ratio (PCT) — Specifies the numerator of
the turns ratio of the main phase current transformers. Obtain from the Ct nameplate or from the
installation drawings, watching for the use of ratio taps on Cts which have tapped windings.
Explanation of Ct Ratio Presentation
The MP-3000 motor relay is available in multiple styles designed for use with current
transformers (Cts) having a nominal or rated secondary current of either 5 amperes or 1 ampere.
Check the relay labeling or the catalog number, and the Ct secondary rating, to confirm a match.
All displayed information is the same for either of the two types of MP-3000 relays. When Ct
ratios are to be set, the value entered is the numerator of the main Ct ratio. The denominator is
assumed to be either 5 or 1, depending on the rating of the cts and relay in use.
For example, a set of three 400:5 phase Cts might be used with an MP-3000 specified for 5 A
Cts. The phase Ct ratio is then set to 400. Alternatively, a set of three 400:1 Cts could be used
with an MP-3000 rated for 1 A cts. Use a setting of 400 in this case as well.
Ct Ratio Selection
Check the following criteria to insure a suitable current transformer ratio:
For a 5 ampere Ct set:
For optimum metering accuracy at low loads, the Ct should deliver between 3.5 and 4 amperes
at 100 percent FLA. Attempt to achieve 3.75 A.
For reliable motor protection, the Ct must deliver between 2.5 and 4 amperes at
100 percent FLA.
For example, if the motor has an FLA value of 300A, a 400:5 Ct will supply:
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