Section 9 - Applications And Settings; General; Motor Protection - Eaton MP-3000 Instruction Leaflet

SECTION 9 - aPPLICaTIONS aND SETTINGS

9.0 General

This section is a supplement to Section 5, providing more engineer-
ing and application guidance for particular MP-3000 functions and
settings.
Use this data in conjunction with Section 5 and Table 4.3 to develop
settings for the MP-3000, as well as for making appropriate wiring de-
sign. Note that particular settings are designated as PnLm, where Pn
is the page number and Lm is the line number of the particular setting
in Table 4.3, and in the page-line-value scheme of accessing settings
on the front panel of the MP-3000.

9.1 Motor Protection

The MP-3000 protects the motor, starter, and load in the following
ways:
• Stator and rotor thermal protection by modeling of heating
and cooling effects, including heating by negative sequence
currents
• Stator over-temperature protection by direct measurement
(with optional URTD module)
• Instantaneous over-current protection for faults
• Ground fault protection
• Phase reversal protection
• Phase unbalance protection
• Motor bearing and load bearing temperature protection (with
optional URTD module)
• Jam protection
• Underload protection
• Incomplete sequence protection (missing status feedback
from load)
• Trip-bypass output for failure of contactor to interrupt current
after a trip
9.1.1 Thermal Modeling and Overload Protection without RTDs
The motor overload protection function, called the I
calculates the rotor and stator temperature based on effective heating
current, integrated over time (see Figure 9.1). Positive and negative
sequence current magnitudes are calculated in separate accurate
algorithms. The effective heating current is the sum of the positive
and negative sequence currents, with a heavy weighting factor on the
negative sequence contribution. This models the disproportionate
rotor heating effect of the negative sequence current (see Motor Ther-
mal Protection Basics, Section 8). Certain harmonic currents, such as
the 5 and 11 , also produce the same heating effects as fundamental
th th
frequency negative sequence current. This harmonic heating effect is
also measured and modeled.
The temperature rise caused by current flow is modeled with a thermal
accumulator or bucket whose size or capacity is derived from motor
nameplate data entered as settings. The flow of effective heating cur-
rent into the bucket causes it to fill. Cooling is modeled by a gradual
emptying of the bucket. The settings that influence the heating and
cooling models are:
• Full load amperes (FLA, P1L1);
• Locked rotor current (LRC, P1L2);
• Maximum allowable stall or locked-rotor time (LRT, P1L3);
• Ultimate trip current (UTC, P1L4), which is usually service
factor times 100%.
The MP-3000 thermal bucket fills and proceeds towards a trip only
when the effective heating current is above the ultimate trip current
setting P1L4. The modeling is based on an ambient temperature of
40°C (104°F). A programmable I2T alarm I2TA, P4L2 informs the
User when the bucket reaches the User-set level between 60% and
100% full.
MP-3000
Without manual process load reduction, automatic process load
shedding (refer to Subsection 9.1.5), or other remedial action after an
alarm, the relay eventually trips and displays the message LRC/I2T
(Locked-rotor/Thermal Overload). The trip contact blocks motor re-
starting until the temperature, as reflected in the thermal accumulator
bucket level, cools below the alarm level setting I2TA, P4L2.
NOTE: If stator RTDs are not used and the ambient may rise above
9.1.2 Overload Protection with RTDs
Connect from one to six stator RTDs to the optional URTD module,
and connect the URTD data communications output to the MP-3000
using an optical fiber (recommended) or wired connection. The
MP-3000 can then perform enhanced motor protection in two ways:
1. Direct measurements of the winding temperature are checked
against User-programmed alarm and trip temperature settings.
2. The thermal modeling combines the measured temperature with
the effective heating current and the motor constants to more
accurately model cooling as a function of temperature (more heat
is dissipated as the temperature rises). Loadability of the motor
is much improved.
If more than one RTD is connected, the hottest of up to six stator RTD
temperature measurements is used for protection. Note that motor
bearing, load bearing, and auxiliary RTD inputs are ignored by the mo-
tor thermal algorithm. These other RTD inputs have their own alarm
and trip settings.
If stator temperature measurements are available, the algorithm may
keep from tripping, even if the effective current is above the ultimate
trip current setting, depending on stator temperature reports. It is still
important to set a correct ultimate trip current so that the motor is well
protected. If the RTDs, the module, or its communications to the relay
fail, the algorithm falls back to use of UTC. Also, note that if the wind-
ing trip temperature WD T is set to OFF, the algorithm reverts to the
T algorithm,
2
non-RTD calculation, which is based strictly on UTC.
NOTE: Many users have the false impression that connecting RTDs
9.1.3 Protection Curve
Figure 9.2 shows an example motor protection curve. A protection
curve defines the current versus time limit that the MP-3000 develops
from programmed setting values. Ideally, this curve is located as
close as possible to the motor protection curve for maximum utilization
of the motor capacity. When the integrated effective heating current
squared exceeds this limit curve at any time in the start or run cycle,
the MP-3000 trips the motor.
The MP-3000 automatically calculates the correct motor protection
curve from nameplate or manufacturer values of full load amperes
(FLA, P1L1), locked-rotor current (LRC, P1L2), maximum allowable
stall or locked-rotor time (LRT, P1L3), and service factor as used to set
ultimate trip current (UTC, P1L4). The following subsections describe
how such a typical curve is obtained.
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40°C (104°F), the ultimate trip current should be set below
that indicated by the nameplate service factor to avoid stator
insulation damage or loss of motor life.
makes the motor relay more conservative and more likely
to trip under heavy load conditions. The reverse is actually
true—use of RTDs greatly increases motor loadability. With
RTD measurements, the MP-3000 can allow the motor to
operate safely with significantly higher sustained levels of
loading at normal ambient temperatures. Along with this, it
can effectively protect the motor when the ambient rises to any
level above 40°C (104°F). Refer to Subsection 9.1.4.
Note that when in the RS-232 mode, thermal modeling is used
since the MP-3000 is not able to communicate with the URTD.
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