Page 5-8
MPS Motor Protection System Rev. 6-F-022117
Protective Functions
5.22 OVERFREQUENCY
OPI Menu: Setup | Protection | Overfrequency
A trip or alarm occurs when the frequency of the input
voltage (VA) is above the set point.
Overfrequency protection is inhibited when the input
voltage is less than 50% of rated input (V
p
).
Trip Level ............................. 30.00 to 80.00 Hz
Trip Delay ............................. 0.50 to 500.00 s
Alarm Level .......................... 30.00 to 80.00 Hz
Alarm Delay ......................... 0.50 to 500.00 s
Protection .............................. Enable/Disable Trip1, 2, 3
Enable/Disable Alarm1, 2, 3
5.23 STARTS PER HOUR / TIME BETWEEN STARTS
OPI Menu: Setup | Protection | Starts Per Hour
Starts-Per-Hour and Time-Between-Starts are useful
limits in a protective relay that incorrectly responds to
current below FLA. If the relay’s thermal model
accurately tracks a motor’s used thermal capacity under
all conditions, Starts-Per-Hour and Time-Between-Starts
are features that provide no additional protection. The
MPS does not require these features to provide protection,
but they are included to satisfy protection strategies
designed for protective relays without dynamic thermal
modeling.
The Starts-Per-Hour feature ensures that the
programmed number of starts per hour is not exceeded
and the Time-Between-Starts feature ensures that the
programmed time has elapsed between starts. The
available number of starts and time between starts is also
a function of the thermal model’s Used I
2
t value.
Consequently, the allowed number of starts may be less
than the starts-per-hour value and the time between starts
may be longer than the set-point value.
The number of starts and time between starts is
checked when the motor is stopped. A Starts/Hour Trip
or Starts/Hour Alarm is issued if a start will exceed the
# Starts Per Hour setting or if the time since the previous
start is less than the Time Between setting.
When a Starts/Hour Trip or Starts/Hour Alarm is
issued, the output relay assigned to Start Inhibit is
energized. The Start Inhibit relay is non-latching and can
be used as a start permissive. A Starts/Hour Trip will
remain latched until a reset is issued. The Start Inhibit
relay is shared with the thermal model’s I
2
t Inhibit
feature.
If motor current is detected regardless of the alarm or
trip condition, the Starts/Hour Alarm is removed, and
Starts/Hour Trip can be reset. The starts-per-hour
algorithm remains active but any trips or alarms are
suppressed until the motor is stopped.
The status of Starts-Per-Hour and Time-Between-Starts
is displayed in the Metering | Thermal Capacity menu. If
there are no trips or alarms, the number of available starts
(Sph Available) is displayed and if a trip or alarm is
present, the inhibit time (Sph Inhibit) is displayed. Since
the Metering | Thermal Capacity menu is also used to
display the thermal model status, messages are prioritized
as follows:
• I
2
t Reset Time
(1)
• I
2
t Trip Time
(1)
• I
2
t Inhibit Time
(1)
• Starts Per Hour Inhibit Time
(3)
• Starts Available
(2) (3)
An Emergency Thermal Reset (ETR) can be used to
initialize all thermal and starts-per-hour variables and to
reset a starts-per-hour trip. See Section 5.2.3.
Time Between Starts ......... 0.00 to 500.00 Minutes
Starts Per Hour
(2)
............... 1 to 10
Protection .......................... Enable/Disable Trip 1, 2, 3
Enable/Disable Alarm 1, 2, 3
(1)
Calculated from thermal model data.
(2)
The display range for the number of available starts is
-9 to +10.
(3)
Initialized when supply voltage is cycled.
5.24 FAILURE TO ACCELERATE AND UNDERSPEED
OPI Menu: Setup | Protection | Underspeed
OPI Menu: Setup | 4-20 Analog In | Input Function
OPI Menu: Setup | Digital Inputs | Tachometer
Failure-to-accelerate and underspeed protection are
available if the MPS has a tachometer signal. The
tachometer signal can originate from the High Speed
Input (HSI) or the analog input. If the analog input is set
to Motor Speed, it is used as the input to the algorithm,
otherwise the digital tachometer (HSI) is used. The
failure-to-accelerate algorithm is activated whenever a
start is detected. Start detection is based on motor
current. Set points 1 to 3 (for both speed and time) are
sequentially checked to confirm acceleration.
Motor at Full Speed (refer to Type T28, Bit 2 in
Appendix F) will be set when the measured tachometer
speed exceeds the Speed 3 threshold setting and the
Underspeed protection feature is enabled. If the Speed 3
threshold is not reached within Time 3, the MPS will trip
on failure-to-accelerate.
While running, the tachometer signal is continuously
measured and a trip occurs if the speed falls below the
Speed 3 setting.
Time 1 must be set less than or equal to Time 2 and
Time 2 must be set less than or equal to Time 3.
To enable display of the speed in the Metering | System
State menu, select Enable in the Setup ⏐ Digital Input ⏐
Tachometer ⏐ Enable/Disable menu, when the HSI input
is used.
Speed 1 ................................. 1.00 to 100% Sync Speed
Time 1 ................................... 1.00 to 1000.00 s
Speed 2 ................................. 1.00 to 100% Sync Speed
Time 2 ................................... 1.00 to 1000.00 s
Speed 3 ................................. 1.00 to 100% Sync Speed
Time 3 ................................... 1.00 to 1000.00 s
Protection .............................. Enable/Disable Trip1, 2, 3
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