Abbreviation Term SI unit I-P unit
I
M,N
Nominal motor current
F
M,N
Nominal motor frequency
P
M,N
Nominal motor power
U
M,N
Nominal motor voltage
par. Parameter
PELV Protective Extra Low Voltage
Watt Power W Btu/hr, hp
Pascal Pressure Pa = N/m
2
psi, psf, ft of water
I
INV
Rated Inverter Output
Current
RPM Revolutions per minute
SR Size related
T Temperature C F
t Time s s, hr
T
LIM
Torque limit
U Voltage V V
3.2 Motor thermal protection
Motor Thermal Protection can be implemented using various techniques: PTC sensor in
motor windings, mechanical thermal switch, (Klixon type) or Electronic Thermal Relay
(ETR).
Protection against motor overheating comes from [1-90] Motor Thermal Protection. If the
ETR function is desired, set [1-90] Motor Thermal Protection to data value [4] ETR trip
(default value) or data value [3] ETR warning.
NOTICE: The ETR function is initialized at 1.16 x rated motor current and rated motor
frequency. The ETR function provides class 20 motor overload protection in accordance
with the NEC.
Motor Thermal Protection prevents the motor from overheating. The ETR function is an
electronic feature that simulates a bimetal relay that is based on internal measurements.
The characteristic is shown in the following figure.
Figure 1: The characteristics of ETR function
The X-axis shows the ratio between I
motor
actual and I
motor
nominal. The Y-axis shows the
time in seconds before the ETR cuts off and trips the frequency converter. The curves
show the characteristic nominal speed, at twice the nominal speed and at 20% of the
nominal speed. The curve shows that at lower speed the ETR cuts off at lower heat due to
less cooling of the motor. In that way, the motor is protected from overheating even at low
3 Product Description
12 Aquavar
®
Intelligent Pump Controller - 150 HP to 600 HP INSTRUCTION MANUAL
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