Electrical Protection - Grundfos SRG 60 Hz Installation And Operating Instructions Manual

5.4.5 Requirements
• Peak voltage and dU/dt must be in accordance with the table
below. The values stated are maximum values supplied to the
motor terminals. The cable influence has not been taken into
account. See the frequency converter data sheet regarding the
actual values and the cable influence on the peak voltage and
dU/dt.
Maximum
Product type repetitive peak
voltage [V]
SRG.xx.30
1500
SRG.35.50
SRG.xx.xx 1000
• In case the above values are too high, a dU/dt filter could
prevent the voltage peaks.
• The thermal protection of the motor must be connected.
• Do not exceed the frequency indicated on the nameplate.
Otherwise, there is a risk of motor overload.
• Local regulations or standards must be fulfilled.
5.4.6 Recommendations
• Do not reduce the motor speed to less than 30 % of the rated
speed.
• Do not set any slip compensation, as it may lead to an over
speed and therefore to motor overload.
• Set the frequency converter U/f ratio to a linear relation, and
use the data from the motor nameplate for settings about rated
current, power, voltage and frequency.
• Use input and output filters on the frequency converter. See
data sheet for the frequency converter used.
• Keep the power cable as short as possible. The peak voltage
will increase with the length of the power cable. See data
sheet for the frequency converter used.
• Use a screened power cable if there is a risk that electrical
noise can disturb other electrical equipment. See data sheet
for the frequency converter used.
• Ramp-up and ramp-down time must be at least 5-10 seconds.
5.4.7 Consequences
• When operating the product via a frequency converter, please
be aware of these possible consequences:
• The locked-rotor torque will be lower. How much lower will
depend on the frequency converter type. See the installation
and operating instructions for the frequency converter used for
information on the locked-rotor torque available.
• The working condition of bearings and shaft seal may be
affected. The possible effect will depend on the application.
The actual effect cannot be predicted.
• The acoustic noise level may increase. See the installation
and operating instructions for the frequency converter for
advice as to how to reduce the acoustic noise.
10

5.5 Electrical protection

5.5.1 Motor protection
The pumps are provided with the following type of motor
protection:
Standard SRG pumps incorporate three bimetallic PTO thermal
switches (PTO = Protection Thermique á Ouverture). See fig. 11.
Function of thermal switches
The motor is protected against overheating by three thermal
Maximum dU/
switches connected in series, one switch in each winding.
dt [V/μs]
When the maximum winding temperature is reached, the switch
will open the circuit and stop the motor.
15000
When the windings have cooled to normal temperature, the
switch will close the circuit and the motor can be restarted.
3000
Manual restarting is necessary.
See wiring diagram in fig. 11.
Thermal switches (F6)
• Two conductors (terminals 11 and 12).
• Maximum operating voltage of switch: 250 V.
Maximum switching current: 2.5 A at cos φ = 1.
•
• Cutting-out temperature: 150 °C.
Function of PTC sensors (optional)
The motor is protected against overheating by three thermal
sensors connected in series, one in each winding. When
overheated, the motor will stop. Automatic restarting is not
permitted in such cases. This requires a thermistor trigger unit
with a reconnection suppressor in the control circuit of the motor
contactor.
See wiring diagram in fig. 12.
ϑ1, ϑ2, ϑ3: PTC sensors:
• Two conductors (terminals 31 and 32).
• Maximum voltage at the terminals: U
• Resistance between terminals 31 and 32:
– at room temperature R = 150 to 750 Ω.
– at cutting-out temperature 266 °F (130 °C) R ≥ 4000 Ω.
max.
For transmission tests at terminals 31 and 32, the
test voltage must not exceed 2.5 V (AC/DC).
Use an ohmmeter for the test.
= 2.5 V (AC/DC).