Frequency Converter Operation; Motor Protection - Danfoss SP-Serie Montage- Und Betriebsanleitung

6.1 Frequency converter operation

6.1.1 Grundfos motors
Three-phase Grundfos motors can be connected to a frequency
converter.
If an MS motor with temperature transmitter is
connected to a frequency converter, a fuse
incorporated in the transmitter will melt and the
Caution
transmitter will be inactive. The transmitter
cannot be reactivated. This means that the motor
will operate like a motor without a temperature
transmitter.
If a temperature transmitter is required, Grundfos offers a Pt100
or Pt1000 sensor for the submersible motor.
The motor should not run at a frequency higher
than the rated frequency (50 or 60 Hz) during
frequency converter operation. In connection
Caution
with pump operation, never reduce the frequency
(and consequently the speed) to such a level that
the necessary flow of cooling liquid past the
motor is no longer ensured.
To avoid damage to the pump part, the motor must stop when the
pump flow falls below 0.1 x nominal flow.
Depending on the frequency converter type, it may expose the
motor to detrimental voltage peaks.
Warning
MS 402 motors for supply voltages up to and
including 440 V (see motor nameplate) must be
protected against voltage peaks higher than
650 V (peak value) between the supply terminals.
We recommend that you protect other motors against voltage
peaks higher than 850 V.
The above disturbance can be abated by installing an RC filter
between the frequency converter and the motor.
Possible increased acoustic noise from the motor can be abated
by installing an LC filter which will also eliminate voltage peaks
from the frequency converter.
We recommend that you install an LC filter when using a
frequency converter. See section
operation.
For further details, contact your frequency converter supplier or
Grundfos.
6.1.2 Other motor makes than Grundfos
Contact Grundfos or the motor manufacturer.
10
6.7.6 Frequency converter

6.2 Motor protection

6.2.1 Single-phase motors
Single-phase MS 402 motors incorporate a thermal switch and
require no additional motor protection.
Warning
When the motor has been thermally switched off,
the motor terminals are still live. When the motor
has cooled sufficiently, it will restart
automatically.
Single-phase MS 4000 motors must be protected. A protective
device can either be incorporated in a control box or be separate.
Franklin 4" PSC motors must be connected to a motor-protective
circuit breaker.
6.2.2 Three-phase motors
MS motors are available with or without a built-in temperature
transmitter.
The following motors must be protected by a motor-protective
circuit breaker with thermal relay, or a MP 204 and contactor(s):
• motors with a built-in and intact temperature transmitter
• motors with or without a defective temperature transmitter
• motors with or without a Pt100 sensor.
MMS motors have no built-in temperature transmitter.
The Pt100 and the Pt1000 sensor are available as an accessory.
6.2.3 Required settings of motor-protective circuit breaker
For cold motors, the tripping time of the motor-protective circuit
breaker must be less than 10 seconds at 5 times the rated
maximum current of the motor. During normal operating
conditions the motor must be running at full speed in less than
3 seconds.
If this requirement is not met, the motor warranty
Caution
will be invalidated.
In order to ensure optimum motor protection, the motor-protective
circuit breaker should be set as follows:
1. Set the motor-protective circuit breaker to the rated maximum
current of the motor.
2. Start the pump and let it run for half an hour at normal
performance.
3. Slowly grade down the scale indicator until the motor trip point
is reached.
4. Increase the setting by 5 %.
The highest permissible setting is the rated maximum current of
the motor.
For motors wound for star-delta starting, the motor-protective
circuit breaker should be set as above, but the maximum setting
should be rated maximum current x 0.58.
The highest permissible startup time for star-delta starting or
autotransformer starting is 2 seconds.