Grundfos MMS 10000, Инструкция по установке и эксплуатации, Страница: 10 / 32

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5.2.4 Required settings of the motor-protective
circuit breaker
For motors with an MP 204 motor protection unit,
Grundfos recommends that a special trip curve with
P-characteristics be used at a setting of Un times 5
for 1 second.
For cold motors, the tripping time for the motor-
protective circuit breaker must be less than
10 seconds at 5 times the rated maximum current of
the motor.
For all Grundfos submersible MMS motors, the
maximum start and stop ramp time is 3 seconds
(minimum 30 Hz).
To ensure optimal protection of the submersible
motor, set the motor-protective circuit breaker in
accordance with the following guidelines:
1. Set the overload to the rated maximum current of
the motor.
2. Start the motor 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 overload setting by 5 %.
The highest permissible setting is the rated
maximum current of the motor.
For motors wound for star-delta starting, set the
motor-protective circuit breaker as above, but the
maximum setting must be 58 % of the rated
maximum current.
The highest permissible startup time for star-delta
starting or autotransformer starting is 2 seconds.
5.3 Cable sizing
Make sure that the submersible drop cable can
withstand permanent submersion in the actual liquid
and at the actual temperature.
The cross-section (q) of the cable must meet the
following requirements:
•
The submersible drop cable must be sized to the
rated maximum current of the motor.
• The cross-section must be sufficient to make a
voltage drop over the cable acceptable.
Grundfos supplies submersible drop cables for a
wide range of installations. A cable sizing tool is
available on Grundfos Insite at: https://
www.grundfos.com/sp-system/download-sp-app-
html.
Fig. 7 Cable sizing tool
Based on the following parameters, the sizing tool
provides an accurate calculation of the voltage drop
at a given cross-section:
•
cable length
• operating voltage
• full-load current
• power factor
• ambient temperature.
The voltage drop can be calculated for both direct-
on-line and star-delta starting.
To minimise operating losses, the cable cross-
section may be increased. This is cost-efficient only
if the borehole provides the necessary space, and if
the operating time of the pump is long. The cable
sizing tool also provides a power loss calculator that
shows the potential savings of an increased cross-
section.
If this requirement is not met, the motor
warranty will be invalidated.
Submersible motor cables are
dimensioned for submersion in the liquid,
and will not necessarily have sufficient
cross-section to be in air.
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