Details

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Grundfos CUE is a series of external frequency converters designed for speed control of a wide range of Grundfos pumps.
When a CUE is installed, the motor requires no further overload protection. If overheating protection of motor windings is desired, Pt100/1000 together with MCB 114 sensor input module can provide this protection.
If the motors have built in Tempcon sensor, this sensor will be disconnected when exposed to frequency convert drive. A internal fuse in the motor blows and cannot be replaced. The motor will work without the sensor, but it is not possible to restore tempcon functionality.
CUE offers quick and easy setup and commissioning compared to a standard frequency converter because of the startup guide. Simply key in application-specific variables such as motor data, pump family, control function (for example constant pressure), sensor type and setpoint, and CUE automatically sets all necessary parameters.
CUE enables gentle pumping and thereby protects the water reservoir and the rest of the distribution system, as water hammer can be avoided by adjusting ramp times up and down.

CUE is available in two enclosure classes:
• IP20/21
• IP54/55.
RFI filters
CUE includes the following types of built-in radio frequency interference filters (RFI).

Functions
CUE has a wide range of pump-specific functions, such as the following:
• constant pressure
• constant level
• constant flow rate
• constant temperature
• constant curve.

CUE features
• Startup guide.
CUE incorporates an innovative startup guide for the general setting of CUE including the setting of the correct direction of rotation. The startup guide is started the first time CUE is connected to the power supply.
• Checking of direction of rotation.
• Duty and standby operation.
• Dry-running protection.
• Low-flow stop function.

Sensors
The following sensors can be used in connection with CUE. All sensors are with 4-20 mA output signal.
• pressure sensors, up to 25 bar
• temperature sensors
• differential-pressure sensors
• differential-temperature sensors
• flowmeters
• potentiometer box for external setpoint setting.
Accessories for CUE
Grundfos offers various accessories for CUE. For further
details, see the next topics or the CUE frequency
converter data booklet.
MCB 114 sensor input module
MCB 114 offers additional analog inputs for CUE:
• 1 analog input, 0/4-20 mA
• 2 inputs for Pt100 and Pt1000 temperature sensors.
Output filters
Output filters protect the motor from overvoltage and increased operating temperature. The filters reduce voltage stress on the motor windings and stress on the motor insulation system. The filters also decrease acoustic noise from the frequency converter-driven motor.

Grundfos offers two types of output filters as CUE accessories
• dU/dt filters
• sine-wave filters.
dU/dt filters
dU/dt filters reduce the voltage peaks and dU/dt of the pulses at the motor terminals. The voltage at the motor
terminals is pulse-shaped; the motor current has a sinewave shape without commutation spikes.
Sine-wave filters
Sine-wave filters have a higher degree of filtering, resulting in high reduction of motor insulation stress and elimination of switching acoustic noise from the motor.
The motor losses are reduced as the motor is fed with a sine-wave voltage and because the filter eliminates the pulse reflections in the motor cable.

Use of output filters
The table below shows in which cases an output filter is required. From the table, it can be seen if a filter is needed, and which type to use. For MS and MMS motors,
Grundfos recommends sine-wave filters.
The selection depends on these factors:
• pump type
• motor cable length
• the required reduction of acoustic noise from the motor.

Cables used in CUE installations
When CUE is installed in connection with SP pumps, we distinguish between two types of installation:
• installation in EMC-insensitive sites. See fig. 26.
• installation in EMC-sensitive sites. See fig. 27.
The two types of installation are different when it comes to the use of screened cable.
Note that drop cables are always unscreened.
Screened cables are required in parts of the installation where the surroundings must be protected against EMC.
CUE is the right choice of frequency converter in SP installations as it meets all basic issues.
CUE has a pre-installed startup guide which takes the installer through all the necessary settings.
The table below shows the different issues to be considered when using frequency converters in SP installations.