Alarms And Warnings - Danfoss VLT HVAC Drive FC 100 Series Design Manual

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VLT HVAC Drive Design Guide
A problem may occur at low RPM values in constant torque applications. In a constant torque application s a motor may over-heat at low speeds due to
less cooling air from the motor integral fan.
Therefore, if the motor is to be run continuously at an RPM value lower than half of the rated value, the motor must be supplied with additional air-cooling
(or a motor designed for this type of operation may be used).
An alternative is to reduce the load level of the motor by choosing a larger motor. However, the design of the frequency converter puts a limit to the
motor size.
Variable (Quadratic) torque applications (VT)
In VT applications such as centrifugal pumps and fans, where the torque is proportional to the square of the speed and the power is proportional to the
cube of the speed, there is no need for additional cooling or de-rating of the motor.
In the graphs shown below, the typical VT curve is below the maximum torque with de-rating and maximum torque with forced cooling at all speeds.
Maximum Load for a Standard Motor at 40 °C driven by a frequency converter type VLT FCxxx
Legend: Typical torque at VT load
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Note 1) Over-syncronous speed operation will result in the available motor torque decreasing inversely proportional with the increase in speed. This
must be considered during the design phase to avoid over-loading of the motor.
8.5.6. Derating for Installing Long Motor Cables or Cables with Larger Cross-Section
The maximum cable length for this frequency converter is 300 m unscreened and 150 m screened cable.
The frequency converter has been designed to work using a motor cable with a rated cross-section. If a cable with a larger cross-section is used, reduce
the output current by 5% for every step the cross-section is increased.
(Increased cable cross-section leads to increased capacity to earth, and thus an increased earth leakage current).

8.6.1. Alarms and warnings

A warning or an alarm is signalled by the relevant LED on the front of the frequency converter and indicated by a code on the display.
A warning remains active until its cause is no longer present. Under certain circumstances operation of the motor may still be continued. Warning messages
may be critical, but are not necessarily so.
In the event of an alarm, the frequency converter will have tripped. Alarms must be reset to restart operation once their cause has been rectified. This
may be done in four ways:
1. By using the [RESET] control button on the control panel.
2. Via a digital input with the "Reset" function.
3. Via serial communication/optional fieldbus.
• • • Max torque with forced cooling
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MG.11.B7.02 - VLT ® is a registered Danfoss trademark
8. General Specifications and Troubleshooting
Max torque
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