How to Select Right Frequency Converter for Variable Speed Drive (VSD)?

Application: Brackish water - 3 APP 2,2 equiped with Danfoss inverters for flexible use at universety. Place of installation: UK — Application: Brackish water – 3 APP 2,2 equiped with Danfoss inverters for flexible use at universety. Place of installation: UK

Selecting of a frequency converter for variable speed drives requires a lot of experience. If the experience is not available, it is often useful to visit either a reference plant with similar applications, or exhibitions or trade shows.

Checklist

The following is a brief checklist of points that should be considered:

Details of the machine to be controlled
Environmental details
Mains
Maintenance, operation, personnel
Financial criteria
Protective measures for operators/converter/motor
Standards/regulations
Environmental considerations
Also important…

VLT Drives Applications (VIDEOS)

Some of the interesting applications done with Danfoss VLT drives:

VLT drives in large desalination plant
VLT drives control cooling tower fans
VLT control optimizes spindle speed in Indian textile factory
VLT frequency converters drive bagage handling system
VLT Drives Save 78% Energy in Chester Zoo

1. Details of the machine to be controlled

Required plant/machine characteristics
Torque characteristics, stalling torque, acceleration torque
Speed control range, cooling
Power consumption of the converter and the motor
Operating quadrants
Slip compensation (dynamic)
Required ramp-up and ramp-down times
Required braking times, brake operating time
Direct drives, gears, transmission components, moment of mass inertia
Synchronisation with other drives
Operating time, controls
Computer linkage, interfaces, visualisation
Design and protection type
Possibility of integrating decentral intelligence in the frequency converter

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2. Environmental details

Installation height, ambient temperature
Cooling requirements, cooling options
Climatic conditions, such as humidity, water, dirt, dust, gas-es
Special regulations, e.g. for mining, the chemical industry, the ship building industry, food technology
Acoustic noise

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3. Mains

Mains voltage, voltage fluctuations
Mains performance
Mains frequency fluctuations
Mains interference
Short-circuit and overvoltage protection
Mains drop-out

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4. Maintenance, operation, personnel

Training and instruction of operators
Maintenance
Spare parts/spare units

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5. Financial criteria

Purchase costs (components)
Space requirement, integrated installation, design
Installation costs
Commissioning of the system
Set-up costs
Operating costs
Efficiency of the system (frequency converter and machine)
Reactive power requirement and compensation for harmonic loads
Product lifetime

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6. Protective measures for operators/converter/motor

Galvanic isolation in accordance with PELV
Phase drop-out
Switching at the converter output
Earth and short-circuit protection
Motor coils to reduce voltage rise times
Electronic thermal monitoring and connection of thermistors

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7. Standards/regulations

National DIN, BS, UL, CSA, VDE, European EN
International IEC, CE, etc.

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8. Environmental considerations

Ability to recycle the product
Manufacturing practice
Energy saving factors

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Also important…

Using this checklist a frequency converter can be selected which covers most of the items as standard, but you should also double check whether:

The converter has mains or intermediate circuit chokes in order to greatly reduce mains interference
A RFI filter for class A or B is standard or has to be purchased separately
Motor derating is required if a frequency converter is used
The converter itself is protected against earth and short-circuit
The converter reacts adequately in a fault situation.

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