VSD Selection

When selecting VSD’s the following should be considered:-

• Application.

Load types and T-N Curve.

• Environment.

IP00, IP20, Cubicalised IP54.

• In coming Supply & protection.

Circuit breaker Protection. Customer responsibility, unless cubicalised.

• KW Power & Output Current.

For most applications, can be used for sizing the VSD.

• Overload and Rapid Acceleration/Torque

Overload 110% (Fan & Pump) to 150% for one minute.

Overload and accelerating torque (current) requirements, must be considered when selecting VSD’s. May result in a larger VSD rating.

• Rapid Deceleration / High Inertia

Need to consider dynamic braking unit and Brake resistors.

• Speed range. 0 - 650HZ . (Different for each unit)

Low speed operation and its effects on motor cooling and noise. Running above base speed and torque reduction.

• Speed holding accuracy.

V/f 1%

Open loop (Sensor less) flux vector. 0.3% to 0.5%.

Flux vector control. Closed loop (encoder). 0.03%


RFI Filter (Input supply)

Output reactors, Filters.

• Motor Cabling.

Cable length. 20-30 meters.

Volts drop (Carrier frequency consideration).

Earthing and screening considerations. Safety & EMC.