Electrical Overview
A frequency inverter or VFD controls an AC motor's speed and torque by varying the voltage and the frequency sent to the AC motor.
There are many suitable applications for VFDs. The most common application for a VFD is to control the speed of a centrifugal pump, fan, or an electrical motor driven compressor. However, there are many more areas where VFDs are used for constant or variable torque, potential energy load, high inertia load, braking, and more. The use of a VFD provides numerous advantages financially and operationally. VFDs enable significant energy savings compared to a motor running on constant speed. The Affinity Law for centrifugal pumps and fans define that the power is proportional to the cube of the shaft speed: 0.8^3 = 0.51. VFDs reduce mechanical wear during start-up and control the torque to prevent mechanical damages. VFD rated motors can have up to 1000:1 speed range that reduces or eliminates gear boxes. The VFDs have advanced control and logic capabilities built in. Therefore, the VFD can handle PID and cascade control directly or work in conjunction with a separate control system, all depending on the way the end-user prefers to handle its applications. As standard, we offer VFDs ranging from ⅛ hp (0.1 kW) to 1475 hp (1100 kW), 1-phase or 3-phase. Other systems like Low Voltage Superpower Four-Quadrat Inverters or High-Voltage Inverters up to 26820 hp (20000 kW) can be quoted on request. To make a proper selection of a VFD, it is important to identify the application and information about the motor. Providing the following information will allow for a proper selection of a VFD:- Existing motor:
- Take a photo of the nameplate, if possible, otherwise record its voltage, rpm, and amps
- Is the motor VFD rated?
- Does the motor have a speed feedback device?
- What is the distance between the motor and the VFD?
- No existing motor:
- Get the mechanical engineer involved and pay special attention to torque and speed requirements of the machine
- Gear reduction may be needed
- Power source:
- 1-phase or 3-phase
- 115 VAC, 230 VAC, or 460 VAC
- Driven machine:
- Any special overload requirements?
- Standard or high inertia?
- Environmental conditions:
- Indoor or outdoor?
- Exposed to water, dirt, dust, or corrosives?
- Enclosure rating?
- Machine control:
- What causes start and stop?
- What is the reference to the drive (speed, position, flow, level, pressure?)
- What is the feedback signal?
