Automated and Manual Motor Control with VFD and DOL Starter

When applies to industrial applications, managing the speed at which motors run and how they are operated is absolutely necessary in order to maximize both the amount of energy consumed and the effectiveness of the process.

In order to accomplish this objective, VFDs provide a technologically sophisticated solution. On the other end, there are some conditions in which a motor must operate at full speed without being controlled by a variable frequency drive (VFD).

These conditions need the combination of a Direct-On-Line (DOL) starter along with an VFD bypass mechanism. using the support of power & control wiring diagrams,  the process of controlling the speed and functioning of a three-phase motor using a variable frequency drive (VFD) and a direct-on-line starter (DOL) in this post.

DOL Starter & VFD

DOL Starter

A Direct-On-Line (DOL) starter, which is based on a contactor and a supplemental thermal overload relay, is a fundamental motor control technique that starts the motor at full voltage instantly since it is linked directly to the power source. DOL starters are affordable and appropriate for uses when speed control is not necessary.

VFD

By changing the frequency and voltage provided to the motor, a Variable Frequency Drive (VFD), on the other end, is a sophisticated control system that permits accurate adjustment of motor speed & torque. VFDs are perfect for applications needing variable speed operation & optimal energy use because they provide energy economy, decreased mechanical stress, and improved process control.

Components

• Three-Phase Motor
• DOL Starter
• 3-P MCCB
• Variable Frequency Drive (VFD)
• 2-P MCB
• 8-PIN Relay
• External Start & Stop pushbuttons
• Single-Phase & Three Phase Supply
• Wires & Cables
• Selector switch for manual ON/OFF & DOL/VFD Operation

Wiring a VFD and a DOL Starter for Automatic/Manual Motor Control

Power Diagram

• Connect the DOL contactor terminals to the 3-phase wires from the 3-P MCCB.
• Connect the contactor output to the motor’s terminals.
• Connect the three-phase wires from the MCCB to the VFD input terminals.
• Connect the VFD’s output terminals to the motor’s terminals as indicated in the power diagram.

Control Diagram

• Connect phase line from the 2-P MCB to the selector switch’s common (OFF) wire.
• Connect a wire from the selection switch’s first terminal (for VFD operation) to the 2-L terminal of the 8-PIN relay.
• Connect a wire from the selector switch’s second terminal (for DOL operation) to the two series-connected buttons (for External OFF & ON in case of manual operation, i.e., bypassing VFD).
• Connect the 2nd terminal of the ON pushbutton to the contactor’s 14-NO and A2 terminals.
• Connect a wire from the ON pushbutton’s starting terminal to the contactor’s 13-NO terminal.
• Connect a wire from the terminal of the VFD (DCM – COM) to the 8-COM terminal of the 8-PIN relay.
• Connect the VFD’s MI1 connection to the 6-NO terminal of the 8-PIN PLA relay.
• Finally, as indicated in the control circuit diagram, connect the neutral wire from the 2-P MCB to the A1 terminal of the contactor and the 7-N terminal of the relay.

Working & Operation of Motor

Automatic Control

• Turn on the “VFD Mode” switch. The VFD will automatically modify the motor speed and direction of rotation based on the program [through external program (or) keypad control button].
• By turning the selector switch to OFF position, the motor and VFD may be turned off.

Manual Control

• Simply move the selector switch to “DOL position” in an emergency or when need to operate the motor at full speed (or) intend to bypass the VFD.
• Because the motor is now directly linked to the 3-phase supply via DOL contactor, it will operate at full load.
• The pushbuttons can be utilized to turn the motor ON or OFF.
• To completely stop the action, just turn the selector switch to OFF position.
• If necessary, just move the selector switch back to the VFD mode to activate the motor automatically. This will bypass DOL starter & allow the motor to be controlled automatically through the VFD.