VFD DOL Changeover circuit- VFD Bypass Arrangement

Why does VFD DOL changeover circuit require:

VFD DOL changeover circuit: Due to some reason the starter or vfd of the induction motor got failured means we need an alternative arrangement immediately or We need a good back up in order to avoid breakdown or stoppage in an industry. Here we are going to discuss about the circuit diagram of VFD to dol or dol to vfd change over drawing. Using This scheme you can run the induction motor with either VFD or DOL. The circuit works as exact alternate for both starting method of the induction motor.

When we have to use VFD DOL changeover circuit?

    1. Permanent failure on vfd or dol starters
    2. Temporary failure on vfd, like software error, cable burning, connector issues, etc
    3. Emergency pumps Ex: Condensate water pump, Boiler DM (demineralized) water pump, firefighting Jacky pump and all emergency pumps.
    4. When motor trial Require.

VFD DOL changeover circuit diagram:

Materials Required for Power circuit: as per your capacity or range

Power circuit:

Required Materials to build VFD DOL changeover circuit:

Power contactors: 2


Thermal Over Load Relay :1

Power cable as per your size.

VFD: as per your amperes of KVA rating

Connectors:3

Connector mounting C channel: 1 meter

Push button: 2 (Stop=1/start=1)

Push Button NO (Normally Open): 1

Push button NC (Normally Close): 1

Indication lamb: 3 reds, 2 yellow, 2 green,

MCB 2 pole, 2 Amps: 1

MPCB or MCCB: 1

Note: While selecting of MCCB Just purchase the protection of short circuit and over current protection is enough to this application. Earth fault protection is not necessary.

Control contactor: 1

Note: While selecting contactor, make sure its coil voltage range (230V), Frequency (50) and which type of power supply required.

Cable 4 sqmm multi stand flexible copper cable: 5 meter each colour R, Y, B

Cable 1.5 Sqmm multi stand Flexible Copper cable: Required

Connector: Required

Connector mounting C channel: 1 full length

Control NO: 2, Control NC: 2

Starter control panel: 1 Size minimum LXDXH (400X450X400)

Note: All the above materials are example for the explanation purpose only, their range and quantity can be changed as per our load requirement

How VFD DOL changeover circuit works:

Whenever vfd has got failured means you can start your motor using DOL starter without delaying. you can perform this action by selector switch or DCS or power selector switch. DCS control works from computer’s software like Honeywell or Siemens or ABB etc. DCS method is the most effective method as compared with other method. It does not require any mechanical action and very fast. But only one drawback is you should check the feeder before making change over. Any abnormal condition leads to flash over in inside the feeder.


Here we have three start/stop, speed increment/decrement option in vfd like Local, Remote and DCS. But in DOL we cannot change motor speed it runs at constant speed but we can make start/stop through local remote and DCS.

Let see the working combination:

ssw1/ssw2 Local Remote DCS Ok => Circuit Works
VFD  ok ok ok
DOL ok ok ok

Ex: When You select VFD + Local => Vfd starts from local or panel control pushbutton likewise all the remaining circuit works.

Also see:

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