Motor Control Panels
Electrical Motor Control Panels are enclosures containing motor starters which could include protection and switchgear components that deliver power to the motor. The types of the starters may be of the types such as Direct-On-Line (DOL), Star-Delta Starter, DOL with reversing contactor, or DOL with contactors for switching to different speed windings. The probable variation to this would include a soft starter or a variable frequency drive after the contactor.
Following are a few other variations
• Multiple motors driven by one VFD
• Multiple motors started by a soft starter or VFD in sequence
A typical motor starter would consist of incoming power connection (Single or three phase) connected to a protection system such as fuse block or a circuit breaker with or without locking option, contactor switchgear with an overload relay integrated or separately connected and the power delivery cable terminated directly to the field motor or to intermediate terminal blocks.
The control elements would include selector switches such as Auto/ Manual, Local / Remote and push buttons such as Motor Start/ Stop and Pilot indicators for the status. The actuation of the motor could happen from a controller such as PLC in automatic control schemes. Depending on where the control system (maybe PLC or Motor control relay) is located, the control and monitoring wiring signals such as motor winding temperature/ vibration/ overload/ motor operation status/ motor run forward reverse signals/driven equipment signals may land inside the panel. VFD Panel: This is essentially a motor starter panel with motor starting option is by variable frequency drive. VFD is a solid-state device which takes AC / DC power as power input and delivers a voltage and frequency-controlled output to the driven motor. The output could be a frequency modulated output or a Pulse width modulated (PWM) output. The modulation is controlled by a computer programmed to deliver the output according to the application. The controlled power delivery happens by controlling the firing angle on power switching semiconductors such as thyristors.
Following are the advantages of VFD that ordinary motor starters can’t offer
• Power saving, accurate speed/torque control, reduction of starting current and best power factor management.
• Regenerative breaking feature which uses the angular momentum force of the driven load converted into power and safely breaking the load to stop accurately
Modern industrial applications need fine control of speed/ torque of the driven motor equipment such as pumps, compressors, fans, rod mills, packaging systems etc.
The VFDs produce a little bit more heat than traditional motor starters and the panel must be designed with proper thermal management.
The motor shall be energy efficient motors with very good magnetic core stamping quality which otherwise would result in a lot of heat due to eddy current losses and acoustic noise.
Unwanted harmonics causes a lot of performance issues. These harmonics are addressed by using proper line side or load side filter chokes
The VFD panel will be engineered and built with all the necessary gears for safety, isolation, protection, busbars or sized & insulated conductors, push buttons, selectors switches, speed adjustment potentiometers, panel mount external display pad, control wiring from an internal control equipment or a remote control equipment, harmonic filters, wiring terminations, mounting structure/ accessories, and may be pre-programmed for target application so that it may in an almost ready to install and use.