Variable Frequency Drives form an essential part of any manufacturing plant. Its continuous operation is necessary for maintaining a plant’s output, and any failure results in a chain reaction, effectively bringing the entire industry to a standstill.
Manufacturing plants are notorious for their harsh work environments, ranging from moisture to dirt to corrosion. Variable Frequency Drives (VFDs) may come in protective shells but still require protection from these elements as well as a comprehensive enclosure for all associated equipment, thus, making it imperative for a plant to have a VFD Control Panel.
Much like any other enclosure or control panel, a VFD Control Panel consists of an enclosure, VFDs and associated equipment like:
- Harmonic filters.
- Protection equipment like relays, circuit breaker and stabilizers.
- A bypass control to keep the VFD running in all conditions.
- PLC for advanced control.
- Communication equipment such as Switches and Modems.
- Temperature control equipment such as anti-condensation heater or air conditioner.
- Motor starters.
A VFD Control Panel is used for four primary reasons such as:1.) Power switching & protection
VFD panels usually host a circuit breaker or a relay that can trip in-case the input power line is struck by any fault such as short-circuit, overload, etc. This protects the drive as well as any equipment connected to the line.2.) Adjustable speed
Usually, the VFD panel’s door has a frequency control potentiometer installed to transmit command signals to the motor as per the operator’s settings. A bypass switch is located nearby to allow functioning of the motors incase the VFD fails.3.) Protection from Environment
This is one of the major concerns for any control engineer as manufacturing units are filled with moisture, dirt, etc. that can result in short-term as well as long-term issues. Most commonly chemical buildup on open-connections can result in reduced performance while dirt accumulation can lead to shorter lifespan for the drive.4.) Visual Control
VFD panels aren’t deployed only for protection against harsh conditions. A number of field indicators are installed to gain real-time information about the drive’s power consumption, frequency and other diagnostic information that is essential for the operator. In addition, controls are embedded to allow the operator to shift the frequency or take precautionary action based on the monitored values.
The National Electrical Manufacturers Association (NEMA) is responsible for creating different resistance levels for enclosures depending on the usage. There are 13 NEMA ratings, some of which include:
- Type 1: General-purpose, for indoor use, provides protection against solid foreign objects.
- Type 2: Drip-tight, similar to type 1 but has additional drip shields.
- Type 3: Weather-resistant, shields the equipment from dripping rain and rice.
- Type 3R: Intended for outdoor use.
- Type 4: Watertight, must shield equipment from at least 65GPM of water.
- Type 13: General-purpose, provides protection against solid foreign objects like dirt, dust, lint, etc. while shielding against water, drippings, seepage of oil and non-corrosive coolants.
The type of protection offered by a VFD Panel should be selected with respect to NEMA guidelines to maintain maximum usability and protection of equipment, and therefore, minimum asset downtime.
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