With the rapid development of my country's industry, inverters, as a part of power and electrical equipment, are increasingly involved in industrial production. However, most users do not understand the environment and safety of the equipment installation, which has caused instability in cost and safety. Understanding the equipment installation options can help users save costs, reduce downtime, and improve the safety of motion control systems.
When choosing where and how to install low-voltage equipment, cost is often the decisive factor. However, putting cost before key decisions about installing equipment can lead to higher cost of ownership. It also increases the possibility of unexpected downtime and causes potential safety problems.
Whether the user plans to install the equipment in a new or existing facility, the following environmental and safety issues should be considered first. Only when the user understands the inherent risks and benefits of the installation options can the performance of the equipment be optimized.
1. Environmental issues of equipment
High temperature is the biggest enemy of equipment reliability. If management is ineffective, heat can accumulate on the junction layer of the transmission's power transistor. This can cause the fuse or melting of the layer. Overheating can also harm the device's intelligent power module. That will affect the hundreds of small discrete components and components that work together inside the device.
From an environmental standpoint, installing equipment inside a motor control center (MCC) is an ideal choice. UL-845: Requirements and Test Procedures for Motor Control Centers addresses thermal management of the entire MCC array. This means that the MCC manufacturer needs to demonstrate that the equipment installed in the MCC will not be damaged, or that the heat generated by the equipment will not damage other equipment within the MCC.
However, it is important to remember that proper thermal management and UL-845 listing of assembled equipment can only be accomplished by the MCC manufacturer. Even a panel builder certified under UL-508a cannot add equipment to an MCC and maintain its UL-845 listing. If one unit within the MCC is not UL-845 listed, the listing of the entire MCC array is invalid.
If a piece of equipment is installed in an industrial control cabinet (ICP) instead of an MCC, the burden of thermal management is placed on the end user. If the ICP must be sealed, an air conditioning unit is usually required to keep the temperature inside within the design limits of the equipment (or the limits of other ICP components). A general rule of thumb is that equipment will release approximately 3% of the total power passing through it as heat to its surroundings.
When ventilating an ICP, the total air change during the hottest outdoor hours must be sufficient to keep the internal temperature within the design limits of the equipment. Also, if the circulating outside air contains dust or moisture, filters must be used to remove contamination. Maintenance failures and periodic filter changes can lead to component overheating.
Another critical heat-related issue for equipment mounted in an ICP is to allow adequate clearance around the equipment for proper air flow. Each equipment design requires minimum clearances, both above, below, and side-to-side, that are critical for cooling the internal boards and components. It is common to see inexperienced panel builders mistakenly assume that slotted cable ducting will not be an obstruction and therefore place it too close to the equipment. However, it becomes an obstruction to proper air flow and does not allow for adequate clearance, which often leads to premature equipment failure.
Wall-mounted equipment is often equipped with fans to move air through the equipment enclosure for cooling. Also consider other materials that may be present in the surrounding air, including moisture, oil, dust, chemicals, and gases. These materials can enter the equipment and cause damage, or cause debris to accumulate and reduce cooling efficiency. Preventing obstructions to air flow is also important for wall-mounted equipment. Certain gases, such as hydrogen sulfide, should be avoided because they can corrode printed circuit boards and connected components. Also, relative humidity must be kept above a minimum when using certain drives because, if it is too low, static electricity can become a problem as air flows over components.
This is especially important for low-voltage equipment that does not use conformal coatings on its circuit boards. For equipment with motors above 400 horsepower, they are too large to be mounted on the wall and must be installed in a free-standing structure that can be fixed to the floor. These so-called cabinet-mounted equipment require a separate air channel to cool the heat sink.
Users should understand the inherent risks and benefits of different mounting options to optimize the performance of the equipment.
II. Proper Equipment Safety
Arc safety issues are a particular concern when deciding how and where to install equipment. The most compelling reason to install equipment in an MCC is that its safety is consistent with the overall MCC design. When installing equipment in an MCC, all personnel safety issues are relevant to the overall MCC decision-making process. If the MCC is to be arc-resistant, the equipment cabinet must also be arc-resistant.
In addition to arc flash protection, there are other personnel safety issues related to MCC installations: In a UL-845 MCC unit, the equipment must be in a tested, listed series combination (which should be performed by the MCC manufacturer) at a level that meets or exceeds the MCC short-circuit rating.
As long as the overall MCC specification requirements meet the site conditions, this ensures that each unit inside the MCC is certified to be connected to the system. The human-machine interface (HMI) required for user access to equipment is usually moved to the outside of the equipment unit cabinet door in the form of an MCC unless otherwise specified. This means that when operators want to read, adjust, program or troubleshoot the device on its display, they do not need to open the unit door and expose it to the safety hazards inside the cabinet.
If the equipment is installed inside the ICP, there are also several safety issues to consider. If the user does not require a short circuit current rating (SCCR) in the purchase specification, some ICP manufacturers will kindly provide ICPs with a 5kA rating. This means that the user cannot connect the ICP to a power system with an AFC above 5kA. However, in reality, 5kA AFC is unlikely to be achieved in industrial applications, especially when using 480V power. Moreover, arc flash safety and lockout and tagout requirements usually mean that the main circuit breaker of the ICP is disconnected and a lockout and tagout operation is performed before any work is done inside the ICP or the ICP is connected.
It is extremely difficult to manage multiple circuit breaker devices that are through the cabinet door. In the case that if part of the system is shut down, the entire system must be shut down, an ICP is more sensible than an MCC or separate device. At the same time, SCCR is also critical for wall-mounted and cabinet-mounted equipment. If possible, purchase equipment as a combined unit, since the main circuit breaker and overcurrent protection are integrated into the equipment package. This solves the SCCR issue as well as other electrical safety issues.
Another issue associated with large equipment is that they are often heavy. For example, maintenance technicians often use tools, cranes, or even forklifts, which puts equipment and workers at risk. A roll-out chassis design uses a special truck-like assembly design that mates with internal rails located at the bottom of the equipment cabinet, which provides a simple and safe method for moving heavy equipment components. The accessibility, safety, maintainability, and suitability of equipment installations have long-term impacts that are not immediately apparent during the design and planning stages. By understanding the inherent risks and benefits of different mounting options, users can optimize the performance of the drive throughout its lifecycle while also potentially reducing downtime and safety risks.