Suppliers of energy feedback devices for frequency converters remind you that in the current state of industrial development in China, frequency converters, as a part of power and electrical equipment, are increasingly involved in industrial production. However, most users are not familiar with the installation environment and safety of frequency converters, which leads to unstable costs and safety. Understanding the installation and selection of frequency converters can help users save costs, reduce downtime, and improve the safety of motion control systems.
Cost is often the determining factor when choosing the location and method for installing low-voltage inverters. However, prioritizing cost over key decisions regarding the installation of frequency converters may result in higher ownership costs. It will also increase the possibility of unexpected shutdowns and create potential safety issues.
Regardless of whether the user plans to install the frequency converter in a new or existing facility, the following environmental and safety issues should be considered first. Only when users understand the inherent risks and benefits of installation options can they optimize the performance of the frequency converter.
1、 Environmental issues of frequency converters
High temperature is the biggest enemy of the reliability of frequency converters. If the management is ineffective, heat can accumulate on the junction of the power transistor in the transmission. This may lead to the melting or melting of social classes. Overheating can also harm the intelligent power module of the frequency converter. That will have an impact on hundreds of small discrete components and assemblies working together inside the frequency converter.
From an environmental perspective, installing a frequency converter in a motor control center (MCC) is an ideal choice. UL-845: Requirements and testing steps for motor control center to address overheating management issues throughout the entire MCC arrangement. This means that MCC manufacturers need to prove that the frequency converter installed in the MCC will not be damaged, or that the heat generated by the frequency converter will not damage other equipment inside the MCC.
However, it is important to remember that proper thermal management and assembly equipment on the UL-845 list can only be completed by MCC manufacturers. Even cabinet manufacturers certified under UL-508a cannot add frequency converters to MCC and cannot maintain their UL-845 inventory. If a unit within the MCC is not in the UL-845 list, the entire MCC arranged list is invalid.
If a set of frequency converters is installed inside an industrial control cabinet (ICP) instead of an MCC, it will burden the end user with thermal management. If ICP must be sealed, a set of air conditioning equipment is usually required to maintain the internal temperature within the design limit of the frequency converter (or the limit of other ICP components). A general rule of thumb is that a frequency converter will release approximately 3% of the total power flowing through it as heat radiation to its surrounding environment.
When ventilating the ICP, the total air exchange volume at the highest outdoor temperature must be sufficient to maintain the internal temperature within the design limit range of the frequency converter. Moreover, if the circulating external air contains dust or moisture, filters must be used to eliminate pollution. Maintaining faults and regularly replacing filters can cause components to overheat.
For the frequency converter installed in ICP, another key issue related to heat is to leave sufficient clearance around the frequency converter to achieve normal air flow. Each frequency converter design has minimum clearance requirements, including top, bottom, and side to side, which are crucial for cooling internal boards and components. It is often seen that some inexperienced cabinet manufacturers mistakenly assume that slotted cable conduits will not become obstacles, and therefore arrange them too close to the frequency converter. However, it becomes an obstacle to normal air flow and cannot leave enough clearance, which often leads to premature failure of the frequency converter.
Wall mounted inverters are usually equipped with fans that drive air through the enclosure of the inverter to achieve cooling. And also consider other substances that may exist in the surrounding air, including water vapor, engine oil, dust, chemicals, and gas. These substances may enter the frequency converter and cause damage, or cause residue accumulation, thereby reducing cooling efficiency. Preventing obstacles from obstructing air flow is equally important for wall mounted inverters. Certain gases, such as hydrogen sulfide, should be avoided as they can corrode printed circuit boards and connecting components. Moreover, when using certain transmissions, it is necessary to maintain the relative humidity above the minimum value, because if it is too low, static electricity will become a problem when air flows through the components.
This is particularly important for low-voltage inverters that do not use conformal coatings on their circuit boards. For frequency converters with motor models above 400 horsepower, they are already too large to be installed on walls and can only be installed in independent structures that can be fixed on the floor. These cabinet mounted inverters require a separate air channel to cool the heat sink.
Users should understand the inherent risks and benefits of different installation options in order to optimize the performance of the frequency converter.
2、 Appropriate frequency converter safety
When deciding how and where to install a frequency converter, the safety of the arc needs special attention. The most convincing reason for installing a frequency converter in MCC is that its safety is consistent with the overall design of MCC. When installing frequency converters in MCC, all personnel safety issues are related to the entire MCC decision-making process. If MCC is to have arc resistance performance, the cabinet of the frequency converter must also be able to withstand arcs.
In addition to arc flash protection, there are also other personnel safety issues related to MCC installation: in a UL-845 MCC unit, the frequency converter must be in a tested series combination located on the list (which should be executed by the MCC manufacturer), and its level must meet or exceed the MCC short-circuit rating.
As long as the overall specifications of MCC meet the site conditions, this will ensure that every unit within MCC can be proven to be connected to the system. The human-machine interface (HMI) required for users to access the frequency converter is usually moved to the outside of the equipment unit cabinet door in the form of MCC, unless otherwise specified. This means that when operators want to read, adjust, program, or diagnose faults in the frequency converter on their display screen, they do not need to open the equipment unit cabinet door and expose it to safety hazards inside the cabinet.
If installing a frequency converter inside ICP, multiple safety issues also need to be considered. If the user does not require a short-circuit current rating (SCCR) in the procurement instructions, some ICP manufacturers will kindly provide ICPs with a 5kA rating. This means that users cannot connect ICP to power systems with potential fault current (AFC) above 5kA. However, in reality, a 5kA AFC is unlikely to be achieved in industrial applications, especially when using 480V power supply. Moreover, the requirements for arc flash safety and lockout/tagout typically mean that the main circuit breaker of the ICP must be disconnected, and any operation or connection within the ICP must be locked and tagged before proceeding.
It is extremely difficult to manage multiple circuit breaker devices that run through cabinet doors. When a part of the system is shut down and the entire system must also be shut down, ICP is wiser than MCC or a separate frequency converter. Meanwhile, SCCR is also crucial for wall mounted and cabinet mounted frequency converters. If possible, try to purchase the frequency converter in the form of a combination unit, as the main circuit breaker and overcurrent protection device will be integrated into the complete set of frequency converter equipment. This solves the SCCR problem and other electrical safety issues.
Another issue related to large frequency converters is that they are usually heavy. For example, maintenance technicians often use tools, cranes, and even forklifts, which puts the frequency converter and workers at risk. A chassis design that utilizes a special truck like assembly can be matched with internal rails located at the bottom of the inverter cabinet, providing a simple and safe method for moving heavy equipment components. The accessibility, safety, maintainability, and suitability of frequency converter installation will have long-term impacts that will not immediately become apparent during the design and planning stages. By understanding the inherent risks and benefits of different installation options, users can optimize the performance of the inverter throughout its entire lifecycle, while potentially reducing downtime and safety risks.