All electrical systems require a power source (or sources) and electro-power conversion/utilization. Between these two, electrical power distribution is required in a safe and efficient manner. Electrical switchgear is an essential element of this distribution. Modern metal-clad switchgear has changed with new tech. But, many traits remain the same. The following is a summary of industry common applications and an attempt to explain what is included in the solutions. LV Electrical Switchgear

Components of Switchgear

As stated in the opening paragraph, modern power systems distribute energy to smaller loads. They use a centralized power supply (usually at 9kV or higher). It has enough capacity to power the total need. A user of that power, often, is tasked with safely distributing this power once the service entrance from a utility is established. The most common way to make such a point is a metal enclosure, made in a factory. It includes at least the following:

Conductors are commonly three phase conductors. They may include a neutral, depending on the power system. Conductors serve as the “roadway” for the flow of large levels of electrical current.

Electrical insulators keep electrical conductors separate from things not at the same voltage. Insulation is effectively the “guardrails” to the conductors.

Circuit isolators are mechanical devices. They allow the electrical power to be isolated from the source. This effectively stops the flow of electrical power.

Switchgear often includes components. They allow unsupervised and automated protection from failures in the electrical distribution system.

Instrument transformers are electrical devices that sense power. They reduce voltage and current to safe levels. These levels are normally 120VAC and 5A. Relays and meters interpret these signals to show the state of the power.

Circuit protectors are extra power sensors. They may or may not work with the instrument transformers. Their job is to stop the electrical system from damage to its insulation. This damage can be from short-circuits (phase to phase) or phase to ground. Examples are circuit breakers, current interrupting fuses, and load-break switches (manual and electrically operated).

Protective relays interpret the power system operation. They often use the outputs of the instrument transformers. Based on those inputs, they send signals to alarm personnel or operate the circuit isolators. This isolates faults or overloads safely.

Metering – allows for monitoring the power system operation. Control power transformer(s) allow for efficient power delivery. They provide power to the devices for operating the switchgear.

Power transformers – unit substations, typically dry-type fan cooled. Using switchgear to hold many of these components has three benefits. It is efficient to make and install. It protects against outside factors that can harm electrical systems. And it guards people and property from the dangers of high voltage.

Enclosure Integrity and Composition

Switchgear enclosures can have various degrees of protection against outside contaminants. They can be for outdoor or indoor use. All switchgear must allow for power conductors to enter and exit. It must also allow for external communications or control circuit conductors. The designs can help users route external systems. They do so while maximizing flexibility for cooling and space. They also maintain enclosure integrity. You can connect switchgear enclosures to transformer enclosures. You can also connect them to motor control centers (MCC). These include large motor control cabinets (for variable speed drives or soft starters) and panel boards. Exterior surfaces can be powder coat painted steel, stainless steel, or aluminum. Structural rigidity can be varied with the gauge or thickness of the material and the fastening means of the supports and sheathing. Enclosure integrity has inherent protection. This can be enhanced by getting an arc-resistant design classification. This means that any arc explosion within the switchgear will be contained and prevented from harming people or equipment.

Electrical Rating: Voltage

The readiness of switchgear for electrical service is defined by its design application rating. This rating is with respect to the operating voltage and maximum current that needs to be distributed. The frequency rating is also a factor, but it is mainly secondary. The voltage rating of switchgear sets the needed dielectric properties. These properties must be for the non-conductive parts of the design. They must be easy to make for the intended use. This is to cut cost and complexity. For instance, low voltage power systems (under 690VAC) use smaller insulation than those at medium voltage (690VAC to 70kV). These design variations result in the voltage classification of the switchgear powerline. Switchgear in North America has industry standard voltage levels. These are typically identified as 480V or 600V for low voltage. For medium voltage designs, they are 5kV, 15kV, 25kV, and 38kV. These levels are for when air is the primary insulating medium. Air insulation. Separation distances for phase to phase and phase to ground are key. They determine the insulation’s classification. The voltage rating is the Power Frequency Withstand Rating. It differs from the user’s operating voltage. The rated voltage of the switchgear must always be higher than the intended operating voltage. This is to ensure reliable operation and to prevent flashover faults. For instance, if the operating voltage is 12.47kV, the switchgear rating will be 15kV. Additionally, switchgear designs will include a Basic Impulse Level or BIL rating. This rating describes the insulation’s ability to withstand overvoltage from lightning.

Electrical Rating: Current

The rating of the switchgear design indicates how ready it is to handle electrical service based on the voltage and current it can manage. It’s key to match the voltage rating of the switchgear. You should also consider the current rating of the conductors. This keeps the system cost-effective and compact. The conductors carry current in a power system. They must follow the laws of physics and thermodynamics. The ampere rating of a switchgear design is set by how much heat the conductor can handle. It also depends on the stress between the conductors. This stress occurs in normal and faulty conditions. The current rating is continuous. It specifies the highest safe heat level for the conductors and insulation. It considers their strength. The conductors must be sized, spaced, and braced well. They must withstand fault currents. These currents could be over ten times the design’s continuous current capability. This is called the maximum allowable short circuit rating of the switchgear system. The current ratings are influenced by the power needs of the end-user. So, cost and technical limits mostly affect them. They limit increasing the app’s operating voltage. By using a higher system voltage rating, the current rating requirements can be reduced.

Manufacturing Standardization

The thresholds for mechanical and electrical ratings come from standards. Industry users and manufacturers develop these standards. They do so to ensure confidence in performance and safety. In North America, OSHA and NFPA regulations, and ANSI/IEEE standards say this. The standards are in articles C37.20. They specify the quality and application of mass-produced switchgear and parts. IEC standards cover switchgear industries worldwide. Many of the two governing standards have been combined. OSHA qualifies NRTL’s, such as UL. It does so to ensure compliance by users and providers. Federal, state, and local municipalities then ensure end-users utilize qualified products. The standards allow standardizing components and assembly. They aim to boost user confidence. They do this by making sure compliant designs are reliable. If applied correctly, the designs limit harm to people and property. Low Voltage Circuit Breakers

Switchgear can be described as any free-standing enclosure that serves as an enclosed distribution system of electrical power. Designs are often a compromise. They minimize cost and complexity to provide an essential solution. This solution uses electrical energy. It safely converts it to another form, such as mechanical or thermal. When used correctly, switchgear is often a silent or invisible part of automated systems. They work as intended and silently protect people and property from harm.

Importance in Power Systems

Switchgear’s importance in electrical infrastructures cannot be overstated. It protects against hazards like power surges and overloads. These are critical in business and industry. Reliable and uninterrupted power is a necessity in today’s world, and Switchgear plays a central role in achieving this. Switchgear may operate silently behind the scenes. But, its role in keeping power systems running smoothly is clear. It is a crucial component, ensuring the safety and reliability of electrical networks.