Switchgear selection is a crucial part of designing an electrical system. You want switchgear that will withstand the system voltage and current, environmental conditions, and so on. In this article, we will guide you through a step-by-step process on how to select switchgear for your project
The main switchgear function is to protect electrical systems against potential problems such as overloads, short circuits, and ground faults. This happens through the combined action of circuit breakers, relays, transformers, and other switching or monitoring equipment.
But switchgear is built to do more than just protect your power distribution system: it’s also designed to make it easier to control, manage, and maintain the electrical system as a whole.
In order to select the best switchgear, your choice must take into account both the protection and the control aspects —which means the need to be careful in your selection process.
Here below, is a step-by-step guide on how to buy switchgear for your project. Note that this is just a general guide: your specific facility may have unique requirements that must be taken into account during the selection process.
How to Select Switchgear
Switchgear selection begins with an evaluation of the electrical system’s requirements and ends with the installation of the chosen switchgear. In between these two steps, there are several factors that every electrician must take into account such as cost, space constraints, and more. Here’s how to go about the switchgear selection process.
1. Get Stakeholder Inputs
Gather input from all stakeholders in the project, be it a new installation or an expansion of an existing one. That includes the input of the project’s general contractor, facility manager, and anyone else who will have a say in the switchgear selection.
Each stakeholder will have their own ideas about what type of switchgear is best for the project, so it’s important to get everyone’s view before making a decision. After all, the switchgear you select will have a direct impact on the project as a whole.
2. Know your Specific Needs
Next, evaluate your system. What are its voltage and amperage requirements? What are the types of loads that will be placed on it? This will give you the basis on which to select your switchgear. You will, therefore, need to determine the following.
- The amount of power (measured in kilovolt-amps or kVA)
- The voltage level (measured in kilovolts or kV)
- The type of loads (e.g. motor, lighting, transformer)
- The duty cycle (50Hz or 60Hz)
Have a clear idea of the environment in which your switchgear unit or assembly will be operating. This includes conditions such as temperature, humidity, and dust levels. Are there factors that might contribute to an accelerated rate of corrosion such as salty conditions and excessive moisture?
Make sure you understand the space constraints of the installation site. This includes both the indoor and outdoor spaces. How much space is there for the switchgear room and what are the access requirements?
All of these things can have an impact on the safety and performance of your switchgear, so it is important to be aware of them from the outset. Once you have a good understanding of your electrical system and its specific requirements, you can begin to narrow down your options.
3. Choose a Type of Switchgear
Decide which type of switchgear suits your project best. This will determine how well the equipment will cope with environmental conditions, as well as how easy it will be to maintain. Your main options in this step are:
- Air-Insulated Switchgear, AIS
- Gas-Insulated Switchgear, GIS
Air-insulated switchgear is less expensive. However, it requires more maintenance than GIS, and it is not as resistant to environmental factors such as dust, salt, and chemicals. Air-insulated switchgear will also require larger space at high voltages.
Gas-insulated switchgear is typically more expensive than air-insulated switchgear, but it has several advantages. It takes up less space and requires less maintenance, seeing that it isn’t exposed to environmental factors such as dust and chemicals.
You can also use gas-insulated switchgear in high voltage applications where space is limited, plus it offers a longer lifetime than AIS. Once you have decided on the type of switchgear that is best for your project, you can proceed to the next step.
4. Switchgear Circuit Breaker
The switchgear circuit breaker is the heart of the switchgear, so it is important to choose the right one for your system. If you’re considering a relatively high switchgear voltage rating, then the interrupting medium of the breaker will be of utmost importance. The four main switchgear breakers options will be:
- Air circuit breaker
- Gas circuit breaker
- Oil circuit breaker
- Vacuum circuit breaker
An air insulated circuit breaker will either use plain air or an air blast to extinguish the arc flash. Gas-insulated breakers use an inert gas, such as sulfur hexafluoride (SF6) to extinguish the arc. Oil-insulated breakers use different types of mineral oils to quench the arc, while vacuum breakers rely on a vacuum to do the job.
5. Select the Switchgear Configuration
How do you want the switchgear designed? Switchgear construction varies widely, with each design offering both advantages and disadvantages. For example, some switchgear types are designed to be more compact or accessible than others while others are meant to be safer. Options for switchgear design include:
- Ring main unit (RMU)
- Open-air breaker
- Single and double busbar configuration
- Drawout type
- Front access
- Rear access
- Metal clad
- Metal enclosed
What you choose will mostly be determined by your needs as well as preferences. For example, draw-out switchgear is easier to maintain while front access switchgear leaves you more room (you can mount it against the wall).
Where do you want your cables terminating? Front, back or side. Depending on your space considerations and other factors, select the best switchgear cable placement. Consider, also, the level of accessibility, especially if space is limited. Accessible switchgear is also easier to maintain.
More importantly, consider its safety. Safe switchgear incorporates safety features such as arc quenching or arc resistance, dead front construction, heavy duty switchgear enclosure, and reinforced panels or doors.
Some switchgear designs also enhance safety by compartmentalizing the switchgear into grounded enclosures. Take every of these features into account in your switchgear selection process.
6. Switchgear Ratings and Standards
Match your system’s requirements to the switchgear ratings. These are the maximum values that the switchgear can handle without sustaining damage. The main switchgear ratings you will be considering include the following.
- Maximum voltage rating (measured in kV)
- Short time withstand current (measured in kA)
- The short-circuit current rating (measured in kA)
- Continuous current rating
- The insulation level and dielectric strength (measured in kV)
- The dielectric strength (measured in kV)
- Power frequency rating (measured in Hz)
- IP rating for switchgear enclosure
Switchgear manufacturers also design their equipment to meet various standards. Different standards may mean different features and capabilities, so be sure to understand the type used by the particular switchgear manufacturing company. The major organizations for switchgear standards are:
7. Determine the Switchgear cost
Your switchgear selection process will ultimately come down to cost. However, the initial purchase price isn’t the only factor you should consider. Installation and life cycle costs, such as maintenance, must also be factored into the equation. The switchgear cost is, therefore summarized into:
- Initial purchase cost or switchgear price
- The switchgear installation cost
- The switchgear operating (energy) cost
- The switchgear maintenance cost
- The switchgear repair and replacement cost
The amount to pay will largely depend on the switchgear type and features. But the good news is that price has come down in price in recent years due to advances in technology. That said, you will want to compare the prices of different switchgear brands.
Be clear, especially, about the particular switchgear maintenance requirements. How often will the switchgear need to be inspected? Are there parts that will need to be replaced on a regular basis? What are the costs associated with its maintenance?
Be sure to also, work with a reputable switchgear manufacturer or supplier to get the most value for your money. Speaking about top switchgear manufacturers, here is the last step of the switchgear selection process: choosing a manufacturer.
8. Switchgear Technology
Switchgear technology has come a long way in recent years. The latest advances now allow for more compact and efficient switchgear designs. That said, you will want to consider the following when choosing your switchgear manufacturer:
- The company’s experience in designing and manufacturing switchgear
- The company’s research and development capabilities
- The company’s switchgear manufacturing process and quality control procedures
In addition to company capabilities, there are modern technologies that may or may not fit your requirements and budget. Some of the switchgear technologies you may want to consider want are given below:
- Remote switchgear monitoring
- Intelligent switchgear
- Arc detection and resistance
- Solid-state switchgear relays
9. Find a Reliable Switchgear Manufacturer
Finally, choose a switchgear company to source your equipment from. There are many switchgear manufacturers and switchgear suppliers, so it is important to do your research before making your decision.
Some things you will want to consider when looking a reliable manufacturer that can provide you with the switchgear you need include:
- The experience of the manufacturer
- The quality of the switchgear
- The price of the switchgear
- The delivery time of the switchgear
- Switchgear warranty
- The customer service
An experienced manufacturer will have the technical know-how to make high-quality switchgear. On the other hand, they must also be able to provide it at a competitive price. On that end, make sure you get quotes from multiple manufacturers before making a decision
In addition to switchgear price, lead time is another important consideration. You will need to know how long it will take for the switchgear to be delivered once you have placed your order. This is especially important if you have a tight deadline.
Lastly, make sure that the manufacturer offers good customer service. How easy is it to get in touch with customer service? What are their hours of operation? How knowledgeable are the customer service representatives? This will come in useful in case you have any questions or problems with your switchgear.
Switchgear selection is a crucial step when designing electrical systems: choose the right switchgear, and your power system will operate smoothly and safely; choose the wrong switchgear, and you may encounter some serious trouble down the line. We hope this guide has provided you with the information you need to make an informed decision about which switchgear is right for your particular project or application.