Protective relays are a complex and critical part of electrical engineering, especially in the solar and energy storage industries. While they may seem intimidating at first, they don’t have to be! This three-part series is designed for non-engineers who want to understand the basics of relay systems and how they play a role in modern energy projects.
**Intro to Relays #1 – What Are Relays, CTs, & PTs?**
**Intro to Relays #2 – ANSI/IEEE Relay Device Numbers**
**Intro to Relays #3 – What Does SEL Stand For? (Below on this page)**
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**What Does SEL Stand For?**
If you’ve ever been involved in a conversation about protective relaying, you’ve probably heard the term “SEL†more than once. But what exactly does it mean?
**The Company Name**
SEL stands for **Schweitzer Engineering Laboratories**, a leading manufacturer of utility-grade protective relays and other monitoring and control devices. Their products are widely used across the electrical industry, from power generation to transmission and distribution. In fact, if you're working on a solar or energy storage project that involves relay systems, there's a strong chance you're using an SEL device.
Here’s a quick look at the SEL logo:
While companies like GE, Basler, and Beckwith are also well-known in the field, SEL is by far the most commonly used in our work at Pure Power. Their reliability, performance, and wide range of applications make them a top choice for engineers and project teams.
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**Model Numbers**
In addition to being the name of the company, "SEL" also appears in their product model numbers. This makes it easy to identify both the manufacturer and the specific model at a glance.
Most SEL relays follow a pattern: **SEL-XXX**, where the three digits represent the model type.
- **SEL-751** – A versatile feeder protection relay often used in solar and storage projects.
- **SEL-351** – A general-purpose protection system relay.
- **SEL-551** – An overcurrent relay used for fault detection and protection.
- **SEL-587** – An overcurrent differential relay for more advanced protection schemes.
- **SEL-651R** – A recloser control relay used in distribution systems.
Here are some images of SEL devices in action:
Beyond just relays, SEL offers a full line of equipment, including:
- **SEL-735** – A high-accuracy meter for power quality and revenue measurement.
- **SEL-3530** – A real-time automation controller used for dynamic control and system curtailment in solar projects.
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**Conclusion**
At first glance, protective relays and their numbering systems might seem complicated. But with the right team and expertise, these systems can be understood and implemented efficiently. At Pure Power, our team of 80+ engineers has designed over 2,000 commercial and utility-scale solar projects. We specialize in ensuring that your relay systems are not only correctly designed but also programmed, tested, and commissioned with speed and precision.
If you’re working on a project that involves protective relays and need expert support, we’re here to help. Whether you're a developer, project manager, or engineer, having a reliable partner like Pure Power ensures your system runs safely and efficiently.
Ready to take your career to the next level? If you love technical content and hands-on engineering challenges, consider joining our team. We're always looking for passionate engineers to grow with us.
[Check out our open positions here.]()
Need help with your relay system? Contact us today to learn more.
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