What is sectionalizer in electrical distribution system?

Electricity is something we often take for granted. It powers our homes, businesses, and the countless devices we use every day. But behind the scenes, a complex distribution system ensures that electricity reaches us reliably and safely. One essential device in this system is the sectionalizer. 

Sectionalizers play a crucial role in ensuring the efficient and reliable operation of electrical distribution systems. These devices, designed to automatically isolate faulted sections of the network while maintaining power supply to unaffected areas, are integral components of modern power grids. Understanding the function and significance of sectionalizer  is essential for enhancing grid resilience, minimizing downtime, and optimizing overall system performance. In this article, we will delve into the fundamentals of sectionalizer in electrical distribution systems, exploring the various types, operating principles, installation considerations, and the benefits they offer.

What is a sectionalizer?

An automatic sectionalizer is a protective device that isolates a faulted section of line from the remainder of the distribution system. Mixing a recloser with a sectionalizer is not recommended, as that device does not interrupt the fault current. Only the number of operations of an interrupting device that supports the circuit, such as a relay-controlled breaker, recloser, or back at the substation, is computed. After a predetermined number of current interrupting processes have been observed, the sectionalizer opens, and the line or feeder on the load side of the sectionalizer is not re-energized.

Since sectionalizers do not require replaceable components, such as fuse-links, and they can be reclosed with a simple hook stick, they simplify the process of restoring service after a fault has been eliminated.

The length of the primary line that each sectionalizer can preserve is contingent upon the value of the loads, lightning probabilities, and tree conditions. Sectionalizers can typically manage up to two or three miles of line effectively. Furthermore, the substation and distribution feeders may be utilized in conjunction with reclosers. Together, sectionalizers and line reclosers operate on distribution circuits to guarantee enhanced reliability. However, their functions are significantly different, despite their similar appearance.

To put it simply, think of a sectionalizer as a traffic controller in the electrical grid. It detects faults and, at the right moment, opens up to isolate the problematic section, allowing the rest of the system to continue functioning smoothly.

How does a sectionalizer work?

To understand how a sectionalizer works, let's first talk about its key components:

The most important components of a sectionalizer include a sensing mechanism, a control unit, and a switching mechanism. A sensing mechanism is placed strategically along the distribution circuit to detect any abnormal conditions, such as a fault or a short circuit. These sensors send signals to the control unit, which analyzes the data and determines whether or not to open the switching device. If a fault is detected, the switching device will open, isolating the faulty section of the circuit and preventing any further damage or disruptions. This process happens quickly and automatically, ensuring minimal downtime and maximum reliability on the electrical grid.

1. Sensing Mechanism: This detects the presence of faults in the distribution line.
2. Control Unit: This decides when to open the sectionalizer based on the fault conditions.
3. Switching Mechanism: This physically opens the circuit to isolate the faulted section.

Now, let's break down the process:

1. Fault Detection: When a fault occurs, such as a short circuit, the sectionalizer senses the abnormal current flow.
2. Count of Operations: Unlike circuit breakers that trip immediately, a sectionalizer counts the number of fault currents it experiences. It typically waits through a pre-set number of operations.
3. Isolation: After the set count, the sectionalizer opens to isolate the faulted section, allowing the rest of the network to remain operational.

Comparison with Circuit Breakers and Reclosers

You might be wondering how a sectionalizer differs from other protective devices like circuit breakers and reclosers. Let's compare them:

1. Circuit Breakers: These devices instantly trip and isolate a faulted section to protect the system. They're usually found in substations and can handle higher fault currents. For example, if a fault occurs in a distribution line, a sectionalizer will wait for a pre-set number of operations before opening to isolate the faulted section, while a circuit breaker will instantly trip to isolate the faulted section. Additionally, circuit breakers are typically found in substations and are designed to handle higher fault currents compared to sectionalizers.
2. Reclosers: These devices can automatically close after opening in an attempt to re-energize the line. They’re designed to handle temporary faults by providing multiple attempts to clear the fault before staying open. For example, if a tree branch falls on a distribution line, causing a temporary fault, a recloser will automatically attempt to close the circuit multiple times to restore power before staying open to isolate the faulted section. In contrast, if a lightning strike causes a permanent fault, a circuit breaker will instantly trip to isolate the faulted section and prevent damage to the system.
3. Sectionalizers: These don’t interrupt fault currents directly. Instead, they count the operations of upstream devices (like reclosers) and then open to isolate the section after a set number of interruptions. For example, if a bird causes a temporary fault on the distribution line, a recloser would attempt to close the circuit multiple times to restore power before the sectionalizer would ultimately open to isolate the faulted section after reaching a certain number of interruptions. Conversely, if a vehicle crash causes a permanent fault on the line, the circuit breaker would instantly trip to prevent any further damage, while the sectionalizer would not come into play in this scenario.

Importance of Sectionalizers in the Distribution System

Sectionalizers play a vital role in enhancing the reliability and efficiency of the electrical distribution system. Here’s why they’re important:

1. Minimize Outages: By isolating only the faulted sections, sectionalizers reduce the number of customers affected by power outages. While sectionalizers may minimize outages by isolating faulted sections, they do not prevent permanent faults like a circuit breaker would, potentially leaving some customers without power. Additionally, other protective devices, such as reclosers, can also help minimize outages in the distribution system.
2. Improve Restoration Time: They help in quickly identifying and isolating faulted sections, making it easier for utility crews to locate and fix problems. Faster restoration time is important during power outages, especially during extreme weather events or emergencies. By pinpointing the exact location of the fault, sectionalizers enable utility technicians to respond promptly and efficiently, ultimately reducing downtime for customers. This not only improves customer satisfaction but also helps maintain the overall reliability of the electrical grid.
3. Enhance System Protection: By working in conjunction with reclosers and circuit breakers, sectionalizers provide layered protection, ensuring that faults are managed efficiently. For example, during a storm, a tree branch may fall on a power line, causing a fault. A sectionalizer would quickly isolate the faulted section, allowing the rest of the distribution system to continue functioning and minimizing the number of customers affected by the outage. Furthermore, if a recloser is also installed in the system, it can attempt to automatically re-energize the line after a brief interruption, further reducing downtime for customers. Together, sectionalizers and reclosers can greatly improve the reliability and resilience of the power distribution system, helping to prevent widespread outages and limit the impact of localized faults.

Types of sectionalizers

There are different types of sectionalizers based on their operating mechanisms:

1. Hydraulic sectionalizers: These use hydraulic mechanisms to operate the switching mechanism.
2. Electronic sectionalizers: These use electronic controls and sensors for more precise operations.
3. Single-phase and three-phase sectionalizers: Depending on the system requirements, sectionalizers can be designed for single-phase or three-phase operations.

Applications and Examples

Let’s look at some real-world applications of sectionalizers:

1. Rural Distribution Networks: In rural areas where fault locations can be challenging to identify, sectionalizers help in quickly isolating and managing faults, ensuring minimal disruption.
2. Urban Distribution Systems: In densely populated urban areas, sectionalizers help in maintaining service reliability by isolating faults without affecting large numbers of customers.
3. Industrial Facilities: Industrial plants with complex electrical networks use sectionalizers to maintain continuous operations and protect sensitive equipment from fault conditions.

Maintenance and Challenges

Like any other component in the electrical distribution system, sectionalizers require regular maintenance to ensure their reliability. This includes checking their operational status, testing sensors, and ensuring proper coordination with other protective devices.

However, there are challenges too:

1. Coordination with Other Devices: Ensuring that sectionalizers work correctly with reclosers and circuit breakers requires careful planning and coordination.
2. Technological Advancements: Keeping up with advancements in technology and integrating new types of sectionalizers can be complex and costly.

To sum up, sectionalizers are indispensable in modern electrical distribution systems. They enhance the reliability, efficiency, and safety of power networks by effectively managing faults and minimizing their impact on consumers. As technology continues to evolve, sectionalizers will undoubtedly play an even more critical role in our electrical infrastructure.