Substations: Basic Principles | Circuit Breakers | Disconnectors | Relays | CTs & VTs | Arresters

Summary

This video explains the key components of an electrical substation, focusing on their functions and importance. It covers assets such as voltage transformers (VTs), current transformers (CTs), disconnectors, circuit breakers, and transformers, highlighting how they measure, isolate, and protect the system. The role of surge arresters, buzz bars, and the earthing grid is also discussed, as well as the importance of protection systems like relays and batteries in safeguarding the grid from faults and power outages. Overall, it provides an informative look into how substations ensure grid reliability.

Takeaways

• 🔌 Most power system assets are located inside substations, which may look similar but serve different purposes.
• ⚡ Substations use voltage transformers (VTs) and current transformers (CTs) to measure voltage and current, passing this data to relays or communication systems.
• 🔗 Disconnectors are simple mechanical switches used to isolate assets like circuit breakers but cannot break load or fault current.
• 💥 Circuit breakers handle the difficult task of breaking load and fault current and are essential for the protection system of a substation.
• 🔋 Transformers are the largest and most expensive assets in a substation, stepping up or down voltage with cooling systems like radiators and oil.
• 🔥 A Buchholz relay is used in transformers to detect failures by monitoring oil levels.
• 🏠 Relay houses contain relays, which monitor voltage and current and trigger circuit breakers if a fault is detected.
• 🔋 Substations are equipped with batteries to power critical equipment during power outages.
• ⚡ Surge arresters protect transformers and other assets from high-frequency surges such as lightning strikes and switching surges.
• 🌍 The substation uses an earthing grid to maintain safe voltages and provide a path to ground during faults, protecting personnel.

Q & A

What is the primary function of an electrical substation?

The primary function of an electrical substation is to house various assets that help manage, measure, and control the flow of electricity. It is responsible for transforming voltage levels, protecting the power grid from faults, and ensuring a stable and continuous supply of electricity.

What role do Voltage Transformers (VTs) and Current Transformers (CTs) play in a substation?

Voltage Transformers (VTs) and Current Transformers (CTs) measure voltage and current in the substation. They then send this information to relays or to the control room, where it is used to make decisions about potential faults and power management.

Why can disconnectors not break load current or fault current?

Disconnectors cannot break load current or fault current because they are not designed to handle such high currents. Attempting to do so would create a large arc, which can be dangerous. Their main purpose is to isolate sections of the circuit for maintenance.

What is the function of a circuit breaker in a substation?

The circuit breaker in a substation is designed to safely interrupt load current and fault current. It is a complex and expensive piece of equipment that protects the system by automatically cutting off the flow of electricity in the event of a fault.

Why are transformers the largest and most expensive asset in a substation?

Transformers are large and costly because they handle the crucial role of stepping up and stepping down voltage levels, which is necessary for efficient power transmission. They also require additional cooling systems, like radiators and fans, to manage the heat generated during operation.

How does the substation’s protection system operate?

The substation’s protection system is composed of VTs, CTs, disconnectors, circuit breakers, and surge arresters. These components work together to monitor electrical conditions, detect faults, and automatically disconnect faulty parts of the system to protect the grid.

What is the purpose of a surge arrester in a substation?

A surge arrester protects the transformer and other assets in the substation from high-frequency surges, such as those caused by lightning strikes or switching operations, which could damage the equipment.

What role does the earthing grid play in a substation?

The earthing grid provides a low-impedance path to ground, which ensures safe voltage levels in the substation and protects personnel from dangerous voltages. It also helps to stabilize the system in the event of a fault.

What is the function of the relay house in a substation?

The relay house contains the relays, which monitor voltage and current levels. In case of a fault, the relays send signals to the circuit breakers to trip and disconnect the affected part of the system.

Why are busbars used in substations, and where are they typically located?

Busbars are low-impedance metal bars that connect various assets within the substation. They are usually positioned high above the ground for safety and play a vital role in distributing power throughout the substation.

Outlines

00:00

🔌 Overview of Electrical Substations

The paragraph introduces the layout and components of an electrical substation, explaining that while substations may look complex, they follow structured patterns. It presents the idea of a single-phase equivalent diagram, acknowledging that real substations typically have three phases and multiple feeders. The focus is on exploring the various assets within the substation, starting with voltage and current transformers (VTs and CTs), and understanding their roles in measuring electrical parameters and relaying information for fault detection.

05:01

🔋 Voltage and Current Transformers (VTs and CTs)

Voltage transformers (VTs) and current transformers (CTs) are essential for measuring electrical parameters in the substation. They can either send information directly to relays for fault detection or communicate with the control room. Modern VTs and CTs use merging units to convert measurements into digital form, integrating with the IEC 61850 protocol for digital data transmission. Older versions send signals directly to relays.

⚡ Disconnector: A Simple but Crucial Component

The disconnector, a basic mechanical switch made up of a swinging arm, isolates parts of the circuit within a substation. Although it cannot interrupt load or fault currents (which would cause arcing), it plays a vital role by ensuring physical separation between components like circuit breakers and the rest of the system. This separation is essential for safe maintenance.

💥 Circuit Breaker: Breaking Load and Fault Currents

Circuit breakers are critical for safely interrupting load and fault currents, a complex task compared to a disconnector. Due to this, they are more expensive and intricate in design. They have mechanisms to separate connections and extinguish arcs, with different types like air blast and SF6 circuit breakers. Despite their high cost, circuit breakers are vital for substation protection systems.

🔥 Transformers: Large and Essential Substation Assets

Transformers are the largest and most expensive substation assets, responsible for stepping up or down voltages. Key features include a radiator for cooling, as they handle large amounts of energy and generate heat. Oil is used as the coolant, circulating through the radiator. Transformers also have built-in mechanisms like oil containment systems to prevent leaks, ensuring operational safety.

🛡️ Transformer Protection: The Buchholz Relay

Transformers are equipped with protective devices like the Buchholz relay, which detects failures by monitoring oil levels. A drop in oil level indicates a fault, and the Buchholz relay provides a cheap and efficient way to trigger alarms or trips. This automated protection system is crucial for maintaining transformer reliability and preventing failures.

🏠 Relay House and Battery System

The relay house contains the relays that monitor voltage and current, making automatic decisions to trigger circuit breakers in case of faults. Additionally, the substation has batteries to provide backup power during outages, ensuring the system remains operational even without external power.

🛡️ Protection System Overview

The protection system of the substation is a combination of VTs, CTs, disconnectors, and circuit breakers. Together, these components safeguard the grid from faults and react automatically when issues arise. The system ensures the stability and safety of the electrical network.

⚡ Surge Arresters: Protecting Against High-Frequency Surges

Surge arresters shield substations from high-frequency surges caused by lightning strikes or switching surges. Traditional protection systems cannot respond quickly enough to such events, making surge arresters essential for safeguarding transformers and other substation assets from damage.

🔗 Buzzbars: Connecting Substation Assets

Buzzbars, low-impedance metal bars, interconnect various substation assets, forming a cohesive system. They are installed high above ground for safety and play a critical role in maintaining the substation's electrical continuity.

⚡ Grounding Grid: Ensuring Safety in the Substation

The grounding grid, located beneath the substation, helps maintain safe step and touch voltages for personnel. It also provides a low-impedance path to the ground, ensuring safety during fault conditions by preventing dangerous voltage buildup.

Keywords

💡Substation

A substation is a key component of a power system where electrical energy is transformed and distributed. The video explains that most assets of a power system are located in substations, which house equipment like transformers, voltage transformers, and circuit breakers that manage the flow of electricity and protect the system from faults.

💡Voltage Transformer (VT)

A Voltage Transformer (VT) measures the voltage levels within the substation and converts high voltage into lower, manageable levels for use in protective relays and control systems. The video highlights the importance of VTs for monitoring the voltage and ensuring the substation's control systems receive accurate data for decision-making.

💡Current Transformer (CT)

Current Transformers (CTs) measure the current flowing through the substation and, like VTs, convert this into a manageable signal for control systems. CTs are critical for fault detection, feeding information into relays that can trigger protective actions when abnormal conditions occur in the substation.

💡Disconnector

A disconnector is a mechanical switch used to isolate parts of the substation for maintenance. Though it cannot interrupt live current, it plays a vital role in ensuring the safety of workers by physically separating parts of the circuit. The video explains that disconnectors are cheap and reliable but incapable of breaking load or fault currents.

💡Circuit Breaker

A circuit breaker is responsible for interrupting load current and fault current within the substation. Unlike disconnectors, circuit breakers are complex and expensive because they must be able to safely break electrical arcs that form when currents are interrupted. The video stresses their role in protecting the system during fault conditions.

💡Transformer

A transformer is the largest and most expensive asset in a substation, used to step up or step down voltage levels. The video discusses its crucial role in transferring energy, as well as the use of oil and radiators for cooling the transformer, since it handles high levels of electrical energy and generates heat during operation.

💡Buchholz Relay

A Buchholz relay is a safety device installed on transformers to detect failures. It monitors the oil levels in the transformer and triggers protective actions if a fault is detected, such as a sudden drop in oil level. The video describes this as a simple but effective way to prevent transformer damage or failure.

💡Surge Arrester

A surge arrester protects the substation's equipment, especially transformers, from high-frequency surges caused by lightning strikes or switching surges. These surge events occur too quickly for conventional protection systems to handle, making surge arresters critical for substation safety, as described in the video.

💡Busbar

A busbar is a low-impedance piece of metal that connects various assets within a substation, ensuring the smooth flow of electricity between different components. The video emphasizes the importance of busbars in linking the protection system and maintaining safe operations by keeping them elevated above ground.

💡Earthing Grid

The earthing grid is a metallic grid installed below a substation to provide a safe path for electrical current to the ground during faults, protecting personnel from dangerous voltages. The video mentions the earthing grid as essential for maintaining safe step and touch voltages, ensuring the safety of the substation environment.

Highlights

Electrical substations house most of a power system's critical assets, many of which look similar and are hard to distinguish without specialized knowledge.

Substations have voltage transformers (VTs) and current transformers (CTs) to measure voltage and current, which are essential for monitoring and protection.

Modern VTs and CTs have merging units that convert measurements into digital form, compatible with the IEC 61850 communication protocol.

Disconnectors are simple mechanical switches that isolate equipment but cannot break load or fault current, as doing so could cause a dangerous arc.

Circuit breakers are more complex and expensive than disconnectors, capable of breaking load and fault currents, and essential to substation protection.

The largest and most expensive asset in a substation is the transformer, which steps up or steps down voltage and requires significant cooling, often involving oil and large radiators.

Transformers have a specialized cooling system with oil radiators and sometimes fans to manage the heat generated by their operation.

A Buchholz relay monitors transformer oil levels and detects failures, providing a low-cost and reliable method for failure detection.

The relay house in a substation contains relays, which automatically monitor voltage and current, sending signals to trip circuit breakers during faults.

Substations have batteries to ensure critical systems remain powered during an outage, making them essential backup power sources.

The VT, CT, disconnector, and circuit breaker form the protection system of a substation, which automatically responds to faults and protects the grid.

Surge arresters protect substations from high-frequency surges, such as lightning strikes, which standard protection systems cannot handle quickly enough.

Busbars, low-impedance metal pieces, connect various substation assets, ensuring efficient electrical flow within the substation.

Substations have an earthing grid under the surface to maintain safe voltages and provide a low impedance path to ground during faults.

The protection system in substations works together to safeguard the grid by automatically handling faults and ensuring safe operation.

Transcripts

most of the assets of a power system

live inside electrical substations but

if you're not familiar with the

equipment

it kind of all looks the same and it's

difficult

to make any sense of it so let's take a

look

inside the substation and will learn

about the different assets

their main duties and how they operate

first of all let's look at the

substation from a very high level

and this diagram shows a single phase

equivalent

of course a real substation will have

three phases and it will likely have

several feeders

so what you see here is replicated many

times over

inside a substation

now the first asset we'll look at is the

voltage transformer or current

transformer normally a substation has

both

vts and cts have the job of measuring

voltage and current in the substation it

then passes this information

either directly to a relay to make the

decision on whether

a fault condition is present or it goes

into the communication infrastructure

of the substation and then passed on to

the control room

modern vts and cts have merging units

these convert the measured voltage and

current

into a digital form that can then be

passed

into iec 61850 which is a new

communication protocol

for handling digital information inside

a substation

old-fashioned cts and vts can send

the recorded signal straight to a relay

next one we'll look at is called the

disconnector

so the disconnector is a very simple

asset in construction it's made up

of a swinging arm so this is just really

a mechanical switch

now disconnectors are cheap they

are reliable but they're not able to

break

load current or fault current so that's

one of the big weaknesses of a

disconnector in fact if you try to break

load current or fault current you just

get a giant arc

so it's a very specialist job actually

to break

fault current and load current but

disconnectors do play an important role

inside the substation because they allow

other assets most importantly the

circuit breaker

to be isolated and it's reassuring if

you're working or maintaining a circuit

breaker

it's reassuring that you have that

physical separation between you

and the rest of the circuit that's a

disconnector

now we move on to the circuit breaker so

as i mentioned before the circuit

breaker

has the important and difficult job

of breaking load current and

fault current and this is really

difficult actually so

circuit breakers tend to be more complex

in construction

and therefore more expensive but they

play such a crucial role

in the protection system of the

substation

so most circuit breakers have some kind

of mechanism

to physically pull the two connections

apart

and then extinguish the arc so examples

of this

are air blast circuit breakers and sf6

based

circuit breakers so that's the circuit

breaker

they're very expensive but really

important inside a substation

now the most expensive and largest

asset inside the substation is the

transformer so the transformers really

are

playing a very important role inside a

substation because they step up

and step down the voltage now one of the

most striking features of the

transformer

is the giant radiator that's normally

bolted

on the side of the transformer now the

purpose of this radiator

is to help with the cooling of the

transformer because

you know transformers transfer vast

amounts of energy and they do run

hot so oil is used as the coolant

the radiator on the side is an

additional measure to help

cool down the transformer and typically

oil will flow through the radiator

and you'll have heat exchange you also

sometimes have

fans underneath the radiator to help

with the cooling

just as you would in a laptop actually

now the main chamber houses the windings

and of course this is where

the um electrical uh role of the

substate of the transformer is carried

out

the stepping up and the stepping down

and we also have

another well a noticeable feature is

an oil containment measure so

transformers contain lots of oil

and if they leak there has to be a way

to contain that oil so normally

an oil containment measure sometimes

these are called buns

they're used to to contain any leak

of oil now on the protection of the

transformer when the transformer fails

normally you get a reaction in the oil

which causes the

level of the oil to fall so a buck holds

relay

is a very cheap and effective way

to monitor this and to detect a

transformer failure so

you'll always see a buckhold relay on a

transformer it's just a way

to detect failure in a transformer in an

automated way

we also have in a substation a building

called the relay house and as the name

suggests this is home

to the relays of course the job of the

relay

is to monitor the voltage and current

and make a decision on whether there's a

fault

if there is a fault it will send the

signal to the circuit breaker to trip

so the relay is an automated way to do

this we also have the battery

so the battery in the substation is a

way to power the equipment

if you get complete power outage

so really important the batteries is so

important in a substation

and we can group together the vt and ct

the disconnectors and the circuit

breaker

and call these the protection system of

the substation

and they perform a really important job

in the substation because

they actually protect the grid from

faults and automatically respond if

there is a fault

so let's group these together and call

them the protection system now there's

also one other type of

asset which is important this is called

the surge arrester and the job of the

surge arrester

is to protect the transformer and other

parts of the substation

against high frequency surges such as

lightning strikes and

switching surges the conventional

protection system isn't fast enough to

protect against

lightning strikes and switching surges

so all these

assets together are called the

protection system

so all of these assets work together to

form

the substation so we've gone through all

of the main assets now

there is one other important element of

the substation

uh called the buzz bars now the buzz

bars are the way

that all of these assets are connected

together so

you can think of buzzbars as just a low

impedance

piece of metal which connects assets

together

within the substation obviously these

buzz bars

are very high above ground so they're at

a safe level

but they're also very important another

important aspect of the substation is

the earthing grid

so underneath the substation you have

a grid a metallic grid and that helps

maintain safe step and touch voltages

within the substation

to protect personnel from dangerous

voltages

and to also provide a low impedance path

to ground if there's a fault