Substations: Basic Principles | Circuit Breakers | Disconnectors | Relays | CTs & VTs | Arresters
Summary
TLDRThis 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
🔌 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.
🔋 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.
Mindmap
Keywords
💡Substation
💡Voltage Transformer (VT)
💡Current Transformer (CT)
💡Disconnector
💡Circuit Breaker
💡Transformer
💡Buchholz Relay
💡Surge Arrester
💡Busbar
💡Earthing Grid
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
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