Protection of transmission lines (distance)Rohini Haridas
This gives idea about necessity of protection of transmission line and protection based on time grading as well as on current grading. Also includes three step distance protection of transmission line
Tutorial on Distance and Over Current ProtectionSARAVANAN A
Contents
• Protection Philosophy of ERPC
• Computation of Distance Relay Setting
• System Study to Understand Distance Relay
Behaviour
• DOC and DEF for EHV system
Bus Bar protection Schemes,Simple Current differential scheme,Need for bus bar protection,requirement of bus bar protection,recommendations for providing bus bar protection,basics of busbar protection,Types of bus-bar protections,High speed differential protection
Protection of transmission lines (distance)Rohini Haridas
This gives idea about necessity of protection of transmission line and protection based on time grading as well as on current grading. Also includes three step distance protection of transmission line
Tutorial on Distance and Over Current ProtectionSARAVANAN A
Contents
• Protection Philosophy of ERPC
• Computation of Distance Relay Setting
• System Study to Understand Distance Relay
Behaviour
• DOC and DEF for EHV system
Bus Bar protection Schemes,Simple Current differential scheme,Need for bus bar protection,requirement of bus bar protection,recommendations for providing bus bar protection,basics of busbar protection,Types of bus-bar protections,High speed differential protection
On Load Tap Changer (OLTC) is used in "High Power Transformers" to control output voltage, when electric load on transformers get increase the output voltage get decrease due to internal voltage drop inside winding, change in tap is required to maintain output voltage. OLTC is a device which perform tap changing in High Power Transformers during On Load conditions and is powered by a motor.
This directional over current relay employs the principle of actuation of the relay....It has a metallic disc free to rotate between the poles of two...
Generator and Transformer Protection (PART 1)Dr. Rohit Babu
Part 1. Generator Protection
Protection of generators against stator faults
Rotor faults and abnormal conditions
Restricted earth fault and inter-turn fault protection
Numerical examples
On Load Tap Changer (OLTC) is used in "High Power Transformers" to control output voltage, when electric load on transformers get increase the output voltage get decrease due to internal voltage drop inside winding, change in tap is required to maintain output voltage. OLTC is a device which perform tap changing in High Power Transformers during On Load conditions and is powered by a motor.
This directional over current relay employs the principle of actuation of the relay....It has a metallic disc free to rotate between the poles of two...
Generator and Transformer Protection (PART 1)Dr. Rohit Babu
Part 1. Generator Protection
Protection of generators against stator faults
Rotor faults and abnormal conditions
Restricted earth fault and inter-turn fault protection
Numerical examples
Amplitude and phase comparators
Over current relays
Directional relays
Distance relays
Differential relay.
Static Relays: Comparison with electromagnetic relay
Classification and their description
Over current relays
Directional relay
Distance relays
Differential relay
Unit I: Introduction to Protection System:
Introduction to protection system and its elements, functions of protective relaying, protective zones, primary and backup protection, desirable qualities of protective relaying, basic terminology.
Relays:
Electromagnetic, attracted and induction type relays, thermal relay, gas actuated relay, design considerations of electromagnetic relay.
Unit-II: Relay Application and Characteristics:
Amplitude and phase comparators, over current relays, directional relays, distance relays, differential relay.
Static Relays: Comparison with electromagnetic relay, classification and their description, over current relays, directional relay, distance relays, differential relay.
Unit-III Protection of Transmission Line:
Over current protection, distance protection, pilot wire protection, carrier current protection, protection of bus, auto re-closing,
Unit-IV: Circuit Breaking:
Properties of arc, arc extinction theories, re-striking voltage transient, current chopping, resistance switching, capacitive current interruption, short line interruption, circuit breaker ratings.
Testing Of Circuit Breaker: Classification, testing station and equipments, testing procedure, direct and indirect testing.
Unit-V Apparatus Protection:
Protection of Transformer, generator and motor.
Circuit Breaker: Operating modes, selection of circuit breakers, constructional features and operation of Bulk Oil, Minimum Oil, Air Blast, SF6, Vacuum and d. c. circuit breakers.
Distance protection scheme for transmission line using back propagation neura...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
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Very many challenges related to protection relay testing are met today in the field and in the research industry.
There are often new and more complex applications such as wind turbines, very fast switching power electronics, photovoltaic cells and the battery and electric vehicle technologies. This implies among other things new converter topologies and smart grid considerations. These systems cannot be protected the same way as what was already being done, so this increases the complexity of the algorithms used.
Real-time simulation is a novel approach to design and test protection relay algorithms.
The CDMA is a broadband single frequency cellular system that maintains resource balance dynamically, mainly by power control. A repeater in the network may serve for enhancement of coverage or capacity. It interacts with the network paramters. Analysis is provided herein.
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Physical channel - Each timeslot on a carrier is referred to as a physical channel. Per carrier there are 8 physical channels.
Logical channel - Variety of information is transmitted between the MS and BTS. There are different logical channels depending on the information sent. The logical channels are of two types
Traffic channel
Control channel
BCH Channels
BCCH( Broadcast Control Channel )
Downlink only
Broadcasts general information of the serving cell called System Information
BCCH is transmitted on timeslot zero of BCCH carrier
Read only by idle mobile at least once every 30 secs.
SCH( Synchronisation Channel )
Downlink only
Carries information for frame synchronisation. Contains TDMA frame number and BSIC.
FCCH( Frequency Correction Channel )
Downlink only.
Enables MS to synchronise to the frequency.
Also helps mobiles of the ncells to locate TS 0 of BCCH carrier.
RACH( Random Access Channel )
Uplink only
Used by the MS to access the Network.
AGCH( Access Grant Channel )
Downlink only
Used by the network to assign a signalling channel upon successfull decoding of access bursts.
PCH( Paging Channel )
Downlink only.
Used by the Network to contact the MS.
PLCC: A promising futuristic technology!!!.. still in India we do not use it due to many reasons.... because PLCC, Power Line Carrier Communication, is an approach to utilize the existing power lines for the transmission of information.
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Builder.ai Founder Sachin Dev Duggal's Strategic Approach to Create an Innova...Ramesh Iyer
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GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
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https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
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All of this illustrated with link prediction over knowledge graphs, but the argument is general.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
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And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Software Delivery At the Speed of AI: Inflectra Invests In AI-Powered QualityInflectra
In this insightful webinar, Inflectra explores how artificial intelligence (AI) is transforming software development and testing. Discover how AI-powered tools are revolutionizing every stage of the software development lifecycle (SDLC), from design and prototyping to testing, deployment, and monitoring.
Learn about:
• The Future of Testing: How AI is shifting testing towards verification, analysis, and higher-level skills, while reducing repetitive tasks.
• Test Automation: How AI-powered test case generation, optimization, and self-healing tests are making testing more efficient and effective.
• Visual Testing: Explore the emerging capabilities of AI in visual testing and how it's set to revolutionize UI verification.
• Inflectra's AI Solutions: See demonstrations of Inflectra's cutting-edge AI tools like the ChatGPT plugin and Azure Open AI platform, designed to streamline your testing process.
Whether you're a developer, tester, or QA professional, this webinar will give you valuable insights into how AI is shaping the future of software delivery.
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Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
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We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
Let's dive deeper into the world of ODC! Ricardo Alves (OutSystems) will join us to tell all about the new Data Fabric. After that, Sezen de Bruijn (OutSystems) will get into the details on how to best design a sturdy architecture within ODC.
"Impact of front-end architecture on development cost", Viktor TurskyiFwdays
I have heard many times that architecture is not important for the front-end. Also, many times I have seen how developers implement features on the front-end just following the standard rules for a framework and think that this is enough to successfully launch the project, and then the project fails. How to prevent this and what approach to choose? I have launched dozens of complex projects and during the talk we will analyze which approaches have worked for me and which have not.
3. Transmission Lines
• A Vital Part of the Power System:
• Provide path to transfer power between generation and load
• Operate at voltage levels from 69kV to 765kV
• Deregulated markets, economic, environmental requirements
have pushed utilities to operate transmission lines close to their
limits.
4. Transmission Lines
• Classification of line length depends on:
Source-to-line Impedance Ratio (SIR), and
Nominal voltage
• Length considerations:
Short Lines: SIR > 4
Medium Lines: 0.5 < SIR < 4
Long Lines: SIR < 0.5
5. Typical Protection Schemes
Short Lines
•
•
•
•
Current differential
Phase comparison
Permissive Overreach Transfer Trip (POTT)
Directional Comparison Blocking (DCB)
6. Typical Protection Schemes
Medium Lines
• Phase comparison
• Directional Comparison Blocking (DCB)
• Permissive Underreach Transfer Trip (PUTT)
• Permissive Overreach Transfer Trip (POTT)
• Unblocking
• Step Distance
• Step or coordinated overcurrent
• Inverse time overcurrent
• Current Differential
7. Typical Protection Schemes
Long Lines
• Phase comparison
• Directional Comparison Blocking (DCB)
• Permissive Underreach Transfer Trip (PUTT)
• Permissive Overreach Transfer Trip (POTT)
• Unblocking
• Step Distance
• Step or coordinated overcurrent
• Current Differential
8. Introduction
• Nonpilot protection using overcurrent and distance relays, contain a
fundamental difficulty :
It is not possible to instantaneously clear a fault from both ends
of a transmission line if the fault is near one end of the line.
• Pilot protection is an adaptation of the principles of differential
relaying that avoids the use of control cable between terminals.
• The term ‘pilot’ refers to a communication channel between two or
more ends of a transmission line to provide instantaneous clearing
over 100% of the line.
• This form of protection is also known as ‘teleprotection’.
10. Pilot Communications Channels
• Distance-based pilot schemes traditionally utilize simple
on/off communications between relays, but can also utilize
peer-to-peer communications and GOOSE messaging over
digital channels
• Typical communications media include:
• Pilot-wire (50Hz, 60Hz, AT)
• Power line carrier
• Microwave
• Radio
• Optic fiber (directly connected or multiplexed
channels)
12. Pilot-Aided Distance-Based Schemes
DUTT – Direct Under-reaching Transfer Trip
PUTT – Permissive Under-reaching Transfer Trip
POTT – Permissive Over-reaching Transfer Trip
Hybrid POTT – Hybrid Permissive Over-reaching
Transfer Trip
DCB – Directional Comparison Blocking Scheme
DCUB – Directional Comparison Unblocking
Scheme
13. Direct Underreaching Transfer Trip
(DUTT)
• Requires only underreaching (RU) functions which
overlap in reach (Zone 1).
•Applied with FSK channel
• GUARD frequency transmitted during normal
conditions
• TRIP frequency when one RU function operates
• Scheme does not provide tripping for faults beyond RU
reach if remote breaker is open or channel is inoperative.
• Dual pilot channels improve security
15. Permissive Underreaching
Transfer Trip (PUTT)
• Requires both under (RU) and overreaching (RO)
functions
• Identical to DUTT, with pilot tripping signal supervised by
RO (Zone 2)
16. PUTT Scheme
Zone 2
Zone 1
To protect end of
line
Bus
Bus
Line
Zone 1
Zone 2
Rx PKP
Zone 2
Zone 1
&
Local Trip
OR
17. Permissive Overreaching Transfer
Trip (POTT)
• Requires overreaching (RO) functions (Zone 2).
• Applied with FSK channel:
• GUARD frequency sent in stand-by
• TRIP frequency when one RO function operates
• No trip for external faults if pilot channel is inoperative
• Time-delayed tripping can be provided
18. POTT Scheme
Zone 2
Zone 1
Bus
Bus
Line
Zone 1
Zone 2
(Z1)
Tx
Zone 1
(Z1)
OR
Rx
AND
Zone 2
t
o
Trip
Line
Breakers
19. POTT Scheme
POTT – Permissive Over-reaching Transfer Trip
BUS
BUS
End
Zone
Communication Channel
20. POTT Scheme Relay
Local
Local Relay
FW IGND
D
Local Relay – Z2
Remote Relay
FW IGND
D
Remote Relay – Z2
TRIP
Communication
Channel
POTT RX
Local Relay
ZONE 2 PKP
OR
Ground Dir OC Fwd
POTT TX
ZONE 2 PKP Remote Relay
OR
Ground Dir OC Fwd
22. POTT Scheme
Current reversal example
TRIP
Local Relay
GND DIR OC FWD
GND DIR OC REV
Timer
Start Communication
Expire
Timer
Channel
POTT RX
POTT TX
Remote Relay
ZONE 2 OR
GND DIR OC REV
GND DIR OC FWD
23. POTT Scheme
Echo example
Remote FWD
IGND
Open
Remote – Z2
OPEN
Communication
Channel
POTT RX
Local Relay
POTT TX
TRIP
POTT TX
POTT RX
Communication
Channel
Remote Relay
24. Hybrid POTT
• Intended for three-terminal lines and weak infeed conditions
• Echo feature adds security during weak infeed conditions
• Reverse-looking distance and oc elements used to identify
external faults
26. Directional Comparison Blocking
(DCB)
• Requires overreaching (RO) tripping and blocking (B)
functions
• ON/OFF pilot channel typically used (i.e., PLC)
• Transmitter is keyed to ON state when blocking
function(s) operate
• Receipt of signal from remote end blocks tripping
relays
• Tripping function set with Zone 2 reach or greater
• Blocking functions include Zone 3 reverse and low-set
ground overcurrent elements
29. Directional Comparison Blocking (DCB)
Internal Faults
Local Relay – Z2
FWD IGND
TRIP Timer
Start
Expired
TRIP
Zone 2 PKP
OR
NO
Local Relay GND DIR OC Fwd
Dir Block RX
Remote Relay
30. Directional Comparison Blocking (DCB)
External Faults
Local Relay – Z2
FWD IGND
TRIP Timer
Start
Remote Relay – Z4
REV IGND
No TRIP
Dir Block RX
Local Relay
Zone 2 PKP
OR
DIR BLOCK TX
Communication
Channel
GND DIR OC Fwd
Zone 4 PKP
OR
GND DIR OC Rev
Remote Relay
31. Directional Comparison Unblocking
(DCUB)
• Applied to Permissive Overreaching (POR) schemes
to overcome the possibility of carrier signal
attenuation or loss as a result of the fault
• Unblocking provided in the receiver when signal is
lost:
• If signal is lost due to fault, at least one
permissive RO functions will be picked up
• Unblocking logic produces short-duration TRIP
signal (150-300 ms). If RO function not picked
up, channel lockout occurs until GUARD signal
returns
34. Directional Comparison Unblocking
(DCUB)
Normal conditions
Load Current
FSK Carrier
GUARD1 RX
FSK Carrier
GUARD1 TX
Local Relay
NO Loss of Guard
NO Permission
GUARD2 TX
Communication
Channel
GUARD2 RX
Remote Relay
NO Loss of Guard
NO Permission
35. Directional Comparison Unblocking
(DCUB)
Normal conditions, channel failure
Load Current
Loss of Channel
FSK Carrier
NO RX
GUARD1 RX
FSK Carrier
GUARD1 TX
Local Relay
Loss of Guard
Block Timer Expired
Started
Block DCUB
until Guard OK
GUARD2 TX
Communication
Channel
GUARD2 RX
NO RX
Remote Relay
Loss of Guard
Block Timer Expired
Started
Block DCUB
until Guard OK
36. Directional Comparison Unblocking
(DCUB)
Internal fault, healthy channel
Local Relay – Z2
Remote Relay – Z2
TRIP
TRIP Z1
FSK Carrier
Local Relay
Zone 2 PKP
Loss of Guard
Permission
FSK Carrier
TRIP1 RX
GUARD1 RX
GUARD1 TX
TRIP1 TX
GUARD2 TX
TRIP2 TX
GUARD2 RX
TRIP2 RX
Communication
Channel
Remote Relay
ZONE 2 PKP
37. Directional Comparison Unblocking
(DCUB)
Internal fault, channel failure
Local Relay – Z2
Remote Relay – Z2
Loss of Channel
TRIP
FSK Carrier
Local Relay
Zone 2 PKP
TRIP Z1
FSK Carrier
NO RX
GUARD1 RX
GUARD1 TX
TRIP1 TX
GUARD2 TX
TRIP2 TX
GUARD2 RX
NO RX
Loss of Guard
Block Timer Started
Duration Timer Expired
Started
Remote Relay
ZONE 2 PKP
Loss of Guard
Communication
Channel
38. Redundancy Considerations
• Redundant protection systems increase dependability of the
system:
• Multiple sets of protection using same protection principle
and multiple pilot channels overcome individual element
failure, or
• Multiple sets of protection using different protection principles
and multiple channels protects against failure of one of the
protection methods.
• Security can be improved using “voting” schemes (i.e., 2-out-of3), potentially at expense of dependability.
• Redundancy of instrument transformers, battery systems, trip
coil circuits, etc. also need to be considered.
39. Redundant Communications
BUS
BUS
End Zone
AND Channels:
POTT Less Reliable
DCB Less Secure
OR Channels:
Communication Channel 1
Communication Channel 2
More Channel Security
POTT More Reliable
DCB More Secure
More Channel Dependability
Loss of Channel 2
41. Pilot Relay Desirable Attributes
•Integrated functions:
• weak infeed
• echo
• line pick-up (SOTF)
•Basic protection elements used to key the
communication:
• distance elements
• fast and sensitive ground (zero and negative
sequence) directional IOCs with current, voltage,
and/or dual polarization
Editor's Notes
Pilot schemes speed up the clearing of faults that occur on the transmission line and inside the end zone of the local relay by communicating with the relay at the remote end of the line to determine if the fault is actually on the transmission line.
Therefore, all pilot aided schemes require a communication channel be provided between the two relays. This communication between the relays can consist of a single channel or multiple channels depending on the particular application.
Over this communication channel, the two relays share information regarding the fault allowing the clearing of faults on the transmission line to occur as fast as possible.
Communication channels include power line carriers, Microwave radio channels, SONET channels to list a few. It is desirable to have a very secure and reliable communications channel for this purpose.
The most common Pilot aided schemes are :
The DUTT scheme, which stands for Direct Under-reaching Transfer Trip
The PUTT scheme which stands for Permissive Under-reaching Transfer Trip
The POTT scheme, which stands for Permissive Over-reaching Transfer Trip
The Hybrid POTT scheme which stands for the Hybrid Permissive Over-reaching Transfer Trip
The Directional Comparison Blocking Scheme
And the Directional Comparison Unblocking scheme
We will discuss the POTT, DCB and DCUB schemes in the following sections.
Direct Under-reaching Transfer Trip
Under-reaching units at each end.
Local Zone 1 PKP causes local trip
Under-reaching units transmit on operation
Received signal trips remote breaker
Permissive Under-reaching Transfer Trip
Under-reaching units at each end
Over-reaching units at each end
Under-reaching units transmit on operation
Received signal trips ONLY IF (permissive)
local over-reach element is operated
Trip = Local Zone 2 + Remote Zone 1
Permissive Over-reaching Transfer Trip
Designed for two terminal lines
Over-reaching units at each end
Over-reaching units transmit on operation
Received signal trips ONLY IF (permissive)
local and remote over-reach element have operated
Strategy:
Communications channel established between relays sending fault/no fault status to the other relay.
Both relays set up for zone 2.
If they both see the fault, the fault is on the line. If only one relay sees the fault, the fault is behind the other relay.
The POTT pilot aided scheme stands for the Permissive Over-reaching transfer trip scheme; and like other Pilot aided schemes, is used to speed up the clearing of faults that occur in the end zone of a transmission line.
As for all pilot aided schemes, a communication channel must be provided between the two relays located at each end of the transmission line for the POTT scheme to operate.
In the POTT scheme, the Remote relay speeds up the tripping of an end zone fault by sending a permission to Trip key from the Remote relay to the local relay under 2 circumstances.
----The first reason that the remote relay will send a Permissive key is when the it detects a fault occurring within it’s over-reaching zone 2.
This is where the expression “over-reaching” comes from in the term Permissive Over-reaching Transfer Trip.
---The second reason that the remote relay will send a permissive key is when it detects that ground directional overcurrent is flowing in it’s forward direction if this feature is enabled and configured.
-----Therefore either Negative sequence directional overcurrent Forward element or the Neutral directional overcurrent Forward element, if configured, will send a POTT key to the Local relay, if both are configured,----- as well as when the over-reaching zone 2 pickup flag turns ON
The Local relay POTT logic will only cause the breaker to trip ---if it gets the POTT key from the remote relay in the form of a receive AND, -----the local relay has detected a fault within it’s zone 2 area of protection
OR, -----it detects that ground directional current is flowing in it’s Forward direction if this function is configured
----Therefore either the local relay’s Forward Negative sequence directional overcurrent element or the Forward Neutral directional overcurrent element as well as the picking up of a Zone 2 fault, will cause the POTT scheme to trip the breaker if it receives a permissive key from the remote relay.
In conjunction with the Phase selector feature which determines which phase is faulted, the D60 distance elements can determine which phases of the transmission line are faulted.
Therefore, the Remote D60 has the ability, -----through the communication key signals, to let the Local D60 know which phases are actually faulted.
------If the breakers used on the transmission line have the ability to trip single pole, the D60 can trip only the faulted pole of the breaker based on the received fault type.
The POTT scheme in the UR D60 handles this signaling of which phase is faulted by having the ability of sending up to 4 different POTT key or transmit signals that are available in the relay.
Therefore, in order to fully utilize this feature the, scheme would need to have a communication channel between the relays that can share more than one bit of information.
If the communication channel you are using can only send and receive on piece of information such as a power line carrier can, which phase of the transmission line is faulted can not be sent and single pole tripping is less secure specially on evolving faults.
Some additional logic has been added to the POTT scheme to add extra security to transmission lines that are connected parallel to other transmission lines.
---For example if a fault had occurred on the paralleled transmission line as shown here, the local and remote relays will operate in the following way.
--The remote D60 will detect that ground current is flowing in it’s transmission line in the Forward direction, and send a permissive key to the Local relay.
---The local D60 will detect that ground current is flowing in its reverse direction. This reverse ground over-current detection does not meet the criteria defined by the POTT scheme and thus the Local relay will not Trip.
After a certain time period, the breaker on the parallel line correctly tripped to attempt to clear the fault. The ground current would now begin to flow through our transmission line in the opposite direction to feed that fault if the remote breaker on the opposite end if it did not open yet.
The local and the remote D60’s would now operate in the following way.
----First the Local D60 would have its Forward Negative Sequence Directional overcurrent identify current the current is flowing in the Forward direction.
----At the same time the the local D60 identified the change in direction of ground current, the remote D60 will identify this change as well.
However, due to the delay in the communications channel, the POTT permissive key will not immediately be removed.
Since the Negative sequence directional element of the local D60 indicates that the fault is in the forward direction and the local relay is still receiving the permission key, the POTT scheme will cause the breaker to trip,---- shutting down the transmission line when it did not need to be.
The POTT scheme has added one more feature to help to speed up the tripping of a faulted transmission line, if one of the ends is open.
If the breaker on the local end of the transmission line is open for any reason, the local D60 will not detect any current flow into the transmission line and therefore will not detect any faults within it’s zones of protection. If a fault did occur on the line, no key will be sent to the remote D60.
----If a fault occurred in the remote D60’s end zone as seen here,--- the remote D60 will detect the fault in it’s zone 2 and send the POTT key to speed up tripping of the local D60.
Since the local D60 will not send a key because it does not see the fault, the tripping of the remote breaker will not occur until zone 2 of that relay has timed out.
The additional logic in the POTT scheme which is called the Echo function works in the following way. The Local D60 must first detects that it’s own breaker is open. If it’s local breaker is open, and it receives a POTT key from the remote D60, ----it will send the POTT key sequence it received directly back to the remote relay. The local D60 is telling the remote D60 that it is ok to trip because the local end of the line is already open and clearing of the fault will be much faster, ensuring the system will not become unstable.
----The remote relay will then take this echoed POTT key and trip it’s breaker.
If the Echo function is going to be used, the Line Pickup protection element must first be configured. The description of the Line pickup function will be covered later in the course.
Typically applied on power line carrier. The line is sending the signal and is faulted therefor communications isn’t very reliable… we use this scheme even though it is slower then POTT because it will eventually trip line where as POTT requires a reliable comms. link.
Operation:
If local zone 2 operates and have not received a block from remote relay local relay will trip.
The Directional Comparison Blocking scheme that is available in the D60 is one of the most popular types of tele-protection schemes used in distance applications today.
The purpose of the scheme is to still speed up the tripping of faults that occur in the end zone of a transmission line, just like the POTT scheme.
As for all pilot aided schemes, a communication channel must be provided between the two relays located at each end of the transmission line for the Directional Blocking scheme to operate.
In the Directional Blocking scheme, the local D60 has an additional delay timer that is started by the detecting of a fault inside it’s zone 2 area of protection, or, ------the detection of ground current flowing in the forward direction. This timer is set considerably shorter than the normal zone 2 delay.
When this additional timer expires the Local D60 will trip the local breaker unless the------Local D60 receives a block message or key from the remote D60.
The remote D60 will only send this blocking key if it detects that the fault is located in it’s zone 4 area of protection, or, it detects that ground current is flowing in the reverse direction. Both of which, would indicate an external fault.
In the event that the communications channel failed, the local relay will misoperate. This is one of the disadvantages of the DCB scheme.
The Directional Comparison Unblocking scheme that is currently not available in the D60, but will be implemented in the near future.
This is a scheme that was developed to operate ONLY with FSK (Frequency Shift Keying) channels, like Power Line Carriers
The purpose of the scheme is to still speed up the tripping of faults that occur in the end zone of a transmission line, just like the POTT and DCB schemes.
As for all pilot aided schemes, a communication channel must be provided between the two relays located at each end of the transmission line for the Directional Comparison Unblocking scheme to operate. This channel is normally a single FSK power line carrier.
This scheme utilizes principles from the POTT and DCB schemes, making it the most reliable scheme when the communications channel is a power line carrier.