Advanced_Protection_APAP_WG_B5_07_Korea_2009.pdf

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Abstract-- CIGRÉ WG B5-07 was formed to produce adocument entitled "Modern techniques for protecting andmonitoring transmission lines". The WG members decided tooffer a summary of their work for the benefit of the conferenceand to the industry. Transmission line intelligent electronicdevices (IEDs) include a large number of additional protectionelements and control functions, which provide the user with anunlimited amount of flexibility to design secure and dependableprotection and control schemes. Traditional pilot relayingschemes require separate protection and monitoring devices withcostly external communication equipments. Modern transmission

line IEDs integrate many flexible protection, control andmonitoring features including communications functionalitywithin the same hardware and provide relay-to-relay digitalcommunications for high-speed line protection, monitoring, andcontrol. Novel, more secure and dependable protection, controland monitoring applications are now possible with transmissionline IEDs including the relay-to-relay communications capability.In this paper, we discuss new protection, control and monitoringapplications with a special focus on telecommunication assistedfeatures used in this modern technology.

Index Terms— Transmission line protection, Functionalintegration, Communication, Control, IEDs, Metering,Synchrophasors.

I. INTRODUCTION

ODERN transmission line IEDs offer significant

number of functional improvements over previous

generations and technologies. The new state of the art of

modern transmission line protection with its multifunctional

integrated capability provides an unprecedented flexibility in

transmission protection principles, control and monitoring

schemes. This paper discusses some improved techniques

related to filtering techniques for fast fault elimination time;

new transmission line protection techniques backed with many

application examples using different levels of integration with

faster and more reliable communications to share synchronizeddata between IEDs within the same substation or between

IEDs in different substations.

WG Contributors: S.R. Chano (CA)-Convenor; J. Afonso (PT)-Secretary; A.

Menon (CH); S. Sofroniou (GR); D. Tziouvaras (USA); Alexander Apostolov

(US); Florin Balasiu (RO); Gareth Baber (UK); Juan Maria García (ES);

Kenneth Opskar (NO); Denys Lellys (BR); François L’Homme (FR); Graeme

Topham (ZA); Leif Koppari (SE); Kai Kühl (CH)

II. PROTECTION, CONTROL & MONITORING

(1) Modern Transmission Line

Protection

A transmission line protection IED must provide a highly

selective protection system that is immune to changes in the

surrounding power system. Applications to two and three

terminal lines, cables and transformer feeders should also be

supported. The device must provide adequate protection with

or without a communications channel to the remote end of the

transmission line. The integration of many functions allowsapplication to a wide range of electrical power systems,

providing both local and remote backup protection.

Protection IEDs often perform as universal metering, control

and recording devices. They provide multiple communications

interfaces which allow them to become the servers in an

integrated substation automation system over a substation

LAN.

One of the main goals in today's extremely competitive utility

environment is to switch from scheduled to event driven

maintenance. A universal protection IED can significantly help

in achieving this goal, by providing tools which monitor the

substation primary equipment and indicate, as necessary, therequirement for specific maintenance actions.

All of the above listed requirements are taken into

consideration in the concept of a Universal Transmission Line

Protection IED.

(2) Universal Transmission Line

Protection IED

A universal transmission line protection IED should be

designed for the protection of a wide range of overhead lines

and underground cables and for both sub-transmission and

transmission voltage levels. It should also include a

comprehensive range of non-protection features to meet the

requirements for substation and power system integration andaid the user with power system diagnosis and fault analysis

facilities. All these features should be accessible locally,

through the substation LAN or remotely through one of the

IED’s serial communications ports.

(3)Integrated Protection and Control Features

A transmission line protection IED must support multiple

integrated protection and control elements to meet the

requirements for primary and backup applications. Phase

Modern Techniques for Protecting and

Monitoring Transmission linesS.R. Chano, Hydro-Québec(CA); J. Afonso, REN(PT); A. Menon, ABB(CH);

S. Sofroniou, HTSO (GR); D. Tziouvaras, SEL(USA)

M



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current differential protection – Phase segregated restrained

differential protection- Distance protection – Overcurrent

protection – Stub bus protection- CB failure protection –

Two-stage CB fail protection. Direct/permissive inter-trip –

Independent inter-tripping facility using the device’s

protection communications channels – Dual redundant

communications – Option for dual communications channels

to provide a high degree of security. Protection

communications supervision – Voltage transformersupervision – To prevent maloperation of voltage dependent

protection elements upon loss of a VT input signal – Current

transformer supervision– Programmable scheme logic –

Allowing user-defined protection and control logic to suit

particular customer applications – Autoreclosing schemes

Integrated for three phase or single/three phase multi-shot

autoreclose applications – Check synchronism capability –

Local/remote measurements – Various measurement values

from the local and remote line ends available for display on the

device or accessed from the serial communications –

Fault/event/disturbance records – Fault locator features –

Synchro-phasor measurements – Real time clock/time

synchronization through IRIG-B input – CB state monitoring –CB control - CB condition monitoring – Remote serial

communications – Continuous self-monitoring – Power on

diagnostics and self checking routines to provide maximum

device reliability and availability.

(4)Protection & Control Applications

R

T

S

1

2

3

L1 L2

4

G1

T1 T2

S

Relay 1

S

5

Relay 5Relay 2

6

Relay 6

Relay-to-RelayCommunications

Figure 1.0 - Blocking High-speed Reclosing for CB Failure

Conditions or to Avoid an Out-of-Synch Reclosing

Attempts

In figure 1.0 , a fault occurs inside Transformer T1, and CB 2

fails to trip at Station T. For this fault, CB 1 at Station R must

open due to the CB failure condition of CB 2 at Station T andnot be allowed to reclose. In a traditional protection scheme, a

separate direct transfer trip is applied between Stations R and

T to perform the above function. Relay-to-relay

communications capability between relays of L1 and L2 in

conjunction with relay programmable logic can be used to

send a direct transfer trip from Station T to Stations R and S

during CB failure conditions at Station T and block reclosing

at the remote stations.

Let us now consider a fault on L1 for which CB 1 at Station R

and CB 2 at Station T open to clear the line fault, and at the

same time a mal-operation occurs at Station S, which opens

CB 6. If high-speed reclosing is applied on both CBs of L1

without any other considerations, there is a possibility to

reclose out of synchronism with generator G1 and cause

considerable damage to the generator. For this scenario, using

relay-to-relay communications and programmable logic, we

can design a protection scheme at Station T to detect L2

tripping at the remote Terminal S, block high-speed reclosing

of CB 2 at Station T, and transmit a reclose blocking bit toblock high-speed reclosing of CB 1 at Station R in order to

prevent possible damage to Generator G1. Slow-speed

reclosing from Station R, followed by CB 2 closing at Station

T with synch-check and slip frequency supervision, allows the

two systems to parallel and improves system reliability.

(5) Auto-reclosing with Secondary Arc Extinction Recognition

A secondary arc extinction detector, in single-pole tripping

applications, could supervise the closing signal to the CB to

prevent auto-reclosing when the secondary arc is still present

and minimize the possibility of unsuccessful reclosings.

Complete reclosing relay supervision requires three secondaryarc extinction detectors, one per phase. These detectors

measure the angle, φ, between the phase-to-ground voltage of

the faulted phase (Vγ) and the sum of the sound-phases phase-

to-ground voltages (VΣ). For -β ≤ φ ≤ β, and | Vγ | > Vthre, the

detector determines the secondary arc extinction and asserts

the SAED bit. Vthre and β determine the region that detects the

secondary arc extinction. Table 1 shows the Vγ and VΣ

voltages for A-, B-, and C-phase SAEDs.

Table 1.0 - Vγ and VΣ Voltages for A-Phase, B-Phase,and C-Phase SAEDS

Detector Vγ γγ γ VΣΣΣΣ

A-phase VA VB + VC

B-phase VB VC + VA

C-phase VC VA + VB

Figure 2. and Figure 3. show that Vγ is inside the SAED region

and the angle φ = 0° during an A-phase single-pole open

condition, after the secondary arc extinguishes. The A-phase

detector asserts the SAED bit for this condition, allowing the

reclosing sequence to continue.

Vγ = V

A

VB

VC

VΣ = V

B + V

C



3

Figure 2.0 – Vγ is inside the SAED region after the arc extinguishes

0.5

1

1.5

30

210

60

240

90

270

120

300

150

330

180 0

Prefault

Fault

Secondary ArcPresent

Secondary ArcExtinguishes

Figure 3.0– A-phase voltage phasor enters the SAED region after the

secondary arc extinguishes

Figure 7. shows the close supervision logic using secondary

arc extinction detection (SAED) for close supervision. The

SAED can minimize the dead time by initiating the reclose

after the secondary arc extinguishes. The SAEDD time delay

provides time for the air formerly occupied by the arc to regain

dielectric capabilities.

SAEDClose

Enable

SAEDD

DO

ReclosingRelaySupervision

Secondary ArcExtinction Detection(SAED)

Figure 4.0 – Reclosing relay close supervision using secondary arc extinction

detection

(6) CB and Station Bypass-CB Bypassing (Substitution)

Different bus arrangements are used in a power network

depending on service reliability requirements, economical

considerations, switching flexibility, and equipment

maintainability. The main and transfer bus arrangement

provides a low-cost solution for switching lines to a transfer or

auxiliary bus, usually to perform maintenance on the line CB.

The transfer bus is rated to feed only one serviced line at a

time. It has been implemented mostly in North America and it

is preferred on sub-transmission applications for its practicality

and low cost.

The double-bus single-CB configuration has two main buses

that are equally rated. This arrangement allows any circuit to

be connected via isolator switches to either bus. A bus parallel

(coupler) CB connects the two buses together and

sectionalizing CBs divide the bus in sections. Each feeder CB

is equipped with a bypass switch and isolator switches to

facilitate CB maintenance. The bus parallel (coupler) CB isused temporarily to protect any of the feeder or transformer

bank circuits when the actual feeder or bank CB is taken out

for maintenance. During the CB substitution, one bus becomes

part of the feeder circuit with all other circuits connected to the

remaining bus, increasing power availability in case of bus

faults. This bus configuration delivers a good compromise

between reliability and flexibility on one hand and economical

considerations on the other.

CB substitution is a switching operation which is used to

isolate a CB for maintenance while maintaining its circuit

energized. The system in figure 5.0 shows a simple double-bus

single-CB arrangement with a bus-tie (coupler) CB. Feeder 2and Feeder 3 could be served by either Bus 1 or Bus 2

depending on which isolator switches are closed.

Figure 5.0 – Double-bus single-CB configuration

In a double-bus single-CB or a main and transfer bus

arrangements, the relay systems installed on the bus-tie CB are

used to protect a transmission line when the line CB is out-of-

service for maintenance. In such an arrangement, the

performance of the protection is degraded unless the

communications channel used for high-speed line protection is

rerouted to the bus-tie CB protection system. This was almost

impossible with earlier electromechanical and static relay

systems. Modern numerical relays having multiple settings

together with intelligent communications channel fibre-optic

transfer switches can be used to maintain high-speed pilot line

protection and system stability and integrity during CB

maintenance.

Let us assume that we desire to maintain CB3 while Feeder 3

is connected to Bus 1. System operators will switch all feeders



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to Bus 2 except Feeder 3 which will be connected to Bus 1.

The bus-tie CB and its isolators are closed connecting the two

buses together. Just before the bypass switch of CB3 is closed,

the operator enables the distance and directional ground

overcurrent relays on the bus-tie CB, and takes out-of-service

the distance protection (21), line differential protection (87L),

and the pilot protection channels of Feeder 3. Distance (21)

and directional ground overcurrent (67N) relays on the bus-tie

CB are now protecting Feeder 3 and Bus 1 which is now partof Feeder 3. The protection of Feeder 3 has now been

compromised because high-speed pilot protection is out-of-

service on Feeder 3 during the duration of CB3 maintenance

that could last several days.

IEDs together with intelligent fibre-optic transfer switches can

be applied to prevent the above mentioned protection

compromise while maintain high-speed protection of Feeder 3

when CB CB3 is maintained. This is illustrated with Figure 6.

and Figure 7. where we show a normal system where the

communications channels of Feeder 2 and Feeder 3 are routed

to the multiplexer via a fibre-optic transfer switch.

Figure 6.0 – Feeder communications channels routed via a fiber-optic switch

IEDs and intelligent fibre-optic transfer switches can be

applied to:

• Maintain high-speed transmission line protection by

communications assisted tripping schemes (POTT,

DCB, DCUB, 87L) during CB maintenance.

• Maintain Main 1 and Main 2 high-speed protection

communications during CB maintenance operations

on main-bus transfer-bus or double-bus single-CBconfigurations.

• Automatically change group protection settings on the

bus coupler relays to accurately match the bypassed

CB relay protection settings.

• Quickly and cleanly reroute any communications

protocol carried on the IEEE C37.94 fibre-optic

interface standard without changing communications

equipment programming.

• Reroute current differential communications or any

synchronous communications converted to the IEEE

C37.94 interface standard.

Figure 7. shows the switching of pilot communications

channels to the bus coupler CB during maintenance of Feeder

3 CB CB3.

Figure 7.0 – CB3 bypassed while Feeder 2 is protected by the bus coupler CB

(CB1)

(7.0) Substation topology and auto-reclosing

applications

The substation layout has a large impact on the integrated AR

function in transmission line protection and its associated

synchro-check functions. Some application examples arepresented below.

(7.1)Double Busbar arrangement

In such kind of layout, Main 1 and Main 2 multi-function

protection relays, the BBP including the BFP and the

teleprotection equipment normally providing two independent

physical channels A and B. Main 1 protection is related to trip

coil 1, while Main 2 is related to trip coil 2. For reclosing

purposes several philosophies could be used as for example:

external separate AR relay started by both Main 1 and Main 2,

internal AR function used by both Main 1 and Main 2 or each

Main 1 and Main 2 use their corresponding internal AR

function. In case of the latter one “master-follower” logic

could be used or the logic based on time delay discrimination.

(7.2)Common External AR

This is a standard arrangement where the AR function could be

located in a Bay Controller. Figure illustrates the various

functions starting AR. Both Main 1 and Main 2 work with the

AR function. The Synchrocheck function is also along with the

AR function in the same numerical terminal. This arrangement



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results in optimum CB related signal requirements besides the

choice of Main 1 and Main 2 from different manufacturers.

Figure 8.0 – AR Function in Main 1 / Main 2

When there is no common numerical terminal housing the AR

function, the function has to be duplicated in the Main

protection terminals itself. Otherwise, loss of a numerical

terminal would take away the reclosing facility possible with

the second Main terminal. It has to be ensured that at any point

of time, only one AR function should have the authority to

issue the reclose command lest different dead times from the

two functions attempt improper reclose upon permanent faults

etc.

There are two different approaches, one approach wherein

only one AR function is active while the other AR is inblocked state whereas the second approach where in both AR

functions are active but only one is allowed to issue reclose.

The first approach is termed Main – Hot standby and the

second approach termed Redundant. This approach eliminates

need for AR functionality in separate hardware besides the

choice of Main 1 and Main 2 from different manufacturers.

However, primary requirements are twice since there are two

AR functions besides additional binary inputs/outputs in the

protection terminals.

The sketches below illustrate the two approaches.

(7.3)Main – Hot Standby

If the AR in Main 1 terminal is Main, then both Main 1 and

Main 2 protections work with this AR function. The AR in

Main 2 terminal as hot standby is kept blocked and is

automatically released by a logic formed out of Main 1

terminal out of service / Test mode or if the Synchrocheck

function is blocked due to a VT MCB failure. In such a

situation, the AR in Main 2 works with its own protection. The

AR in Main 2 working with Main 1 protection is an option.

Instead of a fallback approach, it is also possible to maintain

flexibility in choice of AR between Main 1 and Main 2 by

keeping connections between Main 1 protection and AR in

Main 2. This approach eliminates need for AR functionality in

separate hardware besides the choice of Main 1 and Main 2

from different manufacturers.

Figure 9.0 – Main AR with hot standby

(7.4)Redundant, Master-Follower

Both Main 1 and Main 2 protections work with their own AR

functions. In order to ensure that both AR functions choose the

same type of dead time even upon contradictory protection

operation, the Main 2 signal “Trip three pole” is also

connected to Main 1 AR function. One AR is termed Master

and the other Follower. If Main 1 AR is Master, upon

occurrence of a fault, even if Main 2 operates faster, its AR

function is on hold by the Master AR. However, there has to

be a co-ordination of reclose commands and only one ARfunction shall issue the close command to CB.

The Follower AR is released only after a certain fixed time

after Master AR issues reclose command. If fault persists,

Master AR issues “AR Unsuccessful”. If fault is transient,

Follower AR is released but then shall not issue any reclose

signal. Hence an additional signal comprising of above two

conditions called “Inhibit Output” is sent from Master to

Follower AR and vice versa.

This approach is more suited for Protection/ AR function

terminals from same manufacturer because of the special

signal above



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Figure 10.0 – Redundant AR, Master/Follower

(7.5)Two IEDs with two AR functions

A potential block diagram for such an arrangement is shown infigure 10.0. For proper operation some data exchange is

needed between the two AR functions in case of applying the

logic based on time delay discrimination. This logic applies for

both AR functions to be started by their own allowed

protection functions and the first reclosing command blocks

the other AR function, discrimination being time based. Thus

one AR dead time is a little bit longer and is pre-assigned

usually to Main-2. If the first AR function fails to operate for

one reason, the second one from Main-2 will still operate and

reclose the CB.

Each multi-function relay has to be able to trip single-pole the

CB and to reclose it. For multi-pole faults the trip should be

three-pole.

III. CONCLUSIONS

The integration in modern transmission line protection of

programmable logic, digital relay-to-relay communications,

math capability, and their proper application improves the

security, dependability, and speed of protection systems. As a

result, it improves the reliability of the overall power system.

The addition of synchrophasor measurement in a distance relay

results in increased power system reliability and provides

easier disturbance analysis, protection, and control capabilities.The integration of control functions in the IEDs like

autoreclosing or synchrocheck functions simplifies the

physical wiring in the installation and, in some cases, it

improves their performance.

As for the cases of many other fields, in protection as well a

re-orientation and re-engineering must always be in mind.

Frontiers between studies and site, between protection and

control, protection and operation now do not exist. Engineers

must collaborate, designing intelligent systems and with

synergy, achieving better results, saving money, time and

respecting the environment as well! They must think integrated

solutions, where protection systems, SCADA systems,

recordings or data logger systems, telecommunication systems,

RTU systems, metering systems, control systems, PLC systems,

maintenance systems and algorithms are combined, and finally

can be executed by common devices. In order to fight the

dependability to one device, two systems, based in different

algorithms and principles may be installed assuring

redundancy, flexibility, extensibility, security, high speed, fastreactions hence less possibilities for energy shortages or black

outs, stability, economy, optimization, friendship to

environment, saving room, capitals and manpower. Moreover,

the analyzed auxiliary functions of the IEDs offer usually tools

for executing power system appraisal and system operation

benchmarking, in the new de-or re-regulated competitive

environment, approaching finally the system (total) quality.

Therefore the new term for the protection relays as IEDs or

smart system units is more successful, as we have realized

from the preceded analysis that the so-called non-protective or

auxiliary functions of the IEDs are as much as the

conventional ones and at least of the same importance and

usefulness.

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Advanced_Protection_APAP_WG_B5_07_Korea_2009.pdf