09-1 Teleprotection Fundamentals

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2012-09-17

Sec 09-1 Teleprotectin Fundamentals

Course CHP592 - FOX515





2012-09-17Course CHP592 - FOX515


Teleprotection is:

A discipline between protection and telecommunication.

Sometimes under responsibility of the protection organization, sometimes under the responsibility of the

communication organization.

Sometimes a barrier between the communication engineer and the protection engineer (on customer’s and

on supplier’s site !)

Teleprotection is used:

Mainly at production and transport level where the distances of the transmitted power and short-circuit

currents are much larger than at the distribution level. The requirements for network stability are also

much more in the transport power systems.

At low and medium voltage levels (distribution level) distance protection is usually used without

Teleprotection.

Arguments for Teleprotection:

Minimization of material damage and reduction in time and extent in case of failures

Keeping up the supply and distribution of electric power as long and as well as possible under all

circumstances

At the production and transport level, clearance of line faults must be absolutely selective and faults mustbe cleared within the shortest possible time, so called zone 1 time of the Protection Device.



2012-09-17Course CHP592 - FOX515


A Protection System in a Power Network includes the fol lowing elements:

•The Circuit Breaker to isolate the faulty part

•The Protection Device to detect the fault via Current- and Voltage Transformer and to give the order

to trip the Circuit Breaker

•The Telecommunication and the Teleprotection equipment to transfer the trip to the other end of the

Power Line

A Teleprotection equipment is:

•The interface between Protection Device and telecommunication system

•A converter of the signal from the Protection Device into a signal suitable to transmit over a

telecommunication link

For analog channels FSK modulation is used, for digital channels CODING of different models is applied.

The Teleprotection Unit is also multiplexing several command signals into one telecom channel.

A Telecommunication System is:

•A PLC, an optical Multiplexer, a Microwave or a direct link using a copper wire or an optical fiber



2012-09-17Course CHP592 - FOX515


On this slide the two different signal families used in Teleprotection are listed:

Continuous signals are:

Longitudinal current differential

Phase comparison

Command type signals on/off are:

permissive tripping

direct intertripping

blocking

directional comparison



Here you see different protection schemes which are using telecommunication

COMMUNICATION IS ESSENTIAL in the following Protection schemes using quantitative signal

information:

Phase comparison

Longitudinal current differential

These applications are absolutely selective

COMMUNICATION IS ESSENTIAL in the following Protection schemes using ON/0FF information:

Permissive overreach distance

Blocking Distance

These applications are relatively selective

COMMUNICATION IS SUPPLEMENTARY in the following Protection schemes using ON/0FF information:

Permissive underreach distance

Accelerated distance

2012-09-17Course CHP592 - FOX515




2012-09-17Course CHP592 - FOX515


The distance line Protection Devices use different zones to detect line faults.

The stepped time and distance characteristic of the line protection system provides main protection of the

line section in Zone 1 as well as back-up protection of the adjacent Busbars in Zone 2.

At the production and transport level, clearance of line faults must be absolutely selective and faults must

be cleared within the shortest possible time ,so called ZONE 1 TIME.

For example with the underreaching mode, without command transmission, the distance protection

cannot clear all faults in the protected line section within the zone 1 time. Faults near the ends of the line

section will be cleared at zone 2 time, with additional delay. This is often acceptable at the distribution

level, where fast reclosure is not required.

Fast coordinated tripping at the ends of the protected line section reduces the effect of short circuit current

on network stability as well as the stressing of the plant and finally permits fast auto reclosure.

Absolutely selectivity and fast fault clearance for any fault position on the protected line section requires

Teleprotection between the ends of the line.

Consequently, the reliability of the line protection depends largely on the reliability of the communication

link.

Protective communication links are often duplicated on important lines to improve the reliability of tripping

on internal faults.



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2012-09-17Course CHP592 - FOX515


PUTT mode is used in Line Protection were the protected section is more than about 20 km long.

In PUTT mode the zone 1 of the Protection Device is set to underreaching for example 85 percent of the line section

without delay. Zone 2 is set for example to 120 percent of the line section and is time delayed of for example 200

milliseconds

The sequence of events for thi s example is:

• A fault occurs at point F in zone 1 of Protection Device RBC, zone 1 has no time delay.

•The line is switched off without any delay by the Circuit Breaker in station B.

• At the same time an permissive tripping command is sent to station C by means of the Teleprotection equipment.

•The Protection Device RCB in station C has already detected a fault in Zone 2 which is time delayed for example of

200 milliseconds

• Additional after a transmission time delay of typical 10 milliseconds the tripping command is received by Protection

Device RCB in station C and the zone 2 t ime is accelerated to zone 1 time.

•The Circuit Breaker in station C is tripping the power line without any additional delay

In case the fault happens in the common part Zone 1 of both Relay protection, the relays trip the breakers without

waiting for the command of the Teleprotection.

Advantage: Faster than POTT und Blocking mode

Disadvantage: Not selective for short lines

Without Teleprotection the breaker in station C would be activated only in the zone 2 time after for example 200

millisecond and therefore auto reclosure of the power line is not assured. As the zone 2 is overreaching the section

of the protected line, the selectivity would be not accurate without the communication.



2012-09-17Course CHP592 - FOX515


POTT mode is used in Line Protection were the protected section i s less than about 20 km long or

on Power Lines where PUTT mode can not be set.

In POTT mode the zone 1 of the Protection Device is set to overreaching for example 130 percent of the

line section. It has a AND logic therefore both Protection Device must detect the fault in the first zone and

must receive the trip from the opposite Teleprotection equipment. Only in this case tripping in first zone

time is possible.

The sequence of events of the example is:

• A fault F1 is detected by Distance Relays RBC and RCB. The trips are send to both ends of the line

section via Teleprotection equipment.

•The Relays in station B and station C receiving the tripping command. As they are already started by the

fault detection the AND logic is fulfilled and circuit breakers in station B and C trip in zone 1 time.

•A fault F2 is only detected by distance Relay RCB. Distance relay RBC is not sending a tripping signal to

the Station C therefore relay RCB will not trip the Breaker C in zone 1 time.

Advantage: POTT mode has a high selectivity and prevents tripping of a healthy line section in zone 1

time.

Disadvantage: It is slower than the PUTT mode because of any fault within the protected section will have

the time delay of the Teleprotection equipment. Without telecommunication no tripping in zone 1 is

possible.



2012-09-17Course CHP592 - FOX515


The Blocking mode for Line Protection may work for any length of the protected line section.

The Zone 1 time is delayed of for example 10 millisecond and is adjusted overreaching for example 130%

of the protected line section. Reverse zone towards the Busbars is set for example to -40 percent.


The fault F1 is detected by Distance Relays RBC and RCB in there Zone 1. After countdown of the delay

time both Protection Devices in Station B and C will trip the breakers.

The fault F2 is detected by Distance Relay RBC in Zone 1, the delay counter starts counting down. The

Protection Device RCB is detecting a fault in the reverse Zone and sends through Teleprotection link a

blocking signal DO NOT TRIP to the Protection Device RBC. If this happens within the delay time of Zone

1, the relay will not trip the Breaker.

Blocking mode was developed for PLC which is using the Power line to communicate.

Advantage: Blocking command is only transferred if the line fault is out of the PLC section and the line for

communication is clean.

Disadvantage: The first zone is always time delayed for example of 10 milliseconds; if Teleprotection fails

zone 1 is not selective any more

In new projects the Blocking mode is not used



Breaker Failure Protection is needed to assure the function of the protection system in case of a Line

Breaker failure .

The local Protection Devices for Busbars, Earth fault and Distance Protection are connected to the Line

Breaker. In case of a faulty Breaker the Substation can not be isolated from the power network.


The Breaker control system blocks the opening of the Breaker “B” if the SF6 gas pressure is low.

Trips from the local Protection system are diverted by the breaker control to the Teleprotection equipment.

Through the communication channel “L” the tripping command is transferred to the station “C” where the

Line Breaker opens and isolates the power flow to station “B”.

Remark:

To assure high security and dependability the processing time in the direct tripping feature is longer.

Therefore the total transmission time of the Teleprotection system is more than in the Distance Protection

for Permissive and Blocking mode.

2012-09-17Course CHP592 - FOX515




This a example for direct transfer tripping where the transformer is connected to the system without a

Circuit Breaker:

Line faults from station “A” up to connection of transformer at station “B” are protected by distance relay at

station “A” in overreaching mode.

Faults in station “B” within and beyond the transformer detected by a Buchholtz or a Busbar Protection

Device are transferred to the circuit breaker at “A” by means of the Teleprotection direct tripping signal.

2012-09-17Course CHP592 - FOX515




Configurable settings in the Teleprotection equipment are the followings:

Security is the ability of a equipment to prevent interference and noise from producing unwanted

commands

Dependabil ity is the abil ity of a equipment to issue and receive wanted commands in the presence

of interference and noise

Transmission time is the time elapsed between the instant of change of state at the transmitter

input and the instant of the corresponding change of state at the receiver output .

Bandwidth is the total frequency range or bit rate util ized by the Teleprotection equipment.

In Permissive and Blocking schemes the processing time has to be short and therefore the overall

transmission t ime is also shor ter. In the Direct t ripping applications the Security and Dependabilitymust be high, therefore the processing and transmission time will be longer.

2012-09-17Course CHP592 - FOX515




All these impairments may cause unwanted or missing commands

In case of interference and noise, more processing time will be needed: -The

feature “adaptive transmission time” will act in the Teleprotection equipment

In case of excessive interference and noise, processing time would be too long and commands not save.

To prevent incidents the Teleprotection unit can take different actions:

-Puts in operation the feature “Unblocking”

-Activates Contact Freezing for continuous commands

-Extends the zone 1 of distance Protection Device in PUTT mode from underreaching to overreaching with

the help of the alarm contacts of the Teleprotection equipment

–Blocks the command outputs of the Teleprotection equipment

2012-09-17Course CHP592 - FOX515




On this diagram the available transmission parameters of Teleprotection equipment are shown:

The transmission time is the delay between the moment a command initiated on the input of

Teleprotection equipment until this command is received at the output of the Teleprotection equipment on

the other end of the protection system

The Tx Input delay is used in direct tripping mode to make the system more save against EMC

interference. With this parameter the command is sent delayed by the Teleprotection equipment at the

input side.

The Tx and Rx trip duration time can be limited in Permissive tripping applications. With this parameter,

the duration of the command coming from the Protection Device can be increased, decreased or fixed by

the Teleprotection command.

The Rx trip prolongation time is the delay from the moment the transmission of a command from the input

of the transmitting Teleprotection equipment stops until the receiver contacts of the receiving

Teleprotection equipment are deactivated

2012-09-17Course CHP592 - FOX515




This example is valid for permissive tripping scheme and a Power Frequency of 50 Hertz

The total fault clearance time is the sum of the Protection Device processing time, the Transmission Time

of the Teleprotection equipment and the switching time from the Circuit Breaker.

2012-09-17Course CHP592 - FOX515




2012-09-17Course CHP592 - FOX515


If the Teleprotection equipment is connected to a digital network the addressing facility has to be used. In

the worst case mixed up cross connections without using addressing could cause tripping of a wrong

Circuit Breaker and a wrong Power Line!

In the example in place B, if by mistake of the administrator or the failure of the multiplexer the command

of one of the protection devices goes over a wrong communication line, the remote breaker will not trip

because of the addressing facility.



This summary shows you the Teleprotection products from the ABB portfolio

2012-09-17Course CHP592 - FOX515




In this slide you see the layout of a protection system for an important transmission line.

On this type of critical line, most of the protection equipment are doubled. We speak about Main 1 System

and Main 2 System.

2012-09-17Course CHP592 - FOX515




2012-09-17Course CHP592 - FOX515

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09-1 Teleprotection Fundamentals

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