re closer theory

Theory and Operating principle of

Recloser and

Sectionaliser

Department of Electrical and Electronics Engineering

National Institute of Technology Karnataka,

Surathkal, Mangalore

SOLVE

The Virtual Lab @ NITK Surathkal, Center for

System Design,

Funded by National Mission on Education through

Information and Communication Technology (NMEICT),

MHRD, Government of INDIA.

Recloser and Sectionaliser operation

Department of Electrical and Electronics Engineering, NITK. 2

TABLE OF CONTENTS

1.0 INTRODUCTION TO DISTRIBUTION PROTECTION .......................................................... 4

2.0 ELEMENTS OF DISTRIBUTION PROTECTION ................................................................ 5

2.1 FUSES: .......................................................................................................... 5

2.2 SECTIONALISERS: ........................................................................................... 7

2.3 AUTORECLOSER: .......................................................................................... 10

3.0 DISTRIBUTION PROTECTION AUTOMATION AND CONTROL .......................................... 15



LIST OF FIGURES

FIGURE 1: EXPULSION TYPE FUSE ................................................................................... 5

FIGURE 2: TIME/ CURRENT CHARACTERISTICS OF A) 20A K B) 20A T TYPE FUSE ................. 6

FIGURE 3: BLOCKS OF A REMOTE CONTROLLED SECTIONALISER ......................................... 8

FIGURE 4: MV DISTRIBUTION SECTIONALISER AND CONTROL BOX. ...................................... 9

FIGURE 5: SEQUENCE OF RECLOSER OPERATIONS .......................................................... 11

FIGURE 6: INTERNAL STRUCTURE OF AUTORECLOSER .................................................... 13

FIGURE 7: DISTRIBUTION POLE MOUNTED AUTORECLOSER .............................................. 14



1.0 INTRODUCTION TO DISTRIBUTION PROTECTION

Distribution system is the customer end servicing point which reflects the power utilitys

overall performance to the customer. The distribution network must be robust enough to

handle the load uncertainties and unexpected operating scenarios. Protection of distribution

feeders is important task as large load isolation due to continuous persisting fault reflects to

the loss in consumption of electrical power to the consumers and hence loss of revenue to

the utility. Protection system for distribution network must be capable enough to operate and

isolate only the faulted system elements at the earliest possible time without affecting the

remaining system to maintain reliable power to the load.

Generally utilities build ring feed network till the customer end point to ensure continuous

delivery of quality power. Initially at normal conditions loads would be fed from certain source

points and under certain contingency the other feed point which is normally open points

(NOP) would be closed to feed power from alternate distribution feeder. These distribution

feeders are protected with over current relays at substation end for phase and earth faults.

Additionally, high-set element is used to clear the close-end feeder faults with lesser time

delay. The high-set element also helps in preventing sympathetic tripping [3] along the

multiple feeders when serving distribution loads (particularly while feeding low inertia motor

loads). The distribution feeder planning process mainly concentrates on two aspects while

giving connection to a new consumer. Firstly, consumer connected load should not over load

the existing conductor/line and the voltage at the farthest end of the feeder should not be less

that the voltage limits defined in the regulations. Also as a part of protection requirement

auto-reclosers are strategically placed along the network to make sure that the far end feeder

fault is sensed and recloser operates within specified time. Further, based on the criticality of

load and feeder-span-sectionalisers are placed in strategic points to segregate the feeder

loads. The downstream protection and source reliability issues are met through different

fuses and sectionalisers along the distribution feeder. In the following sections we would

discuss how the distribution protection system can be automated for better performance.



2.0 ELEMENTS OF DISTRIBUTION PROTECTION

Generally distribution protection systems consists of

Substation overcurrent relays,

Autoreclosers,

Sectionalisers,

Fuses.

2.1 Fuses:

Fuse is a protective device connected in series with the circuit, which melts when current

passing through it exceeds a particular limit. A suitably selected fuse should open the circuit

by the destruction of the fuse element, eliminate the arc established during the destruction of

the element and then maintain circuit conditions open with nominal voltage applied to its

terminals, (i.e. no arcing across the fuse element).

Distribution protection fuse statistics reveal that majority of fuses used operate on the

expulsion principle, i.e. they have a tube to confine the arc, with the interior covered with de-

ionizing fiber and a fusible element as shown in below Figure 1.

1 Figure 1: Expulsion type fuse


Department of Electrical and Electronics Engineering, NITK.

The zone of operation is limited by two factors:

1. Lower limit based on the minimum time required for the fusing of the element

(minimum melting time)

2. Upper limit determined by

(maximum clearing time)

There are many standards to classify fuses acc

time/current characteristics, manufacturing features and other considerations. For

there are several sections of

600 V or less. For medium and high voltage fuses within the range 2.

such as IEEE C37.40, 41, 42, 46, 47 and 48 apply. Other organisations

their own standards; in addition, fuse manufacturers have their own classifications and

designations. In distribution system applications

fast and slow types, respectively, depending on the s

ratio is the ratio of minimum melt current that causes fuse operation at 0.1 s to the minimum

melt current for 300 s operation. For the K link, a speed ratio (SR) of 6

10-13 for T link [1]. The T type fuses are used along the main feeder lines and K

used at transformer linking loads.

time- current characteristics. W

its characteristics. The major disadvantage of the fuse is it is one time protective device.

Hence fuse saving techniques under certain fault conditions ar

autorecloser. It will be discussed further in the autorecloser section.

2 Figure 2: Time/ c

0.01

0.1

1

10

100

10

Tim

e i

n s

eco

nd

s


Department of Electrical and Electronics Engineering, NITK.

tion is limited by two factors:

ower limit based on the minimum time required for the fusing of the element

(minimum melting time).

pper limit determined by the maximum total time that the fuse take to clear the fault

(maximum clearing time).

standards to classify fuses according to the rated voltages/

time/current characteristics, manufacturing features and other considerations. For

there are several sections of ANSI/UL 198-1982 standards that cover low voltage fuses of

600 V or less. For medium and high voltage fuses within the range 2.3-138 kV, standards

IEEE C37.40, 41, 42, 46, 47 and 48 apply. Other organisations and countries have


distribution system applications, the use of fuse links designated K and T for

fast and slow types, respectively, depending on the speed ratio, is very popular. The speed


melt current for 300 s operation. For the K link, a speed ratio (SR) of 6-8 is defined

type fuses are used along the main feeder lines and K

used at transformer linking loads. Figure 2 shows a typical 20 A K and 20 A

We can observe discriminative operation of the fuse provided by

The major disadvantage of the fuse is it is one time protective device.

Hence fuse saving techniques under certain fault conditions are employed using

autorecloser. It will be discussed further in the autorecloser section.

: Time/ current characteristics of a) 20A K b) 20A T type fuse

100 1000Current in A

Fuse curves

20T

Type

6

ower limit based on the minimum time required for the fusing of the element

the maximum total time that the fuse take to clear the fault

ording to the rated voltages/currents,

time/current characteristics, manufacturing features and other considerations. For example,

1982 standards that cover low voltage fuses of

138 kV, standards

and countries have


, the use of fuse links designated K and T for

peed ratio, is very popular. The speed


8 is defined and SR of

type fuses are used along the main feeder lines and K type are

A T type fuse link

e can observe discriminative operation of the fuse provided by

The major disadvantage of the fuse is it is one time protective device.

e employed using

T type fuse

20T-Slow

Type



2.2 Sectionalisers:

Sectionalisers are medium/low voltage protective devices usually of single-pole type which

do not have fault interrupting capabilities. It is installed downstream of a MV overhead feeder

protected by a recloser/breaker. Sectionalisers count the operations of the backup device

during fault conditions. Counts are registered by the sectionaliser only when fault current flow

through the sectionaliser had been detected prior to the operation of the backup device. After

a given number of counts, as selected as a part of the sectionaliser setting, the sectionaliser

opens to isolate the faulted section of the line when the backup device is in the open position

and the section of line where the sectionaliser is located is in a deenergised state. The

objective of the sectionaliser to remain closed on temporary faults; the backup device will trip

and reclose to restore the line to service for such faults prior to the sectionaliser opening. For

permanent faults, the sectionaliser recognizes that one or more trips have occurred after the

backup device reclosed, and it subsequently opens to isolate the faulted portion of the line.

Modern day sectionalisers are programmed to sense the current, decide as a fault feed; the

upstream protective device operation (opening) is detected by the zero current flow through it

and then operates (opens). After the sectionaliser opens, the backup device automatically

recloses to restore to service that portion of the line up to the sectionaliser location.

Application of sectionalisers requires that the backup interrupting device be capable of

detecting faults in the sectionaliser zone of protection.

Selectivity of isolating the line section can thus be obtained by installing several

sectionalisers in series on a MV feeder. The tail end sectionaliser (which is farthest from the

recloser) will be opening on the first instance of current fault, then the preceding sectionaliser

opening on the second occasion and so on. These devices are commonly used in North-

American type distribution networks.

Figure 3 shows a typical arrangement [11] of a remote controlled sectionaliser with various

functional blocks in it. The sectionaliser control cubicle which can be placed on the pole

would be having the local control and remote control equipments. The electrical

measurements, mechanism control, RTU and modem can be accessed remotely which are

within the control cubicle. The motor driven SF6 switch along with antenna and various

instrument transformers will be placed along at the top of the distribution pole.



3 Figure 3: Blocks of a remote controlled sectionaliser

Sectionalisers can be operated remotely using different communication lines. Figure 4 shows

a typical remote controlled sectionaliser [11] which can be interfaced with substation

automation control center/ SCADA.



4 Figure 4: MV distribution sectionaliser and control box.



2.3 Autorecloser:

Autorecloser is a protective device with the ability to detect phase and phase-to-earth

overcurrent conditions, to interrupt the circuit if the overcurrent persists after a predetermined

time, and then to automatically reclose to re-energise the line. If the fault that originated the

operation still exists, then the recloser will stay open after preset number of operations, thus

isolating the faulted section from the rest of the system. In an overhead distribution system

between 80 to 95 per cent of the faults are of a temporary nature and last, at the most, for a

few cycles or seconds [1]. Thus, the recloser, with its opening/closing characteristic, prevents

a distribution circuit being left out of service for temporary faults. Typically, reclosers are

designed to have up to three open-close operations and after these a final open operation to

lock out the sequence. The counting mechanisms register operations of the phase or earth-

fault units which can also be initiated by externally controlled devices when appropriate

communication means are available. The operating time/current characteristic curves of

reclosers normally incorporate three-four curves based on the number of shots, one fast

(Definite time, extreme inverse (EI) or very inverse curves (VI)) and further delayed curves

(coordinated normal inverse (NI) or user defined IDMT curves). Most of the modern reclosers

give flexibility for the programmers to either program IEC 60255, ANSI/IEEE C37.112 or any

user defined time current characteristics. Curve settings, recloser settings and number of

recloser shots can be set different for phase and earth faults. This allows reprogramming of

the characteristics to tailor an arrangement to a customer's specific needs without the need

to change components. Co-ordination with other protection devices is important in order to

ensure that when a fault occurs, the smallest section of the circuit is disconnected to

minimize disruption of supplies to customers. Generally, the time characteristic and the

sequence of operation of the recloser are selected to co-ordinate with mechanisms upstream

towards the source. After selecting the size and sequence of operation of the recloser, the

devices downstream are adjusted in order to achieve correct co-ordination. Autoreclosers are

used to apply fuse saving schemes in distribution lines under transient fault conditions with

the help of fast curves. Further numerical autoreclosers are programmed to detect under

voltage, under frequency, live line protections. Directional elements can be enabled for ring

type feeders. Autoreclosers needs to be set with cold load pickup and inrush restraint

settings for better sensitivity.



A typical sequence of a recloser operation for a permanent fault is shown in Figure 5.

5 Figure 5: Sequence of recloser operations

Autorecloser instrument transformers continuously monitor all the phase currents, voltages,

neutral current (using earth current sensitive CTs) and frequency. Whenever fault is

identified, first shot is carried out in instantaneous mode to clear temporary faults before they

cause damage to the lines. This can be achieved using definite time characteristics, EI or VI

curves during high fault currents. Since it is known that most of the distribution feeder faults

are transient in nature, the instantaneous mode of recloser operation helps in saving the

downstream fuses during temporary faults. If the fault is cleared during the first recloser time

delay (first dead time delay), after the reclosing, the fuse would observe normal load current

thus saving the fuse blow. The later shots operate on time delayed curve which are set

based on the coordination (discrimination time delay) of fuse/recloser whichever is present

downstream and upstream of the autorecloser. If the fault is permanent, the time-delay

operation allows other protection devices nearer to the fault to open (sectionalisers / fuses),

limiting the amount of the network being disconnected. Earth faults are less severe and more

in number than phase faults and, therefore, it is important that the recloser has an

appropriate sensitivity to detect them. One method is to use CTs connected residually so that

the resultant residual current under normal conditions is approximately zero under perfectly

balanced loading condition; however the settings are set considering the probable unbalance

condition in the feeder load. The other method of detection is using core balanced CTs to



detect most sensitive earth faults. The recloser should operate when the residual current

exceeds the setting value, as would occur during earth faults.

Single-phase reclosers are used when the load is predominantly single-phase. In such a

case, when a single-phase fault occurs the recloser should permanently disconnect the

faulted phase so that supplies are maintained on the other phases. Three-phase reclosers

are generally recommended to avoid single-phasing of three-phase motors and potential

ferroresonance [2].

Reclosers are fitted with breakers operating on either hydraulic or electronic type operating

mechanisms. Reclosers with hydraulic operating mechanisms have a disconnecting coil in

series with the line. When the current exceeds the setting value, the coil attracts a piston that

opens the recloser main contacts and interrupts the circuit. The time characteristic and

operating sequence of the recloser are dependent on the flow of oil in different chambers.

The electronic type of control mechanism is normally located outside the recloser and

receives current signals from a CT-type bushing. When the current exceeds the

predetermined setting, a delayed shot is initiated that finally results in a tripping signal being

transmitted to the recloser control mechanism. The control circuit determines the subsequent

opening and closing of the mechanism, depending on its setting. Reclosers with electronic

operating mechanisms use a coil or motor mechanism to close the contacts. Vacuum and

SF6 reclosers have the advantage of requiring less maintenance. The electronic control also

provides a wide range of accessory enhancements to meet the specific needs of the user.

Reclosers are designed to use either oil or vacuum as the interrupting medium. Their

operators are magnetic, so that they are rated for many more operations than traditional oil-

type reclosers. Reclosers are used because their cost is generally less than conventional

breakers and separate relays. Figure 6 shows the internal structure of a typical vacuum

interrupter autoreclosers [12]. It can be observed that facility of local mechanical pullout

switch to bypass the complete recloser operations.



6 Figure 6: Internal structure of Autorecloser [12]



When installing reclosers it is necessary to take into account the following factors:

System voltage.

Short-circuit level.

Maximum load current.

Minimum short-circuit current within the zone to be protected by the recloser.

Co-ordination with other mechanisms located upstream towards the source and

downstream towards the load.

Sensitivity of operation for earth faults.

The voltage rating and the short-circuit capacity of the recloser should be equal to or greater

than, the values that exist at the point of installation. The same criteria should be applied to

the current capability of the recloser in respect of the maximum load current to be carried by

the circuit. It is also necessary to ensure that the fault current at the end of the line being

protected is high enough to cause operation of the recloser. Since autoreclosers are used at

distribution feeders, care must be taken for restraining cold load pickup [10] and magnetizing

inrush currents [10] of the downstream transformers. Figure 7 shows the picture of a pole

mounted autorecloser [12] with control cubicle.

7 Figure 7: Distribution pole mounted autorecloser



3.0 DISTRIBUTION PROTECTION AUTOMATION AND CONTROL

Distribution protection automation requires huge data compilation when compared to

transmission network automation. This is because of large number of load details, their

connected phase if single phase loads, different line and cable type data along the line till the

last load point, protection elements along the complete line including the type and fuse

location, settings involved in different protection elements, normal open points and positions

of such points (RMUs) along the feeder.

Distribution protection automation refers to inter linking the protection elements along the line

with the control center so that data and command/request signal exchange can be done

between the elements. Local control center can be arranged in the substation for all the

feeders emanating from the substation. Further one more level of automation control can be

arranged in the vicinity of the distribution company which has higher control authority for all

the substations. Distributed topology has better performance than the centralized topology in

terms of automation architecture [6]. In hardware implementation side, RTU based topology

[6] along with decentralized topology of ring connection of bay modules are well appreciated

in the industry.

For interlinking different elements of protection automation equipments suitable

communication can be established between them. Digital communication is divided into three

main elements. They are

1. The protocol, consisting of the hardware, such as connectors, connector pin

functions, and signal ,

2. The format, consisting of the control of the flow of data,

3. The language or how the information in the data flow is organised.

During the early evolution of automation control, manufacturers of the automation

communication equipments developed proprietary protocols so that the user need to buy the

complete set of equipments with the same manufacturer. Protocols were also dependent on

the number of conductors used and the format of data transfer (serial or parallel).

Considering the advantages of serial communication over parallel communication over long

runs, there are many popular serial communication protocols. Few of them are:

1. RS232C protocol

2. RS485 protocol

3. IEC 60870-5 protocol



The most common protocols in use conform to the International standard organization 7 (ISO

7) layer model of a network. This model is internationally recognised as the standard for the

requirements for communications between data processing systems.

A recent protocol, the Utility Communications Architecture v2.0 (UCA v2.0), seeks to

overcome these handicaps by adopting an object-oriented approach to the data held in a

measurement/control device, plus an internationally recognised protocol (ISO 9506) in the

application layer. Data objects and services available within a device follow a specified

naming system. The client can extract a description of the data objects that a device can

supply, and services that it can perform, so that it is easier to program the client. Scaling

factors and units for data items are built into the self-description, so that the effort required

during commissioning is reduced. Devices are not interchangeable, in the sense that a

device from one manufacturer cannot be removed and replaced by a device of similar

functionality from another vendor. Rather, this protocol ensures interoperability; that is the

ability for devices from different suppliers and of different functionality to communicate

successfully with each other. The transport protocol has been separated from the application

protocol, so problems with register addresses, etc. no longer exist. All that has to be

addressed is the transport protocols used, and clients will normally be able to communicate

with devices using one of a number of common transport protocols. This standard has an IEC

equivalent, IEC 61850. To begin with, IEC 61850 covers only the field of substation

automation, but will gradually be extended to cover the same fields as UCA v2.0.

Manufacturers are increasingly moving away from protocols with a proprietary element in

them to UCA v2.0/IEC 61850. It is likely that within a short time, most protection and control

devices will use one or other of these standards for communications. One important reason

guiding this change is that these standards permit the use of the XML language for exchange

of data between databases. As the information stored in an automation system or control

centre comprises a series of databases, information exchange is therefore facilitated.

Also, it is to be noted that testing of the automation equipments needs to be done at different

levels and a self diagnostic program needs to be always ready to run and detect the faulty

operations within the automation control equipments.

Many programs can be loaded with the control centre for better usage of the system

equipments. Since most of the protection equipments have metering facility, load data can be

precisely monitored and recorded for feeder load analysis. With the help of load details at

feeder level, electricity theft details, feeder wise billing and collection data, area wise load



pattern for the time of day, cost of serving different area/consumer categories can be

analyzed and calculated. These data would help the utility to optimize the revenue collection.

Further by maintaining the precise database of different equipment failures, different

manufacturer can be rated based on the onsite service of the equipments. Since the loads

can be monitored and controlled at very high sensitive readings i.e.at sectionaliser level, load

shedding because of under frequency or based on the quality of load served can be done

remotely.

re closer theory

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