Switchgear

SWITCHGEAR

ii

TABLE OF CONTENTSTABLE OF CONTENTSTABLE OF CONTENTSTABLE OF CONTENTS 1. Scope ............................................................................................................. 1 2. General ......................................................................................................... 1 3. Service condition ......................................................................................... 1

3.1. Normal service conditions ....................................................................................... 1

3.2. Unusual service conditions ...................................................................................... 2

4. Definitions .................................................................................................... 2 5. Circuit breaker type .................................................................................... 6

5.1. Kinds of AC circuit breakers ................................................................................... 6

5.2. Application of circuit breaker type .......................................................................... 7

6. Selection of circuit breaker ......................................................................... 7 7. Selection of MCSG .................................................................................... 10

7.1. Design .................................................................................................................... 10

7.2. Rating ..................................................................................................................... 11

8. Selection of GIS ......................................................................................... 14 8.1. Design .................................................................................................................... 14

8.2. Rating ..................................................................................................................... 15

8.3. DS and ES .............................................................................................................. 18

8.4. Bus ......................................................................................................................... 18

8.5. CT .......................................................................................................................... 18

8.6. PT ........................................................................................................................... 18

8.7. The others ............................................................................................................... 18

9. Nameplates ................................................................................................. 19

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LIST OF TABLESLIST OF TABLESLIST OF TABLESLIST OF TABLES

< Table 1 > Application of circuit breaker type ................................................................ 7 < Table 2 > Rated voltage ................................................................................................. 7 < Table 3 > Rated insulation levels .................................................................................. 8 < Table 4 > Normal current, short-time withstand current and peak current ................... 8 < Table 5 > DC, AC voltage for control ........................................................................... 9 < Table 6 > Rated break time ............................................................................................ 9 < Table 7 > Rated voltage ................................................................................................ 11 < Table 8 > Rated insulation levels ................................................................................ 12 < Table 9 > Normal current, short-time withstand current and peak current ................. 12 < Table 10 > DC, AC voltage for control ....................................................................... 13 < Table 11 > Rated break time ........................................................................................ 13 < Table 12 > Rated voltage ............................................................................................. 15 < Table 13 > Rated insulation levels .............................................................................. 16 < Table 14 > Normal current, short-time withstand current and peak current ............... 16 < Table 15 > DC, AC voltage for control ....................................................................... 17 < Table 16 > Rated break time ........................................................................................ 17 < Table 17 > Rated insulation levels .............................................................................. 22 < Table 18 > Standard current ratings (A) ...................................................................... 23 < Table 19 > Example of fault capacity calculation ....................................................... 28 < Table 20 > Example of circuit breaker application ..................................................... 28 < Table 21 > Rated duration of short circuit ................................................................... 29 < Table 22 > Rated operating sequence in KEPCO ........................................................ 30 < Table 23 > Rated operating sequence .......................................................................... 30 < Table 24 > Application of other countries ................................................................... 30 < Table 25 > Rated break time ........................................................................................ 31

iv

LIST OF FIGURESLIST OF FIGURESLIST OF FIGURESLIST OF FIGURES

< Figure 1 > Circuit-breaker without switching resister .................................................. 5 < Figure 2 > Circuit-breaker with switching resister ........................................................ 6 < Figure 3 > Simulated power system for fault calculations .......................................... 24

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LIST OF APPENDIXLIST OF APPENDIXLIST OF APPENDIXLIST OF APPENDIX

A References 21

B Review of ratings for switchgear 22

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1. Scope This standard is applicable to selection of switchgear including their auxiliary equipment such as DS, LS and ES, GIS and MCSG designed for outdoor and indoor installations for the new 66kV, 30 kV substations. Also the ratings and types are selected among exiting commercial products

2. General a) The circuit breakers for the new 66kV substations shall be selected considering the

short circuit capacity of power systems, substation types, connection of relevant equipment, outgoing and incoming lines and so on

b) If the actual service conditions differ from these service conditions in installation site, circuit breakers associated operating devices and auxiliary equipment shall be designed in accordance with the any special service conditions required by the user.

c) Other information concerning classification of environmental conditions is given in IEC 60721-3-3 (indoor) and IEC 60721-3-4 (outdoor)

d) Also, in this standard, which is not mentioned about the specifications complies with the relevant standards.

3. Service condition a) Normal service conditions are specified or recommended that an agreement shall be

reached concerning alternative or additional technical solutions or procedures

b) Also, such agreement is to be made between the manufacturer and the purchaser. The matters should preferably be raised at an early stage and the agreements included in the contract specification.

3.1. Normal service conditions

The circuit breakers including the relevant equipment shall be installed at outdoor and indoor which shall be suitable for continuous operation at the below site conditions

Maximum altitude: 1 000 m (3 300 ft)

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Maximum ambient air temperature: + 50 C

Minimum ambient air temperature: -10 C

Monthly average temperature of the hottest month: + 40 C

Yearly average temperature: : + 30 C

3.2. Unusual service conditions Conditions other than those listed in above for the power transformer are considered to be unusual. And manufacturers should discuss with purchaser for the unusual service conditions

4. Definitions

Switchgear A general term covering switching devices and their combination with associated control, measuring, protective and regulating equipment, also assemblies of such devices and equipment with associated interconnections, accessories, enclosures and supporting structures, intended in principle for use in connection with generation, transmission, distribution and conversion of electric energy

Control-gear A general term covering switching devices and their combination with associated control, measuring, protective and regulating equipment, also assemblies of such devices and equipment with associated interconnections, accessories, enclosures and supporting structures, intended in principle for the control of electric energy consuming equipment

Indoor switchgear and control-gear Switchgear and control-gear designed solely for installation within a building or other housing, where the switchgear and control-gear is protected against wind, rain, snow, abnormal dirt deposits, abnormal condensation, ice and hoar frost

Outdoor switchgear and control-gear Switchgear and control-gear suitable for installation in the open air, i.e. capable of withstanding wind, rain, snow, dirt deposits, condensation, ice and hoar frost.

Metal-enclosed Switchgear (MCSG) Switchgear assemblies with an external metal enclosure intended to be earthed and

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completely assembled, except for external connections.

Gas-insulated metal-enclosed switchgear (GIS) Metal-enclosed switchgear in which the insulation is obtained, at least partly, by an insulating gas other than air at atmospheric pressure Note) Three-phase enclosed gas-insulated switchgear applies to switchgear with the

three phases enclosed in a common enclosure. Single-phase enclosed gas-insulated switchgear applies to switchgear with each phase enclosed in a single independent enclosure.

Gas-insulated switchgear enclosure Part of gas-insulated metal-enclosed switchgear retaining the insulating gas under the prescribed conditions necessary to maintain safely the highest insulation level, protecting the equipment against external influence and providing a high degree of protection to personnel

Short-circuit current An over-current resulting from a short circuit due to a fault or an incorrect connection in an electric circuit

Disconnect switch A mechanical switching device which provides, in the open position, an isolating distance in accordance with specified requirements

Earthing switch A mechanical switching device for earthing parts of a circuit, capable of withstanding for a specified time currents under abnormal conditions such as those of short circuit, but it is not required to carry current under normal conditions of the circuit. An earthing switch may have a short circuit making capacity.

Breaking capacity A value of prospective current that a switching device is capable of breaking at a stated voltage under prescribed conditions of use and behavior

Making capacity A value of prospective making current that a switching device is capable of making at a stated voltage under prescribed conditions of use and behavior

Short-circuit breaking capacity A breaking capacity for which the prescribed conditions include a short circuit at the terminals of the switching device

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Short-time withstand current The current that a circuit or a switching device in the closed position can carry during a specified short time under prescribed conditions of use and behavior

Opening time The opening time is the interval of time between the instant of energizing the opening release, the circuit-breaker being in the closed position, and the instant when the arcing contacts have separated in all poles. The opening time includes the operating time of any auxiliary equipment necessary to open the circuit-breaker and forming an integral part of the circuit-breaker.

Arcing time The interval of time between the instant of the first initiation of an arc and the instant of final arc extinction in all poles

Break time The interval of time between the beginning of the opening time of a mechanical switching device and the end of the arcing time

Make time The interval of time between energizing the closing circuit, the circuit breaker being in the open position, and the instant when the current begins to flow in the first pole

Closing time The interval of time between energizing the closing circuit, the circuit breaker being in the open position, and the instant when the contacts touch in all poles

Pre-arcing time The interval of time between the initiation of current flow in the first pole during a closing operation and the instant when the contacts touch in all poles for three-phase conditions

Open-close time (during auto-re-closing) The interval of time between the instant when the arcing contacts have separated in all poles and the instant when the contacts touch in the first pole during a re-closing cycle

Dead time (during auto-re-closing) The interval of time between final arc extinction in all poles in the opening operation and the first re-establishment of current in any pole in the subsequent closing operation

Re-closing time

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The interval of time between the beginning of the opening time and the instant when the contacts touch in all poles during a re-closing cycle

Re-make time (during re-closing) The interval of time between the beginning of the opening time and the first re-establishment of current in any pole in the subsequent closing operation

Close-open time The interval of time between the instant when the contacts touch in the first pole during a closing operation and the instant when the arcing contacts have separated in all poles during the subsequent opening operation

Pre-insertion time The interval of time during a closing operation in any one pole between the instant of contact touch in the closing resistor element and the instant of contact touch in the main breaking unit of that pole

< Figure 1 > Circuit-breaker without switching resister

Energizing of opening release

Separation arcing contacts in all poles

Final arc extinction in all poles Energizing of closing circuit

Start of current in first pole

Contact touch in first poles

Contact touch in all poles

Re-closing time

Dead time

Re-make time Open-close time

Closing time

Pre-arcing time

Make time

Break time

Arcing time

Opening time Time

Current flow Current flow

Open position

Closed position Contact movement

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< Figure 2 > Circuit-breaker with switching resister

5. Circuit breaker type A circuit breaker is a mechanical switching device, capable of making, carrying and

breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal circuit conditions such as those of short circuit

5.1. Kinds of AC circuit breakers The circuit breakers are classified according to the arc quenching media as following a) VCB (Vacuum Circuit-Breaker)

A circuit-breaker in which the contacts open and close within a highly evacuated envelope

Energizing of opening release

Separation arcing contacts in all poles

Full current

Arc extinction in all poles

Resister current

Contact touch in the closing resister Start of current in first pole

- Full current

Contact touch in first poles

Pre-insertion time

Energizing of closing circuit Contact touch in all poles

Re-closing time

Dead time

Re-make time Open-close time

Closing time

Pre-arcing time

Make time

Break time

Arcing time

Opening time Time

Current flow Current flow

Open position

Closed position Contact movement

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b) GCB (Gas Circuit-Breaker) A circuit-breaker in which the contacts open and close in gas such as SF6 gas

c) OCB (Oil Circuit-Breaker) A circuit-breaker in which the contacts open and close in oil

d) ABB (Air Blast circuit-Breaker) A circuit-breaker in which the contacts open and close through the compressed air

5.2. Application of circuit breaker type AC circuit breakers apply according to the nominal system voltages as shown in table bellow

< Table 1 > Application of circuit breaker type Nominal voltages (kV) Circuit breaker Remark

11 VCB Indoor MCSG type 30 GCB Indoor GIS type 66 GCB Outdoor AIS type

6. Selection of circuit breaker In this chapter, the characteristics of a circuit breaker including its operating devices and

auxiliary equipment for the primary side of the new 66 kV substation that shall be used to determine the ratings are the following a) Rated voltage

The rated voltage indicates the upper limits of the highest voltage of systems for which circuit breaker is intended

< Table 2 > Rated voltage Nominal voltage (kV) Rated voltage (kV) Remark

66 72.5 Outdoor type

b) Rated insulation level The rated insulation levels of the 66 kV circuit breakers are given as shown bellow

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< Table 3 > Rated insulation levels

Rated voltage (kV, rms)

Power-frequency withstand voltage (kV, rms)

Lightning impulse withstand voltage (kV, peak)

Common value Across the

isolating distance Common value

Across the isolating distance

72.5 140 160 325 375

c) Rated frequency The standard values for the rated frequency is 50 Hz

d) Rated normal current The rated normal current is the rms value of the current which the circuit breaker shall be able to carry continuously without deterioration at its rated frequency, voltage, with a temperature rise not exceeding the values specified in IEC 60694

e) Rated short-time withstand current The rms value of the current which the circuit breaker can carry in the closed position during a specified short-time (2s), the standard value shall be equal to the short-circuit rating assigned the circuit breaker

f) Rated peak withstand current The peak current associated with the first major loop of the rated short-time withstand current which the circuit breaker can carry in the closed position. For a rated frequency of 50 Hz and bellow it is equal to 2.5 times the rated short-time withstand current

< Table 4 > Normal current, short-time withstand current and peak current Rated voltages

[kV] Rated normal current [A]

Rated short-time withstand current [kA, rms]

Rated peak withstand current [kA, peak]

72.5 2,000, (400) 31.5 80 Note)

1. ( ) : For transformer bay 2. Normal current calculation of 66 kV switchgear

Based on ACSR 315 (a 66 kV feeder): 1,040 A90%(Utilization rate) = 936 (A). However, if we assumed the voltage drop by 0.5%, the current is 1,037A (9831.05), therefore, considering the sufficient margin. Set the rated normal current as 2,000 A

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3. Normal current calculation of transformer bay Based on 25 MVA: 219 A, therefore, considering the sufficient margin, set the rated

normal current as 400 A

g) Rated duration of short-circuit The interval of time for which circuit breaker can carry in the closed position, a current equal to its rated short-time withstand current. The standard values of rated duration of short-circuit is 2s

h) Rated supply voltage for control circuit The relative tolerance of AC and DC power supply in normal duty measured at the input of the auxiliary equipment is 85% to 110%

< Table 5 > DC, AC voltage for control DC voltage (V) AC 3, 3W or 4W system (V) AC 1, 2W system (V)

110 400 / 230 230

i) Rated operating sequence The rated operating sequence means successive operating conditions when the circuit breaker is closed and opened more than 1~2 times. For rapid auto-reclosing, the operating sequence is following below

j) Rated break time The rated break time is defined as the limit of the breaking time, under all ratings and regulations of circuit conditions, when the circuit breaker opens the rated short-time withstand current according to the rated operating sequence. The break time should not exceed the rated break time when the circuit breaker opens more than 30% of the rated short-circuit withstand current under the rated voltage

< Table 6 > Rated break time Rated voltage (kV) Rated break time (cycle) Remark

72.5 3

O 0.3s CO 3min - O

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7. Selection of MCSG In this chapter, the characteristics of a MCSG including its operating devices and auxiliary equipment for the secondary side of the new 66 kV, 30 kV substations that shall be used to determine the ratings are the following

7.1. Design

a) MCSG shall be designed so that normal service, inspection and maintenance operations, determination of the energized or de-energized state of the circuit breaker can be carried out safely

b) Also, all removable parts and components of the same type and rating shall be mechanically and electrically interchangeable

7.1.1. Earthing The earthing circuit is normally designed for a single short-circuit withstand.

a) Main circuit To ensure personnel protection during maintenance work, all parts of the main circuit to which access is required or provided shall be capable of being earthed prior to becoming accessible

b) Enclosure Each functional unit shall be connected to earthing conductor. All the metallic parts intended to be earthed and not belonging to a main or auxiliary circuit shall also be connected to the earthing conductor directly or through metallic structural parts. Also, the interconnection between the adjacent units shall be capable of carrying the rated short-time and peak withstand current for the earthing circuit

c) Removable parts The normally earthed metallic parts of a removable part shall remain connected to earth in the test and disconnected position and in any position. On insertion, the normally earthed metallic parts of a removable part shall be connected to earth prior to the making of the contacts of the fixed and removable parts of the main circuit.

7.1.2. Stored energy operation

a) A switching device arranged for stored energy operation shall be capable of making

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and breaking its rated short-circuit current

b) Motor and their electrically operated auxiliary equipment for charging a spring or for driving a compressor or pump shall operate satisfactorily between 85% and 110% of the rated supply voltage.

7.1.3. Interlocking Interlocks between different components of the equipment should be equipped for protections and convenience of operation.

a) The withdrawal or engagement of a circuit breaker, switch or contactor shall be prevented unless it is in the open position

b) Also, the interlock shall prevent the closing of circuit breaker, switch or contactor in the service position unless any auxiliary circuits associated with the automatic opening of these device are connected.

7.1.4. Enclosure

Enclosure shall be metallic and HV parts are completely enclosed by metallic partitions or shutters intended to be earthed. Also, the enclosure shall provide at least the degree of protection IP 2X, according to IEC 60694.

7.1.5. Compartment A compartment shall be designated by the main component therein, for example, circuit-breaker compartment, bus-bar compartment, cable compartment and so on.

7.2. Rating a) Rated voltage



11 12 Indoor MCSG type

b) Rated insulation level The rated insulation levels of the 11 kV MCSG are given as shown bellow

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Rated voltage kV, rms)






12 28 32 75 85









12 2000, (630) 25 63 Note)

1. ( ): For each 11 kV feeder 2. Normal current calculation for 11 kV MCSG

Based on 25 MVA (power transformer capacity): 1312 A, therefore, considering the sufficient margin, set the rated normal current of MCSG as 2000 A

3. Normal current calculation of a 11 kV feeder

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Based on XLPE 2403C(a 11 kV feeder): 363 A90%(Utilization rate) = 327 (A). However, if we assumed the voltage drop by 0.5%, the current is 343A (3271.05), therefore, considering the sufficient margin. Set the rated normal current as 630 A




110 400 / 230 230




12 5

O 0.3s CO 3min - O

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8. Selection of GIS In this chapter, the characteristics of a GIS including its operating devices and auxiliary equipment for the primary side of the new 30 kV substations that shall be used to determine the ratings are the following

8.1. Design a) GIS shall be designed so that normal service, inspection and maintenance operation,

earthing of connected cables, and the elimination of dangerous electrostatic charges can be carried out safely including the checking of phase sequence after installation and extension

b) Also, all components of the same rating and construction which may need to be replaced shall be interchangeable.

8.1.1. Component

GIS shall be composed with circuit-breaker (CB), dis-connector switch (DS), earthing switch (ES), bus, current transformer (CT), voltage transformer (VT or PT), bushing and lightning arrester (LA).

8.1.2. Requirement for gases in GIS The required quantity, quality and density of the gas to be used in GIS comply with the manufacturers recommendation.

8.1.3. Earthing The frame of each device of GIS shall be provided with a reliable earthing terminal having a clamping screw or bolt for connection to an earthing conductor suitable for specified fault conditions a) Main circuit

To ensure safety during maintenance work, all parts of the main circuit to which access is required or provided shall be capable of being earthed. Also earthing may be made by earthing switches with a making capacity equal to the rated peak withstand current, if there is still a possibility that the circuit connected is live (e.g. line earthing switch)

b) Enclosure The enclosures shall be connected to earth. All metal parts which do not belong to a main or an auxiliary circuit shall be earthed. For the interconnection of enclosures, frames, so forth, fastening (e.g. bolting or welding) is acceptable for providing

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electrical continuity.

8.1.4. Gas monitoring The gas density or temperature compensated gas pressure in each compartment shall be continuously monitored. The monitoring device shall be provide at least two sets of alarm levels for pressure or density (alarm and minimum functional pressure or density)

8.1.5. Interlocking a) Apparatus installed in main circuit, which are used for ensuring isolating distance

during maintenance work, shall be provided with locking facilities to prevent closing

b) Earthing switches shall be provided with locking facilities to avoid opening

c) Earthing switches should be interlocked with the associated dis-connector switch

d) Dis-connector switches should be interlocked with the associated circuit-breaker to prevent opening or closing of the switch or dis-connector switches unless the associated circuit breaker is open.

8.1.6. Enclosure

The enclosure shall be capable of withstanding the normal and transient pressures to which it is subjected in service.

8.2. Rating a) Rated voltage



30 36 Indoor GIS type

b) Rated insulation level The rated insulation levels of the 30 kV GIS are given as shown bellow

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Rated voltage kV, rms)






36 70 80 170 195









36 2000, (630) 31.5 80 Note)

1. ( ): For power transformer bay 2. Normal current calculation of 30 kV GIS

Based on XLPE 6301C (a 30 kV feeder): 811 A90%( Utilization rate) = 730 (A). However, if we assumed the voltage drop by 0.5%, the current is 767A (7301.05), therefore, considering the sufficient margin. Set the rated normal

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current as 2,000 A 4. Normal current calculation of transformer bay Based on 25 MVA: 481 A, therefore, considering the sufficient margin, set the rated

normal current as 630 A




110 400 / 230 230




36 3

O 0.3s CO 3min - O

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8.3. DS and ES The ratings and insulation levels for dis-connector and earthing switches comply with the < table 13>, 8.4. Bus

a) The main bus shall be formed as double bus, and each phase for bus composition shall be accommodated in one enclosure

b) Outgoing and branch buses shall be applicable to manufacturers specification unless the user requests for special specifications

8.5. CT

a) The insulation methods of CT applying to GIS shall be applicable to gas type CT or mold type CT

b) CTs shall be suitable for GIS structure, also, characteristics and ratings comply with the relevant specification

8.6. PT The insulation methods of PT applying to GIS shall be applicable to gas type PT or mold type PT

8.7. The others

a) SF6 GAS

Specification of SF6 gas using the insulation medium in GIS complies with IEC 60376

A gas compartment in GIS shall be divided up to pursue a convenience about the management of gas, minimize the faults range when the fault or extension of GIS occurs

Also, limit switches to monitoring the pressure condition and gas pressure gauges shall be settled at suitable places to supervise and check

b) Arrangement of GIS GIS shall be arranged considering the follow items

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Connection of relevant facilities such as the outgoing feeders, power transformers and so on

Final scale of substation and the plan for extension

The operation, inspection and check, maintenance work of substation 9. Nameplates

Switchgear and their operation devices shall be provided with nameplates which contain the necessary information. And for outdoor switchgear, the nameplates and their fixings shall be weatherproof and corrosion-proof

Also, technical characteristics on nameplates and in documents which are common to several kinds of high voltage switchgear shall be represented by the same symbols

Rated characteristics to be given all circuit breakers a) Rated voltage b) Rated insulation level c) Rated frequency d) Rated normal current e) Rated short-time withstand current f) Rated peak withstand current g) Rated duration of short-circuit h) Rated supply voltage of closing and opening devices and of auxiliary circuits i) Rated pressure of compressed gas supply and/or of hydraulic supply for operation,

interruption and insulation , as applicable j) Rated short-circuit breaking current k) Rated short-circuit making current l) Rated operating sequence

Rated characteristics to be given in the specific cases indicated below

a) Characteristics for short-line faults related to the rated short-circuit breaking current, for circuit-breakers designed for direct connection to overhead transmission lines and rated at 52 kV and above and at more than 12,5 kA rated short-circuit breaking current

b) Rated line-charging breaking current, for three-pole circuit-breakers intended for

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switching over-head transmission lines (mandatory for circuit-breakers of rated voltages equal to or greater than 72,5 kV)

c) Rated cable-charging breaking current, for three-pole circuit-breakers intended for switching cables (mandatory for circuit-breakers of rated voltages equal to or less than 52 kV)

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APPENDIX A: References

IEC 60694 Common specifications for high-voltage switchgear and control-gear standards

IEC 62271-100 High-voltage switchgear and control-gear : High-voltage alternating-current circuit-breakers

IEC 62271-102 High voltage switchgear and control-gearAlternating current dis-connectors and earthing switches

IEC 60071-1 Insulation Co-Ordination Part 1: Definitions, Principles and Rules Seventh Edition

IEC 60050-441 International Electro technical Vocabulary Switchgear, control-gear and fuses

IEC 62271-200 High-voltage switchgear and control-gear AC metal-enclosed switchgear and control-gear for rated voltages above 1 kV and up to and including 53 kV

IEC 62271-203 High-voltage switchgear and control-gear Gas-insulated metal-enclosed switchgear for rated voltages above 52 kV

KEPCO Substation Design Standard, Transmission and distribution electrical engineering-second

edition-by Dr C.R. Bayliss CEng FIEE

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APPENDIX B: Review of ratings for switchgear 1. Rated voltages

The rated voltage indicates the upper limit of the highest voltage of systems for which the switchgear is intended. Standard values of rated voltages are given below;

a) Series 3.6 kV 7.2 kV - 12 kV 17.5 kV - 24 kV - 36 kV - 52 kV 72.5 kV - 100 kV - 123 kV - 145 kV - 170 kV 245 kV

b) Series (Based on the current practice in north America) 4.76 kV 8.25 kV - 15 kV 25.8 kV - 38 kV 48.3 kV - 72.5 kV

2. Rated insulation level

The rated insulation level of switchgear shall be selected from the values given in tables. In this tables, the withstand voltage values applies at the standardized reference atmosphere specified in IEC 60071-1. For special service conditions, refer to the relevant standards


Rated voltage

(kV, rms)

Rated power-frequency withstand voltage (kV, rms)

Rated lightning impulse withstand voltage (kV, peak)




3.6 10 12 20 23 40 46

7.2 20 23 40 46 60 70

12 28 32 60 70 75 85

17.5 38 45 75 85 95 110

24 50 60 95 110

125 145 36 70 80 145 165

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170 195 52 95 110 250 290

72.5 140 160 325 375

100 150 175 380 440 185 210 450 520

123 185 210 450 520 230 265 550 630

145 230 265 550 630 275 315 650 750

170 275 315 650 750 325 375 750 860

3. Rated normal and short-time withstand current The values of rated normal currents and rated short-time withstand current shall be selected from the R 10 series, specified in IEC 60059. The R 10 series comprises the

number 1 1.25 1.6 2 2.5 3.15 4 5 6.3 8 and their products n10

< Table 18 > Standard current ratings (A)

1 1.25 1.6 2 2.5 3.15 4 5 6.3 8 10 12.5 16 20 25 31.5 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 12500 16000 20000 25000 31500 40000 50000 63000 80000 100000 125000 160000 200000

Note) 1. The steps may vary according to the equipment concerned, depending on their use or

properties 2. The selection of the values to be adopted should be considered in each case on its

merits and it may be found that there are good grounds for choosing 1.5 3 6 7.5 instead of 1.6 3.15 6.3 8

4. Example of rated short-time withstand current

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4.1. Simulated power system (all data assumed)

< Figure 3 > Simulated power system for fault calculations

G1 G2

Y

Y

Y

Y

Y

%Z 1 =j4.204, %Z 2 =j4.865, %Z 0 =j2.372

%Z 1 =j5.0 (at 100 MVA)

220/66 kV S/S

ACSR 330 2C (50 km) 220 kV #1T/L

66 kV #1T/L ACSR 2402C (15 km)

%Z 1 =0.042+j0.2025 (%/km)

%Z 0 =0.042+j0.3454 (%/km)

%Z 1 =j3.44 (at 100 MVA)

%Z 1 =0.0567+j0.2058 (%/km) %Z 0 =0.0494+j0.3471 (%/km)

66/11 kV A S/S %Z 1 =j9.77 (at 20 MVA)

11kV Line

Z 1 =Positive phase sequence impedance

Z 2 =Negative phase sequence impedance

Z 0 = Zero phase sequence impedance

Z 2 =Taken as equal to Z1

220 kV #2T/L ACSR 330 2C (45 km)

Y

Y Y

66 kV #2T/L ACSR 2402C (20 km)

66 kV #3T/L ACSR 2402C (25 km)

Y

66/11 kV B S/S

11kV Line

Y

66 kV #4T/L ACSR 2402C (30 km)

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4.2. Required data

a) Impedance data

b) Faults Calculation Equation by Percent Impedance

4.3. Calculation for three phase fault current : Consider only the Positive phase sequence impedance ( 1Z )

a) Impedance of bus in power plant Generators and Transformers are connected with series and two sets are composed of parallel

602.42

0.5204.42

% 111 jjjZZZ tg =+=+=

Generator: %Z 1 =j4.204, %Z 2 =j4.865, %Z 0 =j2.372 220 kV step up Tr: %Z 1 =j5.0 (at 100 MVA) 220 kV T/L: %Z 1 =0.042+j0.2025 (%/km), %Z 0 =0.042+j0.3454 (%/km) 220 / 66 kV Tr: %Z 1 =j3.44 (at 100 MVA) 66 kV T/L: %Z 1 =0.0567+j0.2058 (%/km), %Z 0 =0.0494+j0.3471 (%/km) 66 / 11 kV Tr: %Z 1 =j9.77 (at 20 MVA), convert into 100 MVA = 85.48100

2077.9 jj =

Three-phase faults calculation [ baseP = 100MVA]

baseS PZP =

13 %

100

Phase-to-phase faults calculation [ baseP = 100MVA]

SbaseS PPZP 3

12 2

3%100

23

==

Phase-to-ground faults calculation [ baseP = 100MVA]

baseg PZZZP

++=

2101 %%%

300

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b) Impedance of 220 kV #1T/L %Z 1 / km = 0.042 + j0.2025 and two circuits are composed of parallel.

0625.505.12

50)2025.0042.0(% 1 jkmjZ +=+=

c) Impedance of 220 kV #2T/L

%Z 1 /km = 0.042 + j0.2025 and two circuits are composed of parallel.

5563.4945.02

45)2025.0042.0(% 1 jkmjZ +=+=

d) Impedance of 220 kV bus in 220 kV substation

Impedance of bus in power plant + Impedance of 220 kV #1, 2T/L

)56.495.0()06.505.1()56.495.0()06.505.1(602.4% 1 jj

jjjZ+++

+++= = 602.4j + )62.90.2(

)6.908.22(j

j+

+=

602.4j + 0.750.0)62.90.2()62.90.2()62.90.2()6.908.22( jjj

jj+=

+

+

e) Impedance of 66 kV bus in 220 kV substation

Impedance of 220 kV bus in 220 kV substation + Impedance of 220 / 66 kV Tr 2bank

72.850.0244.3)0.750.0(% 1 j

jjZ +=++=

f) Impedance of 66 kV T/L

#1T/L, 54.143.02

15)2058.00567.0(% 1 jkmjZ +=+=

#2T/L, 06.257.02

20)2058.00567.0(% 1 jkmjZ +=+=

#3T/L, 57.271.02

25)2058.00567.0(% 1 jkmjZ +=+=

#4T/L, 09.385.02

30)2058.00567.0(% 1 jkmjZ +=+=

g) Impedance of 66 kV bus in 66/11 kV A substation

Impedance of 66 kV bus in 220 kV substation + Impedance of 66 kV #1, 2, 3T/L

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)12.121.0()72.850.0()/3#/2(#)/1(#)/3#/2(#)/1(#)72.850.0(% 1 jjLTLTLT

LTLTLTjZ +++=++

+++=

84.971.0 j+=

h) Impedance of 66 kV bus in 66/11 kV B substation Impedance of 66 kV bus in 66/11 kV A substation + Impedance of 66 kV #4T/L

93.1256.1)09.385.0()84.971.0(% 1 jjjZ +=+++=

i) Impedance of 11 kV bus in 66/11 kV B substation Impedance of 66 kV bus in 66/11 kV B substation + Impedance of 66 / 11 kV Tr 2bank

%Z 1 = (0.71 + j9.84) + 27.3471.0285.48)84.971.0(% 1 j

jjZ +=++=

Therefore,

AjkVP

ZI

ZI basebases 311,1510113

10100)27.3471.0(

10010113%

100%100

3

6

311

3 =

+=

==

4.4. Calculation for phase-to-ground fault current a) Zero phase sequence impedance (Z 0 )

Since the fault current cant go through the connections when a grounding fault occurs at power system, only consider Y connections Therefore, Zero phase sequence impedance at the fault point

43.242

85.480 j

jZ ==

b) Positive phase sequence impedance (Z 1 ) %Z 1 = 0.71 + j34.27

G 0gZ

0tZ 0lZ 0tZ 0lZ 0tZ

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c) Negative phase sequence impedance (Z 2 ) %Z 2 =Taken as equal to %Z 1

Therefore, ground-to-phase fault current can be calculated as shown.

baseg IZZZI

++=

210 %%%300

AP

jjjbase 931,16

10113)27.3471.0()27.3471.0()43.24(300

3=

++++=

4.5. Selection of the rated short-time withstand current

a) However, in a complicated network system, the handwork is not easy to calculate the faults current and impedance for selection of the rated short-time withstand current. Generally, computer programs are used to manage the network system continuously

b) The maximum fault current shall be selected large value between three phase fault current and phase-to-ground fault current, so that the maximum fault current shall be selected as 16,931 [A] according to the above results

c) Also, the fault capacity shall be calculated according to bellow equation as shown. IVP = 3

P: faults capacity V: rated voltage I: faults current

However, it is necessary to add the sufficient margin at the calculated fault capacity when adopting the circuit breaker

< Table 19 > Example of fault capacity calculation

Rated voltage (V)

Fault current (A)

Equation

)3( IV Fault capacity

(MVA) Adoption (MVA)

12,000 16,931 AkV 931,16123

352 420

< Table 20 > Example of circuit breaker application

Rated voltage (kV) Fault capacity (MVA) Rated short-time withstand current (kA) 12 420 20

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4.6. Rated duration of short circuit a) The rated duration of short circuit is the maximum time capable of carrying rated

short-time withstand current without any interruption

b) The international standards and applications are shown in the following table.

< Table 21 > Rated duration of short circuit

IEC ANSI Hydro-Quebec JEC Thailand / Vietnam (550 kV) KEPCO

345 kV 765 kV 1 sec 3 sec 1 sec 2 sec 1 sec 1 sec 2 sec

c) As shown in the table, the rated duration of short circuit is generally applied within 3

seconds and represents the mechanical strength of the material in the circuit breaker, which means that a longer conducting time needs more conductor insulating strength or a circuit breaker insulating medium

d) Therefore, the rated duration of short circuit usually decided to be within the limit of time that experiences no problems in protective coordination

4.7. Rated operating sequence a) The rated operating sequence means successive operating conditions when the circuit

breaker is closed and opened more than 1 ~ 2 times. In the IEC, the duty cycle is represented as follows:

O - t - CO - t' - CO t = 3 min for circuit breakers not intended for rapid auto re-closing

t = 0.3 sec for circuit breakers intended for rapid auto re-closing t' = 3 min, instead of t' = 3 min, other values t' = 1 min and t' = 15 sec are also used for

circuit breakers intended for rapid auto re-closing

CO - t'' - CO t'' = 15 sec for circuit breaker not intended for rapid auto-reclosing

O: represents an opening operation CO: represents a closing operation followed immediately by an opening operation

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< Table 22 > Rated operating sequence in KEPCO KEPCO

25.8 kV 170 kV and 362 kV 800 kV O-0.3s-CO-15 sec-CO O-0.3s-CO-3 min-CO O-0.3s-CO-1 min-CO

b) Selection of duty cycle When a fault occurs, the circuit breakers frequently repeat opening and closing operation in re-closing processes, and must be done without failure. Considering the rapid auto re-closing and applications, the duty cycle is recommended as shown the following table

< Table 23 > Rated operating sequence

Rated voltage (kV) Rated operating sequence Remark 12, 36, 72.5 O-0.3s-CO-3min-CO Rapid auto re-closing: 1time

c) Operating performance

A circuit breaker including its operating devices shall be capable of completing its rated operating sequence, and designed with a trip-free mechanism.

4.7. Rated break time a) The rated break time is defined as the limit of the break time, under all the ratings and

regulations of circuit conditions, when the circuit breaker opens the rated short-time withstand current according to the rated operating sequence and operating conditions

b) The rated break time should not exceed the rated break time when the circuit breaker opens more than 30 % of the rated short-time withstand current under the rated voltage. For reference, several applications are shown in the following table

< Table 24 > Application of other countries Rated voltage (kV) KEPCO Japan Thailand

Voltage (kV) 25.8 170 and 362 800 550 550 Rated break time (cycle) 5 3 2 2 2

c) For the break time of circuit breakers, a short break time is favorable with consideration of the prevention of fault spreading to the power system and the

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restriction of electromagnetic inductive disturbance

d) However, considering the economical efficiency, the rated break time recommended as shown the following table.

< Table 25 > Rated break time

Rated voltage (kV) 12 36 72.5 Rated break time (cycle) 5 3 3

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