mv switchboards

MEDIUM VOLTAGE SWITCHBOARDS

A Compilation by

Virendra Sahdev

What is MV Switchboard

AC Metal-enclosed Switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV

Relevant Standards IEC 62271- 200, Edition 1.0 2003-11 : High-

voltage switchgear and controlgear – AC metal- enclosed

switchgear and controlgear for rated voltages above 1 kV

and up to and including 52 kV IEC 60694, Edition 2.2, 2002-01: Common

specifications for high-voltage switchgear and controlgear

standards IEC 60815 : Guide for the selection of insulators

in respect of polluted conditions IEC 60060-1, Edition 3.0 2010-09: High-voltage

test techniques– Part 1: General definitions and test

requirements

Standard Ratings Standard Rated Voltages Range I for rated voltages of 245 kV

and below: 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.

Range II for rated voltages above 245 kV

300 kV – 362 kV – 420 kV – 550 kV – 800 kV.

Rated Insulation LevelsRATED

VOLTAGE UrKV (rms)

Rated short duration Power Frequency withstand voltage

- Ud KV (rms)

Rated Lightning Impulse withstand Voltage - Up

KV (peak value)

Common Value

Across Isolating distances

Common Value

Across Isolating distances

3.6 10 12 20 2340 46

7.2 20 23 40 4660 70

12 28 32 60 7075 85

17.5 38 45 75 8595 110

24 50 60 95 110125 145

36 70 80 145 165170 195

52 95 110 250 290

Standard Ratings Rated frequency (fr) The standard values of the rated

frequency are 16 2/3 Hz, 25 Hz, 50 Hz and 60 Hz.

Rated normal current (Ir) The values of rated normal currents

should be selected from the R 10 series, specified in IEC 60059 i.e. 1 – 1,25 – 1,6 – 2 – 2,5 – 3,15 – 4 – 5 – 6,3 – 8 and their products by 10 to the power n.

Limits of Temperature & Temperature Rise

Nature of part Maximum Temp. degrees

C

Temp. Rise at ambient

air Temperatur

e not exceeding 40 degrees

CContacts bare Cu or bare Cu alloy in air 75 35Contacts Silver or Nickel Coated in air 105 65Contacts Tin Coated in air 90 50Connections- bare Cu, bare Cu Alloy or bare Al alloy in air

90 50

Connections- Silver or Nickel Coated in air 115 75Connections- Tin Coated in air 105 65Terminals for External Connection - bare 90 50Terminals for External Connection – Silver , Nickel, Tin coated

105 65

Accessible parts – to be touched in normal operation

70 30

Accessible parts – not to be touched in normal operation

80 40

Standard Ratings Rated short-time withstand current (Ik) In accordance with the R 10 series comprises

the numbers 1 – 1,25 – 1,6 – 2 – 2,5 – 3,15 – 4 – 5 – 6,3 – 8 and their products by 10 to the power n.

Rated peak withstand current (Ip) For a rated frequency of 50 Hz it is 2.5 times

the rated short-time withstand current, and for a rated frequency of 60 Hz it is 2.6 times the rated short-time withstand

Rated duration of short circuit (tk) Standard value : 1 Second; Recommended values : 0.5 , 2 and 3 seconds.

Rated voltages of Closing & Opening devices and Auxiliary & Control Circuits

Rated Voltage (Us) : DC Voltages: 24, 48, 60, 110 or 125, 220 or 250 A C Voltages:

3 Phase, 3 wire or 4 wire systems V

1 ph; 3 wire systems V

1 ph; 2 wire systems V

- 120/240 120120/208 - 120

( 220/380 ) - (220)230/ 400 * - 230 *(240/ 415) - (240)277/ 480 - 277347/ 600 - 347

1. The voltage 230/ 400 V will be in future the only standard voltage

2. The voltages of 220/380 & 240/415 should be brought in 230/400 +/- 10% V.3. Tolerance : 85% to 110%

MV Switchboards Major Power Components

M V Circuit Breakers : Vacuum Circuit Breaker SF6 Circuit Breaker MV Isolator with/ without Fuses MV Contactor Earthing Switch

M V Circuit Breaker The circuit breaker is a device that ensures the

control and protection on a network. It is capable of making, withstanding and interrupting operating currents as well as short-circuit currents.

Compulsory rated characteristics Rated voltage Rated insulation level Rated normal current Rated short-time withstand current Rated peak withstand current Rated short-circuit duration Rated supply voltage for opening and closing devices and auxiliary circuits Rated frequency Rated short-circuit breaking current Rated transient recovery voltage Rated short-circuit making current Rated operating sequence Rated time quantities.

ABB VCB – Vmax

ABB VCB – Vmax Vmax/ L 12 12KV, 630/1250A, 16/20/ 25/31.5KA for 3 sec; 665 mm (Height) X 461 mm (Width) X 665mm (Depth) Vmax/ W 12 : 12KV, 630/1250A, 16/20/ 25/31.5KA for 3 sec; 665 mm (Height) X 503 mm (Width) X 662mm (Depth) Vmax/ L 17 : 17.5 KV, 630/1250A, 16/20/ 25/31.5KA for 3 sec; 665 mm (Height) X 461 mm (Width) X 665mm (Depth) Vmax/ W17 : 17.5 KV, 630/1250A, 16/20/ 25/31.5KA for 3 sec; 665 mm (Height) X 503 mm (Width) X 662mm (Depth)

ABB VCB – VD4

ABB VCB – VD4Characteristic

VD4/P 12

VD4/P 12

VD4/P 12

VD4/ P17

VD4/ P17

VD4/ P17

VD4/ P24

VD4/ P24

Rated Voltage – Ur, KV

12 12 12 17.5 17.5 17.5 24 24

Rated Normal Current – Ir, A

630/ 1250

1600/ 2000

2500 630/ 1250

1600/ 2000

2500 630/ 1250

1600/ 2000

Rated short time withstand current – (3-s) – Ik, KA

16, 20, 25, 31.5

20, 25, 31.5

20, 25, 31.5

16, 20, 25, 31.5

20, 25, 31.5

20, 25, 31.5

16, 20, 25

16, 20, 25

Hieght- mm 632 690 690 632 690 690 794 794

Width - mm 503 653 853 503 653 853 653 653

Depth - mm 664 642 642 664 642 642 802 802Pole centre Distance - mm

150/ 210

210 275 150/ 210

210 275 275 275

ABB HD4 - SF6 BREAKER

Identification of ABB HD4 - SF6 BREAKERHD

Version CBE/CBF C

UNIGEAR ZS1 TYPE PPOWER CUBE/ UNIGEAR ZS2 TYPE W

UNIGEAR ZS 3.2 TYPE ZUNISWITCH (CBW) – UNIMIX (P1E) US

Rated Voltage KV

12 1217.5 1724 2436 3640.5 40

Rated normal current A

630 061250 121600 162000 202500 253150 323600 36

Rated breaking capacity KA

16 16

20 2025 2531.5 3240 4050 50

HD4 … … … ...

ABB VACUUM CONTACTOR

Contactor with fuses

ABB VACUUM CONTACTORElectrical CharacteristicsRated Voltage KV 3.6 7.2 12Rated Power Frequency Withstand KV- 1 min 16 20 28Rated short time current KA ..50 ..50 ..50Max rated current of contactor A 400 400 400Maximum performances of contactor with fusesMotors KW 1500 3000 5000Transformers KVA 2000 4000 5000Capacitors KVAR 1500 3000 4800Maximum Load Currents of the fuses

Feeder Transformers Motors CapacitorsRated

Voltage KVFuse Max load Fuse Max load Fuse Max

load3.6 200A 160A 315A 250A 450A 360A7.2 200A 160A 315A 250A 355A 285A12 200A 160A 200 160A 200A 160A

ABB EARTHING TRUCK

ABB EARTHING TRUCK Earthing truck without making capacityThese trucks carry out the same function as the earthing switches withoutmaking capacity. They therefore have no capacity to earth live circuits infault conditions. They are used to ensure an additional fixed earth, as isrequired by some installation service and maintenance procedures, as afurther guarantee for personnel. Earthing truck with making capacityThese trucks carry out the same function as the earthing switches with Making capacity. They consist of circuit-breakers provided with top (earthingof the main busbars) or bottom (earthing of the power cables) terminals only. The contacts without termials are short-circuited by means of a copper bar and connected to earth by means of the apparatus truck.

ABB EARTHING TRUCK Power cable test truckThese trucks allow the insulation tests on the power cables to be carried out without

accessing thefeeder compartment or disconnecting the cables from the switchgear.The use of these trucks foresees removal of the apparatus from the switchgear (circuit-

breaker or contactor) and its replacement with the truck. The truck, during the racking-in phase,

only activates the bottom shutter and, by means of the connectors it is fitted with, allows connection

of the test apparatus cables. Isolating truckThe isolating truck allows the top switchgear contacts to be connected directly to the

bottom ones. Connection is made extremely safe by using the poles of the circuit-breakers to insulate

the connection busbars from the external environment. In the incoming/outgoing feeder

units it connects the main busbar system to the power cables, whereas in the bus-tie, to the

two sides of thebusbar system.

Earthing Switch

SWITCH DISCONNECTOR

ABB SWITCH DISCONNECTOR

Electrical CharacteristicsRated Voltage KV 3.6 7.2 12Rated Power Frequency withstand voltage

KV- 1 min

16 20 28

Rated Lightning Impulse withstand voltage

KV 40 60 75

Rated short time withstand current KA 50 50 50Max rated current of contactor A 400 400 400Maximum Performances of contactor with fusesMotors KW 1500 3000 500

0Transformers KVA 2000 4000 500

0Capacitors KVAR 1500 3000 480

0

PROTECTION & METERING Current Transformers Voltage / Potential Transformers Protection Relays Metering Auxiliary Circuits

Current Transformers

Current Transformers The current transformers are of the type insulated in resin and

are used to supply the measurement devices and protection instruments. These transformers can have a wound core or a bushing bar with one or more cores, with performances and accuracy classes suitable for the installation requirements. Each CT must be able to withstand the short-circuit current which can flow through its primary circuit both thermally and dynamically until the fault is effectively broken.

Accuracy class (cl) Metering: class 0.5 Switchboard metering: class 1 Overcurrent protection: class 10P sometimes 5P Differential protection: class X Zero-sequence protection: class 5P.

Voltage / Potential Transformers

Voltage / Potential Transformers The voltage transformers are of the type

insulated in resin and are used to supply measurement and protection devices. They are available for fixed assembly or for installation on removable and withdrawable trucks.

We can leave a voltage transformer in an open circuit without any danger but it must never be short-circuited.

They are available with or without medium voltage protection fuses fitted on primary side

Protection RelaysNORMAL PRPTECTIONS FOR VARIOUS FEEDERESIncomer Feeder from EB1. IDMT + Inst. O/C & E/F Relay 50/50N/51/51N 2. Trip circuit supervision Relay (95)3. Master Trip Relay (86)Outgoing Feeders to Transformer1. IDMT + Inst. O/C & E/F Relay 50/50N/51/51N 2. Auxiliary relay, 2 E, for Buchholz Alarm & Trip3. Auxiliary relay, 2 E, for Oil Temperature Alarm & Trip4. Auxiliary relay, 2 E, for Water Temperature Alarm & Trip5. Auxiliary relay, 2 E, for Oil Surge/ Low level Alarm & Trip6. Auxiliary relay, 2 E, for Winding Temperature Alarm & Trip7. Trip circuit supervision Relay (95)8. Anti-pumping relay (aux. contactor may be used)9. Master Trip Relay (86)

Protection RelaysNORMAL PRPTECTIONS FOR VARIOUS FEEDERES

Outgoing Feeder other than to Transformer1. IDMT + Inst. O/C & E/F Relay 50/50N/51/51N 2. Trip circuit supervision Relay (95)3. Anti-pumping relay (aux. contactor may be used)

4. Master Trip Relay (86)Incoming Feeder from DG Set

1. IDMT + Inst. O/C & E/F Relay 50/50N/51/51N 2. Restricted Earth Fault Relay3. Reverse Power relay4. Differential relay5. DC failure relay6. Trip circuit supervision Relay (95)7. Anti-pumping relay (aux. contactor may be used)

8. U/V , O/V relay 9. Master Trip Relay (86)

10. Temperature Scanner

Metering & IndicationsNORMAL METERING & INDICATIONS ( Specifications to be followed)1. Ammeter with SS2. Voltmeter with SS3. Tri vector Meter4. MDM and/or KWH Meter5. Annunciator ( if specified)5. INDICATING LAMPS FOR R/Y/B/ ON/OFF/TRIP/ SPRING CHARGED/ TCH/

TEST POS./ SRERVICE POS. NORMAL ACCESSORIES FOR EACH PANEL (VERTICAL SECTION)1. Space Heater, Thermostat & MCB2. Illumination lamp with switch & socket3. Test Terminal Block4. Control MCBs & Aux. Contactors5. TNC Switch6. Remote Local Switch7. Emergency Push button

SWITCHBOARD CONSTRUCTIONSwitchboards are constructed by placing standardized prefabricatedcubicles side by side. GA drawing of a typical panel is indicated in thenext slide. Each vertical panel is subdivided internally into thefollowing compartments which are segregated from each other with provision for internal wiring.- Metering box- Circuit breaker compartment- Cable compartment- Busbar compartment- PT compartmentThe cubicle version, and therefore the switchboard constructed, is ofthe single-level type, with a single busbar system, a circuit breakercompartment per cubicle.

Typical GA Drawing

SWITCHBOARD CONSTRUCTION

SWITCHBOARD CONSTRUCTION Metering boxAll the low voltage apparatus normally used is housed in this box which is provided above the circuit breaker compartment. In particular;- terminal boards and cables for interconnection of cubicles and for connection of the auxiliary cables;- measuring instruments, protection relays, control and signalling devices, fuses, low voltage miniature circuit

breakers etc.- circuit breaker position contacts (connected - isolated)- provision for inter panel wiring

SWITCHBOARD CONSTRUCTION Circuit Breaker CompartmentThe compartment is preset to hold the withdrawable circuit breaker, with its truck, and includes all the accessories required for its operation. Circuit breaker isolation is carried out with the door closed.The following components are mounted in the compartment -- Insulating monoblocks i.e. the insulator bushings which contain the powerconnections between the circuit breaker compartment, the feeder compartment andthe busbar compartment. The insulator bushings have isolating contacts;- automatic segregation shutters of the medium voltage circuit;- mechanical arrangement for operating the limit switches at connected / isolated positions of the circuit breaker- locking device between circuit breaker and earthing switch, if provided- metal wiring ducts for passage of auxiliary circuit cables.- manual secondary plug and metering box socket arrangement provided

SWITCHBOARD CONSTRUCTION Cable CompartmentThe cable compartment is accessible from the back of the cubicle. For switchboards installed against the wall, to reach the cable area, the removable bottom of the circuit breaker compartment can be taken out.The cable compartment can contain the following components :- earthing switch and relative auxiliary contacts, if provided- current transformers- toroidal current transformers on cable- cable terminalsThere is an opening in the base of the compartment for passageof the power cables.

SWITCHBOARD CONSTRUCTION Busbar CompartmentThe busbar compartment houses the main busbar system mounted

on the terminals connected to the upper fixed contacts of the monoblock

and supported on Insulators PT CompartmentThe potential transformers and relative fuses are mounted in the compartment, and may be in the withdrawable version to facilitate

their replacement in safety or may be in fixed version.

Special constructional feature

Separate Venting flaps are provided for Circuit Breaker, Bus-bar and cabling compartments to releaseexcessive pressure during an arc event. Front, side and rear structuresmaintain their integrity.

BUS BARS The dimensions of busbars are determined

taking account of normal operating conditions. The voltage (kV) that the installation operates at

determines the phase to phase and phase to earth distance and also determines the height and shape of the supports.

The rated current flowing through the busbars is used to determine the cross-section and type of conductors.

It is to be ensured that the supports (insulators) resist the mechanical effects and that the bars resist the mechanical and thermal effects due to short-circuit currents.

BUS BARS The main bus compartment is separated from the other

compartments by a sheet steel barrier and fully encloses the main bus. The main bus compartment is accessible from the rear. Main bus ratings match the highest rated circuit breaker continuous current ratings.

The busbars are of electrolytic grade aluminium or copper . The busbars are with round edges and will have no sharp corners.

The bus bars and support systems are designed to withstand the forces created during short circuit conditions at the rated momentary and short-time (3-second) conditions of the highest rated circuit breaker. Supports are be made of epoxy.

Distance in ambient air between live parts

For installations in which, for various reasons, we cannot test under impulse conditions, the table in publication IEC 71-2 gives, according to the rated lightning impulse withstand voltage, the minimum distances to comply with in air either phase to earth or phase to phase. These distances guarantee correct withstand for unfavourable configurations: altitude < 1 000 m.

Rated Lightning Impulse withstand voltage – Up - KV

Minimum distance in air – phase to earth & phase to phase - mm

40 6060 9075 12095 160125 220

Creepage Distances

11 KV MV Insulator

ROUTINE TESTS Dielectric test on the main circuit Tests on auxiliary and control circuits Measurement of the resistance of the

main circuit Tightness test Design and visual checks.

ROUTINE TESTS Dielectric test on the main circuitA dry, short-duration power-frequency voltage test shall be

applied.The voltage applied will 28KV for 1 minute for 12 KV MVSwitchboard. Tests on auxiliary and control circuitsThe following tests shall be conducted: Inspection of auxiliary and control circuits, and

verification of conformity to the circuit diagrams and wiring diagrams

Functional tests Verification of protection against electrical shock Dielectric tests - The test voltage shall be 1 kV with a

duration of 1 second.

ROUTINE TESTS Measurement of the resistance of the

main circuitThe d.c. voltage drop or resistance of each pole of the main circuit

shallbe measured under conditions as nearly as possible similar with

regard to ambient air temperature and points of measurement to those under

which the corresponding type test was made. The current during the test shall

have any convenient value between 50 A and the rated normal current. Design and visual checksThe switchgear and controlgear shall be checked to verify its

compliance with the purchase specification.

TYPE TESTS Dielectric tests Power-frequency voltage tests Lightning impulse voltage tests Measurement of the resistance of

circuits Temperature-rise tests Short-time withstand current and

peak withstand current tests Verification of the protection Internal arcing test

Power-frequency voltage tests

Switchgear and controlgear shall be subjected to short-duration power-

frequency voltage withstand tests in accordance with IEC 60060-1. The test voltage shall be raised for each test condition to the test

value and maintained for 1 min.The tests shall be performed in dry conditions.Instrument transformers, power transformers or fuses may be

replaced by replicas reproducing the field configuration of the high-voltage

connections. Overvoltage protective devices may be disconnected or removed.

Lightning impulse voltage tests

Switchgear and controlgear shall be subjected to lightning

impulse voltage tests in dry conditions only. The tests shall be performed with voltages of both polarities

using the standard lightning impulse 1,2/50 μs according to IEC 60060-1.The tests shall be performed with the applicable test voltages given in Table 1a or 1b of 4.2 of IEC 60694.

For test voltages to earth and between phases, columns (2) and (4) shall be used. For test voltages across isolating distances columns (3) and (5) shall be used.

Lightning impulse voltage tests

Lightning Impulse voltage tests

Lightning Impulse Voltagae Test

Measurement of the resistance of circuits

Main circuitA measurement of the resistance of the main circuit shall be made for comparison between the switchgear and controlgear type tested for temperature rise and all other switchgear and controlgear of the same type subjected to routine tests.The measurement shall be made with d.c. by measuring the voltage drop or resistance across the terminals of each pole. Special consideration shall be given to enclosed switchgear and controlgear.The current during the test shall have any convenient value between 50 A and the rated normal current.NOTE : Experience shows that an increase of the main circuit resistance cannot alone be considered as reliable evidence of bad contacts or connections. In such a case, the test should be repeated with a higher current, as close as possible to the rated normal current.The measurement of the d.c. voltage drop or the resistance shall be made before the temperature-rise test, with the switchgear and controlgear at the ambient air temperature and after the temperature-rise test when the switchgear and controlgear has cooled to a temperature equal to the ambient air temperature. The measured resistances in these two tests shall not differ by more than 20 %.The measured value of the d.c. voltage drop or the resistance shall be given in the type-test report, as well as the general conditions during the test (current, ambient air temperature, points of

measurement, etc.).

Temperature-rise tests Unless otherwise specified in the relevant standards, the temperature-rise test of the main circuits shall be made on a new switching device with clean contacts, and, if applicable, filled with the appropriate liquid or gas at the minimum functional pressure (or density) for insulation prior to the test. The test shall be made indoors in an environment substantially free from air currents, except those generated by heat from the switching device being tested. In practice, this condition is reached when the air velocity does not exceed 0,5 m/s. Temporary connections to the main circuit shall be such that no significant amount of heat is conducted away from, or conveyed to, the switchgear and controlgear during the test. The temperature rise at the terminals of the main circuit, and at the temporary connections at a distance of 1 m from the

terminals, shall be measured. The difference of temperature rise shall not exceed 5 K. The type and sizes of the temporary connections shall be recorded in the test report.

Temperature-rise tests The test shall be made over a period of time sufficient for the

temperature rise to reach a stable value. This condition is deemed to be obtained

when the increase of temperature rise does not exceed 1 K in 1 h. This criteria

will normally be met after a test duration of five times the thermal time

constant of the tested device.

Short-time withstand current and peak withstand current tests

Verification of the protection

Internal arcing test

A.1 Introduction

Internal arcing testA.2 Types of accessibility

Internal Arc Testing

Room simulation and indicator positioning foraccessibility A, functional unit at or above 1,5 m

Room simulation and indicator positioning foraccessibility B, functional unit above 2 m high

Room simulation and indicator positioning foraccessibility B, functional unit below 2 m high

GRAPHICAL SYMBOLS

DOUBLE BUS BAR SYSTEMS

AUTOMATIC TRANSFER SYSTEMS

HIGH SPEED TRANSFER SYSTEMS (WITH 2 VCBS W/O BUS-COUPLER)

HIGH SPEED TRANSFER SYSTEMS (WITH 2 VCBS & BUS-COUPLER)

TYPICAL SLDs

TYPICAL MOTOR STARTER SLDs

TYPICAL PANELS

Typical VCB Panel

Ring main units

RING MAIN UNIT SF6 GCB

Compact Switchgear systems

RING MAIN UNIT & COMPACT SWITCHGEAR SYSTEM

Outdoor MV Kiosks

Electrical equipments in Compact Secondary Substations

Compact service Substations Designs

Neutral Grounding Resistor Panel

Typical metering panel

Bibliography IEC 62271- 200, Edition 1.0 2003-11 : High-voltage switchgear

and controlgear – AC metal- enclosed switchgear and controlgear for

rated voltages above 1 kV and up to and including 52 kV IEC 60694, Edition 2.2, 2002-01: Common specifications for high-voltage switchgear and controlgear standards IEC 60815 : Guide for the selection of insulators in respect of polluted conditions IEC 60060-1, Edition 3.0 2010-09: High-voltage test techniques– Part1: General definitions and test requirements Merlin Gerin technical guide - Medium Voltage : MV design

guide Vmax Medium voltage vacuum circuit-breakers IEC: ... 17.5 kV; ... 1250 A; ... 31.5 kA ANSI: ... 15 kV; ... 1200 A; ... 31.5 kA – ABB VD4 Medium voltage vacuum circuit-breakers 12...36 kV – 630...3150 A - 16...50 kA – ABB HD4 Gas insulated MV circuit-breakers 12 …40.5 kV - 630 ... 3600A - 16 ... 50 kA - ABB

Bibliography UniGear ZS1 Installation, service and maintenance instruction Manual – ABB PowerCube type PB Preassembled modules and enclosures for Constructin - Medium voltage switchgear – ABB UniGear type ZS1 Medium voltage, arc-proof, air-insulated, metal-clad switchgear – ABB MV Air Insulated Switchgear, Model Unisafe – ABB MV Indoor Air Insulated Switchgear, Model Unisafe MV Vacuum Circuit Breaker, Model VD4 - ABB SF6 insulated Compact Switchgear, type SafePlus and SF6 insulated Ring Main Unit, type SafeRing 12 / 24 kV –ABB PowerIT MV Air Insulated Switchgear - ABB Compact Secondary Substations (CSS - ABB) EK6 Earthing switch – ABB

Bibliography 3D Disconnectors and Earthing Switches – Siemens Indoor Circuit Breaker – Calix AFCONGeneral Catalogue Impulse current testing by Michael Gamlin Outdoor Circuit Breaker – Calix Medium Voltage Motor Control Assemblies - Eaton

THANK - YOU

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