Your SlideShare is downloading. ×
0
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Introduction to mv switchgear
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Introduction to mv switchgear

2,376

Published on

Pengenalan mengenai switchgear tegangan menengah.

Pengenalan mengenai switchgear tegangan menengah.

Published in: Education, Business
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
2,376
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
268
Comments
0
Likes
1
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Introduction to MV EQUIPMENTS Prepared by Triyanto Limantoro
  • 2. Introduction to MV equipments Basic Magnitude in MV switchgear : Voltage Current Frequency Short Circuit power Voltage, rated current and rated frequency: Single line diagram / Specification to define the dielectric withstand of the components such as: CB, insulators, CTs,VTs,etc Short circuit power : to choose various parts of a switchgear: withstand against temperature rises and electro dynamic force. Schneider Electric - Industrial Division Σ July 2009 2
  • 3. VOLTAGE Operating/Service Voltage U (kV): Voltage across the equipment terminals. example : 22kV, 3.3kV,… Rated Voltage Ur (kV) : (nominal Voltage) Max rms (root mean square) value of the voltage that equipment can withstand under normal operating conditions. Rated voltage (Ur) is always greater than the operating voltage. Rated voltage associated with an insulation level Examples : Rated voltage 7.2kV, 17.5kV, 12kV and 24kV Schneider Electric - Industrial Division Σ July 2009 3
  • 4. VOLTAGE Insulation level Ud (kV rms, 1 minute) and Up (kV peak) Definition: the electric withstand of equipment to switching under operation over voltages and lightning impulse. Ud: Over voltage due to of internal switchgear, which accompany all changes in the circuit: opening/closing CB or Switch, breakdown or shorting across an insulator, etc… Simulated in laboratory/factory by the power-frequency withstand voltage for 1 minute. Example : Ur : 24kV Ud : 50kVrms/1 min. Up: over voltage of external switchgear or atmospheric origin occur when lightning falls on or near a transmission line. Simulated in laboratory by the lightning impulse withstand voltage. Examples : Ur : 24kV Up : 125kVp Schneider Electric - Industrial Division Σ July 2009 4
  • 5. IEC Standard Voltage 20 7.2 28 38 50 12 17.5 24 60 1.2/50us 50Hz 75 95 125 70 36 170 Ud Ur Up Schneider Electric - Industrial Division Σ July 2009 5
  • 6. Standard Schneider MV equipment is conformity with list 2 of the series 1 table IEC 60 071 and 60 298. Rated Voltage kV rms 7.2 12 17.5 24 36 Rated lightning Rated powerimpulse frequency withstand withstand voltage 1.2/50us 50Hz voltage . kV peak 1minute kV rms list 1 list 2 40 60 20 60 75 28 75 95 38 95 125 50 145 170 70 Normal operating voltage kV rms 3.3 to 6.6 10 to 11 13.8 to 15 20 to 22 25.8 to 36 Insulation level apply to MV swgr at altitudes of less than 1000 meters, 20 deg.C, 11 g/m3 humidity and press of 1.013 mbar. Above this ,derating should be considered. Schneider Electric - Industrial Division Σ July 2009 6
  • 7. Derating of the switchgear related to the altitude 2500 Altitude 2500 m k is equal to 0.85 Impulse withstand of the switchboard must be :125/0.85 = 147.05 kV Power frequency withstand 50 Hz must be 50/0.85 = 58.8 kV Schneider Electric - Industrial Division Σ July 2009 7
  • 8. Standard Insulation level corresponds to a distance in air which guarantees withstand without a test certificate. Rated Voltage kV rms 7.2 12 17.5 24 36 Rated lightning impulse withstand voltage 1.2/50us 50Hz . kV peak 60 75 95 125 170 Rated powerfrequency withstand voltage 1 minute kV rms 20 28 38 50 70 Distance live to earth in air . cm 9 12 16 22 32 lower than this distance, we need simulation/test in the laboratory to check lightning impulse withstand voltage. Or using additional insulation material such as heatshring, screen,etc Schneider Electric - Industrial Division Σ July 2009 8
  • 9. Current The rms value of current that equipment can withstand when current flow without exceeding the temperature rise allowed in standards. Temperature rises authorized by the IEC according to the type of contacts. Schneider Electric - Industrial Division Σ July 2009 9
  • 10. OPERATING CURRENT : I (Ampere) Calculate from the load power. Actual current passes through the equipment. • generally customer provide its value • calculate if we know the power of the load Exercise: A switchboard with a 630kW motor feeder and a 1250kVA x’mer feeder at 5.5kV, cos ϕ = 0.85 and motor efficiency η = 90% How many ampere the operating current of Transformer and Motor? In motor = 86.44 A The answer In Trafo = 131.22A Schneider Electric - Industrial Division Σ July 2009 10
  • 11. Short Circuit Current Short circuit power depends on : Network configuration (exp: single source, parallel source, network, generators) Impedance of each equipments or devices. (exp: lines, cables, transformers, motors) Power short circuit is maximum power that network or source can deliver to an installation during a fault, expressed in MVA or in kA rms at operating voltage. Exp: Psc = 500MVA @ 20KV or Isc : 31.5kA rms Determination of the short-circuit power requires analysis of the power flows feeding the short circuit in the worst possible case. What is short circuit level for 500MVA @ 20KV ? 14.43kA Answer Schneider Electric - Industrial Division Σ July 2009 11
  • 12. Short Circuit Current D E Isc at main busbar D when bustie D4 close? Isc at the outgoing feeder E? Schneider Electric - Industrial Division Σ July 2009 12
  • 13. Minimum short-circuit current: Isc (kA rms.) Corresponds to a short circuit at one end of the fault point. This value allows us to choose the setting of thresholds for over current protection devices(F50/F51) and fuses Example: Isc: 23 kA rms Ith source Schneider Electric - Industrial Division Σ July 2009 Isc load 13
  • 14. Maximum short-circuit current: Ith (kA rms. 1 s or 3 s) Corresponds to a short circuit in upstream terminals of the switching device, express in : kA for 1s or 3 s thermal withstand of the equipment = Ith Example: Ith: 31.5 kA rms. 1 s or 3 s It h source Schneider Electric - Industrial Division Σ July 2009 Isc load 14
  • 15. Peak Value of the max. short circuit current (kA peak) Value of the initial peak in the transient period I dynamic (kA peak) is equal to : 2.5 x Isc at 50 Hz (IEC) 2.6 x Isc at 60 Hz (IEC) 2.7 x Isc (ANSI) times the short circuit current calculated at a given point in the network. Example: Isc : 25kA Idyn: 2.5 x 25= 63.75kA peak (IEC 60 056) Idyn: 2.7 x 25= 67.50kA peak (ANSI), 25kA at a given point This value determines the breaking capacity and making (closing) capacity of CBs and Switches, as well as the electro dynamic withstand of busbars and switchgear. Isc value based on IEC: 8 – 12.5 – 16 – 20 – 25 – 31.5 – 40- 50 kA rms Schneider Electric - Industrial Division Σ July 2009 15
  • 16. Frequency fr (Hz) 2 different frequency use in the world: 50 Hz in Europe 60 Hz in the USA several countries use both frequencies indiscriminately Instrument Voltage Transformer rated 50 can operate at 60Hz Instrument Current Transformer rated 50 can operate at 60Hz. But CT with rated 60Hz can not be operated at 50Hz. Schneider Electric - Industrial Division Σ July 2009 16
  • 17. Introduction to MV equipments Electrical network can be disconnect, protect and control by using AIS SWITCHGEAR : AIR INSULATED SWITCHGEAR (AIS) METAL enclosed switchgear divided 3 types: Metal clad : example: MC set,NEX Compartmented : example: SM6 Block : example Interface/joggle cubicle. Schneider Electric - Industrial Division Σ July 2009 17
  • 18. DIFFERENT ENCLOSURE TYPE (AIS) LSC2B metal clad LSC2A compartment GIS LSC1 Block type Schneider Electric - Industrial Division Σ July 2009 18
  • 19. MV Switchgear to IEC 62271-200 Fully enclosed in metal enclosure and having some current carrying capacity Loss of Service Continuity Class (LSC) • Architecture based on “safe compartment access” Several levels of service continuity during maintenance LSC 2B Maintainability of defined parts with no need of cable disconnection (separate cable compartment) • Safe access to compartment • With power flow in busbar and the other units • MV Cable in separate compartment • Cable of unit under maintenance can remain energized LSC 2A • Safe access to compartment • With power flow in busbar and the other units • MV Cables must be earthed Maintainability of one functional unit allowing normal service of the remaining units of the switchboard (busbar in a separate compartment) MOTORPACT LSC 1 MCSET or NEX Schneider Electric - Industrial Division Σ July 2009 • Metal enclosed not of LSC2 class 19
  • 20. MV Switchgear to IEC 62271-200 Fully enclosed in metal enclosure and having some current carrying capacity Partition Class I or M • Classification based on electrical field presence in safe access compartment Partition Class PM Personnel comfort during maintenance • All partitions and shutters of safe access compartment shall be metallic with some current carrying capacity “Metal enclosed” compliant during maintenance Applicable mainly to withdrawable system MCset or PIX 3.110 Shutter Part of metal-enclosed switchgear and controlgear that can be moved from a position where it permits contacts of a removable part, or moving contact of a disconnector to engage fixed contacts, to a position where it becomes a part of the enclosure or partition shielding the fixed contacts. Partition Class PI • Partitions or shutters may be partially or totally of Definition insulating material Electrical and mechanical safety according to IEC 60466 or 60137 Motorpact Schneider Electric - Industrial Division Σ July 2009 20
  • 21. MV Switchgear to IEC 62271-200 Fully enclosed in metal enclosure and having current carrying capacity Internal Arc Class IAC • Classification based on consequences of internal arc on personnel safety Accessibility Types • A : restricted to authorized personnel only. • B : unrestricted, including general public. IAC classified Personnel safety in case • No projection of parts of internal arc towards accessible sides • No ignition of indicators Motorpact complies with AFLR type Safety in case of internal fault during service condition Demonstrated by type tests (completely defined by the standard) IAC not classified • No tests performed to assess behavior of enclosure under arc conditions • Enclosure Identification code: F - for Front side • L L - for Lateral side R - for Rear side Schneider Electric - Industrial Division Σ July 2009 21
  • 22. SWITCHGEAR FUNCTION Schneider Electric - Industrial Division Σ July 2009 22
  • 23. STANDARDS DISTRIBUTION FEEDERS (AIS) The MCset range meets the following international standards: 62271-1 : clauses common to high voltage switchgear 62271-200 : metal-enclosed switchgear for alternating current at rated voltages of between 1 and 52 kV IEC 62271-100 : high voltage alternating current circuit breakers IEC 60470 : high voltage alternating current contactors IEC 60265-1 : high voltage switches IEC 60282-2 : high voltage fuses IEC 60271-102 : alternating current disconnectors and earthing switches IEC 60255 : measurement relay and protection unit for the applicable parts IEC 60044-1 : current transformers IEC 60044-2 : voltage transformers IEC 60044-8 : electronic current transformers (for LPCT). Schneider Electric - Industrial Division Σ July 2009 23
  • 24. STANDARDS MOTOR STARTER / MCC (AIS) Motorpact meets IEC standards IEC 62271-1 High-voltage switchgear and controlgear – Part 1: Common specifications IEC 62271-200 AC metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV IEC 60470 High voltage alternating current contactors and contactor based motorstarters IEC 60282-1 High voltage fuses: limiting fuses IEC 62271-102 Alternating current disconnectors and earthing switches IEC 60044-1 Instrument transformers - Part 1: current transformers IEC 60044-2 Instrument transformers - Part 2: inductive voltage transformers IEC 60044-8 Instrument transformers - Part 8: electronic current transformers IEC 61958 High-voltage prefabricated switchgear and controlgear assemblies - Voltage Presence Indicating Systems IEC 60076-11 dry-type transformers Other specifications IACS International Association of Classification Societies Schneider Electric - Industrial Division Σ July 2009 24
  • 25. STANDARDS DISTRIBUTION FEEDERS (GIS) Schneider Electric - Industrial Division Σ July 2009 25
  • 26. SF6 and Vacuum SF6 is used for insulation and breaking functions: That is the only used technique for all voltages, in secondary distribution (switches, RMU) and in high voltage up to 800 kV. Vacuum is limited to the breaking function and only in medium voltage (mainly up to 36 kV): The vacuum bottles have dielectric weakness (NSDD - contact surface state). Schneider Electric - Industrial Division Σ July 2009 26
  • 27. SF6 and Vacuum are two modern breaking techniques used in Medium Voltage. They ensure the continuity of service expected by the users together with complete safety. The SF6 technique has differentiating advantages : for specific applications (capacitor banks, motor breaking, generator , etc …), for particular network operating modes (e.g. on line monitoring of breaking medium). Schneider Electric - Industrial Division Σ July 2009 27
  • 28. Equivalent reliability of SF6 and Vacuum CB ’s Excellent reliability for both techniques: experience built up by manufacturers and users, upgrading and optimization of equipment through the use of modern development methods (CAD-CAM, FMECA, …) mastering of « sensitive » components such as operating mechanism and tightness. The actual failure rate on the installed 180 000 circuitbreakers throughout the world is : 4/10 000 per year ==> MTBF ~ 2800 years. Schneider Electric - Industrial Division Σ July 2009 28
  • 29. Minimum maintenance for SF6 and Vacuum installed circuit-breakers SF6 pole-units and vacuum enclosures: are sealed for life, are maintenance free, have mechanical and electrical endurance that is much greater than actual needs (several tens of times Isc, 10,000 Ir). Operating mechanism: is based on the same technology, whatever the technique, and is a component with high mechanical endurance (10,000 operations minimum). The lifetime of the SF6 Merlin Gerin circuit-breakers is 30 years. Schneider Electric - Industrial Division Σ July 2009 29
  • 30. Installation security: assets of SF6. On-line monitoring of the breaking medium is possible thanks to a pressure switch . All the ratings at the pressure switch level. Schneider Electric - Industrial Division Σ July 2009 30
  • 31. Installation security: assets of SF6. No overvoltage having detrimental effect on the equipment: No reignition nor restrike, during the switching of capacitors banks. No or weak overvoltage during the switching of inductive loads (unloaded transformer, starting motor). No NSDD ’s during breaking, nor multiple prestrikes in making. The use of vacuum circuit-breakers requires to have overvoltage protection (ZnO-RC). Schneider Electric - Industrial Division Σ July 2009 31
  • 32. U source side U load side SF6 circuit-breaker (12kV) Schneider Electric - Industrial Division Σ July 2009 32
  • 33. U source side U load side 45 kV Vacuum circuit-breaker (12kV) Schneider Electric - Industrial Division Σ July 2009 33
  • 34. Installation security: assets of SF6. Rated characteristics maintained at 0 bar gauge SF6 pressure with breaking once at 80 % or 100 % of the maximum breaking capacity and a dielectric withstand at least 80 % of the insulation level, for example: SF1 circuit-breaker at 0 bar gauge: 25 kA at 24 kV 125 kV BIL. Schneider Electric - Industrial Division Σ July 2009 34
  • 35. Safety of people related to the switchboards which the circuit breakers are integrated. Preponderance of the toxicity of copper vapours present in all electrical equipment in the event of internal arcing, whatever breaking technique. The information is in the IEC report 1634: Use and handling of SF6 in high voltage switchgear and controlgear. Schneider Electric - Industrial Division Σ July 2009 35
  • 36. A COMPARISON OF SF6 AND VACUUM CIRCUIT BREAKERS SF6 or vacuum which one is the best technology in circuit breakers to the user’s view point ? • Both can be safe, long lasting, adapted to the utilisation. • It all depends upon who is the manufacturer. • You can be confident when he is Schneider (Merlin Gerin-MG) who is the most experienced maker of MV switchgear with SF6 and an expert in vacuum. •But the technologies have different features and merits which are compared in the attached document. Schneider Electric - Industrial Division Σ July 2009 36
  • 37. Schneider Electric - Industrial Division Σ July 2009 37
  • 38. Schneider Electric - Industrial Division Σ July 2009 38
  • 39. Schneider Electric - Industrial Division Σ July 2009 39
  • 40. DIELECTRIC WITHSTAND depends on 3 parameters: The Dielectric strength of the medium The Shape of the parts The distance : ambient air between the live parts insulating air interface between the live parts Schneider Electric - Industrial Division Σ July 2009 40
  • 41. Dielectric Strength of air depends on ambient conditions: Pollution reducing the insulating performance by a factor <10. Pollution may occur from external dust, lack of cleanliness, breaking down of an internal surface, pollution & humidity causes electrochemical conduction which will worsen discharge phenomena. Condensation reducing the insulating performance by a factor 3 Pressure related to the altitude, derating performance. . Humidity % of humidity can cause a change in insulating performances. (liquid always leads to a droop in performance) Temperature temp. increases can cause decreases insulation performance. Thermal shock can be the cause of the micro fissuration which can lead very quickly to insulator breakdown. Insulator expands by 5 and 15 times more than a conductor. Schneider Electric - Industrial Division Σ July 2009 41
  • 42. The Shape of the parts It is essential to eliminate any “peak” effect to avoid disastrous effect on the impulse wave withstand in particular and on the surface ageing of insulator. Air Ionization Generate Ozone Breakdown of insulator surface or skin Distance between parts (there is ambient air between live parts) For installations sometime we can not test under impulse conditions, the table below gives the minimum distance to comply with in air either phase to earth or phase to phase . The table based on IEC 71-2 according to the rated lightning impulse withstand voltage and these distances guarantee correct withstand for unfavorable configurations: altitude < 1 000 m. Note : the table above does not include any increase which could be required to take account of design tolerances, short circuit effects, wind effects, operator safety, pollution, etc. Schneider Electric - Industrial Division Σ July 2009 42
  • 43. INSTRUMENT TRANSFORMER Schneider Electric - Industrial Division Σ July 2009 43
  • 44. Schneider Electric - Industrial Division Σ July 2009 44
  • 45. Schneider Electric - Industrial Division Σ July 2009 45
  • 46. Current transformer Metering transformer applications Instrument transformers are necessary to provide values that can be used by these devices which can be analogue devices, digital processing units with a microprocessor, after analogue/digital conversion of the input signal (e.g.: Sepam or Power Logic System). Current transformers (CT) meet standard IEC 60044-1. Schneider Electric - Industrial Division Σ July 2009 46
  • 47. Characteristics Of Current Transformer: Based on standard IEC 60044-1. Insulation Characterized by the rated voltage: of the insulation, which is that of the installation (e.g.: 24 kV) of the power frequency withstand 1 min (e.g.: 50 kV) of the impulse withstand (e.g.: 125 kV). Rated frequency 50 or 60 Hz. Rated primary current (Ipn) Rms value of the maximum continuous primary current. Usual values are 25, 50, 75, 100, 200, 400, 600 A. Schneider Electric - Industrial Division Σ July 2009 47
  • 48. Characteristics Of Current Transformer: Based on standard IEC 60044-1. Rated secondary current (Isn) This is equal to 1 A or 5 A. Rated transformation ratio Kn = I rated primary / I rated secondary (e.g.: 100 A / 5 A) Short-time thermal current Ith - 1 second This characterizes the thermal withstand under short circuit conditions for 1 second. It is expressed in kA or in a multiple of the rated primary current (e.g.: 80 x Ipn) for 1 second. The value for a duration that is different to 1 second is given by: I’th =SQRT ( Ith^2 / t ) Ith : 16kA/1 sec, I’th for 2 sec : SQRT (16^2/2) = 11.31kA/2sec Schneider Electric - Industrial Division Σ July 2009 48
  • 49. Characteristics Of Current Transformer: Based on standard IEC 60044-1. Short-time thermal current peak value This value is standardized from Ith - 1 s at: IEC: 2.5 Ith at 50 Hz and 2.6 Ith at 60 Hz ANSI: 2.7 Ith 60 Hz. Accuracy load The value of the load on which is based the metered current accuracy conditions. Accuracy power Pn Apparent power (VA) that the CT can supply on the secondary for the rated secondary current for which the accuracy is guaranteed (accuracy load). Usual values 5 - 7.5 - 10 - 15 VA (IEC). Schneider Electric - Industrial Division Σ July 2009 49
  • 50. Characteristics Of Current Transformer: Based on standard IEC 60044-1. Accuracy class Defines the limits of error guaranteed on the transformation ratio and on the phase shift under the specified conditions of power and current. Classes 0.5 and 1 are used for metering class P for protection. Current error ε (%) Error that the transformer introduces in the measurement of a current when the transformation ratio is different from the rated value. Phase shift or phase error ψ (minute) Difference in phase between the primary and secondary currents, in angle minutes Schneider Electric - Industrial Division Σ July 2009 50
  • 51. Characteristics Of Current Transformer: Based on standard IEC 60044-1. Schneider Electric - Industrial Division Σ July 2009 51
  • 52. magnetization curve (for a given temperature and frequency). This magnetization curve (voltage Vo, magnetizing current function Im) can be divided into 3 zones: 1 - non-saturated zone: Im is low and the voltage Vo (and therefore Is) increases virtually proportionately to the primary current. 2 - intermediary zone: there is no real break in the curve and it is difficult to situate a precise point corresponding to the saturation voltage. 3 - saturated zone: the curve becomes virtually horizontal; the error in transformation ratio is high, the secondary current is distorted by saturation. Schneider Electric - Industrial Division Σ July 2009 52
  • 53. Schneider Electric - Industrial Division Σ July 2009 53
  • 54. Metering CT This requires good accuracy (linearity zone) in an area close to the normal service current; it must also protect metering devices from high currents by saturating earlier Protection CT This requires good accuracy at high currents and will have a higher precision limit (linearity zone) for protection relays to detect the protection thresholds that they are meant to be monitoring. Schneider Electric - Industrial Division Σ July 2009 54
  • 55. Schneider Electric - Industrial Division Σ July 2009 55
  • 56. Safety The CT secondary is used at low impedance (virtually in short circuit). The secondary circuit should never be left open, since this would mean connecting across an infinite impedance. Under these conditions, hazardous voltages for personnel and equipment may exist across the terminals. Terminal marking CT connection is made to the terminals identified according to the IEC: P1 and P2 on the MV side S1 and S2 on the corresponding secondary. In the case of a double output, the first output is identified by 1S1 and 1S2, the second by 2S1 and 2S2. Schneider Electric - Industrial Division Σ July 2009 56
  • 57. Schneider Electric - Industrial Division Σ July 2009 57
  • 58. CT for metering Accuracy class A metering CT is designed to send as accurate an image as possible of currents below 120% of the rated primary. Accuracy guaranteed from load 25% and 100% of the accuracy power. IEC standard 60044-1 determines the maximum error: Schneider Electric - Industrial Division Σ July 2009 58
  • 59. CT for metering Safety factor: FS In order to protect the metering device connected to the CT from high currents on the MV side, instrument transformers must have early saturation characteristics. The limit primary current (Ipl) is defined for which the current error in the secondary is equal to 10%. The standard then defines the Safety Factor FS. : This is the multiple of the rated primary current from which the error becomes greater than 10% for a load equal to the accuracy power. Schneider Electric - Industrial Division Σ July 2009 59
  • 60. CT for protection Accuracy class A protection CT is designed to send as reliable an image as possible of the fault current (overload or short circuit). IEC standard 60044-1 determines the maximum error for each accuracy class in the phase and in the module according to the indicated operating range. For example for class 5P the maximum error is y ± 5% at the accuracy limit current and y ± 1% at the rated current. Standardized classes are 5P and 10P. The choice depends on the application. The accuracy class is always followed by the accuracy limit factor. Schneider Electric - Industrial Division Σ July 2009 60
  • 61. Accuracy limit factor: FLP A protection CT must saturate at sufficiently high currents to enable sufficient accuracy in the measurements of fault currents by the protection device whose operating threshold can be very high. The limit primary current (Ipl) for which current errors and phase shift errors in the secondary do not exceed values in the table below The standard then defines the accuracy limit factor FLP. In practice this corresponds to the linearity limit (saturation curve) of the CT. Schneider Electric - Industrial Division Σ July 2009 61
  • 62. Schneider Electric - Industrial Division Σ July 2009 62
  • 63. If ϕ and η are not known, use approx value cos ϕ: 0.8 and η = 0.8 Capacitor Feeder :Derating coefficient of 30% to take into account of temp. rise due to capacitor harmonic Bus section The greatest value of current that can flow in the bus section on a permanent basis. Ips = In bus Standardized values : 10-12.5-15-20-25-30-40-50-60-75-80 and their multiples and factors CT must be able to withstand 120% the rated current Schneider Electric - Industrial Division Σ July 2009 63
  • 64. CURRENT TRANSFORMER Example: A thermal protection device for a motor has a setting range of between 0.6 and 1.2 x Ir (CT). In order to protect this motor, the required setting must correspond to the motor’s rated current. If we assume that Ir for the motor = 45 A, the required setting is therefore: 45A If we use a 100/5A CT, the relay will never see 45A , because: 100A x 0.6 = 60A > 45A. If we use a 75/5A CT, the relay will see , 75 x 0.6 = 45 A The range of setting will be: 0.6 < 45/75 < 1.2 . This CT is suitable. RATED THERMAL SHORT CIRCUIT CURRENT (Ith) Value of the installation max. short circuit current and the duration 1s or 3 s. Each CT must be able to withstand short circuit current both thermally and dynamically until the fault is effectively cut off. Ith = Ssc / (U x V3), Ssc = power short circuit MVA When the CT is installed in a fuse protected, the Ith = apprx. 80 Ir. RATED SECONDARY CURRENT: Local use or inside switchgear Isr = 5A Remote use or long distance Isr = 1A Schneider Electric - Industrial Division Σ July 2009 64
  • 65. Schneider Electric - Industrial Division Σ July 2009 65
  • 66. INSIDE MV CURRENT TRANSFORMER Schneider Electric - Industrial Division Σ July 2009 66
  • 67. Schneider Electric - Industrial Division Σ July 2009 67
  • 68. Schneider Electric - Industrial Division Σ July 2009 68
  • 69. Schneider Electric - Industrial Division Σ July 2009 69
  • 70. RATED PRIMARY VOLTAGE (Upr) According to the design, VT will be connected : Phase to earth 22.000V/V3 / 110V/V3, where Upr = U/V3 Phase to phase 22.000 / 110V, where Upr = U RATED SECONDARY VOLTAGE (Usr) Phase to phase VT, rated secondary voltage : 100V or 110 V Phase to Ground VT, rated secondary voltage : 100/V3 or 110V/V3 RATED OUTPUT The apparent power output that VT can supply the secondary circuit when connected at rated primary voltage and connected to the nominal load. It must not introduce any error exceeding the values guaranteed by the accuracy class . (S = V3. U. I in 3 phase circuit) Standardized value are: 10-15-25-30-50-75-100-150-200-300-400-500 VA Schneider Electric - Industrial Division Σ July 2009 70
  • 71. ACCURACY CLASS The limits of errors guaranteed in terms of transformation ratio and phase under the specified conditions of both power and voltage. PROTECTION ACCORDING TO IEC 60 186 Classes 3P and 6P (but in practice only class 3P is used) The accuracy class is guaranteed for values : of voltage of between 5% of the primary voltage and the max. value of this voltage which is the product of the primary voltage and the rated voltage factor (kT x Upr) For secondary load between 25% and 100% of the rated output with a power factor of 0.8 inductive. Schneider Electric - Industrial Division Σ July 2009 71
  • 72. Schneider Electric - Industrial Division Σ July 2009 72
  • 73. INSIDE MV VOLTAGE TRANSFORMER Schneider Electric - Industrial Division Σ July 2009 73
  • 74. INDEX PROTECTION OF THE SWGR INDEX PROTECTION Protection of people against direct contact and protection of equipment against certain external influences. Requested by international standard for electrical installations and products (IEC 60 529) The protection index is the level of protection provided by an enclosure against access to hazardous parts, penetration of solid foreign bodies and of water. The IP code is a coding system to indicate the protection index. Schneider Electric - Industrial Division Σ July 2009 74
  • 75. INDEX PROTECTION- first index Schneider Electric - Industrial Division Σ July 2009 75
  • 76. INDEX PROTECTION: second index Schneider Electric - Industrial Division Σ July 2009 76
  • 77. INDEX PROTECTION : third index Definitions The protection mentions correspond to impact energy levels expressed in joules hammer blow applied directly to the equipment impact transmitted by the supports, expressed in terms of vibrations therefore in terms of frequency and acceleration The protection indices against mechanical impact can be checked by different types of hammer: pendulum hammer, spring-loaded hammer or vertical free-fall hammer (diagram below). Schneider Electric - Industrial Division Σ July 2009 77
  • 78. PROTECTION INDEX: third index Schneider Electric - Industrial Division Σ July 2009 78
  • 79. Make the most of your energy™

×