力特有效保护变压器和控制变压器的重要性—变压器保护（英文）.pdf力特有效保护变压器和控制变压器

文件名称: 力特有效保护变压器和控制变压器的重要性—变压器保护（英文）.pdf

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详细说明：力特有效保护变压器和控制变压器的重要性—变压器保护（英文）pdf,力特有效保护变压器和控制变压器的重要性—变压器保护（英文）Transformer Protection Basics Expertise AppliedAnswers Delivered Table 1. Fuses for transformers over 600 volts For more specific sizing recommendations, refer to Tables Maximum Fuse Rating in Percent 4 and 5 for Class j fuse protection and tables 6 and 7 for of transformer Rated Current Class cc fuse protection Transformer Primary Secondary Fuse Rating Rated Fuse Rating 600 volts600volts Table 4 shows recommended Class J fuse ratings Impedance Over 600 or less in or less in for standard transformers below 600 Volts without 600 volts in Volts all locations unsupervised supervised secondary protection, while Table 5 shows the similar locations ocations recommendations in applicatians with secondary protection Not more than 6% 300% 250% 125% 250% Table 4 More than 6% Class J fuse Protection Of Standard Transformers Without Secondary nd not more 300% 225% 125% 250% Protection--230, 460, 575 Volts Single-Phase than 10% NEC and UI Maximum Allowable Fusing iamps)With anly Primary Protection 1. Littelfuse IDSR, LLNRK /LLSRK/LLSRK ID, FLNR ID/FLSR ID, and JTD ID series 230 Volts 460 Volts 575 Volts time-delay fuses may be rated at 125% of transformer secondary current Single-Phase Single-Phase Single-Phase 2. Where the required fuse rating does not correspond to a standard fuse rating Primary JTD or Primary JTD or Primary JTD or the next higher standard rat ng is permitted 3. An individual primary fuse is not required if the primary circuit fuse is not Transformer Current JTD ID Current JTD_ID Current JTD_ID kVA (A) Series (A) Series A Series greater than 300 of transformer primary current 0.15 065112033810026KLDR3/ 035 1.52 0.76 0.61 1-1/2 Transformers Rated 600 Volts and less 05 2.17 310930721/2 UL Industrial Control Standards(No 508) and motor 业电 075 100 4.35 6 Control Center Standards(No 845) specify control power 2.17 1.74 150 6.52 10 3.26 ransformer protection corresponding to NEC Article 200 8.70 12 4.35 63485 430.72(C). In addition UL requires the primary of control 250 10.87 15 543 4.35 powertransformersusedincontrollershavingshort-circuitwww.3000113.04(171216.52105.228 350 15.22 20 761 12 6.09 10 UL Class CC, J, R, or T fuses. For maximum fuse ratings 500214301087158:7012 permitted by the nec, refer to Table 2 for sizing of primary 800 45 13911712 fusing and table 3 for sizing of secondary fusing y+:010=0)们21352 Table 2 Maximum Acceptable Rating of Primary Overcurrent Device Fuse recommendations are based on maximum acceptable rating of prima fuse as per NEC 450.3(/, UL 508 32.7, and UL 845 11.16 and 11.17, as sum Rated Primary Maximum Rating of Overcurrent Protective Device marized in Table 4A below. Current Amperes of Transformer Primary current Rating No secondary Secondary fusing provided Table 4A fusing provided accordance with Table 7 Less than 2 300 Rated Primary Maximum Rating of Fuse %o of Transtormer 2 to less than 9 167 Current Amperes Primary Current Rating (No Secondary Fusing Provided) 9 or more 125 250 Less than 2 300 Table 3 2 to less than g Maximum Acceptable Rating of Secondary Overcurrent Device C ar 125 Rated Secondary Maximum Rating of Overcurrent Protective Device 2. If 125% does not correspond to a standard fuse rating, the next higher s andard Current Amperes % of Transformer Secondary Current Rating rating may be used Less than g KLDR= Littelfuse UL Class CC time-delay serie g or more 1252 1. 500 for Motor circuit control power transformers 2. If 125% does not correspond to a standard fuse rating the next higher standard rating may be used Reference NEC 430.72(c) Exception No. 2: 450.3(b) 1 and 2 UL 508 32. 7: 845 11.16 nd1117 C 2010 Littelfuse POWR-GARDQ Products ww. littelfuse com Transformer Protection Basics Expertise AppliedAnswers Delivered 直目目里目 Table 5 Class j Fuse Protection Of Standard Transformers with Secondary Table 6 shows recommended Class cc fuse ratings for Protection-230, 460, 575 Volts single-Phase transformers with single-winding 240 Volt primaries while NEC anc UL Maximum Allowable Fusing amps) With Secondary Protection Table 7 shows similar recommendations for transformers 230 Volts Single Phase 460 Volts Single-Phase 575 Volts Single-Phase with single-Winding 480 Volt primaries JTD or JTD or kvA Current(A) JTD ID Primary TD In Primary Table 6 Series Current(A)JTD_ID Series Class cc fuse Protection Of Transformers With single-Winding Primaries- 0.15 0.65 1-1/2 033 8/10 26 KLDR 3/4 240 Volt Primary 0.76 061 1-1/2 NEC and UL Littelfuse Maximum Allowable Fusing(amps) Recommended 087 212 With Only Primary Prote ction 0.75 3.26 130 4.35 1021761745 Transformer Primary Control Power Standard Time di Current(A) Transformer Transformer KLDR Series 261 0.10 1/2 0 2.00 8.70 4.35 10 8 0.21 1087 5.43 1-12 10 657 0.42 1522 17-1/2 609 21745010972587020 54 21/2 1-6/10 8/10 5.00 63 18/10 40 13.91 80173401435 200 0.83 2-1/2 1-1/2 1000 4348 100 21 1739 业电 250 04 已30012561431/2 2-1/2 KLDR- Littelfuse UL Class CC time-delay series 1.46 4-1/2 Fuse recommendat ons are based on maximum acceptable rating of primary fuse as oer nec 3-12 3-1/2 3-1/2 450.3(b UL 508 32 7, and UL 845 11.16 and 11. 17, as summarized in table 53 below 3.13 5-7/10 57/10 Table 5B 公可网:wW, 93 10 10 Rated Primary Maximum Rating of Fuse of Transformer These fuse ratings permissible only when secondary protection is provided in accordance with Current Amperes Primary Current Rating (Second ary Fusing Provided Table 6B. (See reverse side) Less than 2 动线:01 I Based on NEC 430. 73(C) 0111 2 or more Table Class cc fuse Protection Of Transformers With single-Winding Primaries sEcondary fusing provided in accordance with Table 5C shown below 480 Volt Primary See NEC Table 45031B)for exceptions MECS and UL Maximum Table 5c Allowable Fusing (am ps) I ittelfuise With Only Primary Protection Recommended fuse Rated Secandary Maximum Rating of Fuse of Transformer Current Amperes Secondary Current Rating Transformer Primary Currert Control Power Time Delay KLDR Less than 9 Transformer Transformer g or more 1252 25 1/4 15/100 1/1C 50 0.10 1/2 10 3/1E If 125% does not correspond to a standard fuse rating the next higher standard rating 3/10 3/10 may be used 0.21 6/10 4/C 27 8/10 1/2 0.42 1-1/4 5 0.73 31/2 500 10C0 15[0 3.13 200 2500 5 10 10 "These fuse ratings permissible only when secondary protect on is prcvided in accordance w th Table B For Maximum Acceptable Rating of Primary Overcurrent Device refer to table 2 For Maximum Acceptable Rating af Secondary Overcurrent Device refer to table 5c C 2010 Littelfuse POWR-GARD Products ww. littelfuse com Transformer Protection Basics Expertise AppliedAnswers Delivered Transformer Protection for Medium Voltage pad-mounted transtormers, and at other similar locations Applications (above 600 Volts) When properly applied, E-Rated fuses can protect against high and low value fault currents. a supplemental device is Introduction needed in series to remove currents below the minimum Medium voltage fuses are applied quite differently than melting current rating of the fuse fuses rated 600 volts and less. The biggest difference is that Guidelines for E-Rated Fuses medium voltage fuses are not intended to provide overload protection. They should only be applied in situations where Fuses with a rating of 100e or less will open(blow) it will not be required to open small overcurrents Medium within 300 seconds (5 minutes) at a current between voltage fuses offer a much wider range of system voltages 200%and 240 of the"E"rating thereby resulting in a correspondingly large number of fuse Fuses with a rating above 100E will open(blow) within voltage ratings 600 seconds(10 minutes) at a current between 220% Descriptions and ratings of Littelfuse and 264% ot the E rating medium voltage fuses, along with Fuse Sizing some application data, are located in the Medium Voltage Fuse section of Fuses are sized at a percentage of the full load current the Littelfuse POWR-GARD Catalog Generally fuse size is based on 133 to 150 of To download a copy visit full load current cswww.littelfuse.com/catalogs Always round up to the next standard fuse rating For questions, contact our Technical Support andE As an example, .with a full load current of 104 amperes, the fuse size based on 133 of full load current would be a Engineering Services Group at 800-TEC-FUSE 138 ampere fuse. Such a fuse rating size does not exist, so (800-832-3873 ). Definitions of terms used in this white is permissible and recommended to round up to the next paper can be found in the Technical application guide standard size which in this instance is 150 amperes (150E) section of the POWR-GARD Catalog. XX e WWWBe sure to note that nuisance fuse openings can occur if The following is a more detailed discussion of factors which the fuse is sized too closely nust be considered when properly selecting and applying medium voltage fuses in electrical systems Table 8 线 Suggested Minimum current limiting medium voltage fuse current ratings for What are Medium Voltage Fuses? self-cooled 2.4-15.5 kv power transformer applications Littelfuse medium voltage fuses are silver-sand 48 7.2 non-expulsion design, current-limiting type devices Fus Max kV When properly applied, they are designed to carry their Trans-former Full Fuse nominal current rating continuously without" fatigue failure kVA Rated Current Rating This means that the fuse will not age, become brittle, or Self-Coole Amps(E) , Fuse Fuse Amos (ey Current Amps(E) deteriorate under the most severe duty cycling Single Phasa Transformers 5715 5 304 When talking current-limiting medium voltage fuses, there 2.1 14 3 are two basic types: general purpose and back-up. genera 25 10.4 purpose fuses have the ability to interrupt both large and 2212056 52 3.5 1562 255050 580500 1133458 small short-circuits down to currents that would cause the 75 3134 1562 5.2 100 208 13.9 3.6 fuse to open within one hour. They are used to provide 104 348 50 174 short-circuit protection for transformers, switchgear, and 333 192006951046365231 8000 similar equipment 278 400 CO 9.6150 E83 173 250 1155 578 85 Back-up fuses are designed to protect only against high 60 868 fault currents, and must be used in series with equipment Three Phase Transformers that provides the circuit's required overload and low value 15 short-cIrcuit protection 6 24451.2 75 18 While"R-Rated"medium voltage(MV) fuses are specifically 125 524[ b80 10 5 136 15 4.5 designed to provide short-circuit protection for medium 27.2 18 15 voltage motor controllers and associated equipment, 77 100 36 35 18 E-Rated"MV fuses are considered to be general purpose 5 0540505 9012 10 301 45 fuses. Their mounting dimensions permit them to be 350 120 40.1 241 802 installed in a wide variety of medium voltage switches, in 2500 600 C 2010 Littelfuse POWR-GARDQ Products ww. littelfuse com Transformer Protection Basics Expertise AppliedAnswers Delivered 直目目里目 Continuing with sizing of E-Rated fuses. the transformer 7. And where and whenever possible, fuses should sizing guide in Table 8 shows the suggested minimum protect the transformer against higher impedance current limiting medium voltage fuse current ratings for secondary faults self-cooled 2. 4-15.5 kv power transformer applications Transformer magnetizing or inrush current depends on several tactors including the transtormer's design, the amount of residual flux in the transformer core at the Transformer protection instant the transformer is energized, the point on the A principle use of medium voltage fuses is to provide voltage wave at which the switch is closed, and the primary short-circuit protection for transformers characteristics of the electrical system powering the When selecting MV fuses to protect transtormers transtormer. A power transtormers in-rush current the following factors must be considered in descending approximates 12 times the transformer full load current, order of importance While a distribution transformer s in-rush current can exceed 25 to 40 times of the full load current. The 1. The fuse's voltage and interrupting ratings must equal current generally lasts less than one-tenth of a second or exceed system requirements at the point where the fuses will be applied Fiqure 2 Typical Example of Double-ended Loadcenter Operated with 2. The fuse's continuous current rating must be large Normally Open Bus tie enough to withstand transformer magnetizing (in-rush current (Minimum Fuse rating) 3. The fuse's continuous current rating must be able to withstand transformer overloading and emergency 业电器有限 rners operation, while meeting all nEce requirements like this (Maximum Fuse Rating 4fusesromuthbreftectsesortmrcuitseontheleadsidewww.aphpo.com of the fuses. Utility System Coordination 5. Fuses must coordinate with the transformer seconda protection where and whenever possible ( Facility 010-5927 System Coordination) 6. Fuses must protect the transformer against secondary bolted faults Figure 1 Time-current Curves for Transformer Protection Application To determine the minimum size fuse that will withstand 1000 the in-rush current it is recommended that the in-rush current be obtained from the transformer manufacturer 400 Typical transformer damage curve for Then, note the current on the fuse s minimum melting 200 3-pha time-current curves at o10 second. this is illustrated in anc single-phase faults more detail in Figure 1. The fuse whose minimum melting on 1-phase transformers curve is just to the right and above the transformer inrush point becomes the minimum fuse rating to use for properly Melting Curve protecting the system Medium voltage fuses with current ratings that equal exceed a transformer s self-cooled. full load current will Fuse maximum Clearing Curve usually meet such a requirement when the in-rush current Maximum does not exceed 12 times transformer full load current Transformer Overload However, transformers are generally operated at close to full cUrrent oad current on a continuous basis and are often overloaded under emergency conditions. a typical example is a double- ended loadcenter operated with a normally open bus tie See Figure 2 ”°°R月883月罰导冒 CURRENT IN AMPERES C 2010 Littelfuse POWR-GARDQ Products ww. littelfuse com Transformer Protection Basics Expertise AppliedAnswers Delivered 直目目里目 Each transformer is rated to carry 150%of the load on its half of the loadcenter With loss of service to one transformer, the main switch for that line is opened and the bus tie switch is closed. this shifts all load to the remaining transformer. The system is operated in an overloaded state until the other line is back in service the outage continues for a long period of time, manual load shedding can be used to control transformer overloading Other similar operating schemes also result in transtormer overloading. As a result, medium voltage fuses usually have continuous current ratings larger than required to withstand transformer in-rush current NECQ Article 450 covers transformer installations an establishes the maximum ratings of transformer overcurrent protective devices. Regarding medium voltage fuses, NEC Article 450.3 states, in part Overcurrent Protection of transformers shall comply with NEC Article 450.3(A)-Transformers Over 600 Volts Nominal, and shall be provided in accordance with Table 9. NOTE/n this section. the word"transformer shall a业电器有限公司 mean a transformer or polyphase bank of two or more single-phase transformers operating as a single unit Table 9 公司网址:ww.pepo.com Based on NEC Table 450.3(A)Maximum Rating or Setting of Overcurrent Protection for Transformers Over 600 Volts (as a Percentage of Transformer-Rated current 销售热 Primary Protection Over9/90 Secondary Protection(See Note 2) Over 600 volts 600 Volts or less Location limitations Transformer rated Circuit Breaker Circuit Breaker Impedance (see Note 4) Fuse Rating see note 4 Fuse Rating Circuit Breaker or Fuse Rating Not more than 6%(see Note 1) 600% 300% 300 250 125% Any location More than 6% but not more than 10%(see Note 1) 400% 300% 250% 225% 125% any (see Note 1) 250% Not Required Supervised Not more than 6%(see Note 5 for 300 25 Locations Only /see Secondary protection 6U0% 250% Note 3 More than 6% but not more than 10%(see Note 5 for Secondary 400% 300% 250% 225% Protectio Note 1-I the required fuse rating or breaker setting does not correspond to standard rating/settings, the next higher rating/setting may be used. Note 2-If secondary overcurrent protection is reguired, no more than six breakers or sets of fuses may be grouped in any one location. When multiple overcurrent devices are usei, the sun ofall device ratings shall not exceed the allowed value of any sinigle device. ir bolh breakers and /uses are used, the lola o/ device ratings shall noi exceed that if using only fuses Note 3-A supervised location" is one where maintenance and supervision conditions ensure that only qualified persons are allowed to monitor and perform installation service on the transformer Note 4- Electronically actuated Tuses set to open at a specific current shall be set and calibrated in accordance with the corresponding settings of the circuit breakers involved. Note 5- Separate secondary protection is not necessary if the transformer is equipped with a coordinated thermal overload protection provided by the manufacturer. Additional technical information and application data for Littelfuse POWR-GARD protection relays, fuses and other circuit prote ction and safety products canbefoundonwww.littelfuse.com.ForquestionscontactourTechnicalSupportGroup(800-832-3873).Definitionsoftermsusedinthiswhitepapercan befoundintheTechnicalApplicationGuidesectionofthepOwr-gardCatalog.Todownloadacopyvisitwww.littelfuse.com/catalogs Form No. pf753 C 2010 Littelfuse POWR-GARDQ Products ww. littelfuse com

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