1ZSE en, Rev. 9. On-load tap-changers, type UC and VUC Technical guide

Transcription

1 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC Technical guide

2 The manufacturer Hereby declares that The products Manufacturer s declaration ABB AB Components SE LUDVIKA Sweden comply with the following requirements: On-load tap-changers, type UC and VUC with motor-drive mechanisms, types BUE2 and BUL By design, the machine, considered as component on a mineral oil filled power transformer, complies with the requirements of Machinery Directive 89/392/EEC (amended 91/368/EEC and 93/44/EEC) and 93/68/EEC (marking) provided that the installation and the electrical connection be correctly realized by the manufacturer of the transformer (e.g. in compliance with our Installation Instructions) and EMC Directive 89/336/EEC regarding the intrinsic characteristics to emission and immunity levels and Low Voltage Directive 73/23/EEC (modified by Directive 93/68/EEC) concerning the built-in motor and apparatus in the control circuits. Certificate of Incorporation: The machines above must not be put into service until the machinery into which they have been incorporated have been declared in conformity with the Machinery Directive. Date Signed by... Hans Linder Title Manager of Division for Tap-Changers This Technical Guide has been produced to allow transformer manufacturers, and their designers and engineers, access to all the technical information required to assist them in their selection of the appropriate tap-changer. The information provided in this document is intended to be general and does not cover all possible applications. Any specific application not covered should be referred directly to ABB, or its authorized representative. ABB makes no warranty or representation and assumes no liability for the accuracy of the information in this document or for the use of such information. All information in this document is subject to change without notice.

3 Content General information... 5 Design principles... 8 On-load tap-changer... 8 Diverter switches... 8 Conventional diverter switch... 8 Diverter switch with vacuum interrupters... 9 Tap selector... 9 Design differences over the UC range of on-load tap-changers Diverter switch housing and top section Painting Operating mechanism Transition resistors Special applications, load conditions, environments and insulating liquids Special designs On-line oil filtration (for diverter switch with arc quenching in oil only) Motor-drive mechanism Type BUE Type BUL Accessories Tap-changer principles of operation Switching sequence, UC Switching sequence, VUCG Type of regulation Linear switching (type L) Change-over selector for plus/minus switching (type R) Change-over selector for coarse/fine switching (type D) Type of connection Three-phase star point (N) Single-phase (E) Three-phase delta (B) Three-phase delta fully insulated (T) Auto transformer (T) Tap-changer characteristics and technical data Type designation Diverter switches Maximum number of positions Tap selectors Possible combinations of diverter switches and tap selectors Enforced current splitting In position During operation Rated phase step voltage Coarse fine regulation leakage inductance switching Contact life Standards and testing Rating plate Insulation levels Insulation levels to earth (g1)... 26

4 Withstand voltages UCG and VUCG with tap selector C UCG and VUCG with tap selector III unshielded version UCG and VUCG with tap selector III shielded version UCL with tap selector III unshielded version UCL with tap selector III shielded version UCD with tap selector III unshielded version UCD with tap selector III shielded version UCC with tap selector IV Short-circuit current strength Highest phase service voltage across the regulating winding Rated through-current Occasional overloading Oil temperature Coarse/fine regulation leakage inductance switching Installation and maintenance On-load tap-changer Installation Drying Weights Oil filling Maintenance Pressure Accessories and protection devices Motor-drive mechanism Design Installation Maintenance Operating shafts Dimensions Type UCG/C and VUCG/C Type UCG/III and VUCG/III Tables UCG and VUCG Type UCL/III Tables UCL Type UCD/III Tables UCD Type UCC/IV Tables UCC Oil conservator Appendices: Single-phase diagrams Appendix 1: Single-phase diagrams for UCG/C and VUCG/C Appendix 2: Single-phase diagrams for UCG/III, VUCG/III, UCL/III and UCD/III Appendix 3: Single-phase diagrams for UCC/IV... 63

5 General information When the on-load tap-changer operates, the insulating oil will be contaminated. To avoid contamination of the transformer oil, the diverter switch has its own housing separate from the rest of the transformer. The tap selector, which is mounted beneath the diverter switch housing, consists of the fine tap selector and usually also of a change-over selector. The operating principle for the UC and VUC range of on-load tapchangers is called the diverter switch principle. The UC types of on-load tap-changers are usually mounted inside of the transformer tank, suspended from the transformer cover. Power to operate the on-load tap-changer is supplied from the motor-drive mechanism, which is mounted on the outside of the transformer. The power is transmitted by means of shafts and bevel gears. The UC types of on-load tap-changers come in a wide range of models with a rating suitable for every application. Oil conservator Shaft Bevel gear Transformer cover Transformer tank Diverter switch Shaft On-load tap-changer Tap selector Motor-drive mechanism Fig. 1. Main parts, on-load tap-changers types UC and VUC. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 5

6 Buffer springs Cover Top section Bevel gear with position indicator Lifting eye Flange for connection to gas operated relay Top section Shielding-ring Insulating shaft Oil draining tube Shielding-ring Diverter switch Transition resistors Fixed and moving contacts Insulating cylinder Plug-in contacts Guiding pins Connections from the tap selector Driving disc for the diverter switch Valve for use at processing Bottom section Intermediate gear Current terminal Fig. 2. On-load tap-changer type UCG. 6 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

7 Transition resistors Plug-in contacts Vacuum interrupters Spring drive mechanism Fig. 3. On-load tap-changer type VUCG. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 7

8 Design principles On-load tap-changer When the on-load tap changer operates, the oil is contaminated. UC with conventional arc quenching in oil contaminates the oil heavily while VUC with arc quenching in vacuum interrupters only contaminates slightly due to current commutation sparks and heat dissipation from the transition resistors. To avoid contamination of the transformer oil the on-load tapchanger is built in two separate sections, the diverter switch, which has its own housing, and the tap selector. The tap selector is mounted below the diverter switch housing and the complete unit is suspended from the transformer cover. Conventional diverter switch The diverter switch is designed as a system of moving and fixed contacts. Movement of the moving contact system is controlled by a self-locking polygon link system with a set of helical springs. The link system is robust and has been carefully tested. The fixed contacts are placed on the sides of the diverter switch, which are made of insulated board. The current-carrying contacts are made of copper or copper and silver, and the breaking contacts of copper-tungsten. VUC and UC are of the diverter switch type. UC works according to the flag cycle principle and VUC works according to the pennant cycle principle. Diverter switches Two different types of diverter switches are available, the conventional type with arc quenching in oil and the new type with vacuum interrupters. The diverter switch is of the high-speed, spring-operated type with resistors as transition impedance. The diverter switches are equipped with plug-in contacts that automatically connect it to the bushings in the diverter switch housing when the switch is lowered into the housing. Guiding facilities keep the diverter switch in correct position when lowering it into the housing. Mechanical coupling to the motordrive mechanism is automatically established when the driving pin enters the slot in the driving disc. The design and dimensioning of the diverter switches offer high reliability and long life with a minimum of maintenance and easy inspection. Fig. 4. Examples of diverter switches UCG and VUCG. 8 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

9 Diverter switch with vacuum interrupters Combines all the advantages of the conventional type with improved breaking capacity, increased contact life and reduced maintenance. It works according to the pennant cycle, which gives the lowest complexity and allows full power flow in both directions. A mechanical rectifier ensures operation in only the direction that gives the lowest breaking stresses and contact wear. The load is commutated from one tap to the other by aid of the vacuum interrupters and auxiliary contacts. The auxiliary contacts are also able to break the load current in the unlikely event of a vacuum interrupter failure should occur. In service position the current is transferred through the auxiliary contacts and the vacuum interrupters. All current carrying contacts are made of low resistance material. The vacuum interrupters have a very long life time but yet mounted for easy replacement when needed, for instance in industrial applications when the number of operations might be extremely high. Tap selector Although the tap selector for the UC and VUC range of onload tap-changer is available in various sizes, all have similar functions with different ratings. The fixed contacts are mounted around the central shafts. The moving contacts are mounted on, and are operated by, the shafts in the center of the selector. The moving contacts are connected, via current collectors, to the diverter switch by means of paper insulated copper conductors. Depending on the load current, the moving contacts have either one, two, or more contact arms in parallel with one, two or four contact fingers each. The fingers make contact at one end with the fixed contact, and at the other with the current collector. The moving contacts slide on the fixed contacts and the current collector rings, giving a wiping action which makes the contacts self cleaning. This arrangement promotes good conductivity and negligible contact wear. The contact system is powered by a compact mechanical system with integrated driving springs, mechanical rectifier, robust mechanical system for vacuum interrupter actuating and geneva gears for operating the auxiliary contacts. All manufactured conventional UCG diverter switches can be easily replaced by the vacuum diverter switch and gain benefit of the improvements made on this type. Fig. 5. Tap selectors: size C and size III. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 9

10 Design differences over the UC range of on-load tap-changers The UC range of tap-changers consists of five diverter switches and three tap selectors. The diverter switches, from the smallest to the biggest type, are UCG, VUCG, UCL, UCD and UCC. VUCG has arc quencing in vacuum, all others have arc quencing in oil. The VUCG diverter switch fits without modification in all UCG tap-changers as manufactured 1977 and later, which enables all UCG tap-changers to be easily upgraded to vacuum technology. The tap selectors, from the smallest to the biggest type, are C, III and IV. Tap selector C can be combined with UCG and VUCG diverter switches. Tap selector III can be combined with all diverter switches except UCC. Tap selector IV can be combined with UCC only. For correct selection, use this Technical Guide or the ABB selection program Compas. UCG is available in two versions (standard and short) and manages MVA star connected transformers and up to approximately 500 MVA Auto transformers. UCL manages star connected transformers up to MVA and auto transformers up to 1000 MVA. UCD and UCC manages star connected transformers >600 MVA and >1000 MVA respectively. For winding connections where three single-phase tap-changers are needed, each single phase of the UCD and UCC must have it-s own motor-drive mechanism. In tap selector IV the fixed contacts are mounted on insulating bars, whereas the C and III types use a complete, un-divided glass fibre reinforced epoxi cylinder. UCG.N/C VUCG.N/C 650 kv UCG.N/III VUCG.N/III 650 kv UCL.N/III 650 kv UCD.N/III 650 kv UCC.N 650 kv L (m) Fig. 6. On-load tap-changers type UC, size comparison. 10 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

11 Diverter switch housing and top section The top section forms the flange that is used for mounting to the transformer cover, and for carrying the gear box for the operating shafts. The top section includes a connection for the conservator pipe, draining and filtering connections, an earthing terminal, the supervisory device, and the cover with its gasket. The top section is available in two designs, one for cover mounting and one for pre-mounting (yoke-mounting) on the transformer s active part. The diverter switch housings have high quality sealings that guarantee vacuum and overpressure-proof performance under all service conditions. In case of material ageing after extremely long service the sealings can be re-tightened. The bottoms and heads of the cylinders are made of cast aluminium. The driving shafts and bevel gears are placed beside the diverter switch cylinders, thereby providing easy access to the diverter switches. The bottom section has locating holes for the diverter switch, bearings, brackets for the tap selector mounting and the current terminal for the diverter switch. There is also a draining valve in the bottom which should only be opened during the drying process of the transformer. The top and bottom sections are fixed to a cylinder of glassfibre reinforced plastic. The bushings through the cylinder wall are sealed by O-ring gaskets with elastic pressure. Each ready-made unit is tested under vacuum and the outside is exposed to helium and checked for leaks with the use of a helium gas detector. Painting The diverter switch housing top sections are finish coated with a blue-grey colour, Munsell 5,5 B 5,5/1,25, corrosion class C3 according to SS-EN ISO For higher corrosion classes such as C4 or C5, please contact ABB for further information. Operating mechanism The bevel gear, mounted on the top section flange transfers the drive from the motor-drive mechanism, via the vertical shaft, to the intermediate gear for the diverter switch and the tap selector. From the intermediate gear, a drive shaft transfers the energy to the diverter switch through an oil tight gland in the bottom of the diverter switch housing. When the diverter switch is lowered into the housing (after inspection), the drive is automatically re-connected by a system that ensures that the drive shaft and the guiding pin of the diverter mechanism is correctly aligned. The intermediate gear also drives the geneva gear of the tap selector, via a free wheel connection. The geneva gear provides alternate movement to the two vertical shafts of the tap selector. The external drive shaft, that does not need to be removed during maintenance work, minimizes the risk for misalignment in the system. However a mechanical end limit stop for the tap selector is available on request. Special shaft systems are also available on request. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 11

12 Transition resistors The transition resistors are made of wire and located above the diverter switch contacts. The resistors are robust and designed to withstand the lifetime of the mechanism under normal service conditions. Special applications, load conditions, environments and insulating liquids Please contact the supplier for advisory in the following cases: For special applications such as: -- Arc furnace -- HVDC -- Rectifiers -- Shunt reactors -- Series reactors -- Phase shifters -- Traction -- Industrial applications in general -- OLTCs working in parallel In case of unusual load conditions such as overloads beyond IEC or IEEE C , extreme inductive or capacitive loads or loads beyond the given data in this document. In case of service in extreme environments such as very high humidity, very high or low temperatures, indoors, etc. In case of requirement of other insulating liquids than mineral oil. Special designs On request, the UC and VUC tap-changers are also available for regulation with bias winding and for Y/D regulation. On-line oil filtration (for diverter switch with arc quenching in oil only) On-line oil filtration is not required in any application and does not extend lifetime of contacts, but can give benefits for OLTCs with arc quenching in oil in certain applications such as: Arc furnace applications (prolongs mechanical life and maintenance interval and shortens maintenance time) High voltage line end applications (maintains the high dielectric withstand of the insulating liquid) Whenever short outage time is important when carrying out maintenance At any application with a high number of operations or high dielectric stresses. The on-line oil filtration works with continuous low flow filtration giving the best filtration result, less risk of gas bubbles and requires less control equipment. Filter cartridges are easily replaced without taking the transformer out of service. For further information about the oil filter, see manual 1ZSC AAA. The filtration reduces the number of particles and keeps the moisture level at a dielectric safe level. 12 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

13 Motor-drive mechanism The motor-drive mechanism provides the drive to allow the on-load tap-changer to operate. Energy is provided from a motor through a series of gears and out through a drive shaft. Several features are incorporated within the mechanism to promote long service intervals and reliability. There are two sizes of motor-drive mechanisms that can be used. If there are any doubts about which type to select, please consult the supplier. Type BUE2 The BUE2 (Fig. 7) is intended for all on-load tap-changers types UC and VUC. For detailed operation description, see Technical Guide for Motor-Drive Mechanisms type BUE2. Type BUL The BUL (Fig. 8) is intended for on-load tap-changers types UCG, VUCG, and UCL at star point or single-phase applications. However, when extra space is required for optional accessories the type BUE2 might have to be selected due to limited space in the BUL. For detailed operation description, see Technical Guide for Motor-Drive Mechanisms type BUL. Accessories For a list of accessories available for both the on-load tapchangers and the motor-drive mechanisms, consult the supplier. Fig. 7. Motor-drive mechanism type BUE2. Fig. 8. Motor-drive mechanism type BUL. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 13

14 Tap-changer principles of operation Switching sequence, UC The switching sequence of the on-load tap-changer from position 6 to position 5, is shown in the figures below. The sequence is designated the symmetrical flag cycle. This means that the main switching contact of the diverter switch, breaks before the transition resistors are connected across the regulating step. This ensures maximum reliability when the switch operates with overloads. At rated load the breaking takes place at the first current zero after contact separation, which means an average arcing time of approximately 4-6 ms. The total time for a complete sequence is approximately 50 ms. The tap change operation time of the motor-drive mechanism is approximately 5 s/step. (10 s for through-positions). Fig 9a. Position 6 Selector contact V connects tap 6 and selector contact H on tap 7. The main contact x carries the load current. Fig. 9d The resistor contact u has closed. The load current is shared between Ry and Ru. The circulating current is limited by the resistance of Ry plus Ru. Fig. 9b Selector contact H has moved in the no-load state from tap 7 to tap 5. Fig. 9e The resistor contact y has opened. The load current passes through Ru and contact u. Fig. 9c The main contact x has opened. The load current passes through the resistor Ry and the resistor contact y. Fig. 9f. Position 5 The main contact v has closed, resistor Ru is bypassed and the load current passes through the main contact v. The on-load tapchanger is now in position On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

15 Switching sequence, VUCG By using an auxiliary contact system (MC, RC) in combination with the vacuum interrupters (MVI, RVI) only two vacuum interrupters are required per phase. Fig. 10a shows the current path during normal operation, from x to the star point (could also be to the next phase). When commuting the load from x to v, the first part of the operation sequence is to open the main vacuum interrupter (MVI) and hence let the current flow through the transition resistor (TR), Fig. 10b. The main contact (MC) is then rotated (Figs. 10c and 10d) in order to connect to v. The main vacuum interrupter then closes, leading to an associated circulating current driven by the difference in voltage potential, Fig. 10e. In Fig. 10f, the transition resistor is disconnected when opening the resistor vacuum interrupters (RVI). The load current is now via the normal path from v to the star point. The resistor contact (RC) is then rotated and put in position according to Fig. 10g. Finally, the sequence is completed and next service position is reached when the resistor vacuum interrupter is closed, see Fig. 10h. x x MVI MC RC TR RVI MVI MC RC TR RVI v v Fig. 10a. Fig. 10e. x x MVI MC RC TR RVI MVI MC RC TR RVI v v Fig. 10b. Fig. 10f. x x MVI MC RC TR RVI MVI MC RC TR RVI v v Fig. 10c. Fig. 10g. x x MVI MC RC TR RVI MVI MC RC TR RVI v v Fig. 10d. Fig. 10h. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 15

16 Type of regulation Linear switching (type L) The regulating range is equal to the voltage of the tapped winding. No change-over selector is used. Fig. 12. Fig. 12. Change-over selector for plus/minus switching (type R) The change-over selector extends the regulating range to twice the voltage of the tapped winding, by connecting the main winding to different ends of the regulating winding. Fig. 13. Reversing Change-over selector Fig. 13. Change-over selector for coarse/fine switching (type D) In type D switching the change-over selector extends the regulating range to twice the voltage of the tapped winding, by connecting or disconnecting the coarse regulating winding. Fig. 14. Change-over selector, coarse/fine Fig On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

17 Type of connection Three-phase star point (N) Only one unit is required for all three phases. The transformers neutral point is in the OLTC. Fig. 15. Single-phase (E) Only one unit is required Fig. 16. Three-phase delta (B) Two units required. Driven by a common motor-drive. One unit common for two phases. Fig. 17. Three-phase delta fully insulated (T) Three units required. Driven by a common motor-drive. Fig. 18. Auto transformer (T) Several configurations of auto transformers exist. This example shows the tap-changer in auto-tap. Fig ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 17

18 Tap-changer characteristics and technical data Type designation UCG.. VUCG.. UCL.. UCD.. UCC.. XXXX/YYYY/Z XXXX/YYYY/Z XXXX/YYYY/Z XXXX/YYYY/Z XXXX/YYYY Example UCGRE 650/700/C Type of tap-changer UC... Diverter switch with arc quenching in oil VUC... Diverter switch with vacuum interrupters Type of switching L Linear R Plus/Minus D Coarse/Fine Type of connection N Three-phase star point (one unit) E Single-phase (one unit) T Three-phase fully insulated (three units) B Three-phase delta (two units; single-phase and two-phase) Impulse withstand voltage to earth UCG, VUCG: 380 kv, 650 kv, 750 kv, 1050 kv UCL: 380 kv, 650 kv, 750 kv, 1050 kv UCD, UCC: 380 kv, 650 kv, 1050 kv Maximum rated through-current See tables for diverter switches and tap selectors respectively. The lowest rating of the two determines the overall rating. Tap selector size C tap selector for UCG and VUCG only III tap selector for UCG, VUCG, UCL and UCD IV tap selector for UCC 18 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

19 Diverter switches Tap selectors Type Max. rated through-current VUCG.N, B, E, T 450, 600, 700, 800 A VUCG.N, B, E, T, short version 1 ) 450, 600 A UCG.N, B 400, 500, 600 A UCG.E, T 500, 600, 900, 1200, 1500 A UCG.N, B, short version 1) 300 A UCG.E, T, short version 1) 900 A UCL.N, B 600, 900 A UCL.E, T 600, 900, 1800, 2400 A UCD.N 2) 1000 A UCD.E 2) 1600 A UCC.N 2) 1600 A UCC.E 2) 1600 A Table 1. Diverter switches. 1) Shorter diverter switch housings, see dimension drawings in this guide. See also limits in Fig ) UCC and UCD requires one motor-drive mechanism for each OLTC unit. Type Connection Max. rated through-current Max impulse test voltage across range C N, B 600 A 350 kv E, T 600, 1200, 1500 A 350 kv III N, B 1000 A 550 kv 2) E, T 1000, 1800, 2400 A 550 kv 2) IV 1) N, E 1600 A 500 kv Table 2. Tap selectors. 1) UCC requires one motor-drive mechanism for each unit and is therefore not available in connection B and T. 2) Note that for certain positions, these values are lower. See Insulating levels. Possible combinations of diverter switches and tap selectors Diverter switch UCG, VUCG UCL UCD UCC Tap selector C III IV Maximum number of positions Type of switching Tap selector Max. number of positions Linear C 18 III 22 IV 18 Plus/minus C 35 III 35 IV 35 Coarse/fine C 35 III 35 IV 35 Table 3. Maximum number of positions. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 19

20 Enforced current splitting In certain applications, two or more poles of an on-load tapchanger, or more than one on-load tap-changer can work in parallel. However, it is important to make this in a correct way. It differs between whether it should work in position (not during operation) only or if it should work during operation. In position Enforced current splitting in position is used only between poles within one on-load tap-changer for operation in one phase. It is used when having a tap selector with a lower current rating than the diverter switch. By having the same number of conductors through the regulating winding as there are poles in the tap selector and connect each of them to one pole of the tap selector, the rating for one pole times the number of poles can be made use of. Otherwise a certain reduction in current rating has to be done due to unequal current splitting between the poles. During operation Enforced current splitting during operation can be used when the diverter switch has a lower current rating than the tap selector or when two or more on-load tap-changers work in parallel in the same phase. By having the same number of conductors in parallel through the windings as there are poles or on-load tap-changers in parallel, parallel working conditions can be made to work. However, the impedance between these parallel paths must be such that the current through any of the poles or any of the on-load tap-changers must not exceed the rating of any of them. The reason is that the poles in the diverter switch or the diverter switches do not operate at exactly the same time. To achieve this impedance, it is normally required that the parallel conductors are kept separated through both the regulating and the main winding. However, the impedance between them must be calculated by the transformer manufacturer in each case where enforced current splitting during operation should be made use of. See also IEC , paragraph for information. 20 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

21 Rated phase step voltage The maximum permitted step voltage is limited by the electrical strength and the switching capacity of the diverter switch. The rated phase step voltage is a function of the rated through current as shown in the diagrams below. For arc furnace transformers, only up to 75 % of the given step voltages below are allowed. In case the current during electrode short circuits exceeds twice the rated through-current, please contact the supplier for advice. UCG and VUCG in short version have a 220 mm shorter diverter switch housing, see dimension drawings in this document. For short version, there might be restrictions in applications other than network. Coarse fine regulation leakage inductance switching When operating from the ends of the fine or the coarse winding a high leakage inductande might appear causing a phase shift between the switched current and the recovery voltage. This value has to be given when ordering an OLTC so a proper dimensioning is possible. The leakage inductance value can be given in our order data sheet or be calculated by us from active part dimensions and number of turns. For more information, see IEC or product information UCG.N,B UCG.E,T Step voltage (V) UCG.N,B Short version UCG.E,T Short version Rated through-current (A) Fig. 20. Rated phase step voltage for type UCG Step voltage (V) VUCG.N,B,E,T Short version VUCG.N,B,E,T Rated through-current (A) Fig. 21. Rated phase step voltage for type VUCG. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 21

22 5000 Step voltage (V) 4500 UCL.N,B 4000 UCL.E,T Rated through-current (A) Fig. 22. Rated phase step voltage for type UCL. Step voltage (V) UCC.N For higher values contact ABB UCC.E Rated through-current (A) Fig. 24. Rated phase step voltage for type UCC. Step voltage (V) UCD.E UCD.N 3000 For higher values contact ABB Rated through-current (A) Fig. 25. Rated phase step voltage for type UCD. 22 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

23 Contact life The predicted contact life of the fixed and moving contact of the diverter switch, is shown as a function of the rated through current in the diagrams below. It is based on the type test with switching operations, and a current corresponding to the maximum rated through current. The contact life is stated on the rating plate. Fig. 26. Contact life for type UCG. No.of operations UCG.N,B 100% load 80% average load Rated through-current (A) UCG.E,T 100% load 80% average load No.of operations VUCG.N,B,E,T Rated through-current (A) Fig. 27. Contact life for type VUCG. No.of operations UCL.N,B % load % average load UCL.E,T 100% load % average load Rated through-current (A) Fig. 28. Contact life for type UCL. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 23

24 No.of operations UCC.N 100% load % average load Rated through-current (A) UCC.E 100% load Fig. 30. Contact life for type UCC. No.of operations UCD.E 100% load UCD.N 100% load Rated through-current (A) 1600 Fig. 31. Contact life for type UCD. 24 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

25 Standards and testing The on-load tap-changers made by ABB fulfil the requirements according to IEC , , and IEEE C The type tests include: Contact temperature rise test Switching tests Short-circuit current test Transition impedance test Mechanical tests Dielectric tests The routine tests include: Check of assembly Mechanical test Sequence test Auxiliary circuits insulation test Vacuum test Final inspection Rating plate Fig. 32. Example of rating plate. fm_ ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 25

26 Insulation levels LI is the lightning impulse (1.2/50 µs) to earth. pf is the power frequency test voltage to earth (60 s). The insulation levels are indicated as impulse withstand voltage power frequency withstand voltage. a2 b1 corresponding contact in adjacent phase The tests were carried out according to IEC , , with a new on-load tap-changer and clean insulation transformer oil I -30 C according to IEC The withstand voltage value of the oil was higher than 40 kv/2.5 mm (IEC 60156). a1 e1 b1 b2 g1 Fig. 33. Linear switching (L). Insulation levels to earth (g1) For UCG and VUCG kv, kv, kv and kv For UCL kv, kv, kv and kv For UCC and UCD kv, kv and kv corresponding contacts in adjacent phase b1 Lightning impulse levels (LI) and power frequency levels (Pf) corresponds to the following U m -values acc. to IEC: a2 a1 LI (kv) Pf (kv) Um (kv) Table 4. a1 Between electrically adjacent contacts in the tap selector, not connected. a2 Between the ends of the fine regulating winding (across range). For coarse/fine switching in minus position, this means between the freely oscillating end of the coarse winding and any end of the fine winding. b1 Between not connected taps of different phases in the fine selector b2 Between open contacts of different phases in the diverter switch. c1 Between ends of the coarse winding in coarse/fine switching d1 Between not connected taps of different phases in the coarse selector (coarse/fine switching) e1 Between preselected tap and connected tap of one phase in the diverter switch and in the tap selector. f1 Between any end of the coarse winding and connected tap f2 Between any end of the coarse winding and the middle of the fine winding. g1 Connected tap to earth Fig. 34. Reversing switching (R). a2 f2 c1 Fig. 35. Coarse/Fine switching (D). a1 f1 e1 e1 b1 corresponding contacts in adjacent phase d1 b1 d1 b2 g1 b2 g1 26 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

27 Withstand voltages UCG and VUCG with tap selector C All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). a1 is not valid since the contact locations are such that electrically adjacent contacts are never physically adjacent, see connection diagrams in this document. Type of No. of Within one phase Between phases for neutral point switching positions a2 c1 f1 f2 e1 b2 b1 d1 L L L R R R R R D D D D D Table 5. UCG and VUCG with tap selector III unshielded version All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of switching No. of positions Within one phase Between phases for neutral point a1 a2 c1 f1 f2 e1 b2 b1 d1 L L L R R R R R R D D D D D D Table 6. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 27

28 UCG and VUCG with tap selector III shielded version All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of switching No. of positions Within one phase Between phases for neutral point a1 a2 c1 f1 f2 e1 b2 b1 d1 L L L L R R R R R R D D D D D D Table 7. UCL with tap selector III unshielded version All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of switching No. of positions Within one phase Between phases for neutral point a1 a2 c1 f1 f2 e1 b2 b1 d1 L L L R R R R R R D D D D D D Table On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

29 UCL with tap selector III shielded version All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of switching No. of positions Within one phase Between phases for neutral point a1 a2 c1 f1 f2 e1 b2 b1 d1 L L L L R R R R R R D D D D D D Table 9. UCD with tap selector III unshielded version All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of switching No. of positions Within one phase Between phases for neutral point a1 a2 c1 f1 f2 e1 b2 b1 d1 L L L R R R R R R D D D D D D Table 10. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 29

30 UCD with tap selector III shielded version All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of switching No. of positions Within one phase Between phases for neutral point a1 a2 c1 f1 f2 e1 b2 b1 d1 L L L L R R R R R R D D D D D D Table 11. UCC with tap selector IV All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of switching Shielded (s)/unshielded No. of positions Within one phase Between phases for neutral point a1 a2 c1 f1 f2 e1 b2 b1 d1 (us) L us L s L us L s R us R s R us R s R us R s R us R s D us D s D us D s Table On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

31 Short-circuit current strength The short circuit current strength is verified with three applications of 2 or 3 seconds duration, without moving the contacts between the three applications. Each application has an initial value of at least 2.5 times the rms value. Diverter switch Tap selector Max rated through-current, Type of connection 2 s duration, ka 3 s duration, ka Peak value, ka A rms rms rms UCG C 300, 400 N,B,E,T C 500, 600 N,B,E,T C 500 E,T C 600 E,T C 900 E,T C 1200 E,T C 1500 E,T III 300 N,B,E,T 7 1) 6 1) 18 III 500 N,B,E,T 7 1) 6 1) 18 III 600 N,B,E,T 7 1) 6 1) 18 III 900 E,T III 1200 E,T III 1500 E,T VUCG C 600 N,B,E,T C 800 E,T 8 1) 8 1) 22 III 800 N,B,E,T 8 1) 8 1) 22 UCL III 600 N,B,E,T 11 1) 11 1) 30 III 900 N,B,E,T 11 1) 11 1) 30 III 1800 E,T III 2400 E,T UCD III 1000 N,B,E,T III 1600 E,T ) 45 UCC IV 1600 N,E ) 45 Table 13. 1) In case of UC..E,T or VUC..E,T higher values are possible on request. 2) Available for reinforced performance with 24 karms and 60 kapeak. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 31

32 Highest phase service voltage across the regulating winding The table below show the highest permissible phase service voltage for the different types of connections. Across the regulating winding (kv) Across the coarse and fine winding (kv) Contact shieldings: with without with without Tap-changer, tap selector UCC.N IV UCD.N III UCL.N III UCG.N III UCC.E IV UCD.E, III UCL.T, E, B III UCG.T, E, B III UCG.N C UCG.T, E, B C VUCG.T, E, B III VUCG.N C VUCG.T, E, B C Table 14. Highest permissible phase service voltage across the regulating winding. 32 On-load tap-changers, type UC and VUC, Technical guide 1ZSE en, Rev. 9

33 Rated through-current The rated through-current of the on-load tap-changer is the current which the on-load tap-changer is capable of transferring from one tapping to the other at the relevant rated step voltage, and which can be carried continuously whilst meeting the technical data in this document. The rated through current is normally the same as the highest tapping current. The rated through-current is limited by the step voltage according to the curves in the diagrams, Figs The rated throughcurrent determines the dimensioning of the transition resistors and the contact life. The rated through-current is stated on the rating plate, Fig. 23. Occasional overloading If the rated through-current of the tap-changer is not less than the highest value of tapping current of the tapped winding of the transformer, the tap-changer will not restrict the occasional overloading of the transformer, according to IEC , , and ANSI/IEEE C To meet these requirements, the UC models have been designed so that the contact temperature rise over the surrounding oil does not exceed 20 K when loaded with a current of 1.2 times the maximum rated through current of the tap-changer. The contact life stated on the rating plate is given with consideration that currents of maximum 1.5 times the rated through current occur during a maximum of 3 % of the tapchange operations. Overloading beyond these values, results in increased contact wear and shorter contact life. For more information about overloading, read the appropriate parts of IEC , Oil temperature Provided that insulating oil of class Transformer oil -30 C according to IEC 60296, , is used, the temperature of the oil surrounding the on-load tap-changer shall be between -25 and +105 C for normal operation, as illustrated below. The range for UC (not VUC!) can be extended to -40 C provided that the viscosity does not exceed 2500 mm 2 /s (=cst). 1. No operations allowed. 2. Emergency overloading. The on-load tap-changer will not restrict the occasional overloading of the transformer according to the standards stated in section Occasional overloading. 3. Normal operating range. Individual brands need to be evaluated from case to case because of differences in viscosity compared to transformer grade mineral oil and the subsequent difference in heat dissipation. Also dielectric strengths and influence form moisture needs to be considered. Switching in vacuum generally opens for use of a wider range of insulating fluids. 4. UC: When operating within this range, no overloading is allowed. VUC: No operation allowed. 5. UC: Operation with de-energized transformer only. VUC: No operation allowed. Fig. 36. Oil temperature. 1ZSE en, Rev. 9 On-load tap-changers, type UC and VUC, Technical guide 33