1ZSC AAW en, Rev. 2. On-load tap-changers, type UC Technical guide

Transcription

1 1ZSC AAW en, Rev. 2 On-load tap-changers, type UC Technical guide

2 Original instruction 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. This document must not be copied without our written permission, and the contents thereof must not be imparted to a third party nor be used for any unauthorized purpose. Contravention will be prosecuted.

3 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 with motor-drive mechanisms, types BUE and BUL By design, the machine, considered as a component of 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 are 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 has been declared in conformity with the Machinery Directive. Date Signed by... Erik Backström Title Manager Tap-Changers, Local Product Group Unit Components

4 Content Design principles... 6 On-load tap-changer (OLTC)... 6 Diverter switches... 8 Insulating liquids Motor-drive mechanism Accessories Tap-changer principles of operation Switching sequence, UC 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 neutral point (N) Single-phase (E) Three-phase delta (B) Three-phase fully insulated, delta (T) Tap-changer characteristics and technical data Type designation Type of tap-changer Type of regulation Type of connection Impulse withstand voltage to earth Maximum rated through-current Tap selector size Tap selector shielding Diverter switches Tap selectors Possible combinations of diverter switches and tap selectors Maximum number of positions Enforced current splitting Rated phase step voltage Coarse fine regulation leakage inductance switching Contact life Standards and testing Rating plate Insulation levels Insulation levels to earth (g1 and g2) Withstand voltages UCG with tap selector C UCG with tap selector III unshielded version UCG with tap selector III shielded version UCG with tap selector F UCL with tap selector III unshielded version UCL with tap selector III shielded version UCL with tap selector F UCD with tap selector III unshielded version UCD with tap selector III shielded version UCC with tap selector IV... 28

5 Short-circuit current strength Highest phase service voltage across the regulating winding Oil temperature Alternative insulating liquids Rated through-current Occasional overloading Coarse/fine regulation leakage inductance switching Tie-in resistor and tie-in resistor switch Installation and maintenance Tap-changer Installation Drying Weights Oil filling Maintenance Pressure Accessories and protection devices Motor-drive mechanism Design Installation Maintenance Operating shafts Dimensions Dimensions, type UCG Type UCG.E and UCG.N with tap selector type C and cover mounting Type UCG.E and UCG.N with tap selector III and with tie-in resistor switch Type UCG.E with tap selector F and with tie-in resistor switch Type UCG.B with tap selector F and with tie-in resistor switch Dimensions, type UCL Type UCL.E and UCL.N with tap selector III and with tie-in resistor switch Type UCL.B with tap selector III and with tie-in resistor switch Type UCL.E and UCL.N with tap selector F and with tie-in resistor switch Type UCL.B with tap selector F and with tie-in resistor switch Dimensions, type UCD Dimensions, type UCC Motor-drive mechanisms Oil conservator Appendices: Single-phase diagrams Appendix 1: Single-phase diagrams for UCG/C Appendix 2: Single-phase diagrams for UCG/III, UCL/III and UCD/III Appendix 3: Single-phase diagrams for UCG/F and UCL/F Appendix 4: Single-phase diagrams for UCC/IV... 72

6 Design principles On-load tap-changer (OLTC) UC diverter switch tap-changer family comes in a range of models with ratings suitable for the most frequent transformer applications. The UC types of tap-changers are usually mounted inside the transformer tank, suspended from the transformer cover. This design consists of two separate sections: the diverter switch, which has its own housing separate from the rest of the transformer, and the tap selector. 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. Power to operate the 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, with arc quenching in oil, contaminate the oil heavily. To avoid contamination of the transformer oil the tapchanger is built in two separate sections: the diverter switch, which has its own housing separate from the rest of the transformer, and the tap selector. 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. 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 type UC. 6 Technical guide UC 1ZSC AAW en, Rev. 2

7 Buffer springs Cover Bevel gear with position indicator Lifting eye Connection flanges (x4) Flange for connection to gas operated relay (transformer main tank) Top section Shielding-ring Insulating shaft Oil draining tube Shielding-ring Diverter switch Transition resistors Fixed and moving contacts Insulating cylinder Plug-in contacts Guide pins Bushings connecting from the tap selector Driving disc for the diverter switch Valve for use at processing Bottom section Intermediate gear Current terminal Fig. 2. Diverter switch, type UCG, with housing. 1ZSC AAW en, Rev. 2 Technical guide UC 7

8 Diverter switches The diverter switches with arc quenching in oil, are of the high-speed, spring-operated type with resistors as transition impedance. They are equipped with plug-in contacts that automatically connect the switch to the bushings in the diverter switch housing when it is lowered into the housing. Guiding facilities keep the diverter switch in the correct position when lowering it into the housing. Mechanical coupling to the drive is easily established by making three operations in the same direction. The design and dimensioning of the diverter switches offer high reliability and long life with a minimum of maintenance and easy inspection. 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. Fig. 3. Examples of diverter switches UCG and UCL. 8 Technical guide UC 1ZSC AAW en, Rev. 2

9 Tap selectors Although the tap selectors for the UC range of tap-changer are 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. The tap selectors available for the UC range of tap-changers are C, III and F. Tap selector C can be combined with UCG diverter switches. Tap selectors III and F can be combined with both UCG and UCL. All tap selector types use a complete, un-divided glass fiber reinforced epoxy cylinder for the fine selector. The change-over selector contacts are all made of silver for high long-time stability and resistance against fretting. 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. Fig. 4. Tap selectors: size C, size III and size F. 1ZSC AAW en, Rev. 2 Technical guide UC 9

10 Design differences across the UC range of on-load tapchangers The UC range of tap-changers consists of four diverter switches and three tap selectors. The diverter switches, in order from the smallest to the biggest, are UCG, UCL, UCD and UCC, which all have arc quenching in oil. UCG is available in two versions (standard and short) and manages MVA star connected transformers and up to approximately 500 MVA Auto transformers. 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 its 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, undivided glass fiber reinforced epoxy cylinder. UCL manages star connected transformers up to MVA and auto transformers up to 1000 MVA. UCG.N/C 650 kv UCG.N/III 650 kv UCG.N/F 650 kv UCL.N/III 650 kv UCL.N/F 650 kv UCD.N/III 650 kv UCC.N 650 kv L (m) Fig. 5. On-load tap-changers type UC, size comparison. 10 Technical guide UC 1ZSC AAW en, Rev. 2

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 sampling 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 seals that guarantee vacuum and overpressure-proof performance under all service conditions. In case of material ageing after extremely long service the seals can be re-tightened from the inside of the housing. The bottoms and heads of the cylinders are made of cast aluminum. The drive 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 drain 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 glass fiber reinforced epoxi. 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 color, Munsell 5,5 B 5,5/1,25, corrosion class C3 according to SS-EN ISO and SS-EN ISO For higher corrosion classes such as C4 or C5, or higher, 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 insulated 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 easily re-connected by a simple procedure that ensures that the drive shaft and the guide pin of the diverter mechanism are 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, which does not need to be removed during maintenance work, minimizes the risk of 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. Transition resistors The transition resistors are made of wire and located above the diverter switch contacts. The resistors are robust and designed to last the lifetime of the mechanism under normal service conditions. Special applications, load conditions, and environments Please contact the supplier for advice in the following cases: For applications other than network. (Limitations in number of operations might be valid.) 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. Current measurement in phase before neutral point. Applications for reactors. Insulating liquids All data in this guide is based on the use of mineral oil according to IEC 60296, Other liquids, such as esthers and HMWH are accepted under certain conditions. Please consult ABB for advice. 1ZSC AAW en, Rev. 2 Technical guide UC 11

12 Special designs On request, the UC tap-changers are also available for regulation with bias winding and for Y/D regulation. On-line oil filtration On-line oil filtration is not required in any application and does not extend lifetime of contacts, but can give benefits for on-load tap-changers 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 ABB 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. The filtration reduces the number of particles and keeps the moisture level at a dielectric safe level. Motor-drive mechanism The motor-drive mechanism provides the drive to allow the 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. Accessories For a list of accessories available for both the tap-changers and the motor-drive mechanisms, contact ABB. 12 Technical guide UC 1ZSC AAW en, Rev. 2

13 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 Figs The sequence is designated the 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 for nonvacuum types 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 6. Position 6 Selector contact V connects tap 6 and selector contact H on tap 7. The main contact x carries the load current. Fig. 9. 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. 7. Selector contact H has moved in the no-load state from tap 7 to tap 5. Fig. 10. The resistor contact y has opened. The load current passes through Ru and contact u. Fig. 8. The main contact x has opened. The load current passes through the resistor Ry and the resistor contact y. Fig. 11. Position 5 The main contact v has closed, resistor Ru is bypassed and the load current passes through the main contact v. The tapchanger is now in position 5. 1ZSC AAW en, Rev. 2 Technical guide UC 13

14 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. Linear switching. 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, and thereby reversing the magnetic flux generated by the regulating winding. Reversing Change-over selector Fig. 13. Change-over selector for plus/minus switching. 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. Change-over selector, coarse/fine Fig. 14. Change-over selector for coarse/fine switching. 14 Technical guide UC 1ZSC AAW en, Rev. 2

15 Type of connection Three-phase neutral point (N) Only one unit is required for all three phases. The transformers neutral point is in the tap-changer. 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 fully insulated, delta (T) Three units required. Driven by a common motor-drive, except tap-changer types UCC and UCD. Fig ZSC AAW en, Rev. 2 Technical guide UC 15

16 Tap-changer characteristics and technical data Type designation UCG.. XXXX/YYYY/Z. UCL.. XXXX/YYYY/Z. UCD.. XXXX/YYYY/Z. UCC.. XXXX/YYYY/Z. Example UCGRE 650/700/C Type of tap-changer UC... Diverter switch with arc quenching in oil Type of regulation L Linear R Plus/Minus D Coarse/Fine Type of connection N Three-phase neutral 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: 380 kv, 650 kv, 750 kv, 1050 kv UCL: 380 kv, 650 kv, 750 kv, 1050 kv, 1175 kv UCD, UCC: 380 kv, 650 kv, 1050 kv Maximum rated through-current See tables for diverter switches and tap selectors respectively. The lower rating of the two determines the overall rating. Tap selector size C tap selector for UCG only III tap selector for UCG, UCL and UCD F tap selector for UCG and UCL IV tap selector for UCC Tap selector shielding us unshielded s shielded 16 Technical guide UC 1ZSC AAW en, Rev. 2

17 Diverter switches Type UCG.N, B UCG.E, T UCG.N, B, short version 1) UCG.E, T, short version 1) UCL.N, B UCL.E, T UCD.N 2) Max. rated through-current 300, 400, 500, 600 A 300, 500, 600, 900, 1200, 1500 A 300 A 300, 600, 900 A 600, 900, 925 A 600, 900, 1800, 2400, ) A 1000 A UCD.E 2) 1200, 1600 A 3) UCC.N 2) 1600 A UCC.E 2) 1600 A 3) Table 1. Diverter switches. 1) Shorter diverter switch housings, see dimension drawings in this guide. See also limits in Fig ) UCC and UCD require one motor-drive mechanism for each tap-changer unit. 3) For higher ratings, please contact ABB. 4) Enforced current splitting. Tap selectors Type Connection Max. rated through-current Max impulse test voltage across range C N, B 600 A 350 kv 2) E, T 600, 1200, 1500 A 350 kv 2) III N, B 1000 A 550 kv 2) E, T 1000, 1800, 2400 A 550 kv 2) F N, B 1800 A 550 kv E, T 1800, 3000 A 550 kv 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 UCL UCD UCC Tap selector C III F IV Maximum number of positions Type of switching Tap selector Max. number of positions Linear C, F, IV 18 III 22 Plus/minus C, III, F, IV 35 Coarse/fine C, III, F, IV 35 Table 3. Maximum number of positions. Enforced current splitting In certain applications, two or more poles of a tap-changer, or more than one tap-changer can work in parallel. However, it is important to implement this in a correct way. There is a difference between whether it should work in position (not during operation) only or if it should work during operation. If the current split is only needed in position, a weaker current split will work. By having the same number of conductors in parallel through the windings as there are poles or 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 tapchangers 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 must be calculated by the transformer manufacturer in each case where enforced current splitting during operation should be made use of. If the parallel conductors are located in separate parallel limbs (for single-phase transformers), the current split will be very strong. A strong current split may also be achieved if the parallel conductors are located in different coils in an axial split winding. Unless the parallel conductors are on separate parallel limbs, the impedance between parallel conductors must be calculated by the transformer manufacturer, when enforced current splitting during operation should be made use of. See also IEC , , paragraph for information. 1ZSC AAW en, Rev. 2 Technical guide UC 17

18 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. UCG in the short version has a 220 mm shorter diverter switch housing, see dimension drawings in this document. For short versions, there might be restrictions in applications other than network. For industrial applications or any other application where the number of operations is expected to exceed 100 operations per day, certain exceptions might apply, see product information 1ZSC ACM. Coarse fine regulation leakage inductance switching When operating from the ends of the fine or the coarse winding, a high leakage inductance might appear causing a phase shift between the switched current and the recovery voltage. This value has to be given when ordering a tapchanger so that proper dimensioning is possible. The leakage inductance value can be given in the order data sheet or can be calculated by ABB from active part dimensions and number of turns. For more information, see IEC , , or product information If values higher than acceptable for UC tap-changers are obtained, the VUC tap-changer is an alternative since it withstands higher values. Step voltage (V) UCG.N,B UCG.E,T UCG.N,B,E,T short version UCG.E,T short version Rated through-current (A) Fig. 19. Rated phase step voltage for type UCG. Step voltage (V) UCL.N,B UCL.E,T Rated through-current (A) Fig. 20. Rated phase step voltage for type UCL. 18 Technical guide UC 1ZSC AAW en, Rev. 2

19 Step voltage (V) UCC.E UCC.N For higher values contact ABB Rated through-current (A) Fig. 21. Rated phase step voltage for type UCC. Step voltage (V) UCD.N For higher values contact ABB UCD.E Rated through-current (A) Fig. 22. Rated phase step voltage for type UCD. 1ZSC AAW en, Rev. 2 Technical guide UC 19

20 Contact life The predicted contact life of the fixed and moving contacts of the diverter switch, are shown as a function of the rated through current in the diagrams below. It is based on the type test with 50,000 switching operations, and a current corresponding to the maximum rated through current. The contact life is stated on the rating plate. No. of operations UCG.N,B 100% load 80% average load UCG.E,T 100% load 80% average load Rated through-current (A) Fig. 23. Contact life for type UCG. No. of operations UCL.N,B 100% load 80% average load UCL.E,T 100% load 80% average load Rated through-current (A) Fig. 24. Contact life for type UCL. 20 Technical guide UC 1ZSC AAW en, Rev. 2

21 No. of operations UCC.N 100% load 80% average load Rated through-current (A) UCC.E 100% load Fig. 25. Contact life for type UCC. No. of operations UCDL.N 100% load UCD.E 100% load Rated through-current (A) Fig. 26. Contact life for type UCD. 1ZSC AAW en, Rev. 2 Technical guide UC 21

22 Standards and testing The on-load tap-changers made by ABB fulfill the requirements according to IEC , , and IEEE C Rating plate 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 Fig. 27. Example of rating plate. 22 Technical guide UC 1ZSC AAW en, Rev. 2

23 Insulation levels LI is the lightning impulse (1.2/50 µs), and Pf is the power frequency test voltage (60 s). The insulation levels are indicated as impulse withstand voltage power frequency withstand voltage. a2 e1 b1 b2 corresponding contact in adjacent phase The tests were carried out according to IEC , , with a new tap-changer and clean insulation transformer oil I -30 C according to IEC 60296, The withstand voltage value of the oil was higher than 40 kv/2.5 mm (IEC 60156, ). Fig. 28. Linear switching (L). a1 b1 g1 Insulation levels to earth (g1 and g2) For UCG and UCL kv, kv, kv, kv, and kv 1) For UCC and UCD kv, kv, and kv corresponding contacts in adjacent phase b1 Lightning impulse levels (LI) and power frequency levels (Pf) correspond to the following U m -values acc. to IEC: LI (kv) Pf (kv) Um (kv) a2 a ) e1 b1 b2 g1 Table 4. 1) Only UCL. 2) Covers 76 kv that is not an IEC value. Fig. 29. Reversing switching (R). a1 Between any 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 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 g2 Pre-selected tap to earth a2 Fig. 30. Coarse/Fine switching (D). f2 c1 corresponding contacts in adjacent phase d1 a1 f1 e1 b1 d1 g2 b2 g1 1ZSC AAW en, Rev. 2 Technical guide UC 23

24 Withstand voltages UCG 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 regulation positions a2 c1 f1 f2 e1 b2 b1 d1 L L L R R R R R D D D D D Table 5. Withstand voltages, UCG with tap selector C. UCG 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 No. of Within one phase Between phases for neutral point regulation positions a1 a2 c1 f1 f2 e1 b2 b1 d1 L L R R R R R R D D D D D D Table 6. Withstand voltages, UCG with tap selector III unshielded version. 24 Technical guide UC 1ZSC AAW en, Rev. 2

25 UCG 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 No. of Within one phase Between phases for neutral point regulation positions 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 7. Withstand voltages, UCG with tap selector III shielded version. UCG with tap selector F All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of No. of Within one phase Between phases for neutral point regulation positions a1 a2 c1 f1 f2 e1 b2 b1 d1 L R D Table 8. Withstand voltages, UCG with tap selector F. 1ZSC AAW en, Rev. 2 Technical guide UC 25

26 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 No. of Within one phase Between phases for neutral point regulation positions a1 a2 c1 f1 f2 e1 b2 b1 d1 L L R R R R R R D D D D D D Table 9. Withstand voltages, UCL with tap selector III unshielded version. 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 No. of Within one phase Between phases for neutral point regulation positions 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. Withstand voltages, UCL with tap selector III shielded version. 26 Technical guide UC 1ZSC AAW en, Rev. 2

27 UCL with tap selector F All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of No. of Within one phase Between phases for neutral point regulation positions a1 a2 c1 f1 f2 e1 b2 b1 d1 L R D Table 11. Withstand voltages, UCL with tap selector F. 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 No. of Within one phase Between phases for neutral point regulation positions a1 a2 c1 f1 f2 e1 b2 b1 d1 L L R R R R R R D D D D D D Table 12. Withstand voltages, UCD with tap selector III unshielded version. 1ZSC AAW en, Rev. 2 Technical guide UC 27

28 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 No. of Within one phase Between phases for neutral point regulation positions 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 13. Withstand voltages, UCD with tap selector III shielded version. UCC with tap selector IV All values given as 1.2/50 µs impulse withstand voltage (kv) power frequency withstand voltage (kv). Type of regulation Shielded (s)/ unshielded (us) No. of positions Within one phase Between phases for neutral point a1 a2 c1 f1 f2 e1 b2 b1 d1 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 14. Withstand voltages, UCC with tap selector IV. 28 Technical guide UC 1ZSC AAW en, Rev. 2

29 Short-circuit current strength The short circuit current strength is verified with three applications of 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 3 s duration, ka Peak value, ka A rms rms UCG C 300 N,B 6 15 C 500, 600 N,B,E,T 6 1) 15 C 900, 1200 E,T 12 1) 30 C 1500 E,T C ) E,T III 300 N,B 8 20 III 500, 600 N,B,E,T 8 1) 20 III 900 E,T III 1200, 1500 E,T III ) E,T F 450, 600, 700, 800 N,B,E,T 9 23 F 1000, 1200, 1500, 1800 E,T UCL III 600 N,B,E,T 11 1) 27.5 III 900, 925 N,B,E,T 11 1) 27.5 III 1800 E,T III 2400 E,T F 700, 1000, 1300 N,B,E,T UCD III 1000 N,E III 1600 E 18 2) 45 UCC IV 1600 N,E 18 2) 45 Table 15. Short-circuit current strength. 1) In case of UC..E,T higher values are possible on request. 2) Available for reinforced performance with 24 karms and 60 kapeak. Maximum rated through current is then reduced to 1500 A. 3) Requires enforced current splitting during operation. See section Enforced current splitting. 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) Tap-changer, tap selector with contact shieldings without contact shieldings with contact shieldings without contact shieldings UCG.N C UCG.N III 1) UCG.N F UCL.N III 1) UCL.N F UCD.N III 1) UCC.N IV UCG.B, E, T C UCG.B, E, T III 1) UCG.B, E, T F UCL.B, E, T III 1) UCL.B, E, T F UCD.E III 1) UCC.E IV Table 16. Highest permissible phase service voltage across the regulating winding. 1) Higher values available on request. Please contact ABB. 1ZSC AAW en, Rev. 2 Technical guide UC 29

30 Rated through-current The rated through-current of the tap-changer is the current which the 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 relation between rated through-current and step voltage is shown in Figs The rated through-current determines the dimensioning of the transition resistors and the contact life. The rated through-current is stated on the rating plate, Fig. 27. 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 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 tap-changer shall be between -25 and +105 C for normal operation, as illustrated below. The range for UC can be extended to -40 C provided that the viscosity does not exceed 2500 mm 2 /s (=cst). For tap-changers in applications with >100 operations/day, thermal monitoring is recommended. See product information 1ZSC ACM. Alternative insulating liquids Individual brands need to be evaluated from case to case because of the differences in viscosity compared to transformer grade mineral oil and the subsequent difference in heat dissipation. Also dielectric strengths and influence from moisture needs to be considered. Please contact ABB for more information. 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 the consideration that currents of a maximum 1.5 times the rated through current occur in a maximum of 3 % of the tap-change 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 , C No operations allowed. 2. Emergency overloading. The tap-changer will not restrict the occasional overloading of the transformer according to the standards stated in section Occasional overloading. 3. Normal operating range. 4. Operation possible under certain conditions. Please contact ABB for advice. 5. No operation allowed. Fig. 31. Oil temperature. 30 Technical guide UC 1ZSC AAW en, Rev. 2

31 Coarse/fine regulation leakage inductance switching When changing from the end of the fine winding to the end of the coarse winding, a high leakage inductance can be set up with the two windings in series. The critical moment occurs at switching the tap-changers mechanical mid-position, since switching of complete windings is performed. The leakage inductance that occurs from one loop, Fig. 32, is neglegible but can be substantial from the complete coarse and fine winding, Fig. 33. This leakage inductance causes a phase shift between switching current and recovery voltage that makes the breaking more severe. The tap-changer must be dimensioned accordingly. The leakage inductance shall be specified in the ordering data sheet. For certain winding configurations, such as coarse and fine windings located axially, this value might be so high that it requires a larger tap-changer than would be needed otherwise. In general, vacuum type tap-changers are less sensitive to this and might be an alternative for high values of leakage inductance. For more information, see IEC , , or consult ABB for advice. Tie-in resistor and tie-in resistor switch When the change-over selector operates, the tapped winding is disconnected for a short time. The voltage of that winding is then determined by the voltage of, and the capacitances to, the surrounding windings or tank wall/core. For certain winding layouts, voltages and capacitances, the capacitive controlled voltage will reach magnitudes that are too high for the change-over selector. In these cases potential controlling resistors, so called tie-in resistors, should be connected according to Fig. 34. The tie-in resistor is connected between the middle of the tapped winding and the connection point on the bottom of the diverter switch housing, see single phase diagrams in this document. This means that power is continuously dissipated in the resistors that add to the no-load losses of the transformers. The resistors must also be dimensioned for the power dissipation. The tie-in resistors are normally mounted separately from the tap-changer but can be mounted underneath the tap selector provided that tie-in resistor switch is not used. Please contact ABB for advice in such cases. Main winding Main winding Coarse winding Coarse winding Fine winding Fine winding Fig. 32. Normal operation. Fig. 33. Operation with high leakage inductance. 1ZSC AAW en, Rev. 2 Technical guide UC 31

32 The following limits apply to the change-over selectors of the different tap selectors: Tap selector Max recovery voltage (kv rms) Max capacitive current (ma rms) C III F F IV Table 17. The capacitive current is the current going through the change-over selector before it opens. In Fig. 34 there is a switch, the tie-in resistor switch, which connects the tie-in resistors only when they are needed. The switch is a part of the tap selector and is mounted on the bottom plate of the tap selector, see dimension drawings in this document. high. The tie-in resistor switch is available for all tap selectors except tap selector C. When ordering, give the winding layout and information according to the example in Fig. 35 and Table 18, and the supplier will calculate whether tie-in resistors are needed or not. If needed, the supplier will choose the correct tie-in resistors. When a tie-in resistor switch is needed to limit the no-load losses, give that information in the ordering data sheet. If anything is unclear, contact the manufacturer. Winding Phase voltage Connection High voltage (HV) 132 kv (H1) Delta Regulating winding (RW) (Voltage across) 13.2 kv (U) Plus/Minus C 1 = 3.8 nf (Capacitance between HV and RW) C 2 = 2.0 nf (Capacitance between tank and RW) Frequency 50 Hz. Table 18. Example of winding layout and information. This switch is used when the no-load losses must be kept low or/and when the continuous power in the tie-in resistors is too Main winding Diverter switch Tank Regulating winding with change-over selector Tap selector Tie-in resistor switch Tie-in resistor H1 HV U RW C1 + - C2 Fig. 34. Tie-in resistor example. Fig. 35. Example of winding layout and information. 32 Technical guide UC 1ZSC AAW en, Rev. 2