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IL 

44-751-1 

  

Instruction 

Leaflet 

 

 

Page 9  November, 2001 

Electrostatic Shielding and Insulation 

 

Electrical spacing requirements between the tap decks and the tank wall and between the tap 
decks and adjacent phases or other metallic objects is a complex subject.  When designing the 
transformer, required electrical clearance distances should be calculated between phase decks 
and between phase decks and ground or other parts of the transformer.  Three levels of shielding 
and insulation are available for the tap decks.  

1.  Unshielded: Tap decks do not have any electrostatic shields.  This configuration is typically 

used for applications, which have a impulse voltage withstand requirement of 200 kV or less.  
See Figure 8. 

2.  Level 1 Electrostatic Shielding: A cast-aluminum electrostatic shield ring is placed between 

the tap changer deck and the transformer tank wall.  This ring is referred to as the “outer 
shield”.  The ring is bolted to an aluminum mounting plate, which is, in turn, bolted to the 
worm gear housing.  The ring portion of each shield is insulated with a layer of crepe paper 
wrap.  This configuration is, typically, used for applications, which require a impulse voltage 
withstand of 650 kV or less.  See Figure 9. 

3.  Level 2 Electrostatic Shielding: Cast-aluminum, electrostatic shield rings are mounted on both 

the tank wall side and the coil side of each tap deck.  Both the inner and outer shield rings 
are bolted to the shield mounting plate, which was described above.  The outer ring portion of 
each shield is a continuous ring.  The inner shield consists of two half-circle rings.  See 
Figure 10.  In addition to the aluminum rings, a pressboard disk is placed in front of the 
aluminum mounting plate and a pressboard box shield is added to the tank wall side of each 
tap deck.  This box shield is attached to the transformer support structure with cotton tape.  
The pressboard disk is attached to the aluminum mounting plate with cotton tape.  This 
configuration is, typically, used for applications which require a impulse voltage withstand 
greater than 650 kV; the upper limit of impulse withstand in this configuration is determined 
by the electrical clearances designed into the transformer. 

 

 

 

Figure 8. DTW without any shielding. 

 

Figure 9. DTW with shield on tank side. 

 

 

 

 

Figure 10. DTW with both inner and outer 

shielding. NOTE: only one of the inner shields 

are assembled in this figure. 

Summary of Contents for DTW

Page 1: ...IL 44 751 1 Instruction Leaflet Page 1 November 2001 Type DTW De energized Tap Changer Application Installation Selection Guide ...

Page 2: ... the amount of the tap winding connected into the circuit is changed This permits the adjustment of the voltage ratio of the transformer to best suit the voltage requirements at the transformer s installation site The de energized tap changer is usually installed into the high voltage circuit of the transformer and most of the time it is used to adjust the primary voltage of the transformer within...

Page 3: ...ation of the type DTW tap changer All materials used in the construction of the type DTW tap changer have been chosen for their superior electrical properties mechanical strength temperature extremes capability corrosion resistance transformer oil compatibility and light weight ...

Page 4: ...ightning Impulse 60 Hz Power Frequency See note 3 N A Between Adjacent contacts Lightning Impulse 60 Hz Power Frequency 220 kV 70 kV A B B C C D D E E F F A 1 Short circuit current 10 000 A r m s N A Rated Current2 850 A N A 1 See Figure 2 2 Based on a steady state contact temperature rise of 15 C at a continuous current equal to 120 of rated current 3 The dielectric withstand from tap deck to gro...

Page 5: ...r set 3 Moving contacts 4 Stationary contacts 5 Mounting post and 6 Drive shaft and External operating mechanism These individual components except number 6 are shown in Figure 3 and Figure 4 1 3 4 5 Contact Drive Shaft Tap Deck Plate Moving Contact Assembly Stationary Contact Copper Mounting Post Silver Copper Contact Button Figure 3 Contact structure Figure 4 Worm gear set 2 and ball end fitting...

Page 6: ...electrical stress concentration The copper mounting posts serve as the connection point for the tap leads The tap leads from the coil should be terminated with a two hole flat connector The flat connector is bolted to the mounting post with two 0 375 9 5 mm bolt sets The mounting posts capture the bolt head so that only the nut has to be turned to tighten the joint The moving contact set is a pinc...

Page 7: ...ball joint connectors telescoping and slip joint shaft tubes allows the drive mechanism to accommodate misalignments between tap changer decks or the operating mechanism and permits the shaft and drive mechanism to adjust to dimensional changes that occur as the transformer responds to temperature variations The shaft seal of the external operating mechanism consists of a packing gland backed up b...

Page 8: ...any position pad lock not supplied by ABB Figure 7 shows the location of the pad lock All external parts are made of non corrosive materials 2 1 3 4 Worm Gear Assembly Ball End Fitting Drive Shaft Tap Changer Deck Sliding Fit Connection Ball End Fitting Inter Phase Shaft Mounting Boss welded to tank External Operating Mechanism Figure 6 Drive System mounting boss not supplied by ABB Alamo Figure 7...

Page 9: ...his configuration is typically used for applications which require a impulse voltage withstand of 650 kV or less See Figure 9 3 Level 2 Electrostatic Shielding Cast aluminum electrostatic shield rings are mounted on both the tank wall side and the coil side of each tap deck Both the inner and outer shield rings are bolted to the shield mounting plate which was described above The outer ring portio...

Page 10: ...and mechanism set is available which permits the external operating mechanism to be located at ground level This is called Configuration C Configuration B Two tap decks per phase coil six tap decks in total In this configuration two sets of operating shafts are brought to the outside of the transformer in two gearboxes The mechanical connection between the two sets of deck drive shafts being made ...

Page 11: ...on of leads to the tap deck and for assembly of the aluminum shield casting Screwdriver with flat head used together with 9 16 inch 14 3 mm hex socket wrench in assembly of aluminum shield casting Two wrenches with 3 4 inch 19 mm hex socket for tightening bolt and nut on external operating mechanism Installation guide this document Pre installation Work Required by Customer Make the appropriate si...

Page 12: ...he hole spacing on the tap changer stationary contact posts NOTE It might be easier to prepare the tap leads from the coil if the DTW deck is not mounted to the superstructure 4 If the decks are not mounted to the superstructure in Step 2 now is the time to do so The leads are connected to the tap changer s Stationary Contact Copper Mounting Post according to the transformer specifications Each le...

Page 13: ...e number 1 position when connecting this shaft 8 Mount the Drive Shaft to the DTW at the appropriate end Left or Right as specified on the transformer drawings The drive shaft is assembled to the ball end fitting in the same way as the Inter Phase Shafts NOTE Make sure that the two Spring pins at the end of the Drive Shaft are undamaged Proper operation of these pins is necessary for proper operat...

Page 14: ...boards to the Super structure are tightened by once again 13 Before the core and coil is mounted into the tank the Main Drive shaft should be positioned at the correct height so that it is aligned with the hole in the mounting boss A length of cotton tape or similar material can be used as a sling to assist in this alignment process Once the drive shaft is properly aligned tie the cotton tape slin...

Page 15: ...ng Tube through the mounting boss onto the Main Drive shaft The slot in the Connecting Shaft should engage the spring pins on the Main Drive Shaft Note the spring pin should not be forced against the bottom end of the Connecting Shaft slot There should be approximately 0 25 to 0 50 inches of space between the pin and the bottom of the slot The purpose for this clearance space is to provide for mov...

Page 16: ...of tap decks or if the height of the operating mechanism is to be different from the height of the tap decks a Bevel Gear Housing is needed When the Bevel Gear Housing is used the Connecting Shaft is mounted to the Bevel Gear assembly in the same manner as was described above for the Operating Mechanism The Bevel Gear Housing is mounted to transformer tank in the same manner as the Operating Mecha...

Page 17: ... checked for proper operation To operate pull out the locking pin until it disengages the Geneva Indicator Dial and turn the operating mechanism handle one complete turn This should put the tap changer into Position number 2 Verify that the Geneva Indicator Dial reads 2 and verify that each tap deck is in position 2 Continue verification through all positions NOTE all DTW tap changers have the sam...

Page 18: ...ication numbers model style catalog number from the unit s nameplate Repairs In normal use the DTW tap changer will not require repairs We recommend that the transformer manufacturer be contacted before any repairs are made Maintenance ABB de energized tap changers require little or no maintenance to ensure proper mechanical and electrical operation of the switch The transformer should be de energ...

Page 19: ...IL 44 751 1 Instruction Leaflet Page 19 November 2001 ...

Page 20: ...recommendations description and safety notations in this document are based on our experience and judgement THIS INFORMATION SHOULD NOT BE CONSIDERED TO BE ALL INCLUSIVE OR COVERING ALL CONTINGENCIES If further information is required ABB Inc should be consulted NO WARRANTIES EXPRESSED OR IMPLIED INCLUDING WARRANTIES OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY OR WARRANTIES ARISING FROM...

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