Design of bushings of voltage classes 110 kV and higher

For voltages of 110 kV and higher, domestic transformers use oil-filled bushings that are not connected to the oil of the transformer tank (Fig. P. 4.4). The input consists of a “core”, upper and lower conical porcelain tires, a metal connecting sleeve and auxiliary parts. In the center of the core there is a “current-carrying pipe”, outside – a grounded cylindrical screen. The oil gap between the pipe and the screen is subdivided into a number of channels by paper-bakelite cylinders, or the space between the pipe and the screen is filled with paper – this is the so-called core with continuous solid insulation. Equalizing plates are placed on paper-bakelite cylinders or between layers of paper [ 10]. The core is enclosed in a closed, oil-filled “case” formed by two porcelain tires and a connecting sleeve located between them. The core is dried and the bushing is filled with oil under a relatively deep vacuum (residual pressure 15 … 20 mm Hg or less – depending on the type of internal insulation). An oil expander is installed above the top tire. The space inside the central pipe communicates with the transformer tank (bushings of 110…220 kV classes); a cable passes through the pipe, connected at one end to the outlet from the winding, and at the other – to the external fittings of the input.

For a long time, bushings for voltages of 110–220 kV were used with oil- barrier internal insulation (with paper-bakelite cylinders) and with tires reinforced with flanges [1, fig. 6, 5]. With the help of flanges, the tires are fastened (bolted) to the connecting sleeve; lower and upper metal parts are attached to the flanges, covering the input from the ends. Recently, they switched to a design with a spring axial tightening of the inlet on the central pipe (Fig. P. 4.4), and flanges and their cement bonding with porcelain, sometimes giving oil leakage during operation, became unnecessary. The destruction of porcelain in the reinforcement with uneven tightening of the bolts on the flanges also disappeared. The “wafer” design allows reducing the insertion height by the axial dimension of the flanges.

In recent years, the design of bushings with a “solid core” of oil-impregnated paper has been introduced. This allows you to significantly reduce the diameter and, accordingly, the weight of the input. For example, the weight of a 400 kV bushing has been reduced by almost
twice.

The bushings for power transformers are designated as MT – “oil-filled, for transformers” or MTP –
with PIN connection device (see below).

Annex 5

DEVICE AND GENERAL VIEW
POWER TRANSFORMER

A modern transformer is a complex device consisting of a large number of units, parts and metal structures. Its main parts are the magnetic system (magnetic core) and windings. The magnetic system serves to localize the main magnetic field of the transformer in it.

Winding – a set of turns of conductors, in which the EMF induced in them is summed up to obtain higher, medium or lower voltages (HV, MV or LV) of the transformer. Electrical steel and copper (aluminum), from which the magnetic system and windings with taps are made, are called active materials.

The assembled magnetic system with its connecting parts and yoke beams forms the core of the transformer.
The core of the transformer with windings, taps, elements of the switching device and parts for their mechanical fastening is called the active part of the transformer.

The taps are used to connect the windings to the inputs and the switching device, and the switching device is used to regulate the voltage of the transformer. active part
an air transformer is sometimes covered with a casing
(protected version), which provides free access of cooling air, while protecting the active part from foreign objects.

The active part of the oil transformer is placed in a tank filled with transformer oil or other liquid dielectric, which is the main insulating medium and coolant in the cooling system.

The tank consists of a bottom, a wall and a lid. A tank with a removable lid is called a tank with a top connector (usually the bottom of the tank is welded to the wall); with a connector near the bottom (for separating and lifting the upper part) – bell-shaped (usually the cover is welded to the wall); with seals that exclude communication between the internal volume and the surrounding atmospheric air – sealed.

Coolers, a drive mechanism, sometimes contactors of a switching device, as well as a thermosiphon filter and boxes of contact connections for control and signaling devices are placed on the walls of the tank. The tank cover is used to install the inputs, expander and safety pipe.

The bushings are used to connect the transformer windings to the network, the expander is used to compensate for fluctuations in the oil level in the tank with changes in load and ambient temperature. The dilator is always placed above the level of the lid.

To protect the oil in the expander from moisture, an air dryer is used, which is a vessel (filled with silica gel), which communicates, on the one hand, with atmospheric air, and on the other hand, with air filling the internal volume of the expander above the oil “mirror”.

To monitor the oil level in the expander, oil gauges are used either with a glass tube or plate, or with a pointer. A gas relay is placed in the expander pipeline, which reacts to the release of gas in case of damage in the active part of the transformer.

A safety pipe (sometimes called an exhaust pipe) is a protective device that prevents damage to the tank during a sudden increase in internal pressure and is a steel cylinder, one end of which communicates with the tank, and the other is closed with a glass disc.

In the cover, sleeves are installed for sensors of thermal alarms that measure the temperature of the upper layers of the transformer oil. The temperature alarm has an electrical contact device that turns on at a predetermined temperature. The contacts of the thermal alarm switch on an alarm or other circuit, warning the maintenance personnel about an unacceptable increase in the oil temperature in the transformer.

On fig. Clause 5.1 shows a transformer with an expander and an exhaust pipe. Its design is hermetic: the internal volume has no communication with the environment. The transformer is completely (up to the cover) filled under vacuum with transformer oil, expanders are not installed. Temperature changes in the volume of oil that occur during operation are compensated by a change in volume due to the mobility of the corrugated walls of the tanks. Hermetically sealed design allows to refuse preventive repairs of the transformer during its operation.

The transformer consists of an active part, a tank, a tank cover with HV and LV bushings and a switch drive brought to the cover. The active part is rigidly connected to the tank lid. The magnetic core of the transformer is twisted, spatial, made of electrical steel strips.

The windings are multilayer, cylindrical, wound, made of APB wire.

HV taps are made of copper wire with reinforced paper insulation, LV taps are made of aluminum bus. The transformer switch is installed on the active part.

The welded tank of the transformer consists of an upper frame, a corrugated wall, a shell, a bottom with channels welded to it. The tank is triangular in plan. In its lower part there is a grounding unit and a drain plug. In the channels welded to the bottom of the tank, there are holes for attaching the transformer. Adjustable transport rollers are installed on the same channels, allowing longitudinal or transverse movement of the transformer.

On the cover of the transformer there are inputs LV and VN; switch drive; grounding unit of the cover and active part; branch pipe for filling the transformer with oil; mano-vacuum gauge with a valve and a box of clamps; lifting earrings
assembled and oil-filled transformer; plates with holes for mounting the transformer on vehicles during the transportation of the product.

The pressure vacuum gauge is equipped with electrical contacts, which serve to turn on the alarm circuit or turn off the transformer in case the internal pressure in it exceeds the permissible value. The contacts of the pressure vacuum gauge are brought to the terminal box.

A blowout fuse, supplied by customer’s order, is designed to protect the low voltage network.

On fig. Clause 5.2 shows a general view of a type transformer
TMA – 1600/35 voltage class 35 kV, power 1600 kVA with cooling system M and control system PBV. The figure shows radiators, as well as all the main equipment installed on the wall 11 and on the cover 23 of the tank. Here 1 is a tap for connecting the thermosiphon filter, and 2 is the filter itself. It consists of a casing filled with silica gel, i.e. substance is very hygroscopic, actively absorbing water. The oil heated at the active parts of the transformer circulates through the thermosyphon filter as through a radiator, while giving off the moisture present in it to the silica gel. The thermosiphon filter is a device for continuous oil regeneration.

An oil conservator 6 is installed on the cover of the transformer tank, which is a tank, the volume of which is approximately equal to 10% of the volume of oil in the transformer tank. The expander has an oil measuring tube 5 with marks showing what oil level should be at a given temperature. If the level is below the required level, oil must be added. The expander is connected to the tank through a branch pipe on which a gas relay 27 is installed. The air space of the expander is connected to the atmosphere through an air dryer 3 , as well as to a safety pipe 4 . The air dryer is filled with silica gel, to which the air entering the expander releases moisture. The supply of air from the atmosphere occurs only when the air pressure inside the expander becomes lower than atmospheric pressure. For this purpose, the air dryer has an oil valve that opens at a known pressure difference between the atmosphere and the air space of the expander.

The main purpose of installing an expander is to reduce the intensity of wetting and oxidation of transformer oil. If there were no expander, then it would be impossible to completely fill the transformer tank with oil. It would be necessary to leave a layer of air between the tank cap and the surface of the oil, allowing the volume of oil to change when its temperature changes. Since atmospheric air always contains moisture, a large surface of its contact with oil would lead to a rapid dampening of the latter. The relatively high temperature of the upper layers of the oil would contribute to its intense oxidation and loss of electrical strength. In the presence of an expander, this process proceeds more slowly due to the smaller surface of contact between oil and air, and also because the temperature of the oil in the expander is much lower than in the upper layers of the tank. The oil in the conservator does not participate in the convection circulation of the oil, and water that has entered the oil from the atmosphere can be deposited in the conservator sump without entering the tank. Filling the transformer tank with oil in the presence of an expander provides adequate insulation of the taps and the lower part of the inputs located under the transformer tank cover.

Rice. Clause 5.1. Power transformer device
power 1 000…6 300 kVA voltage class 35 kV:
1 – tank; 2 – valve; 3 – ground clamp; 4 – thermosiphon filter; 5 – radiator;
6 – switch; 7 – expander; 8 – oil indicator; 9 – air dryer; 10 – exhaust pipe; 11 – gas relay; 12 – HV input; 13 – drive of the switching device; 14 – input HH; 15 – an earring for lifting; 16 – LV outlet; 17 – skeleton; 18 – VN outlet; 19 – yoke beam of the skeleton (upper and lower); 20 – adjusting branches of the HV windings;
21 – HV winding (inside LV); 22 – trolley roller

The safety pipe has a glass plug at its end, which is squeezed out and oil is ejected from the tank to the substation if the pressure in the tank has reached a value that is dangerous for its integrity. Such an increase in oil pressure can occur due to internal damage in the transformer, such as a short circuit or a fire in steel, associated with the decomposition of oil and solid insulation and the release of gas. In order for the operation of the safety pipe not to be erroneous, its air space is connected by a tube to the oil expander and through the air dryer 3 to the atmosphere. Due to this, the oil level in the pipe will be balanced by atmospheric pressure and will be maintained the same as in the expander.

A fire in steel is a very severe accident, it occurs due to a violation of the insulation between the sheets of the transformer steel of the magnetic circuit and a strong increase in eddy currents in the steel. The gas relay 27 is used to protect the transformer from internal damage associated with the release of gases. There are two floats in the gas relay housing: upper and lower. When gases appear in the transformer, they penetrate through the pipe between the transformer tank and the expander into the upper part of the gas relay housing, displace oil from there, as a result of which the upper float drops and closes the alarm circuit. With the development of an accident and a significant increase in oil pressure in the transformer tank, oil rushes through the pipe from the tank to the expander and acts on the lower float, which closes the circuit for disconnecting the transformer from the network.

In addition to the listed equipment, the following equipment is installed on the lid and wall of the tank: VN 7 inputs, LV 8 inputs, VN 25 zero input, transformer lifting hooks 9 , PBV 10 three-phase switch drive, thermometric alarm 13 , factory shield 14 , ground bolt 15 , trolley rollers for moving the transformer at the substation 16 , valve for oil sample 17 , plug for draining sludge 18 , bracket for lifting the expander 19 , crane for disconnecting the radiator 20 , brackets for lifting the tank cover 21 , valve for connecting the filter press 22 , thermometric alarm sensor 24 , cock for draining oil from the tank 26 .

On fig. Clause 5.3 shows a general view of a type transformer
TDN-16000/35 voltage class 35 kV, rated power 16,000 kVA with voltage regulation under load. This transformer uses 160-pipe radiators 16 , under each of which two fans 22 are installed, driven by motors 19 . Radiators are located differently here (see Fig. P.5.2). Each pair of radiators is connected to a collection pipe through branch pipes and taps 17 , and the latter is connected by two flanges to the transformer tank. VN inputs 4 are installed on feed-through current transformers 3 . The latter serve to measure the current in the transformer, as well as to connect the current windings of relay protection. Each current transformer consists of an annular magnetic circuit wound with a tape of electrical steel in the form of a hollow cup. The secondary winding covers the entire surface of the magnetic circuit. The primary winding of the current transformer is the input rod of the HV winding, passing inside the magnetic circuit along its axis. Each current transformer has its own casing mounted on the tank cover. The ends of the secondary winding are removed from the casings through special holes in them and go to the terminal box 27 .

The voltage regulator of the on-load tap-changer is much more complex than the PBV. It consists of contactors, switches and current-limiting resistors. The voltage regulator, equipped with a cover 1 , has the shape of a cylinder and is immersed inside the tank. The casings of the voltage regulator and current transformers are connected through the oil pipeline 5 to the branch pipe going from the expander to the tank cover. A gas relay 11 is installed on the branch pipe. The second gas relay 33 is located on the oil line. For remote control of the voltage regulator, a motor drive 26 is installed on the tank.

In order not to increase the size of the tank, (Fig. P. 5.2) an expander 9 was used. Since there was no place for it on the tank cover (see Fig. P. 5.2), and it is installed on special brackets.

To reduce losses in the tank cover from the magnetic field of the LV inputs, where the currents are high enough, the LV inputs 6 are installed on a non-magnetic plate (Fig. P.5.3, b ).

On fig. Clause 5.3 also indicates the following details: 2 – brackets for lifting the lid; 7 – safety pipe; 8 – pointer oil indicator; 10 – sensor of the thermometric signaling device; 12 – air dryer; 13 – filter; 14 – ground bolt;
15 – carriage; 18 – thermometric signaling device; 20 – a roller with a flange; 21 – a lifting device and an emphasis under the jack (it replaces here the hook shown in Fig. P. 5.2); 23 – plug for draining oil residues; 24 – valve for taking oil samples; 25 – valve for draining oil from the regulator; 28 – transformer tank;
29 – transformer tank cover; 30 – valve for draining oil from the transformer tank; 31 – automatic blow control cabinet; 32 – zero input of HV; 34 – tap for connecting the filter press.

A general view of a transformer type ТМН-6300/110 with a power of 6,300 kVA, voltage class 110 kV with voltage regulation under load is shown in fig. Clause 5.4. The M cooling system is used here and 160-pipe radiators are installed. Due to the fact that the rated power of the transformer is relatively small, and the voltage class, which determines the insulation gaps, is high, there was not enough space on the cover for the location of the HV inputs. In order not to artificially increase the transformer tank and the volume of oil in it, the leftmost HV input is placed in a specially made pocket.

On fig. Clause 5.4 are marked: 1 – HV input; 2 – case of the current transformer; 3 – HH input; 4 – zero input of HV; 5 – device for lifting and jacking the transformer; 6 – motor drive for the voltage regulator of the on-load tap-changer; 7 – voltage regulator cover.

On fig. P. 5.5, a and b shows a type transformer
TD-16000/110, voltage class 110 kV, power 16,000 kVA with PBV control system. 160-pipe radiators with fans are used here (cooling system D ). Unlike the transformer shown in Fig. Clause 5.2, where one three-phase PBV regulator is used, in this case three single-phase regulators are installed. The rest of the equipment is the same as in the previous figures. Oil conservator, as in fig. P. 5.3, located on the bracket.

Rice. Clause 5.2. General view of the transformer voltage class 35 kV
with M cooling system and PBB control system

a

b

Rice. Clause 5.3. General view of the transformer voltage class 35 kV
with cooling system D and OLTC control system:
a – front view of the transformer; b – top view

Rice. Clause 5.4. General view of the voltage class transformer 110 kV
with cooling system M and tap changer control

a

b

Rice. Clause 5.5. General view of the voltage class transformer 110 kV
with cooling system D and PBB control system:
a – front view; b – top view

Rice. Clause 5.6. Three-phase two-winding transformer with a capacity of 40,000 kVA, voltage class 110 kV with split LV windings
and regulation of HV voltage under load:
1 – input 110 kV; 2 – input LV 10 kV; 3 – hook for lifting the transformer;
4 – tank; 5 – radiator; 6 – thermosiphon filter; 7 – bracket for lifting with a jack; 8 – vertical valve for draining oil; 9 – fan; 10 – skating rink;
11 – half bandages of the yoke tie; 12 – vertical tie rod of the frame;
13 – yoke beam; 14 – device for switching branches of the HV winding;
15 – bandages of the rod tie; 16 – plate with an eye for lifting the active part; 17 – expander; 18 – oil indicator; 19 – safety pipe

Rice. Clause 5.7. The windings of the transformer shown in fig. Clause 5.6:
1 – steel pressing ring; 2 – winding of fine regulation;
3 – coarse regulation winding; 4 – HV winding; 5 – LV winding;
6 – angular insulating washer; 7 – intercoil spacers;
8 – insulating cylinder; 9 – supporting rings made of insulating cardboard; 10 – yoke insulation from electrical insulating cardboard;
11 – equalizing insulation; 12 – wooden plank; 13 – wooden rod; 14 , 15 – rail made of insulating cardboard

Rice. Item 5.8. General view of the voltage class transformer 110 kV
with PMB control system

Rice. Item 5.9. Three-phase two-winding transformer
oil cooled:
1 – valve for the release of gases; 2 – a box of clips; 3 – cover; 4 – flange;
5 – viewing window; 6 – body; 7 – mercury contact of the alarm circuit; 8 – alarm circuit clamp; 9 – clamps of the trip circuit; 10 and 12 – upper and lower clamps; 11 – mercury contact of the shutdown circuit; 13 – safety pipe; 14 – expander;
15 – oil indicator; 16 – gas relay; 17 – input HH; 18 – HV input; 19 – lifting ring;
20 – tank cover; 21 – lifting pin; 22 – switch; 23 – tap from the winding;
24 – wooden planks; 25 – magnetic circuit; 26 and 29 – upper and lower yoke beams of the magnetic circuit; 27 – adjusting taps to the switch; 28 – HV winding; 30 – tank; 31 – rollers; 32 – oil drain valve; 33 – circulation pipes

Rice. Item 5.10. Three-phase magnetic system
with pressing of rods with glass bandages

Rice. Item 5.11. Dry transformer 320 kVA without casing:
1 – HV winding; 2 – vertical tie rods;
3 – porcelain gaskets for pressing windings; 4 – steel pressing ring; 5 – support insulators for HV taps; 6 – VN outlets;
7 – porcelain linings for fixing PN bends; 8 – BN clamp board;
9 – adjusting holes of the HV winding

Rice. Item 5.12. General view of the transformer voltage class 15 kV
with air cooling and PBB control system

Rice. Item 5.13. Placement of windings and insulation of the transformer
with a capacity of 1600 kV . A voltage class 35 kV:
1 – equalizing insulation; 2 , 10 – lower and upper taps of the LV winding; 3 , 9 – lower and upper yoke insulation; 4 , 8 – lower and upper support rings of the HV winding; 5 , 21 – HV and LV windings; 6 – supporting wedge (rail) of the HV winding; 7 , 19 – cylinders; 11 – paper insulation of the upper branch of the LV; 12 – grounding tape of the pressing ring; 13 – pressing screw; 14 – yoke beam; 15 , 16 – steel and insulating cups; 17 – pressing ring; 18 , 23 – upper and lower supporting rings of the LV winding; 20 – wedge (rail); 22 – gaskets between the coils

Rice. Item 5.14. The structure of the windings and insulation of the transformer
voltage class 35 kV; power 1600 kV . BUT:
1 , 2 – wooden rods; 3 – magnetic circuit; 4 – wooden plank; 5 – paper-bakelite cylinder of LV winding; 6 – LV winding; 7 – paper-bakelite cylinder of the HV winding;
8 – HV winding; 9 – interphase partition; 10 – insulating shield; 11 – supporting rings of the HV winding; 12 – yoke insulation; 13 – rail; 14 – supporting rings of the LV winding; 15 – rail;
16 – HV winding gasket; 17 – washer made of electric cardboard; 18 – vertical steel stud, insulated with a paper-bakelite tube; 19 – yoke beam; 20 – leveling insulation bar; 21 , 22 – insulated winding tap

Rice. Item 5.15. Longitudinal section of LV and HV windings
with dedicated control winding

Rice. P. 5.16. Dry power transformer

Rice. Item 5.17. General view of the transformer ТМ-5600/10 and ТМ-5600/35

Rice. Item 5.18. General view of the transformer with voltage regulation under I load TDN-10000/35 ( a ) and sketch of transformer covers
TDN-1500/ TDN-2000/35 ( b ); general view of transformers
from TDNG-10000/110 TDNG-20000/110 ( in )
and a sketch of the cover of the transformer TDNG-3500/110 ( d ):
1 – thermosiphon filter; 2 – blower fan;
3 – OLTC drive mechanism; 4 – box of contacts

Rice. Item 5.19. General view of transformers ТМ-3200/10 and ТМ-3200/35

a b

Rice. Item 5.20. General view of transformers:
a – from TM-20 to TM-50; b – from TSM-20 to TSM-100

Rice. Item 5.21. General view of transformers from ТМ-180 to ТМ-320/6-10
and from TSM-180 to TSM-500 ( a ) and sketches of transformer covers
TM-180/35 and TM-320/35 ( b ); TM-560/10 and TM-560/35 ( in )
and from TM-750 to TM-1800 ( g )

Rice. P. 5.22. General view of transformers with voltage regulation under load TMN-560/35, TMN-1000/35, TMN-1800/35 ( a ) and sketches of covers of transformers TMN-3200/35 ( b ) and TMN-5600/35 ( c ):
1 – gas relay; 2 – thermal alarm; 3 – grounding; 4 – switching
device; 5 – removable handle of the switching device

Appendix 6

TMZ transformers

Three-phase transformers with natural oil cooling (Fig. P. 6.1) are designed to convert electrical energy in power grids, as well as to power various consumers in alternating current networks with a frequency of 50 Hz. The transformers provide the possibility of voltage regulation: 5 steps with a regulation range of ±2 × 2.5% of the nominal. Type of regulation – PBV (switching without excitation). Switching the transformer to another range is done manually in the off state.

The transformers are made in a sealed design, dry nitrogen is used as a structural oil protection (the principle of a nitrogen cushion between the oil mirror and the transformer cover). Transformer bushings are flanged, located on the end walls of the tank: Transformers of the TMZ type can operate as an independent product, or as part of a package transformer substation.

TMZ-250-2500 kVA 6-10 kV – three-phase oil sealed power transformers with natural oil circulation with voltage regulation without excitation (PBV), with a regulation range of 2.0 × 2.5%, general industrial design. They are made for regions with a temperate climate with a temperature difference from -45 to +40 ° С. The transformers have a flat-laminated magnetic system made of high-quality electrical steel. The windings are cylindrical multilayer, made of aluminum wire.

Name unit of measurement TMZ (250) TMZ (400) TMZ (630) TMZ (1000)
Rated power kW 1000
Rated voltage higher kV 6; ten
Rated voltage low kV 0.4
Idle loss kW 0.61 0.9 1.25 1.9
Short circuit loss kW 2.8 5.5 7.9; 8.5 12.2
No-load current % 1.9 1.7 1.0
Short circuit voltage % 4.5 5.5
Scheme and winding group U/Un-0 U/D-11 D/Un-11
Oil mass kg
Gross weight kg 1230 2645 3614
Length mm 1 200 2012 2234
Width mm 1 160 1 220
Full height mm 1776 1 825 1 827
Height to cover mm 1 332 1737

Rated power kW
Rated voltage higher kV 6; ten
Rated voltage low kV 0.4
Idle loss kW 0.61
Short circuit loss kW 2.8
No-load current % 1.9
Short circuit voltage kW 4.5
Scheme and winding group U/Un-0
Oil mass kg
Gross weight kg 1230
Length mm 1 200
Width mm
Full height mm 1776
Height to cover mm

Rice. Clause 6.1. Power oil transformers type TMZ

Power oil step-down three-phase two-winding oil-tight transformers with power from 630 to 2,500 kVA with voltage up to 10 kV (Table P. 6.1) are designed for indoor and outdoor transformer substations (Fig. P. 6.2).


Table P. 6.1

TMZ dimensions

Power, kV . BUT No-load losses, W No-load current, % Short circuit losses, W Short circuit voltage, % Dimensions, mi Weight, kg
L AT H D BUT E F M N To
1050 1.8 7600 5.5 2150
1000 1550 1.2 10 800 5.5 3 160
1600 2050 1.0 16 500 6.0 18S5 4 300
2500 2800 0.3 24 000 6.0 6 900

Rice. Clause 6.2. Hermetic power oil transformers TMZ series
power from 630 to 2500 kV . BUT:
1 – mosloindicator; 2 – HH input; 3 – HV input; 4 – hook for lifting the transformer;
5 – factory shield; 6 – plug for taking oil samples; 7 – plug for sediment descent;
8 – ground bolt; 9 – switch drive; 10 – safety diaphragm;
11 – pressure vacuum gauge; 12 – thermal alarm

Appendix 7

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