On Load Tap Changer Type A

8/12/2019 On Load Tap Changer Type A

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On Load Tap Changer Type AGeneral & Operating Manual

CONTENTS

1. Specification Detail

1.1 General......................................................................................................4

1.2 Functional principles................................................................................. 5

1.3 Basic connection of the tap winding..........................................................5

1.4 Designation of the tap changer model.......................................................6

1.5 Number of steps and basic connection diagram.......................................6

Table I Rated withstand voltages of insulating distances...........................8

Table II Rated step voltage and Relevant rated currents........................... 8

2. Principal parts of the on-load tap changer.......................................................... 8

2.1 Tap changer head...................................................................................... 8

2.2 Oil Compartment....................................................................................... 9

2.3 The tap changer insert............................................................................... 9

3. Installation of the tap changer............................................................................. 10

4. Connection of the tapped winding and take-off lead........................................... 10

5. Accessories ....................................................................................................... 10

5.1 Motor Drive.................................................................................................10

5.2 Protective Relay.........................................................................................11

APPENDIX

A III 100 - D - 24kV - 09 - 0 Dimension Drawing ------------A0011 R2

A 111 100 - D - 24kV - 09 - W/G Dimension Drawing ------------A0012 R2

A 111100-D-36kV-09-0 Dimension Drawing ------------A0010R1

A lit 100 - D - 36kV - 09 - W/G Dimension Drawing ------------A0002 R2

Coupling of OLTC and Drive B25556


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On-Load Tap Changer Type A

1. Specification Details

Layout Installed fully sunk in the transformer tank.

(Can also be mounted in a separate tank)

Selector switch operates in its own oil space (Oil Compartment) isolatedfrom the transformer tank oil.

Application On-load tap changer Alll 100, as star point tap changer for three phase star

connected transformers.

On-load tap changer Alll 100 D for application to delta connected transformer.

or

On-load tap changer A I 100 as single-phase tap changer for single phase

transformer or for three phase transformers in any mode of connection

Insulation: Insulation level voltages to earth 24, 36 & 52 kV

A.C test voltage According to IS,BS,IEC,VDE,ASA etc

(50Hz.;1.2/50Microsec.) Internal selector insulation: Withstand voltages for all insulation distances on

applicationCurrent rating 100 A when Star or Delta connected, single phase in any connection.

Rated frequency 50 ~ 60 Hz

Short-Circuit Withstand Thermal: Over 20 times the rated current (rms), duration 3 seconds.

Dynamic test; Over 50 times the rated current (peak value)

Step voltage Max 450 V.

Number of taps Tap selector with pre-selector (coarse tap selector or reversing switch):

8 steps with one mid-position (up to a maximum of 17 working positions

differing in voltage)

Tap selector without pre-selector


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1.2 Functional principle

The on-load tap changer type A is designed as aselector switch combining the function of a diverterand a tap selector in a single compartment. Theload current transfer from one tap of the winding tothe next is initially performed by 2 transition contactsand then by the main switching contact.

a, b - main switching contacts

a1. b1 - transition contacts

R - transition resistance

1.3 Basic connections of the tap winding

The selector switch of the tap changer is equippedwith 9 stationary contacts on each contact plane.The stationary contacts are arranged in a circle andcan be connected successively to the tap changertake-off lead by means of the movable switchingelement.

Without change-over selector Fig.2 (a)

The linear voltage regulation may be achieved witha maximum of 8 steps (i.e., 9 operating positions atthe most).

With change-over selector Fig. 2 (b) & (c)Where required, the selector switch can be provided

with a change-over selector which can be usedeither as reversing switch for the buck and boostconnection or as coarse tap selector to connect thebeginning or end of a coarse tap winding to the mainwinding. In either case the regulating range will bedoubled to 8 steps (i.e. 17 operating positions).


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1.4 Designation of the tap changer model

Every tap changer is available in different models

varying according to the number of poles, maximum

rated through-current, insulation according to

highest voltage for equipment (Um) and basic

connection diagram. The designation of a particular

tap changer must, therefore, indicate thesecharacteristics. (fig:3). This coding ensures

unmistakable designation of every tap changer.

Example:

On-load tap changer type : A,

Number of pole : III (for three

pole appln.)

Max. rated through-current : 100 Amps.

Insulation voltage to earth : 24 kV

Basic connection diagram : 09 17 1W

1.5 Number of steps and basic connectiondiagram

The selector switch can be adapted to the tap

winding with respect to the number of steps

required. The connection diagram is referenced to

the number of operating positions, number of mid-

positions and kind of change-over selector. The

designation of the basic connection diagrams with

their inherent number of steps is shown in fig. 4.

Example:Pitch of the selector switch


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Fig.5 Shows in schematic illustration the specific voltage stress applied to the transormer winding prior tothe final choice of a particular tap changer. Be sure that the voltage stress of the transformer winding doesnot exceed the rated withstand voltages in table 1 even in the most unfavourable operating position of thetap changer.


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Table 1

Rated withstand voltages of distance in kV on OLTC (Lightning impulse withstand voltage, powerfrequency withstand voltage)

Insulating Shape and A lll 100 Y Onload tap changer A I 100

Distance period of voltage Um = 24 kV Um = 36 kV Um = 52 kV

a kV 1.2/50 60

kV, 50Hz 1 min 30b kV 1.2/50 60 150 200 250 -

kV, 50Hz 1 min 30 50 70 95 -

c1 kV 1.2/50 150

kV, 50Hz 1 min 50

c2 kV 1.2/50 150 150 200 250 -

kV, 50Hz 1 min 50 50 70 95 -

d kV 1.2/50 85

kV, 50HZ 1 min 31

Table II

Rated through-currents (lu),

relevant rated step voltage ( U

i)

and rated switching capacities PstN), highest and lowest step voltage

On load tap changer AIII 100 Y, AIII 100 D A I 100

Rated through current lu (A) 75 100 75 100

Rated step voltage Ui (V) 450 280 450 280

Rated switching capacity PstN (KVA) 37.5 28 37.5 28

2. Principal parts of the On-load Tap changer

2.1 Tap Changer Head

Th i f h h A h

1 2

4


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The oil compantment is connected through theprotective relay RS 2001 to the oil conservator by a

pipe connection R.

2.2 Oil Compartment

The oil compartment is a cylinder made of excellent

electrical and mechanical properties with its upper

end attached to the tap changer head and its lowerend closed by the oil compartment bottom. The oil

compartment of the tap changer is thus separated

from the transformer tank oil.

The oil compartment bottom moreover serves for

bearing the lower end of the switching shaft.

The fixed contacts of the change-over selector and

selector switch are arranged in separate contact

levels, mounted on the inside of the oil compartment

cylinder and connected to the outside terminals.

These feed-through contacts have been sealed by

extensive measures to obtain oil tightness.

2.3 The Tap Changer Insert

The tap changer insert comprises the entire

movable contact system of the tap changer. It

consists of the selector switch drive shaft and the

switching elements .

The selector switch drive shaft is connected at its

upper end to the gearing mechanism and with itslower end to a bearing centered in the oil

compartment bottom. The changeover selector

contact carrier is concentrically outside the oil

vessel cylinder and independently movable.

The switching elements are mounted to the drive

shaft in the level of corresponding fixed contacts.

There are three sets of contact rollers side by side

per switching element, which function as main and

auxiliary arcing contacts respectively during the tap

changer operation.

The contact material is of electrolytic copper. The

contact rollers of the arcing contacts are connected

to the transition resistor. Every contact roller ismovable against spring pressure independently

from the other. The transition resistors are wound

upon grooved ceramic carrier from coiled wire of

chrome nickel alloy particularly resistant to

excessive temperature. The ambient oil is very

effective in cooling so that the resistor materials

cool down to oil temperature within shortestpossible no-load periods.

The entire tap changer insert can be withdrawn for

Inspection after removal of the gearing mechanism.

The distance between arcing contact rollers is such

that they bridge properly two fixed adjacent

contacts.


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3. Installation of the tap changer3.1 Mounting flange

For mounting the tap changer head on the

transformer cover the use of a mounting flange

welded to the cover is recommended. This

mounting flange is to be made in accordance with

the gasket surface of the tap changer head. For

positioning the studs we recommend use of a drillingtemplate which will be supplied with the first

tapchanger on request free of charge.

3.2 Attachment of the tap changer to the

transformer cover

Proceed as follows:

Clean the sealing surfaces (bottom of head &mounting flange).

Put an oil-proof gasket on the mounting flange of

the transformer cover. Lift the tap changer over the

transformer cover and lower it carefully into the

opening of the mounting flange. Take care not to

damage the connecting contacts of the tap changer.Check the correct position of the tap changer head.

Fasten the tap changer head to the mounting flange.

4. Connection of the Tapped Winding and

Take-Off Lead

The tap leads have to be connected to the tapchanger according to the particular tap changer

connection diagram which will be supplied together

with equipment.

Pl t All l d ti t t h

Terminals of the change-over selector and

take-off lead

The terminals are designed as screw bolts. Connect

the tap leads and lock the screws to a torque of

4Nm max.

Change-over selector

The terminals are designed as strips with through-

hole for screws. Connect the leads and lock the

screws firmly

5. Accessories Equipment

5.1. Motor Drive

The on-load tap changer type A is operated by a

motor drive unit MA9 mounted outside the

transformer tank. All the components which

constitute the motor drive are contained in a sheet

metal housing designed for outdoor mounting and

f

Fig. 8


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Over travel in either direction is prevented byComprehensive mechanical and electrical safetySystems. The equipment also includes a six-figureMechanical counter showing the number of tapChange operations performed and a dial indicatingthe present position of the on-load tap changer.

Provision can be given for remote tap positionIndication as well.

The drive shaft is the mechanical connectionbetween motor drive and tap changer head. Thebevel gear translates the motion from the vertical tothe horizontal direction. Accordingly, the verticaldrive shaft has to be mounted between Motor drive

and bevel gear and the horizontal drive Shaftbetween bevel gear and tap changer.

The built-in electric heater prevents condensateFormation in the housing.

For emergency operation and for setting up themotor drive unit when putting the on-load tap changer

into service, a crank handle is provided. Whenpushed on to its shaft, this interrupts the motorcircuit.

5.2 Protective Relay

The protective relay is needed for disconnecting thetransformer in which a fault condition has occurred

in the OLTC. For connection of the protective relaya pipe connection with flange must be screwed inoil tight into the bore R of the tap changer head.Install the protective relay RS 2001 in accordancewith our operating instruction manual for the same.

Fig. 9MA 9


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Date post:	03-Jun-2018
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On Load Tap Changer Type A

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