I.L. 46-300-4

INSTRUCTIONS

OPERATION AND MAINTENANCE OF

DRY TYPE TRANSFORMERS

FIG. L Section of Three-Phase ASL Pcwer Center with Class B Insulation.

OPERATION

Tap Connections. In type ASL dry type trans· formers changes in voltages are made by the chang­ing of connector links on "stub taps", (see Fig. 2) which are brought out on the face of the coil. The panel that must be removed, by removing all screws in that panel, is indicated by a nameplate located directly below the transformer's Instruction Plate.

Type AVR transformers have the tap leads brought to a terminal board, (see Fig. 3) where connector links are used to connect the proper studs to obtain the desired voltage. The panel tha is to be removed will be indicated by a nameplate

NEW INFORMATION

Before changes are made the Instruction Plate should be consulted for the proper terminals to be connected to give the desired voltage. When tap connections are made the same numbered studs must be always connected in all phases.

Caution: Transformer case panels should never be removed while transformer is ener­

gized.

Effect of Humidity. As long as the trans­former is energized, humidity conditions are un­important. In the event that a dry type transformer is de-energized and allowed to cool to ambient tem­perature, consideration must be given to the possible effects of humidity.

If the shutdown period occurs during low humid­ity conditions, no special precaution should be re­quired before energizing the unit.

Should a shutdown exceeding 12 hours occur during a period of high humidity, particularly if atmospheric conditions are such as to cause con­densation within the housing, then precautions should be taken. Small strip heaters may be placed in the bottom of the unit shortly after shutdown to

FIG. 2. Type ASL Transformer Stub Taps.

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DRY TYPE TRANSFORMERS--------------------------------------------

DRY TYPE TRANSFORMERS---------------------------------------------

The transformer should be located to allow free circulation of air through the coils from the bottom to the top of the case. One winding should be short circuited, and sufficient voltage at normal frequency should be applied to the other winding to circulate approximately normal current. The impedance of the transformer will normally be found on the In­struction Plate. If for any reason the impedance is not known it should be obtained from the Westing­house Electric Corporation, Sharon, Pennsylvania. When inquiring, complete transformer data as given on the Instruction Plate should be included.

It is recommended that the winding temperature not be allowed to exceed 100°C., as measured by resistance or by thermometers placed in the ducts between the windings. The thermometers used should be of the spirit type because mercury ther­mometers give erroneous readings due to the gen­eration of heat in the mercury as a result of induced eddy currents. The end terminals of the windings (and not the taps) must be used in order to circulate current through the entire winding. Proper pre­cautions should be taken to protect the operator from dangerous voltages.

3. Drying by External and Internal He•t· This is a combination of the two methods preViously described, and is by far the quickest method. The transformer core and coil assembly should be placed in a non-flammable box, or kept in its own case if suitable, and external heat applied as described in the first method, and cwrent circulated through the windings as described in the second method. The current required will' be considerably less than when no external heating is used but should be sufficient to produce the desired temperature of the windings. It is recommended that the temperatures attained not exceed those stated in the foregoing.

4. Use of Insulation Resistance for Deter­mining Drying Time. Drying time depends on

the condition of the transformer, size, voltage, amount of moisture absorbed, and the method of drying used.

The measurement of insulation resistance is of value in determining the status of drying. Measure­ments should be taken before starting the drying process and at two hour intervals during drying. The initial value, if taken at ordinary temperatures, may be high even though the insulation may not be dry. Because insulation resistance varies inversely with temperature, the transformer temperature should be kept approximately constant during the drying period to obtain comparative readings. As the transformer is heated, the presence of moisture will be evident by the rapid drop in resistance measurement.

Following this period the insulation resistance will generally increase gradually until near the end of the drying period when it will increase more rapidly. Sometimes it will rise and fall through a short range before steadying because moisture in the interior of the insulation is working out through the initially dried portions. A curve with time as abscissa and resistance as ordinate should be plotted and the run should be continued until the resistance levels off and remains constant for from three to four hours.

Insulation resistance measurements should be taken for each winding to ground with all windings grounded except the one being tested. Before taking insulation resistance measurements the cur­rent should be interrupted and the winding should be short circuited and grounded for at least one minute to drain off any static charge. All readings should be for the same time of application of the test voltage, preferably one minute.

Caution: Constant attendance during the

drying process is desirable.

9 WESTINGHOUSE ELECTRIC CORPORATION

� SHARON PLANT • TRANSFORMER DIVISION • SHARON, PA.

(Rep, 6-58) Printed in U.S.A.

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I.L. 46-300-6-B

INSTRUCTIONS

DRY TYPE TRANSFORMERS

FIG. l. Type ASL Distribution Transformer

DESCRIPTION

THE MODERN DRY TYPE TRANSFORM­ER has been developed to supply the need for a safe transformer for indoor applications. It is designed to be essentially fireproof and explosion proof for economical installations without vaults near its load center.

Explosion and fire, the hazards of liquid filled transformers, are greatly reduced in air cooled transformers because they are constructed with A.S.A. Class B and Class H materials and utilize the surrounding air for their cooling medium.

Metal cases with suitable covered openings are used to encase air cooled transformers. The open· ings, which are necessary for the free circulation

SUPERSEDES I.L. 46-300-6-A

of air within the transformer, are not weather tight and so limit these transformers to indoor installa­tions.

Dry type transformers are manufactured in two types, the "DT-3" and the ASL. The type "DT-3" consists of the smaller ratings and the type ASL the larger ratings.

The normal kva limit of self-cooled dry type transformers is 5000 kva single-phase and 7500 kva three-phase. It is possible to increase these limits by the addition of air blast equipment (which must be provided for at the time of design} or by the paralleling or banking of two or more units mounted in a common case.

The maximum voltage for which air cooled trans­formers are built is 15000 volts.

Dry type transformers are supplied with pro­vision for grounding the case and an instruction

FIG. 2. Type DT -3 Power Center TraiU.Iformer

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DRY TYPE TRANSFORMERS-------------------------------------------

FIG. 3. Type ASL Power Transformer Crated for Export Shipment

plate which gives the electrical connections and details of the transformer. Other accessories are supplied in accordance with the specific trans­former and customer requirements.

High and low voltage leads may be brought out of the case by several different methods. The most common are: porcelain bushings (see the Instruc­tion Leaflet "Dry Type Transformer Bushings")1 terminal chambers with potheads or conduit con­nections1 and direct connection to switchgear/ switches or bus work.

SHIPMENT

Except for lightning arresters and LCB switches1 air cooled transformers are usually shipped ready for installation complete with bushings and acces­sories in place and connected for operation. They are completely covered with a weatherproof cover­ing which should not be removed until the trans­former is ready to be moved indoors and then1 only when there is no danger of exposing the transformer to dampness.

Shipping braces and shims under the transformer feet with their respective bolts when provided should be removed after installation. The outline drawing will show which braces are to be removed.

FIG. 4. Type ASL Power Center Transformer Loaded on a flat Car for Domestic Shipment

For foreign shipment air cooled transformers are completely covered with a weather tight wrapping and crated with a sturdy wooden box and securely braced to take the extra handling and movement to which they are subjected while in transit. Aside from the crating, all details are the same as for domestic shipment.

UNPACKING

It is only necessary to remove the weather proof covering to completely unpack an air cooled trans­former, however precautions to keep the trans­former dry as outlined above must be followed. Occasionally bushings or other accessories are shipped separately. If this is done1 care must be taken when unpacking as items such as bushings are quite fragile.

SERVICE

Further information/ or renewal parts1 may be obtained by contacting the nearest Westinghouse office. The facilities of the Engineering and Service Departments may be obtained through the nearest Westinghouse office.

WESTINGHOUSE ELECTRIC CORPORATION SHARON PLANT • TRANSFORMER DIVISION • SHARON, PA.

Printed In U.S.A.

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I. L. 46-300-2

INSTRUCTIONS

RECEIVING AND INSTALLATION OF

DRY TYPE TRANSFORMERS

RECEIVING

New transformers should be inspected when re­ceived for damage during shipment. Examination should be made before removing from cars or trucks and if any injury is evident or any indication of rough handling is visible, a claim should be filed with the carrier at once and the manufacturer should be notified.

After the transformer has been placed indoors, the panels should be removed and an internal in­spection made for injury or displacement of parts, loose or broken connections, cracked porcelain, dirt or foreign material and for the presence of free water or moisture. Any damaged condition should be reported at once to the nearest Westinghouse Office. If w:ater or moisture is evident see the Instruction Leaflet "Operation and Maintenance of Dry Type Transformers" for methods of testing for moisture and methods of drying out.

HANDLING

Lifting holes are provided on each side of the case for the insertion of hooks to lift the complete trans­former. These holes should be closed with the steel cover provided, so as to prevent the entrance of foreign materials.

For power centers and unit substations, eye nuts are provided for lifting the complete unit. After in­stallation, these may be removed and the openings covered with cap provided.

The base of these transformers is constructed so that the transformer can be moved on rollers in any horizontal direction. Under no circumstances should the transformer be moved with ropes or cables placed around the case. The transformer case is suitably designed for jacking. Jacks should be placed as indicated on the outline drawing.

STORING

Dry type transformers should be stored in a warm, dry location with a uniform temperature. Ventilating openings should be covered to keep out dust and foreign objects. If it is necessary to store a trans­former outdoors it should be thoroughly protected

SUPERSEDES ADVANCE I. L. 46-3Q0-2

to prevent moisture and foreign material from enter­ing. Condensation and the absorption of moisture can be prevented or greatly reduced by the installa­tion of space heaters or other small electric heaters.

Testing of transformers that have been in storage as described in the Instruction Leaflet "Operation­Maintenance" should be performed before the trans­former is placed in service.

INSTALLATION

Factors which should be kept in mind in locating dry type transformers are accessibility, ventilation, and atmospheric conditions.

Dry type transformers are normally designed for installation indoors in dry locations. They will oper­ate successfully while energized where the humidity is high but under this condition it may be necessary

FIG. 1-Normal Air Circulation in a Dry Type Transformer.

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DRY TYPE TRANSFORMERS---------------------------------------------

to take precautions to keep them dry if they are shut down for appreciable periods. Precautions should be taken to guard against accidental entrance of water, such as might be obtained from an open win­dow, by a break in a water or steam line, from use of water near the transformer, or from constantly dripping water.

Adequate ventilation is essential for the proper cooling of transformers. Clean, dry air is desirable. Filtered air may reduce maintenance if the location presents a particular problem. When transformers are installed in vaults or other restricted spaces, sufficient ventilation should be provided to hold the air temperature within established limits when meas­ured near the transformer inlets. This usually will require approximately 100 cubic feet of air per min­ute per kilowatt of transformer loss. The area of ventilating opening required depends on the height of the vault, location of openings, and the maximum loads to be carried by the transformer. For self­cooled transformers, the required area will be at

least one square foot each of inlet and outlet per 100 Kva of rated transformer capacity, after deduc­tion of the area occupied by screens, gratings or louvers.

Dry type transformers should be installed in loca­

tions free from unusual dust producing mediums or

chemical fumes. Transformers should be located 12

to 36 inches away from walls or other obstructions

that might prevent free circulation of air through

and around each unit. The distance between ad­jacent transformers should not be less than this

value. Also accessibility for maintenance should be

taken into account in locating a transformer. If the

transformer is to be located near combustible mater­

ials, the minimum separations established by the

national electrical code should be maintained.

The transformer case is designed to prevent the entrance of most small animals and foreign objects. However, in some locations, it may be necessary to give consideration to additional protection.

WESTINGHOUSE ELECTRIC CORPORATION SHARON PLANT • TRANSFORMER DIVISION • SHARON, PA.

(Rep. MIS) Printed in U.SA.

www . El

ectric

alPar

tMan

uals

. com

I.L. 46-300�6-B

INSTRUCT IONS

DRY TYPB TRANSFORMBRS

FIG. l. Type ASL Distribution Transformer

DESCRIPTION

THE MODERN DRY TYPE TRANSFORM� ER has been developed to supply the need for a safe transformer for indoor applications. It is designed to be essentially fireproof and explosion proof for economical installations without vaults near its load center.

Explosion and fire, the hazards of liquid filled transformers, are greatly reduced in air cooled transformers because they are constructed wi.th A.S.A. Class B and Class H materials and utilize the surrounding air for their cooling medium.

Metal cases with suitable covered openings are used to encase air cooled transformers. The open­in9s, which are necessary for the free oircul;;dion

SUPERSEDES LL. 46-3Q0..6-A

of air within the transformer, are not weather tight and so limit these transformers to indoor installa­tions.

Dry type transformers are manufactured in two types, the "DT-3" and the ASL. The type "DT-3" consists of the smaller ratings and the type ASL the larger ratings.

The normal kva limit of self-cooled dry type transformers is 5000 kva single-phase and 7500 kva three-phase. It is possible to increase these limits by the addition of air blast equipment (which must be provided for at the time of design) or by the paralleling or banking of two or more units mounted in a common case.

The maximum voltage for which air cooled trans­formers are built is 15000 volts.

Dry type transformers are supplied with pro­vision for grounding the case and an instruction

FIG. 2. Type DT-3 Power Center Transformer

OCTOBER, 1960 www . El

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alPar

tMan

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. com

DRY TYPE TRANSFORMERS------------------------------------------

FIG. 3. Type ASL Power Transformer Crated for Export Shipment

plate which gives the electrical connections and details of the transformer. Other accessories are supplied in accordance with the specific trans­former and customer requirements.

High and low voltage leads may be brought out of the case by several different methods. The most common are: porcelain bushings (see the Instruc­tion Leaflet "Dry Type Transformer Bushings"), terminal chambers with potheads or conduit con­nections, and direct connection to switchgear, switches or bus work.

SHIPMENT

Except for lightning arresters and LCB switches, air cooled transformers are usually shipped ready for installation complete with bushings and acces­sories in place and connected for operation. They are completely covered with a weatherproof cover­ing which should not be removed until the trans­former is ready to be moved indoors and then, only when there is no danger of exposing the transformer to dampness.

Shipping braces and shims under the transformer feet with their respective bolts when provided should be removed after installation. The outline drawing will show which braces are to be removed.

FIG. 4. Type ASL Power Center Transformer Loaded on a Flat Car for Domestic Shipment

For foreign shipment air cooled transformers are completely covered with a weather tight wrapping and crated with a sturdy wooden box and securely braced to take the extra handling and movement to which they are subjected while in transit. Aside from the crating, all details are the same as for domestic shipment.

UNPACKING

It is only necessary to remove the weather proof covering to completely unpack an air cooled trans­former, however precautions to keep the trans­former dry as outlined above must be followed. Occasionally bushings or other accessories are shipped separately. If this is done, care must be taken when unpacking as items such as bushings are quite fragile.

SERVICE

Further information, or renewal parts, may be obtained by contacting the nearest Westinghouse office. The facilities of the Engineering and Service Departments may be obtained through the nearest Westinghouse office.

WESTINGHOUSE ELECTRIC CORPORATION

SHARON PLANT • TRANSFORMER DIVISION • SHARON, PA. Prillted in U.S.A.

-

www . El

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alPar

tMan

uals

. com

I. L. 46-300-2

INSTRUCTIONS

RECEIVING AND INSTALLATION OF

DRY TYPE TRANSFORMERS

RECEIVING

New transformers should be inspected when re­ceived for damage during shipment. Examination should be made before removing from cars or trucks and if any injury is evident or any indication of rough handling is visible, a claim should be filed with the carrier at once and the manufacturer should be notified.

After the transformer has been placed indoors, the panels should be removed and an internal in­spection made for injury or displacement of parts, loose or broken connections, cracked porcelain, dirt or foreign material and for the presence of free water or moisture. Any damaged condition should be reported at once to the nearest Westinghouse Office. If water or moisture is evident see the Instruction Leaflet "Operation and Maintenance of Dry Type Transformers" for methods of testing for moisture and methods of drying out.

HANDLING

Lifting holes are provided on each side of the case for the insertion of hooks to lift the complete trans­former. These holes should be closed with the steel cover provided, so as to prevent the entrance of foreign materials.

For power centers and unit substations, eye nuts are provided for lifting the complete unit. After in­stallation, these may be removed and the openings covered with cap provided.

The base of these transformers is constructed so that the transformer can be moved on rollers in any horizontal direction. Under no circumstances should the transformer be moved with ropes or cables placed around the case. The transformer case is suitably designed for jacking. Jacks should be placed as indicated on the outline drawing.

STORING

Dry type transformers should be stored in a warm, dry location with a uniform temperature. Ventilating openings should be covered to keep out dust and foreign objects. If it is necessary to store a trans­former outdoors it should be thoroughly protected

SUPERSEDES ADVANCE I. L. 46-300-2

to prevent moisture and foreign material from enter­ing. Condensation and the absorption of moisture can be prevented or greatly reduced by the installa­tion of space heaters or other small electric heaters.

Testing of transformers that have been in storage as described in the Instruction Leaflet "Operation­Maintenance" should be performed before the trans­former is placed in service.

INSTALLATION

Factors which should be kept in mind in locating dry type transformers are accessibility, ventilation, and atmospheric conditions.

Dry type transformers are normally designed for installation indoors in dry locations. They will oper­ate successfully while energized where the humidity is high but under this condition it may be necessary

FIG. 1-Normal Air Circulation in a Dry Type Transformer.

JANUARY 1952 www . El

ectric

alPar

tMan

uals

. com

DRY TYPE TRANSFORMERS---------------------------------------------

to take precautions to keep them dry if they are shut down for appreciable periods. Precautions should be taken to guard against accidental entrance of water, such as might be obtained from an open win­dow, by a break in a water or steam line, from use of water near the transformer, or from constantly dripping water.

Adequate ventilation is essential for the proper cooling of transformers. Clean, dry air is desirable. Filtered air may reduce maintenance if the location presents a particular problem. When transformers are installed in vaults or other restricted spaces, sufficient ventilation should be provided to hold the air temperature within established limits when meas­ured near the transformer inlets. This usually will require approximately 100 cubic feet of air per min­ute per kilowatt of transformer loss. The area of ventilating opening required depends on the height of the vault, location of openings, and the maximum loads to be carried by the transformer. For self­cooled transformers, the required area will be at

least one square foot each of inlet and outlet per 100 Kva of rated transformer capacity, after deduc­tion of the area occupied by screens, gratings or louvers.

Dry type transformers should be installed in loca­tions free from unusual dust producing mediums or chemical fumes. Transformers should be located 12

to 36 inches away from walls or other obstructions

that might prevent free circulation of air through and around each unit. The distance between ad­

jacent transformers should not be less than this value. Also accessibility for maintenance should be taken into account in locating a transformer. If the

transformer is to be located near combustible mater­ials, the minimum separations established by the national electrical code should be maintained.

The transformer case is designed to prevent the entrance of most small animals and foreign objects. However, in some locations, it may be necessary to give consideration to additional protection.

WESTINGHOUSE ELECTRIC CORPORATION SHARON PLANT • TRANSFORMER DIVISION • SHARON, PA .

(Rep. ll-60) Printed in U.S.A.

www . El

ectric

alPar

tMan

uals

. com