dimmer-tech note

WHAT IS A "Dimmer Dot"

SALIENT FEATURES

CONSTRUCTIONAL FEATURES

The "Dimmer Dot" is a Variable Transformer and provide continuously adjustable voltage A.C.supplies. In its "Auto Transformer" from (type-D, as manufactured by Green Dot ElectricCorporation), it is an efficient, reliable method of controlling A.C. voltage from zero to linevoltage by amplitude modulation of the A.C. waveform. Since the Current, Power, Heat, Lightand Motor speed are further functions of the voltage, the "Dimmer Dot" Variable Transformerfinds its varied use. A few of the applications are

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The versatility of control are further high lighted in a separate publication "Tech Note" on"Dimmer Dot" Variable Transformers. The circuitories there in are only a few of theapplications.

Control of A.C. voltage in testing and development work.

Over voltage and undervoltage tests.

Voltage control of aging racks for lamps, vacuum tubes,

dry disk rectifiers, etc.

Voltage control in power supplies -as for Servo-type,

Automatic Voltage Stabilizers, constant current supplies etc.

Voltage control for meter calibration, phase-angle control in

the calibration of wattmeters and power-factor meters.

* Motor speed control.

Control of electric heaters and ovens in laboratory, pilot plant,

and production line.

Lighting control in theater, auditoriums, photographic studio

and dark rooms.

The "Dimmer Dot" Variable Transformer, type-D consists of single layer winding on toroidalsilicon-steel core. As the control knob is rotated, a carbon traverses the winding, tapping off aportion of the total voltage across the winding. The brush is in continuous contact with thewinding, and the voltage between turns is always less than I volt, even in the largest model; inthe smallest model it is only about 0.3 volt. The discrete voltage increments obtained as theknob is rotated are always less than the voltage between turns. Since the brush spans morethan one turn, the change in voltage is practically continuous. The brush is so designed thatexcessive heating can not occur in the turns that it spans.

"Dimmer Dot" have many operating advantages over any other manually operated voltagecontrol device for alternating-current use. Amongst the more important features are:

GOOD REGULATION - Output voltage is substantially independent ofload.

SMOOTH CONTROL - The "Dimmer Dot" can be set very closely set toany output within its range.

HIGH EFFICIENCY - Very low losses under all load conditions.

LONG LIFE - With the exclusive "Dura Dot" contact surface,the life of the "Dimmer Dot" Variable Transformer is

essentially the same as that of any standard fixed-ratio power trans

LINEAR OUTPUT VOLTAGE - Output voltage is continuously adjustablefrom 0 to 112% of line by approximately 340degrees and in certain models it is more in certainmodels. The dial reads directly in no load outputvoltage at rated line voltage or some dials arecalibrated fo rpercentage of the full range control.

MODERATE TEMPERATURE RISE - Less than 50 degrees forcontinuous operation.

ADVANCED MECHANICAL DESIGN - Rugged construction - no delicateparts-two or more units can be ganged on sameshaft-shaft is reversible for simple conversion

from front to back-of-panel mounting.

Constructional features as different from other Variable Transformers lie in respect ofINSULATION - that the insulation between windings and core is provided by mouldings so as toprevent any possibility of slackening of the turns during use and also to proved for a uniformhard bed under surface for the winding so as to make a strong base and under surface for longlife of the track.

Green Dot

Electric Limited

Tech NotesTech Notes 1

R

Variable VoltageAuto Transformers

Dimmer Dot

WINDINGS

BRUSH MECHANISM

FRAMES

BACK OF PANEL

-

BEARINGS -

GENERAL - the "DIMMER DOTS”

- are of high conductivity copper insulated with synthetic enamel of

thepolyvinyl acetal-phenol formaldehyde resin type providing good space factor,

extremely high abrasion resistance and having a good ability to resist the effects of

prolonged heating. The windings are done by toroidal winding machines specially

designed and developed by Green Dot during the past number of years to produce

Constant winding tension and even pith. The winding are prevented from any possible

movement during use by providing serrations on the winding rings and the further

fixing the under pressure & use of high temperature bearing epoxies, through a special

technique developed over years of experience.

- "DIMMER DOT" Transformers are known for their trouble free

brush gear. They have produced a self aligning brush mechanism which fulfils the

following requirements.

- Minimum heating and wear

- Maximum contact area

- Constant contact resistance and losses

The temperature rise of brush mechanism and winding in any Variable Transformer, is

dependent upon the contact pressure and the area of contact, which in turn decides the

current in the short circuit, which in turn decides the current in the short circuited turn

and brush face. "DIMMER DOT" brush mechanism have been developed to provide a

constant brush contact area. The brush mounting holds the brush vertically in the

direction of travel, so as to ensure that the same contact are is presented to the winding

at all times with constant pressure. This enables the full contact are to be maintained,

with resultant minimum contact temperature. They are provided with extra grip holder,

greatly increasing their physical strength and offering great resistance to damage from

shock and rough usage. The track cannot be shorted by metal brush holder fittings

even in the worst conditions.

the wound core are held strongly and insulated from mounting fixture so as

to proved minim high voltage standing of 2.5KV. The economised models are also

available for OEM uses. The facilities can be provided for fitting stops and micro

switches.

the units are fitted with bearings, of bush type of nylon or glass filled

nylon, for higher sizes, heat and light stabilized unaffected by atmospheric conditions,

or sintered modified bronze or sintered bronze, self lubricating type as not to need

lubrication through the life time of the product or the ball bearings as optional or the

motorised unit. While ganging up the units of two or more numbers, the intermediate

bearing guides are removed to provide rotary smooth operation. The Torque figures for

various models can be had on request.

are manufactured in certain fixed sizes determined by

the voltage and current ratings. Type-D are manufactured in 0.7, 2, 4, 8, 15, 28, 40,

50, 60, 75, 100, 150 and 200Amps., and voltages of Input 270 Volts for 1Phase with

taps at 0-30-240-270 voltages so that for 3 Phase operations, 3 single Phase unit can

be connected in Star so as to provide for 470 Volts phase to phase connection facility.

Invariably all 3 Phase units are ganged assemblies of 3 single Phase units

mounted on a common shaft. The facility exists for changing the shaft to make front

shaft unit to back shaft unit suitable for back of panel mounting for 4, 8, 15 and 28

Amps units of single phase type. The 3 Phase units of back of panel and mounting have

to be placed on supported structure at the back of the panel and the frond shaft can be

brought through panel hole, obviously such arrangements can be for the air natural

cooled unit. For the oil cooled units the containers have to be placed at the back of the

panel and mounted or suitably held by keeping the unit with shaft in vertical position. 3

phase units are not available in 0.7 Amps. All the units are either fitted with screen

printed insulating plates with schematic wiring diagram shown thereon or with a

connection marking plate fixed there upon. The standard connection diagram and

markings on the terminal plates are as follows

- "DIMMER DOT" Units type D, of 4, 8, 15 & 28 Amps. ratings, single

phase may be used either surface mounted or back of panel mounted. For ease of

packing and transportation, at times, standard models are supplied for surface

mounting, but the user can easily convert them to back of panel mounting, simply by

removing the shaft locks or clamping rings by simply loosening he screws thereupon.

The spindle or shaft is then adjusted after inserting from the other end,

spacers/washers are suitably placed so that proper free movement of the moving arm

without getting disturbed from the tail end and stopper is obtained with proper usable

length of the Carbon from the Carbon Brush Holder available on track. Sufficient

pressure from the spring holding the Carbon Brush must be ensured as available on the

winding track.

BRUSH MECHANISM

GreenDot Tech NotesTech Notes

-2-


Dimmer DotR

1

METRIC CONVERSION

TRACK PREPARATION

LONGER LIFE

-

OVER LOADS

LESS MAINTENANCE

DIMMER DOT TECHNICAL SPECIFICATIONS :

RATING :

Small screws used in the models at present are B.A. sizes, 2, 4

& 6 B.A. having been used at small paces and conversions are being carried out to metric

size. The changes are being carried out in a phase manner & is being intimated by sales

department separately.

- "DURA DOT" track-" Green Dot " has developed over the years

sophisticated track preparation method which provide fine tracks, designed to providing

close tolerance surfaces. The optically ground tracks are plated with a hard silver alloy,

ensuring constant resistance. After a quarter of million operating cycles, the Brush wear

is only approximately 0.001 inch. This will allow for approximately 30 millions operating

cycles before Brush wear demands a replacement Brush. "DURA DOT" contact surface is

one of the most exclusive achievement made by "Dimmer Dot" for greater reliability, less

maintenance and longer life of the "DIMMER DOT" variable Transformers. The contact

surface eliminates all oxidation problems involved in the use of a carbon brush and care-

copper contact and have the further following features to claim

- essentially the same as that of any fixed ratio transformers. Failures in

any "DURA DOT" Dimmer are almost unknown. They are caused only by some

factorswhich affect any standard fixed ratio transformer: such as due to failure of

insulation because of prolonged over extended periods at currents in excess of rated.

HIGH INITIAL SURGE CURRENTS- all Dimmer with "DURA DOT" contact surface will

withstand initial surges ten times the rated current; they do not have to derated even for

incandescent lamp loads (with may draw up to nine times rated current when first turned

on)

- the time - current curve given in these pages is the safe allowable

overload for "DURA DOT" Coated Dimmer-these overloads are considerably higher than

the older types of Dimmers.

- under normal conditions, maintenance of "DURA DOTS" is

negligible-an occasional wiping of the contact surface with an alcohol-moistened rag

being all that is required-the "DURA DOT" contact surface is subject to no deterioration

when "DIMMER DOT" is operated with their rated loads.

Ratings quoted are for use in ambient temperature from -20'C to +50'C. Current

derating figures for temperatures above 50'C are as follows :

55'C 60'C 65'C 70'C

0.95 0.87 0.78 0.68

Generally, when the operation is required in ambient temperatures higher than

50'C output current must be reduced according to the curve shown below:

The current that may be drawn from a "Dimmer Dot" transformer through the brush is

not constant as in fixed auto wound transformers, but varies according to brush

position. At 50% and 110% of the line voltage, winding heat is the current limiting

factor. Near zero and line voltage, winding heat is low and brush heat becomes the

current limiting factor. Both factors operate at intermediate brush positions. This is

common to all continuously variable "Dimmer Dot" Transformers. The "Dimmer Dot"

ratings, in terms of "Rated Currents" "Maximum Currents" etc. should be fully

understood for optimum results.

100

90

80

70

60

50

40

30

20

10

03086 104 122 140 158 176 194 Deg. F

40 50 60 70 80 90 Deg.C

"Dimmer Dot" Auto Transformerderating resus ambient

temperature

%N

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AMBIENT TEMPERATURE

-3-


R


Dimmer DotR

1

CURRENT RATINGS

RATED CURRENT :

MAXIMUM CURRENT:

It is general practice to specify the current rating of Variable Transformer by two

values, the rated current and the maximum current.

Dimmer Dot have two current ratings because in any adjustable auto transformer,

heating of the winding varies with the brush setting. To limit these useful devices to

the current that can be drawn at any setting (RATED CURRENT) places an undue

restriction on the capabilities.

Most load (possible exceptions are some kind of motors and incandescent lamp loads)

which draw MAXIMUM CURRENT at line voltage may be safely regulated from zero to

line voltage without danger of overload. This MAXIMUM CURRENT is generally 20 to 30

percent above the RATED CURRENT and this concept may be safely used to full up the

gap in the capacities of the RATED CURRENT of the various model available.

The rated current can be drawn at any brush setting. When the over-voltage connection is

used, the load should not be drawn more than rated current.

May only be drawn near zero or near maximum output voltage when t h e

Dimmer Dot transformer is line connected, i.e. when connected for an output voltage

range of zero to line voltage. See Current Rating Curves.

CURRENT RATINGS

It is general practice to

The Maximum Current can only be drawn in line-voltage connection with the listed

(or lower) input voltage across the whole "Dimmer Dot" winding (e.g. 240 volts on a

240/270 volt unit), and can only be drawn near zero or at or near full output

voltage. A load having linear voltage/current load, line (constant impedance load

drawing maximum current at the line voltage can be controlled from zero to line

voltage.

The knowledge of the maximum current and the rated current for the particular end

application can be useful for filling in the capacity gap for the "Dimmer Dots" in the

range and thus intermediate current requirements can at time be met from the

particular rating valued "Dimmer Dots".

KVA RATINGS

OVER VOLTAGE CONNECTIONS:

SHORT TERM RATTING FOR INTERMITTENT OF SHORT TIME OPERATION:

Equals nominal input voltage multiplied by maximum current output. KVA rating for

over voltage connection, equals output voltage multiplied by rated current.

A "Dimmer Dot" transformer connected for over voltage provides an output of 12 %

above the supply voltage on load. Most models have terminations for line voltage or

over voltage connection, at the option of the user.

Rated' current only may be drawn when over voltage connected.

The short term rating is also indicated on the curve and this is a maximum current

that can be drawn on intermittent duty. This has been further discussed under the

heading "Overloading" how to select a "Dimmer Dot", load rating and a trade off-life

Vs increased rating. These all demonstrate high overload capacity of Dimmer Dot

transformers, particularly where high initial surge currents may be expected or

where high current is required for a short period of time. Care must be taken to

ensure that these rating are not exceeded.

120

MAX. CURRENT MAYBE DRAWN HERE

MAX. CURRENT MAYBE DRAWN HERE

110

100

90

80

70

60

50

40

30

20

10

10 20 30 40 50 60 70

BRUSH SETTING AS PERCENTAGE OF SUPPLY VOLTAGEOU

TPU

TC

UR

RE

NT

INP

ER

CE

NTA

GE

OF

RAT

ED

CU

RR

EN

T

80 90 100 1100

RATED CURRENT MUST NOT

BE EXCEEDED HERE

TUNGSTEN LAMP

LOAD

CURRENT DRAWN

BY CONSTANT

IMPEDANCE LOAD

LINE VOLTAGE LIMIT OF

Dimmer Dot RANGE WHEN

OVER VOLTAGE CONNECTION

IN NOT USED

MAX. PERMISSIBLE

CURRENT

"GREEN DOT "

RATING CURRENT

RATED CURRENT

-4-

GreenDot Tech NotesTech Notes Variable Voltage

Auto Transformers

Dimmer DotR

R

1

The load current capacity of the "DIMMER" is limited temperature

and life. Specified ratings assume a maximum ambient

temperature of 50'C and minimum life span of 7 years. If the

expected ambient is lower or forced cooling is possible, the auto

transformer can be updated without affecting life. Also, if a

shortened life is not a problem in your application, a further

uprating can be realized.

Further, if the load is expected to be switched on and off regularly

(as with a thermostatically-controlled heater), the Dimmer can be

uprated. In general, if the time for an on-off cycle is 2 hours or less

and the off time is 10% or more of the total cycle time, some

significant improvement in rating can be realized.

Thus the careful overloading of the "DIMMER DOT" Auto

Transformer can take advantage of any design trade-offs. To

amplify it further, as an example, the current rating of all models

assume trouble-free operation 24 hours a day, after day. If a

"DIMMER" IS TO BE U SED ONLY FOR 2 Hours or less per day,

significantly more than rated current can be drawn for that short

period. The figure below shows how upto 10 times the normal

rating can be realized.

EFFECT OF DUTY CYCLE

When the duty-cycle operation is contiguous, the rating should be

determined by considerations of "off-puls-on' time to "on-time";

the rated current can be multiplied by the square root of this ratio to

obtain the allowable uprated current. The following examples will

illustrate the calculations of permissible overloads for a typical 4

Amps. model.

Example 1: The load is on for 15 seconds out of every 4

minutes (240 seconds).

duty cycle = 4

duty-cycle uprated current = 4 A x 4 = 16 A

From figure for the "Short-time overload characteristic of "DIMMER

DOT" Auto Transformers with Line voltage connections", 15

seconds overload uprates the current by 500% so that,

short-term overload current =4 A x 5 = 20 A.

Since the lower rating takes precedence, the 16 Amps, limitation

imposed by the duty ratio is the maximum current permissible.

Note, on the overload curve of the figure, the lower curve must be

used for models with build-in-fuses.

Example 2: The load is one for 6 seconds out of

each minute (60 seconds) over a duration of one-

half hour.

Duty cycle = = 3.16

Short-term overload for 30 minutes = 133%

from duty cycle and 30 minute short-term overload

considerations:

uprated current = 4 A x 3.16 x 1.33 = 16.4 A

short-term overload current = 4 A x 7.25 = 29 A.

Since the lower rating takes precedence, the 16.4 A limitation

imposed by the duty-cycle and 30 minute short-term overload is

the maximum current permissible.

When the effects of temperature upon rating and upon insulation

life are combined, a new life load ambient relationship is obtained.

The figure "Life-load-ambient-curve" illustrates this relationship.

Except for reference to the effect of duty, cycle, all previous rating

methods have been based on steady-state, 24 hours-a-day

operation for a calculated minimum for increased rating or vice-

versa. Following the load-ambient curve, uprating or derating

could be done on the "DIMMER DOT" rating. The limit of ten times

the rated current should never, under any circumstances, be

exceeded.

As an example, consider the case of a 4 Amps. unit again. For

operation at 30'C ambient temperature, suppose there is a

requirement of 400 hours of minimum life expectation of the unit.

It is desired to find out the value of the allowable current under

such operating conditions. The calculations are as follows:

Uprating for 30'C ambient , 400 hours life 1.65

Duty cycle (as of the example 1) x 4

Resultant uprating factor 6.60

Rating of the unit x 4 A

Allowable current from duty cycle 26.6

Uprating for 30'C ambient, 400 hour life 1.65

15 second short-term overload factor .. x 5

Resultant uprating 8.25

Rating of the unit x 4 A

Allowable current from short-term overload . 34A

Since 26.6 is the smaller, it is the limiting value; thus the allowable

current is 26.6 amperes.

The Dimmer Dot variable transformers are manufactured to

conform to Indian Standard Specifications. IS:5142, Specification

for continuously variable voltage Auto-Transformers and the

manufacturers Test Report for the relevant Routine Test can be

furnished on demand. The Type Test are carried out only on sample

units in the production run to ensure conformity to the designs.

60'C average temperature rise measured by change of winding

resistance at rated current with brush set in maximum heating

position, i.e. with out voltage set at half input voltage on full load.

The temperature rise of the winding im immediately under the

brush, will of course higher than this. Operating temperatures of

the brush contact can be permitted up to 200'C depending on

model.

Standard Dimmer Dots are designed for 50/60 Hz. Supplies. All

models may be used on higher frequencies upto 400Hz. but slight

deterioration of regulation, and output current must be derated by

25%. High frequency models designed for 400-2500 Hz. Supplies

can be available.

Dimmer Dot transformer can be used on frequencies below 50 Hz.

if the input voltage is reduced in proportion. Output current

remains as listed and must not be increased.

All "Dimmer Dot" transformers are flash tested at 2500 Volts

R.M.S. for one minute during test.mediately under the brush, will

of course higher than this. Operating temperatures of the brush

contact can be permitted up to 200'C depending on model.

STANDARD SPECIFICATIONS

FREQUENCY:

TEMPERATURE RISE:

FLASH TEST:

606

-5-


20

40

60

80

100

120

140

160

180

200

0.109 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

0.219 0 +10 20 30 40 50 60 70 80 90 100 110 120 130 140

0.438 10 0 10 20 30 40 50 60 70 80 90 100 110 120 130

0.675 20 10- 0 +10 20 30 40 50 60 70 80 90 100 110 120

1.75 30 20 10- 0 +10 20 30 40 50 60 70 80 90 100 110

3.5 40 30 20 10- 0 +10 20 30 40 50 60 70 80 90 100

7 50 40 30 20 10- 0 +10 20 30 40 50 60 70 80 90

14 60 50 40 30 20 10- 0 +10 20 30 40 50 60 70 80

28 70 60 50 40 30 20 10- 0 +10 20 30 40 50 60 70

56 80 70 60 50 40 30 20 10- 0 +10 20 30 40 50 60

112 90 80 70 60 50 40 30 20 10- 0 +10 20 30 40 50

100

80

60

40

20

PercentNormalRating

Normal Rating

Normal Derating Point +50 Co

NormalMinimum

Life

MinimumLife-Years

Ambient TemperatureDegree Centigrade

MinimumLife-Hours

0.001

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TIME IN MINUTES

0.01 0.1 1 2 5 10 100

200

300

400

500

600

700

900

800

1000

1000 10000

OVERLOAD LIMIT

Shaded area for units withover load protector ¼ HOUR-150%

½ HOUR-133%

1 HOUR-120%

24 HOUR-100%

Short- time over load characteristicof Green Dot Auto Transformers


Dimmer DotR

R

240

15

1

NO LOAD LOSS

DRIVING TORQUE:

REGULATION:

OVERLOAD PROTECTION:

OUTPUT CONNECTIONS :

Measured in Watts at 50 Hz. for standard models and 400 Hz. for

higher frequency models at rated input voltage.

The no load losses include the core and brush loss and since the

brush always spans 2 more turns this also include the watt losses

due to the short circuit current over the brush position.

The figures for driving torque required to turn the shaft can be

provided on request. The figures quoted are maximum figures.

Although 'Dimmer Dot" are designed for arduous industrial use,

damage will occur if they are subjected to short circuit or

continuous severe overload.

It is therefore recommended that protective devices be fitted such

as a circuit breaker in the input circuit & and H.R.C. fuse in the load

circuit.

It is normal practice to provide a protective device in the input

circuit. Improved core materials, permitting higher flux densities

than was possible in the past, allow high inrush transient surges of

up to 10 times the rated current to occur at switch on. This is not

harmful except H.R.C. fuses or protective devices of instantaneous

operation. It is therefore recommended that input protection

"Dimmer Dot" is obtained by employing slow blow fuses or circuit

breakers with slight operating delay. Input protective devices

should be capable of handling 1000% overload for one cycle of the

supply frequency.

It is not always appreciated that a variable transformer with an

input voltage of 250 V and delivering say 10 amps to a load at 50 V

(0.5 KVA), will draw a current of only 2 amps from the supply

mains. It this instance, a 10 amp. fuse laced in the input circuit

would not rupture until the load current reached 50 amps . It is

obvious, therefore, that input protective device afford little

protection to the transformer against overloads at low output

voltage. The solution is, of course, to fuse the load circuit with an

H.R.C. fuse link.

"Line voltage connection" refers to the connection of a "Dimmer

Dot" transformer for an output voltage of zero to line voltage. "Over

voltage connection" refers to the input voltage connection for a

range of output voltage from zero to 12% of line voltage.

Regulation expressed as a percentage of supply voltage is defined

as output voltage change from no load to full load, with constant

input and set output voltage. Regulation varies because copper loss

will vary with brush setting. Resistance of the brush and leakage

reactance caused by stray flux also contributes to the regulation.

Typical regulation figures vary between 0.5% to 3.0% according to

model and brush setting.

The figure shows the regulation drop under load for the Dimmer

Dots. This curve applies to all model operated normally or rated

input voltage and RATED load current.With insignificant change it

applies equally to both OVERVOLTAGE and LINE-VOLTAGE output

connections.

The figure shows the regulation curve of Dimmer Dot operation

under conditions similar to those of previous figure except that this

curve applies to all models operating at one-half normal rated line

voltage and one-half normal rated current . This covers such

special connections as to secure 0 to 270 Volts output from a 155

Volts line.

RESOLUTION

KNOBS & HANDWHEELS:

DIALS:

ANGLE OF ROTATION:

WHEELED UNITS AND SEMI PORTABLE-LABORATORY

MODELS:

METERED UNIT:

:

"Dimmer Dot" resolution is extremely good as the resistive brush

always covers two or more turns, therefore the voltage increments

obtained by rotation of the knob will always be less than the

voltage between turns. Careful design of the brush ensures that

excessive heating cannot occur in the turns that it covers. Number

of turns for standard models data can be supplied on request.

"Dimmer Dot" standard fitting knob and handwheels are used

through out the range of "Dimmer Dot". For OEMs applications,

where knob, handwheels or dials are not needed suitable reduction

in prices is given.

Dials are anodized aluminium, printed either in percentage of

output voltage or approximately of output voltage for 240 Volts

input voltages. For panel applications, there type of dials are

available for variety purpose. Dials of 0-270 V, are also available

a fixed censor on the panel or alternately they may be mounted

on the panel and used to the pointer which is provided on

underneath of the knob.

All models, are supplied with a angle of rotation of approx. 320'

and effects are being made to increase the angle of rotation so as

to have better utilization of core and winding.

Enclosed unit of 40 Amps capacity and above are transportable on

wheeled enclosures. Smaller units can be supplied with 4 wheeled

enclosures or 2 wheel enclosures with additional two front stud

supports and a push trolley type handle on the wheeled end to

make them SEMI PORTABLE for laboratory use.

Metered units, fitted with Volt meter, or a Volt meter and an

Ammeter or only an Ammeter can be provided on request at extra

cost.

0 20 40 60 80 100

1

2

3

REG

ULATIO

NIN

%O

FLIN

EVO

LTS

DIAL SETTING IN PERCENT OF LINE VOLTAGE

LINE VOLTS

REG

ULATIO

NIN

%O

FLIN

EVO

LTS

DIAL SETTING IN PERCENT OF LINE VOLTAGE

15

10

5

040 80 120 160 200 240

6

5

4

3

2

1

60 90 120 150 180 210 240 27030

LINE VOLTAGECONNECTION

NO LOAD VOLTAGE

DRO

PIN

VO

LTAG

EO

NLO

AD

ING

LINE VOLTS

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Auto Transformers

Dimmer DotR

R

1

CONNECTIONS (INSTALLATION)

STARTING UP (INSTALLATIONS)

MOTOR DRIVE (INSTALLATION)

INSTALLATION

MAINTENANCE

All transformers listed in our standard range are designed for continuous operation in

normal operating mode. Enquiries should be submitted as to loading capacities where

operation under severe loading is to be anticipated. The variable transformers are

connected after comparing the existing mains voltage supply with that shown on the

transformer data plate. The main input is to be connected at the places shown very

carefully. It has been seen that large number of damages to the variable transformers take

place on wrong connections at input mains, at the time of installations, and these damages

are at the time of permanent nature as to totally damage the variable transformer. In the

case of three phase toroidal variable transformers the neutral point is led out, and can be

subjected to full loading. In the case of distinctly a symmetrical mains systems the

transformer can suffer damage. Depending on local regulations it will either be necessary

for the transformer frame to be earthed or connected with the neutral conductor in the

mains system.

In the case of variable transformers in economizing circuit no winding terminal should be

earthed mains systems. If necessary a transformer with separate wending must be

coupled in series or a toroidal variable transformer with separate winding used.

With starting up care must be taken to ensure that the shaft on toroidal variable

transformer is not arrested at the top and bottom ends of the winding. Any attempt to

turn the shaft further will cause serious damage to the mechanical equipment.

Variable transformer must be protected sit with the plant against overload and short

circuits, e.g. fusible cutouts, circuit breakers or similar. It is also necessary to take account

of the current time parameter of the protective measure used. Attention is drawn to the

fact that unilateral protection can be inadequate, as the current transformation ratio is

variable.

Where fuse protection is the input end the user must take full account of the switch-on

process which in the case of transformers with core material of high permeability,

generates a cut in current surge which, in unfavorable circumstances, can achieve 20 times

the level of the current rating. This current surge may achieve 30 times the level of the

current rating in the case of variable transformers with separate windings. As this current

surge falls off extremely quickly it does not result in any damage to the transformer.

Automatic cutout and quick-action fuses can, however, react to this current surge, so that,

wherever possible, the use of slow action fuses or circuit breakers is recommended.

After checking the voltage data AC motor drive systems can be connected to the terminals

marked accordingly. Mains supply is connected to the terminals marked with relevant

voltages, the push-button for downward motion to "Min" and the centre terminal, the push

button for upward motion to "Max" and centre terminal. Three phase motor drive systems

are connected accordingly and these drive systems are controlled by reversing contactors.

DC motor drive systems are connected as per the recommended circuit diagram. With all

motor drive systems limit switches are normally set to "Min" and "Max". The switching

points can be varied as required by simply resetting the completes, where so ever

provided.

When installing the Dimmer Dot toroidal variable transformers care must be taken to avoid

impairing the cooling system, as otherwise the variable transformer could be subject to

overload as a result of heat buildup, even at rated operation levels and ambient

temperatures of 40 degree Centigrade. The transformer shaft may not be given any

mutually conductive connection with the surrounding metallic housing, as this will result in

shorted turns and consequent permanent damage to the transformer.

The carbon brushes and carbon rolls are subject to natural wear and tear which, in turn, is

governed very much by local operating condition and functional circumstances to which the

variable transformer is subject. Rapid wear, however, can result only form persistent

overloading and extraordinary fouling of the contact track. Regular maintenance is

advisable and, in normal operation, should be carried out at six-month intervals, as

follows:

The contact track must be cleaned of all traces of dirt, using a soft fluff-free cloth moistened

with a suitable degreasing fluid, e.g. alcohol or similar. The carbon roll bearings must not be

oiled.

Regular maintenance will guarantee satisfactory functioning and greatly increase

operational liability and durability. Fulfillment of warranty obligations is conditional upon

proof being furnished as to compliance with instructions for use. Where parts have to be

replaced only genuine replacements approved or manufactured by us may be employed.

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OIL-IMMERSED DIMMER DOTS:

MOTOR DRIVES :

Oil immersion provides increased current rating of approximately

70% and protection for use in adverse environments. Some of the

models are economical on a rating/cost basis when compared with

air-cooled types, providing intermediate or increased ratings.

When environmental protection, such as in electroplating

workshops, textile mills, oil and ghee plants, is needed, the

Dimmer Dots must always be used in oil immersed form.

Right angle drives can be fitted, for use when the Dimmer Dots, oil-

immersed types stand behind a panel.

Motor drives, with time for full sweep of 15, 30, 45, 60, 90 or 120

seconds, fitted with "Stepper Dot" A.C. Synchronous motor,

workable on 220-240 Volts, Single phase A.C. Supply. The motor

drives are fitted with micro switches at limits, to cut off the motor

supply extreme positions. The covered motorised units are fitted

with push button controls for raise and Lower operations and have

to be indicated at the time of ordering. The remote control facility

can be provided at extra cost, if the same is not amounted on the

unit.

Special motor drives fitted with D.C. motors or Low voltage motors

can be supplied to special order. Special assemblies can be

provided with switching and relays, giving a programmed

automatic sequence of operation.

Further details on the motor drives, separate technical note is

available.

SPECIAL VOLTAGE RANGE:

DRAWINGS:/

TECHNICAL ASSISTANCE:

HAZARD WARNING:

Where quantities are sufficient to warrant special productions,

special windings to suit customer's particular requirements can be

supplied.

Detailed drawings can be supplied in cases where dimensions are

critical.

Our sales Engineers are will qualified to advise and assist you with

the selection and application of "Dimmer Dot" transformers.

Dimmer Dot operate at mains voltage and above, and installation,

connection and maintenance must be carried out in accordance

with good engineering practice by qualified personnel. Open

models are intended only for installation as components and must

be considered carefully and the notes on installation and

maintenance and any specific information supplied with Dimmer

Dots adhered to strictly.

No warranty is implied as to fitness for use in any specific

application or installation unless full details have been provided

and we have given specific approval in writing.

Dimmer DotR

Variable Voltage AutoTransformers

D i v i s i o n

Green Dot

Electric CorporationGreen Dot Electric Corporation (the "Company"), New Delhi, warrants to the first end user purchaser (the "Purchaser",) of equipment

manufactured by the Company that such equipment, if new unused and in original unopened cartons at the time of purchase will be

free from defects in material and workmanship under normal use and service for a period of one year from date of delivery for the

Company or for a period of one year form the date of delivery from the business establishment of an authorised dealer of the Company

in the event that the equipment is purchased from an authorised dealer.

THE COMPANY'S OBLIGATION UNDER THIS WARRANTY SHALL BE STRICTLY AND EXCLUSIVELY LIMITED TO REPAIRING OF

REPLACING AT THE FACTORY OR A SERVICE CENTRE OF THE COMPANY, ANY SUCH EQUIPMENT OR PARTS THEREOF WHICH AN

AUTHORISED REPRESENTATIVE OF THE COMPANY FINDS TO THE DEFECTIVE IN MATERIAL OR WORKMANSHIP UNDER NORMAL USE

AND SERVICE WITHIN SUCH PERIOD OF ONE YEAR. THE COMPANY RESERVES THE RIGHT TO SATISFY SUCH OBLIGATION IN PULL BY

REFUNDING THE FULL PURCHASE OF ANY SUCH DEFECTIVE EQUIPMENT.

This warranty does not apply to any equipment which has been tampered with or altered in any way, which has been improperly

installed or which has been subject to misuse, neglect or accident.

THE FOREGOING WARRANTY IS IN LIEU OF ANY OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATIONS,

ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, and of any other obligations or liabilities

on the part of the Company: and no person is authorised to assume for the company any other liability with respect to equipment

manufactured by the Company. The Company shall have no liability with respect to equipment not of its manufacture. THE COMPANY

SHALL HAVE NO LIABILITY WHATSOEVER IN ANY EVENT OF ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES, INCLUDING, WITHOUT

LIMITATIONS, DAMAGES FOR INJURY TO ANY PERSON OR PROPERTY.

Written authorisation to return any equipment or part thereof must be obtained from the company. The Company shall not be

responsible for any transportation charges.

IF FOR ANY REASON ANY OF THE FOREGOING PROVISIONS SHALL BE INEFFECTIVE, THE COMPANY'S LIABILITY IS BASED ON

WARRANTY, CONTRACT, NEGLIGENCE, STRICT LIABILITY IN TORT OR OTHERWISE, SHALL BOT IN ANY EVENT EXCEED THE FULL

PURCHASE PRICE OF SUCH EQUIPMENT.

Any action against the Company based upon any liability or obligation arising hereunder or under any law applicable to the sale of

equipment, or the user thereof, must be commenced within one year after the cause of such action arises.

W A R R A N T Y

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