assignment 4 introduction elwe powder brake

Exercises with ELWE - equipment

Content:

MAGNETIC-POWDER BRAKE AND CONTROL GEAR ES 602DESCRIPTION AND OPERATING INSTRUCTIONS

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MAGNETIC POWDER BRAKE AND CONTROL GEARFUNCTIONAL DESCRIPTION

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INSTRUCTION/WORKSHEET

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STARTING OF THE MAGNETIC-POWDER BRAKE

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INSTRUCTION/WORKSHEET

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ADJUSTING THE CONTROL GEAR TO MEASURE THE CHARACTERISTICS, n = f (T) AND T = f (n) FROM A 3-PHASE INDUCTION MOTOR

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INSTRUCTION/WORKSHEET 1/3

DC- SHUNT GENERATORMEASURE THE LOAD CHARACTERISTIC FROM A SEPARATELY EXCITED DC-GENERATOR

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Version: February, 2006


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- 1 -

1.0 Magnetic-Powder brake1.1 Notch for torque cheque1.2 Connection line with plug

“Magnetic-powder brake – Control gear”

2.0 Mounting frame2.1 Tube with opto-coupler2.2 Star-handle screws2.3 Intermediate coupler with 60 black-and-white

fields2.4 Coupler guard bow2.5 Connection line with plug

“Mounting frame – Control gear”2.6 Connecting line with plug

“Mounting frame – Temperature switch

3.0 Control Gear3.1 Speed Indicator3.2 Torque indicator3.3 Connection socket for digital speed

measurement3.4 Connection socket for analogue speed

measurement3.5 Connection socket for analogue torque

measurement3.6 Connection socket “Frame point”3.7 Connection socket for external set-point

adjuster of load3.8 Change-over switch “speed range”3.9 Selector switch “Function”

Duty type of the brake3.10 Selector switch “Ref. source”3.11Change-over switch “Torque range3.12 ”Adjuster “Electrical zero of the torque

meter”3.13 Connection sockets for pen control of an XY-

recorder3.14 Mains switch with equipment-on indicator3.15 Adjuster “Load”3.16 Connection socket for connection line

“Mounting frame – Control gear”3.17 Connection socket for connection line

“Magnetic-powder brake – Control gear”3.18 Relay contact for blocking circuit (motor and

coupler guard bow over-temperature)3.19 Reset key “Reset” with pilot lamp;

Will light up: In case over motor over-temperature In case of unattached coupler guard bow In case of disconnected connection line

Mounting frame – Temperature switch inside the motor

2


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- 2 -Power supplyConnection to the control gear to a protective-contact socket in accordance with regulations is imperative. When the control gear is build in in supply panel this is automatically arranged. The protective wires of control gear and motor must be connected to the same current circuit.

Speed measurementInside the tube section on the magnetic powder brake unit, below the intermediate coupler, an opto-coupler is provided which will record the pulses created by the 60 black-and-white fields of the intermediate coupler (60 per revolution).

The measuring result will be shown by the circular-scale speed counter of the control gear or by the indicator plate. The measurements are taken in three speed ranges.(0…1500, 0…3000, 0…6000min-1 ).

Attention! Check whether the black-and-white field of the intermediate coupler and the surface op the opto-coupler are clean before speed measurements.

Connection socket for digital speed measurementThrough an operational amplifier, the signals are supplied to an integrated pulse shaper. The rectangular pulses are available at the connection socket for digital speed measurement “ ” for digital counting. At this socket, 60 pulses with a voltage value of Upp = 15 V are measured per revolution.

Connection socket for analogue speed measurementSocket “n” is provided for analogue speed measurement. A direct voltage of 1 V is output at 1000 revolutions/min in that case.

Load adjustment

Adjuster “Load ” The machine to be tested is loaded by the coupled magnetic-powder brake. The torque reduced by the magnetic-powder brake depends upon the exciting current of the magnetic-powder brake. The value of this exciting current is adjusted at the multiple potentiometer (adjuster “Load”). The adjustable control voltage is supplied to a voltage-controlled current source through an operational amplifier, which supplies the exciting current of the magnetic-powder brake.

Selector switch “Function”In position “off” , the exciting current is switched off; the magnetic-powder brake is being demagnetized at the same time. The machine to be tested is only loaded by the friction resistance of the magnetic-powder brake.

Position “nc” is for load at constant speed. This position is required in case the speed is the value to be adjusted (the independent influencing variable) e.g. M = f (n).

In position “Mc” (constant moment), the load of the motor is independent from speed. This position is required in case the torque is the value to be adjusted (the independent influencing variable); e.g. n = f(M).

The set-in point of the braking effect of the magnetic-powder brake is achieved by turning the adjuster “Load” clockwise from the left limit stop by several revolutions according to speed.

- 3 –

3


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Torque measurement and torque indication

The torque of the magnetic-powder brake is picked-up at a wire strain gauge measuring bridge through a torque-force transducer, supplied to a differential amplifier an rectified and amplified by a further stage. The result of the measurement will be shown by the circular-scale torque instrument of the control gear or by the indicator plate. The measurement is taken in 2 ranges.

Module 100W

Measuring range 1 Nm2 Nm

External/internal indication internal

Mechanical balance-correction

The balance of the instrument is mechanically corrected with a screwdriver at the adjusting screw.

Electrical zero-correction

The electrical zero is corrected st the adjuster “0” Nm Adj. Of the control gear.

With a potentiometer, the correction of a base deflection, due to static deformation of the torque-force transducer, is possible.

Connection socket for torque measurement

The result of torque measurement can be picked –up at the connection socket for analogue torque measurement “M”. A measured direct voltage of 1 V corresponds to a torque of 1 Nm in that case.

4


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- 4 –Selector switch “Ref. Source” (Reference source)

Position “man” (manual). In case of manual variable adjustment, i.e. at the adjuster “Load”, the selector switch “Ref. Source” must be in position “man”.

Position “auto” (e,g. recording of a characteristic with XY-recorder)In case of automatic variable adjustment, the selector switch “Ref. Source” must be in the position “auto” The exciting current of the magnetic-powder brake will be continuously increased in this switch position.

In position “auto”, the braking effect of the magnetic-powder brake as a function of speed will set in with time delay. In case of undesired time delay, proceed as follows:- set adjuster “Ref. Source” to position “man”- turn adjuster “Load” clockwise from the left limit stop by several revolutions up

to the set-in point of the braking effect- set adjuster “Ref. Source” to position “auto”; the characteristic will now be

recorded automatically at once. Upon recording of the characteristic, reset adjuster “Ref. Source” to position “man”.

Position “ext” (external). In case of external control of the brake, the external direct voltage will be applied at the connection sockets “U in” to the control gear (0…10V).

Recording of a characteristic with the XY-recorderConnect the connection lines of the XY-recorder to the following connection sockets of the control gear or the indicator plate respectively:- XY-lines to connection socket “n” analogue speed measurement and to connection

socket “M” analogue torque measurement.- Frame line to connection socket “ ” frame point.

Adjust the input sensitivity of the XY-recorder to the outputs of the control gear (1V per Nm for torque and 1V per 1000min-1 for speed).

Start the magnetic-powder brake and set selector switch “Ref. Soured” to position “auto”. In case the pen of the XY-recorder is supposed to contact or lift automatically, the sockets “pen” of the XY-recorder must be connected to the sockets “pen” of the control gear. In case the selector switch “Ref. Source” is set to position “auto”, the pen will contact automatically.

Protection of the magnetic-powder brake against thermal overloadA temperature switch is provided in the winding of the magnetic-powder brake for protection against thermal overload. It is connected in series to the exciting winding of the magnetic-powder brake. In case of excessive temperature increase of the brake, the temperature switch will switch off the exciting winding and switch it on again upon cooling down.

Protection of the motor against thermal overloadA temperature switch is provided inside the motor for protection against thermal overload. In case of excessive temperature increase of the motor, the temperature switch will switch off the exciting current of the magnetic-powder brake through the connection line “Motor terminal box-Mounting frame-Control gear” and the pilot lamp of the “Reset key” will light up.

The same function is achieved without inserting the jack plug into the motor terminal box.

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- 5 -Safety measures

Coupler guard bowIt’s imperative to attach the plug-in coupler guard above the intermediate coupler for protection against danger due to rotating parts.

In case the unattached safety guard bow, its sockets are electrically disconnected. The pilot lamp of the “Rest key” will light up and the exciting current of the magnetic-powder brake will be switched off through the control gear. When contacting the coupler guard bow and the motor respectively the brake at the same time the exciting current will be switched off as well.

Structure of the magnetic powder brake 100WThe magnetic powder brake consists of an inner rotor and outer rotor. The inner and outer rotors run on independent bearings. The field coil is located inside the inner rotor. The torque acting upon the inner rotor is transmitted to the flat special spring steel with 4 wire resistance strain gauges by shaft and power arm. Consequently, the inner rotor is only slightly rotatable. The outer rotor is driven by the machine to be loaded. A magnetic powder is located in the air gap between the rotors.

FunctionAs long as no current flows in the field coil, the magnetic powder is pressed outward by the centrifugal force and only a very low residual friction will occur, which will already be detected and indicated, however, by the measurement of torque. As soon as the coil is excited by direct current, the powder will orientate according to the magnetic lines of force and form a compact mass to connect inner and outer rotors friction-tightly. The value of torque depends upon the value of field current.

Note: In case of decreasing braking power, magnetic powder can be refilled without difficulties.Instructions for refilling magnetic powder (2 g) for WB 51. Remove protective screen2. Remove hexagon socket locking screw, located in the outer rotor of the brake, with hexagon socket

screw key (4mm)Using a small paper funnel, fill in powder while very slightly moving the rotor pipe to and fro.

3. Screw in the locking screw again until the upper edge of the screws is even with the outer rotor.4. Install the protective screen.

6

INSTRUCTION/WORKSHEET 1


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- 6 -

OBJECT:Practise the starting of control gear and magnetic-powder brake.

PROCEDURE:1. Place the motor and the brake on the power supply duct on the table (motor left,

brake right)

2. Insert the coupler between the motor and brake. Slide motor and brake together.

3. Attach the coupler guard bow.

4. Insert the plug of the connection line “Mounting frame-Control gear” into the connection socket “ “of the control gear.

5. Insert the plug of the connection line “Magnetic-powder brake-Control gear” into the connection socket “ “ of the control gear.

6. Insert the tulip plug of the connection line to the temperature switch into the socket “ “ of the motor terminal box. In case of generator experiments the jack has to be inserted into the socket of the driving machine.

7. Connect the grounding sockets of the mounting frame and the motor to the protective wire.

8. Attach the corresponding connection mask onto the terminal box of the motor.

9. Adjust the connections according to the current diagram.

Module system

Equipment designation 100W

Three-phase supply ES 340

Control gear ES 602

Magnetic-powder brakeWith frame, coupling guard bow

WB 5

Three-phase slip-ring induction motor Ms-071

Connection mask 20



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- 7 –Current diagram

10. If necessary, perform the mechanical zero adjustment at the adjusting screw of revolution counter and the torque meter with a screwdriver.

11. Switch on the control gear by operation of the mains switch (equipment-on indicator lamp and the pilot lamp “Reset key” will light up).Important! The control gear must remain switched-on during the experiment.

12. Operate the “Reset key” .

13. Set the adjuster “Load “ to the left limit stop.

14. Set the speed-range selector to: “1500”.

15. Set the function selector switch to “off”. In this position, the excitation of the brake is switched off.

16. Set the selector switch “Ref. Source” (reference soured) to “man” (manual, i.e. manual operation).

17. Set the torque-range selector switch to x1.

V1U1

M L K

L1

L2L3

PE

N

BS 5.10

W2 U2 V2

W1

3 stator coils are already connected



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- 8 –

18. Perform the electrical zero adjustment by turning the adjuster of the control unit slowly. (High clamping of movement) The torque can be measured at clockwise and anti-clockwise rotation without switching, thus an electrical adjustment of the pointer is not possible below 0.

19. Start the motor. The value indicated by the torque indicator must not exceed 4% of the total value (the value indicated during no-load running is produced by the frictional resistance of the brake). In case the said value is exceeded, the magnetic-powder brake must be demagnetized.

DemagnetizationSet the function selector switch to position “Mc” (constant moment) and to position “off” again while the motor is running.

20.Examine the function of coupler guard bow and temperature switch. Start the motor and adjust a load of 1 Nm.

20.1 Remove the coupler guard bow and describe the result.

The torque meter goes to 0 and the reset light lights up. Cannot display the adjusted value at the Torque meter anymore with the adjustment of the load adjuster even when the coupler is attached again. To make it working again, do the step described below. Working for safety purposes, in the case of undesired physical contact.

20.2 Reattach the coupler guard bow and operate the reset key.

After the coupler is attached and reset key operated,( first set the function selector to off position. ) and set the function selector again to Mc, we can adjust again the load adjuster and the torque meter is displaying the measurement again.

20.3 Remove the tulip plug from the socket of the motor terminal box and describe the result.

The reset lamp goes on and the torque meter goes to 0 again. Do the same step as above to make it working again. All of this process is working for safety purposes, in this case for preventing overheating in the machine.

Examine the influence of the black-and-white fields of the intermediate coupler on speed measurement.

Before starting the circuit, conduct the following adjustments at the operating elements of the control devices.Rotational-frequency selector “n” : 1500Function selector “Function” : offTorque-range selector “M” : x 1

Start the motor.Measure speed n01 Speed n01 = 1500 rpm.

Switch off the motor. Remove the coupler guard bow and cover a white field of the intermediate coupler with black insulating tape.

Reattach the coupler guard bow. Start the motor.Measure speed n02 Speed n02 = 1450 rpm



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Compare speeds n01 and n02 give the reasons for the result.

1500-1450 = 50 rpm. Because the opt-coupler measures just 59 black and whites instead of 60 per revolution, decreasing the measured speed. But the actual speed is still the same. This shows how the intermediate coupler and the opto-coupler works together to measure the speed.



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- 9 –-

Regarding the intermediate coupler, what must be observed before starting the motor?no blocked black and white. It should measure 60 per revolution.

Cover the opto-coupler with white paper and describe the result.The opto-coupler can not measure a revolution of 60 blacks and whites of the intermediate coupler , so it displays no velocity.


ADJUSTING THE CONTROL GEAR TO MEASURE THE CHARACTERISTICS,

n = f (T) and T = f (n) FROM A 3-PHASE INDUCTION MOTOR

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-10-OBJECT: Adjust the control gear so that you can measure the characteristics

n = f (T) and T = f (n).

PROCEDURE: 1. Adjust the connections according to the current diagram.

Current Diagram:

2. Adjust the adjusters from the control gear according the table

Control gearAdjusters ES 602Change-over switch “n” 1500Selector switch “Function”

Mc

Change-over switch “M” x 2

When the Selector switch “Function” is in the position “Mc” the torque that has been adjusted with the “Load” adjuster will be kept constant. This position is required in case the torque is the value to be adjusted. (the independence influencing variable); e.g. n = f (M).

V1U1

M L K

L1

L2L3

PE

N

BS 5.10

W2 U2 V2

W1



n = f (T) and T = f (n)FROM A 3-PHASE INDUCTION MOTOR

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-11-3. Start the motor. Turn the adjuster “Load” from the left limit stop clockwise until you

notice the braking effect of magnetic-powder brake. Adjust with the adjuster “Load” the torque according to the in the table given values and read the belonging speed. Note down the results in the table.

T [nm] 0,00 0,20 0,40 0,60 0,80 1,00 1,20 1,40 1,60 1,80

n [rev/min] 1490 1485 1465 1445 1420 1400 1360 1315 1225 0

4. Start up Excel and take over the results from object 3.

5. Draw up the characteristic: n = f (T)

6. Print out the table and the characteristic: n = f (T)

n = f(t)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

n[re

v/min

]

1490

1485

1465

1445

1420

1400

1360

1315

1225 0

N [ Rpm]

T [

nm

]

7. Adjust the adjusters from the control gear according the table

Control gearAdjusters ES 602Change-over switch “n” 1500Selector switch “Function”

nc

Change-over switch “M” x 2

When the Selector switch “Function” is in the position “nc” the speed that has been adjusted with the “Load” adjuster will be kept constant. This position is required in case the speed is the value to be adjusted. (the independence influencing variable);



n = f (T) and T = f (n)FROM A 3-PHASE INDUCTION MOTOR

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e.g. M = f (n).

8. Start the motor. Turn the adjuster “Load” from the left limit stop clockwise until you notice the braking effect of magnetic-powder brake. Adjust with the adjuster “Load” the speed according to the in the table given values and read the belonging torque. Note down the results in the table.

Direction:During this experiment the motor has to brake until it comes to a standstill that’s why it will be overloaded.When you take too much time to do your experiments the motor will be overheated and the temperature switch off the exciting current of the magnetic-powder brake. The measurement will be interrupted.To prevent that the motor will be overheated the experiments to measure the load characteristics T = f (n) have to be done rapidly

Table 5.3n [rev/min] ……. 1450 1350 1250 1000 750 500 250 0

T [nm]0 0.4 1.08 1.58 1.52 1.34 1.12 1.02 0.96

9. Start up Excel and take over the results from object 8.

10. Draw up the characteristic: T = f (n)

11. Print out the table and the characteristic: T = f (n)

T= f(n)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

n [re

v/min] 0

1450

1350

1250

1000 75

050

025

0 0

N [rev/min]

T[n

m]


DC- shunt generatorMeasure the load characteristic from a

separately excited DC-generator

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- 12 -

OBJECT: Measure the load characteristic from a separately excited DC shunt-generator and describe the characteristic features.

PROCEDURE:1. Slide the Magnetic-Powder Brake to the right and place the DC-generator between the

3-phase induction motor and the brake. Slide the 3 machines together and attach the coupler guard bows.

2. Adjust the connections at the 3-phase induction slip-ring motor according to the next current diagram.

3. Adjust the connections at the DC-generator according to the following current diagram.

V1U1

M L K

L1

L2L3

PE N

BS 5.10

W2 U2 V2

W1




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- 13 -Current diagram

4. Before switching on the motor verify if the Magnetic-Powder Brake is in the zero-load position.

5. Bs 5.2 should be in position “q’ and the load Rb is not connected yet.

6. Switch on the motor.

7. Switch on the power supply ES 340 and adjust a voltage of 110V.

8. Adjust with Bs 5.2 a current (Im) from 80mA through the magnetic field.

9. Measure the zero load output voltage (Uk) and current (Ia) from the generator and write the values in the table 5.1.

10. Connect the maximum load (500 ) and measure the belonging load current (Ia) and output voltage (Uk).

11. Adjust the load until you have reached the given load current (Ia) and measure the asked voltage (Uk) values.

12. Calculate the output power (Pa).

L+

A

A1

L+

A2E2 E1

G

E

q

L-

A

VL+ L-

PE

Bs 5.2

Rb = 0 …. 500 / 1A

110V

ImIa

Uk

Use ES 340 to supply the magnetic field of the generator




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- 14 -

Table 5.4

Ia [A] 0 ……….

0,3 0,4 0,5 0,6 0,7 0,8 0,9

Im [A] 0,08 0,08 0,08 0,08 0,08 0,08 0,08 0,08 0,08

Uk [V] 129.8 116.7 113.3 110.2 105.3 99.2 93.4 87.0 81.2

Pa [ W] 0 27.19 33.99 44.08 52.65 59.52 65.38 69.6 73.08

13. Take over the results in an Excell file and draw up the characteristics: Uk = f (Ia) and Pa = f (Ia).

Uk= f(Ia)

0

20

40

60

80

100

120

140

Ia[A] 0 0.233 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Ia [A]

Uk[

V]




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Pa=f (Ia)

0

10

20

30

40

50

60

70

80

Ia[A] 0 0.233 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Ia[A]

Pa[

W]

14. Looking at the characteristics, what can you say about the behavior of a separately excited DC-Generator?

assignment 4 introduction elwe powder brake

Documents

l1 l2 l3

independence

left limit

separately

independent

coupler guard

excessive

selector switch