CH639224A5 - Engine electrical burner liquid fuel. - Google Patents

Description

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CLAIMS Electric motor for liquid fuel burner, having an auxiliary starting winding provided with a resistance with positive temperature coefficient, characterized in that this electric motor, ensuring the burner a stabilized speed and having effective protection of its windings, comprises firstly, as a resistance with a positive temperature coefficient, a resistance having a time of 0.5 to 2 seconds to change its ohmic resistance going from a minimum value allowing the passage to an electric current to a maximum value hindering the passage at this current, secondly, in its main winding and its auxiliary winding, and with locked rotor, a speed of temperature rise respectively less than or equal to 7 ° C. / second and 55 "C. / second.

The present invention relates to an electric motor for a liquid fuel burner.

Originally, liquid fuel burners such as those with oil were usually equipped with single-phase asynchronous motors operating in a version with an auxiliary starting resistance winding.

Special devices such as relays, centrifugal couplers ensured the elimination of the auxiliary winding after the engine started up.

This type of engine of classic design, sold at a very advantageous price, had electrical characteristics which quite well met the operating requirements on burner, namely a starting torque greater than or equal to 3 cm Kg and a low slip under load.

This engine was not thermally protected, and its protection was provided by a flame monitoring device.

This monitoring device, operating by photocell, cut off the power to the engine in the event of an unexpected flame extinction, after a preset time.

The security ensured by this surveillance was able to intervene as soon as the device was put into service.

Thus, one or more successive refusals to start the engine may be sufficient for the supply of the latter to be cut off as a result of the absence of flame within a maximum period of ten seconds for domestic burners of power less than or equal to 100,000 Kcal / h and two seconds for gas burners with a power greater than 60 th / h.

After the engine power supply was cut by this monitoring device, the engine could only be restarted by manual reset.

After many years of using the engine of the heavy-duty auxiliary start-up winding type, the burner manufacturers considered that it was no longer possible to ignore the thermal state of this type of engine.

In fact, by design, the motor with a resistant starting auxiliary winding has a very resistant auxiliary winding which requires the use of fine wires.

Therefore the current density in this starting winding is very high and the temperature rise oscillates between 8 and 15 ° C / second.

It follows that in the accidental case of refusal to start with a hot engine, the rise in temperature in the auxiliary winding leads to the destruction of the winding, since the response time of the photoelectric monitoring cell is too long.

Furthermore, as soon as abnormal overloads appear on the motor, this results in a drop in speed and very often a reclosing of the relay or of the centrifugal coupler which re-energizes the auxiliary winding for a prolonged time without the intervention of the monitoring device since there is always the presence of a flame.

This untimely phenomenon results in a reduction in the air bit rate, the fuel flow rate being not very sensitive to variations in the speed of the engine, and results in poor combustion.

Restoring the auxiliary winding for extended periods of time causes the winding to be destroyed.

Some manufacturers have considered protecting this winding by installing a thermal protector on the motor.

Unfortunately, this project was quickly abandoned due to the increase in the cost of the appliance and above all the difficulties encountered in associating the triggering times of the protector with the burner control device.

Currently, cases of destruction of the auxiliary winding due to accidental disturbances at the time of startup have become very rare.

This marked improvement results from the fact that the motor with a resistant auxiliary starting winding has been progressively replaced by a more powerful motor designed with a much less resistant auxiliary phase, the winding being carried out with a wire having a larger diameter. On this auxiliary phase, a permanent capacity has been placed in series. On this type of motor, the auxiliary phase coupled in parallel with the main phase is kept energized during operation.

The torque-speed curve of this motor shows that the speed-up takes place without a "dip" thanks to constant acceleration.

It is obvious that despite the elimination of the starting device, this engine is more expensive than the previous one. This is due to the addition of a permanent capacitor and a higher weight of copper on the auxiliary phase. 35 However, this price is more or less justified by greater reliability in the case of abnormal operations.

But it must be recognized that from a purely technical point of view and in particular with regard to the operating points and the yield under load, this solution is not as well suited as the previous solution, that is to say the heavy duty auxiliary starting motor.

Indeed, it is known that for an oil burner a large starting torque is essential to drive the oil pump and the pump-motor coupling. This starting torque is usually greater than or equal to 3 cm / kg.

The starting torque can be expressed in the following simplified form:

50 / \

Cd = Ki • K • Ip • la • sine (Ip la) Rr in which K is the ratio of the effective turns of the main phase on the auxiliary phase (PP / PA).

K] is a coefficient which depends on the magnetic circuit, on 55 the frequency, etc ... and for a locked rotor.

Ip is the current in the Main Phase.

la is the current in the Auxiliary Phase.

ïpla is the phase shift of these intensities.

Rr is the resistance of the rotor.

60 In order to obtain a starting torque of the order of 3 cm Kg with permanent capacity motors, the manufacturers have been led to produce high power motors comprising fairly resistant rotors.

In fact, K is generally less than 1.5 because at 65 beyond this value, the voltage across the terminals of the capacitance becomes greater than 450 volts. This results in a limitation in supplies and an increase in the cost price of the capacity.

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The capacitance always has a large impedance for resistant starting auxiliary link includes a coil

mute the auxiliary current. As a result, the most main capacities 1 supplied with electrical current in perma-

commonly used are less than 5 microfarads. during operation, and an auxiliary winding

liaire 2 says start-up winding energized uni-The phase shift angle (Ip • la) is always close to * 2 in squement during the start-up period. According to the invention, reason for the presence of permanent capacity. to cut the supply of this winding at the end of the diel, only two parameters remain: Ip and Rr. moorings we mount in series with this winding a resi-Gold Ip is mainly a function of the engine power. stance with positive temperature coefficient 3.

Thus, these motors have a high maximum power. In fact at the time of powering up the motor, the aunt with respect to their loads and a high slip due to the resistance 3 which is placed in series with the winding. auxi-

rotor resistance (see figure 1). liaire lets pass the current necessary to supply this

The extra power obtained with this kind of engine, bearing.

if it is necessary for starting, is harmful for rota- When the current flows, this resistance 3 heats up stabilized tion. by Joule effect and its resistance which is a function of its temperature-

In Figure 1, on curve F we notice that this model rises.

tor has a maximum efficiency of 67% but only at its point As soon as this resistance 3 reaches a corresponding temperature

operating on oil burner, point of interconnection at its Curie point, an abrupt change is recorded.

tion N of the curve F with the line representing the torque reduction of its ohmic value. It goes from a few ohms sistant, the efficiency is only 52%. several thousand Ohms.

However, for the reasons mentioned above, it is difficult to adjust the power of the engine to its use. with a very large impedance which limits the passing current

Because of this, this type of motor is always used to the third of in this winding at a few milliamps and eliminates the

its maximum power, and has a poor yield to the fluence of this winding in the operation of the mo-

point of use. tor. When applying this engine to an oil burner,

The object of the present invention is to produce a motor 25 Ion an important characteristic of the invention, the time of

electric for economical liquid fuel burner conduction of the resistance 3 must be defined as a function of the reliable having electrical characteristics suitable for ensuring starting conditions on this oil burner,

the starting of the fuel burner and their functioning We can observe in figure 4 which represents

in steady state. bes of instantaneous oil and air flow rates of a do-burner

The motor according to the invention is in accordance with the claim fitted with a motor of the present invention, that cation. ignition occurs from a mixture richness of 0.7

To make the invention easier to understand, a description is given below of fuel and that the stabilized speed of the burner is established after a certain number of exemplary embodiments illustrated after 0.5 seconds.

of the attached drawings, of which: The richness of the fuel mixture depends on the

- Figure 1 shows two groups of characteristic curves of electrical motors, some being curves of ratio p ', Q their speeds in revolutions / minute as a function of their torques in cm-Kg, namely A the torque curve -speed of an en-engine F is the quantity of fuel in kg,

resistant auxiliary bearing, B the torque-speed curve of a 0 is the oxidant tity in m \

auxiliary winding motor fitted with a resistance 40 St ^ ^ Stoichiometry (k / m3)

with a positive temperature coefficient during the conduction time of this resistor in accordance with a first example- It follows that the conduction time of the resistor 3

pie of realization of the invention, C the torque-speed curve must be greater than 0.5 seconds, but it is not necessary to have a known motor with permanent capacity, the others being to increase this time beyond two seconds.

efficiency curves namely D the curve of the resisting torque 45 The presence of the resistor 3 provides self-protection of the burner as a function of the speed, E the efficiency curve of the auxiliary winding and allows according to the invention to be defi

of a motor in accordance with the first embodiment of a motor on which the auxiliary winding at a speed the invention indicated above, F the yield curve of a relatively high temperature rise greater than

known engine with permanent capacity and R on the right are commonly accepted representations on conventional engines.

as the abscissa of the resistive torque of the fuel burner, so The most critical case is usually located at the time such as fuel oil, of the restarting of the hot engine, after a cycle of operation-

- Figure 2 shows a schematic view of the normal memory circuit. In this case, the motor cannot restart an electric motor according to a first example of since the resistor 3 is always at a super-realization temperature of the invention, lower than that corresponding to its CURIE point.

- Figure 3 shows a schematic view of the ss circuit In this case the main winding is supplied with electricity from an electric motor according to a second example the intervention time of the monitoring device by cel-embodiment of the invention , Photoelectric cell, that is to say for a period of ten se-

FIG. 4 represents different maximum function curves for an oil burner with an output of an oil burner, the curve G being that of less than 100,000 Kcal / hour.

bit of air in cubic meters at normal temperature conditions-60 It is common for engines with pressure and pressure insulation, as a function of time in seconds, class B and F to withstand a peak temperature on the in-

curve H being that of the fuel oil flow rate in kilograms in bearings of approximately 200 ° C.

as a function of time in hours, and curve I being that of the r. Assuming that the engine is operating in stabilized regime instantaneous average chesse of the fuel mixture in meters at 130 ° C (maximum value allowed in insulation B), and that subi-

air cube per kilogram of fuel oil and zone J on the 65th for an unknown reason it operates with a curved rotor I of richness being that where ignition occurs. blocked (without supply to auxiliary winding) during

In a first exemplary embodiment of the invention during the ten seconds preceding the intervention of the gloss device in FIG. 2, an electric motor of the type with winding-cell monitoring, it is necessary that the speed of elevation

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temperature does not exceed 7 "C / second on the main winding.

In an engine produced in accordance with the present invention, a speed of temperature rise does not exceed 2.5 ° C / second on the main winding with a current density of 16 A / mm2.

The most critical case for protecting the auxiliary winding is when restarting after a shutdown of around two minutes. This time corresponds to the duration which is necessary for the resistance 3 to pass from a resistance of several thousands of Ohms to a few Ohms.

After two minutes, the motor goes from 130 ° C to approximately 90 ° C which gives a temperature difference with the maximum temperature 200 ° C in class B insulation of 110 ° C for a maximum conduction time of two seconds.

This corresponds to a temperature rise speed not exceeding 7 ° C / second on the auxiliary winding with a current density of 47 A / mm2.

From the limit values defined above and which relate to the rate of temperature rise, a comparison can be made with those obtained on the engine according to the invention shown in FIG. 2.

We note that the degree of protection of this engine is very important.

Elevation speed Values Maximum admissible temperature values obtained

Main winding 7 ° C / sec 2.5 ° C / sec

Auxiliary winding 55 ° C / sec 7 ° C / sec

Curve E in FIG. 1 shows that the maximum efficiency of the engine of the invention is 67%. This efficiency point P is located just at the resistive torque corresponding to the use of the engine on the burner.

The gain on the power absorbed compared to that of the older design motors represented by the curve F in FIG. 1 is 39 Watts or approximately 22%.

In addition, a gain of 9% on the sheet weight is recorded.

In a second embodiment of the invention illustrated in FIG. 3, an electric motor of the permanent capacity type comprises a main winding 4, an auxiliary winding 5 provided with a series capacity 6 and a resistance with a positive temperature coefficient 7 connected in parallel across the terminals of capacity 6.

In the auxiliary winding 5, the impedance of the resistance being very low with respect to that of the permanent capacity, the motor behaves at start-up like a motor with a resistant auxiliary phase as described above.

This example of embodiment has the advantage compared to the permanent capacity motors of older design used on oil burners, to have a power just necessary to drive the pump and the turbine, and to have a low rotor resistance owing to the fact that the problems of exceeding the resistive torque at start-up are resolved by the presence of a resistor 7 described above.

At its point of use Q on its torque-speed curve D in FIG. 1, this motor has an efficiency of 72%, greater than that of the other solutions represented by their efficiency curves in E and F.

So that it can achieve a starting torque greater than 3 Cm. Kg, a higher yield than that of the first example represented by the curve E, a power dissipated in the resistor 7 as low as possible and an economy resulting in a lesser weight of copper, a value of reduced capacity, this motor according to the he invention is constructed with the following main characteristics, namely the main winding:

A ratio of effective turns of the auxiliary winding to those of the main winding between 0.40 and 0.60.

A chosen capacity value between 1 and 3 | JF. An ohmic value of the resistor 7 close to that of the auxiliary winding 5.

A conduction time of the resistor 7 located between 0.5 and 2 seconds, temperature rise speeds on the main and auxiliary windings of the motor respectively below 7 ° C / sec and 55 ° C / sec.

The ratio of the effective turns of the auxiliary winding to those of the main winding also has the advantage of delivering relatively low voltages across the terminals of capacitor 6.

In fact, with such a motor supplied at 220 v the service voltage across the terminals of the capacity is of the order of 250 volts instead of 450 volts in an engine of conventional construction.

In addition, this leads to reductions in the size and price of the capacitors.

To illustrate the advantages indicated above, the data below correspond in I, to a known motor with permanent capacity, in II to a motor in accordance with the first embodiment of the invention and having the same sheet diameter, and in III, to an engine in accordance with the second embodiment of the invention and having the same sheet metal diameter: 25 / - Known engine with permanent capacity

- Sheet metal outside diameter 81 mm

- Iron length 57 mm

- Rotor resistance (reduced to primary) 45 ohms

- Weight of copper (Windings) 355 gr 30 - Maximum efficiency 67%

- Efficiency at the point of use on 52% (3 cmkg) burner

- Starting torque 3.15 cmkg

- Maximum torque 8.50 cmkg 35 - Effective turns ratio of the auxiliary winding to those of the main winding 1.45

- Permanent capacity 5 microfarads

- Voltage at the terminals of the capacity 450 volts 40 - Rotation speed on burner 2860 rpm current density, with locked rotor:

- main winding 27 A / mm2

- auxiliary winding 5 A / mm2 II Motor conforming to the 1st embodiment of

45 the invention

- Sheet metal outside diameter 81mm

- Iron length 52 mm

- Rotor resistance (reduced to primary) 28.7 ohms

- Weight of copper (Windings) 360 gr

- Maximum yield 67.5%

- Efficiency at the point of use on 67% (3 cmkg) burner

- Starting torque 3.35 cmkg

- Maximum torque (6.60 cmkg 55 main winding)

- Maximum torque (Two windings) 8.65 cmkg

- Effective winding ratio of the winding - 0.41 auxiliary to that of the main winding

60 - Rotation speed 2860 rpm

- PTC resistance 50 ohms

- Instantaneous power dissipated in this resistance (at start-up) 300 W

current density, locked rotor:

65 - main winding 17.4 A / mm2

- secondary winding 63 A / mm2 Gain in consumption compared to the motor in I: 39 W

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III- Motor conforming to the 2nd exemplary embodiment of the invention

- Sheet metal outside diameter 81mm

- Iron length 52 mm

- Rotor resistance 27.8 ohms 5-

- Weight of copper 300 gr

- Maximum efficiency 72%

- 72% point-of-use efficiency

- Starting torque 3.32 cmkg

- Maximum torque (without PTC resistance) 6.80 cmkg io

- Maximum torque (with PTC resistance) 9 cmkg

- Ratio of effective turns of the auxiliary winding to those of the main winding 0.46

Rotation speed Permanent capacity Voltage across capacity PTC resistance

Power dissipated in the resistor

PTC at current density start, with locked rotor:

main winding auxiliary winding

Gain in consumption compared to the motor in I:

2860 rpm 2 microfarads 235 volts 40 ohms

260 W

22 A / mm2 66 A / mm2 47 W

VS

2 sheets of drawings