WAYS TO AUTOMATE MINE FAN INSTALLATIONS

Associate Professor G. P. Ksyonin

While in recent years much attention has been devoted to the automation of mine pumping installations, no attempts have been made to raise the question of automating mine fan installations.

In our opinion, the automation of mine fan installations is not only of no less, but of far greater importance than the automation of mine pumping installations.

The point is that the operating regime of a mine pumping installation remains unchanged throughout the entire service life of that installation, and therefore the idea of automating mine pumping installations essentially comes down only to the automatic starting of pumps when the water level in the water collectors rises and to switching them off when the water level reaches the lower limit. Ultimately, the automation of mine pumping installations can provide only a certain economy in the cost of pump operation (there is as yet no need to speak of increasing operating reliability).

The situation is entirely different with mine ventilation installations.

The operating regime of a mine ventilation installation, as is known, never remains unchanged.

Stoping operations continuously move within the limits of the mine field. They advance from the shaft toward the boundaries of the mine field, or conversely (depending on the direction of extraction), and pass from upper horizons to lower ones.

In connection with this, the equivalent orifice of the mine is constantly changing, and consequently so is the operating regime of the ventilation installation.

During the development of any one horizon, the equivalent orifice changes continuously; moreover, if extraction is carried out in the direction toward the boundaries of the mine field, then the equivalent orifice gradually decreases, while if extraction is carried out in the direction away from the boundaries of the mine field, then the equivalent orifice gradually increases.

When passing from an upper horizon to a lower one, the equivalent orifice changes abruptly, and then, during ...

in the development of a new level, the same pattern of change in the magnitude of the equivalent opening that occurred on the overlying level is repeated, with small deviations.

Under these conditions of a changing equivalent mine opening, since its change entails a change in the delivery of the ventilation installation, one has to think about regulating the fan.

It should be noted that the need for regulation arises not only when, owing to a decrease in the equivalent opening of the mine, the fan reduces its output. It also arises when, with an increase in the equivalent opening of the mine, the fan delivery increases, since increasing the fan output above the norm not only entails excessive energy consumption but also creates technical inconveniences—an increase in the velocity of individual air jets above the values established by the “Safety Rules”—drafts.

As is known, the most economical method of regulating fans, at least centrifugal ones (which are still mainly used), is regulation by changing the number of revolutions of their impellers.

For small fans driven by asynchronous motors, with a small range of regulation, it is still considered economical to use a rheostat in the rotor circuit. With a wider range of regulation, one usually resorts to changing the pulleys of the belt drive.

Large fans are regulated by means of stepped reduction gears, and in some cases even cascade groups are installed (Kremer, Scherbius, and others).

The least economical method of regulation is regulation by means of a slide damper (shiber).

In most of our mines, and especially in the Kuzbass, the slide damper is the only means of regulating fans, since most installations do not even have regulating rheostats.

Thus, at present, in most of our mines, fan regulation can be carried out only by a very imperfect method, leading to large losses of energy. However, even this means is used far from sufficiently, because mines do not always have a clear idea of when fan regulation should be resorted to.

A detailed calculation of mine ventilation, constructed on the basis of the development plan for mining operations, makes it possible to ascertain the pattern of change in the equivalent opening of the mine by years and, consequently, makes it possible to draw up a plan for regulating the fan. But in the process of mine operation there are always deviations from the initial design outlines; moreover, the ventilation calculation itself under mining conditions is never...

can be sufficiently accurate. Therefore, in the calculation of ventilation this graph of the change in the magnitude of the equivalent orifice is in reality never maintained, and the fan regulation plan drawn up in the design can be regarded only as approximate. Hence follows the need for constant monitoring of the operation of mine ventilation installations, on the basis of which the fans should be regulated. At the present level of technological development, for monitoring the operation of mine fan installations we have such instruments as a self-recording depression meter and a volume meter. But even these instruments, unfortunately, have not yet found sufficient application in our mines. Thus, in Kuzbass there is only one such instrument, at the Yemelyanovskaya mine in Leninsk, and it must be said that even it has been idle for a number of years.

In practice, at present, only an anemometer is used to monitor the operation of mine ventilation installations; moreover, the measurements of air velocity in this case have the character of very rough measurements.

It is not surprising that in the mines there is little confidence in this monitoring of the operation of ventilation installations, and it is resorted to only in cases of extreme necessity, when the shortage of air becomes entirely obvious and makes itself felt in practice—that is, when complaints from workers begin to come in, cases of “gassing” become more frequent, and so on.

As for cases when fans deliver an excessively large quantity of air, here, as a rule, no thought is given to regulating the fan, and very often there is great overconsumption of energy.

Thus, at present, in most mines we not only lack sufficiently advanced means for regulating fans, but we also lack properly organized monitoring of their operation.

Moreover, between the monitoring of the operation of mine fan installations and their regulation there is a certain gap.

The state of ventilation in our mines urgently requires reconsideration of the question of monitoring the operation of fans and their regulation, and the elimination of the aforementioned gap between them.

The question of monitoring and regulating mine fans can be fundamentally solved only by automating mine fan installations. From what has been said above it follows that automation should first and foremost concern the regulation of fan output. Automatic starting of the fan is a secondary matter.

However, the automation of fan starting is also a very urgent issue for many mines where, as for example at the Tsentralnaya mine in Kemerovo, there is a large number of ventilation installations, since the introduction of automation will bring great savings there.

The question of automating ventilation installations is fully ripe, and we now need ventilation installations that would stand at the level of the achievements of world technology.

How, then, is one to explain the fact that the question of automating ventilation installations has still not been raised by anyone? In recent years a definite tendency has emerged in the mining industry (as in other branches of industry) toward the gradual replacement of centrifugal fans by axial fans.

Axial fans, in comparison with centrifugal ones, possess a whole series of advantages, namely: they have a higher efficiency, are reversible, simple, relatively inexpensive, and permit broad regulation of output at an unchanged number of revolutions (regulation is also possible at a variable number of revolutions). Regulation of axial fans at a constant number of revolutions is carried out either by removing part of the impeller blades, or by turning part of the blades into a non-working position (neutralization), or by simultaneously turning all blades. Since regulation of axial fans can also be performed at a constant number of revolutions, then, when they are used, there is no need to change the pulleys of the belt drive at low powers, and correspondingly no need for stepped reduction gears and cascade units at high powers. Thus, regulation of these fans is in practice considerably simplified.

In this connection the impression is evidently created that the use of axial fans, thanks to the simplicity of their regulation, will be a measure that completely solves the problem of ventilating mines under conditions of variable equivalent opening and that, consequently, the undertaking of any additional measures, such as, for example, automation of ventilation installations, is superfluous.

Nevertheless, the regulation of axial fans of ordinary designs by turning the blades is not carried out so simply.

To perform this regulation, the fan must be stopped, and each blade individually must be set in a new position (at a new angle). The same may be said of the neutralization of individual blades.

As for the regulation of axial fans by removing individual blades, here, in addition to what has been said above, it is also necessary to take into account the possibility of disturbing the balance of the impeller—an extremely important circumstance at the high peripheral speeds at which axial fans operate (100–120 m/sec). There are, it is true, also such designs of axial fans (not yet manufactured in our country) in which all blades are turned simultaneously, but stopping the fan during its regulation is necessary here as well.

Still, however simply the regulation of axial…

of the fan itself, the gap between monitoring the operation of the fan and regulating it is not eliminated here either. In every case, regulation of the fan must be preceded by the calculated determination of the required blade-setting angle, which must be carried out on the basis of the readings of instruments monitoring the fan. It is quite obvious that in mines regulation of axial fans will be resorted to, just as at present regulation of centrifugal fans is resorted to, only in cases of extreme necessity. In other words, in the absence of automation, installations with axial fans will exhibit the same abnormalities as are currently present in installations with centrifugal fans; consequently, it is necessary to automate all mine fan installations, regardless of the type of fans.

The question of automating mine ventilation installations cannot be solved entirely independently of the question of the drive.

It must be said that the types of electric drive for mine fan installations currently in use, from the standpoint of regulation in general and especially from the standpoint of automatic regulation, leave much to be desired.

Thus, the asynchronous motor that has become most widespread for driving mine fans permits regulation of the number of revolutions, but this regulation is associated with large losses in the rheostat and is uneconomical.

The synchronous motors sometimes used practically do not allow the fan speed to be changed at all. Therefore, when asynchronous or synchronous motors are used, only coarse regulation of the fan speed is carried out by means of stepped reducers and, consequently, a certain overconsumption of energy is incurred, permissible only for installations of low power.

Automating the regulation of such installations is a difficult task.

Cascade units, used occasionally for more powerful installations (above 300 kW), allow smooth and therefore economical regulation of the number of revolutions. They can be automated comparatively simply. However, these installations are too cumbersome, and their use at the present level of technological development is hardly rational.

The question of the type of electric drive for mine fan installations must be reconsidered both in general and in connection with their automation.

Recently, controlled ionic devices—thyratrons and mercury rectifiers with grid control—have been finding ever wider application for regulating the speed of an electric drive.

Abroad there already exists a considerable number of completed installations of this type, and for the most varied power ratings...

systems. In particular, the firm A.E.G. used a similar installation for driving a mine fan with a capacity of 1000 kW.

Using, as the drive of a mine centrifugal fan, a direct-current motor in connection with a thyratron (at low powers), or with an adjustable mercury rectifier (at high powers), one can simply and economically regulate the fan speed; moreover, the automation of such an installation presents no difficulties.

For installations of low power, this type of electric drive will, of course, lead to somewhat higher capital costs; however, it provides such operational advantages that they fully justify these costs. Indeed, having an actual ability to regulate the fan, we not only always supply the mine with the necessary quantity of air, but also save energy. As for installations of high power, here all the advantages will be on the side of a direct-current motor supplied from an adjustable mercury rectifier, since such an installation will also require lower costs than an installation with a cascade group and will be considerably cheaper in operation.

In our opinion, for mine fan installations with centrifugal fans this type of electric drive is the most appropriate.

As for installations with axial fans, which can be regulated at a constant speed of rotation (by turning the blades of the impellers), for them all the advantages will be on the side of the asynchronous motor (at low powers) and the synchronous motor (at high powers).

It is entirely possible to automate installations with axial fans. It is only necessary to automate the turning of the blades of the impellers.

As is clear from what has been said above, one must keep in mind two automation schemes for mine fan installations: one for centrifugal fans (regulation by changing the speed of rotation), and the other for axial fans (regulation by turning the blades of the impeller).

Below is given a description of preliminary sketches of automation schemes for both of the aforementioned types of mine fan installations.

Automation of a mine fan installation with a centrifugal fan and with a drive from a direct-current motor supplied from a controlled mercury rectifier (or from a thyratron) presents no difficulties.

Figure 1 shows an approximate scheme of such an installation, designed for the case of a powerful (on the order of 300–1000 kW) mine fan.

As can be seen from the drawing, a measuring orifice plate \(sh\) is installed in the suction duct of fan B, serving to create the pressure difference necessary for operation of the regulator.

The regulator is constructed on the principle of a self-recording volumometer. One of the two floats of this instrument, \(n\) (in the volumometer serving to actuate the recording mechanism), when lowered closes contacts 1--1, and when raised closes contacts 2--2, thus acting on the motor control circuit in the sense of increasing or decreasing the number of revolutions and, consequently, in the sense of increasing or decreasing the fan output.

When the equivalent opening of the mine decreases, and the reduction in fan output exceeds the permissible limit, float \(n\) of the regulator will descend so far that it closes contacts 1--1.

When these contacts close, through the normally closed contact KRV-2, time relay RV-1 will be switched on. If the closing of contacts 1--1 was caused by a short-term decrease in the difference of liquid levels in the chambers of the volumometer, due to an accidental decrease in the value of the equivalent opening (for example, the coincidence of the moments when hoisting vessels meet in the shafts of the hoisting and ventilation pits), then this relay, set for 5--10 sec., will not operate. Relay RV-1 will operate and close its contacts KRV-1 only in the case of a more or less prolonged decrease in the fan output.

When contacts KRV-1 close, intermediate relay PR-1 will be switched on; it will cause the two-pole contactor K-1 to switch on, which serves to start (in a definite direction of rotation) the servomotor SM.

After the servomotor SM is switched on by contactor K-1, the latter, through the double (worm and gear) transmission P and the coupling M, rotates the shaft of the phase regulator F in the direction corresponding to a decrease in the angle of displacement of the ignition moment of the controlled mercury rectifier UR feeding the fan motor D.

At the same time, the voltage at the motor terminals (a separately excited direct-current motor) begins to rise, and, accordingly, its number of revolutions begins to increase.

Corresponding to the increase in the motor speed, the fan output will also increase; float \(n\) of the regulator will move upward and, when the fan output reaches the normal value, contacts 1-1 will open, intermediate relay PR-1 will be switched off, and contactor K-1 will disconnect the servomotor SM.

The position of the phase regulator F will then remain as it was at the moment the servomotor was switched off (self-braking of the worm gear).

The operation of the regulator when the equivalent opening of the mine is increased and, consequently, when the fan output is raised, proceeds in an analogous manner.

Here, when the difference in levels in both arms of the regulator increases, float P rises and closes contact 2–2. At the same time time relay RV-3 operates, switching on intermediate relay PR-2, which in turn switches on contactor K2.

The direction of rotation of servomotor SM now corresponds to an increase in the firing-angle shift of the controlled mercury rectifier UR and to a reduction in the fan speed.

When the fan output has been reduced to the normal value, contacts 2–2 open, intermediate relay PR-2 is de-energized, contactor K-2 is switched off, and servomotor SM stops; the motor speed ceases to decrease.

With such a simple circuit, however, it may turn out that, owing to the influence of the inertia of the moving parts of the installation and of the regulator itself, the regulation will be unstable.

Thus, for example, because of the inertia of the rotating masses of the fan, the motor speed will increase more slowly than the voltage rises. Therefore, after the servomotor is switched off, the motor speed and, correspondingly, the fan output will still continue to increase. In a similar manner, the inertia of the air and the inertia of the regulator itself will have an effect. Since after the opening of contacts 1–1—which occurs after the fan has reached normal output—the latter may still continue to increase, contacts 2–2 may close following the opening of contacts 1–1.

In order to make regulation stable, time relays RV-2 and RV-4 are provided in the proposed circuit. The purpose of these relays is, by opening the normally closed contacts KRV-2 and KRV-4, to switch off servomotor SM, allowing it to operate continuously only for a limited amount of time (5–10 sec.). In the latter case the influence of inertia will be considerably weakened.

It is not difficult to automate the starting of the fan as well.

In the proposed circuit, starting is to be carried out as follows: by pressing button KP, auxiliary mercury rectifier R, which has automatic ignition and is supplied from transformer T, is switched on by means of contactor K3.

After this mercury rectifier has been ignited, the controlled mercury rectifier UR, which also has automatic ignition, is automatically switched on by means of solenoid drive SP. After this latter rectifier has ignited, contactors K4 and K5 operate simultaneously. The first of them switches on the regulator circuit, while the second, by means of clutch M, connects the shaft of phase regulator F with the shaft of transmission P.

While clutch M was disengaged, the rotor of the phase regulator with load G was set in a position in which the firing-angle shift of the controlled mercury rectifier was at its maximum, and therefore the voltage at its terminals was at its minimum. Since, during starting, contacts 1—1 are closed, immediately after contactors K 4 and K 5 are switched on the servomotor SM begins to operate, gradually increasing the speed of motor D to a value corresponding to the normal output of the fan.

Thereafter, regulation of the fan takes place automatically, as described above.

Starting the fan with such a circuit can also be carried out remotely.

In particular, it is entirely possible to provide for automatic starting of the standby fan when the operating fan stops.

For this purpose, the proposed circuit includes a centrifugal relay TsR. This relay is driven from the shaft, not shown in the diagram, of the operating fan, and, upon its sudden stoppage, closes contacts 3—3, which corresponds to starting the fan V shown in the diagram, which we shall now regard as the standby fan.

It goes without saying that (in an automatic installation) the fan gate must also open and close automatically.

Usually, the fan is started with the gate closed, with the aim of reducing the starting current. In our case the gate is needed only so that air in the operating fan cannot pass through the diffuser of the standby fan. Therefore the circuit provides for automatic opening of the gate before starting, immediately after the mercury rectifier R is switched on.

The process of opening the gate takes place as follows: after rectifier R has been switched on and has ignited, contactor K 6 is switched on, contacts 4—4 close, and motor MZ opens the gate, automatically switching off by means of switch b 1.

If fan V stops for any reason, contactor K 6 is de-energized, and contacts 5—5 are closed; as a result, the gate motor MZ is switched on again, closing the gate and stopping automatically by means of switch b 2.

As was stated above, the present circuit is designed for a powerful installation. For small installations with centrifugal fans, instead of controlled mercury rectifiers it would be more convenient to use thyratrons.

Since there are no fundamental differences between these two variants, a description of the automation circuit for a small mine fan installation with a centrifugal fan is not given in the present article.

It is possible to automate a mine ventilation installation with axial fans and with a drive from an asynchronous or synchronous motor only in the case when the fan has a special design.

As has already been said, at present such a design of axial fan has been developed in which the rotation of all its blades, necessary for changing its output, takes place simultaneously. In this design, each blade has on the spindle serving as its axis, inside the hub of the impeller, a bevel gear. All these bevel gears are simultaneously in mesh with a gear wheel which, being located inside the hub and rotating freely on the fan shaft, links all the blades together. At the same time, one of the blades on its axis has, in addition to the bevel gear, also a worm wheel connected with a worm passing inside the hub in the axial direction.

The rotation of the blades in the design described is effected by rotating the worm, which is done by hand with the fan stopped.

It would be quite possible to alter this design of axial fan in such a way that the rotation of the blades could be carried out without stopping the fan.

For this purpose the gear wheel by means of which the individual blades are linked together must be provided with a long sleeve extending beyond the limits of the fan hub and having an external helicoidal thread. This sleeve must be gripped by a coupling having helicoidal projections of the same kind and capable of moving freely along the shaft in the axial direction on a key.

By shifting the coupling in one direction or the other along the shaft, it will be possible to rotate the fan blades and, consequently, to regulate the fan “while running.”

This design is shown schematically in Fig. 2.

As regards automation of the process of blade rotation, it can be carried out approximately according to the same scheme as in hydraulic turbines. The scheme proposed by the author is shown in Fig. 2.

For monitoring the output of the axial fan, the scheme provides for using the same device that was discussed above in the description of the automation scheme for an installation with centrifugal fans.

However, since here, according to the attached scheme, the regulator must produce a somewhat greater force than in the previous case, it is connected through a Rato multiplier. In this case the regulator may be filled with mercury instead of water, and the lifting force of its floats will increase by 13.6 times.

As can be seen from the diagram in Fig. 2, in the case when the fan, owing to a change in the equivalent opening of the mine, changes its output, the float will rise or fall—

It is possible to automate a mine ventilation installation with axial fans and with a drive from an asynchronous or synchronous motor only in the case where the fan has a special design.

As has already been said, at present such a design of axial fan has been developed in which the rotation of all its blades, required in order to change its capacity, takes place simultaneously. In this design each blade has on its spindle, which serves as its axis, inside the hub of the impeller, a conical gear. All these conical gears are simultaneously in mesh with a toothed wheel which, being located inside the hub and rotating freely on the fan shaft, connects all the blades with one another. At the same time, one of the blades on its axis has, in addition to the conical gear, also a worm wheel connected with a worm passing inside the hub in the axial direction.

The rotation of the blades in the design described is effected by rotating the worm, which is done by hand with the fan stopped.

It would be quite possible to modify this design of axial fan in such a way that the rotation of the blades could be carried out without stopping the fan.

For this purpose the toothed wheel, by means of which the individual blades are connected with one another, must be provided with a long sleeve extending beyond the limits of the fan hub and having an external helical thread. This sleeve must be embraced by a coupling having helical projections of the same kind and capable of moving freely on the shaft in the axial direction along a key.

By shifting the coupling to one side or the other along the shaft, it will be possible to turn the fan blades and, consequently, to regulate the fan “while running.”

This design is shown schematically in Fig. 2.

As regards the automation of the process of turning the blades, it can be carried out approximately according to the same scheme as in hydraulic turbines. The scheme proposed by the author is shown in Fig. 2.

To control the capacity of the axial fan, the scheme provides for using the same instrument as was discussed above in the description of the automation scheme for an installation with centrifugal fans.

However, since here, according to the attached scheme, the regulator must create a somewhat greater force than in the preceding case, it is connected through a Rateau multiplier. In this case the regulator may be filled with mercury instead of water, and the lifting force of its floats will increase 13.6 times.

As can be seen from the scheme of Fig. 2, in the event that the fan, owing to a change in the equivalent opening of the mine, changes its capacity, the float will rise or fall ...

Automation diagram of a mine fan installation with a centrifugal fan

Fig. 1

Automation diagram of a mine fan installation with an axial fan

Visible labels in Fig. 2: Multiplier; Regulator; Spool valve; Oil reservoir; Gear pump; Coupling; Motor; Servomotor.

Fig. 2

the regulator float, connected by means of a lever to the servomotor spool valve. When the spool valve is shifted from the middle position upward or downward, its middle chamber, to which oil is supplied under pressure (created by a special gear pump), communicates with one of the chambers of the servomotor cylinder.

Under the pressure of the oil supplied from the spool-valve box, the servomotor piston can move in one direction or the other, producing the regulating action; the direction of its motion is determined by the nature of the spool-valve displacement.

When one of the chambers of the servomotor cylinder is connected with the middle chamber of the spool-valve box, its other chamber is connected with one of the side chambers of the spool-valve box and, through them, with the lower oil reservoir.

The pressure in the upper oil reservoir is created, as already stated, by a gear oil pump driven directly from the fan shaft. When, during regulation, the fan capacity has reached the normal value, and the difference in levels in both chambers of the regulator has likewise reached the normal value, the servomotor spool valve is set in the middle position, closing the channels of both chambers of the servomotor cylinder. The position of the blades of the fan impeller is thereby also fixed.

With small cross-sections of the spool-valve channels and a low capacity of the oil pump on the one hand, and with a large area of the servomotor piston on the other, regulation according to the scheme considered will be stable.