CA1310688C

CA1310688C - Operational method and control switching apparatus for monitoring the starting-cycle circuit of electric high-voltage motors with asynchronous start-up

Info

Publication number: CA1310688C
Application number: CA000592872A
Authority: CA
Inventors: Jurgen Bredthauer; Werner Hirmke
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1988-03-08
Filing date: 1989-03-06
Publication date: 1992-11-24
Anticipated expiration: 2009-11-24
Also published as: ATE84386T1; DE58903194D1; FI891083A; EP0332568B1; DE3808028A1; EP0332568A1; FI891083A0; JPH01268474A

Abstract

ABSTRACT OF THE DISCLOSURE
Operational method and control switching apparatus for monitoring the starting-cycle circuit of an electric high-voltage motor with asynchronous start-up. A known operational method to protect electric motors from overloading determines rotor rotational speed and power input and compares them to stored, temperature-rise values assigned to operating condition data, in order to derive an accumulated total value, which corresponds to the relative temperature-rise condition of the motor. The new operational method and the control switching operation for large high-voltage motors with a conversion of the starting losses in the rotor should guarantee an overload protection for the rotor parts affected during asynchronous start-up and in the stalled state, under consideration of their heating and cooling behavior, also in the case of these transient processes. In the case of the operational method and the control switching operation to monitor the rotor parts of the high-voltage motor affected during start-up, the type and duration of the respective, also transient operating conditions, the stator current and rotational speed are determined and compared to operation condition matrices. Based on a theoretical temperature-rise model, a temperature-rise condition matrix represents the time-dependent, dynamic temperature-rise behavior of the rotor parts affected during start-up by displaying discrete values, which are used to monitor the possible start-ups and to control the protective devices. The method and apparatus are applicable to slipringless high-voltage asynchronous motors or high-voltage synchronous motors with asynchronous, high-performance start-up.

Description

1310~88 OPERATI~NAL HET~OD AND CONTRQL SWITCHING APPARATUS FOR
MONITORING THE STARTING-CY~LE CIRCUIT ~F ELECTRIC HIGH-VOLTAGE
HOTORS WITH ASYNCHRONOUS ST~RT-UP

BACKGROUND OF THE INVENTION
The present invention relates to an operational method for electric motors, whereby the rotational speed of the rotor and the power input are calculated and the temperature-rise values are stored. These temperature-rise val~es represent the relative temperature-rise condition of the motor, when the motor is operated under diverse rotational speeds and load conditions. A temperature~rise value is assigned to each designated operating mode and, based on the rotational speed of the rotor and the power input, it is periodically determined, in which of the designated operating modes the motor is currently running.
In the case of a known method, operating modes are configured for each steady-state operating condition of the motor. These operating modes are defined by the rotational speed and the power consumption of the motor. Temperature-rise values are assigned to these operating modes and are then compiled, together with the operating mode of the motor and, consequently, the elements of the temperature-rise condition matrix are determined, for example, from the value pairs, which are rotational speed and moment of rotation. By evaluating the signals of a sensor, operating as a tachometer, and the operating angle of the electronic controlling system, provided to adjust the power input of the motor, the rotational speed and power consumption or moment of rotation are determined.
Each operating mode, defined by the rotational speed and the operating angle, is assigned a temperature-rise value, calculated empirically, which is stored in a first storage unit. Thereby, the stored temperature-rise values range from positive to negative values. Positive temperature-rise values are stipulated, if the temperature of the motor rises in an operating mode, while negative temperature-rise values are assigned to operating modes with falling temperatures. The value zero is designated for constant motor temperatures. In the known procedure, a monitoring device periodically compares the temperature-rise condition matrix stored in the first storage unit with the actual operating mode, on the basis of a processor unit, and the appropriate temperature-rise values are input in a second storage unit and added to an accumulated total value. When a predetermined upper limit value for the storage unit is exceeded, it is assumed that the motor is overloaded, based on the actual operating condition. On the other hand, one assumes normal operating conditions, when the storage unit is below a predetermined lower limit.
The known operating procedure i5 especially intended for machine-tool motors and their overload protection, whereby very small motorsr especially universal motors, are used. As a rule, these motors have a power supply controlled by electronic components. The known operating procedure can be integrated in its control engineering plan without entailing additional expenditure, since an electronic load regulation is provided.
Furthermore, the operation of machine tools, for example, hand drills and the like, is accompanied by constantly changing stress with variable driving tor~ues. These require, however, only a modest driving power, so although an expensive automatic control is necessary, it can be realized with relatively low-;~ 1310~88 1 I cap~clty componentS.2 ji As a rule, small universal motors are used in these 3 ll types of low-capacity machine tools, whereby the injected 4 ~I current is carried over the stator, as well as over the rotor, 1¦ so that the current flowing in the rotor equals the injected 6 1¦ current. Therefore, the rotor current can be immediately 7 1I determined by measuring the stator current. The spectrum of 8 ll operating modes of this type of universal motor ranges, in the g l case of small hand machine tools, from standstill over start-0 1 1 Up! to full load, idling, running down, etc., whereby very ~ diversified combinations of rotational speed and rotor current 12 l ¦ can also occur. The temperature rise in such a motor during 13 1 ¦ start-up operation is hardly different than during an operation 14 ¦ ¦ in a stalled state. Furthermore, there are no special rotor ,ll parts, which are stressed or endangered by starting operations 16 l¦ alone.
17 'l on the other hand, when large high-capacity, high-18 ¦¦ voltage electric motors are used, for example, to drive wood-19 ¦¦ proces~ing machines (refiners), compressors, ventilators, pumps i I or mills, it is not practical to regulate the supply power with 21 'I electronic means in most cases. This is due to the fact that 22 ~ the expenditure would be too high, as a result of the large 23 1 1 amount of power required to operate these motors. Therefore, 24 ¦ I these types of large motors are usually designed as high-I voltage asynchronous or synchronous motors.
26 ¦' Such large electric high-voltage motors are generally 27 ,~ started up asynchronously from the mains. Either a special 28 ~ starting windingJ such as, for example, a cage winding may 29 ~ serve for this purpose, or certain parts of the available rotor winding, for example, the upper part of the tapered deep-bar !

131~88 l ll cages in a tapered deep-bar cage rotor winding or the top bar 2 ll of a double-cage rotor winding, can be stressed during start-3 ~l up. In addition, however, the rotor body itself or parts of it ¦

4 l, can be used to carry the induced currents, which occur during ll asynchronous start-up, without a distinct rotor winding or 6 1! specific rotor winding part being present. For this purpose, 7 ~l for example, non-laminated subsections of the rotor body, which 8 ll allow eddy currents to form, when there is an asynchronous 9 ~¦ start-up inside the rotor, can be useful. In these types of l¦ slipringless high-voltaqe motors, the rotor starting losses, ~ which are in proportion to the starting torque, are virtually 12 ll completely converted inside the rotor starting windings or l3 ll rotor winding parts, respectively, in the rotor body or in the 14 ¦I rotor body parts. Contrary to the slipring motors, the li conversion of the starting losses does not take place in the 16 1 external starting resistors. Instead, it occurs mainly inside 17 1 the rotor itself, which is why the previously mentioned, 18 1 affected parts heat up a great deal during start-up.
l9 ¦~ In comparison with a small machine-tool motor, the l start-up of a large high-voltage motor does not represent a 21 ¦ ¦ normal operating condition. It is a transient process, as set 22 ll forth in the British standards for electric machines, British 23 1~1 Standard 5000, Part 16, 1981, Art. 10, paragraph 1. For the 24 ll most part, this transient process only stresses the rotor parts ll in the high-voltage motor, which are affected during 26 ¦ asynchronous start-up. Therefore, the total thermal load 27 capacity of the high-voltage motor in starting operations is 28 determined by the load capacity of these parts.
29 llA control switching operation to monitor the operating temperature of an electromotor, especially a 13101;8~

1 ¦¦ machine-tool universal motor, is also known from 2 ~l E-Bl OO 33 161. However, this control switching operation only ¦
3 1~ consid~ers actually occurring operating conditions, which have 4 '¦ been asæigned empirically calculated temperature-rise values.
'll Specific details on circuit construction are not provided - 6 1 ¦ concerning the special stresses that a large high-voltage motor 7 ~l is subject to during the transient asynchronous start-up 8 ll process, and the thereby occurring, time-dependent heating or g ¦I cooling of the rotor parts, affected during start-up; nor does I the known control switching operation go into details concerning the conditions, under which such a large high-12 I voltage motor is operated. Furthermore, the known control 13 ~ switching operation cannot consider the interests of plant 14 1¦ management, especially relative to the frequency and marginal ,¦ conditions of starting operations, because said control 16 ¦ I switching operation is conceived on the basis of an 17 1 ¦ electronically regulated power input for a small machine-tool 18 ¦ I universal ~otor.
19 I Contrary to a small machine-tool universal motor, in 1 asynchronous starting operations of a large high-voltage motor, 21 1 the conditions, under which the start-up itself takes place, 22 ¦ I must be particularly considered. This is due to the fact that 23 ¦~ the rotational speed and current characteristics have the most 24 ll important effect on the loading of the parts affected during '¦ start-up and determine their thermal stress.
26 ,l The operating procedure for such electric high-27 l~ voltage motors must, therefore, consider that the power supply 28 ll can only be switched on or off, thus there is no externally-29 ll commutated automatic control of the motor power. For physical reasons, the therral loading capacity of the starting winding , 5 ,l 13101~88 1 ~ Of such a high-voltage motor is time-limited. As far as 2 1 conditions during asynchronous start-up are concerned, there is !
3 ¦ I a danger of thermally overloading parts affected during start- ¦
up. This is especially true in large high-voltage motors, 'j since the parts cannot be designed for constant starting loads.
6 jl Also, the machines to be driven often have a very high 7 ,I counter-torque or can even stall if the motor blocks. This a ~1 I means that the current flow in the starting windings can last a 9 1, long time on a different level.
1~ SUMMARY OF THE INVENTION
11 ll An object of the present invention is to provide an 12 ,¦ operational method for large electric higb-voltage motors, 13 ll especially for those with an asynchronous automatic start-up, 14 il which, using simple means, detects the starting conditions, ll even in the case of a complicated start-up or a stalled motor, 16 1l and which insures an overload protection of the rotor parts 17 ¦1 affected during asynchronous start-up. Thus, the start-up rate , 18 ll of occurrence is orientated to the individual thermal loading 19 ¦I capacity of these parts and is limitsd by it. In addition, one Ij should be able to determine the operating state of the high-21 ~¦ voltage motor by acquiring as-few-as-possible, easily 22 ¦¦ accessible variables. Also, installing this protective feature 23 ~ should not restrict the availability of this important capital 24 1 item.
I The above and other objects of the invention are 26 ~i achieved by an operational method for an electric motor, 27 I whereby the rotational speed of the rotor and the power input 28 1 are calculated and the temperature-rise values are stored.
29 ,I These temperature-rise values represent the relative temperature-rise condition of the motor, when the motor is ~' ~

1310~

1 jl operated under diverse rotational speeds and load conditions.
2 1l A temperature-rise value is assigned to each designated 3 ¦ operating mode and, based on the rotational speed of the rotor 4 ,l and the power input, it is periodically determined, in which of ¦

5 1 ¦ the designated operating modes the motor is currently running, 6 1 ¦ whereby, to protect asynchronously starting high-voltage 7 1 ¦ motors, with a conversion of the starting losses, mainly inside 8 ll the rotor, from overloading during start-up or, in a stalled g ¦¦ state, to determine the through-rating in the rotor, only the ,! stator winding current is measured. The number and the 11 I duration of the starting operations of the high-voltage motor 12 1l are monitored and the dynamic heating and cooling of the rotor 13 j parts affected during start-up, during the starting operations, 14 1 the different operating conditions, slowing operations and 1 stoppageæ are each represented by specific discrete value 16 1~ combinations, which take into account the time lapse of all 17 ll these transient and steady-state operating conditions and 18 Ij stoppages, as well as the thereby occurring stator current and 19 1I the rotational speed of the rotor. These value combinations ~ are in the form of temperature-rise condition matrices of the 21 1 1 affected rotor parts and operational condition matrices of the 22 ~ high-voltage motor. From these are derived heating and cooling 23 1l values of the affected rotor parts. They are added with 24 1l opposite signs to an accumulated total value, stored and l¦ registered. This total value determines how many starting 26 l~ operations are still possible, and that with a specific first 27 value of the accumulated total value, the motor is switched off 28 l and that any switching-on is prevented by an inhibiting 29 ~ll function, as long as the accumulated total value has not ~ reached a specific second value.

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l 1l Using an operational method of the type mentioned in 2 1¦ the beginning, the objective is solved, according to the 3 Il invention, by measuring only the stator winding current to 4 ¦I determine the through-rating in the rotor. This is done to ! ! protect asynchronously starting high-voltage motors, with a 6 ~¦ conversion of the starting losses, mainly inside the rotor, 7 I from overloading during start-up, or in a stalled state, only 8 ¦ I the stator windin~ current is measured, to determine the g !~ through-rating in the rotor. The nu~ber and the duration of ¦ the starting operations of the high-voltage motor are monitored ll I and the dynamic heating and cooling of the rotor parts affected 12 during start-up, during the starting operations, the different 13 I operating conditions, slowing operations and stoppages are each 14 represented ~y specific discrete value combinations, which take 1 into account the time lapse of all these transient and steady-16 I state operating conditions and stoppages, as well as the 17 ¦ I thereby occurring stator current and the rotational speed of 18 1~ the rotor. These value combinations are in the form of l9 ¦I temparature-rise condition matrices of the high-voltage motor.
¦~ From these are derived heating and cooling values of the 21 ll affected rotor parts. They are added with opposite signs to an 22 ¦1 accumulated total value, stored and registered~ This total 23 I value determines how many starting operations are still 24 1 possible, and that with a specific first value of the ¦ ¦ accumulated total value the motor is switched off, and that any 26 I switching-on is prevented by an inhibiting function, as long as 27 ll the accumulated total va ue has not reached a specific second 28 I value.
29 This procedure makes it possible to consider a ,I theoretical temperature-rise model for the time-dependent, .1 ; -8-i I!

1 1, dynamic heating and cooling of the parts affected during 2 1I start-up in the rotor of a large high-voltage motor for all 3 jl steady-state and transient operating conditions and, above all, I
4 1I for the transient operation of the asynchronous start-up. For il this purpose, the number and the duration of the starting 6 ¦ ¦ operations, the thereby occurring currents in the stator, as 7 ll well as the rotational speed of the rotor are registered and, 8 ¦j based on these transient operations, as well as the occurring g l¦ operating conditions, such as idling, rated operation, slowing ~¦ down, stalling, standstill, or also data pertaining to known 11 ll operating conditions, they are entered into the theoretical ¦-12 ll temperature-rise model, and criteria are derived to form 13 ¦ discrete heating and cooling values of the rotor parts affected 14 ll during start-up. Thereby, it is also considered, that the I heating and cooling values correspond to time-dependent heating 16 ¦1 and cooling Punctions, which are determined by the theoretical 17 ¦! temperature-rise model. This means that the fact, whether the 18 I high-voltage motor runs or stands still during heat 19 ¦ dissipation, is also fully entered into the operating procedure.
21 ll Altogether, all the input data that the operating 22 ¦ 1~ procedure requires are the rotational speed, the stator current 23 1~ and the time duration (or the starting operations or the 24 ¦ steady-state operating conditions, the slowing operations and I the stoppages), in order to continuously determine therefrom, 26 with the help of the theoretical temperature-rise model, the 27 ll temperature-rise condition of the rotor parts affected during 28 start-up. It i5 not necessary to measure the energy converted 29 1 in these parts. In large high-voltage motors, this would require temperature ~ensors or current-measuring devices in the _g_ I

!
131~S88 1 ¦ normally not accessible rotor parts, which are affected during 2 ¦ start-up. The measured values of these sensor~ or devices 3 I would have to be passed along from the rotating rotor over 4 I sliprings or other transmitting means to stationary parts, for ,l example, in order to be able to measure the current flowing 6 ,1 into them and, thereby, to be able to be close to their 7 I converted power loss. Thus, an additional constructional 8 l, expense is avoided in the monitoring of the temperature-rise g li condition of the rotor parts of the high-voltage motor affected 1~ during start-up.
11 l The steady-state and transient operating conditions, 12 ¦I which occur, are catalogued in the form of operating condition 13 ,I matxices, which are made up of the elements stator current and 14 1i rotor rotational speed or stator current and conduction l interval. They also contain the transient operations, 16 ¦ I especially the starting operations. With the help o~ the 17 ll theoretical temperature-rise model, temperature-rise condition 18 1 ll matrices are formed for the rotor parts affected during start- i 19 1¦ up, which contain the elements stator current, rotor rotational l, speed and conduction interval, as well. Moreover, they contain 21 ,I the heating and cooling values resulting from the theoretical 22 ll temperature-rise model, which correspond to the time-dependent 23 ,I heating and cooling functions. During start-up, operation and 24 1I standstill, and also in the case of a stalled high-voltage ll motor, values are selected from the operating condition 26 i matrices, based on the actual operating condition data, and are 27 1 ¦ each assigned to the elements of the temperature-rise condition 28 ll matrix. In this way, specific heating or cooling values are 29 l selected. This selection process for heating and cooling values takes place periodically.

., , . , .

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1 1l The heating values, which are derived periodically, 2 ' are continuously added with a negative sign and the cooling 3 l' values with a positive sign, to an accumulated total value.
4 ;I Thus an actual, discrete value, which is inversely proportional 5 ll to the temperature-rise condition of the rotor parts affected 6 ll during start-up, is constantly present.
7 1 Based on the end result of the accumulated total ~ 1I value, an estimation can be made of the total possible starting 9 ! operations, which are still available without overloading: for ll one start-up, for example, a specific measure of discrete 11 ¦I values is provided, which rapidly lowers the level of the 12 11 accumulated total value. During those operating conditions or 13 l! stoppages, in which the starting windings cool down, the 14 I I discrete values, which are inversely proportional to the li cooling, are graded in finer steps. This slowly raises the 16 j ¦ level of the accumulated total value up to a previously 17 ¦ established maximum value, which, at the same time, indirectly 18 1~ establishes the maximum number of starting operations. If the 19 l! accumulated total value indicates a level, which is less than 1I the required measure for a start-up, then one will realize that 21 11 ! no additional start-up can be performed. A start-up only makes 22 ll sense, if the level of the accumulated total value is 23 1 sufficient, after the rotor parts affected during start-up, 24 l¦ have cooled down.
25 l l Among other factors, the procedure also considers 26 j I that a very effective cooling takes place during the no-load 27 l operation of the high-voltage motor, so that the accumulated 28 l total value rises again very quickly. As a result, one can 29 read off from the indicated level of the accumulated total 30 I value, if it is possible to initiate a renewed start-up under , ~ .

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1 ¦ load conditions.
2 ¦ In addition, a minimum value is defined for the 3 ¦' accumulated total value, at which a break in the stator current 4 ,l is released. An interlocking device ensures that a renewed ~I start-up can only take place, if the accumulated total value 6 1 I shows a sufficiently high level. It can be advantageous to 7 ! ~ select elements of the operating condition matrices from the 8 ll last slow-down operation and, from these elements, to g 1l predetermine and also display temperature-rise values for the ll next start-up. This provides the plant management with some ~ flexibility, which is especially advantageous for controlling 12 ll the driving mechanisms of large wood-processing machines 13 1 ¦ (refiners). Based on the indicated level of the accumulated 14 1I total value and the additional display of the change in this l~ level to be expected at the next start-up, the plant personnel 16 I can decide which type of further speration is still possible 17 ! and which one offers the greatest efficiency, without, however, 18 1 endangering the high-voltage motor. In this way, for example, l9 1 by quickly unloading the refiner after an unsuccessful heavy ll I starting, a start-up without load can be implemented with a 21 lll subsequent highly cooling no-load operation, so that the high-22 ll voltage motor cools down very quickly and is ready for a new 23 ¦! start-up under load. In this way, one can avoid operating 24 ~I stoppages, which can result from long cool-down phases of the 2S ll high-voltage motor and can lead to long down-times, especially 26 l in wood-processing processes in paper factories.
27 I f It can also be advantageous, if the accumulated total 28 ,ll value is displayed in natural, whole numbers. This type of 29 ¦ representation of the accumulated total value makes it easily 1 possible for the plant personnel to follow the actual , I , "

, ~

~ 131~o88 1 l~ temperature-rise condition of the rotor parts affected during 2 ¦I start-up and, consequently, the operating readiness of the 3 ll ! high-voltage motor, and to set-up plant management accordingly.
4 i Moreover, it can be advantageous, if additional ~j threshold values of the stator current and of the rotor's 6 1I rotational speed are defined, which act as a criterion to 7 1 I release transformed functions and are superimposed on the 8 il accumulated total value. In this way, additional criteria, g 1l which provide additional information for plant management, are 1I formed, under consideration of the temperature-rise condition 11 1 of the high-voltage motor, based on specific values of the 12 ~I stator current and of the rotor's rotational speed. For 13 ¦¦ example, when the motor is at a standstill (rotor rotational 14 l ¦ speed = O), and there is a full stator current at the same 1 ! time, one can recognize that the motor is apparently stalled, 16 ¦¦ so that it is necessary to discontinue the start-up, although 17 ¦ the heating of the rotor parts affected during start-up would 18 not yet make this necessary. The necessity of discontinuing 19 the start-up would not be recognizable solely by evaluating the 1l level of the accumulated total value.
21 An especially advantageous further embodiment of the 22 invention relates to a control switching operation to implement 23 ~I the previously mentioned operational method concerning an 24 ¦~ asynchronously starting electric high-voltage motor, with a 1¦ conversion of the starting losses, mainly inside the rotor, to 26 ll protect it from overloading during the asynchronous start-up or 27 ¦ I in the stalled state. The control switching operation 28 ~ comprises a rotational-speed sensor to determine the rotational 29 ! speed of the high-voltage motor and to generate a first input ll signal, proportional to the rotational speed. It also . I
, il -13-. I , 1310S~8 1 1¦ comprises a first digital storage means to store operating 2 j~ condition matrices of the high-voltage motor and temperature-3 ~l rise condition matrices of its rotor parts affected during 4 ,¦ start-up. In addition, it contains a digital processing unit ll to read in, process and output digital signals, as well as to 6 ll select the appropriate heating and cooling values for the rotor i 7 1 I parts affected during start-up, according to the actual 8 11 operating condition of the high-voltage motor from the first g l¦ digital storage means, as well as a second digital storage !~ means to store the accumulated total value, made up of heating 11 1l and cooling values, corresponding to the temperature-rise 12 ¦~ condition of the rotor parts affected during start-up.
13 I Furthermore, according to the invention, the control 14 'I switching operation is characterized by a measuring device, I which determines the stator current and generates a digital 16 '¦ current signal proportional to this, and a counter, both of 17 jj which are connected to the processor unit. The counter is 18 '! started or stopped or set back, in accordance with the actual 19 l¦ operating condition data of the high-voltage motor, derived li fro~ the digital rotational speed and current signals. The 21 l¦ operating condition matrices and temperature-rise condition 22 Ij matrices for the first digital storage means contain value 23 ~I combinations of the stator current, rotational speed and 24 ¦I counter status. Also, the processor unit forms value 1, combinations, based on the actual digital stator current 26 l~~ signals and digital rotational speed signals supplied to it, 27 ll and also based on the counter content fed to it. The processor 28 1 unit also selects corresponding value combinations of the 29 . operating condition or temperature-rise condition matrices from the first digital storage means which is connected to it. From ' I ~
.

I l 1 3 ~ 8 1 ~! these, the processor unit derives discrete heating and cooling 2 ll values and reads them into the second digital storage means, 3 ~l' which is connected to the processor unit. Means are provided 4 ll to discontinue the start-up and to automatically control the 1I starting sequence. These means are connected to the processor 6 ¦¦ unit and to a switching device to interrupt the stator circuit 7 l! of the high-voltage motor. The breaking operation and the 8 1l automatic starting sequence control result, hereby, according 9 ~¦ to the contents of the second digital storage means. Also, the ~¦ position of the switching device is signalled back to the ~ processor unit by signalling devices. First display devices 12 !, are provided, which are linked over the processor unit with the 13 ll second digital storage means.
14 ll BREIF DESCRIPTION OF THE DRAWINGS
1 In the following, the invention will be described in If 16 ll greater detail, based on a simplified exemplified embodiment, 17 ll represented in FIGS. 1 to 3 of the drawing, which depicts the 18 ¦~ start-up monitoring of large electric high-voltage motors.
19 l~ With reference to the drawings, ll1 EIG. 1 illustrates a simplified example of an 21 l! operating condition matrix;
22 l' FIG. 2 is a graphic representation of a start-up 23 ll example of the operational method, in the form of an 2 4 ¦ I operational sequence chart; and ~I FIG. 3 illustrates a simplified block diagram for a 26 1l control switching operation to implement the operational 27 ~ method.
28 li DETAILED DESCRIPTION:
29 ~I Generally, electric high-voltage motors are started l~ asynchronously from the mains. In the case of slipringless 1, , ~; 1310a88 1 'I high-voltage motors, a special starting winding, such as, for 2 ll example, a cage-winding, serves for this purpose. Certain 3 ll parts of the available rotor winding, for example, the upper 4 ll part of the tapered deep-bar cages in the case of a tapered l' deep-bar cage winding or the top bar of a double-cage winding, 6 1 I can also be stressed during an asynchronous start-up. It is 7 ~ also possible, however~, that non-laminated parti~ of the rotor 8 1 I body, or the rotor body itself, can be used to guide currents g l¦ in the rotor, which occur during start-up, in which the rotor 1I power loss, which is proportional to the starting torque, is 11 I converted.
12 l l This asynchronous start-up leads to a very intense 13 l¦ heating of the parts of the rotor affected during start-up.
14 lI This heating is not accessible to a direct measurement, 15 1 I however, as a result of the present operational method, it can 16 be considered. The starting point of the operational method is 17 I the operational condition matrix shown in FIG. 1. It 18 ¦1 illustrates combinations of the measured stator current Il, 19 1I rotor rotational speed n and time duration t of the starting 1 operations; steady-state operating conditions, slowing 21 ~ operations, and stoppages. Furthermore, some threshold values 22 ~ for the stator current I1, and the rotor rotational speed n are 23 ~ still defined, which are drawn upon as additional criteria to 24 ll assess each operational or starting, slowing or standstill 25 1I condition, at hand, and which facilitates the selection of an 26 l assigned temperature-rise value, which is used to form the 27 l accumulated total value. A limit speed nO, which corresponds 28 1I to approximately 10% of the nominal rotational speed of the 29 I high-voltage motor, and the nominal current IN are definded as '~ additional values.
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1 ll The following combinations result from the 2 ll operational condition matrix shown in FIG. 1: If the stator 3 ! ' current Il = 0 and the rotational speed n is less than the 4 ~l limit speed nO, then there is a stoppage. On the other hand, li if the rotational speed n is greater than or equal to the limit !
6 1 ¦ speed nO and the stator current Il = 0, then the high-voltage 7 1~ motor is in slowing operation. If the stator current Il is 8 ,¦ greater than 0 and less than 1.2 times the nominal current IN, g ¦I then, in the case of an actual rotational speed n, which is l¦ less than the limit speed nO, then the high-voltage motor is ~ starting up with too low a switching error, a cut-off is 12 1 I provided, as soon as the conduction interval exceeds a 13 ¦ I predetermined value t1. If, on the other hand, the rotational 14 1I speed n is greater than or equal to the limit speed nO, then 15 !' the normal operating condition exists, so that it is not 16 1~ necessary to interrupt the operation as a result of a possible 17 ¦ overheating of the starting windin~ or starting winding parts.
18 l I For the case that the stator current Il is greater 19 1I than or equal to 1.2 times the nominal current IN and, at the ¦¦ same time, the rotational speed n is less than the limit speed 21 ~I nO, then it i5 obvious that ther~ has been a switching-on with 22 ! I a stalled rotor, so that a cut-off must follow, if the 23 ¦I conduction interval exceeds a predetermined second value t2.
24 ~¦ If, on the other hand, the rotational speed n is greater than ~ the limit speed nO, then, in the case of such an increased 26 ~I stator current Il = 1.2 IN, there is a start-up under severe 27 l operating conditions, so that , if after exceeding a third 28 !I predetermined time t3, an increased stator current Il = 1.2 IN
29 'I continues, the start-up operation must be interrupted.
1 In the case of the operational method, accordin~ to ll l ~ -17-., ;

~ 131~8~
1 l~ the invention, the times t1, t2 and t3 are variable values.
2 ll These values are determined from the logical evaluation of the 3 1 I stator current I, after a stipulated time to. Furthermore, 4 I based on the knowledge of the theoretical temperature-rise model of the rotor parts affected during start-up, time-6 1I dependent heating or cooling functions are established for each 7 1, operating condition of the high-voltage motor.
8 1 I By combining the elements of the operating condition g 1¦ matrix, depicted as an example in FIG. 1, with the calculated, l~ time-dependent heating or cooling functions of the affected 11 11 rotor parts, a temperature-rise condition matrix, not shown 12 ¦ I here, is set up. With this matrix, discrete heating or cooling ¦
13 ~¦ values are defined, which consider the time dependency of the 14 ll ~ temperature-rise condition of the rotor parts affected during 11 start-up.
16 ~l Thus a chronological sequence of heating or cooling 17 ¦I values is assigned to each steady-state and, above all, to each 18 , transient operating condition of the high-voltage motor, which 19 ~ enables the dynamic thermal characteristic of the rotor parts 1 affected during start-up to be determined.
21 ¦ Based on the operating condition matrix, heating or 22 1 cooling values can thus be selected from the temperature-rise 23 jI condition matrices and added to an accumulated total value and 24 ¦I stored. In the continuation of the operational method, the 'I temperature-rise condition, valid at any one time, of the rotor ' 26 l~ parts of the motor affected during start-up is represented by a 27 11 display of the accumulated total value. This representative 28 l`, value is presented in the form of natural numbers and extends 29 ~ to the temperature-rise condition of the rotor parts affected during start-up. It is also constantly dynamically determined Il i' .
, ll 1 1 during the changeover from one operating condition to the , other, whereby transient transition conditions and, thereby, 3 ¦ especially the start-up, are also considered.
4 1I FIG. 2 depicts an example of the operational sequence ll of a high-voltage motor, whereby its rotor parts affected 6 ! I during start-up are protected according to the operational 7 1I method of the invention. On the abscissa, the time t is 8 1 represented in hours, and on the ordinate, the accumulated g Ij total value is displayed in the negative direction with numbers i j~ from 30 to 0. Assuming an operation lasts several hours, the ll !I rotor of the high-voltage motor constantly heats up, so that 12 ¦I the starting winding also shows a definite temperature-rise 13 ¦I value, corresponding to the constant temperature-rise condition 14 1~ in the steady-state operating condition l. This value is 20.
il At the four-hour mark, as represented, the motor is switched 16 11 off and slows down in a short time, until it reaches 17 1 standstill. The starting winding cools off, thereby, in 18 ¦ accordance with its standstill cooling function 2, and after 19 1 approximately 2.5 hours, a value of 25 is obtained for the 1 accumulated total value. If a new start-up is initiated now, 21 after 6.5 hours, and a rotor is stalled, then this is 22 ¦¦ determined by analyzing the operating condition, this means by 23 1 I comparing the actual operating condition data to the stored 24 ¦ I operating condition matrices. The starting operation is then ~ immediately interrupted. The indicated accumulated total value 26 1I diminishes after that by the value lO to 15. A heavy starting 27 ll follows, and after its successful completion, the indicated 28 value of the accumulated total value falls to zero.
29 ' Since the motor runs subsequently in a normal, li steady-state operating condition, for the time-being, a delay 1, 1 ,.

~ 131(~8 1 l! time 3 is considered for the temperature distribution within 2 ! I the rotor, and the accumulated total value is kept constant.
3 ll After approximately one hour of operating time, cooling values, 4 jl corresponding to the operational cooling function 4, are I supplied to the accumulated total value, so that its display 6 1I rises again relatively quickly.
7 l If, after a total of 8 hours, the motor is switched 8 ll Off and slows down and then comes to a standstill, then the g ll display of the accumulated total value only rises slowly, in 11 accordance with the standstill cooling function 2.
11 li If the accumulated total value reaches a sufficient 12 ¦ level again, then renewed start-ups can be performed. Thereby, 13 ll the operating cooling function 4 and also the standstill 14 ! ~ cooling function 2, as well as the constant temperature-rise 5 ¦I condition in the steady-state operating condition 1, are 16 ~I considered. When the motor is completely cooled off, as shown 17 1 in the operational sequence chart in Fig. 2, a total of three 18 1 normal start-ups are possible, one after the other, at the 22-19 ¦ hour mark. These start-ups can be effected without causing the ¦ rotor parts affected during start-up to be overloaded or, on 21 i the other hand, without improperly restricting the availability 22 ! 1 of the high-voltage motor.
23 ll As depicted in the operational sequence chart in Fig.
24 ll 2, a simple control is provided for the temperature-rise ¦I condition of the rotor parts of the high-voltage motor affected 26 ll during start-up. This control results from operating condition 27 1l data consisting of a stator current I1, rotor rotational speed 28 l n, as well as the times t for the various starting, operating 29 ll and standstill conditions, in combination with the heating and ~ cooling functions 2.4, valid at any one time, acquired from the ' I
. . .

"

;~ 131~i)8~ 1 1 I theoretical temperature-rise model of the rotor winding. This 2 I makes it possible to have a safe, but also flexible, plant 3 'l management, that will be able to make decisions with foresight, 4 1 in order to achieve the best-possible availability of the ll high-voltage motor. This enables a method of operation to be 6 sustained, in which, after a failed start-up at 5.5 hours, for 7 1l example, one can quickly transfer over to the normal operating ~ ll condition with a good cooling function, by immediately g ll executing a second start-up of the high-voltage motor.
ll The previously described exemplified embodiment of the operational method for a large high-voltage motor can be 12 1, accomplished with the control switching operation depicted, 13 ll greatly simplified, in FIG. 3, in the form of a block diagram.
14 j For this purpose, a sensor working as a tachometer 31 l~ is provided on the high-voltage motor 30 and a stator current 16 ll measuring device 33 is provided in the stator ci~cuit 32 of the 17 1 I high-voltage motor 3~; both transmit their data to a processor 18 ¦1 unit 34. A time standard or clock 35 is also provided to 19 ll standardize a counter 35, which is connected bidirectionally to i , the processor unit 34 and is reset, started, ~topped and tested 21 il by the processor unit. In a ~irst digital storage 37, which is 22 ll connected to the processor unit 34, operating condition 23 1 I matrices 39, 40 are stored, which consist of v~rious single 24 li data collections and contain a stator current/time - operating ¦~ condition matrix 39 and a stator current/rotational speed -26 ll operating condition matrix 40. In addition, a temperature-rise 27 1¦ condition matrix 41, dependent on the stator current Il, 28 , rotational speed n and time t parameters, is stored in the 29 1, first digital storage 37. This matrix is formed on the basis of the occurring start-up, operating, slowing and standstill ' ., 13~ 8 1 ll conditions of the high-voltage motor 30, in accordance with the 2 I operating condition matrices 39, 40. The temperature-rise 3 ll condition matrix 41 contains the dynamic, time-dependent 4 ll temperature-rise behavior of the rotor parts of the high-ll voltage motor 30 affected during start-up, in the form of 6 ll temperature-rise and cooling values or heating and cooling 7 ¦¦ functions 2.4, assigned to the elements of the operating 8 ll condition matrices 39~ 40 (see FIG. 2).
9 , The processor unit 34 selects the time-dependent 1 heating and coolinq values from the temperature-rise condition 11 ¦ matrix 41 by comparinq the actual operating condition data on 12 1! rotational speed 31, stator current 33 and time measurements, 13 acquired by the counter 36, to the data in the operating 14 lj condition matrices 39, 40.
l l A second digital storage 42 is connected to the 16 1 I processor unit 34. The heating and cooling values ~rom the 17 1l processor unit 34 are read into and stored in the storage 18 1 means, whereby the accumulated total value is formed. since .~ the heating and cooling values of the rotor parts of the high-~ voltage motor 30 affected during start-up are each added with 21 1~ an inverted sign in the digital storage 42, its contents 22 ~I correspond exactly to the actual temperature-rise condition of 23 ¦ these rotor parts of the high-voltage motor 30, affected during 24 ll start-up. The contents of the digital storage 42 are converted ll by the processor unit 34 into numerical values of natural 26 I numbers and presented by means of a first display device 43, 27 ~l which is connected to the processor 34. A second display 28 device 44, supplied by the processor unit 34, is also provided, 29 l~ so that the actual operating condition of the high-voltage I motor 30 can be monitored with the display of the acquired .

1 ¦¦ values Il and n.
2 1 ¦ A third display device 45 is connected to the 3 I processor unit. It displays the change in the accumulated 4 jl total value, which is to be expected with the next start-up and ¦
¦l is predetermined on the basis of the last slowing operation 6 ¦I from the operating condition matrices 39, 40 and the 7 1~l temperature-rise condition matrix 41. In this way, the plant 8 1 I personnel can very easily read off, which temperature-rise g ¦¦ value the parts of the rotor affected during start-up would ¦¦ have after the next start-up. They could then alleviate the starting conditions of these parts using appropriate preventive ¦
12 I measures, for example by relieving the high-voltage motor 30.
13 ! In addition, start-ng interruption device 46 and 4 1 ¦ automatic starting sequence control device 47, are connected to ¦
5 ! I the processor unit 34 and controlled by it, according to the 16 ¦~ temperature-rise condition of the rotor parts of the high-17 ¦¦ voltage motor 30 affected during start-up, thus according to 18 1 the me~ory contents of the second digital storage 42. In 19 ¦ addition, the switching arrangement 48 is connected by a 1 signalling circuit 49 with the processor unit 34. A fourth f 21 ¦ display device 50, which is connected to the processor unit 34 22 !1 as well, indicates the position of the switching arrangement 48 23 l! and, in addition, makes it easier for plant personnel to 24 ¦I monitor the operating condition of the high-voltage motor 30.
ll The accumulated total value, stored in the second 26 j¦ digital storage ~2, represents the temperature-rise condition 27 ll of the rotor parts of the high-voltage motor 30 affected during 28 1I start-up. On this basis, when the value falls below a 29 1 I previously established threshold value, the processor unit 34 I initiates the device 46 to interrupt the start-up, whereupon .

i 1310~8~ ~

1 ' the switching arrangement 48 interrupts the stator current I1.
2 1 Since the accumulated total value and, therewith, the contents 3 1 of the second digital storage 42 and the operating condition 4 1 l analysis, i.e., the comparison between the actual operating 5 ll I condition data Il, n and t with the data stored in the first 6 11 digital storage 37, also considers, above all, starting 7 ll operations, the interruption of the stator circuit 32 is also 8 l~ provided, already before a starting operation. Thereby, the g ll parts are protected, which are stressed the most during lll asynchronous starting operations, namely the starting winding, ~ starting winding parts or the rotor body, or parts of it.
12 1~ Moreover, the automatic starting sequence control device 47 13 ¦ I ensures that a renewed start-up is only possible, if, according 14 I to the contents of the second digital storage 42 (accumulated 15 l, I total value), the temperature-rise condition of the rotor parts 16 Ij affected during start-up is sufficient.
17 j~ Consequently, the high-voltage motor is automatically 18 ~I protected, on the one hand, from overloading during the 19 ll asynchronous start-up, although only the stator current and the l¦ rotor rotational speed are measured as motor-specific 21 l~ variables. on the other hand, by visualizing the actual and 22 ji the expected temperature-rise condition, as well as the actual 23 ,1 operating condition, an instrument is created for the plant 24 1 I personnel, which permits a flexible plant management, within 11 the bounds of the permissible temperature-rise of the rotor 26 ;~ parts affected during start-up. Thus the number and duration 27 l of shutdowns are considerably reduced, in the case of the 28 ~ high-voltage motor 30, because the execution of start-ups of 29 ll the high-voltage motor 30 is oriented to the rotor parts, which ' are thereby stressed the most.
;

' i~ 1310~88 1 1¦ In the foregoing specification, the invention has 2 1 ! been described with reference to a specific exemplary 3 11 embodiment thereof. It will, however, be evident that various 4 I modifications and changes may be made thereunto without I`j departing from the broader spirit and scope of the invention as j 6 ¦j set forth in the appended claims. The specification and 7 ! ¦ drawings are, accordingly, to be regarded in an illustrative 8 ¦I rather than in a restrictive sense.

10 Ij ~I f 17 ¦!`
18 1~ j 19 ~I 1 20 1!

21 1l 22 i1 l l l , f

Claims

1. An operational method for an electric motor, comprising calculating rotational speed of the motor rotor and power input and storing temperature-rise values; said temperature-rise values representing the relative temperature-rise condition of the motor when said motor is operated under diverse rotational speeds and load conditions, a temperature-rise value being assigned to each designated operating mode of the motor, and, based on the rotational speed of the rotor and the power input, further comprising periodically determining in which of the operating modes the motor is currently running, whereby, to protect an asynchronously starting high-voltage motor, with a conversion of starting losses, mainly inside the rotor, from overloading during start-up or, in a stalled state, to determine a through-rating in the rotor, measuring only the stator winding current; monitoring the number and the duration of the starting operations of the high-voltage motor and the dynamic heating and cooling of rotor parts affected during start-up; during starting operations, different operating conditions, slowing operations and stoppages each being represented by specific discrete value combinations, said combinations taking into account a time lapse of all transient and steady-state operating conditions and stoppages, and the thereby occurring stator current and rotational speed of the rotor; said value combinations being in the form of temperature-rise condition matrices of the affected rotor parts and operational condition matrices of the high-voltage motor;
deriving from said matrices heating and cooling values of the affected rotor parts; adding said values with opposite signs to an accumulated total value; and storing said accumulated total value, said total value determining how many starting operations are still possible, and at a specific first value of the accumulated total value, switching off the motor and preventing any switching-on by an inhibiting function, as long as the accumulated total value has not reached a specific second value.

2. The operational method recited in claim 1, further comprising selecting elements of the operating condition matrices from a last slowing down operation of the motor and, from said elements, predetermining temperature-rise values for a next start-up and displaying said values.

3. The operational method recited in claim 1, further comprising displaying the accumulated total value in natural, whole numbers.

4. The operational method recited in claim 1, further comprising defining additional threshold values of the stator current and rotational speed of the rotor, which serve as releasing criterion for transformed functions superimposed on the accumulated total value.

5. A control switching apparatus for an electric high-voltage motor, with a conversion of starting losses, mainly inside the motor rotor, to protect the motor from overloading during asynchronous start-up or in a stalled state, said control switching apparatus comprising a rotational-speed sensor for determining the rotational speed of the high-voltage motor and for generating a first input signal proportional to the rotational speed; and further comprising a first digital storage means for storing operating condition matrices of the high-voltage motor and temperature-rise condition matrices of rotor parts affected during start-up; digital processing means for reading in process and output digital signals and for selecting appropriate heating and cooling values for affected rotor parts according to the actual operating condition of the high-voltage motor from the first digital storage means; and a second digital storage means for storing an accumulated total value comprising heating and cooling values, corresponding to a temperature-rise condition of the rotor parts affected during start-up; and further comprising a measuring device for determining the stator current and for generating a digital current signal proportional to the stator current and a counter coupled to the digital processing means, said counter being started, stopped or set back in accordance with the actual operating condition data of the high-voltage motor derived from the digital rotational speed and current signals; said operating condition matrices and temperature-rise condition matrices of the first digital storage means containing value combinations of the stator current, rotational speed and counter status; the digital processing means forming value combinations, based on the actual digital stator current signals and digital rotational speed signals supplied to the digital processing means, and further being responsive to said counter; said processing means selecting corresponding value combinations of the operating condition or temperature-rise condition matrices from the first digital storage means, said processing means deriving discrete heating and cooling values and storing said values in the second digital storage means coupled to the processing means; and further comprising means for discontinuing start-up and for automatically controlling the starting sequence, coupled to the processing means and to a switching means for interrupting the stator circuit of the high-voltage motor, a stopping operation and automatic starting sequence control being controlled according to contents of the second digital storage means, a position of the switching means being transmitted to the processing means by a signalling means, and further comprising a first display device coupled to the processing means by the second digital storage means.

6. The control switching apparatus recited in claim 5, wherein the actual current and rotational speed signals of the high-voltage motor are supplied by the processing means to a second display device.

7. The control switching apparatus recited in claim 5, wherein the processing means is connected to a third display device which displays a change in the accumulated total value, which is to be expected with the next start-up and is predetermined on the basis of the last slowing-down operation.

8. The control switching apparatus recited in claim 5, further comprising fourth display means coupled by the processing means to the switching arrangement.