SE516408C2 - Power consumption control method for alternating current machine, involves measuring temperature of rotor which is used as control parameter to optimize power conversion in thermally controlled manner - Google Patents

Abstract

The temperature at critical points of rotor winding and its insulation is measured continuously or intermittently. The measured temperature is used as control parameter for rotor current and the power conversion of the machine is performed in a thermally controlled manner by controlling continuous operation of the machine. Independent claims are also included for the following: (a) Rotating electric alternating current machine; (b) Electric power plant.

Description

516 408, ._, .._.__. .... ... . - 2 'iiïïiš * §..ï = II =' -. IÉ¿.É 5 "'Transmission of both reactive and active power contributes to power losses in power grids. Furthermore, lack of reactive power, or an unfavorable distribution of it in a electric power plant or an electric power grid lead to so-called voltage collapse.

This is especially important in connection with major faults in the power grid, e.g. when larger generators or motors suddenly fail. When this happens, the properties of the power grid change. Various regulators in the electricity grid or power plant will try to maintain the frequency and voltage within the predetermined limit values. This can be done today, among other things, by changing the active and reactive production of generators and by changing the turnover ratio through winding coupler control in transformers. However, on some occasions it has been shown that this has not been enough. If the need for reactive power is greater than that which the electric power grid can satisfy, then the transmission capacity in the electric power grid can collapse very quickly by the maximum point on the so-called The PV curve is passed or by further disconnections of the remaining production units due to overload. The limitation in the amount of transmitted power is due in many electric power lines to a lack of reactive power, above all to critical places in the grid and not to the fact that thermal limit values for transmission lines are exceeded. It is therefore of great importance for an electricity network operator to be able to control the voltage of the electricity network, to maintain an appropriate distribution of sources and depressions for reactive power, and to be able to change this distribution for shorter periods.

One way of controlling the reactive effect is the introduction of phase-compensating elements in the electricity grid. For large and complex networks, especially if the load changes nature from one period of time to another, such solutions require extensive analyzes and simulations to optimally determine the location and electrical power of these phase compensators. Furthermore, ïyflO requires procedures for how these are to be controlled for different operating conditions in. in the net. Another measure to control the amount of reactive power may be to change the operating conditions of AC machines, in order to reduce or increase the delivered or consumed reactive power. However, since many 516 good AC machines, both in generator operation and in motor operation, operate close to their nominal effects, the margins for such changes are normally very small. In order to be able to significantly influence the ratio between reactive and active power, the active power of the machine must typically also be reduced, so that magnetization or winding temperatures do not exceed their nominal values. Phase compensation via AC motors can therefore normally only take place by reducing the active power, which in most cases is unsatisfactory.

Prior art AC machines are normally provided with various types of overload protection and / or limitation devices.

The limits of how hard an AC machine can be used are often set by considerations regarding temperatures, e.g. the temperatures of the stator and rotor windings. Permissible currents in the windings are generally estimated using simple theoretical models. For the rotor winding, a limit is typically set for the current of the magnetizing equipment. This can have a limit at e.g. rated rotor current. Larger machines are often equipped with a rotor current limiter which, in addition to an instantaneous limiter, can contain a time delay that allows a certain overcurrent for a shorter period.

However, this limitation is static and does not take into account the actual thermal condition of the synchronous machine.

The stator winding on AC machines is normally protected by an overcurrent protection. In the event of an overload of the machine, such as the current exceeding a limit given by the rated power, the machine is switched off. *: "É Synchronous machines can be equipped with a stator current limiter. You can then regulate the rotor current to limit the reactive power so that the operating point is maintained within the permitted working range in a well-known" PQ pie chart ", which is often referred to by those skilled in the art. also independent of the actual temperature of the stator winding.

AC machines with an output above 5 MVA are today equipped with resistive temperature gauges (eg Pt100 elements) that are placed in or near 516 408 .... ... . - -4 '-.-' ':: 2' :: 2-a.f = :: = -.:% Connection to the stator winding. These provide good information about the working temperature of the winding. These are connected to a protection that disconnects the machine when the temperature reaches a certain limit value. These limit values are typically determined from the temperature class or from measurements during commissioning of the machine.

A problem with machine protection and limiters according to the state of the art is that in many cases they are based on rough static models of loss generation and conduction as well as temperature rise. The actual conditions, such as variation in ambient temperature, are generally considered very little. In order for protection to be obtained even for rather extreme conditions, large safety margins must be used. In less extreme cases, this leads to the protections triggering unnecessarily early in a process. Furthermore, if a load drop or fault in the electric power grid causes an unfavorable distribution of reactive and active power, this can easily lead to an increase in temperature and / or current in certain parts of an AC machine. If the protection is set at a far too low level, such a mains power situation can lead to the protection of the machine being activated and the machine being switched off. This in turn can lead to a deteriorating condition of the electricity grid.

SUMMARY A general object of the present invention is thus to provide methods and devices for AC machines, which increase the possibilities and flexibility to temporarily change consumed or added active or reactive power to an electric power grid. Another object is to provide alternating electric machines which have greater margins for changing its operating state. A further purpose of the present invention is to eventually provide a power grid with expanded ë-: ÅO opportunities for planned and / or coordinated power changes. Furthermore, it is also an object of the invention to provide an improved overpower protection for AC machines. 5165408 š3, ¿,,, ._., _- H,., The above objects are achieved by methods and devices according to the appended claims. In general terms, the temperature of the rotor and / or stator winding is measured during operation. The measured temperature is then used to utilize in a controlled manner the margin in thermal material utilization that the insulation material in alternating current machines generally has. Rotor and / or stator current can be regulated to give rise to the desired production or consumption of active and reactive power. Even if the regulation of the currents and the temperatures of the windings is made to exceed nominal values, the temperature monitoring can deliberately allow this for a limited time, possibly at the expense of the material life. The same monitoring principle can also be used to give the AC machine fl more protection against overload. An electric power grid with AC machines of this kind can utilize considerable temperature margins in connected machines, and in the event of operational problems, these margins can be used for a shorter period of time to facilitate the continued operation of the electric power grid. If information about the margins of the different machines is stored, measures can be planned for different types of operational problems and a coordination of measures can then be taken when errors occur.

The present invention is particularly suitable for use with generators and large motors with an output above about 10 MVA. It is also particularly suitable for use with machines with conventional voltage when connected to the electricity grid, ie. for voltages below 25 kV.

BRIEF DESCRIPTION OF THE DRAWINGS »afuv The invention and further objects and advantages achieved thereby are best understood by reference to the following description and the accompanying __ drawings, in which:: I-: ÉO Fig. 1a is an equivalence diagram for a synchronous machine when the resistance i 'i the stator winding is neglected; Fig. 1b is a combined capability and pointer diagram for a synchronous machine in over-magnetized generator operation; 516.6 408 Fig. 2a is a schematic sketch of how the current can be increased in a stator or rotor winding, when the temperature margins are used; Fig. 2b shows a typical relationship between service life and temperature for an insulation material; Fig. 3 shows the change in the operating state of a synchronous generator when it is overloaded with reactive power; Fig. 4a shows a time course of the temperature of the rotor winding when a synchronous generator is overloaded with reactive power in two intervals; Fig. 4b shows a time course of the temperature of the stator winding when a synchronous generator is overloaded with reactive power in two intervals; Fig. 5a shows a controlled time course of the rotor current to regulate reactive power and temperature in the synchronous generator at reactive overload; Fig. 5b shows the time course of reactive power production when the synchronous generator is overloaded according to Fig. 5a; Fig. 6a shows a reformulated equivalence diagram for an asynchronous machine with wound rotor; Fig. 6b shows the change in the operating state of an asynchronous machine in generator operation when it is overloaded with active power; Fig. 7a shows a time course for active power production when an asynchronous machine in generator operation is overloaded with active power in an interval; Fig. 7b shows a time course of the temperature of the stator winding when an asynchronous machine in generator operation is overloaded with active power in an interval; Fig. 8 shows the change in the operating state of a synchronous motor when it is overloaded for a short time with a reactive power which cannot be allowed for continuous operation; Fig. 9a shows a time course for reactive power production when a synchronous motor is overloaded with time-varying reactive power; Fig. 9b shows a time course of the temperature of the rotor winding when a synchronous motor is overloaded with time-varying reactive power; Fig. 10 shows a block diagram of a synchronous machine according to the present invention with static magnetization; Fig. 11 shows a block diagram of a synchronous machine according to the present invention with brushless magnetization; Fig. 12 shows a block diagram of an asynchronous machine according to the present invention with wound rotor and slip rings; Fig. 13 shows a block diagram of a control system for an AC machine according to the present invention; Fig. 14a shows a block diagram of an electric power plant with two alternating current machines according to the present invention; Fig. 14b shows a block diagram of communicating electric power plants; Fig. 15 shows a fate diagram of a control method for an AC machine according to the present invention; Fig. 16 shows a fate diagram of a protection method for an AC machine according to the present invention; and Fig. 17 shows a fate diagram of a control method for an electric power plant according to the present invention.

DETAILED DESCRIPTION AC machines can be used under different operating conditions, emitting or absorbing different active and reactive power. I ñg. 1a shows an equivalence diagram for a synchronous machine in stationary operation. In this case, the difference in reactance between the direct and the transverse axis is disregarded, ie. it is assumed that you have a round rotor. A machine with pronounced poles does not have a corresponding scheme, with the basic principles of the present invention nevertheless working for such machines as well. IA denotes the stator current and jXs denotes the synchronous reactance 2. A pole voltage Us is applied to the connection terminals and an internal magnetomotor force EA, which is controlled by the rotor current IF, is formed in a principal voltage generator 1.

Figure 1b shows a corresponding capability diagram. P denotes the active effect and Q the reactive effect. In Figure 1b, it has been assumed that the I '' pole voltage assumes its rated value Us. The current in the windings has 2:11: specified rating IFN and IAN, which must not be exceeded. These benchmarks IFN and IAN get in ñg. lb is represented by the circular arcs 6 u-u- vw.- v -. 516 šIÛS and 7. Thus, the permitted operating conditions are limited to an area where both IFSIFN and IASIAN. This means that area 3 is not allowed because IA is restrictive and area 4 is not allowed because IF is restrictive. According to IEC 34-1, sect. 9, a synchronous generator with apparent rated power SN and its rated power factor cos dm is marked. From these data, active and reactive rated power can be calculated (PN or QN). reasoning can be applied to synchronous motors. Any control of the machine's Corresponding operating conditions is thus limited to an area 5. An operating condition is given by the effects Pi and Qi, which are within the area 5.

A change in the pole voltage Us to the machine changes the capability diagram, which affects the efficiency of the method, but not the principle of the method.

Since the speed of the machine is assumed to be constant, ventilation and friction losses are normally constant as well. Although the pole voltage Us can vary, this has very little effect on the excitation losses in the machine.

The machine is then limited as indicated in fi g. lb of the rated values of the stator and rotor currents IAN and IFN, respectively.

If the machine operates at rated power PN and QN, it is quickly realized that an increase in the reactive power Q cannot take place without exceeding the rated currents IAN or IFN. The only way to increase the reactive power Q, is to simultaneously reduce the active power P, something that is usually not sufficient. The margins within which the active and reactive effects can be varied are in practice very limited with this approach.

Thus, as discussed above, the temperature of the rotor windings in an AC machine is often a limiting parameter of the AC machine's ability to produce electrical torque as well as its ability to produce reactive power via the stator winding to the power grid. Limits for temperatures and currents are set to protect the machine against destructive overload. Existing AC machines have often a large thermal margin by the designer built into U U U U U u u uu uu uu uu oooo uu v v u u u u u u u u u u u u u u u u u u uu u u u u u u u u u u u u uu u u u u u u iii ii; i í 6 ::: ät i I I i I f 9 9 Û 5 u u u u u u u u u u u u u u - u n 0 Å 4 u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u.

The following is a description of the thermal utilization of the insulation and what margins are normally available in a large AC machine and which can be utilized by the present invention.

The insulation in AC machines with conventional insulation is divided into temperature classes that indicate how high a temperature is allowed. For rotating machines, these are described in IEC publication 34 "Rotating electrical machines", sect. 7, "Thermal performance and tests". In addition, large machines often have their own customer specifications that place additional demands on the temperature in the winding insulation in different operating modes. Maximum temperature in the winding insulation in the stator for the different classes is given in Table 1.

Class Maximum temperature Temperature difference to coolant 105 ° C 65 ° C 130 ° C 90 ° C l55 ° C 1 15 ° C 180 ° C 140 ° C I'11CU> Table 1. Insulation classes for indirect lift-cooled rotary machines when the temperature is measured with a thermometer. Maximum allowable temperature varies slightly with measurement method.

For air-cooled electric generators, it is normally a requirement that the machine be able to operate with a temperature on the cold cooling air of up to 40 ° C. The machine should then be dimensioned based on a temperature increase from this. The same applies largely to large industrial engines. The last column in Table 1 therefore shows the temperature difference to the maximum temperature coolant that should be used in calculations. The actual temperature of the cold cooling air is in many cases colder. An open - air machine I - ïço 516 408 ventilation uses the air in its surroundings for cooling, or it may have an air intake for the cooling air. This normally means that the temperature of this air at least during certain periods during the day thus allowing an increase or the year is much colder. You can increase the temperature in the machine without exceeding the absolute limit values in table 1. For machines with closed ventilation, the water temperature to the air cooler will similarly vary during the year or day. The same will apply to machines with direct water cooling, ie. where water is led into live conductors and / or laminated parts of the machine.

For large AC machines that are built in small series, due to uncertainty in the dimensioning data, you want to dimension the machine to work with a temperature that is slightly below the specified temperature. This is attributed to the costs associated with redesign and rebuilding if the temperature limit is exceeded.

For some machines, such as large electricity generators, the customer wants the machine to be designed for a temperature class lower than what the insulation can withstand, e.g. that the machine is words with windings for class F, while it is used thermally after class B. This is to have an extra security in case of temporary faults and to be able to take care of increased long-term effects that were unknown at the time the machine was delivered and put in Operation.

For electric generators, the price is determined partly on the basis of the efficiency of the machine. For a supplier, it is therefore important to optimize the machine with regard to losses. It can therefore on some occasions be economically optimal to make a machine that is used in this way. that losses are reduced.

This normally leads to the machines getting colder than what is allowed according to the temperature classes.

The specified temperatures for each temperature class apply to continuous operation. For intermittent operation, a higher temperature can be allowed for a short time without the insulation being destroyed. For organic insulation, it is normally assumed that the service life is halved for every 8-12 ° C as the operating temperature is increased. This is illustrated in ñg. 2b. For an increase in the operating temperature of AT, the service life decreases from to to t1. This can also be expressed as t, = to - e- (mzßï), where r assumes the value 8-12 ° C. One can thus for shorter periods, e.g. for 30 minutes or one hour, raise the temperature above the maximum temperatures in Table 1 without significantly shortening the total life of the insulation.

From this it is realized that through standard setting, customer requirements, uncertainty in dimensioning and inherent tolerance in insulation margins, there is today for large electricity generators and motors a significant thermal capacity that can be temporarily used to increase the power on the machine. This is illustrated in fi g. 2a. The diagram shows a number of current levels Io to 14. lo corresponds to the calculated rated current, taking into account temperature class, maximum coolant temperature and dimensioning margins, ie. the normally specified maximum current. If direct measurement of the temperature is performed, no dimensioning margins need to be used and a current I1 can be used without risk of damage. In addition, if a cooling medium with a temperature lower than 40 ° C is used, the current can be increased further Iz without exceeding the desired temperature of the insulation. In addition, if the actual -z - š temperature resistance of the material is used, instead of the maximum temperature for the insulation temperature class, there is an additional margin to utilize and a current Is can be used. This current can thus be used in continuous operation without the insulation aging faster than calculated. For shorter periods of time, the current can be further increased, to a value I4, when a deliberate power increase is replaced by a faster aging of the insulation material.

However, the value 14 should be kept below an absolute maximum level, above which the risk of material damage within a short time is considered to be too great. bšo 516 408 šßåñšä $ ¥ @ ¥ §;? ¥ ë? “p 1, .... - - - There are today a large number of AC machines installed in power plants, which were built several decades ago and which are gradually undergoing renovations. The development of insulation materials over the years has led to opportunities that, in dangerous tracks, it is possible to fit more copper and / or more current in the windings because the voltage strength and / or temperature class has increased.

In connection with the renovation of a non-hazardous AC machine, you can thus increase the rated power of the machine. This is sometimes taken out as increased active power by rebuilding turbines and other mechanical arrangements. It can also be taken as an increased reactive effect, whereby in particular the ability of the rotor winding / field winding to thermally withstand current is used.

Renovated machines thus constitute outstanding objects for applying the present invention to.

Further discussions about rotor temperatures can be found e.g. i "Rotor heating as an indicator of system voltage instability", IEEE Trans. on Power Systems, Vol. 10, no. 1, Feb. 1995, p. 175-81.

Some examples of situations where AC machines can be overloaded will now be described, in order to clarify the possibilities for temporary changes of the power conversion in an AC machine.

First, it is described how an AC machine can be overloaded with reactive power when operating as a generator. Figure 3 shows how the continuous operating state of the machine changes when reactive power production is increased from Q2 to Qs for a synchronous machine with maintained active power production P2. The temporary limitations for stationary operation which the machine has when the insulation is used thermally are shown by the arcs 8 and 9. These limitations 8, 9 can be estimated from the continuous or intermittent temperature measurements. Since the measurements are updated continuously, the restrictions can also be updated continuously, e.g. in case of unexpected external effects: Inna f - ïgo 151613408 occurs, such as a sharply elevated cooling water temperature. The total effect can thus be laid outside the area 5 without risk of damage to the insulation, which was not possible in the state of the art. In this respect, it is possible to still deliver the same active power to the electricity power grid, despite an increased reactive power consumption. The increased reactive power output will result in an increased temperature in the rotor and stator windings, but this temperature increase is closely monitored and thus can not lead to unwanted material damage. In the case shown, where the reactive power Qs is taken out, the continuous operation of the rotor current is limited.

Figures 4a and 4b show how the temperature in the windings of the rotor and stator, respectively, increases during a period when the machine delivers extra reactive power.

SN indicates the nominal temperature for the respective windings, SM indicates the maximum temperature for shorter overloads for the respective windings, SB indicates the initial temperature for increased power consumption started and SE indicates the temperature at a steady state and windings before it during increased power output. The figure shows three time intervals. The first corresponds to continuous operation. The time interval Ati corresponds to a temperature increase phase and the time interval Atz corresponds to a stationary phase at elevated temperature. The intervals are described more below.

The rotor current is regulated according to a curve, which is shown in Figure 5a, whereby a reactive power output according to ñg. 5b is obtained. The rotor current is increased in the range Ati to a temporary value IT, slightly above that allowed for static conditions. The reactive effect obtained then follows a similar curve, according to fi g. 5b. The temperature of stator and rotor windings will then gradually increase according to conventional heat conduction principles. When the maximum temperature for either stator or rotor winding is reached, the rotor current is reduced to a value Im, which is adapted to keep the temperatures constant at this higher level. This range is indicated by Atz. In this case, it is the rotor windings which first reach the maximum temperature and which therefore have a limiting effect, in accordance with fi g. 3.: # 0 51614408 Thus, when the monitoring system, enabled by the continuous or intermittent temperature measurement, shows that the rotor winding temperature SR has reached its maximum value SM, the rotor current IR is regulated down again to a value IF2, which keeps the rotor winding at a constant high temperature in close to the maximum SM. During the interval Atz, the reactive power Q assumes a value that exceeds the nominal SN. This utilization of the temperature margins in the machine means that the service life of the insulation material can be shortened. Atz should therefore be limited in time, after which the rotor current IR is reduced again to allow the temperature to return to a level below the nominal SN. The duration of the Atz interval can typically be from 10-15 minutes up to an hour, or until the temporary need for reactive power is reduced or eliminated.

The temporary limitations of rotor and stator current shown in fi g. 3 applies to stationary or semi-stationary conditions. During the transient phase Ati where the temperatures are regulated up, the currents can be further increased, since the machine is then not in thermal equilibrium. This is not shown in the diagram in fi g. 3, but it is obvious to a person skilled in the art that such a further increase according to fi g. 5a can happen.

Figure 6a shows a reformulated equivalence scheme for an asynchronous machine with wound rotor where XM is the excitation reactance, while XLs denotes the leakage reactance in the stator winding reactance and is denoted XA. The IR value of the rotor current and the stator winding. The sum of these constitutes phase is referred to the stator side of the machine. It should be noted that unlike the equivalence scheme in fi gur la, fi g is. 6a is also valid when the rotor rotates asynchronously.

Figure 6b shows how the continuous operating state of an asynchronous machine changes when active power production from P4 to Ps. The limitations that the machine has when the insulation is used thermally are increased temporarily with the arcs 8 and 9. These limitations 8, 9 can, as above, be estimated from the continuous or intermittent temperature measurements. n ø n u no c 516 lgos The total effect can thus also here without danger of damage to the insulation be laid outside the area 5, which was not possible within the state of the art.

In this respect, it is possible to increase the delivery of active power to the electricity grid.

The increased active power output will result in an increased temperature in the rotor and stator windings, but this temperature increase is closely monitored and can therefore not lead to unwanted material damage.

A time course for a controlled overload is shown in Figures 7a and 7b.

By controlling the rms current's effective value according to fi g. 6b, an increased active power can be obtained during a time interval Ats, as shown in fi g. 7a. This active power corresponds in this example to the estimated power which during stationary operation gives a maximum temperature for the stator. After the time interval Ats, the power is regulated down back to normal. I fi g. 7b shows the temperature response in the stator winding. During the interval Ata, the temperature rises gradually towards the expected final value SM, but does not really reach before the time interval is over. In other words, the stator temperature always stays within permissible temperature values.

Figure 8 shows how the continuous operating state of the synchronous machine changes when reactive power production is temporarily increased from Qß to Q? in engine operation. The temporary limitations for stationary operation that the machine has when the insulation is used thermally are shown by the arcs 8 and 9. These limitations 8, 9 can, as above, be estimated from the continuous or intermittent temperature measurements. The total effect can thus also here without danger of damage to the insulation be laid outside the area 5, which was not possible in the state of the art. The operating point can even, as in this case, be located outside limits 8 and 9 for a limited time, thanks to a continuous or intermittent temperature monitoring. _ _ In this respect, it is possible to increase the delivery of reactive power to the electric power grid. i. .3: O The increased reactive power output will result in an increased temperature i in the rotor and stator windings, but this temperature increase is closely monitored and thus can not lead to unwanted material damage. sauna Qm o n w u on 516 408,, m A time course for a controlled overload is shown in Figures 9a and 9b.

By controlling the rotor current according to fi g. 8, an increased reactive power can be obtained during two time intervals At4 and Ats, as shown in fi g. 9a. During the time interval At4, the withdrawal of reactive power is regulated up to a very high level Qv, which gives a very rapid temperature rise in the rotor, as shown in fi g. 9b. This can e.g. correspond to an emergency situation where the electricity grid risks collapsing due to lack of reactive power. As the rotor approaches its maximum temperature SM, the reactive power Q must be limited, so as not to cause acute damage to the rotor. Therefore, the reactive power is regulated down when the electric power grid has hopefully had time to recover or when another machine takes successively during the time interval Ats, over the production of reactive power. I fi g. 9b shows the temperature response in the rotor winding. During the interval At4, the temperature rises sharply, but when the reactive power is regulated down, the temperature eventually begins to fall to return to a normal value. In other words, the rotor temperature always stays within the permitted temperature values despite a very strong temporary load.

The time course when the power to the AC machine is temporarily increased can be varied in relation to the previous description. In a general embodiment, the output power can be varied arbitrarily, provided that the measured or estimated temperature is kept under control.

It is further obvious that a combination of regulation of active and reactive effect can be made. One can thus e.g. reduce the active effect in order to further increase the reactive effect. It is also possible to maintain the ratio between active and reactive power, but to increase the total power yield.

The method can thus be used in principle to increase or decrease the active or reactive power for synchronous or asynchronous machines in motor or generator operation. However, those skilled in the art will recognize that some of the cases lead to unfavorable operating conditions for the machines and are of less practical importance, although in principle possible. The most useful case is judged to be reactive overload of an electric generator. The present invention which uses the thermal material utilization of an alternating current machine can be utilized by various types of instrumentation to measure or estimate the temperature of the insulation in the stator and / or rotor. The controlled time course of the increased power conversion can be varied in different ways according to the basic idea that the present invention conveys.

The present invention presupposes that during operation the temperature of the stator and / or the rotor winding is known with a sufficient accuracy and time resolution. The temperature of the insulation in the rotor and / or stator winding can be determined in different ways depending on the accuracy required.

Fig. 10 illustrates a sketch of how the method can be used for a synchronous machine with static magnetization. A rotor 14, arranged around a rotating shaft 10, is provided with windings 12. The rotor rotates inside a stator 28 with stator windings 26. A power transformer 46 supplies the stator windings 26 with current through lines 44. A further, smaller, power transformer 42 provides an alternating current. DC converter 36 with current through lines 40. The direct current from the AC-DC converter 36 is passed over brushes 38 to slip rings 24 arranged on the rotor shaft 10 and further to the rotor windings 12 via lines 22. This is in principle a synchronous machine with static magnetization according to the prior art. . the temperature in the windings continuously or intermittently. The temperature in According to the present invention, the windings are measured in the presented embodiment directly by measuring during operation. This is accomplished by placing one or more sensors in the winding or winding insulation ("Embedded Temperature Detector", ETD). Thus, rotor temperature sensors 16 are placed in or near the rotor windings 12 and stator temperature sensors 30 in or adjacent to the stator windings 26. The sensors are placed at positions that have been found critical for winding due to analysis and / or experimentation. The sensors can be realized by placing e.g. resistive thermometers (Pt100 elements or similar thermocouples) in the stator winding 26 and / or the rotor winding 12. For AC machines over 5 MVA, it is a requirement in relation to IEC 34 to provide the stator winding 26 with ETD for thermal protection of the machine. Equipping the stator winding 26 with a resistive thermometer is a preferred embodiment when using the present invention. This therefore provides a very good control of the temperature and a safe and accurate material utilization of the machine.

The signals from the rotor temperature sensors 16 are collected via a measuring unit / signal processor 18 which is connected to a transmitter 20 for wireless communication, mounted on the rotating shaft 10. A corresponding receiver 21 for wireless communication is mounted at the stationary parts of the machine. The communication is described in more detail below.

The signals from the stator temperature sensors 30 as well as the measurement results transmitted to the receiver 21 are collected via a measuring unit / signal processor 32 the results to one which forwards processing unit 34.

The processing unit is preferably a microprocessor.

The processing unit 34 can then control the AC-DC converter 36 so that a suitable rotor current is obtained.

Fig. 11 shows a synchronous machine according to the present invention, where brushless magnetization is used. Similar parts as in fi g. 10 has been denoted by the corresponding reference numerals and will not be described again.

Only the new parts that are important for the function are described below. Instead of supplying the rotor windings 12 with a current via slip rings, a current is provided by a magnetizing machine 58 arranged on the rotor shaft 10.

The AC-DC converter 36 supplies a winding 50 on the stator 48 of the magnetizer. Upon rotation of the rotor shaft 10, a current is obtained in the windings 52 of the rotor 54 of the magnetizing machine. 1:30 516 408 = ::; = ::; § ";: = 1; .j'1 :;"; The current is converted by a direct current-alternating current converter 56 and fed to the rotor windings 12. In the same way as before, temperature sensors are arranged at suitable places in or near the windings.

Fig. 12 shows a slip ring based asynchronous machine according to the present invention. Similar parts as in fi g. 10 has been denoted by the corresponding reference numerals and will not be described again. Only the new parts that are important for the function are described below. The power transformer 42 here supplies a frequency converter 60 with current. The frequency converter 60 in turn transmits alternating current via brushes 62 and slip rings 64 to the rotor 14. provided with temperature sensors 16 and 30. However, the rotor temperature sensors 16 are in This machine is similar to this embodiment connected to a further slip ring 66 on the rotor shaft 10, and transmits the measurement information to a brush member 68 on the stationary part of the machine.

The method of the present invention can be used by monitoring the temperature of the insulation also by indirect measurement. Indirect measurements combined with calibration measurements of the relationship between measured indirect quantities and temperature can in some cases provide sufficient accuracy. Rotor current is in some cases a suitable quantity that can be used for indirect temperature measurement. For an AC machine, when the machine is not in normal operation, a heat test can be performed, where the relationship between stator and rotor current and temperature is measured. Then, during operation, measurement of current can be used to estimate the temperature. Since the temperature in e.g. the stator winding is dependent on the current in both the stator and rotor winding, the heat tests should be performed with different combinations of stator and rotor current. As it can be difficult to load the machine with its rated power or higher during the heat tests, the refrigerant will be able to have a different operating temperature than during the test. This should be taken into account in an uncertainty when calculating the temperature based on measurement of current in the rotor and stator. Indirect measurement therefore generally gives a slightly poorer accuracy. Other quantities that can also be used for an improved temperature estimate are e.g. refrigerant temperature and previous temperature measurements.

Equipping the rotor winding with resistive temperature sensors is a preferred embodiment when using the present invention for both synchronous and asynchronous machines. However, for the rotor winding on a synchronous machine, the average temperature can be determined with good accuracy by measuring current and voltage to the rotor winding. For an asynchronous machine, this method is a little less useful because the leakage reactance and lag affect the connection. Other, more complicated methods should then be used which introduce a current in the winding with a different frequency. However, this requires a thorough analysis of how the machine responds to currents at different frequencies.

For AC machines with a wound rotor, the control unit that controls the rotor current is traditionally stationary on the outside of the machine. With brushless magnetization of a synchronous machine, the rotor current is generally regulated by controlling the magnetization of the magnetizing machine, as shown in fi g. 11. With static magnetization of a synchronous machine, the normal DC-DC converter is located outside the machine and the current is transmitted via slip rings to the rotor winding, as shown in fi g. An asynchronous machine with a wound rotor is normally designed with slip rings so that the rotor winding can be supplied with an alternating voltage or current from a frequency converter located outside the machine. A common feature of these alternatives is that when the control unit for the rotor current is located outside the machine (and not on the shaft) a communication line between rotor and stator is needed. This can be realized in your ways depending on the requirements for the number of measuring points and accuracy and what _ _ is to be measured.

: .. I: 30 n For measuring rotor temperature, it is a preferred embodiment to mount 2 - 10 temperature sensors (eg Pt-100 elements) at selected locations in the rotor winding and to transmit the measurement signals to the stationary m. Í: ____________ »Unan *, _: åo øøøø oo 516 408 _ _21 the control unit via a digital radio connection between stator and rotor, as shown in 10 and 11. Energy for the communication line and the measuring system is taken from a stabilized power supply which is located on the shaft of the machine and which takes its energy from the rotor winding.

Alternatively, analogue communication can be used. The communication can then be done wirelessly or, as shown in fi g. 12, via slip rings.

In the embodiments described above, measurement data regarding winding temperature is sent to a processing unit. This processing unit is used in an embodiment of the present invention to control the rotor current. This can be easily done by, as indicated in ñgurema -12, connecting the processing unit to a converter or power generator.

The temperature data can also be used to control stator currents. In a simple realization of this control method, the control of the current is based only on the measured temperatures and externally supplied data on the desired operation. However, other information may also be useful in controlling the currents. Such information can e.g. consist of calibration measurements, similar to those needed for the use of indirect temperature measurement.

In recent decades, there has been a clear trend to miniaturize electronics for signal processing. Telecommunications can be said to be almost completely digital today in its essential parts. Signal processing in control and regulation circuits has also been miniaturized and it is easy to implement internal digital signal processing in e.g. converters, both AC-DC converters and AC-DC converters. Performing such circuits with analog technology does not add value, since the digital resolution in both amplitude and time is large enough.

Digital communication is also preferred due to other aspects such as the ability to set and tune the parameters of the control circuits remotely. An initial parameter setting can thus be replaced during operation to a modified parameter setting based on previous operating data. un: n: n I a a 0 a n _30 o o n v al: 51622408 A preferred embodiment of the control system is shown schematically in fi g. 13. A processing unit 100 is arranged to receive measurement results from temperature measurements from stator and / or rotor temperature sensors 102 and 104, respectively. The processing unit 100 is further connected to a control means 108, which relates to control of stator and / or rotor current.

The processing unit 100 in this preferred embodiment is also connected to a storage unit 106 for temperature data. This temperature data may include simple limit value information that can be supplied by manual input, such as information on nominal and maximum stator and rotor temperatures. The data may also include measured and / or estimated relationships between rotor and stator current, and rotor and stator temperature at steady state. Such data can e.g. applied during calibration runs.

Furthermore, the measured temperatures during operation can be stored and processed gradually, in order to update and correct such relationships. Data describing the temperature history of the rotor and stator can also be stored, for use in deciding how hard the machine can be run.

A processing unit 100 having access to a well-stocked database of temperature data can be programmed to provide a control of a material margins. The contents of the database can be used to calculate the total temperature margin available in an AC machine at any suitable time for the very intelligent machine. In an emergency, e.g. if a voltage collapse on the electricity grid is dangerously close, such temperature margins can then easily be used to temporarily save the situation. According to the present invention, a conscious operation of the machine above its rated values can take place due to the reliable monitoring of the temperature event in the machine.

The processing unit 100 can also be used to realize an och visible and intelligent protection or limiting device for the machine. If something abnormal occurs, such as a faulty mains voltage, a normal oøøøø o 516 408 is changed. 23 operating condition of the machine. By being able to detect e.g. time derivative of temperatures in the windings, an error can be quickly detected. This can also be used as a pure indication of certain mains faults, as described in "Rotor heating as an indicator of system voltage instability", IEEE Trans. on Power Systems, Vol. 10, no. 1, Feb. 1995, p. 175-81. In order to avoid a machine being switched off completely, and thus aggravating the condition of an already unstable electricity grid, in such situations the machine can be controlled to run in another operating condition, which does not risk heating the stator or rotor to impermissible temperatures. In addition, in such situations one could deliberately let the machine become hotter than the nominal temperature, while the error causing the heating is rectified. However, it must always be ensured that the temperatures always remain below a maximum level, where there is a risk of damage to the machine even during a shorter operating period.

A control of the machine, to avoid shutdown, can normally be driven to a certain limit, when e.g. the ratio between active and reactive power becomes so abnormal that the machine risks becoming unstable. A soft and well-regulated shut-off can then take place.

The concept of information on thermal material margins can also be implemented at the power plant level or the power grid level. In this application, electric power plant refers to a plant comprising a group of alternating current machines, which are located within a limited area and are operated in a coordinated manner and which preferably belong to the same operator. An electric power plant according to the above definition can typically consist of a number of AC machines, transformers, wires, cables, busbars, disconnectors and switches and associated measuring and steel devices.

For the purposes of this application, "electricity network" means a network of interconnected power plants which are typically spread over a wider geographical area; ' ': 3 0 area.

Figs. 14a and 14b schematically show an electric power plant, in which a number of alternating current machines 202 are included. Together with control equipment for 1 6244 0 8 i ': É ": ï: °:" :: "::": ° ff' “Éiziï machine, the AC machine 202 constitutes a machine unit 211. Each machine unit 211 forms part of an electric power plant (according to previous definition), which is connected via power lines or cables 201 to an electric power grid 200. The machines are equipped with temperature sensors 203 according to the present invention, and temperature data are collected by a control unit 204 at each machine. The control unit 204 logically comprises the processing unit in the previous description. A group of machine units 211 is generally controlled by an operation control unit 206. According to the present invention, a number of communication devices 205 are established between the control units 204 for the machines and the operation control unit 206. If an error occurs in the network, the operation control unit 206 may transmit information to the various control units. coupled with a desire to be able to temporarily operate the machines in a special way. The respective control units 204 can in turn inform the network monitoring unit 206 of their current operating condition and if any tendencies to network instability have been detected.

Such a configuration becomes particularly powerful if the operating line unit 206 has access to the current temperature condition of the various machines, i.e. to the temperature measured values or associated quantities calculated therefrom. In the same way as for the control of each individual machine, additional temperature data is also interesting. If the operation control unit 206 has access to both the current temperature for the different machines and stored information about how large temperature margins are in each of the machines, this can be used to continuously update the operating plans for how to 'z-'É be able to handle different types of faults or operating situations. If the operation control unit 206 knows that a certain machine has a large margin to utilize, this can be requested in the event of an error situation, in order to perhaps be able to BO save other machines with a smaller margin left in the network.

A database with temperature data for the various machines is thus preferable. This can be arranged in connection with each control unit, as anno »24.30 a ø v n a. 516 408. Described above. The temperature database or a copy of it can also be made available in the operation line unit 206, so that no temporarily interrupted information lines can jeopardize the control possibilities. The operations management unit 206 therefore preferably comprises a memory means for storing the database.

The information in the database can at a later time be used for analysis to increase knowledge of the plant's behavior during both normal operation and in the event of disturbances. The data can also be used to analyze the plant's efficiency and to be able to plan future operating methods.

The database thus includes both historical information concerning the previous operation of the machines, but also information needed to achieve a suitable control of the machines. The database can e.g. contain the machine's response to previous disturbances.

The network communication devices 205 can operate according to different communication methods according to the prior art. Such methods can be based on fixed connections in the form of e.g. metallic wires or ñberoptics, or on wireless transmission, such as radio or radio link. When interconnecting produktion your production management units, a network of communication devices can be built up. Such a network contributes to alternative communication paths, which can be used in cases where one or more communication devices for some reason are not available.

Through appropriate combinations of redundant communication paths and storage of information in databases, the production management unit 206 can perform calculations and updates of operating plans, for example by extrapolating the condition of machines and using the results of self-care calculations, even if some communication devices and / or sensors do not currently work.

The possibility of building a reliable network is of particular importance, for example in strained operating situations or during operational reconstruction after a major operational disruption.

As previously pointed out, the concept of utilizing construction margins can also be implemented at the electricity grid level. Control and annuity bodies: šfw 516 408, 26 Electricity grid monitoring, a grid monitoring unit 212, is responsible for the operation of the electricity grid in general, and may in the same way as described above communicate with the electric power plant operating units 206 or individual electrical machines 202, to obtain information on possible margins. These margins can then be used for an optimization of larger areas or the total operation of the electricity grid.

The information transmitted from an electric power plant or individual electrical machine to a grid monitoring unit 212 at the power grid level should preferably be of a more summary type than lower down in the hierarchy. An electricity network operator is primarily interested in knowing the available power resources in various places in the network and the possible costs associated with utilizing these. The detailed conditions regarding the individual temperature margins of the machines are of less interest, especially for a hierarchically superior electricity network operator. It is also in the interest of an operator of an electric power plant to be able to limit the exchange of information, since some of the available information can be used as a means of competition against competing operators.

The tasks of the grid monitoring unit 212 consist of ensuring the possibilities for a safe and economically optimal operation of the electricity power grid.

This may include communication of both information exchange and setpoints as well as control signals to both production line units 206 and power grids 200. Under normal operating conditions, the control of production line units 206 may be based on economic control signals, while it may be necessary to send direct control commands in case of severe power outages. and continuous operation. The exchange of information between the network monitoring unit 212 and other units should take the form of messages, which may, in addition to the address and message, contain security keys (encryption) to restrict who has the right to access the information. By utilizing different authorization criteria for different units (users) in the communication system, sufficient confidentiality against unauthorized dissemination of information can be obtained.

The ability to determine what information each user has access to -uuøn: na:, 3O oooo nu 516 408 = ïïš * ffš-ê "'=; ïï; - - =' I _27.... .. .. ... reduces the risk of disseminating sensitive information and enables, for example, partners to have access to more information than other completely external parties.

Thus, a preferred embodiment of an operating line unit 206 in an electric power plant comprises a means for external communication.

This means is arranged to receive and interpret messages from extreme devices, such as e.g. an operator of an electric power grid and partly send selected information to the extreme units.

The present invention can of course be used when installing new equipment in an electric power grid. However, the methods and devices are of such a nature that they can also be used to advantage in the renovation of permanent equipment. In many cases, renovation of old equipment leads to large thermal material margins, if turbines or other mechanical arrangements can not be upgraded to the same degree, whereby these machines can be used to advantage for control purposes.

Fig. 15 schematically shows the control method for a rotary electric machine according to the present invention. The process starts in step 300. In step 302, the temperature of the stator and / or rotor windings is measured continuously or intermittently. In step 304, this measurement data is used to control the continued operation of the AC machine, so that a terinically controlled optimization of the power conversion is obtained. The process ends in step 310.

Fig. 16 schematically shows the protection method for a rotating electric current machine according to the present invention. The process starts in step 300. In step 302, the temperature of the stator and / or rotor windings is measured continuously or intermittently. In step 306, this measurement data is used to control the winding currents so that the temperature of the winding series is regulated within permissible values. The process ends in step 310.

Fig. 17 schematically shows the control method for an electric power plant according to the present invention. The process starts in step 300. In step 302, the temperature of the stator and / or rotor windings in AC machines in the electric power plant is measured continuously or intermittently. In step 308, this measurement data is used to control the power conversion of the electric power plant in a controlled and optimal way. The process ends in step 310.

Those skilled in the art will appreciate that various modifications and changes may be made to the present invention without departing from the scope of the invention as defined by the appended claims.

Before 516 years) s g __. = .. E_š..š¿¿ _ ny;

Claims (35)

10 15 20 25 30 516 408 llq '' ° '- "-' J. J. J? NYA PATENTKRÅV A method of controlling the power conversion of a rotating alternating electric machine having a stator (28) and rotor (14) with windings (26, 12) having fixed insulation, characterized by the steps of direct measurement, continuously or intermittently, of the temperature at critical points for the rotor windings (12) and / or their insulation; and optimizing the power conversion of the AC machine in a thermally controlled manner by controlling the continued operation of the AC machine by using the measured temperature as the control parameter for rotor current. The method according to claim 1, characterized by the further step: direct measurement, continuously or intermittently, of the temperature at critical points for the stator windings (26) and / or its isolation, the optimization step being performed using also the measured stator winding temperature. The method according to claim 1 or 2, characterized in that the optimization step in turn comprises the step of controlling the rotor current for a time-limited period to a value which exceeds its rated value. The method according to claim 3, characterized in that the optimization step further comprises the step of controlling the stator current for a limited period of time to a value exceeding its rated value. The method according to any one of claims 1 to 4, characterized in that the optimization step during generator operation changes the ratio between the drawn active power and the drawn / applied reactive power. The method according to any one of claims 1 to 5, characterized in that the optimization step in generator operation changes the magnitude of the drawn / applied reactive power. 10 15 20 25 30 516 408 'ao a-a: es The method according to any one of claims 1 to 4, characterized in that the optimization step in motor operation changes the ratio between applied active power and withdrawn / applied reactive power. The method according to any one of claims 1 to 4 and 7, characterized in that the optimization step in motor operation changes the magnitude of the drawn / applied reactive power. The method according to any one of claims 1 to 8, characterized in that the optimization takes place so that a predetermined maximum value for the temperature of the rotor windings (12) and / or its insulation is never exceeded. The method according to claim 9, characterized in that the optimization takes place so that a predetermined maximum value for the temperature of the stator windings (26) and / or its insulation is never exceeded. The method according to any one of claims 1 to 10, characterized in that the optimization takes place so that the nominal value of the temperature of the rotor winding (12) and / or its insulation is only exceeded for a limited period of time. The method according to claim 11, characterized in that the optimization takes place so that the nominal value of the temperature of the stator windings (26) and / or its insulation is only exceeded for a limited period of time. The method according to any one of claims 1 to 12, characterized in that the control of the continued operation of the AC machine uses calibrable parameters, the method further comprising the step of: modifying the calibrable parameters based on previous operating data. 10 15 20 25 30 5 1 6 4 0 8 A ': ax A method for controlling power conversion in an electric power plant, comprising at least one rotating electric machine (202) having a stator and rotor with windings having fixed insulation, characterized by the steps: direct measurement, continuous or intermittent, of the temperature of critical points for the rotor winding of the AC machine and / or its insulation, and optimization of the power conversion of the AC machine (202) in a thermally controlled manner, when the electric power plant has an undesirable distribution of active and reactive power conversion, by controlling the continued operation of the AC machine using as control parameter for rotor current. The method according to claim 14, characterized in that the optimization of the power conversion takes place based on stored data on the temperature margins of the AC machine (202). The method according to claim 14 or 15, characterized by the further step: communicating data regarding the operation of the AC machine (202) from the control unit (34; 204) to an operating line unit (206) belonging to the electric power plant. The method according to claim 14, 15 or 16, characterized by the further step: communicating instructions and / or requests regarding the operation of the AC machine (202) from the control line unit (206) to the control unit (34; 204). The method according to claim 16 or 17, characterized in that the communication between the operating line unit (206) and the control unit (34; 204) takes place via metal lines or optical fibers. 10 15 20 25 30 516 4 0 8, # 52 The method according to claim 16 or 17, characterized in that the communication between the operating line unit (206) and the control unit (34; 204) takes place via radio or radio link. The method according to any one of claims 14 to 19, characterized by the step: transmitting messages between the operations management unit (206) and external units. A rotary electric AC machine comprising a stator (28) with windings (26) having fixed insulation, a rotor (14) with windings (12) having fixed insulation and a control unit (34; 204) for controlling rotor current, and characterized of a rotor temperature sensor (16; 203) arranged at the rotor windings (12) and / or its insulation, which communicates with the control unit (34; 204), whereby signals from the rotor temperature sensor (16; 203) representing temperature values form the basis for controlling the rotor current. The rotary electric AC machine according to claim 21, characterized in that the control unit (34; 204) is arranged for controlling stator current; and by a stator temperature sensor (30; 203) arranged at the stator windings, which communicates with the control unit (34; 204); wherein signals from the stator temperature sensor (30; 203) representing temperature values form the basis for controlling the stator current. The rotary electric AC machine according to claim 21 or 22, characterized in that the control unit (34; 204) is arranged at a stationary part of the AC machine and that the AC machine further comprises communication means (20, 21; 66, 68) for transmitting information from the rotor temperature sensor (16, 2Q3) to the control unit (34; 204). The rotary electric AC machine according to claim 21, 22 or 23, characterized in that the communication means is a wireless communication means (20, 2 1). The rotary electric AC machine according to any one of claims 21 to 24, characterized by a storage unit (106) for storing temperature data for the AC machine. The rotary electric AC machine according to claim 25, characterized in! that the temperature data includes at least one of the following types of data: nominal stator temperature, nominal rotor temperature, maximum stator temperature, maximum rotor temperature, rotor current and rotor temperature at steady state, stator current to stator temperature at steady state, rotor temperature history, and stator temperature history. An electric power plant comprising a plurality of rotating electric shafts (202) having a stator (28) and a rotor (14) having windings (26; 12) having fixed insulation, a power line assembly (206); and characterized in that at least one of the rotating electric current machines (202) comprises a control unit (34; 204) for controlling rotor current and a temperature sensor arranged at the rotor winding (12) and / or its insulation. (16, 30; 203), which communicates with the control unit (34; 204), whereby signals from the temperature sensor (16, 30; 203) representing the temperature maintenance form the basis for the control of the rotor current. The electric power plant according to claim 27, characterized by communication devices (205) between the control unit (34, 204) and the operating line unit (206) for transmitting information associated with the signals from the temperature sensor (16, 30; 203). The electric power plant according to claim 28, characterized in that the communication devices (205) comprise physical wires in the form of metal wires or optical fibers. The electric power plant according to claim 28, characterized in that the communication devices (205) comprise means for transmission via radio or radio link. The electric power plant according to any one of claims 27 to 30, characterized by a storage unit (106) for temperature data for the alternating current. The electric power plant according to claim 31, characterized by the storage unit (106) for temperature data is included in the control unit (34; 204). The electric power plant according to claim 31, characterized by the storage unit (106) for temperature data is included in the operating line unit (206). The electric power plant according to claim 31, 32 or 33, characterized in that the temperature data of the alternating current machine comprises at least one of the following types of data: 10 ... »v>» vo 51.6 4.08 jš nominal stator temperature, a oo nu o ~. -an other u c n oo nominal rotor temperature, maximum stator temperature, maximum rotor temperature, relationship between rotor current and rotor temperature at state, relationship between stator current and stator temperature at steady state, rotor temperature history, and stationary stator temperature history. ' The electric power supply according to any one of claims 27 to 34, characterized in that the operating line unit (206) comprises means for transmitting messages to and from external units.