FI116107B - Method and apparatus for magnetizing a clock generator - Google Patents

Description

116107

METHOD AND EQUIPMENT FOR THE MAGNETIZATION OF A PACIFIC GENERATOR

The invention relates to a method according to the preamble of claim 1 and to an apparatus according to the preamble of claim 6 for magnetizing a synchronous generator 5.

The magnetization of a synchronous machine, in particular a synchronous generator, is nowadays arranged in a brushless manner, in which a controlled magnetizing current is supplied via a magnetizing machine to the magnetizing coils. The magnetizing current is produced, for example, by a voltage transformer connected to the mains voltage 10, the secondary voltage of which is regulated by a voltage regulator. In exceptional situations, particularly in the case of short circuits in the mains, when the mains voltage drops substantially, the excitation thus developed is not sufficient.

In the short-circuit situation, in the prior art, excitation is ensured, for example, by 15 separate current transformers which are dimensioned so large that a sufficient level of excitation is guaranteed. The disadvantage of this solution is that it is not possible to adjust the excitation current, but the excitation is determined by the design of the current transformer. On a case-by-case basis, a case-by-case transformer has to be designed and manufactured, which is often not a competitive solution.

20 .:. The object of the invention is to solve the problem described above and to provide an advantageous and; cost-effective magnetization of the synchronous generator to situations where the network voltage is present. ' · *; essentially dropped. The method according to the invention is known according to claim 1; · · The characteristics of the character part. Accordingly, the apparatus according to the invention is known '; · Characteristics of the characterizing part of claim 25. Other preferred embodiments of the invention are known from the features of the dependent claims.

The solution according to the invention reliably provides a suitable level of excitation in short-circuit situations. The solution according to the invention is simple and inexpensive to implement. The same implementation is easily applicable over a wide power range, reducing design and manufacturing costs. In this case, a limited number of standardized short-circuit current transformers can be used, which has a significant impact on the efficiency of the entire production chain. It is also possible to connect the solution according to the invention to the existing 2 116107 generators, since the equipment can be combined with readily available components. Previous installations can also be tuned to a better operating point if the current transformer is incorrectly sized too large. Apart from short-circuiting situations, the invention is also applicable in other exceptional situations, such as when starting large motors, whereby the voltage of the generator tends to fall below the permissible limit.

The invention will now be described with reference to the accompanying drawings, in which: - FIG. .

15

Figure 1 illustrates a magnetizer circuit for a synchronous generator which provides for magnetization under normal conditions as well as a known solution in a short-circuit situation.

The pace generator a 10 is magnetized with the magnetization current Im applied to the magnetization coil 6. A three-phase transformer 20 T1 is connected to the phase conductors of the generator, the secondary winding 1 of which is arranged to supply voltage to the voltage regulator 3. The second secondary winding 7 of the transformer:! · * T1 provides the actual voltage of the generator to the regulator 3.

The current transformer T2 connected to the generator phase S measures the actual value of the current, which is also applied to the voltage regulator. In normal operation, the excitation current Im required by the generator is supplied by the voltage regulator, which is passed through diode 12 to winding 6.

* · * · ♦ '' 25 ··· * In accordance with prior art, three current transformers T3 are provided in the phase conductors R-S-T of the main circuit of the synchronous generator for short-circuit situations. In normal ... operation, the transformer secondary is short-circuited by switch K2, which is controlled by a voltage regulator. Alternatively, switch K2 may also be controlled by a contactor connected to the output of the voltage transformer T1, whereby the contacts of switch K2 will open as the voltage drops enough for the contactor to release. A voltage relay can also be used to control the switch. The current transformers are simple ring transformers having a primary circuit formed by the phase conductor of generator 3 116107 in a manner known per se and without any control means. The current transformer secondary is connected to a rectifier 4, the output of which is connected to supply the excitation coil 6 via diode 14. The current transformer is designed to provide a short-circuit current of three times the rated current for at least three seconds. Higher currents could destroy not only the magnetization apparatus but also the generator itself.

Figure 2 illustrates the characteristics of a prior art solution. Curve 1a depicts the short-circuit current of the generator as a function of the excitation current and curve 2a the characteristic of the current transformer. The generator operating point is located at the intersection K2 of the generator and 10 current transformers. Curve 2b illustrates the characteristic of another current transformer, whereupon the operating point receives the value Ikj, respectively.

Figure 3 illustrates a solution according to the invention. For normal operation, the implementation corresponds to the apparatus of Figure 1 and the corresponding parts are denoted by the same reference numerals as in Figure 1. In the short-circuit situation, the magnetization current is generated in a new way. Accordingly, a control circuit 8 is connected to the secondary transformers 2 whose output is connected to the magnetization windings 6 of the synchronous generator 10. The secondary winding 7 of the voltage transformer T1 connected to the phase conductors R, S AND T of the synchronous generator 10 obtains the actual voltage. The actual voltage value is compared with a predetermined voltage reference value in the voltage comparator circuit 20 of the voltage regulator 3. When the voltage drops below the threshold, the regulator opens the contacts K2, whereby: the current transformers supply the magnetizing coils 6 via the control circuit 8.

': * ·· The control circuit 8 consists essentially of three parts: filter 22, trigger circuits *: ··: 25 42 and 44 and thyristors 28, 30, 32 and 34. The function of filter 22 is to filter high voltage overvoltages that can destroy rectifier components or even regulator . The actual control circuit comprises two pairs of resistive coupled thyristors. Thyristors 28 and 30 are coupled between current transformer output conductors 36 and 38 and ... · respectively, thyristors 32 and 34 are connected between current transformer output conductors 38 and 40: 30. The trigger circuit 42 controls the thyristors 28 and 30, and the trigger circuit 44 respectively controls the thyristors 32 and 34. The trigger circuits conduct the thyristors 32 and 34. 6. The control circuit limits the current supplied by the current transformers to the desired level, so that standardized current transformers can be used.

5 On the other hand, in the case of a short-circuit, the magnetization current must be high enough to achieve a suitable current relay function. However, the magnetizing current must not grow too high to avoid damaging the magnetizing circuit or the generator. Typically, the operation is designed so that the generator short-circuit current 1¾ (Fig. 4) is about three times the nominal value In. The characteristic of the current transformer (Fig. 4, curve 2c) gives a 10 short-circuit current value I b, whereas, by limiting the current of the current transformer to the desired value In *, the short-circuit current can be limited to the desired value Ika. According to the invention, the maximum value of the excitation current can be adjusted (Fig. 4, line 3a) by selecting the trigger voltages of the trigger circuit at a suitable magnitude. In practice, this can be done, for example, with jumpers. The magnetization voltage and the controller settings 15 are set with presetting values from the design steps and a short circuit test is performed before the generator is commissioned to check the appropriate magnetization voltage. The jumpers of the trigger circuits are then placed at positions corresponding to the voltage level to provide proper short-circuit magnetization. Since this is a device specific characteristic, there is no need to change the setting during operation.

20

Generator magnetization can be practiced generally in the practice of the present invention; in addition to the brushless magnetization used, especially with small generators in conjunction with the brushless magnetization. Implementation of the normal situation magnetization does not substantially affect the application of the present invention. Although in the short-circuit situation 25, normal magnetization is not available especially in the embodiment described above, the invention can also be utilized in situations where the voltage drops momentarily, such as when starting a large motor. In this case, normal magnetization is in operation, but it is combined with additional magnetization produced by the current transformer and controlled by the regulator in the manner required by the load.

'*: 30' · '': The invention has been described above by means of an embodiment thereof. However, there is no presentation:. whereas the scope of the patent should be considered as limiting, but its embodiments may vary; ' '' · Within the scope of the appended claims.

Claims (11)

116107 A method for diagnosing a synchronous generator (10) when the mains voltage drops below a threshold that is magnetized by an excitation coil, comprising measuring the mains voltage and comparing the mains voltage with a reference value, providing at least one current transformer (R, S, T) the primary is in series with the mains cable, characterized in that when the mains voltage drops below the reference value, the short-circuit switches (K2) of the current transformer (2) are opened, and the current of the current transformer is controlled to the magnetizing circuit (6). Method according to Claim 1, characterized in that the current (Im) directed to the excitation circuit by the control circuit (2) is proportional to the mains current. Method according to claim 1, characterized in that the excitation current generated by the current transformer is combined with the current of the actual excitation circuit. 4 Method according to Claim 1, characterized in that by adjusting the settings of the control circuit, the magnetization level is adjusted to achieve a sufficient magnetization level. 20 Method according to claim 1, characterized in that the operating point of the control circuit is adjusted based on the nominal magnetization voltage of the synchronous generator. An apparatus for diagnosing a synchronous generator when the mains voltage 25 of the synchronous generator (10) drops below a predetermined threshold, comprising a mains voltage measuring device and a reference means for comparing the actual voltage of the mains voltage to: (2) a primary, characterized in that and the secondary of the current transformer (2) are connectable ,,,; to the control circuit (8) by opening the secondary short-circuit switches (K2), which control circuit (8) is, ·. 30 to produce the required excitation power when the mains voltage drops below a threshold. 116107 Apparatus according to claim 6, characterized in that short-circuit magnetization can be coupled with normal magnetization, wherein the total magnetization of the generator (10) is a combination thereof. 8. Apparatus according to claim 6, characterized in that the control circuit comprises control elements with which the magnitude of the short-circuit magnetization is adjustable as a function of the magnetizing voltage of the synchronous generator. 9. Apparatus according to claim 8, characterized in that the control means are formed as jumpers with a level of excitation voltage. Apparatus according to one of Claims 6 to 9, characterized in that the excitation can be controlled by controlling the secondary voltage of the current transformer. * · • 1 i «i · t 1 i t» 1 »•« 1 1 »• I t I * ·» t 116107