JPS6127977B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the monitoring of the current collection action between a collector ring and brushes used for the field current supply of a synchronous machine used as a generator, a phase changer or an electric motor.

As shown in FIG. 1, the excitation current is supplied to the field winding 11, which is the rotating part of the synchronous machine 1, through the rotating shaft 1a.
A brush 13 is attached to the collector ring 12 arranged above.
This is done by making contact with the

In large-capacity synchronous machines, brushes are made from a material that combines natural graphite and various components.
Low friction effect and good self-lubricating properties. A pigtail wire 13a is attached to the brush 13, and a connecting terminal 13b is provided at the tip of the pigtail wire 13a. Pressure is applied to the brush in the radial direction by a spring attached to the brush holder. The brush holder is fixed to a steel bus ring in such a way that the contact angle between the brush and the collector ring can be adjusted. The bus ring is installed so as to insulate each pole from each other and between each pole and ground.

The rotor of a synchronous machine rotates at high speed, and the brushes are susceptible to (a) incomplete brush contact due to lack of brush pressure, and (b) dust and corrosion in the environmental atmosphere. (3) If some of the brushes are damaged, the current density of the remaining brushes will be reduced. Due to the increase in the amount of heat generated, sparks such as sparks and arcs are generated between the brush and the collector ring, which causes the brush to overheat. Furthermore, as these phenomena progress, the brush becomes red hot. This also causes red heat damage to the brush holder and connection leads. Furthermore, a vicious cycle occurs in which continuous arcing occurs between the brush and the collector (i.e., flashover occurs), which again causes damage to the brush. Furthermore, accidents involving loss of the collector ring may be induced. Therefore, maintenance around brushes is important.

Conventionally, in order to detect this type of failure at an early stage, a method of optically detecting arcs in the brush portion has been known. This method can be expected to be effective in small-scale synchronous machines. However, in large-capacity synchronous machines, the number of installed brushes is large,
Due to the large diameter and length of the collector ring, it is difficult to mount an optical sensing device close to the contacts and to cover the entire brush area. A further disadvantage is that the invisible portion of the brush arc is essentially undetectable.

The present invention continuously monitors and detects the occurrence of spark-arc phenomena between the collector ring and the brushes during operation of the synchronous machine, and issues an alarm or causes the synchronous machine to trip. Aims to provide an effective brush monitoring system.

Hereinafter, a case where the monitoring device according to the present invention is incorporated into a synchronous generator will be described with reference to FIG. 2. A field current is supplied from the excitation device 2 to the field winding 11 via the collector ring 12 and the brush 13 . The output voltage of the excitation device 2 is adjusted so that the voltage Vg generated at the stator terminal 14 is maintained at the value set by the voltage setting device 7. According to the present invention, for the target system as described above, the output voltage of the excitation device 2, that is, the collector voltage is detected at the detection point 2.
2, this is input to the abnormal voltage detector 3, and the comparison circuit 4 connected to receive the output 34 of the voltage detector 3 analyzes the brush arc phenomenon.
The alarm device 5 is operated based on this analysis result.

An expected value generator 6 is further added to the system with the above contents, and the magnitude of the load (for example, the stator current detected by the current transformer 16) is input to this expected value generator 6. The expected value 33 thus obtained is used as an auxiliary input to the voltage detector 3 to back up brush arc phenomenon detection.

Hereinafter, the functions of each device that characterize the present invention will be described in detail.

When a spark occurs between the collector ring 12 and the brush 13, the collector ring voltage Vc at the detection point 22 oscillates with a steep waveform. It has been found from various observations that this waveform is much steeper and has a smaller time constant than the control voltage waveform in excitation control as shown in FIGS. 3a and 3b. Therefore, the abnormal voltage detector 3 detects the collector voltage
When Vc is input and the waveform has a steep rise (Fig. 3a) or fall (Fig. 3b) and their time constants t ₁ and t ₂ are smaller than predetermined limit values, and the voltage This is detected when the amount of change in the magnitude of exceeds a predetermined limit value.
In this way, a sudden change in voltage due to a brush arc or spark included in the collector voltage Vc is detected. These detection sensitivity levels (limit values) are set by a time constant setter 31 and a change amount setter 32.

In addition to the above basic functions, an additional function is to detect when a voltage is continuously maintained at an abnormal level with respect to the normal level d, as shown as waveform c in the graph of FIG. That is, when the level of the voltage waveform becomes abnormally different from the expected level 33 (Fig. 3 h) (Fig. 3 f),
This is detected and the output 35 is provided to the comparator.

In addition, there is usually a part g with a steep rise in the waveform c.
The steep waveform e that occurs in the abnormal level portion of the waveform c is detected by the basic function described above.

The outputs 34 and 35 of the voltage detector 3 can be analog signals or digital signals.

The comparator 4 measures the number or frequency at which the output 34 of the voltage detector 3 is generated, and outputs an output signal to the alarm device 5 when the value exceeds a predetermined value.

In some cases, an output is output to the alarm device 5 when the abnormal voltage waveforms a, b, g, and e appear only once, but normally, when the occurrence of abnormal voltage is only an accidental occurrence, , in order to not activate the alarm device, the frequency is measured and the frequency is set to a constant value (for example, 3 times in 5 minutes).
An output is given to the alarm device 5 only in the above cases.

The comparator 4 also measures the number or frequency with which the output 35 of the voltage detector 3 is generated, and similarly issues an output signal to the alarm device 5 when the value exceeds a predetermined value. The predetermined value for the output signal 35 is normally the number of occurrences of one. This is because if the abnormal level continues, that alone is sufficient to determine that the condition is abnormal.

The expected value generator 6 has the following functions. The field current If required by the synchronous machine is determined by the terminal voltage, armature current, and power factor, and can be obtained, for example, by the following estimation formula.

If=√ ² _f1 + ^{2 2} _f2 +2 _{f1 f2} …
...(1) However, I _f1 and I _f2 are constants specific to the generator, cosφ is the power factor, and k is a constant determined by φ.

Next, the field voltage V _f is determined by the following equation.

V _f =R _f I _f (2) However, R _f is the field winding resistance.

The value of the field voltage V _f thus determined is given to the spike voltage detector 3 as the expected level 33 .

Note that the base value of this estimated value can also be corrected using the actual value of the field voltage during normal operation.

Furthermore, by predicting the approximate value of sinφ (=√1−() ² ), k can also be determined, and the contents of the expected value generator can be simplified.

The alarm device 5 receives the signal from the comparator 4 and issues an alarm or a trip signal for the synchronous machine.

As described above, according to the present invention, a steep change in the voltage between the brushes is detected, and based on this detection result, it is determined that an abnormal situation has occurred in the brushes. Causes of damage in the surroundings can be detected early, and protection can be provided to prevent damage to the synchronous machine.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a synchronous generator to which a monitoring device according to an embodiment of the present invention can be applied, Fig. 2 is a block diagram of a monitoring device according to an embodiment of the present invention, and Fig. 3 is a voltage between collector rings. FIG. 3 is a diagram showing waveforms. 1... Synchronous generator, 2... Excitation device, 3... Abnormal voltage detector, 4... Comparison device, 5... Alarm device, 6... Expected value generator, 11... Field winding, 1
2...Field circuit collector ring, 13...Field circuit brush.

Claims (1)

[Claims] 1. A brush monitoring device for a synchronous machine that monitors the occurrence of an abnormality in a brush used for supplying field current to a synchronous machine, comprising: an expected value generation circuit that generates a corresponding expected value of the voltage between the brushes; an abnormal voltage detector that detects when the voltage level between the brushes continues to be abnormal when the voltage level between the brushes is taken as a reference; A synchronous machine comprising: a determination circuit that determines that an abnormality has occurred in the brush when the voltage exceeds the voltage level, and determines that an abnormality has occurred in the brush when it is detected that the abnormality in the voltage level continues. brush monitoring device.