JPS5911718A - Device for protecting generator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a protection device for a generator, and particularly to a protection device for a generator that protects a unit generator armature winding from a ground fault. be.

[Technical background of the invention]

Conventionally, as a relay used to protect the armature winding of a unit generator from a ground fault, a ground fault overvoltage relay has been used to detect the fundamental wave zero-sequence voltage that appears at the neutral point of the generator when a ground fault occurs. Figure 1 is a system diagram of a unit generator to which this relay is applied.The neutral point of the generator 1 is grounded by a grounding transformer 2, and each feed end is grounded by a surge absorber 4 and the transformer It is connected to the device 5. Grounding transformer 2
A resistor 3 is connected to the secondary side of the resistor 3, and a ground fault protection overvoltage relay 6 is further connected to receive the voltage across the resistor 30.

[Problems with background technology]

However, ground fault protection using relays is not sufficient in terms of protection performance. In other words, as the ground fault point approaches the generator neutral point, the zero-sequence voltage at the time of a ground fault decreases, and the range approximately 10 inches from the generator winding neutral point lacks sensitivity, causing a ground fault. cannot be detected and becomes a blind spot in protection.

Therefore, in order to perform detection at this blind spot, a method has been proposed in recent years that utilizes the third harmonic that is constantly generated at the neutral point of the generator. This method focuses on the fact that the third harmonic voltage is generated in almost all of the generator's windings due to the structure of the generator. FIG. 2 shows that the third harmonic voltage 7 and the fundamental wave phase voltages R, S, and T are synchronous.

As shown in Fig. 3, this harmonic voltage 7 is generated by the generator 1, grounding transformer 2, neutral point,
Or, it circulates through a circuit consisting of M-)4. In this state, if a ground fault occurs near the neutral point of the generator, a bypass path is formed as shown in FIG. 4, and as a result, the third harmonic voltage at the neutral point decreases. Therefore, if an undervoltage relay is used to determine a ground fault in the smeared contact winding based on a decrease in the third harmonic voltage, a ground fault in the armature winding near the generator neutral point can be detected. can be detected.

However, the third harmonic voltage generated in the generator generally changes depending on the generator output as shown in Figure 5, so if the undervoltage detection value is set considering the minimum voltage at no-load, it will approach the rated load. As a result, the sensitivity decreases and sufficient protective action cannot be performed.

[Object of the Invention] The present invention has been made with the aim of solving the above-mentioned problems, and it is an object of the present invention to provide a protection device for a generator that can reliably detect a ground fault regardless of the magnitude of the generator output. The purpose is

[Summary of the invention]

In the present invention, the generator field box is proportional to the generator output.

The purpose is to operate an undervoltage relay using the voltage and the third harmonic voltage generated at the neutral point of the generator to provide ground fault protection without being affected by the output voltage of the generator.

[Embodiments of the invention]

Examples will be described below with reference to the drawings. IVI! ! 1
FIG. 6 is a configuration diagram of an embodiment of a generator protection device according to the present invention.

In FIG. 6, numerals 1 to 5 correspond to those in FIG. Reference numeral 8 denotes an undervoltage relay whose sensitivity changes as a generator field circuit current is applied through the current transformer 7. A rectifier 10 supplies current from an AC power source to the generator field winding 11.

In this configuration, the undervoltage relay 8 detects the third harmonic voltage of the generator among the voltages occurring across the resistor 3.

Also, undervoltage relay 8 has v:1, current transformation.

A signal proportional to the generator output is also applied via section 9, thereby changing the detection sensitivity.

FIG. 7 shows an example of setting the sensitivity characteristics of the undervoltage relay 8, in which the horizontal axis represents the generator output or the generator field circuit current, and the vertical axis represents the voltage. In this figure, 7 shows the change characteristics of the third harmonic of the generator, and 12 shows the detection characteristics of the undervoltage relay. Both of these characteristics are the generator output and the generator field circuit current. increases linearly as . Therefore, the third harmonic voltage can be reliably detected no matter what value the generator output is, for example, the rated value.

The reason why we use the generator field circuit electricity quantity instead of the generator output is that to use the generator output, it is necessary to introduce the generator voltage and generator current, and a voltage transformer and current transformer are required. It will be made of tatami mats and will require a high insulation class. On the other hand, if a generator field circuit current proportional to the generator output is used, for example, only a current transformer is required, and the insulation class is also low.

Figure 8 shows the circuit configuration of 80 undervoltage relays.
Generator neutral point voltage V taken from both ends of resistor 3. is applied to the primary side of the auxiliary transformer 13, and the generator field circuit current IΣ extracted from the secondary side of the current transformer 9 is applied to the primary side of the auxiliary current transformer 14, thereby generating the third harmonic. Detects voltage. That is, the secondary voltage of the auxiliary transformer 13 is applied to the filter 16 and becomes the third harmonic voltage V. ' is taken out and applied to the transformer 18, and the secondary current of the auxiliary current transformer 14 is applied to the resistor 151C, converted to a voltage signal, and then applied to the rectifier and smoothing circuit 17, which creates a curved current. It is converted into a voltage signal VE and applied to the adder 18. In the adder 18, the third harmonic voltage V. ′ to DC voltage M v! ! is subtracted and the third
Harmonic voltage■. A voltage signal VΣ is formed in which only the peak of ' is left. This voltage signal VΣ is applied to a level detector 19, converted into a rectangular wave signal VD, and applied to a continuity circuit 20. The continuum circuit 2° time-diffuses the output VD of the level detector 19 to form a continuous signal VT, which is applied to the NOT circuit 21.

The negative circuit 21 does not generate a signal while the continuous signal VT is present,
j! Ij Output V after H signal Vt disappears. produce ut.

Figure 9 shows waveforms of signals at various parts in the circuit of Figure 8.
and the third high me voltage V. By subtracting the DC voltage signal V from the electrical quantity of the generator field circuit from '', a voltage VΣ+ corresponding to the peak part of the third harmonic voltage is obtained, which is detected by the level detector 19 as a rectangular voltage. The wave signal is converted to VoK and time-deferred to become a continuous signal Vt, which is further inverted to become an output signal V. It becomes ut.

FIG. 10 shows another embodiment of the invention. Reference numerals 1 to 5, 8, 10, and 11 in the figure correspond to those in FIG. In the case of this embodiment, the only difference is that a power/current converter 22 is used instead of the current transformer 9 in FIG.
The treatment of Shingetsu is the same as in Figure 6.

〔Effect of the invention〕

As described above, the present invention provides a generator field circuit in which the sensitivity characteristic of a third harmonic undervoltage relay for detecting a ground fault in the armature winding near the neutral point of the generator is proportional to the generator output. Since the voltage is changed depending on whether the amount of electricity is large or small, it is possible to always reliably detect when the third harmonic voltage of the generator, which changes depending on the generator output, changes due to the occurrence of a ground fault. (Since the electric power of the generator field circuit is used, the number of transformers can be reduced, and the insulation class can be reduced, so that a low-cost protection device can be provided.

[Brief explanation of the drawing]

Fig. 1 is a system application diagram of the conventional generator winding earth fault protection device 7f'5, Fig. 2 is an explanatory diagram of the third harmonic voltage at the neutral point of the generator, and Fig. 3 is an illustration of the third harmonic voltage at the neutral point of the generator. An explanatory diagram showing the path through which current flows due to harmonic voltage. Figure 4 is an explanatory diagram showing the path through which the third harmonic current flows when a ground fault occurs. Figure 5 is a generator of the third harmonic current. Fig. 6 is a diagram showing the change characteristics according to the output, Fig. 6 is a system application diagram of an embodiment of the present invention, Fig. 7 is a diagram showing the sensitivity characteristics of the undervoltage relay used in the same embodiment, Fig. 8 is a diagram showing the sensitivity characteristics of the undervoltage relay used in the same embodiment. A block diagram showing a configuration example of a voltage relay,
FIG. 0 is a time chart showing waveforms of various parts in the configuration of FIG. 8, and FIG. 10 is a system application diagram showing another embodiment of the present invention. ■... Generator 2... Grounding transformer 3.1
5...Resistor 4...Zarge absorber 5...
・Transformer 6... Overvoltage relay for earth fault protection 7... Third high V4V voltage 8... Undervoltage relay 9... Current transformer 10... Rectifier 11...
・Generator field winding 12...Insufficient 1i5 pressure characteristics 13・
...Auxiliary transformer 14...Auxiliary current transformer 16...
Filter 17... Rectifier smoothing circuit 18... Adder 19... Level detector 20... Continuation circuit 21... Negation circuit 22... Power/current converter (7317) agent Patent attorney Nori Chika Kensuke (and 1 other person)-8: 6 AA figure board ■Zu Mino i

Claims (1)

[Claims] In a generator protection device that detects a ground fault in the generator neutral point and the armature winding near the neutral point by detecting a shortage of the third harmonic voltage at the generator neutral point, A protection device for a generator, characterized in that an undervoltage relay is activated by a third harmonic voltage derived from a neutral point of the machine and an amount of electricity in the generator field circuit.