JPH01198256A - Ground-fault protective device of synchronous generator - Google Patents

Abstract

PURPOSE:To prevent an unnecessary operation of a ground-fault protective device caused by extrinsic factors of a system side by monitoring and detecting variations in the terminal voltage and the power-factor of a generator. CONSTITUTION:A neutral point circuit of a synchronous generator 1 is grounded through an earth transformer. An earth resistor 3 and a third harmonic undervoltage element 4 are connected to a secondary circuit of the earth transformer 2. The terminal voltage and the power-factor of the synchronous generator 1 are respectively detected by a voltage detector 8 and a power-factor detector 9. A third harmonic voltage of the neutral point of the synchronous generator 1 is reduced by extrinsic factors of the system side and even if the third harmonic undervoltage element 4 operates, a ground-fault protective device 10 does not operate when the voltage detector 8 and the power-factor detector 9 detect a drop in voltage and in power-factor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a ground fault protection device for an armature circuit of a synchronous generator.

(Prior Art) Various types of earth fault protection devices have conventionally been applied to the armature circuit of a synchronous generator. In the case of large-capacity generators that are grounded by resistance via a grounding transformer, the common method is to use a ground fault overvoltage relay. In this method, a ground fault near the neutral point of the armature circuit of a synchronous generator is a blind spot in protection due to limitations in detection sensitivity and a balance with transition voltage due to a ground fault in an external system. However, the influence of ground faults on generator damage is extremely large, so the third harmonic that constantly circulates through the neutral point of the synchronous generator is used to protect the ground fault near the neutral point of the synchronous generator. In recent years, a method of detecting and protecting by undervoltage of the third harmonic has been adopted.

This takes advantage of the fact that the third harmonic voltage at the neutral point of a synchronous generator is roughly proportional to the load current, and suppresses it by the load current, multiplying the actually measured third harmonic voltage by (k x 1, e.g. The method uses a third harmonic undervoltage with an operating value of 0.7).

(Problem to be solved by the invention) However, what is usually actually measured is the third harmonic voltage near the rated power factor of a synchronous generator, and as a general characteristic of a synchronous generator, if the power factor decreases, This third harmonic voltage also tends to decrease. Therefore, if the undervoltage of the third harmonic voltage at the neutral point of the synchronous generator is detected alone, the earth fault protection device will operate even if the power factor of the synchronous generator is extremely reduced due to an external factor on the grid side, for example. This may unnecessarily increase the burden on power plant operators.

The present invention has been made in consideration of the above circumstances, and is a ground fault protection for synchronous generators that prevents unnecessary operation of conventional ground fault protection devices caused by external factors on the grid side and maintains stable continuous operation of power generation plants. The purpose is to provide equipment.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the synchronous generator ground fault protection device of the present invention provides a The configuration includes a voltage detector that is connected to the main circuit of the generator and operates when the generator terminal voltage decreases, and a power factor detector that operates when the generator power factor decreases.

(Function) Since the present invention is configured as described above, the third harmonic voltage at the neutral point of the synchronous generator decreases due to an external factor on the grid side, and the third harmonic undervoltage element operates. However, if the terminal voltage of the generator decreases or the power factor decreases, that is, if the voltage detector or power factor detector operates, the earth fault protection device will not operate and unnecessary operation can be prevented. can.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing the configuration of a ground fault protection device for a synchronous generator according to an embodiment of the present invention, in which a neutral point circuit of a synchronous generator 1 is grounded via a grounding transformer 2. A grounding resistor 3 and a third harmonic undervoltage element 4 are connected to the secondary circuit of the grounding transformer 2.

On the other hand, the armature side of the synchronous generator 1 is connected to the generator main circuit 5, and the secondary side of the instrument transformer 7 that detects the terminal voltage of the synchronous generator 1 has a voltage that detects a drop in the generator terminal voltage. It is input to the detector 8. Further, a power factor detector 9 that detects a decrease in the power factor of the synchronous generator 1 is connected via an instrument current transformer 6 that detects the load current of the synchronous generator 1 . Naturally, the secondary output of the instrument current transformer 7 is input to the power factor detector 9 as a terminal voltage component. Also, the third harmonic undervoltage element 4
The output of the meter current transformer 6 is also inputted to the current transformer 6 for suppression by the load current ■L.

Next, a first explanation of the operation of the present invention configured as described above will be explained.
This will be explained with reference to FIG. 2, which is a control/operation block diagram of the ground fault protection device 10 indicated by broken lines in the figure.

If there is no ground fault and the synchronous generator 1 is in a normal operating state, the third harmonic undervoltage element 4 is inoperative, so the ground fault protection device 10 does not operate.

In such a situation, for example, if the grid voltage drops significantly due to a power outage in the vicinity, and the terminal voltage of the synchronous generator 1 also drops abnormally, the operation of the excitation device of the synchronous generator 1 (not shown) The field current increases rapidly and the power factor of the generator drops significantly.

Here, the operating state of the synchronous generator 1 and the third harmonic voltage CV
3t) generally depends on the load current (It, ) and power factor of the synchronous generator, as shown in FIG.

Therefore, in the above-mentioned state, the third harmonic undervoltage element 4 may operate depending on the load current.

However, in such a case, the voltage detector 8 or the power factor detector 9 operates as shown in FIG. 2, so the earth fault protection device 10 does not operate.

Furthermore, when a ground fault occurs near the neutral point of the synchronous generator 1, the third harmonic undervoltage element 4 operates normally, but the voltage detector 8 and power factor detector 9 Since there is almost no change and no operation occurs, the ground fault protection device 10 operates normally.

Therefore, according to this embodiment, unnecessary operations caused by external factors on the grid side when only the third harmonic undervoltage element 4 is used as ground fault protection near the neutral point of the conventional synchronous generator 1 are prevented, It can only be activated in the event of an actual ground fault.

In other words, it is possible to prevent the ripple effects caused by unnecessary emergency stoppage of the power generation plant and the increased burden on the power generation plant operators caused by unnecessary alarms.

(Other Examples) Note that the present invention is not limited to the above embodiments. For example, (1) In the above embodiment, as shown in FIG. 2, the non-operating condition of both the voltage detector 8 and the power factor detector 9 is considered as the operating condition of the ground fault protection device, but the configuration of either one Even under non-operating conditions, the same effects as in the above embodiment can be obtained.

■ Also, the suppression circuit due to the load current of the third harmonic undervoltage element 4 is removed when the voltage detector 8 or power factor detector 9 is activated (for example, by short-circuiting the input circuit from the instrument current transformer 6). In this way, the characteristics of the third harmonic undervoltage element 4 shown in FIG. 3 are set to a constant value (I
The same effect as in the above embodiment can also be obtained by fixing the value L=O.

〔Effect of the invention〕

As described above, the present invention monitors and detects changes in the terminal voltage and power factor of the generator, thereby preventing unnecessary operation of the ground fault protection device due to the conventional third harmonic undervoltage element caused by external factors on the grid side. Therefore, it is possible to provide a ground fault protection device for a synchronous generator that can prevent this and maintain stable continuous operation of a power generation plant.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a ground fault protection device for a synchronous generator according to an embodiment of the present invention, and Fig. 2 explains the operation of the ground fault protection device for a synchronous generator shown in Fig. 1. FIG. 3 is a control/operation block diagram showing the characteristics of the third harmonic voltage at the neutral point of the synchronous generator. 1... Synchronous generator 4... Third harmonic undervoltage element 8... Voltage detector 9... Power factor detector 10.
...Earth fault protection device agent Patent attorney Nori Chika Ken Yudo Ken Daishimaru Figure 2 Figure 3

Claims (1)

[Claims] 1. Earth fault protection near the neutral point of the armature circuit
A ground fault protection device for a synchronous generator using a harmonic undervoltage element includes a voltage detector connected to the main circuit of the generator and activated by a drop in generator terminal voltage, and a voltage detector activated by a drop in generator power factor. A ground fault protection device for a synchronous generator, characterized by comprising a power factor detector. 2. The third harmonic undervoltage element at the neutral point operates and operates when both the voltage detector and the power factor detector are inoperative. Ground fault protection device for synchronous generators.