JPH0811026Y2 - Field loss relay malfunction prevention circuit - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to a loss-of-field relay malfunction prevention circuit for preventing malfunction of a protection relay against loss of field of a synchronous generator, and in particular, a top pressure generator, etc. To a field loss relay malfunction prevention circuit suitable for a low-load generator.

B. Outline of the Invention The present invention relates to a field loss relay malfunction prevention circuit for preventing malfunction of a protection relay against field loss of an alternator when starting a synchronous motor connected to an output circuit of the alternator. The current transformer provided in the main circuit of the synchronous motor gives a loss-of-field relay a pseudo signal that compensates for the voltage drop or phase-advancing current that occurs when the synchronous motor is started, and the loss-of-field relay activates the synchronous motor on the load side. It was designed so that it would not be affected.

C. Conventional technology A synchronous generator may lose its field due to an accident such as a switch or exciter, or an accident between a synchronous machine slip ring and a brush. When the synchronous generator loses the field, it becomes an induction motor and rotates at a speed higher than the synchronous speed to generate a large induced current in the rotor. At this time, if there is no braking winding in the cylindrical rotor or the like, the induced current flows through the rotor iron core, the iron core heats up rapidly, and reaches a dangerous state in about 2 minutes at the end where the temperature rises significantly. There are even things. In addition, when the generator loses the magnetic field, it loses 2 to 4 times the rated capacity of the generator from the grid, so unless the grid is immediately disconnected, the stability will be lost rapidly and each part will operate. It leads to a pause.

Therefore, a protection method in which a field loss relay such as an undervoltage relay or a distance vertical switch is provided in the field circuit is generally used. D. Problems to be solved by the device However, for example, in the case of a top pressure generator, etc. , When a synchronous motor with a relatively large capacity (hereinafter abbreviated as SM) is started for a generator with a low load depending on its operating condition, the field loss relay as the generator protection relay is It may malfunction. This is because a large amount of Var (reactive power) is generated when the SM starts, so there is a phenomenon such as a voltage drop and a phase-advancing operation associated with it, which causes the loss-of-field relay to appear as if the loss of field of the synchronous generator had occurred. Due to the occurrence.

The most common measure to avoid this phenomenon is to use a start signal and a timer for the SM start-up sequence and keep the field loss relay inactive during SM start-up. However, this method has a drawback that it involves a danger because it loses the protection function of the loss of field relay even though it is a short time, and it is troublesome to reset the timer each time the startup time of the SM is shortened by the load. There is.

The present invention was devised in view of such problems, and an object thereof is to provide a field loss relay malfunction prevention circuit that is not affected by the SM start on the load side.

E. Means for Solving the Problem The means for solving the above problem in the present invention is to input the secondary current of the current transformer and the secondary voltage of the transformer for the meter provided in the output circuit of the AC generator. A field loss relay is provided, and a synchronous motor is connected to or cut off from the output circuit of this AC generator. A resistance is provided on the field loss relay connection line on the secondary side of the instrument transformer, and A current transformer is provided in the main circuit of the synchronous motor, and a secondary side of the current transformer is connected to the resistor so as to compensate for a voltage drop or a phase-advancing current generated when the synchronous motor is turned on.

F. Function The present invention is to make use of the relay protection function at all times by giving a pseudo signal to the field loss relay only when the SM is activated. The original loss of field is captured by voltage drop and phase advance operation as a phenomenon seen from the generator terminal. Therefore, if a resistor is inserted in series on the secondary side of the voltage transformer for detecting the generator voltage and it is connected to the current transformer arranged on the SM main circuit, the SM starting current The secondary current of the current transformer proportional to the time flows into the resistor to generate a voltage, and as a phenomenon seen from the generator terminal, it is not affected by the SM start.
It should be noted that even when the SM enters the steady operation, a voltage is generated through the current transformer, but it is a small amount and does not pose a problem.

G. Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, 1 is a synchronous motor (SM), 2 is an AC generator that drives the SM1, 3 is a field loss relay, and an instrument transformer 4 and a current transformer arranged in the output circuit of the generator 2. The secondary output of 6 is used as an input to detect the loss of field and perform a protective operation. Reference numeral 5 is a resistance interposed between the secondary side of the instrument transformer 4 and the field loss relay 3, and 7 is a current transformer (CT) arranged on the main circuit of the SM1. The secondary side of the current transformer 7 is connected to the resistor 5.

In the above circuit, the secondary current flows through the resistor 5 through the current transformer 7 even during the steady operation of SM1, but since it is minute, it does not affect the operation of the field loss relay 3. Since a much larger starting current is generated when the SM1 starts up, the SM starting current and the CT secondary current proportional to the time flow into the resistor 5 to generate a large voltage, which causes a voltage drop or phase advance seen from the generator terminal. Compensates for the current, is not affected by the SM start, and prevents the loss of field relay from malfunctioning.

The configuration of the present invention is similar to the cross current compensation circuit conventionally used for parallel operation of generators, but the operation and purpose are completely different.

H. Effect of the Invention As described above, according to the present invention, the secondary current of the current transformer 7 flows into the resistor 5 in proportion to the starting current of the synchronous motor and its flowing time. It is possible to provide a field loss relay malfunction prevention circuit that is not affected by the above.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention. 1 ... Synchronous motor (SM), 2 ... AC generator, 3 ... Loss of field relay, 4 ... Transformer for instrument (PT), 5 ... Resistance, 6,7 ... Current transformer (CT).

Claims (1)

[Scope of utility model registration request] Claim: What is claimed is: 1. An alternating current generator provided in an output circuit of an alternator, comprising a field loss relay for inputting a secondary current of a current transformer and a secondary voltage of a transformer for an instrument. In a case where a synchronous motor is connected or cut off, a resistance is provided in the field loss relay connection line on the secondary side of the instrument transformer, and a current transformer is provided in the main circuit of the synchronous motor and the current transformation is performed. A field loss relay malfunction prevention circuit characterized in that the secondary side of the transformer is connected to the resistor to compensate for a voltage drop or a phase advance current that occurs when the synchronous motor is turned on.