JPH04295221A - Protective relay system for electric station - 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]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power equipment protection relay system.

0002

[Prior Art] The conventional protection relay system is a current transformer installed for each device to be protected, as shown in the backup protection relay system of Electric Kyodo Research Vol. 37, No. 1 (1982-6). Each protection interval is constructed using the signals from the equipment.

[0003] In addition, backup protection includes remote backup that detects from a distance, and local backup that opens the line connected to the accident location if the accident continues for a predetermined period of time at the own electric power plant. .

0004

[Problems to be Solved by the Invention] The above-mentioned conventional technology has the following problem: As the short-circuit capacity of the busbar or the power transmission line to which the power equipment is connected increases compared to the short-circuit capacity of the power equipment to be protected,
The larger the difference in fault current between fault points becomes, and the more sensitive the fault current is to be detected, the wider the linearity of the current signal input circuit must be, and the more difficult it becomes to maintain the stability of the characteristics. In addition, for current transformers, if the overcurrent constant is set to about n>20 based on the rated value of the power equipment, when the fault current increases extremely, there is a risk of distortion of the output waveform due to air saturation, so stable protection is not possible. It becomes difficult to satisfy the performance.

[0005]Furthermore, in the above-mentioned protection by remote backup or local backup, the protection performance is generally lower than that in main protection, such as an increase in the cut-off area and a longer cut-off time.

[0006] An object of the present invention is to prevent the above-mentioned deterioration of the protective performance.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides signals for current transformers provided for the protection of power equipment as well as other purposes for the lines connected to the power equipment. The signals from the current transformer installed in the system and, if necessary, the signal from the voltage transformer are used to protect power equipment.

[0008]

[Operation] Current transformers installed to protect the bus or line of a system with a large short-circuit capacity generally have a rated current larger than the rated current for a single power device. . Therefore, if a current transformer with a different rated current is used on the same terminal line as the one used for power equipment protection,
Assuming that both have the same overcurrent constant n>20, the range in which signals can be measured with high performance will be widened by the ratio corresponding to the large and small rated currents.

The present invention aims to improve the characteristics of a protective relay by utilizing the output signals of a plurality of current transformers having different current measurement target levels.

0010

[Embodiments] Hereinafter, embodiments of the present invention will be explained with reference to the drawings.

FIG. 1 is an overall explanatory diagram of the present invention. In the figure, reference numerals 1 and 2 are power supply terminals connected to the busbar, which are a composite power source of a large number of power plants (not shown). 3 is also a load group, to which power is supplied via the bus bar. 4 is a transformer connected to the busbar, and 5 is also a generator. The objects to be protected according to the present invention are a transformer (4) and a generator (5).

The power supply terminals 1, 2, load group 3, transformer 4, generator 5, etc. are connected to the bus bar by electric lines L1, L2, L3, L4, L5, respectively. Breaker CB1, CB2, CB3, CB4, C
It is connected to the bus bar via B5. 10 is a bus protection relay, and current transformers CT1, CT2, CT3, CT4, CT
For example, when detecting a current differential signal in the bus bar surrounded by 5 and detecting an internal fault in the bus bar, the circuit breaker CB1, C
A cutoff output is given to each of B2, CB3, CB4, and CB5 at the same time.

40 is a protection relay for the transformer 4, which includes a high-sensitivity relay 41 that issues a cutoff command to the circuit breakers CB4 and CB41 when a fault in the circuit surrounded by the current transformers CT41 and CT42 is detected; It consists of a low-sensitivity relay 42 that gives a cutoff command to the circuit breakers CB4 and CB41 when a fault in the electric line L4 or the transformer 4 is detected by a signal from the transformer CT4 or the voltage transformer PT41.

The high sensitivity relay 41 is a current differential relay that can detect a fault current of about 10 to 30% based on the rated current of the transformer 4, and the rated values of the current transformers CT41 and CT42 are also based on the rated current of the transformer 4. Highly sensitive accident detection performance is obtained by using a device that approximately matches the rated current.

However, in the case of a terminal fault on the power line L4 or the power line L4 side of the transformer 4, the fault current from the power supply groups 1 and 2 becomes extremely large, similar to a busbar fault, and is 100 times the rated current of the transformer 4. It is possible that it will be to some extent.

In such a serious accident, current transformers CT41,
The CT42 has a rated overcurrent constant far exceeding its rated overcurrent constant, and it is no longer expected to output a correct waveform. For example, when the signal is converted into a digital signal and taken into the protection relay 41, it is conceivable that the full scale of quantization is reached, making it difficult to correctly determine an accident.

On the other hand, the current transformer CT installed for bus protection
1, CT2, CT3, CT4, CT5 are, of course,
Since it is equipped with a waveform output conversion that can reliably detect a bus internal fault current, it can be expected that the waveform conversion performance will be sufficiently high even in the event of a fault on the electric line L4.

Therefore, serious accidents such as terminal accidents on the electric line L4 and the voltage generator 4 can be stably detected by the low sensitivity relay 42, which is used in conjunction with the bus protection relay 10, for the signal of the current transformer CT4.

The reason for the name "low sensitivity relay" is that since the low sensitivity relay 42 does not have current differential characteristics, it is designed to avoid unnecessary detection in the event of an external fault of the transformer 4, that is, a fault beyond the electric line L41. , in order to have a sensitivity that does not operate due to the above-mentioned external fault current. Moreover, the reason why the voltage signal is used by using the voltage transformer PT41 in the low sensitivity relay 42 is to measure the voltage of the electric line L4 and increase the reliability of accident detection.

Next, the protection relay 50 of the generator 5 connected to the busbar will be explained.

[0021] Basically, it is the same as the protection relay 40 of the transformer 4 described above, and includes a high-sensitivity relay 51 that detects an accident in the area surrounded by current transformers CT51 and CT52, and a current transformer CT5, or , a low-sensitivity relay 52 that receives a signal from the voltage transformer PT51 and detects a terminal fault in the generator 5 or a serious fault in the electric line L5. When each accident is detected, a command is given to shut off the circuit breaker CB5.

Next, the contents of the protection relays 40 and 50 will be explained in more detail. Since the protection relay 50 is basically the same as the protection relay 40 by replacing the numerical symbol 4 with 5, the protection relay 40 will be described below as a representative example.

FIG. 2 shows the configuration of the protection relay 40, and the same symbols as in FIG. 1 hereinafter refer to the same operations as those described above.

The input signal of the high-sensitivity relay 40 is a current transformer CT.
41 output signal I41, current transformer CT42 output signal I4
This is a current differential relay according to No. 2, but if necessary, it is a ratio differential relay with passing current suppression added, or measures against excitation inrush current of the object to be protected are added.

The low sensitivity relay 41 receives the output signal I4 of the current transformer CT4 and the output signal V41 of the voltage transformer PT41.

421 is an overcurrent relay that determines the level of the output signal I4, and 422 inputs an output signal V41 corresponding to the voltage signal of the electric line L4 in addition to the output signal I4, and detects a voltage drop in the electric line L4. It is a fault detection relay equipped with an undervoltage element for detecting or a directional element for detecting the presence of a fault in the direction of the transformer 4 connected to the electric line L4.

The output of the low-sensitivity relay 41 meets the matching condition (AND) of the overcurrent relay 421 and accident detection relay 422 described above.
).

The output of the protection relay 40 is a high-sensitivity relay 41
The signal is output based on the OR condition of the output of the low sensitivity relay 42 and the output of the low sensitivity relay 42.

In the configuration of the low sensitivity relay 42 shown in FIG. 2, a modified configuration shown in FIG. 3 can also be used.

In the figure, 426 is a current differential element;
An internal fault is detected using the output signal I4 of the current transformer CT4 and the output signal I42 of the current transformer CT42 as input signals.

427 is a directional element whose input signal is the output signal I4, I of the current transformer CT4, CT42, respectively.
42 and the output signal V41 of the voltage transformer PT41.

For direction determination, I4 may be used alone as a current signal based on output signal V41, but I4 and I42
A differential output signal may also be used.

When a fault exists on the transformer 4 side, the polarity of the direction determination is set so that the direction element 427 operates.

An undervoltage detection element 428 detects a drop in the voltage signal V41 of the electric line L4 and generates an operation output.

The output of the low sensitivity relay 42 is generated by the coincidence condition (AND) of the above detection elements, that is, the current differential element 426, the direction element 427, and the undervoltage element 428.

Of course, if necessary, the directional element 42
7. The undervoltage element 428 may be omitted.

The contents of FIG. 3 can be applied to the low sensitivity relay 52 shown inside the protection relay 50 of the generator 5 in FIG. A similar function can be obtained by replacing 5 with 5.

The present invention is also applicable to the case where each signal uses a digital data transmission path, an optical data transmission path, or the like, and each protection relay is processed by a computer capable of digital calculation. In addition, the output signal I4 of the current transformer CT4 is
Since it can also be obtained by a composite value of the outputs of CT2, CT3, and CT5, this can also be used.

[0039]

According to the present invention, protection performance and operational reliability are improved by combining current transformers having a wide range of current measurement functions.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a detailed explanatory diagram of an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a modified example of application of the present invention.

[Explanation of symbols]

L4...Electric line, CT4, CT41, CT42...Current transformer,
4...Transformer, 40...Protection relay, 41...High sensitivity relay,
42...Low sensitivity relay.

Claims (6)

[Claims] Claim 1: A relay system for protecting power equipment such as transformers, generators, and motors connected to the busbar or transmission line of a power system, in which a signal from a current transformer installed to protect the power equipment is used. An electrical station protection relay system comprising: one protection relay; and a second protection relay that uses a signal from a current transformer installed to protect the busbar or the power transmission line. 2. The electric station protection relay system according to claim 1, wherein an overcurrent relay is used as the second protection relay. 3. The electric station protection relay system according to claim 1, wherein a directional distance relay is used as the second protection relay. 4. In claim 1, an overcurrent relay and a directional distance relay are used as the second protection relay, and according to an AND condition or an OR condition of both relay output signals,
An electrical station protection relay system in which the output of the second protection relay is used. 5. The electrical station protection relay system according to claim 1, wherein an undervoltage relay is used as an operating output condition for the second protection relay. 6. An electric station protection device according to claim 1, wherein the second protection relay has a differential relay function using an output signal of the bus bar protection current transformer and an output signal of the power equipment protection current transformer. Relay method.