JPH0559649B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a ground fault protection device for parallel banks in a power system.

B. Summary of the Invention The present invention provides a ground fault protection means for detecting a ground fault in each feeder or bus bar and tripping the breakers and breakers of each feeder in sequence for each feeder in a power system that performs bank parallel operation. In addition, by detecting ground faults from the zero-sequence voltage of the busbars and tripping the bus ties and disconnectors interposed between the busbars of each bank, it is possible to detect ground faults during bank parallel operation without modifying the existing protective relays. This ensures that ground fault feeders can be selectively removed.

C. Prior Art FIG. 2 shows a power system diagram of a two-line power receiving substation, and shows a parallel bank configuration that allows power to be supplied by connecting the transformer secondary side bus bars in parallel. In the figure, CBr ₁ and CBr ₂ are power receiving circuit breakers, and only one of the circuit breakers is operated in the on state. CBt ₁ to CBt ₃ are bus ties and disconnectors for interconnecting the bus bars of each bank B ₁ to B ₃ . DS ₁ and DS ₂ are disconnectors, which are normally operated in the on state, and connect the power receiving line to the main transformers Tr ₁ , Tr ₂ ,
Powers Tr ₃ . F ₁ to _{F 3} are feeders of each bank, and each bank has a plurality of feeders to supply power to each consumer, and each feeder has a feeder shield and a disconnector CB ₁₁ , CB _1o to _{CB 31} , Connected to busbar at CB _3o .

Here, the shingle breakers CBt ₁ to CBt ₃ are normally operated in an OFF state. In other words, normally each bank
_B1 to _B3 are operated independently. The reason for this is: (1) In the case of bank parallel operation in which the breakers CBt ₁ to _{CBt 3} are operated in the on state, for example, the first bank B ₁
When a complete short circuit occurs on the load side of the Noshiya circuit breaker CB ₁₁ , a short circuit current flows not only from the main transformer Tr ₁ of the bank concerned but also from Tr ₂ and Tr ₃ of the other banks. For this reason, an economical problem arises in that it is necessary to extremely increase the shear cutting capacity of the feeder and the cutter CB ₁₁ .

(2) Bank parallel operation complicates system protection and increases the cost of the protective relay system. In particular, if an attempt is made to enable bank parallel operation in an existing system that is premised on bank independent operation, it will be necessary to completely remodel the protection control system.

For these reasons, the conventional system operation system uses bank isolated operation, and its protection control system is also constructed on the premise of bank isolated operation.

D Problems to be Solved by the Invention In a power system having banks in parallel, there are various advantages in enabling bank parallel operation. For example, even if there is an imbalance in load distribution between banks, the load on each main transformer is averaged, thereby increasing the overall power supply equipment efficiency. Furthermore, even when some main transformers are out of service, power can be supplied from other transformers (with load restrictions), thereby increasing the reliability of power supply.

Despite these advantages, the above (1) and (2)
The problem in section 1 was an impediment to bank parallel operation. Here, regarding the above item (1), the short circuit current is controlled by providing current limiting elements in series with each of the feeder tie and disconnectors CBt ₁ to CBt ₃ , and the feeder tie and disconnectors are operated in the same way as bank independent operation. It becomes possible to get by with just a load or a shear capacity. However, the method for solving the problem in item (2) above is not yet known, and the purpose of the present invention is to enable bank parallel operation without complicating the protection control system and without requiring major modification of the existing system. The purpose of the present invention is to provide a ground fault protection device that provides improved protection against ground faults.

E Means and Effects for Solving Problems The present invention detects a ground fault in each feeder from the current flowing from the bus bar to a plurality of feeders and the zero-sequence voltage of the bus bar, and trips the feeder break or disconnection of the feeder. a plurality of ground fault direction relays that detect ground faults in each feeder in the bank from the zero-phase voltage and sequentially trip the feeder shields and disconnectors; a ground fault overvoltage detection relay provided for each bank that has a zero-sequence voltage detection value that is less than or equal to the smallest zero-sequence voltage detection value among the selected relays and detects a ground fault from the zero-sequence voltage of each bus; It is equipped with a timer that trips the bus tie or disconnector of the bank when the relay detection continues for a set time period or longer, and is equipped with a timer that trips the bus tie or disconnector of the bank in question. When fault protection is not achieved, the bank parallel connection by the ground overvoltage relay is canceled, and then the ground fault direction relay or the slight ground fault selection relay causes the ground fault feeder to be disconnected.

F. Embodiment FIG. 1 is a diagram showing the configuration of an apparatus showing an embodiment of the present invention, and the same parts as in FIG. 2 are given the same reference numerals, and the explanation thereof will be omitted. In Figure 1, each bank B ₁
~ _B3 feeder wires and disconnectors (only the first bank is shown, and will be described hereinafter using that bank as a representative) _CB11 and _CB1o are connected by dedicated ground fault direction relays _67G11 and _67G1o , respectively. It is configured so that the shear disconnection control and the shear disconnection control are performed by a common micro-ground fault selection relay _10G1 for each bank. The ground fault direction relays 67G ₁₁ and 67G _1o are transformers that detect the detected current from the current transformers ZCT ₁₁ and ZCT _1o , which respectively detect the zero-sequence current of the feeder to be protected, and the bus zero-sequence voltage.
It is configured to determine the ground fault of the feeder to be protected from the detected zero-phase voltage Vo of GPT ₁ and obtain a trip output of the feeder, and the micro ground fault selection relay 1
0G ₁ determines from the zero-sequence voltage Vo from the transformer GPT ₁ whether the ground fault in the feeder system within the bank has continued for a predetermined period of time or more, and sequentially outputs trip signals from each feeder and disconnector CB ₁₁ to CB _1o . Configured to detect and eliminate micro-ground faults.

These ground fault direction relays 67G ₁₁ to 67G _1o and slight ground fault selection relay 10G ₁ are known as ground fault protection elements of the conventional power system protective relay system that assumes bank isolated operation, and are also used in existing power systems. It has been adopted.

Here, in this embodiment, earth fault overvoltage detection relays OVG ₁ to OVG ₃ and timers T ₁ to T ₃ as time-limiting elements are provided for each bank as a means for providing a ground fault protection function to bank parallel operation. . Relay OVG ₁
~ OVG ₃ takes in the zero-sequence voltage Vo of the bus in the bank from the transformer GPT ₁ ~ GPT ₃ , and determines the rise in the voltage level, and timers T _{1 ~ T 3 each take in the zero-sequence voltage Vo of the bus in the bank from the transformer GPT 1} ~ GPT ₃ ,
When the judgment outputs of OVG ₁ to OVG ₃ continue for a set time or longer, an output that trips the tie and disconnectors CBt ₁ to CBt ₃ is obtained. In addition, the detection sensitivity of the zero-sequence voltage Vo of the ground fault overvoltage detection relays OVG ₁ to _{OVG 3} is as follows: relays 67G ₁₁ to 67G _1o and 10G ₁
Below the lower of the two setting values (usually the setting value of relay 10G ₁ ) for the zero-sequence voltage Vo of
It is set to a value that allows reliable detection when a ground fault occurs in parallel banks.

These relays OVG ₁ to OVG ₃ and timers T ₁ to _{T 3}
By providing a protection system for a power system with a parallel bank configuration or by adding it to an existing power system protection system with a parallel bank configuration, a reliable protection operation can be obtained even in the case of a feeder ground fault during bank parallel operation. The protection operation will be explained in detail below.

Ground fault protection using only the aforementioned ground fault direction relays 67G ₁₁ to 67G _1o and the slight ground fault selection relay 10G ₁ is as follows:
This method is based on the assumption that banks are operated individually, and ground faults may not be detected when banks are operated in parallel.
In other words, in bank parallel operation, the main transformer Tr ₁ ~
The secondary side of Tr ₃ will be directly linked, and the ground capacitance of the linked system will be approximately three times that of bank independent operation (in the case of three banks parallel operation). Therefore,
When a ground fault occurs in one of the feeders in this interconnected system, the zero-sequence voltage Vo will be approximately 1/3 that of bank independent operation, assuming the ground fault point resistance is the same. However, the ground fault direction relay 67G ₁₁ ~ 67
G _1o and slight ground fault selection relay 10G ₁ have set values etc. on the premise of bank independent operation, so
The sensitivity of these relays may make it impossible to determine if a ground fault occurs during bank parallel operation because the zero-sequence voltage Vo is low.

For example, when a ground fault occurs in feeder F ₁₁ , if the ground fault resistance is large, the zero-sequence voltage Vo will be small;
In addition to this, in the bank parallel operation state, it only appears as a lower zero-sequence voltage Vo, and if the ground fault direction relay 67G ₁₁ is set to be able to detect the above-mentioned zero-sequence voltage Vo when the van is operating alone, it will not appear in the bank parallel operation. becomes undetectable. In order to increase the sensitivity of the ground fault direction relay _67G11 so that it can respond even to this low zero-sequence voltage Vo, it is necessary to modify all the existing ground fault direction relays for the feeder, which requires a large number of relays and is costly and time consuming. Such a problem may also occur regarding the relationship between the low zero-sequence voltage Vo and the zero-sequence voltage detection sensitivity of the micro-ground fault selection relay _10G1 .

Furthermore, regarding the slight ground fault selection relay 10G ₁ ,
The backup protection function is based on the premise of bank independent operation, and in case of ground fault failure of each feeder, each ground fault direction relay 67G ₁₁ ~ 67G _1o
If the ground fault cannot be removed, _and the ground fault continues to occur for more than a predetermined time and a predetermined zero-sequence _voltage , it is possible to remove the Attempts to detect and eliminate ground faults. However, in the case of bank parallel operation, if the above conditions are met for the occurrence of a slight ground fault in any bank, the feeders of all banks will be sequentially opened at the same time, and as a result, feeder errors and If it is unnecessary or unnecessary, it will be cut off. In addition, if the zero-sequence voltage detection sensitivity of the micro-ground fault selection relay 10G ₁ is not achieved due to low zero-sequence voltage, the backup protection function of the micro-ground fault selection relay cannot be performed, and the ground fault cannot be permanently eliminated. It becomes a big problem.

In order to solve this problem, in this embodiment, the ground fault direction relays 67G ₁₁ , 67G _1o and the slight ground fault selection relay 10G ₁ are set as they were before, and the setting values for each bank are set on the assumption that the bank will operate independently. , ground fault overvoltage detection relay OVG ₁ ~ which can trip the bus tie breakers CBt ₁ ~ CBt ₃ respectively.
Equipped with earth fault protection means consisting of OVG ₃ and timers T ₁ to _{T 3} . In this configuration, if a ground fault occurs in any bank, the existing relay 67
G ₁₁ , 10G _1, etc.), the zero-sequence voltage Vo of the ground fault overvoltage detection relays OVG ₁ to _{OVG 3}
Since the sensitivity of the relay is equal to or lower than the zero-sequence voltage Vo sensitivity of the existing relay, the relay OVG ₁ to OVG ₃
This detection can trip the bus ties and disconnectors CBt ₁ to CBt ₃ after the timers T ₁ to _{T 3} have expired. At this time, due to variations in the time limits of the timers T ₁ to _{T 3} , there is a difference in the time it takes for each of the bus ties and disconnectors CBt ₁ to _{CBt 3} to disconnect. Regarding the variation in this time limit, for example, when a ground fault occurs in feeder F ₁₁ ,
Even if the bus ties CBt ₂ and CBt ₃ are disconnected first, the zero-sequence voltage Vo remains, so it is detected by the ground fault overvoltage detection relay OVG ₁ and the bus tie is disconnected.
You can get a cut of CBt ₁ . On the other hand, when the shingle breaker CBt ₁ is cut off before CBt ₂ and CBt ₃ , only bank B ₁ becomes isolated, and the zero-sequence voltage Vo disappears due to the ground fault on the banks B ₂ and B ₃ side. The parallel operation of banks B ₂ and B ₃ continues.
This is the most ideal case, and after the bank tie breaker CBt ₁ is disconnected, only bank B ₁ will operate independently and the existing relays 67G ₁₁ , 67G _1o or 1
By 0G ₁ , the ground fault feeder can be removed from the system, and banks B ₂ and B ₃ remain in parallel operation.

Therefore, earth fault overvoltage detection relay OVG ₁ ~ _{OVG 3}
and timers T ₁ to _{T 3} to disconnect the bus tie and disconnect CBt _1.
~ By creating a configuration that allows CBt ₃ to be disconnected,
Ground fault feeders can also be eliminated in bank parallel operation.

Here, regarding the time limits of timers _T1 to _T3 , if there is no time limit, that is, if timers _T1 to _T3 are not provided, bank parallel operation is immediately canceled by the response of ground fault overvoltage detection relays _OVG1 to _OVG3 . By using the existing relays 67G ₁ and 10G ₁ of the bank where the ground fault has occurred, the ground fault can be removed without much difference from the conventional fault removal time. This method has the disadvantage that bank parallelism is solved for all ground faults.

On the other hand, when timers T ₁ to _{T 3} are provided and the time limit of these timers is set longer than the time limit of the ground fault direction relays 67G ₁₁ and 67G _1o and shorter than the time limit of the slight ground fault selection relay 10G ₁ , in this case, Since feeder ground faults that can be detected with the sensitivity of the ground fault direction relays 67G ₁₁ to 67G _1o can be removed by the ground fault direction relays, the frequency of bank parallel release can be reduced. Furthermore, since the bank parallelism is canceled by the time the slight ground fault selection relay 10G ₁ operates, the relay 1
Eliminates feeder errors and disconnections due to 0G ₁ . This method has the disadvantage that removal of faulty feeders is delayed by a set time period compared to fault removal using existing relays during bank independent operation.

The advantages and disadvantages of setting the time limits of the timers T ₁ to _{T 3} are appropriately considered according to the power system configuration to which the timers are applied, and the time limit settings are determined according to the bank system configuration.

In addition, in the embodiment, in addition to the relays OVG ₁ to OVG ₃ and timers T ₁ to _{T 3} as ground fault fault means, the timer T ₁ is used to detect the breakage of the bush ties and disconnectors CBt ₁ to CBt ₃ .
Bank parallel operation can be resumed by storing the information from the trip output of ~ _T3, etc., and re-closing the relevant bus ties and disconnectors _{CBt1 ~ CBt3} after the processing time of the slight earth fault selection relay 10G1. I can do it.

G. Effects of the Invention As described above, according to the present invention, by providing a ground fault overvoltage relay and a timer that trip the bus ties and disconnectors from the bus zero-sequence voltage, it is possible to replace the conventional or existing ground fault protection device. By simply adding a relatively simple ground fault overvoltage relay without making any changes to the system, ground faults during bank parallel operation can be reliably detected and ground fault feeders can be reliably removed.

[Brief explanation of the drawing]

FIG. 1 is an apparatus configuration diagram showing an embodiment of the present invention;
Figure 2 is a system diagram of a two-line power receiving substation. Tr ₁ , Tr ₃ ... Main transformer, CBt ₁ , CBt ₃ ... Bus tie breakout, CB ₁₁ , CB _1o ... Feeder breakout, 67G ₁₁ , 67G _1o ... Ground fault direction relay, 1
0G ₁ ...Slight ground fault selection relay, OVG ₁ , OVG ₃ ...
Ground fault overvoltage relay, T ₁ , T ₃ ... timer.

Claims (1)

[Claims] 1. In a power system where the secondary side buses of each main transformer of multiple banks are connected in parallel via bus ties and disconnectors to perform bank parallel operation, the zero-sequence current from the bus to multiple feeders and the bus a plurality of ground fault direction relays that detect a ground fault in each feeder from the zero-sequence voltage of the bank and trip the feeder switch or disconnector of the feeder; a micro-ground fault selection relay that sequentially trips the ground fault circuit breakers; a ground fault overvoltage detection relay provided for each bank that detects a ground fault from the zero-phase voltage of A parallel bank earth fault protection device characterized by comprising: