JPH03251057A - Independent operation transfer unit for power station facility - Google Patents

Abstract

PURPOSE:To detect external fault without exception by constituting an independent operation transfer unit in the station of a frequency drop protective relay or a backup protective relay for generator and at least one of undervoltage protective relay, voltage suppression overcurrent protective relay or frequency drop rate protective relay. CONSTITUTION:When two-phase or three-phase function of a system bus undervoltage relay 10 is superposed on the two-phase or three-phase function of a station bus undervoltage relay 8, a circuit breaker 2 is closed after a predetermined time limit set by a timer 16. lf opening function of the circuit breaker 2 is not carried out at that time, the circuit breaker 2 is opened after a predetermined time limit set by a timer 17 through two-phase or three-phase function of second state station bus undervoltage relay 9 having different operation set point and two-phase or three-phase function of the system bus undervoltage relay 10.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention disconnects the generator of an operating thermal power generation facility from the power transmission line and consumes the output of the generator only for the electrical load within the power plant including the power generation facility. This relates to a device that determines whether or not it is necessary to shift to in-house independent operation, that is, the conditions for shifting to in-house independent operation.

[Conventional technology]

When it is determined that this is the case, the circuit breaker connecting the generator to the power transmission line is temporarily opened, and the output of the generator is consumed only by the electrical load within the power station, thereby limiting the load on the generator and connecting it to the external grid. The system is on standby for power to be retransmitted due to recovery from the accident.

Detection of external system accidents (hereinafter referred to as external accidents) is as follows:
Originally, multiple protective relays arranged in the external system should be operated according to the location of the accident point, depending on the relationship between life insurance and back-up protection.

Even in the unlikely event that an external accident cannot be eliminated, the generator frequency that appears as a result of most external accidents or a significant imbalance in supply and demand has been set to Has the drop exceeded a preset tolerance limit, or has an accident occurred that satisfies the operating conditions for an impedance relay installed as a backup protection in case the ratio differential protection of the generator windings fails? It is done depending on whether or not.

[Problem to be solved by the invention]

However, it has been found that these two operating conditions alone are likely to cause external accidents that cannot be prevented. For example,
Even if the amount of frequency drop is within the allowable limit, the system connected to the power station busbar connected to the illumination output terminal of a generator or via a transformer, or the high voltage side terminal of the power station main transformer. If the voltage on the bus bar drops to such a level that it is impossible to transmit power from the generator to the transmission line, or if the external fault is a short circuit and the circuit breaker at the power plant has to be opened, the fault point of the fault is If the power transmission line that is outside the operating range of the generator backup impedance relay or is connected to the generator is disconnected from another system connected to this power transmission line! In cases such as when power fluctuations are large and the rate of frequency decline becomes significant, and when the wave number itself is within the allowable limit, conventional frequency drop protection relays and power generators are used. Aircraft backup protection relays cannot respond to external accidents or changes in system status, making it impossible to shift to isolated operation within the station, and making it impossible to limit the load on ITS.

An object of the present invention is to provide an in-station isolated operation transition device that can detect all external accidents that are the result of most external accidents and that require disconnection of the generator from the power transmission line. .

[Means to solve the problem]

In order to solve the above problem, in this invention,
The station isolated operation transition device is configured using at least one of a frequency drop protection relay and a generator back-up protection relay.

[Effect]

This invention was made based on the experience of actually operating an in-station isolated operation transition device having a conventional configuration.

That is, undervoltage protection relays in addition to traditional underfrequency protection relays or generator backup protection relays.

By configuring an in-station islanding operation transition device using at least one of an overcurrent protection relay with voltage suppression and a frequency reduction rate protection relay, it is possible to prevent the frequency from dropping beyond the permissible limit or when the fault point is at the generator. It is possible to catch all external accidents that are not within the backup protection range, and it is possible to shift the thermal power generation equipment to isolated operation within the station while continuing stable operation. In other words, the undervoltage detected by the undervoltage protection relay is caused by the ground voltage of the station bus connected directly to the output terminal of the generator or via the station transformer and the source '1! The voltage to the ground of the system bus connected to the high-voltage side terminal of the main transformer that is supplied with power from the L machine.If this undervoltage is, for example, in a system where the neutral point is not directly grounded, it will be applied to two of the three phases. When this is detected, it is assumed that a short-circuit current or overcurrent has occurred in the external system, and the generator is disconnected from the power transmission line, and the overcurrent protection relay with voltage suppression It is caused by a driving torque and a voltage or a combination of voltage and current. The operating impedance area of the relay, which is determined by the current value at which the equilibrium point between the contact driving torque and the suppressing torque in the opposite direction is located, is roughly the same as the operating area of the generator backup protection relay. Set to cover a large area. The frequency drop rate protection relay is used to prevent the power passing through the power transmission line from the power transmission line connected to the generator. If the rate of frequency decrease caused by a change is greater than the set value, but the wave number itself is within the permissible limit, this frequency decrease rate is detected and the generator is disconnected from the power transmission line to ensure stable operation of the power generation equipment. It will be continued and prepared for retransmission.

Thus, in accordance with the present invention, a conventional underfrequency protection relay is detected. This can occur in the case of short-circuit currents or overcurrents in external systems that do not lead to a frequency drop exceeding permissible limits, fault points within the backup protection range of generators, or system separation necessary for stable system operation. It is possible to disconnect the generator from the power transmission line in response to power fluctuations, such as a frequency drop rate that exceeds an allowable value, and shift to isolated operation within the plant while maintaining stable operation of the power generation equipment. Therefore, depending on the situation or character of the system to which the power plant belongs, an undervoltage protection relay, an overcurrent protection relay with VT pressure suppression 9
By adding at least one of the frequency drop protection relays to a conventional frequency drop protection relay or generator back-up protection relay and configuring an in-station isolated operation transition device, power generation equipment can be switched to in-station operation in response to external accidents without fail. It is possible to shift to independent operation.

〔Example〕

FIG. 1 shows an embodiment of the present invention in a configuration example of a main circuit of a thermal power plant. The generator 4, whose neutral point is grounded via the primary winding of a transformer having a neutral point resistance on the secondary side, is connected to the system motherboard via the main transformer 3 and the high voltage circuit breaker 2. 1, and is also connected to the station bus 5 via the station transformer 6 and medium voltage circuit breaker 14. Send tHn to lineage mother 1111
, 12 two-circuit wires are connected to the station bus IR 5, and a plurality of medium voltage circuit breakers 15 used for switching and protecting electrical loads within the power station are connected to the station bus IR5.

A generator frequency relay 7 that operates when the generator frequency drops beyond a set permissible limit is used as a relay constituting an isolated operation transition device in a thermal power plant where the main circuit is configured in this way. A station bus undervoltage relay that is connected to the main circuit on the output terminal side of the generator 4 via an appropriate electrical quantity conversion means, and operates when the ground voltage of the station bus w15 drops beyond a set permissible limit. 8, and a second-stage station bus undervoltage relay 9, which has different operating point setting values (operating voltage and operating time) from this undervoltage relay 8, connects the three phases of the station bus 5 to the ground voltage of the system bus 1. A system bus undervoltage relay lO, which operates when the voltage drops beyond a set permissible limit, is connected to the three phases of the system bus IQ) through appropriate electrical quantity conversion means.

In the station isolated operation transition device configured in this way,
For example, the transition to in-station independent operation based on detection of undervoltage is performed as shown in FIG. Assuming that the system to which the power plant belongs is non-directly grounded at the neutral point, it will be necessary to disconnect the generator from the system in the event of a two-phase ground fault or a two-phase ground fault that produces a two-phase or three-phase short-circuit current. 3-phase ground fault (
It has been statistically confirmed that correlated short circuits without ground faults, that is, short circuits in the air in transmission line conductors, rarely occur in practice, but even in this case, the voltage to ground will decrease due to the impedance drop in the main circuit. (the temperature drops to 8 degrees), so
At least 2 out of 3 phases of each of the system bus*i and the station bus 5
When the phase undervoltage relay operates, the circuit breaker 2 is operated to open, and first, the system bus undervoltage relay 10 is activated.
2-phase or 3-slide operation and station bus undervoltage relay 8-2
Timer 16 is activated when a phase or three-slide operation occurs in the summer.
After a predetermined time period, the circuit breaker 2 is opened. At this time, if the opening operation of the circuit breaker 2 is not performed, the 2-phase or 3-slide operation of the second-stage local bus undervoltage relay 9, which is the operating point setting value, and the system bus undervoltage relay 10 are activated. By the two-phase or three-slide operation, the circuit breaker 2 is opened after a predetermined time period via the timer 17. Furthermore, if the system to which the power plant belongs is directly grounded at the neutral point, short-circuit current will also occur in the case of an L-phase ground fault. Configure your protection system to do so.

Note that the in-station isolated operation transition device according to the present invention has the same load responsiveness (amount of change in load and a change in generator output commensurate with this amount of change) as thermal power generation equipment, instead of the four characteristics of thermal power generation equipment. Needless to say, it can also be applied to nuclear power generation facilities that have a relationship with the time required for

〔Effect of the invention〕

As described above, in the present invention, the generator of the thermal power generation equipment in operation is disconnected from the power transmission line, and the generator output is consumed only for the electrical loads in the power plant, including the 1L equipment, to achieve isolated operation within the plant. A device that determines whether or not migration is necessary.
Since it is constructed using at least one of a frequency drop protection relay and a generator back-up protection relay, and at least one of an underpressure protection relay and a voltage suppression relay, the frequency does not drop beyond the permissible limit. It is possible to catch all external accidents when the accident point is not within the backup protection range of the generator, and it is possible to shift to isolated operation within the station while continuing stable operation of the thermal power generation equipment. Became. In addition, if power fluctuations are large during system separation, etc. performed for stable operation of the system, and the rate of decrease in frequency is abnormally large, @electronic equipment may be disconnected from the system before the frequency itself reaches a predetermined permissible limit. It has become possible to switch to independent operation within the station without interfering with the operation of the power generating equipment.

[Brief explanation of drawings]

Figure @1 shows an example of the arrangement of relays, which are components of the device, when configuring the in-house isolated operation transition device for thermal power generation equipment according to the present invention, targeting the main circuit configuration of an example of a thermal power plant. The circuit diagram and FIG. 2 are explanatory diagrams showing the process from detection of undervoltage by an undervoltage relay constituting a device for shifting to isolated station operation to transition to isolated station operation. 1... System bus, 2... Circuit breaker, 4... Generator,
5... Station busbar, 7... Generator frequency relay (frequency drop protection relay), 8, 9... Station bus undervoltage relay (undervoltage protection relay), lO... Piezoelectric relay for system bus shortage. (Undervoltage protection wk relay), 11, 12・
・・Transmission 2 77f electric wire diagram diagram

Claims (1)

[Claims] 1) A device that determines whether or not it is necessary to switch to in-station isolated operation in which the generator of an operating thermal power generation facility is disconnected from the power transmission line and the output of the generator is consumed only by the electrical load within the power station, including the power generation facility. characterized by comprising at least one of a frequency drop protection relay and a generator backup protection relay, and at least one of an undervoltage protection relay, an overcurrent protection relay with voltage suppression, and a frequency drop rate protection relay. A device for transitioning to isolated operation within a thermal power generation facility.