JPH0561862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for protecting parallel operation of generators.

[Conventional technology]

FIG. 3 shows a conventional protection device in a system in which an electric power company system and a private power generation system installed in a factory or the like are operated in parallel. In the figure, 1 is the electric power system of the electric power company, 2 is the connecting power line, 3 is the power receiving circuit breaker, 4 is the CT, 5 is the power receiving transformer,
6 is a generator circuit breaker, 7 is a CT, 8 is a private generator or a group of private generators, and 9 is a factory load (or load group). 10 is a PT, 11 is an active power directional relay, and 12 is an overcurrent relay. The active power direction relay 11 operates when the power flow is from the receiving transformer 5 to the power grid 1, and the overcurrent relay 12 operates when the output current of the private generator 8 exceeds the rated current value. When both relays operate, the power receiving circuit breaker 3 is tripped due to the AND condition of the output during operation, and the connection between the electric power system 1 and the private power generation system is interrupted.

Note that the private power generator 8, under normal operating conditions,
If power is being supplied to the factory load 9 and the required power of the factory load 9 exceeds the output of the private generator 8,
The shortage is supplied from the power system 1 through the power receiving transformer 5. Conversely, when the power demand of the factory load 9 decreases, the difference between the power demand and the output of the private generator 8 becomes surplus power, and this surplus power is transferred to the power system 1.
It will be supplied (backward) to.

[Problem that the invention seeks to solve]

In this way, conventionally, the active power directional relay 11 is used to detect the power flow, and the active power directional relay 11 operates from the time when the reverse power transmission starts until the overcurrent relay 12 operates. , is in an operating state, so if it is an induction coil type or a plunger type, there is a problem that the life of springs etc. that deform during operation is shortened and it is difficult to ensure long-term reliability.

This invention was made to solve the above problem, and an object thereof is to provide a parallel operation protection method that can ensure reliability over a long period of time.

[Means to solve the problem]

In order to achieve the above object, the present invention detects the reverse current flowing from the generator side to the power grid, and also detects the surplus current of the generator, and detects when the value of the reverse current exceeds the value of the surplus current. In this case, the power reception circuit breaker installed in the power reception line is activated.

[Effect]

In this invention, the operation is performed when the magnitude relationship between the reverse current and the surplus current of the generator reaches a predetermined relationship,
Since there is no need to use a relay that responds to the presence or absence of reverse current, reliability can be ensured over a long period of time.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 20 is a current detector,
The output current of the CT 4 is taken in and the current flowing through the power receiving line 2 is detected. 21 is a polarity discriminator that determines the current value IR when the polarity of the current detected by the current detector 20 is in the direction of the arrow shown, that is, when the current flowing through the power receiving line 2 is a reverse current. The signal is supplied to the comparator 25. 22 is a current detector, which receives the output current of the private generator 8 via CT 7;
Detect the output current. Reference numeral 23 is a margin current detector, and the current detector 22 compares the current Ig and the set current value (rated current value of the private generator 8) Igo of the setting device 24, and compares the deviation ΔIg = Igo - Ig. vessel 25
supply to. The comparator 25 compares the reverse current IR and the margin current ΔIg, and determines that IR>ΔIg (however, ΔIg>0)
When this happens, the output operates and a cutoff command signal is sent. This cutoff command signal is supplied to the output relay 27 through the delay circuit 26 to prevent operation due to erroneous detection, and the output relay 27 closes the contact 28 by its energization, and the power receiving circuit breaker 3 is tripped by the contact output. Ru. 20 to 28 constitute the protection device of this embodiment, and its operating area is shown in FIG. 2 (shaded area indicated by symbol A).

In this embodiment, the reverse current IR is
The output relay 27 does not operate while the operating margin is within the range of ΔIg, but when it becomes larger than ΔIg, the output relay 27 immediately operates and the power receiving circuit breaker 3 is tripped by the contact output.

In terms of actual operation, in a system with one private generator and one power receiving circuit,
If ΔIg is large, it can be assumed that the operating output of the private generator is small, so IR will not increase more than ΔIg.

In this embodiment, the operation of the components 20 to 26 is static except for the output relay 27, and the output relay 27 can also be of a stationary type, and an active power directional relay or the like as described above may be used. Since this is not necessary, high reliability can be maintained over a long period of time.

〔Effect of the invention〕

As explained above, this invention statically monitors the reverse current and the margin current, compares the magnitude of these two current values, and operates a power receiving circuit breaker etc. when a predetermined magnitude relationship is reached. This eliminates the need to use relays such as relays that operate in response to the presence or absence of reverse current as in the past, ensuring high reliability over a long period of time, and reducing the need for surplus generators. It becomes possible to easily transmit back power to the power grid to the maximum extent within its rated output range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of this invention.
FIG. 2 is a diagram showing the operating characteristics of the above embodiment, and FIG. 3 is a circuit diagram showing a conventional protection device. In the figure, 1...Power system, 2...Connection power receiving line, 20, 22...Current detector, 21...Polarity discriminator, 23...Marginal current detector, 24...Setter, 25... Comparator, 27...output relay. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a power system that has a generator and a load group connected to the power system via a common power receiving line,
A reverse current flowing from the generator to the power system is detected, and a margin current of the generator is detected, and when the value of the reverse current exceeds the margin current value, the power receiving line is interposed. A parallel operation protection method characterized by operating a power receiving circuit breaker.