JP2809792B2 - Power system protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a winding type induction machine (hereinafter referred to as a variable speed machine) which operates at a variable speed by supplying a variable frequency current to a secondary winding. ) Relates to a protection device for a power system connected to a transmission line.

(Prior art) Conventionally, in a power plant, a synchronous machine connected to a transmission line is operated as a generator or a motor, and if an accident occurs in the power plant, the impedance seen from the system side is reduced. A protection system has been adopted to detect the accident and prevent the influence of the accident from spreading to the system.

FIG. 3 shows an equivalent circuit in the case where the synchronous machine is connected to the system and operated. In FIG. 3, 1 is an equivalent power supply simulating the system, 2 is the impedance of the transmission line, 3
Is the impedance of the main transformer, 4 is the equivalent impedance of the synchronous machine, and 5 is the internal induced voltage of the synchronous machine.

In such an equivalent circuit, the impedance Z viewed from the power station end (point P in FIG. 3) is represented by the following equation.

_{Z = V P / I T =} {E (Z T + Z G) + VZ L} / (E-V) ...... (1) where voltage vector V _P is the point P, current vector I _T is the point P , Z _L is the impedance of the transmission line, Z _T is an impedance of the main transformer, the equivalent impedance of Z _G are synchronous machine, E
Is a voltage vector of an equivalent power supply simulating a system, and V is an internal induced voltage vector of the synchronous machine.

In the above formula (1), since EV is usually small, Z
Is a large value, but when an accident occurs at the power plant, Z is a small value because EV is large. For example, if the voltage at point A becomes zero due to a power plant accident, Z
= The Z _T. Therefore, when the impedance Z seen from the end of the power plant becomes a small value, the point P or the point A is opened to prevent the influence of the accident at the power plant from affecting the system. However, the impedance Z seen from the end of the power plant becomes a small value not only in the case of a power plant accident,
Even in the case of a transmission line accident, the value is small. In such a case, the point P or the point A is interlocked so as not to be opened, and when the transmission line accident is eliminated, the operation returns to normal operation promptly. I can do it.

(Problems to be Solved by the Invention) By the way, in a power plant in which a variable speed machine is connected to a transmission line and this variable speed machine is operated as a generator or a motor, if the above-described protection method is applied, a transmission line accident may occur. In this case, since the variable speed machine is connected to the transmission line, an overvoltage occurs in the secondary winding of the variable speed machine. Therefore, when an accident occurs in the transmission line, the secondary winding of the variable speed machine is short-circuited with low resistance to suppress the occurrence of overvoltage. Keeps flowing. Therefore, the phase difference angle (the phase difference with respect to the voltage vector E of the equivalent power supply simulating the system) of the internal induced voltage vector V _V of the variable speed machine is determined by the slip of the variable speed machine immediately before the occurrence of the accident in the transmission line (electricity of the system voltage). Angular velocity). For this reason, depending on the slip of the variable speed machine immediately before the transmission line accident, even if the transmission line accident is removed, the impedance Z
May become a small value, and in such a case, it becomes close to a state where the accident of the transmission line could not be eliminated, which may lead to an increase in system accidents.

The present invention prevents the spread of a system accident due to a variable speed machine even if an accident occurs in the transmission line when the variable speed machine is operated at a slip frequency at which the impedance seen from the connection end with the transmission line becomes a small value even if an accident occurs in the transmission line It is an object of the present invention to provide a power system protection device capable of performing the following.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a winding type induction machine which is driven at a variable speed by supplying a variable frequency current to a secondary winding and connected to a transmission line. In an electric power system, an accident detecting means for detecting an accident of a transmission line, a slip detecting means for detecting a slip of the wire-wound induction machine and following the slip and storing the slip, and an impedance as viewed from a connection end with the transmission line in advance The upper and lower limits of the slip of the wire wound induction machine is set to a small value,
When a fault in the transmission line is detected by the fault detecting means, it is determined whether or not the slip of the wound-type induction machine immediately before the occurrence of the fault stored in the slip detecting means is within the set range, and within the set range. If so, a shutoff commanding means for separating the winding type induction machine from the transmission line is provided.

(Operation) In the protection device for the power system having such a configuration, even if the accident of the transmission line is eliminated, the wound-type induction machine operates in a slip in which the impedance seen from the connection end with the transmission line becomes a small value. When an accident occurs in the power transmission line, the wound wire induction machine is quickly disconnected from the power transmission line, so that it is possible to prevent the system from being expanded by the wound wire induction machine. Also, if the wound induction machine is operated outside the slip range where the impedance seen from the connection end with the transmission line becomes a small value, and if an accident occurs in the transmission line, the winding induction machine will Since it is not disconnected from the power transmission line, it is possible to promptly return to normal operation when the accident of the transmission line is eliminated.

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

FIG. 1 shows a configuration example of a power system protection device according to the present invention. In FIG. 1, reference numeral 11 denotes a variable speed machine. The primary winding of the variable speed machine 11 is a circuit breaker 12 and a main transformer.
The secondary winding of the variable speed machine 11 is excited by an AC exciting device 15 connected to an electric circuit between the circuit breaker 12 and the main transformer 13. And
These constitute a main circuit. In this case, the variable speed machine 11
The excitation circuit of the secondary winding is connected to an overvoltage suppression device 16 that operates when an accident occurs in the transmission line.
A rotation angle detector 17 for detecting a rotor rotation angle for controlling the AC excitation device 15 is attached to the rotor shaft.
On the other hand, the system voltage signal 18 detected by the voltage transformer 19 connected to the electric circuit between the circuit breaker 12 and the main transformer 13 and the output signal of the rotation angle detector 17 are input to the variable speed machine 11. Slip detector for detecting slip, 20 is the slip detector 18
The slip detected at and the output signal of the overvoltage suppression device 16 are input, and when the overvoltage suppression device 16 operates, it is determined whether or not the slip of the variable speed machine 11 immediately before it is within a preset slip setting range, Only when it is within the slip setting range, a break command is given to the breaker 12 and the AC exciting device 15
This is a shutoff command device that gives a stop command to the power supply.

FIG. 2 shows the slip detector 18 and the shutoff command device.
20 shows a block circuit of an internal configuration example of No. 20. Second
In the figure, a slip detector 18 is a subtractor 18 that detects a difference between an electrical angle _ＬL of a system voltage, which is an output signal of the voltage transformer 11, and a rotor rotation angle _ωωR , which is an output signal of a rotation angle detector 17.
-1 and a signal (logic "1") b indicating that the differentiator 18-2 for obtaining the slip S from the output of the subtracter 18-1 and the overvoltage suppressor 16 are operating, and then the differentiation is performed. And a tracking storage unit 18-3 for storing the slip S output from the unit 18-2. Moreover, interruption command device 20 and the slip range setting values 20-1 impedance Z as viewed from the pre-plant end is set by predicting the upper values S ₁ and the lower limit value S ₂ of the slip as a small value, tracking Memory 18-3
Whether the output signal in the range between the upper limit values S ₁ and the lower limit value S ₂ that is set to S _M sliding range setter 20-1, that is S ₁
> S _M > S ₂ is determined, and if S _M is within the range between S ₁ and S ₂ , a slip range detector 20-2 that outputs an output signal (logic “1”) a and an overvoltage When a signal (logic "1") b indicating that the suppression device 16 is operating and an output signal (logic "1") a of the slip range detector 20-2 are input, the logical product signal c is generated. It is composed of an AND gate 20-3 which outputs a shutoff command and a stop command.

Next, the operation of the thus configured power system protection device will be described.

First, the upper limit value and the lower limit value of the slip range set in the slip range setting device 20-1 will be described. Now, assuming that the slip of the variable speed machine 11 immediately before the transmission line fault is S _N and the transmission line fault duration is T _F , when the secondary winding of the variable speed machine 11 is short-circuited with low resistance, it flows into the secondary winding. Since the decay time constant of the current (transient DC current) is sufficiently larger than _TF , the internal induced voltage vector V _V of the variable speed machine 11 can be approximated by the following equation.

V _V = E (1−α) (2) α = EXP (jΦ−jω _L S _N T _F ) where Φ is the phase difference angle of the variable speed machine immediately before the power line accident, ω
_L is the electrical angular velocity of the system voltage.

Therefore, the impedance Z seen from the power station end is expressed by the following equation.

Z = {E (Z _T + Z _G ) + V _V Z _L } / (E−V _V ) = (Z _T + Z _G + Z _L ) / (α−Z _L ) (3) From equation (3), α It can be seen that the impedance Z seen from the power plant end can vary from zero to infinity depending on the value of. In this case, ω _L and T _F are almost constant, and Φ is determined by _SN , so α is the slip of the variable speed machine immediately before the power line accident.
It can be said that it is determined by _SN . Further, from the viewpoint of preventing the spread of the system accident, the allowable impedance Z seen from the power station end must satisfy the following expression.

Z> Z _MIN (4) Here, Z _MIN is a lower limit value of the impedance viewed from the end of the distribution substation determined from the allowable _fault current.

Therefore, the upper and lower limits of α satisfying the expression (4) are α
_1, and alpha _2, when the value of S _N and its corresponding _{S 1, S 2, S 1} , S 2 becomes the upper limit value and the lower limit value of the slip which the impedance Z as viewed from the power plant end exceeds the allowable range, the upper limit values S ₁ and the lower limit value S ₂ is set to the set 20-1.

By the way, when the variable speed machine 11 is operated in a slip range where the impedance Z seen from the end of the power plant becomes a small value, that is, when the impedance Z exceeds a permissible range, if an accident occurs in the transmission line, the overvoltage suppressing device is used. 16 operates, and the output signal b of logic “1” is input to the shutoff command device 20. At this time, the slip detector 18 uses a subtractor 18-1.
S obtained by differentiating the output of
There are stored and held in the follow-up memory unit 18-3 is input to the range detector 20-2 slip its output signal S _M. In this case, following the output signal S _M of the storage unit 18-3, since the follow slowly slip S _N of the variable speed motor 11, variable speed motor 11 immediately before the transmission line fault when the overvoltage suppression device 16 is operated It has become a slip S _N, while the overvoltage suppression device 16 is operating is held to the value of the S _N. That lies between the sliding range detector 20-2 slip S _N that the stored and held in the follow-up memory unit 18-3 is set in the slip range setting unit 20-1 upper limit values S ₁ and the lower limit value S ₂ Judgment is made and the output signal a of logic "1" is input to the AND gate 20-3. In the AND gate 20-3, the logical product of the output signal "a" of the slip range detector 20-2 and the output signal "b" of the voltage suppressor 16 becomes logic "1". At the same time, the AC excitation device 15 stops. Therefore, it is possible to prevent the system accident from spreading due to the variable speed machine 11.

Further, if the variable speed machine 11 is operated outside the slip range where the impedance Z seen from the power plant end is a small value, that is, when the impedance is within the allowable range, and an accident occurs in the transmission line, The output signal b of logic "1" is input to the AND gate 20-3 by the operation of the overvoltage suppression device 16, but the output signal stored and held in the tracking memory 18-3.
Since S _M is outside the range of the upper limit values S ₁ and the lower limit value S ₂ in the slip which is set to a range detector 20-2 slip, the slip range detector 20-
2 is a logic "0" and the AND gate 20-3
Is a logical "0". Therefore, in this case, the circuit breaker 12 is not interrupted, and the AC excitation device 16 is also in the operating state.
11 can be promptly returned to normal operation.

In the above embodiment, the occurrence of an accident in the transmission line is detected by the operation of the overvoltage suppression device 16.
The detection may be performed by operating the protection relay of the transmission line.

[Effects of the Invention] As described above, according to the present invention, when the variable speed machine is operated at the slip frequency at which the impedance seen from the connection end with the transmission line becomes a small value, an accident occurs in the transmission line. In this case, since the variable speed machine is separated from the transmission line, it is possible to provide a power system protection device capable of preventing the system accident from being expanded by the variable speed machine.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a power system protection device according to the present invention, FIG. 2 is a block circuit diagram showing an internal configuration of a slip detector and a cutoff command device in the embodiment, and FIG. FIG. 5 is an equivalent circuit diagram when the machine is connected to a system and operated. 11… variable speed machine, 12… breaker, 13… main transformer, 14
... transmission line, 15 ... AC excitation device, 16 ... overvoltage suppression device, 17 ... rotation angle detector, 18 ... slip detector, 20 ...
Shut-off command device.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hirokazu Kaneko 1-3-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Inside Tokyo Electric Power Company (72) Inventor Tadahiro Yanagisawa 1-Toshiba-cho, Fuchu-shi, Tokyo Inside the plant (72) Inventor Shinobu Takeda 1 Toshiba-cho, Fuchu-shi, Tokyo Inside the Fuchu plant, Toshiba Corporation (56) References JP-A-2-155500 (JP, A) (58) Fields investigated (Int. . ^6, DB name) H02P 9/00 - 9/48 H02P 3/00 - 3/26 H02P 1/00 - 1/58

Claims (1)

(57) [Claims] An accident detecting means for detecting an accident in a transmission line in a power system in which a winding type induction machine that operates at a variable speed by supplying a current of a variable frequency to a secondary winding is connected to the transmission line. Slip detecting means for detecting the slip of the linear induction machine and tracking and storing the slip, and upper and lower limits of the slip of the wire wound induction machine in which the impedance seen from the connection end with the transmission line becomes a small value in advance are set. When a fault in the transmission line is detected by the fault detecting means, it is determined whether or not the slip of the wound-type induction machine immediately before the occurrence of the fault stored in the slip detecting means is within the set range. And a disconnection commanding means for disconnecting the wound induction machine from the transmission line.