JPS631812B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital distance relay system having a direction determining function that is applied to a power system.

FIG. 1 shows the structural concept of the distance relay method that has been conventionally applied. A power source 3 is installed on the power transmission line 1 via a back impedance 2. The current and voltage of the power transmission line 1 are level-converted to predetermined values through a current transformer 4 and a voltage transformer 5, respectively, and are input to a distance relay (for example, a Maw type distance relay) 6 having a direction determining function. The Moh type distance relay (abbreviated as Moh relay) 6 measures the direction of the fault point and the distance to the fault point based on a predetermined operation formula.
It is determined whether the object is within a predetermined direction and distance.
In such a distance relay system, the Maw relay is provided with a memory function in order to prevent the distance relay from malfunctioning for a certain period of time even if the voltage drops to zero level in the event of a short-circuit failure. The technology will be explained in more detail below.

The operating principle of the Moh relay is shown in Figures 2 and 3.
There is a method shown in the figure. The method shown in FIG. 2 is called a phase detection method and is based on the operating principle expressed by the following equation.

V _P (IZ ₁ −V) = |IZ ₁ |・|V _P | ・cos(−θ) |V _P | ・|V|x cos αK ₁ …(1) In equation (1), I and V are Current, voltage, V _P respectively
is the polarity voltage and K ₁ is the minimum sensitivity constant. or the maximum sensitivity angle, θ is the leading phase angle of V with respect to I, Z ₁
is the set value, the mark represents the inner product, and α is V _P
The angle between V and V, which is usually 0. The operation of equation (1) is determined based on whether the phase of the composite electrical quantity (IZ ₁ -V) (=EF→) is smaller or larger than 90° with respect to the polarity voltage V _P (=OP→).

On the other hand, the determination method shown in FIG. 3 is called the absolute value comparison method and is based on the following equation.

|IZ _O +k′V _P |−|IZ _O −V−k′V _P |K _O …(2) In equation (2), Z _O and K _O correspond to Z ₁ and K ₁ in equation (1). do. k' is a positive constant.

In Fig. 3, the composite electrical quantity (IZ _O −V−k′V _P )
The magnitude of (=EM→) is the composite electrical quantity (IZ _O +k′V _P )
The operation is judged based on whether it is larger or smaller than the magnitude of (=ON→). However, MN→=FE→=k′V _P.

There are two methods of operation of the Moh relay as described above, and it goes without saying that it must also have a direction determination element to detect whether or not the location of the failure point is in a predetermined direction. . In that case, the relay must respond accurately even if the voltage drops to zero in the most severe internal close-point accident. For this reason, in conventional electromagnetic type and transistor type Moh relays, the pre-failure voltage is stored using a series resonant circuit with the same frequency as the frequency of the electrical quantity in the system as a polarity quantity of vector OP→ shown in Figures 2 and 3. This prevents misperception of direction even if the fault voltage drops to zero level in the event of a close point fault. FIG. 4a shows the configuration of such resonant circuits R and C, and FIG. 4b shows an input/output waveform diagram. The V _P output of FIG. 4a is shown in FIG. 4b. Even when the voltage (solid line) reaches the zero level at time _tA , an output V _P as shown by the dotted line is obtained, and the time Tm until the V _P voltage level reaches the zero level is the effective time of the memory action.
The memory voltage V _M can be obtained by the following method in a modern Moh relay using a digital computer.

(a) V _M =V _o : Use voltage V _o n cycles before the current voltage.

(b) V _M =-V _o : Use voltage V _o (n-1/2) cycles before the current voltage.

However, n is an integer satisfying n≧1.

However, since such a memory function has a limited effective time, it goes without saying that when the memory function disappears, the ranging and direction detecting functions of the relay also disappear. In the current distance relay system, a Moh relay is used as the starting element, and in the case of a near-end failure, a distance relay with reactance characteristics as shown by X in Figure 5 instantly issues a power failure command. Therefore, the fault can be removed within the effective time of the memory action. However, it goes without saying that it would be extremely difficult to apply the Moh relay to a relay system that requires issuing a cut-off command after the effective time of the memorization action has elapsed. Furthermore, the operating principle for obtaining a Moh relay is the method of equations (1) and (2) as mentioned above, but when trying to realize a Moh relay using a digital computer, the latter absolute value comparison method requires multiplication. It is characterized by being easy to process in that it does not require

The present invention applies a Moh relay based on the operating principle of the absolute value comparison method to the starting element, and provides a digital distance relay system that can respond correctly even after the effective time of memory action in the event of a short-circuit accident. The purpose is to

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 6, the voltage and current obtained by converting the power transmission line 1 to a predetermined level through a voltage transformer 5 and a current transformer 4 are sampled at a constant period by a digital-to-analog converter 7 and converted into digital quantities. The data is converted and imported into the digital computer 8. The digital computer 8 uses the digital amounts of current and voltage taken in to carry out protection calculations based on the flowchart shown in FIG.

In step 701 in FIG. 7, the product of the set value Z _O and the current I is calculated. Next, in step 702, the difference between the composite electrical quantity _IZO obtained in step 701 and the voltage V taken in from the A/D converter is determined.
In step 703, the voltage data stored in the memory circuit n cycles or (n-1/2) cycles ago, that is, the memory voltage V _M , the voltage V, and the constant k,
The composite electrical quantity (KV _M −kV) is obtained from K. Here, the composite electrical quantity (KV _M −kV) is defined as k′V _P in equation (2). In the next step 704, the composite electricity quantity c (= _{IZ O + KV M}
−kV). Furthermore, in step 705, from the composite electrical quantity (IZ _O -kV) obtained in step 702 and step 703, the synthetic electrical quantity D=(IZ _O -V-
(KV _M −kV)). In step 706 (2)
It is confirmed in a predetermined memory whether the motor relay is operating or not based on the operation judgment formula of the formula, and if it is confirmed that it is not operating, the process proceeds to step 707 and the The absolute values of the composite electric quantities C and D are compared, and the operation of the above-mentioned equation (2) is determined. If it is not operating, the process proceeds to step 709, where the non-operation is stored in a predetermined memory used to check the operation of the morley relay in step 706, and the process proceeds to step 713. Furthermore, if the operation of the morley relay is confirmed in step 706, the step
Proceed to 710. If the operation is determined in step 707, the process proceeds to step 708. In step 708, the operation is stored in a predetermined memory for checking the operation of the morley relay, and the process proceeds to step 710.
Combined quantity of electricity C obtained in steps 704 and 705
(=IZ _O +KV _M −kV), D(=IZ _O −V−(KV _M −
From the magnitude of kV)), use the following formula k _O |C|-|D|K _O ...(3) Perform operation judgment. The operating characteristic of equation (3) is a characteristic circle indicated by the offset mode OM in FIG. However, the constant k _O in equation (3) is a value greater than 1. By giving such a constant _kO , OA→=(1+ _kO )・_IZO , OB→=( _kO −1)・_IZO , which becomes a characteristic circle including the relay installation point O. If there is no operation in the operation determination of equation (3) representing the offset mor characteristic described above, the process proceeds to step 709. If it is in operation, the process proceeds to step 711, where it is detected whether or not the offset mode relay shown by equation (3) is in operation even after a predetermined time To, which is longer than the effective time Tm of the memorization effect described above, and whether or not it is in operation. If so, proceed to step 712, issue a command to stop, and proceed to step 713. If not working, step
Proceed to 713 and execute the next process.

As described above, the present invention provides an offset mode relay as shown by the operating principle equation based on absolute value comparison shown in equation (3) on the condition that the motor relay based on absolute value comparison shown in equation (2) operates. By switching, that is, by switching the characteristic circle from the Moh characteristic shown in Fig. 8 to the offset Moh characteristic, the fault point is included even when the voltage reaches zero level at the time of a close-end short-circuit fault and the memory function described above disappears. The operating characteristics may enable longer time limits than the memory action.

Furthermore, the present invention is also possible by applying an undervoltage detection relay to the conditions for switching to an offset mode relay. An example is shown in FIG. Preprocessing up to step 901 follows steps 701 to 705 in FIG. In step 901, it is checked whether the undervoltage detection relay (UV relay) is operating or not in the specified memory, and if it is confirmed that it is not operating, step 902 (corresponding to step 707) is performed.
The process proceeds to step 910, where the operation of the motor relay is determined based on the above-mentioned equation (2), and if it is not in operation, the process proceeds to step 910, which corresponds to step 713. If it works, proceed to step 903. If the UV relay operation is confirmed, the process proceeds to step 905.In step 903, the magnitude of the voltage amount V is determined.

|V|<V _O …(4) In equation (4), the undervoltage detection level V _O is A/D
The value should be set to a sufficiently low level that it will not be affected by conversion errors, etc., and should enable detection of short-circuit failures at the close end. If the UV relay does not operate, the non-operation is stored in a predetermined memory for confirming the operation of the UV relay, and the process proceeds to step 908 (corresponding to step 711). If the operation is performed, the operation is stored in a predetermined memory in which the operation is confirmed, and the process proceeds to step 906. step
In 906, the operation of the offset mode relay is determined based on the above-mentioned formula (3), and if it is not activated, the step
Proceeding to step 907, a predetermined memory for confirming the UV relay operation is memorized to indicate that it is inoperable, and the process proceeds to step 910. If it is in operation, proceed to step 908, perform the same process as step 712 in Figure 7, and complete the set time.
If T _O is exceeded, the process proceeds to step 909, where a command to stop the process is issued, and the process proceeds to step 910. If T _O is not exceeded, the process proceeds to step 910 and performs the next process.

As described above, in the Moh relay system based on the absolute value comparison method, the present invention enables time-limited disconnection by creating a characteristic circle that includes the relay installation point even when the memory function disappears. . In addition, by appropriately selecting the constant k _O expressed by equation (3) in accordance with the system conditions, a sufficiently accurate response can be expected with respect to the effects of fault point resistance and load.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the conventional distance relay system, Figures 2 and 3 are diagrams explaining the operating principle of the Moh relay, and Figure 4 is a diagram explaining the conventional memory circuit and its input/output waveforms. , FIG. 5 is a diagram explaining the necessity of the present invention, FIG. 6 is a block diagram explaining the hardware configuration of the present invention, FIG. 7 is a flowchart explaining an embodiment of the present invention, and FIG. 8 is a diagram explaining the present invention. FIG. 9, which is a diagram for explaining the operation of the invention, is a flowchart for explaining a modification of the invention. 1...Power transmission line, 2...Back impedance, 3
...Power source, 4...Current transformer (CT), 5...Voltage transformer (PT), 7...A/D converter, 8...Digital computer.

Claims (1)

[Claims] 1. An analog-to-digital converter that samples the voltage and current taken in from the power system and digitally encodes these sampling values, and an analog-to-digital converter that includes a built-in memory and that takes in the output of this analog-to-digital converter. , and a digital calculator that calculates a predetermined arithmetic formula, obtains vector quantities IZ _O and IZ _O −V from the digitally encoded voltage and current I, and a known constant Z _O , and stores them in the memory. A memory voltage V _M is obtained from a voltage n cycles or (n-1/2) cycles before the stored voltage V, and a composite vector ( _{KV M} −
kV) is obtained, and the resultant vector quantity (IZ _O +KV _M −kV) is obtained from the above calculation result, and the resultant vector quantity (IZ _O −
V-(KV _M -kV)) is obtained, the resultant vector quantity (IZ _O +KV _M -kV) is converted to the first DC quantity, and the resultant vector quantity (IZ _O -V-(KV _M -kV) ) into a second DC amount, and the first DC amount and the second DC amount are compared until a predetermined output is obtained from the comparison result between the first DC amount and the second DC amount. After the predetermined output is obtained through this comparison, instead of comparing the first DC flow rate and the second DC flow rate, the first DC flow rate is
A digital distance relay system characterized in that a third DC amount obtained by multiplying (ko>1) and a second DC amount are compared.