JPH0341009B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load relief calculation device in a unit substation or the like.

Figure 1 is an explanatory diagram showing the connection and disconnection status of each system and busbar connection and disconnector in the unit substation. In Figure 1, BK ₁ to _{BK 3} are banks, B is busbars, and CB ₁ to CB ₃ is the busbar connection and disconnection, CBaCBb
is a protective shield.

Conventionally, in the system shown in FIG. 1, the busbar connections and disconnectors CB ₁ to _{CB 3} have been manually turned on. Therefore, in the event of a bank accident, the operator had to make a judgment to support the damaged bank from a healthy bank by manually connecting the busbars and turning on the disconnectors CB ₁ to CB ₃ .
Therefore, it takes time to turn on the power, and in the case of a bank failure, the automatic switching device of the power distribution substation operates in the configurations "1" and "3" in FIG. In addition, in configuration "2" in Figure 1, there is a possibility that bank BK ₂ will be overloaded in the event of an accident in bank BK ₁ , and in this case, the overcurrent relay of bank BK ₂ will operate, causing a bus connection and disconnection. CB ₂
As a result, banks BK ₁ and BK ₂ are completely stopped.

In order to solve the above problem, a device is required to quickly input the busbar connection and disconnection CB ₂ . However, if a healthy bank becomes overloaded as described above after the busbar connection or disconnector CB ₂ is turned on, the substation will be completely shut down, so it is necessary to prevent this. In other words,
A load relief calculation device is required that calculates whether an accidental bank can be relieved from a healthy bank.

The following formula is a determination formula to determine whether the busbar contact or disconnector can be turned on, and was manually turned on by the operator.

(i ₁ + i ₂ + i ₃ ) ≦ β (I ₂ + I ₃ ) where i ₁ is the load current of bank BK ₁ before the accident, i ₂
is the load current of bank BK ₂ before the accident, i ₃ is the load current of bank BK ₃ before the accident, I ₂ is the rated current of bank BK ₂ , I ₃ is the rated current of bank BK ₃ , and β is the allowable current of bank This is the overload rate. The above judgment formula is bank
When a cross flow occurs between BK ₂ and BK ₃ , banks BK ₂ and
Since the overload rate of BK ₃ is different, this will not hold true.
For this reason, it becomes necessary to determine bank overload in consideration of cross current.

Below, FIG. 1 will be explained.

In Figure 1, the busbar connecting and disconnecting switches CB ₁ to CB ₃ and the protective shield disconnectors CBa and CBb are shown in Figure 1, where white circles indicate the closed state, and x marks indicate the disconnected state.
and black circles indicate the state to be added from now on. Now, assume that an accident occurs in bank BK 1 in configuration "1" shown in FIG. ₁ before the accident. Then, the cutter CBa is cut off. At this time, the sound bank
In order to be able to accommodate power from BK ₂ and BK ₃ , the operator manually turns on the busbar connection and disconnector CB ₁ to save bank BK ₁ . The conditions for turning on CB ₁ are the load current i ₁ of BK ₁ , BK ₂ , BK ₃ ,
The total of i ₂ and i ₃ is less than the allowable overload rate β of BK ₂ and BK ₃ . In other words, in the case after the accident of form "1" in Fig. 1 that satisfies the above judgment formula, the bank
BK ₂ and BK ₃ are operated in parallel, so no cross current normally flows between them. In addition, in FIG. 1, the protective shield breakers CBa and CBb are automatically opened and closed.

Next, in the case of configuration "2" in Figure 1, before the accident, the busbar connection and disconnector CB ₃ was disconnected, but when an accident occurs in bank BK ₁ and disconnector CBa opens. Bank BK ₂ provides power interchange. but,
In this case, bank BK ₂ becomes overloaded and the bank
BK ₂ 's overcurrent relay operates and both banks BK ₁ ,
Both BK ₂ will experience a power outage. To prevent this, in configuration "2", after the accident, it is sufficient to connect the busbar or turn on the disconnector CB ₃ using the above judgment formula, but if there is a tap difference between the two banks BK ₂ and BK ₃ , the disconnector CB 3 can be turned on.
There is a drawback that a cross current occurs between banks BK ₂ and BK ₃ when CB ₃ is inserted. When cross current occurs,
The above judgment formula no longer holds true, and it is necessary to perform cross-flow compensation calculations and make a decision to turn on. In this case, the operator cannot judge whether or not it is possible to input the product.

In addition, in the case of configuration "3" in Figure 1, when the bridges and disconnectors CB ₁ to CB ₃ were disconnected before the accident, there was an accident in bank BK ₁ , and banks BK ₂ and BK ₃ requested for accommodation. Once this is completed, the breaker circuit breakers CB ₁ to CB ₃ are turned on (after the accident type “3” in Figure 1). At this time, if there is _a tap difference between banks BK ₂ and BK ₃ ,
There is a drawback that cross current occurs between BK ₃ . In this case as well, the operator cannot make a judgment as in the case of form "2". Therefore, in the case of configurations "2" and "3", there is a possibility that load relief may not be possible.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a load relief calculation device that enables load relief that compensates for cross current.

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

In FIG. 7, 10 is a bank accident detection section;
This detection unit 10 outputs bank accident detection information. Reference numeral 11 denotes a current value detection section using a bank current transformer, and current value detection information is output from this detection section 11. 12 is a bank tap position detection section, and this detection section 12 outputs tap position detection information. 13 is the first step to calculate the total current I of the load current.
In the calculation section, this first calculation section is connected to the detection section 10, 1.
1 is supplied, and when a bank fault occurs, the total current of the bank load current before the fault is calculated and output. Reference numeral 14 denotes a second calculation unit that calculates the percentage from the tap position of the bank that will operate in parallel after connecting the bus or disconnecting the circuit.The second calculation unit 14 is supplied with the outputs of the detection units 10 and 12. 15 is a transformer % impedance information output section with a constant to be set; 16 is a bank rated capacity information output section with a similar constant; and 17 is an overload coefficient information output section with a similar constant. The transformer % impedance information output section 1
The output of 5 is input to the transformer % impedance determining section 18. Reference numeral 19 denotes a bank capacity determination section, and this determination section 19 receives the output of the output section 16 and the detection section 10.
The output of is input. Reference numeral 20 denotes an overload coefficient determining section, into which the output of the overload coefficient information output section 17 is input.

Reference numeral 21 denotes an arithmetic judgment section, and this judgment section 21 receives the calculation outputs of the first and second arithmetic sections 13 and 14, the output of the transformer impedance determination section 18, and the outputs I _A , I _B of the bank capacity determination section 19. and the output of the overload coefficient determining section 20 are input. The calculation/judgment unit 21 uses the above input information to calculate the equations (15) and (16) described below, and when the AND of the equations (15) and (16) is satisfied, outputs the overload relief calculation. is sent. That is, FIG. 9 is a functional explanatory diagram of the calculation/judgment section 21, and 30 is a division section which calculates %ΔV/%IZ. The calculation results are output to a first multiplication section 31 and a second multiplication section 32, respectively, and multiplied by _I〓B and _I〓A . 33 is a first addition section, which combines the calculation result obtained by the first multiplication section 31 and I〓
are added and output to the first determination section 34. 3
Reference numeral 5 denotes a subtraction unit that subtracts I〓 from the calculation result obtained by the second multiplication unit 32 and outputs the result to the second determination unit 36. 37 is a second addition section in which I〓 _A + I〓 _B is calculated, and the resulting value is multiplied by β in a third multiplication section 38 and compared and determined in first and second judgment sections 34 and 36, respectively. Ru. Reference numeral 39 denotes an AND section, which generates an output under an AND condition of the output signals of the first and second determination sections. As a result, power can be exchanged from the healthy bank without cross current, and the output is supplied to a control device (not shown) that connects the busbar and turns on the disconnector. By using the embodiments described above, banks can be rescued at high speed, and power outages due to overloads and cross currents can be prevented.

The above figure 7 shows an example of a unit substation, but in the case of a double bus substation, as shown in figure 8, the bank line switch condition information output unit 2
2 is provided, and the output of the output section 22 is inputted to the second calculation section 14, and the bank capacity determination section 19
, and the calculation judgment unit 21 as in the above embodiment.
All you have to do is calculate it.

Next, we will discuss load relief calculations that compensate for cross currents using mathematical formulas. FIG. 2 is an explanatory diagram for explaining the outline of parallel operation of transformers, and cross currents generated by parallel operation of transformers will be explained with reference to FIG. In the figure, T _A and T _B are transformers, I〓 _A ′ and I〓 _B ′ are secondary shared currents, I is a load current, and V ₁ and V ₂ are primary and secondary voltages.

The equivalent circuits of the transformers _TA and _TB shown in FIG. 2 when operating in parallel are shown in FIGS. 3 and 4.
Below, formula (1) is derived from Fig. 4 in order to find the secondary shared currents _I〓A ', _I〓B ' and the cross current _ic .

I〓＝I〓 _A ＋I〓 _B V〓 _A ＝V〓 ₁ /a V〓 _B ＝V〓 ₁ /b V〓 _A −I〓 _A Z〓 _A ＝V〓 _B −I〓 _B ′Z〓 _B ＝ V〓 ₂ ...(1) In formula (1), a is T _A , b is the turns ratio of T _B , Z〓 _A
is T _A and Z〓 _B is the impedance of T _B.

In equation (1), if we set ΔV=V〓 _A −V〓 _B , then equation (1) becomes
Equation (2) is obtained.

I〓 _A ′＝I〓Z〓 _B / (Z〓 _A +Z〓 _B
) + ΔV〓 / (Z〓 _A +Z〓 _B ) I〓 _A ′=I〓Z〓 _B / (Z〓 _A +Z〓 _B
) + ΔV〓 / (Z〓 _A +Z〓 _B ) I〓 _B ′=I〓Z〓 _A / (Z〓 _A +Z〓 _B ) − ΔV〓 / (Z〓 _A +Z
〓 _B )……(2) Here, further I〓Z〓 _B / (Z〓 _A + Z〓 _B ) = i〓 _a I〓Z _A / (Z〓 _A + Z〓 _B ) = i〓 _b ΔV/( Z〓 _A + Z〓 _B )=i〓 _c ...(3) If we set, equation (2) becomes equation (4).

I〓 _A ′=i〓 _A +i〓 _c I〓 _B ′=i〓 _A +i〓 _c ……(4) Figure 5 is a vector diagram when transformers are operated in parallel.

Generally, % impedance is used as impedance, so the rated voltage is V〓, the rated current is I〓 _A , I〓 _B , the % impedance is % _A , % _B ,
If the capacitance ratio is m=P _A /P _B =I〓 _A /I〓 _B , the following equation (5) holds true.

Z〓 _A =% _A /100×V〓/I〓 _A Z〓 _B =% _B /100×V〓/I〓 _B m=I〓 _A /I _B ……(5) Expression (5) is converted into (3) ), we get equation (6).

i〓 _a = m・% _B / (% _A +
m% _B ) × I〓 i〓 _b = % _A / (% _A + m% _B ) × I〓 i〓 _c = % / (% _A + m% _B ) × I %ΔV = (ΔV〓 / V〓) × 100...(6) In equation (6), % is the voltage difference (ΔV) due to tap difference deviation expressed in %.

Next, we will discuss cross-current compensation during parallel operation.

From equations (4) and (6), the secondary phase split currents I〓 _A ′, I〓 _B become equation (7).

I〓 _A ′＝x ₁ I〓＋x〓 ₃ I〓 _A I〓 _B ′＝x ₂ I〓−x〓 ₃ I〓 _A x ₁ = m・% _B / (% _A + m
% _B ) x ₂ = % _A / (% _A + m% _B ) x ₃ = % / (% _A + % _B ) ... (7) Here, the overload states of transformers T _A and T _B are respectively β If _A and β _B , then β _A = |I〓 _A ′| /I〓 _A = |x ₁・I
〓／I〓 _A ＋x〓 ₃ ｜ β _A ＝｜I〓 _A ′｜ /I〓 _A ＝｜x ₁・I
〓／I〓 _A ＋x〓 ₃ ｜ β _B ＝｜I〓 _B ′｜ /I〓 _B = ｜x ₂・I／I _B ＋x ₃・I〓 _A ／I〓
_B | ... is expressed as (8).

I is the total load, and if the overload state can be tolerated up to β (overload coefficient) up to the set value, mA × (β _A・β _B ) ≦ β ... (9) If the following holds, then the overload state is caused by cross current. Overload relief with compensation is established. From formulas (8) and (9), the overload relief calculation formula is the AND of the following formulas (10) and (11).

｜x ₁ I〓＋x〓 ₃ I〓 _A ｜≦β・I〓 _A ……(10) ｜x ₂ I〓＋x〓 ₃ I〓 _A ｜≦β・I〓 _B ……(11) Here, % When _A = % _B = %, the following equation (12) is obtained from equation (7).

x ₁ = m/1 + m x ₂ = 1/1 + m x ₃ =%ΔV/(1+m)%IZ ... (12) From the above formulas (10), (11), and (12), the overload relief calculation formula is as follows. It becomes the logical product of equations (13) and (14).

｜mI〓+%/%×I _A ｜ ≦β(1+m)I〓 _A ……(13) ｜I〓−%/%×I _A ｜ ≦β(1+m)I〓 _B ……(14) Above ( From equations 13) and (14) and m=I〓 _A /I〓 _B , we obtain the AND output according to the following equations (15) and (16).

｜I〓＋％／％× _I〓B ｜≦β（ _I〓A ＋ _I〓B ）……(15)｜I〓−%／％× _I〓A ｜≦β（ _I〓A ＋ _I〓B ）… ...(16) In the above formula, %, I〓 _A , I〓 _B , and β are the set values, I〓 is the total load before the accident, and % is a value that can be calculated if the tap position is known. , also I〓
and I〓 _A , I〓 _B are in phase, I〓 and %/%×I〓 _A ,
%/
The phase difference of %IZ×I〓 _B is determined by the power factor of the load, but it is calculated as being almost constant.

Although the case of a unit substation has been described above, a double bus substation can also be treated by considering two transformers equivalently as shown in FIG. However, I〓A is the sum of the rated capacities of the healthy banks connected to the first bus, and I〓B is the sum of the rated capacities of the healthy banks connected to the second bus. In the case shown in FIG. 6, information on the opening/closing status of the switches of each bank is required.

As described above, according to the present invention, there is an advantage that operation can be performed by making judgments with high precision and high speed to compensate for cross currents and prevent healthy banks from being overloaded.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the connection and disconnection status of each system and bus line in the unit substation,
Figures 2 to 6 are for explaining embodiments of the present invention. Figure 2 is an explanatory diagram outlining the parallel operation of transformers, and Figures 3 and 4 are illustrations of the transformers shown in Figure 2. 5 is a vector diagram when transformers are operated in parallel, FIG. 6 is an equivalent circuit diagram of a double bus substation, and FIG. 7 is an embodiment of the present invention. FIG. 8 is a block diagram showing another embodiment of the present invention, and FIG. 9 is a functional configuration diagram of the calculation/judgment section of the present invention. DESCRIPTION OF SYMBOLS 10...Bank fault detection part, 11...Current value detection part by bank current transformer, 12...Bank tap position detection part, 13...First calculation part, 14...Second calculation part, 15...Transformation % impedance information output section, 16... Bank rated capacity, 17... Overload coefficient information output section, 18... Transformer impedance determination section, 19... Bank capacity determination section, 20...
Overload coefficient determining unit, 21... calculation determining unit.

Claims (1)

[Claims] 1. A first calculation section into which bank fault detection information and current value information of the current transformer of the bank are respectively input, and obtains the total current of the load current as an output from these information; The information is inputted to a second calculation unit which performs a calculation representing the voltage difference due to the tap difference deviation as a percentage as an output from these information, and the bank fault detection information and the bank rated capacity information of a constant set in advance are inputted, a bank capacity determination section that determines the rated capacity of a healthy bank from this information; a transformer % impedance determination section and an overload coefficient determination section to which transformer % impedance information and overload coefficient information are respectively input; and the first , and an arithmetic judgment section to which the output of the second arithmetic section and each output of each of the determination sections are inputted, and which calculates these outputs and sends an overload relief arithmetic output as an output.