JPS5947526B2 - Transformer protection method - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a transformer protection method for protecting transformers based on power system information, which makes it easier to distinguish between transformer power-on and transformer internal accidents. Regarding the protection method.

Computer-based power system protection devices are being researched by manufacturers in various countries.

Figure 1 shows the concept of conventional transformer protection, where G is the power supply, L is the load, SWI, 2 is the circuit breaker, and CT1 is the
, 2 indicates a current transformer, Tr indicates a transformer, and R indicates a protection device.

The protection device R takes in the transformer primary and secondary currents from the current transformer CTL2 and outputs tcrl.

Detect accidents that occur between the two.

Always supply power to load L. At this time, circuit breaker SW1
, and then SW2.

In this process, when SW1 is turned on, a large excitation current flows, and if the second harmonic content is small, the protection system with the configuration shown in Figure 2 f will incorrectly judge that it is an internal fault in the transformer. The circuit breaker SW1 sometimes issued a disconnection command and caused an erroneous disconnection.

Next, the configuration of FIG. 2 will be explained. Current transformer CT15
The transformer primary current 112 obtained through the transformer 2 is taken in, the DC component is removed by the filters 1 and 2, and the
The difference between the outputs of filters 1 and 2 is calculated, and the output l of calculation unit 3 is
Filter processing is performed using a filter 11 that allows only the fundamental wave component to pass, and the operating force is obtained.

On the other hand, the suppressing force is calculated by calculating the sum of the outputs of filters 1 and 2.
filter 5 that passes only the fundamental wave.
Filtering is performed by inputting a filter 6F that passes only the second harmonic.

The output of the filter 5 is multiplied by the suppression coefficient in the multiplier 7, and the arithmetic unit 8 calculates the sum of the outputs of the multiplier 7 and the filter 6.

In the arithmetic unit 9, the output of the arithmetic unit 8 is subtracted from the output of the filter 11, this output is squared in the arithmetic unit 10, and this output is added to the filter 12 for a certain period of time.From this, a DC level operating force is obtained, Compare this with a certain value, and above a certain value,
It was detected as an accident.

For this reason, there were problems as described above.

If this is the case, here we will explain the factors that determine the famous shore of the second harmonic, which has great significance.

The major factors that determine the content of the second harmonic are the residual magnetic flux of the transformer and the voltage input phase.

This relationship is shown in FIG. 3, in which the horizontal axis shows the residual magnetic flux and the vertical axis shows the second harmonic content.

Curve A has a loading angle of 0 degrees and 180 degrees, and curve B has a loading angle of 90 degrees.
degree, 270 degrees.

Further, curve C indicates a limit where a large current can flow as an excitation inrush current.

In this figure, the straight line Lv. If is the conventional second harmonic suppression coefficient, the range surrounded by the straight line C2Lv and curves A and B is
This was the area where the magnetizing inrush current caused malfunctions.

Although this range is narrower in modern transformers, it cannot be completely eliminated.

Furthermore, in recent transformers, due to improvements in custom-made iron cores and economical design, the relationship between fundamental wave current and second harmonic content is as follows.
It is expressed as f as shown in FIG.

In the figure, the curved line indicates the relationship at the time of excitation inrush, the curve E indicates the relationship at the time of an accident, and the area F indicates the area where the second harmonic wave is difficult to separate between the time of excitation inrush and the time of an accident. .

In this way, it is not possible to completely separate the accident event and the excitation inrush event using only the second harmonic-containing signal.

Therefore, it is an object of the present invention to provide a protection method for a transformer that overcomes this drawback and makes it possible to distinguish between an internal transformer fault and a power-on fault.

In the present invention, electrical coefficients such as winding resistance and leakage reactance of the transformer do not change during excitation inrush, and l
This focuses on the fact that electrical coefficients such as resistance and leakage reactance change.

Next, the principle of the present application will be explained.

Figure 5 shows the equal circuit of a transformer, 'I j
r2 is the primary and triple winding resistance, L3. L2 is the primary and double leakage inductance, vl and v2 are the primary and double terminal voltages, +1212 is the primary and secondary current, Φ is the magnetic flux, nl)n2 is the primary and Indicates the number of volumes with two missing parts.

In addition, rl, r22 L12 L25 nl) n2
is the electrical coefficient of the transformer.

From this figure, It can be expressed as

From this formula, if we eliminate Rewrite this, It can be expressed as

Here, n12 n22 rl, r22 L) 2L2
is determined once the transformer is determined, and in addition, if the instantaneous values of voltage and current Vl) V2) 11>12 are found, then when the transformer is healthy and during excitation inrush, equation (4) can be obtained. To establish.

In the above equation (4), the number in parentheses on the left does not take into account the number of windings.
Next-side overall voltage, the number in parentheses on the right does not take into account the number of turns2
It is called the next-side overall voltage.

Therefore, equation (4) can be said to be the overall voltage on the primary and secondary sides taking into account the number of windings.

On the other hand, in the event of an internal fault in the transformer, n.

n2 tr 1. Since r 22 L+ and L2 are different from those determined in advance, the following is obtained.

Here, ■1', v2', 11', and 12' indicate the voltage and current at the time of the accident.

In this way, an attempt is made to detect an accident by focusing on the fact that the relationship between voltage, current, and impedance is different between a normal state and an accident state.

FIG. 6 shows the relationship between voltage, current, and the output of equation (5) under various conditions.

In this way, the output of equation (5) is, except for an internal accident,
Does not occur.

From this, internal accidents can be clearly detected.

Next, a specific processing method will be explained.

As shown in Figure 1E, in addition to the primary and secondary currents of the transformer,
Transformer primary and secondary voltage is converted to voltage transformer PTI.

Through PT2, the digital information is converted by the AD converter A/D in the same way as the current information, and the protection device R converts it into (3) or (4).
It is determined whether the formula holds true or not, and if an accident is detected, a command to shut off circuit breaker 5W1F is issued.

Next, the processing flow will be explained with reference to FIG. 8.

At time t1, input voltage v1 of transformer 2 is 0-100.
．． The i-order current 11.2 input voltage v2.The secondary current 12 is taken in, and in flow 101, the transformer 1 which is stored in advance
Find the product of the secondary winding resistance '1 and the primary current 11, and
At step 02, the difference between the current value of the transformer primary current and the previous value of the -sample is taken and divided by the sizing interval.

In step 0-103, the result of step 102 is multiplied by the transformer primary leakage inductance L1, which is stored in advance.

In flow 104, the results of F0-101 and F0-1oa are subtracted from the transformer primary voltage v1, and in flow 105, the result of flow 104 is multiplied by the pre-stored transformer secondary winding number n2.

Step 0-106 calculates the relationship between the transformer secondary winding resistance 2 and the secondary current 12, which are stored in advance, and step 101 calculates the current value of the transformer secondary current - the value before the sample. Take the difference between and divide by the sampling interval.

In flow 108, the result of flow 107 is multiplied by the transformer secondary leakage inductance L2, which is stored in advance.

In flow 109, the results of steps 0-106 and 108 are subtracted from the transformer secondary voltage v2, and in steps 0-110, the result of step 109 is multiplied by the pre-stored transformer primary winding number n1.

At step 0-111, the result of flow 110 is subtracted from the result of step 70-105, and assuming that this value is normal within a certain value, the flow waits until the time to start the primary processing at step 112.

If the result of flow 111 is above a certain value, it is detected as an accident inside the transformer, and a command to shut off the corresponding circuit breaker is issued.

This kind of rubbing is a relatively simple process,
Internal faults in the transformer can be detected, and the economic effect is very large.

In addition, since the detection time of an accident is quick, it has a large effect on improving the stability of the power system.3 The explanation so far has been that if the result of equation (4) exceeds a certain value even once, it will be detected. Method E has been explained in detail, but one way to increase the detection reliability is to add a process to count the number of times after 111 in Fig. 6.Also, the explanation so far is an example of digital processing. I ran into one problem, but it is of course possible that it could be processed using analog.

As described above, according to the present invention, each voltage V1 on the primary side and secondary side of the transformer. V2, current 11. ■ Take in 2, and the winding resistance r of the primary and secondary sides of the transformer when it is normal,
, r2, leakage inductance LH, L2, and number of turns nI2 (n2) are calculated, and when C is within a certain range, it can be determined that the transformer is normal and turned on, so the process is relatively simple. In addition, it is possible to accurately distinguish between the time when the transformer is turned on and an internal fault, and the fault detection time is quick.

[Brief explanation of drawings]

Figure 1 is an overall diagram of the conventional system, Figure 2 is a specific configuration diagram of the conventional system,
Figure 3 is an explanatory diagram, Figure 4 is a diagram explaining the drawbacks of the conventional example,
FIG. 5 is an equivalent circuit diagram of the transformer, FIG. 6 is a time chart, FIG. 7 is an overall diagram of the present invention, and FIG. 8 is a processing flow diagram. T ``...Trance, PT'l, PT2...
...Transformer, CTI, CT2...Current transformer, R.
...Protective device.

Claims (1)

[Claims] 1 The primary side of the transformer during normal operation, which is obtained in advance by taking in the primary side voltage 1 and current 11 of the transformer, and the secondary side voltage v2 and current 12 of the transformer, which are given in advance. Secondary winding resistance rl 2 r2, leakage inductance L12 L2 s
and the number of turns nI)n2, calculate 1, and when the calculation result C is within a certain range, 1 is normal and the transformer is turned on,
A transformer protection system in which when the calculation result C exceeds a certain range, it is identified as an internal fault in the transformer, and the transformer is protected in accordance with this identification result. 2.Claim 1, l, wherein the transformer 0)
l i[t Vl, current ■2. Secondary voltage v2, current ■
2 is taken in by sampling, and each of the above-mentioned processes after the acquisition is performed digitally.
This is a transformer protection method.