CN101789584A - Method for differential protection of sampling value of abrupt change and differential relays - Google Patents

Abstract

The invention discloses a differential protection method and a differential relay for the sudden change sampling value used for transformer internal faults. Due to the problem that the conventional steady-state quantity differential protection relay has a slow action speed when the transformer is severely faulted, the present invention proposes a differential protection method and a differential relay for sudden change quantity sampling values. The differential protection method and the differential relay adopt the product of the differential current square integral of the sampled value of the sudden change and the equivalent current on both sides of the sampled value of the sudden change to form a relay with a high fixed value and a relay with a low fixed value. The test result shows that the present invention has good safety and rapidity.

Description

Differential Protection Method and Differential Relay of Sampling Value of Sudden Change

technical field

The invention relates to the field of relay protection technology and transformer protection, in particular to a transformer differential protection technology.

Background technique

As the capacity of the transformer is getting bigger and bigger, the cost of the transformer is very expensive, and the short-circuit capacity of the system is getting bigger and bigger. Serious faults occur on the transformer leads, and the short-circuit current is very large, and it passes through the transformer body. The insulation is damaged, and the mechanical stress generated in the winding produces a great distortion on the winding and core of the transformer. Therefore, it is an important and urgent subject to study the fast protection of transformers.

At present, the fast protection of the transformer is mainly the current differential break protection without any blocking. In order to ensure its reliability, the fixed value is generally 5 to 12 times the rated current of the transformer, and a filtering algorithm is required, so the protection has a certain length of data Therefore, its usual operating time is more than 20ms, and due to the fixed value method, no matter how large the fault current is, the operating time is the same, which is not conducive to reducing the impact on the transformer when a large current fault occurs.

If the new algorithm can be used to dynamically adjust the action time according to the size of the fault current without reducing the safety, the fault can be quickly removed according to the severity of the fault, and the impact on the transformer body can be reduced.

Contents of the invention

In order to solve the fast action of the transformer and take into account the safety of the relay, the present invention proposes a differential protection method for a transformer with a sudden change sampling value and a differential relay with a sudden change sampling value based on the differential protection method.

The present invention specifically adopts the following technical solutions:

A method for differential protection of a sudden change sampling value transformer, characterized in that the method comprises the following steps:

(1) Collect the current on each side of the transformer and the sudden change current value on each side through the current transformers on each side of the transformer;

(2) Convert the multi-side differential of the transformer into the difference between the two sides of the sampling value of the sudden change of the transformer: the side with the maximum absolute value of the sampling value of the sudden change current collected in the multi-side of the transformer is set as one end of the transformer differential protection, and the The sudden change current sampling value and equivalent of the other sides are defined as the other end of the transformer differential protection, where,

Δi _∑ (t)——The differential current of the sampling value of the sudden change of the transformer;

Δi _M (t)——The maximum value of the sudden change current sampling value on each side of the transformer;

Δi _{∑ - M} (t) = Δi _∑ (t) - Δi _M (t) - the sum of the sampling values of sudden changes in other sides of the transformer;

(3) When the following action equation is satisfied, the differential protection of the sampling value of the sudden change of the transformer operates:

The action equation is as follows:

$\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; MAX</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

∑Δi _M (t)Δi _∑-M (t)＞C ₃ I _e ² N+C ₄ |[Δi _M (t)Δi _∑-M (t)]| _MAX (2)

In the formula: N is the number of cycle sampling points;

C ₁ , C ₂ , C ₃ , and C ₄ are constants, and the value range is determined based on the distinction between internal faults and external faults, and the value range is between 1 and 10.

I _e is the rated current of the transformer;

η依据《大型发电机变压器继电保护整定计算导则》进行取值。

The value of η is determined according to the "Guidelines for Calculation of Relay Protection Setting of Large Generator and Transformer".

Δi _∑ ² (t) _MAX is the maximum value of the square of the differential current of the transformer sudden change sampling value;

[Δi _M (t)Δi _∑-M (t)] | _MAX is the maximum value of the product of "the maximum value of the current sampling value of the sudden change on each side of the transformer" and "the sum of the sampling values of the sudden change current at other sides of the transformer";

Δi _∑ ² (t) _MAX reflects the severity of the fault, and [Δi _M (t)Δi _∑-M (t)]| _MAX reflects the nature of the fault. When a serious fault occurs in the transformer, the operating time characteristic of the differential protection method will change with the magnitude of the fault current. When the operating current is larger, the operating speed will be faster, which has an inverse time-limit characteristic.

The present invention also discloses a transformer differential relay based on the above-mentioned differential protection method, which is characterized in that:

The relay adopts the product of the difference current square integral of the sudden change current sampling value and the equivalent current on both sides of the sudden change current sampling value to form a relay with a high fixed value and a relay with a low fixed value, wherein,

The action equation of the high-set value relay is as follows:

$\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; MAX</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

The action equation of the low fixed value relay is as follows:

∑Δi _M (t)Δi _∑-M (t)＞C ₃ I _e ² N+C ₄ |[Δi _M (t)Δi _∑-M (t)]| ^MAX (2)

In the formula: N is the number of cycle sampling points;

C ₁ , C ₂ , C ₃ , and C ₄ are constants, and the value range is determined based on the distinction between internal faults and external faults, and the value range is between 1 and 10.

I _e is the rated current of the transformer;

The value of η is determined according to the "Guidelines for Calculation of Relay Protection Setting of Large Generator and Transformer".

Δi _∑ ² (t) _MAX is the maximum value of the square of the differential current of the transformer sudden change sampling value;

[Δi _M (t)Δi _∑-M (t)] | _MAX is the maximum value of the product of "the maximum value of the current sampling value of the sudden change on each side of the transformer" and "the sum of the sampling values of the sudden change current at other sides of the transformer";

Δi _∑ ² (t) _MAX reflects the severity of the fault, and [Δi _M (t)Δi _∑-M (t)]| _MAX reflects the nature of the fault.

η依据《大型发电机变压器继电保护整定计算导则》进行取值；

The value of η is determined according to the "Guidelines for Calculation of Relay Protection Setting of Large Generator and Transformer";

When the high fixed value relay action equation is satisfied, or when the high fixed value relay action equation is not satisfied but the low fixed value relay action equation is satisfied, the sudden change sampling value transformer differential relay operates.

The value of η is based on the "Guidelines for Calculation of Relay Protection Setting of Large Generator and Transformer", as shown in Table 1: Table 1

Transformer capacity Differential speed break setting value The value of η 6300kVA and below 7.0～12.0 times Ie 12

Transformer capacity Differential speed break setting value The value of η 6300kVA~31500kVA 4.5～7.0 times Ie 10 40000kVA~120000kVA 3.0~6.0 times Ie 8 Above 120000kVA 2.0~5.0 6

Compared with the prior art, the present invention has the following advantages:

At present, the fast protection of the transformer is mainly the current differential break protection without any blocking. In order to ensure its reliability, the fixed value is generally 5 to 12 times the rated current of the transformer, and a filtering algorithm is required, so the protection has a certain length of data The calculation and discrimination can only be started after the window, so its usual action time is above 20ms, and due to the fixed value method, no matter how big the fault current is, the action time is the same.

When the relay proposed by the present invention has a serious fault in the transformer, its operating time characteristic will change with the size of the fault current. When the operating current is larger, the operating speed will be faster, and it has the characteristic of inverse time limit, which is more in line with the existing technology. Basic principles of transformer protection. At the same time, the relay has obvious directional characteristics (Δi _M (t) Δi _Σ-M (t)), and has a good ability to resist CT saturation, CT transmission error, and excitation inrush current. Therefore, the sudden change sampled value differential relay greatly improves the removal speed of serious faults and has high safety at the same time.

Description of drawings

Figure 1 is a system diagram of a typical substation transformer and a description of the range of differential protection;

Figure 2 is a typical current quick-break action curve of a conventional transformer;

Fig. 3 is a flowchart of the function realization of the present invention.

Detailed ways

In order to make the above objects, features and advantages of the present invention more comprehensible, specific implementations of the present invention will be described in detail below in conjunction with the accompanying drawings.

See Figure 1, the system diagram of a typical substation transformer and the description of the differential protection range.

The range covered by the curve in Figure 1 is the range protected by the differential protection relay, which is called the fault in the area, and is formed by the current on each side of the transformer. Faults outside the curve are called out-of-area faults.

See Figure 2, which is a typical differential relay action curve of a conventional transformer. Its action equation is:

$<span\; class="notranslate">\; |</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&Greater\; Equal;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula: is the transformer differential current, calculated from the vector sum of the currents on each side;

I _sd is the fixed value of transformer differential cut-off current, which is usually set at 5 to 12 times Ie;

The method for differential protection of a transformer with sudden change current sampling value disclosed in the present invention specifically includes the following steps in this embodiment, as shown in FIG. 3 :

(1) Collect the current on each side of the transformer and the sudden change current value on each side through the current transformers on each side of the transformer;

(2) In the present invention, the other side currents of the transformer are preferably attributed to the high voltage side:

Based on the current of the high-voltage side, other sides are reduced to the high-voltage side. Calculate the balance factor for each side as:

Calculate the primary rated current of each side of the transformer:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; let\text{'}s\; go</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In the formula: S _e is the maximum rated capacity of the transformer; U _1e is the rated voltage of each side of the transformer (the actual operating voltage should prevail).

Calculate the secondary rated current of each side of the transformer:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; LH</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

In the formula: I _1e is the primary rated current of each side of the transformer; n _LH is the CT transformation ratio of each side of the transformer.

Based on the high-voltage side, calculate the balance coefficient of the medium and low-voltage sides of the transformer:

${\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; pH</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; m</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; LH</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; LH</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; m</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}}}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; m</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; LH</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; m</span>}}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; LH</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; m</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; LH</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; m</span>}}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; LH</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; pH</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; L</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; LH</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; L</span>}}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; LH</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Multiply the current of each phase on the other side with the corresponding balance coefficient to obtain the current of each phase after amplitude compensation.

(3) It is further preferred to perform phase compensation on the currents on each side of the transformer:

The CT secondary current phase on each side of the transformer is self-corrected by software, taking the phase correction on the Δ->Y side, Y0/Δ-11 transformer as an example. Its correction method is as follows:

Delta side:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; NA</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; NA</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; NC</span>}}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; NB</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; NB</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; NA</span>}}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; NC</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; NC</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; NB</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Y side:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; MA</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; MA</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\\ \mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; MB</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; MB</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\\ \mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; MC</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; MC</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\\ \mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; MA</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; MB</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; MC</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

为Y侧CT二次电流；

为Y侧校正后的各相电流。为Δ侧CT二次电流；

为Δ侧校正后的各相电流；其它接线方式可以类推。In the formula:

is the Y-side CT secondary current;

is the corrected current of each phase on the Y side. is the CT secondary current on the Δ side;

It is the corrected current of each phase on the Δ side; other wiring methods can be analogized.

The relevant calculations of the relay are all carried out on the basis of current phase correction and balance compensation.

(4) The side with the maximum absolute value of the sudden change current in the multi-sides of the collected transformer is defined as one end of the transformer differential protection, and the sudden change current and equivalent of the other sides are set as the other end of the transformer differential protection, among which,

Δi _∑ (t)——The differential current of the sampling value of the sudden change of the transformer;

Δi _M (t)——The maximum value of the sudden change current sampling value on each side of the transformer;

Δi _{∑ - M} (t) = Δi _∑ (t) - Δi _M (t) - the sum of the sampling values of sudden changes in other sides of the transformer;

The calculation method of the differential current of the sampling value of sudden change is as follows:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

为突变量采样值差动电流；

为所有侧相电流的突变量采样值之和。In the formula:

The differential current is the sampling value of the sudden change;

It is the sum of the sudden change sampling values of all side phase currents.

The calculation formula of the square integral of the differential current of the sampling value of the sudden change is as follows:

∑Δi _∑ ² (t)(11)

The integral calculation formula of the product of the sudden change sampling value is as follows:

ΣΔi _M (t)Δi _Σ-M (t)(12)

Calculate the maximum value of the square of the differential current Δi _∑ ² (t) _MAX of the sampled value of the sudden change, and |[Δi _M (t) Δi _∑-M (t)]| _MAX of the product of the sampled value of the sudden change.

(5) When any of the following action equations is satisfied, the differential protection action of the sampling value of the sudden change of the transformer:

The action equation is as follows:

$\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; MAX</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

∑Δi _M (t)Δi _∑-M (t)＞C ₃ I _e ² N+C ₄ |[Δi _M (t)Δi _∑-M (t)]| _MAX (14)

In the formula: N is the number of cycle sampling points;

C ₁ , C ₂ , C ₃ , and C ₄ are constants, and the value range is determined based on the distinction between internal faults and external faults, and the value range is between 1 and 10.

I _e is the rated current of the transformer;

η依据《大型发电机变压器继电保护整定计算导则》进行取值。

The value of η is determined according to the "Guidelines for Calculation of Relay Protection Setting of Large Generator and Transformer".

Δi _∑ ² (t) _MAX is the maximum value of the square of the differential current of the transformer sudden change sampling value;

[Δi _M (t)Δi _∑-M (t)] | _MAX is the maximum value of the product of "the maximum value of the current sampling value of the sudden change on each side of the transformer" and "the sum of the sampling values of the sudden change current at other sides of the transformer";

Δi _∑ ² (t) _MAX reflects the severity of the fault, and [Δi _M (t)Δi _∑-M (t)]| _MAX reflects the nature of the fault.

The value of η is based on the following principles:

According to the "Large Generator Transformer Relay Protection Setting Calculation Guidelines":

Transformer capacity Differential speed break setting value The value of η 6300kVA and below 7.0～12.0 times Ie 12 6300kVA~31500kVA 4.5～7.0 times Ie 10 40000kVA~120000kVA 3.0~6.0 times Ie 8 Above 120000kVA 2.0~5.0 6

Satisfies formula (13) or formula (14), then protection action.

The action equation of the transformer differential relay according to the above protection method is as follows:

$\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; MAX</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

∑Δi _M (t)Δi _∑-M (t)＞C ₃ I _e ² N+C ₄ |[Δi _M (t)Δi _∑-M (t)]| _MAX (16)

In the formula: N is the number of cycle sampling points;

C ₁ , C ₂ , C ₃ , and C ₄ are constants, and the value range is determined based on the distinction between internal faults and external faults, and the value range is between 1 and 10.

I _e is the rated current of the transformer;

η依据《大型发电机变压器继电保护整定计算导则》进行取值。

The value of η is determined according to the "Guidelines for Calculation of Relay Protection Setting of Large Generator and Transformer".

Δi _∑ ² (t) _MAX is the maximum value of the square of the differential current of the transformer sudden change sampling value;

[Δi _M (t)Δi _∑-M (t)] | _MAX is the maximum value of the product of "the maximum value of the current sampling value of the sudden change on each side of the transformer" and "the sum of the sampling values of the sudden change current at other sides of the transformer";

Δi _∑ ² (t) _MAX reflects the severity of the fault, and [Δi _M (t)Δi _∑-M (t)]| _MAX reflects the nature of the fault. The value of η is based on the following principles:

According to the "Large Generator Transformer Relay Protection Setting Calculation Guidelines":

Transformer capacity Differential speed break setting value The value of η 6300kVA and below 7.0～12.0 times Ie 12 6300kVA~31500kVA 4.5～7.0 times Ie 10 40000kVA~120000kVA 3.0~6.0 times Ie 8 Above 120000kVA 2.0~5.0 6

If formula (15) or formula (16) is met, the protection will operate.

At present, the fast protection of the transformer is mainly the current differential break protection without any blocking. In order to ensure its reliability, the fixed value is generally 5 to 12 times the rated current of the transformer, and a filtering algorithm is required, so the protection has a certain length of data The calculation and discrimination can only be started after the window, so its usual action time is above 20ms, and due to the fixed value method, no matter how big the fault current is, the action time is the same.

When the relay proposed by the present invention has a serious fault in the transformer, its operating time characteristic will change with the size of the fault current. When the operating current is larger, the operating speed will be faster, and it has the characteristic of inverse time limit, which is more in line with the existing technology. Basic principles of transformer protection. At the same time, the relay has obvious directional characteristics (Δi _M (t) Δi _Σ-M (t)), and has a good ability to resist CT saturation, CT transmission error, and excitation inrush current. Therefore, the sudden change sampled value differential relay greatly improves the removal speed of serious faults and has high safety at the same time.

Claims (3)

1. a sudden change amount sampling value transformer differential protection method, is characterized in that, described method comprises the following steps: (1) Collect the current on each side of the transformer through the current transformers on each side of the transformer and calculate the sudden change current value on each side; (2) Convert the multi-side differential of the transformer into the difference between the two sides of the sampling value of the sudden change of the transformer: the side with the maximum absolute value of the sampling value of the sudden change current collected in the multi-side of the transformer is set as one end of the transformer differential protection, and the The sudden change current sampling value and equivalent of the other sides are defined as the other end of the transformer differential protection, where, Δi _∑ (t)——The differential current of the sampling value of the sudden change of the transformer; Δi _M (t)——The maximum value of the sudden change current sampling value on each side of the transformer; Δi _{∑ - M} (t) = Δi _∑ (t) - Δi _M (t) - the sum of the sampling values of sudden changes in other sides of the transformer; (3) When any of the following action equations is met, the differential protection of the sampling value of the sudden change of the transformer operates: The action equation is as follows: $\mathrm{<span\; class="notranslate">\; \&Sigma;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; \&Sigma;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; MAX</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ ∑Δi _M (t)Δi _∑-M (t)＞C ₃ I _e ² N+C ₄ |[Δi _M (t)Δi _∑-M (t)]| _MAX (2) In the formula: N is the number of cycle sampling points; C ₁ , C ₂ , C ₃ , and C ₄ are constants, and the value range is determined based on the distinction between internal faults and external faults, and the value range is between 1 and 10; I _e is the rated current of the transformer; $\mathrm{\&rho;}=\mathrm{\&eta;}-3\cos \frac{\mathrm{\&pi;}}{20\mathrm{ms}}t,$ The value of η is determined according to the "Guidelines for Calculation of Relay Protection Setting of Large Generator and Transformer"; Δi _∑ ² (t) _MAX is the maximum value of the square of the differential current of the transformer sudden change sampling value; [Δi _M (t)Δi _∑-M (t)] | _MAX is the maximum value of the product of "the maximum value of the sudden change current sampling value on each side of the transformer" and "the sum of the sudden change current sampling values of the other sides of the transformer"; Δi _∑ ² (t) _MAX reflects the severity of the fault, and [Δi _M (t)Δi _∑-M (t)]| _MAX reflects the nature of the fault. 2. The transformer differential protection method with sudden change sampling value according to claim 1, characterized in that: when a serious fault occurs in the transformer, the operating time characteristic of the differential protection method will change with the magnitude of the fault current, when The larger the action current, the faster the action speed, which has the characteristics of inverse time limit. 3. A transformer differential relay based on claim 1 or 2, characterized in that: said relay adopts the differential current square integral of the sudden change current sampling value and the equivalent two-side current of the sudden change current sampling value The product constitutes a high-set relay and a low-set relay, where, The action equation of the high-set value relay is as follows: $\mathrm{<span\; class="notranslate">\; \&Sigma;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; \&Sigma;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; MAX</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ The action equation of the low fixed value relay is as follows: ∑Δi _M (t)Δi _∑-M (t)＞C ₃ I _e ² N+C ₄ |[Δi _M (t)Δi _∑-M (t)]| _MAX (2) In the formula: N is the number of cycle sampling points; C ₁ , C ₂ , C ₃ , and C ₄ are constants, and the value range is determined based on the distinction between internal faults and external faults, and the value range is between 1 and 10. I _e is the rated current of the transformer; $\mathrm{\&rho;}=\mathrm{\&eta;}-3\cos \frac{\mathrm{\&pi;}}{20\mathrm{ms}}t,$ The value of η is determined according to the "Guidelines for Calculation of Relay Protection Setting of Large Generator and Transformer"; Δi _∑ ² (t) _MAX is the maximum value of the square of the differential current of the transformer sudden change sampling value; [Δi _M (t)Δi _∑-M (t)] | _MAX is the maximum value of the product of "the maximum value of the current sampling value of the sudden change on each side of the transformer" and "the sum of the sampling values of the sudden change current at other sides of the transformer"; Δi _∑ ² (t) _MAX reflects the severity of the fault, and [Δi _M (t)Δi _∑-M (t)]| _MAX reflects the nature of the fault. When the high fixed value relay action equation is satisfied, or when the high fixed value relay action equation is not satisfied but the low fixed value relay action equation is satisfied, the sudden change sampling value transformer differential relay operates.

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