CN105119256A - Method for preventing power grid distance protection misoperation under condition of voltage loss after start - Google Patents

Abstract

The invention relates to a method for preventing power grid distance protection from starting first and then voltage loss and misoperation. It is used for judging whether the secondary circuit of a three-phase voltage transformer is disconnected after the distance protection device in the power grid is started due to an out-of-area fault. In order to prevent the misoperation of the distance protection device, the method is as follows: consecutive n sampling points meet the following criteria: ① the voltage mutation of any phase is greater than the set voltage mutation threshold; ② the three-phase voltage calculated by the half-cycle algorithm is less than 2V; ③ The three-phase current mutations within 20ms are all less than the start-up value of the distance protection device; where n is a positive integer; it is determined that the three-phase voltage transformer is disconnected; prevent the distance protection device from malfunctioning according to the judgment result. Through the method, after the distance protection is started, it can be judged whether the three-phase voltage transformer is disconnected, so as to avoid the distance protection malfunction and improve the safety of the system.

Description

Method to prevent power grid distance protection from starting first and then losing voltage and malfunctioning

technical field

The invention belongs to the field of power grid dispatching control, and in particular relates to a method for preventing a potential transformer disconnection from causing malfunction after a distance protection device of the power grid is started.

Background technique

The distance protection is an under-level protection with the current as the action amount and the voltage as the braking amount. When the voltage braking capacity is lost after the voltage transformer is disconnected, the measured impedance tends to zero, and the distance protection will malfunction under the action of the fault current or load current outside the zone. At present, the widely used method of distance protection to prevent misoperation is to judge the disconnection and voltage loss of voltage transformers. Usually, the three-phase voltage vector sum is not zero to detect the disconnection of one-phase or two-phase voltage transformers; The method to detect the disconnection of the three-phase voltage transformer is generally delayed for 1-2s to block the protection and send out an alarm signal, and it is generally self-recovery. The above criterion presupposes that the protective device does not activate. At present, it is generally believed that once the system fails, the voltage transformer disconnection will not be judged after the starting element is started, because any kind of failure is characterized by the voltage transformer disconnection, regardless of the simultaneous occurrence of system failure and voltage transformer disconnection Case.

However, the actual operation situation shows that the possibility of system failure and voltage transformer disconnection occurring at the same time is very small, but the accidents of voltage transformer disconnection occurring in a short period of time (after 20 ms) due to the inducement of system failure have already happened. It occurs many times, and causes the distance protection of multiple circuits running on the same bus to malfunction, seriously threatening the safe operation of the system.

The analysis of the misoperation of the voltage transformer disconnection protection after the distance protection is started first is as follows:

1. As shown in Figure 1, the double-bus connection substation, lines 1, 2, 3, and 4 are system tie lines, and the double buses run in parallel. The secondary voltage circuits of the transformers are paralleled, so that the distance protection of lines 1, 2, 3, and 4 all use the secondary voltage of the II bus voltage transformer. But at this time, if the busbar II fails, the distance protection of lines 1, 2, 3, and 4 will all start. When the busbar protection action cuts off all the components of the busbar II, it will cause the distance protection of lines 1 and 2 on the busbar I to lose the measured voltage after starting. , because the start-up and widening time of the protection device is generally 5-7s, at this time, under the action of the load current, the distance protection of lines 1 and 2 may malfunction, and there is a risk of power failure in the whole station. Similarly, if the fault point is on the outgoing line of line 1 or line 2, but the outgoing circuit breaker refuses to move, the same consequences will also result.

2. Intermittent voltage transformer disconnection will also cause the line distance protection to malfunction when it starts first and then loses voltage. On-site often encounter voltage transformer disconnection caused by loose wiring screws of the voltage secondary circuit or poor contact of the secondary line. Sometimes such disconnection occurs intermittently and intermittently. If a fault occurs outside this time zone, the distance protection will start If the potential transformer disconnection occurs intermittently, the related line distance protection will malfunction under the action of the through-type short-circuit current. The disconnection of the voltage transformer still causes the risk of false operation of the distance protection.

3. The secondary voltage circuit of the bus voltage transformer generally needs to be equipped with a voltage resetting circuit to prevent the voltage transformer from recharging from the secondary to the primary. This circuit is generally realized by driving the resetting intermediate relay with the normally open auxiliary contact of the voltage transformer knife switch. When the voltage transformer is out of operation and the primary switch is opened, the relay is released, and the secondary voltage circuit is disconnected from the voltage transformer; when the voltage transformer is put into operation, the primary switch is closed, the reset relay is excited, and the secondary voltage circuit Automatic access to the secondary side of the voltage transformer. The working power supply of the reset relay uses the power supply of the DC system of the substation. The operation reliability of the power circuit is directly related to the operation reliability of the protection equipment using the bus voltage transformer voltage, and the distance protection bears the brunt. In actual operation, the DC working power of the voltage reset circuit has been lost after a system failure for many times. The main reasons are the DC circuit breaker leapfrog tripping caused by the DC signal circuit failure after a system failure, and some are external interference when the system fails. The resulting trip of the DC circuit breaker is caused by the loss of the floating charging source of the DC system battery after the system failure, and the loss of the DC power supply caused by the battery disconnection. A system fault becomes the direct cause of power loss in the secondary DC system. In this case, all distance protections operating with the busbar have the risk of malfunction. In 2007, a 220kV substation in a large urban area lost power. The reason was that After the failure of the 110kV system in the station, the short circuit of the DC signal circuit led to the tripping of the DC space, which caused the secondary reset power supply of the 220kV voltage transformer to be lost. caused by a trip. The accident load loss was serious, and the lesson was painful.

To sum up, although the probability that the distance protection starts first and then loses the measured voltage is not too high, once it occurs, it is often caused by successive misoperations of the distance protection of multiple lines running on the same bus, and there is a risk of power failure in the whole station , which seriously threatens system security. Therefore, it is necessary to take precautions based on the protection principle. It is necessary to improve the disconnection criterion of the distance protection voltage transformer, so that the distance protection can continue to judge the disconnection of the voltage transformer after it is started, so as to prevent the distance from the fault when the fault is outside the zone. Protection against misoperation.

Contents of the invention

The purpose of the present invention is to provide a method for preventing malfunction caused by disconnection of a three-phase voltage transformer after the distance protection device is activated.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A method for preventing power grid distance protection from starting first and then voltage loss and misoperation. It is used to judge whether the secondary circuit of the three-phase voltage transformer is disconnected after the distance protection device in the power grid is started due to an external fault, so as to prevent all The above-mentioned distance protection device malfunctions, the method is: consecutive n sampling points meet the following criteria:

①The voltage mutation of any phase is greater than the set voltage mutation threshold;

②The three-phase voltage calculated by the half cycle algorithm is less than 2V;

③ The three-phase current mutations within 20ms are all less than the start-up setting value of the distance protection device;

where n is a positive integer;

Then it is determined that the three-phase voltage transformer is disconnected;

According to the judgment result, the above-mentioned distance protection device is prevented from malfunctioning.

The voltage mutation threshold value is greater than the voltage mutation amount during the minimum oscillation period.

The minimum oscillation period mentioned is 200ms.

Further, the voltage mutation threshold value is the sum of the voltage mutation amount at the minimum oscillation period and the floating threshold.

Further, the voltage mutation threshold value is formed by adding a setting margin on the basis of the sum of the voltage mutation amount at the minimum oscillation period and the floating threshold.

The threshold value of the voltage sudden change is 0.4U _n , wherein U _n is a rated voltage value.

The value of n is 3.

Due to the application of the above-mentioned technical solution, the present invention has the following advantages compared with the prior art: through this method, after the distance protection is started, it can be judged whether the three-phase voltage transformer disconnection occurs after 20 ms, thereby avoiding the distance protection misoperation and improving the system performance. security.

Description of drawings

Accompanying drawing 1 is the wiring schematic diagram of double-bus connection substation.

Accompanying drawing 2 is the criterion principle block diagram of the method of the present invention.

Detailed ways

The present invention will be further described below in conjunction with embodiment.

Embodiment 1: A method for preventing power grid distance protection from starting first and then losing voltage and malfunctioning. This method is used to judge whether a three-phase voltage transformer secondary fault occurs after 20 ms after the distance protection device in the power grid is started due to an out-of-area fault. The loss of voltage caused by the disconnection of the secondary circuit, so as to prevent the misoperation of the distance protection device. Specifically, the method is: consecutive n (n is a positive integer, usually 3) sampling points meet the following criteria, that is, determine the occurrence The three-phase voltage transformer is disconnected, and then the distance protection device can be prevented from malfunctioning according to the judgment result.

The criteria include the following three conditions, which must be met simultaneously:

①The voltage mutation of any phase is greater than the set voltage mutation threshold;

②The three-phase voltage calculated by the half cycle algorithm is less than 2V;

③ The three-phase current mutations within 20ms are all less than the start-up setting value of the distance protection device.

It is known from the case analysis of several misoperation accidents that start first and then lose voltage when the fault occurs outside the area, the secondary voltage of the voltage transformer is three-phase loss of voltage, and from the analysis of its recorded wave data, the residual stray voltage of the secondary is very large. Low, the maximum secondary value generally does not exceed 2V, and the moment of voltage loss generally lags the start time of current mutation by more than 20ms, so the above criterion is obtained.

Criterion condition for item ①: When the three-phase voltage transformer is disconnected, the voltage will have a certain amount of sudden change, and it will be large. The sudden change threshold should be greater than the voltage sudden change during the minimum oscillation period. The system oscillation period is considered as a minimum of 200ms. When the protection installation is located at the oscillation center, the voltage mutation value |U(t)-U(t-T)| will have a maximum value. U(t) is a sinusoidal waveform with a period of 200ms, and T is 20ms. but

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>$

According to the sum-difference product formula $\sin a-\sin b=2\mathrm{the\; s}i\mathrm{no}\left(\frac{a-b}{2}\right)co\mathrm{the\; s}\left(\frac{a+b}{2}\right)$

$\begin{array}{c}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</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">\; 2</span>}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>\\ <span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; cos</span>}\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 10</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; |</span>\end{array}$

It can be seen from the above formula that when t=10, the voltage mutation has a maximum value.

$\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 18</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.618</span>}\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; u</span>}$

After increasing the floating threshold, the maximum sudden change in the voltage within one cycle is:

$\begin{array}{c}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>\\ <span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>\\ <span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 40</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>\\ <span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>\end{array}$

It can be seen from the above formula that when t=70, the voltage mutation has a maximum value

$\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.382</span>}\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; u</span>}$

Considering that there is a certain margin for the threshold, the threshold value is 0.4Un. At the same time, considering the possibility that one or two phase faults have occurred outside the area, when a three-phase voltage transformer disconnection occurs, only the healthy phase There is a sudden change in the voltage, so this criterion meets the condition when the sudden change in any one phase voltage of the three-phase voltage is detected.

Criterion condition for item ②: When the voltage transformer is disconnected, the sudden change in voltage can be felt within one cycle, but based on the Fourier window of the full-cycle Fourier algorithm, the voltage Fourier value cannot be reduced to 0. If the half-cycle algorithm is used, the calculated Fourier value of the voltage is 0 after 10ms after the voltage transformer is disconnected, so the Fourier value of the three-phase voltage calculated by the half-wave algorithm is used. The steady-state amplitude of the three-phase voltage is less than 2V as the condition for three-phase loss of voltage of the voltage transformer.

Criterion condition for item ③: Since this condition does not consider the fault occurring at the same time as the disconnection of the voltage transformer, there is no change in the current while the voltage has a sudden change, so the increased three-phase current sudden change is less than the start-up fixed value condition, which is mainly used to distinguish the voltage drop caused by the fault or just the disconnection of the voltage transformer.

When the above three conditions are all met, and continue for three sampling points, it can be judged that the voltage transformer disconnection has occurred in the line after startup, as shown in Figure 2.

In the process of starting the distance protection through the above method, if it is judged that the disconnection of the voltage transformer occurs, the distance protection will be blocked, and the judgment of the disconnection of the voltage transformer will not be carried out during the entire starting process until the protection group is reset, and then use The conventional voltage transformer disconnection criterion continues to judge the voltage transformer disconnection.

At present, the longitudinal protection dominated by optical fiber phase-separated current differential protection is the main protection of high-voltage transmission lines and an important guarantee for the safe and stable operation of the power grid. The staged distance and zero-sequence protection as the backup protection are necessary supplements to the protection of high-voltage transmission lines. Only by improving the reliability of the backup protection can the powerful advantages of the main protection be reflected, which is of great significance to ensure the safe operation of the power grid.

The above-mentioned embodiments are only to illustrate the technical concept and characteristics of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and not to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (7)

1. the method preventing electrical network distance protection from first starting rear decompression malfunction; after starting due to external area error for the distance protection equipment in electrical network; judge whether threephase potential transformer secondary circuit broken string occurs; thus prevent described distance protection equipment malfunction, it is characterized in that: the method is: n sampled point meets following criterion continuously:

1. the voltage jump amount of any phase is greater than the voltage jump threshold value of setting;

2. the three-phase voltage utilizing half cycle algorithm to calculate all is less than 2V;

3. in 20ms, three-phase current Sudden Changing Rate is all less than the startup definite value of described distance protection equipment;

Wherein n is positive integer;

Then judge threephase potential transformer broken string occurs;

Described distance protection equipment malfunction is prevented according to result of determination.

2. the method preventing electrical network distance protection from first starting rear decompression malfunction according to claim 1, is characterized in that: described voltage jump threshold value is greater than voltage jump amount during minimum cycle of oscillation.

3. the method preventing electrical network distance protection from first starting rear decompression malfunction according to claim 2, is characterized in that: described minimum cycle of oscillation is 200ms.

4. the method preventing electrical network distance protection from first starting rear decompression malfunction according to claim 2, is characterized in that: voltage jump amount when described voltage jump threshold value is described minimum cycle of oscillation and floating threshold sum.

5. the method preventing electrical network distance protection from first starting rear decompression malfunction according to claim 2, is characterized in that: the basis of the voltage jump amount of described voltage jump threshold value when described minimum cycle of oscillation and floating threshold sum increases and sets nargin and formed.

6. the method preventing electrical network distance protection from first starting rear decompression malfunction according to claim 5, is characterized in that: described voltage jump threshold value is 0.4U _n, wherein U _nfor voltage rating.

7. the method preventing electrical network distance protection from first starting rear decompression malfunction according to claim 1, is characterized in that: n value is 3.