TWO NEW EARTH-FAULT REACTANCE RELAYS BASED ON FAULT-COM PONENT LIU Shi-ming, TAO Hui-liang, YANG Chun-ming (DongFan_g Electronic Information Industry Co. Ltd., YanTai 264001, China) ABSTRACT: Based on 0n the theoretical analysis of high-resistance earth-fault characteristics of HV/EHV transmimiOn line, two kinds of rle3iv type earth—fault reactance relays based On faultcomponent are proposed in this paper． These relays can overcome the overreach problem existed in the earth-failure dlstance protection with excellent performance within the protective z. ne. The steady-state characteristics of these protective relays are studied thoroughly in the paper. KEY WORDS: high-resistance earth-huh; reactance relay; fault component Summary: "Same questions" regarding the fault component reactance relay criterion. Based on the study of the characteristics of high-resistance grounding faults, dozens of new switching criteria were proposed. Two complete new types of fault component reactance relays were constructed: dual-reactor element fault component reactance relays and dual-reference quantity fault component reactance relays, which completely overcame the same problem. This paper also made a more comprehensive analysis and discussion of some static characteristics of the relays. Keywords: high-resistance grounding fault; reactance relay; fault component 1 Introduction How to improve the response capability of grounding distance relays, especially single-phase grounding distance relays, to high-resistance grounding faults is an important part of distance relay research. Among them, reactance relays are not affected by transition resistance in principle and only reflect the fault distance, so they have great practical application value and have been studied in depth. At present, the most practical one is the zero-sequence reactance relay. In addition, a fault component reactance relay was discussed in the paper [1]. Referring to Figure 1 and Figure 2, the resistance component in the system and line impedance was ignored. The relay criterion is that if the following formula is satisfied, then it is a fault within the zone. Using plane analytical geometry, this expression is transformed into a phase comparison form. In the formula, U'Y is the compensation voltage of the faulty phase; ΔU'Y = U'Y - U'Y/01 is the fault component of the compensation voltage. The subscript "|0|" indicates that the quantity is the quantity before the fault. Since all quantities are phasors, phasor markings are omitted for simplicity. In Figure 1, ES is the sending-end power supply; ZS is its electrical impedance; ER is the receiving-end power supply; ZR is its internal impedance; ZL is the impedance of line MN. The relays at line 2 are installed at busbars M and N respectively. Figure 2 is the corresponding voltage phasor diagram. Point Y is the relay protection setting end; F is the fault point. Reactor relays have the advantages of being unaffected by transition resistance and having a stable protection range. However, they have a significant drawback. As shown in Figure 2, depending on the transition resistance of the single-phase ground fault at point F, the voltage phasor after the fault falls on different points of the arc OHF. The larger the transition resistance, the closer its position is to point F. If the transition resistance is too large, causing the voltage phasor after the fault to fall on the HF segment of the arc (as shown by point F2 in the figure), then the criterion of the reactor relay will be completely reversed, that is, the fault within the zone will not operate while the fault outside the zone will operate erroneously. This situation is called the so-called "in-phase problem". The boundary point H on the arc is called the "in-phase point". In order to avoid the influence of the "in-phase problem", one solution is to increase the closing condition [1]. In the interval where the "in-phase problem" occurs, the relay is locked to prevent the relay from operating erroneously when there is a fault outside the zone, but this comes at the cost of sacrificing its ability to withstand the transition resistance when there is a fault within the zone; another solution is to switch the criterion before and after the in-phase point so that the criterion can be correctly judged on the entire arc, such as the double-lower-zero sequence reactor relay in the article [2]. This article analyzes the characteristics of single-phase grounding and finds two switching criteria for the fault component reactor relay, thus forming two new types of reactor relays. 2 The analysis and protection scheme for single-phase grounding takes the receiving end (the relay at bus N) as an example. The characteristics of single-phase grounding are analyzed on a simplified voltage phasor diagram. As shown in Figures 3 and 4, rays RS and RS' represent the voltage distribution curves of the system before and after the fault, respectively. O is the zero potential point. F is the fault point, and Y1 and Y2 are the protection setting ranges for the two cases. If the setting range is Y1, then a short circuit at point F is an in-zone fault; for Y2, a fault at point F is an out-of-zone fault. The "in-phase problem" is represented in planar geometry by the different positions of point O: before the "in-phase point," point O is located between rays RS and RS' (Figure 3); after the "in-phase point," point O is located outside rays RS and RS' (lower half) (Figure 4). 2.1 Observation of the dual-element fault component reactance relay in Figures 3 and 4 shows that before the "in-phase point," the in-zone fault < For faults outside the fault zone, OY'1Y1 < 90℃, and OY'2Y2 > 90℃. However, after the "phase point," the opposite is true: for faults within the fault zone, OY1Y1 > 90℃, and for faults outside the fault zone, OY2Y2 < 90℃; the criteria are completely opposite. But regardless of whether it's before or after the "phase point," one thing remains consistent: the criteria on both sides of the fault point are necessarily opposite. Therefore, using two reference points, it's possible to determine whether the fault point is within or outside these two reference points. Based on this characteristic, a new reactive relay can be constructed. Clearly, these two... The reference point should be selected as point N at the protection installation location and point y at the end of the protection range. Considering NN'∥YY' (i.e. △UN∥△U'Y), the new operating condition of the reactor relay can be obtained. This relay is formed by adding argUN/AU'Y as the switching criterion on the basis of the original fault component reactor relay (criterion (1)). If the added criterion is also regarded as a reactor element, then this reactor relay can be called "dual-element fault component reactor relay", or simply "dual reactor relay". 2 2 Dual reference quantity fault component reactor relay The fault component reactor relay realizes fault discrimination by using the fault component of the compensation voltage at the end of the protection range and the quantity after the fault. The previous section introduced the criterion switching before and after the "in-phase point" by adding the criterion of the fault component voltage at the protection installation location and the voltage after the fault. The following discusses the method of realizing criterion switching without adding a reference point. By comparing the mathematical expression of the relay with the voltage phasor diagram, it can be seen that the fault component reactor relay uses the fault component voltage YY' (Y can be Y1 or Y2) and the post-fault voltage OY. To achieve the switching of criteria before and after the "in-phase point," an additional condition must be added, such as adding one phasor for comparison. As shown in the figure, this phasor can be the phasor on the post-fault system voltage distribution curve RS'. Because one voltage phasor is added for comparison, this type of relay is called a "dual-reference fault component reactance relay," or simply a "parameter-selective relay." By comparing the two voltage phasors in the reactance relay with the phasor on RS', two switching criteria can be formed respectively. 2.2.1 The phase ratio between the voltage phasor after the fault and the phasor on RS' is based on the correspondence between the "in-phase problem" and the position of point O. Before the "in-phase point," OY1, OF, and OY2 are on the upper side of ray RS' (Figure 3); while after the "in-phase point," OY1, OF, and OY2 are on the lower side of ray RS (Figure 4). This relationship can be expressed mathematically as a phase ratio between the voltage phasor after the fault and the phasor on RS'. Combining this with the criterion of the reactive relay, the operating condition of this new reactive relay can be written as follows: The switching criterion here is sinusoidal, hence it is called a "sinusoidal switching criterion type dual-reference quantity fault component reactive relay," or simply a "sinusoidal dual-parameter relay." 2.2.2 Phase Ratio Between the Fault Component Voltage Phasor and the Phasor on RS Similarly, based on the correspondence between the "in-phase problem" and the position of point O, and considering that <FF0=90° at the fault point, from plane geometry, we know that before the "in-phase point," <Y1Y1S'= <FF'S'= Y2Y2 S' > 90 ℃ (Figure 3); and after the "in-phase point", <Y1Y1 S' = <FF'S' = Y2Y2 S' > 90 ℃ (Figure 4). Expressing this relationship mathematically involves comparing the phase of the fault component voltage phasor with the phasor on RS'. Combining this with the criteria for the reactive relay, the operating condition of this new reactive relay can be written as 3. Analysis of Relay Operation under Various Conditions The previous section, starting with the analysis of single-phase short circuits through the transition resistor within and outside the positive zone of the system's receiving terminal, derived several new reactive relays. Theoretically, they are unaffected by the transition resistor and have high sensitivity. Because the operating range of these reactive relays is very wide (theoretically allowing the transition resistor to be infinitely large), their reliability under various conditions must be carefully analyzed. 3.1 The operation of three types of relays is analyzed based on whether the relay is installed on the power supply side or the power receiving side, whether the fault occurs in the protection zone or outside the zone, whether it is forward or reverse, and whether the transition resistance exceeds the critical value for the "in-phase problem". (1) The dual-reactor relay has good performance and does not fail to operate or maloperate under various conditions; (2) The dual-parameter relay is prone to maloperation in reverse faults. For example, the sinusoidal dual-parameter relay installed on the power receiving side will maloperate in reverse faults, while the cosine dual-parameter relay installed on any side will maloperate in reverse faults. Therefore, they all need to add directional elements when applied; (3) The judgment conclusion of the sinusoidal dual-parameter relay installed on the power receiving side is completely opposite to the requirements in forward faults, that is, it does not operate in the zone when there is a fault in the zone, but operates in the zone when there is a fault outside the zone. The solution is not to reverse the criterion when power is supplied, because considering that after adding the directional element, the dual-reactor relay does not have the "in-phase problem", so at this time the relay directly uses the criterion 90°>arg. UY／△U'Y>-90° is sufficient. 3.2 Situation of short circuit at the outlet Since the voltage phasor at the protection installation point is used in the criterion of the dual reactor relay element, it is necessary to analyze the operation of the relay when a single-phase ground fault occurs at the protection installation point. When a single-phase ground fault occurs at the protection installation point, arg UN／△UN=arg UN／△U'Y=90°, and criterion (2) cannot operate. It is possible to consider adding the operation criterion (arg UN／△UN=arg UN／△U'N =90°)∩(arg U'Y／△U'Y≠90°), but considering the influence of calculation error and measurement error, adding this criterion will risk the reverse fault false operation. Of course, this can be compensated by adding the direction criterion; however, since the ground fault occurs at the outlet at this time, other single-phase distance relays can generally judge correctly, so even if these cumbersome measures are not added, it will not have a great harm to the overall effect of the protection. 3.3 Short circuit cases with different transition resistances (1) Metallic short circuit (point O in Figures 2-4) At this time, the dual-reactor relay is not affected and can still make a correct judgment; for the sinusoidal dual-parameter relay, since the phasor U'Y and (U'Y-UN) are on the same straight line, the relay loses the judgment standard and cannot make a judgment; since it is a metallic short circuit, other single-phase distance relays can react correctly, so it is not a major defect; for the cosine dual-parameter relay, according to the analysis, it may malfunction in the case of reverse fault, and it is also necessary to rely on adding a direction discrimination element to avoid malfunction. (2) Transition resistance is a critical value (point H in Figures 2-4) Because the voltage phasors at all points on the line are on the same straight line after the fault, the various reactor relays mentioned in the article cannot be correctly judged. In fact, other reactor relays will also fail in the case of "in-phase point". Since the reactor relays mentioned in the article do not introduce any compensation, theoretically, there is no protection dead zone for the relays except for "in-phase point". Of course, in practical use, in order to avoid false operation due to measurement error and calculation error, the protection will be locked near "in-phase point", creating a certain size dead zone. The range of this dead zone is not large and relatively stable, and it is not related to the system operation or the location of the short circuit point. (3) The transition resistance is infinite (point F in the figure). This is the normal operating condition, and the relay should not operate. If any small interference causes the compensation voltage phasor at any point within the protection range to fall on the semicircular arc of its grounding characteristic, it will cause the relay to malfunction. This is also a problem that exists in all reactor relays. Therefore, reactor relays must have strong anti-interference measures in application. How to take practical and effective anti-interference measures to ensure the stability and correct operation of the relay is a key issue in the research of this type of relay. 4 Characteristics of Fault Component Reactor Relays on Impedance Plane Since fault component reactor relays utilize the fault component of the measured voltage or compensation voltage, their characteristics are difficult to express on the impedance plane using a single measured impedance. To facilitate understanding and recognition of their characteristics, the following simplifications are used to derive a schematic diagram of criterion (2) on the impedance plane to show the impedance characteristics of this type of relay. The other two types of reactor relays in this paper are also difficult to show their effects on the impedance plane even under simplifications. First, it is assumed that the voltage at each point in the system is equal before the fault. This assumption also indicates that the current flowing through the system before the fault is zero, so the current after the fault is equal to the fault component of the current (ΔI=I). Considering [1], we have the following formula: z is the measured impedance of the relay at point ~ after the fault, Z=UN/I. Therefore, the relay operation condition expressed by formula (2) can be expressed as the expression of the measured impedance, where y is the system impedance angle, γ=arg(Zr+Zy). Based on this, the measured impedance characteristics of the relay can be shown on the impedance plane (Figure 5). According to the assumed premise, it can be deduced that IF is the current flowing through the transition resistor RG. Given IF I/γ, the phase angle of the additional component caused by the transition resistance in the relay's measured impedance is argZR = arg(IF/I)RG = -90° + γ. In equation (5), the impedance Z and (Z-Zy) are rotated by (90° - γ) = -(-90° + γ'). This is to compensate for this angle. The shaded area in the figure represents the relay's operating range, which is parallel to the R-axis. The protection range is not affected by the transition resistance. The operating range is distributed in a strip shape, indicating that it has a clear directionality, which is also an advantage of the dual-reactor relay compared to other reactor relays. 5 Conclusion (1) After adding the switching criterion, the fault component reactor relay fully utilizes the advantages of the reactor relay, has a strong ability to withstand the transition resistance, and has a stable protection range. (2) Since the criterion is "self-switching" and no approximation is introduced, there is no protection dead zone or overshoot problem in principle. It is only an exception at the "in-phase point". It can be called the "blind spot" of protection. (3) The expression of the relay criterion is clear and simple to calculate, with a small amount of calculation. (4) Problems also arise in the application of fault components. Due to the use of fault components, these reactor relays must operate within a short time after the fault, which is not conducive to using them as backup protection; the large number of harmonic components and non-periodic components present in the transient process after the fault are extremely unfavorable to the anti-interference of reactor relays. These problems can be solved by using the method of measuring the load component of the fault phase power in real time with the power of the non-fault phase in the literature [1]. References: [1] Zhu Shenshi The principle and technology of high voltage relay protection [M] Beijing: China Electric Power Press 1995 [2] Ye Ping, Chen Deshu A new scheme of 10 polarized earth-fault distance relay which can overcome the overreach problem [J] Proceedings of the Chinese Society for Electrical Engineering CSEE), 1995, (3); 199-203 . Author Biographies: Liu Shiming, PhD, Postdoctoral Researcher. Engaged in research on relay protection for ultra-high voltage transmission lines; Tao Huizhao, PhD. Engaged in the development and research of relay protection and substation integrated automatic relay equipment; Yang Chunming, PhD. Engaged in the development and research of relay protection and substation automatic relay equipment. (Source: Power Electronics Network)