Question

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SEL-321相间距离保护静态特性及试验方法
相间距离保护静态动作特性的试验方法：
SEL-321微机线路保护，具有相间及接地距离保护、方向过流保护和故障定位的功能，针对不平衡故障，它的方向元件采用了带补偿的负序方向元件。其相间距离保护的方向阻抗元件与负序方向元件是结合在一起的，因此，在对该保护元件特性进行测试时，不能用测试一般方向阻抗保护特性的方法，而必须注意试验的电流、电压的幅值和相位，若与保护装置所在实际系统故障时的情况相差太远，就可能造成距离元件已起动，但由于具有特定整定值的负序方向元件没有起动而使保护无法动作的情况。
某变电站综合自动化系统中110 kV线路采用了SEL-321，该线路全长为3.8 km。GR为保护对侧系统电源，GS为保护后方经110 kV/35 kV变压器所接的1个小水电。保护配置为3段相间距离保护，4段零序保护。保护的负序方向元件定值设置为：正向Z2基本阈值Z2F=-12.5 Ω，反向Z2基本阈值Z2R=0.5 Ω；相间距离保护的设置为：第1段定值Zzd1=0.07 Ω，第2段定值Zzd2=0.33 Ω，第3段定值Zzd3=2.8 Ω，线路阻抗角�L=70°，方向阻抗特性圆如图2所示。110 kV线路保护SEL-321相间距离保护方向阻抗圆MHO特性。
各段阻抗特性动作区在阻抗平面上分别在下式表示的阻抗圆内，由各段阻抗定值Zzd决定阻抗圆的大小：
即有边界圆：
式中 U——阻抗继电器测量的母线电压；
Zzd——阻抗继电器的阻抗整定值；
I——阻抗继电器测量的电流；
U-Zzd.I——阻抗继电器补偿后电压；
Zf——阻抗继电器测量的故障阻抗。
试验仪器采用OMICRON的CMC-156继电保护测试仪，CMC-156提供在阻抗平面上对距离保护测试的2种基本方法：一种是恒定电流法，另一种是恒定源阻抗法。
对相间距离保护方向阻抗圆元件特性的测试，一般可采用恒定电流法。例如模拟L2-L3相间短路故障，进行阻抗圆边界搜索(相当于在阻抗圆边界附近每隔一定角度做动作值检验)。这种测试方法模拟线路故障前为空载状态，故障测试的短路电流大小一定(相电流均为测试电流Itest：｜IL2｜=｜IL3｜=Itest)，故障电压(L2，L3相间电压UL2-L3)的相位保持为-90°(以L1相电压UL1相位为0°)，L2，L3相电流的相位∠IL2，∠IL3由故障阻抗Zf的阻抗角θ决定，∠IL2=-90°-θ，∠IL3=90°+θ；故障电压UL2-L3的大小由短路阻抗Zf的大小确定：｜UL2-L3｜=2.Itest｜Zf｜。
用恒定电流法固定Itest=3.0 A，对SEL-321相间距离保护方向阻抗特性测试得到的结果是：当短路阻抗的阻抗角在阻抗圆最大灵敏角(线路阻抗角�L)附近时保护动作正常，作出动作阻抗圆的边界，与图2的理想动作阻抗圆较好吻合；但当短路阻抗的阻抗角偏离最大灵敏角区域时，保护动作情况则与预期的不符，阻抗圆边界根本无法作出。例如若短路阻抗Zf=2.35∠40° Ω，短路点应在第3段阻抗圆内，但相间保护不动作，甚至在Zf=0.2∠10° Ω时保护都不动作。
究其原因，从试验所加电量来看，由Zf=2.35∠40°Ω时IL2=-IL3=3.0∠-130°A，UL2-L3=14.1∠-90° V，可推算出：此时正向故障电源GS的系统阻抗ZS=14.317∠40° Ω，SEL-321计算出的正向动作阈值(详见文献〔1〕，〔2〕及SEL提供的SEL-321/321-1指导手册)为：Z2Fb=0.75Z2F-0.25｜Z2S｜=-12.579 Ω.

式中 Z2S——正向故障电源系统负序阻抗。
而SEL-321计算出负序阻抗在阻抗角方向的投影大小为：

z2=Re〔Z2S.1∠70°〕=-12.399 Ω.

Answer 1

SEL-321 phase distance protection static characteristics and test method
Phase distance of the movement to protect static test methods:
SEL-321 computer line protection, and a phase grounding distance protection, over-current protection and direction of the fault location function, in view of imbalance fault, it used components in the direction of the negative sequence with the direction of the compensation components. The protection of its phase distance in the direction negative sequence impedance components and the direction of the combination of components is, therefore, the protection of components for testing, testing can not be used to protect the general direction of the impedance method, and must pay attention to test the current, voltage The amplitude and phase, and if the protective device of the actual system failures far short of the circumstances, it could have been caused from the starting components, but because the whole set with a specific sequence of the negative direction of components did not start no action for protected situation.
A substation automation system using the 110 kV line SEL-321, the line length of 3.8 km. GR contralateral system for the protection of power, the GS 110 for the protection of the rear kV/35 kV transformer by the next one small hydropower. Protection configuration for the phase 3 of the distance protection, paragraph 4 of zero-sequence protection. Protection of the negative sequence set the direction of fixed-value components: the basic threshold Z2 positive Z2F =- 12.5 Ω, reverse Z2 basic threshold Z2R = 0.5 Ω; phase distance protection is set to: Paragraph 1 fixed-value = 0.07 Ω Zzd1 , paragraph 2 of the value Zzd2 = 0.33 Ω, paragraph 3 of the fixed value Zzd3 = 2.8 Ω, line impedance angle � L = 70 °, the direction of impedance characteristics circle shown in Figure 2. 110 kV line protection SEL-321 phase distance protection direction round MHO impedance characteristics.
The impedance characteristics of the resistance movements in the area were on the plane that the impedance of the next round, set by the value of the impedance Zzd decision impedance circle size:
That is, the border round:
Where U - impedance measurement of bus voltage relay;
Zzd - impedance relay setting the impedance value;
I - impedance measurement of current relay;
U-Zzd.I-- impedance voltage relays compensation;
Zf - impedance relay fault impedance measurement.
OMICRON test apparatus using the CMC-156 relay tester, CMC-156 impedance provide protection from the plane on the two kinds of tests basic methods: One is the constant current law, and the other is a constant source impedance method.
Direction of the phase distance impedance round protection components of the test, the general use of constant current. For example, simulation L2-L3-and short-circuit fault, circular border search impedance (equivalent impedance circle near the border every angle to do the movements of inspection). This test method for the simulation of a malfunction before the empty state, the failure of short-circuit current test certain size (the current tests are current Itest: | IL2 | = | IL3 | = Itest), fault voltage (L2, L3-phase voltage UL2 L3) remain at -90 ° phase (L1 phase voltage UL1 phase 0 °), L2, L3 phase current phase ∠ IL2, ∠ IL3 fault impedance from the impedance angle θ Zf decision ∠ IL2 =- 90 ° -- θ, ∠ IL3 + θ = 90 °; fault voltage UL2-L3 size from the size of short-circuit impedance Zf identified: | UL2-L3 | = 2.Itest | Zf |.
With a constant current of fixed Itest = 3.0 A, the SEL-321 phase distance protection direction impedance characteristics is the result of test: When short-circuit impedance of impedance angle in the round largest sensitive impedance angle (angle line impedance � L) protection action near normal , to act impedance circle borders, and Figure 2 the ideal impedance round action anastomosis better, but when short-circuit impedance of the most sensitive impedance angle from the regional angle, the situation is the protection of action inconsistent with the desired impedance circular boundary is not made. For example, if short-circuit impedance Zf = 2.35 ∠ 40 ° Ω, short-circuit should be in paragraph 3 impedance round, but not action - and protection, even in the Zf = 0.2 ∠ 10 ° Ω to protect not move.
The reason, the increase of electricity from the pilot, from 2.35 ∠ Zf = 40 ° Ω, IL2 =- 3.0 ∠ IL3 = -130 ° A, UL2-L3 = 14.1 ∠ -90 ° V can be calculated: At this time Power failures positive GS system impedance ZS = 14.317 ∠ 40 ° Ω, SEL-321 calculated positive action threshold (see the literature [1], [2] and SEL-321/321-1 guidance provided by the SEL Manual): 0.75Z2F-Z2Fb = 0.25 | Z2S | =- 12.579 Ω.
Type in Z2S - positive power system fault negative sequence impedance.
SEL-321 and negative sequence impedance calculated impedance angle in the direction of projection size:

Z2 = Re [Z2S.1 ∠ 70 °] =- 12.399 Ω.

Answer 2

The SEL-321 interaction interaction is away from the protection static state movement characteristic from the protection static characteristic and testing method the testing method: the SEL-321 microcomputer line protection, has the interaction and the touchdown distance protection, the direction overflow protection and the fault location function, in view of not the balanced breakdown, its directional element has used the belt compensation negative sequence directional element. Its interaction from the protection direction impedance part and the negative sequence directional element is unifies in together, therefore, when carries on the test to this protection part characteristic, cannot use the test general direction impedance protection feature method, but must pay attention to experimental the electric current, the voltage peak-to-peak value and the phase, if is too far with the protective device in the reality system failure's time situation difference, possibly creates from the part started, but as a result of has the specific installation value negative sequence directional element starting not to cause the protection to be unable the movement situation. in the some transformer substation synthesis automated system 110 kV lines have used SEL-321, this line span is 3.8 km. GR is the protection opposite side system power source, GS is rear area the protection 1 small water and electricity which transformer meets after 110 kV/35 the kV. The protection disposition is 3 sections of interactions is away from the protection, 4 section of zero foreword protection. The protection negative sequence directional element definite value establishment is: Forward Z2 basic threshold value Z2F=-12.5 OMEGA, reverse Z2 basic threshold value Z2R=0.5 OMEGA; The interaction from the protection establishment is: 1st section of definite value Zzd1=0.07 OMEGA, 2nd section of definite value Zzd2=0.33 OMEGA, 3rd section of definite value Zzd3=2.8 OMEGA, the line impedance angle L=70°, direction impedance characteristic circle as shown in Figure 2. 110 kV lines protect the SEL-321 interaction to be away from the protection direction impedance circle MHO characteristic. the each section of impedance characteristic movement area in the impedance plane in the equation below expression's impedance circle, decides the impedance circle separately by each section of impedance definite value Zzd the size: namely has the boundary circle: in the formula U-- impedance relay surveys bus bar voltage; Zzd-- impedance relay's impedance installation value; the I-- impedance relay surveys electric current; after U-Zzd.I-- impedance relay compensation, voltage; the Zf-- impedance relay surveys breakdown impedance. the testing instrument uses OMICRON the CMC-156 relay protection reflectoscope reflector, CMC-156 provides in the impedance plane to is away from the protection test 2 essential methods: One kind is the constant current law, another kind is the constant source mesh method. to alternates with is away from the protection direction impedance circle part characteristic test, generally may use the constant current law. For example simulates the L2-L3 phase fault, carries on the impedance circle boundary search (to be equal to makes movement value examination in impedance circle boundary vicinity every other certain angle). Before this kind of test method artificial line breakdown, is the light condition, the failure test short-circuit current size certain (interphase current is tests electric current Itest:|IL2|=|IL3|=Itest), breakdown voltage (L2, L3 voltage between phases UL2-L3) the phase maintains for - 90° (take L1 the phase voltage UL1 phase as 0°), the L2, L3 interphase current's phase ∠IL2,∠IL3 Theta decided by the breakdown impedance Zf impedance angle, ∠IL2=-90°-θ, ∠IL3=90°+θ; The breakdown voltage UL2-L3 size determined by the short-circuit impedance Zf size: |UL2-L3|=2.Itest|Zf|. with constant current law fixed Itest=3.0 A, to the SEL-321 interaction the result which obtains from the protection direction impedance characteristic test is: When short-circuit impedance impedance angle when impedance circle most greatly keen angle (line impedance angle L) neighbor protects the movement to be normal, makes the movement impedance circle the boundary, ideal movement impedance circle is good with Figure 2 tallies; But works as the short-circuit impedance the impedance angle deviation most greatly keen angle region, protects the movement situation with the anticipated symbol, the impedance circle boundary is not unable to make. If the example the short-circuit impedance Zf=2.35∠40° OMEGA, the short dot should in the 3rd section of impedance circle, but the interaction protection does not act, even when Zf=0.2∠10° OMEGA protects does not act. investigates its reason, adds the electric quantity looking from the laboratory, by Zf=2.35∠40°Ω when IL2=-IL3=3.0∠-130°A, UL2-L3=14.1∠-90° V, may calculate: This time the forward trouble power GS system impedance ZS=14.317∠40° OMEGA, SEL-321 calculates the forward movement threshold value (for details sees SEL-321/321-1 instruction manual which literature (1),(2) and SEL provides) is: Z2Fb=0.75Z2F-0.25|Z2S|=-12.579 OMEGA. in the formula Z2S-- to trouble power system negative sequence impedance. but SEL-321 calculates the negative sequence impedance in the impedance angle direction projection size is:
Z2 = Re [Z2S.1 ∠ 70 °] =- 12.399 Ω.