Adaptive Distance Relaying Scheme for Power Swing Tripping Prevention

Transcription

1 Adaptive Distance Relaying Scheme for Power Swing Tripping Prevention 1 NOR ZULAILY MOHAMAD, AHMAD FARID ABIDIN, 3 ISMAIL MUSIRIN Centre of Electrical Power Engineering Studies Universiti Teknologi MARA Selangor, MALAYSIA 1 norzulailymohamad@yahoo.com, ahmad94@salam.uitm.edu.my, 3 ismailbm1@gmail.com Abstract: - Starting function in distance design is a crucial in order to detect a short circuit in power system. However, this function prove vulnerable to distance operation as it could falsely send a signal during power swing. To overcome those issues, this paper presents a simple and effective adaptive protection algorithm for power swing false prevention based on Under Impedance Detector (UIFD) characteristics. In order to evaluate the effectiveness of the proposed scheme, the testing has been conducted under IEEE 39 bus system. Simulation results prove that the scheme can be reliably deployed for identifying the power swing conditions and adjusting the setting accordingly. Key-Words: - adaptive distance ing; starting function; Under Impedance Detector (UIFD) 1 Introduction Distance s have been used generally for protecting transmission line from any abnormal power system conditions. But in some circumstances, the may operate falsely and consequently trigger a cascading event that contributed to widespread system separation and outages [1]. Therefore, improvements in the application of distance s are required to avoid such false operation. One of the possible approaches is to use an adaptive concept in distance protection; which is defined by the ability of the protection systems to automatically change its operating characteristics in response to changing power system conditions in order to maintain optimal performance [-4]. An adaptive scheme for transmission system with Static Synchronous Compensator (STATCOM) device has been developed in [5] which is used for mitigating the effects of device fast dynamic response time. The fast dynamic response time of the STATCOM device might overlap with the response time of distance, in which contributes to protection error during fault. An adaptive distance for the protection of parallel transmission line is introduced in [6] in order to diminish the effect of mutual coupling. In this adaptive scheme, the is based on the quadrilateral trip characteristics with directionality feature for three zone protection. Xiangning et al. has developed a self-adaptive scheme for distance based on concentric circle in order to solve the power swing false issue [7]. arious adaptive approaches have been developed by previous researchers to overcome the limitation of the conventional distance s. But still, there is a need to improve the operation of distance especially for correct action during power swing. This paper presents an adaptive ing scheme for power swing prevention based on Under Impedance Detector (UIFD) characteristics. Under Impedance Detector Under Impedance Detector (UIFD) is a type of fault detector function which is normally installed at transfer lines and generator buses. UIFD is special among other type of fault detector because it could sense the faults which are located beyond the zone 3 of boundary setting [8]. The UIFD characteristics are commonly drawn in currentvoltage (I-) plane as shown in Fig. 1. The x-axis corresponds to the measured current, while y-axis corresponds to the measured voltage. Fig. 1 illustrates the UIFD characteristics of a distance and its I- trajectory before and after a fault condition. Before a fault occurrence, the I- trajectory is located in the load. Once a fault occurs, the I- trajectory will instantaneously enter the fault detection and consequently a trip signal will be activated for fault clearing operation. ISBN:

2 Monitoring I- trajectory (I>>) I- trajectory before fault detection No Enter fault detection? (I>) I- trajectory after fault No Yes std_dev < 1 Zset_adapt = Zset + x I> I>> Fig. 1. UIFD characteristics of a distance and I- trajectory before and after fault I Yes k f / k ref > 1 No The function of UIFD is basically based on overcurrent protection, but with an additional feature of current threshold influenced by the measured voltage. Its characteristics is based on two different main settings, namely minimum current pickup, I> with the voltage associated to minimum current pickup, (I>) and over-current pickup, I>> with the voltage associated to over-current pickup, (I>>). Typical settings for each of parameter are given in [8] as per followed; I> =.5 x I N I>> =.5 x I N (I>) =.7 x R (I>>) = R where I N is equal to nominated current and R is equal to rated voltage. 3 Adaptive Under Impedance Detector As shown in Fig. 1, during power swing the I- trajectory is entering the fault detection, leading to action by associated circuit breaker. For unstable power swing, it is no issue for action to take place as the unstable part needs to be separated and isolated from the entire power system. However, for stable swing, the action should be avoided at any cost. Thus, it is important to develop an adaptive technique that is able to prevent such undesired operation. The approach of the proposed adaptive concept is based on ability of the UIFD characteristics to dynamically make an automatic adjustment to its region during stable power swing, and stop the adjustment process once the senses the fault occurrence during stable power swing. The flowchart of the proposed adaptive protection algorithm for power swing prevention based on UIFD characteristics is shown in Fig.. Yes Trip signal Fig.. The flowchart of the proposed adaptive protection algorithm for power swing prevention based on UIFD characteristics At first, the will continuously monitoring the I- trajectory line. Once the line enters the fault detection, the shall distinguish between a fault and power swing by using the two different indicators that previously proposed by authors in [9] and [1]. The first indicator, namely as power swing indicator detects the existence of stable swing in the system if the parameter std_dev is smaller than 1. Consequently, the automatic adjustment of the region will take place to prevent the action. The second indicator, namely as fault indicator is necessary for sensing the fault occurrence in the system. If the parameter k f / k ref is greater than 1, it means the fault is detected and consequently the automatic adjustment will stop in order to allow fault clearing operation. 3.1 Power Swing Indicator The developed power swing detection technique proposed by author in [9] is based on the use of S- Transform feature of active power at the distance point. The detection process starts with retrieving the active power at distance point. Then, the retrieved active power is processed using S-Transform through following equation, S kt, n NT = N 1 Pbus m + n e NT m ρ n. e mk jµ N (1) ISBN:

3 Further, the magnitude of the S-matrix is computed by using following equation, N 1 m ρ n mk jµ N m + n δ P = Pbus e. e () NT where k, m, and n, 1, N-1, T sampling interval, and N total sampling point. From (), the summation of elements in each of column in S-matrix magnitude is calculated by using following equation, ( m) ( ) ( ) m N 1 ρ m k + n jµ = n N φ P Pbus e. e (3) NT Based on (3), the summation returns a row vector of the sums of each of column. From this obtained vector, the standard deviation, std_dev is calculated. The detection criterion is defined as if std_dev smaller than 1, the swing is a stable swing, whereas if std_dev greater or equal to 1, the swing is an unstable swing. 3. Indicator A fault detection technique proposed by author in [1] is based on S-Transform as well as per used in above-mentioned power swing indicator. Initially, the fault detection process repeats the same process as before, such as to retrieve the input signal at distance point and afterwards to process the retrieved signal using (1) and (). From (), the smallest value of each of m column in the S-matrix is computed by using following equation, ( ( )) min m ( min( )) N 1 ρ m k ( ) min + jµ m n = n N ξ P Pbus e. e (4) NT Based on (4), the calculation returns a row vector with the length of n, filled with the smallest value of m column. From this obtained vector, the largest value of elements in the array of vector is further calculated. The obtained value which is symbolized by k is mainly used for the detection of fault in the power system. The two different variable of k which represent by k ref and k f are used; where k ref represents the largest value in array during no fault, and k f represents the largest value in array in the event of fault occurrence. Further, the detection criterion for the fault detection technique can be defined as, k σ = (5) k f ref From (5), the fault detection criterion is defined as, if k f / k ref is greater than 1, a genuine fault occurs in the system; whereas if k f / k ref is smaller or equal to1, it means there is no fault detected in the system. 3.3 Adaptive Coefficient of Distance Relay The adaptive concept is employed to the distance design in order to prevent the I- trajectory entering the region during an event of stable power swing. To achieve this, the adaptive coefficient, x is introduced to the setting function for changing the setting. The setting function occupied with an adaptive coefficient, x is shown in following equation, Z set_adapt = Z set + x (6) The adaptive coefficient, x is separated into three different values, according to the different threshold value. Each of adaptive coefficients, x1, x and x3 can be formulated as, For measured current greater than I> and measured voltage less than (I>) x1 = (Ι trip Ι>) +.1 (7) For measured current greater than I>> and measured voltage greater than (I>>) x = (Ι trip Ι>>) +.1 (8) For measured current and voltage that between two setting values, x3 = (Ι trip Ι>) + 1 (9) where Z set = conventional function Z set_adapt = adaptive function I trip = measured current that enters the region I> = minimum current pickup I>> = over-current pickup ISBN:

4 As aforementioned in [8], the minimum current pickup, I> is equal to.5 times the nominated current, I N and the over-current pickup is equal to.5 times the nominated current. Thus, the new setting function can be expressed as, For measured current greater than I> and measured voltage less than (I>), Z set_adapt = Z set + (Ι trip.5ι Ν ) +.1 (1) For measured current greater than I>> and measured voltage greater than (I>>), Z set_adapt = Z set + (Ι trip.5ι Ν ) +.1 (11) For measured current and voltage that between two setting values, Z set_adapt = Z set + (Ι trip.5ι Ν ) + 1 (1) The new scheme will operate as an adaptive with the ability to make an automatic readjustment of the region based on the value of the adaptive distance ing setting, Z set_adapt. 4 Results The proposed adaptive protection for power swing prevention based on UIFD is tested on IEEE 39 bus test system as illustrated in Fig 3. The performances of the proposed scheme in preventing false during stable power swing are presented in this section. 39 G1 9 G G G G G5 Fig. 3. Single line diagram of the test system G4 G G7 38 G9 4.1 Operation of Under Impedance Detector (UIFD) Tripping Characteristics For illustration purposes, the characteristics of UIFD are modeled by using MATLAB algorithm based on the Siemens Siprotec4-7SA6 type. For this type of, all the threshold values are set based on the triggering setting values of Siemens Siprotec4-7SA6 type. Fig. 4 illustrates the characteristics for UIFD with the given threshold value; I> set at A, I>> set at 1A, (I>) set at 35, and (I>>) set at 5. 6 (I>>) =5 4 (I>) = 35 oltage-dependent and Overcurrent Detection I> = A I>> =1 A Fig. 4. UIFD characteristics of a Siemens Siprotec4-7SA6 type From the simulation of IEEE 39 bus system in PSCAD, each of voltage and current are obtained for various power system conditions, such as; normal, fault, and power swing conditions. Further, the obtained voltage and current are plotted into UIFD characteristics in order to observe the behavior of I- trajectory during normal, fault, and power swing conditions. Fig. 5(a)-(d) illustrate the behavior of I- trajectory under different power system conditions. In Fig. 5(a), it is shown that the I- trajectory is located in the load during normal condition. Fig. 5(b)-(d) confirm the earlier hypothesis that the I- trajectory will enter the fault detection during fault and both stable and unstable power swing conditions. If the I- trajectory remains in this fault detection, the distance will send a signal to associated circuit breaker. For the stable swing condition, the action should be avoided at any cost. Thus, it is important to introduce an adaptive technique that is able to prevent such false signal triggered by the. ISBN:

5 a. Normal condition oltage-dependent and Overcurrent Detection b. oltage-dependent and Overcurrent Detection c. Stable power swing oltage-dependent and Overcurrent Detection detection detection detection oltage-dependent and Overcurrent Detection 8 detection d. Unstable power swing Fig. 5. UIFD characteristics of a Siemens Siprotec4-7SA6 type and the behaviour of I- trajectory during normal, fault and power swing conditions 4. Results of Adaptive Distance Relaying during Power Swing In order to prevent the distance from operating during power swing, the adaptive coefficient, x is employed to the conventional function, so that the will be able to adaptively change its region. The operation of adaptive scheme is explained in Fig Fig. 6. Conventional and adaptive function based on UIFD characteristics Fig. 6 illustrates the behavior of I- trajectory for stable swing condition, where it first crossed the conventional region at the minimum current threshold, I>. Once the conventional region is crossed, the first indicator, std_dev will be imposed where it will identify the type of power swing. In this case, the simulation of std_dev returns the value of.178, which means the stable swing is detected. After the first condition is satisfied, the function will be adjusted to the new function, Z set_adapt. It is shown in Fig. 6 that after the adjustment, the I- trajectory for stable swing condition is located outside the fault detection, thus false can be avoided. Based on the simulation testing with IEEE 39 bus system, several power swing cases are used to test the effectiveness of the proposed adaptive distance protection technique. Table I shows the operation for various power swing conditions when employing the conventional and adaptive function. TABLE I. THE RELAY OPERATION DURING POWER SWING CONDITION WHEN USING CONENTIONAL AND ADAPTIE TRIPPING RELAY location Line ABC- G oltage-dependent and Overcurrent Detection Conventional function, Z set Minimum current threshold, I> Adaptive function, Z set adapt Period Swing detection Over-current threshold, I>> Relay Operation Conventional Adaptive.1s Stable Not Trip Not Trip.35s Unstable Trip Trip ISBN:

6 location Line 5-6 Line AB A-G ABC- G AB A-G ABC- G AB A-G Period Swing Relay Operation Conventional Adaptive.1s Stable Not Trip Not Trip.35s Stable Trip Adjust the setting.1s Stable Not Trip Not Trip.35s Stable Not Trip Not Trip.1s Stable Not Trip Not Trip.35s Unstable Trip Trip.1s Stable Not Trip Not Trip.35s Stable Trip Adjust the setting.1s Stable Not Trip Not Trip.35s Stable Not Trip Not Trip.1s Stable Not Trip Not Trip.35s Stable Not Trip Not Trip.1s Stable Not Trip Not Trip.35s Stable Not Trip Not Trip.1s Stable Not Trip Not Trip.35s Stable Not Trip Not Trip Referring to the results in Table I, it is shown that there are two cases where the has been identified to operate falsely, which means the trips in the event of stable power swing. With the employment of the adaptive setting to the function, the could detect and classify the stable swing condition, and subsequently adjustment could be done to the setting. Thus, false action during stable power swing can be avoided at any costs. 5 Conclusion This paper presents a new adaptive scheme for distance for adjusting its setting during stable power swing in order to avoid false operation. The adaptive scheme is based on employing the adaptive coefficient, x to the conventional UIFD characteristics. The simulations on the IEEE 39 bus system validate the proposed adaptive scheme where it can be concluded that the application of an adaptive setting to the function is proven to be reliable as it could accurately detect the stable power swing and successfully adjusting the setting accordingly. References: [1] Hua Bai and Ajjarapu,., Relay margin trajectory based identification of transmission vulnerability for power system security assessment, 7 irep Symposium - Bulk Power System Dynamics and Control - II, Revitalizing Operational Reliability, 7, pp [] Damborg, M.J., Kim, M., Huang, J., enkata, S.S., Phadke, A.G., Adaptive protection as preventive and emergency control, IEEE Power Engineering Society Summer Meeting, vol.,, pp [3] IEEE Power System Relaying Committee, Feasibility of adaptive protection control, IEEE Trans. Power Delivery, vol. 8, no. 3, 1993, pp [4] Sham, M.., Chethan, K.S., and ittal, K.P., "Development of adaptive distance for STATCOM connected transmission line", 11 IEEE PES Innovative Smart Grid Technologies - India, pp , Dec. 11. [5] Srivani, S.G., Panduranga,.K., and Atla, C.R., Development of three zone quadrilateral adaptive distance for the protection of parallel transmission line, IEEE International Conference on Industrial Technology, 9, pp [6] Xiangning Li n, Zhengtian Li, Shuohao Ke, Yan Gao, Theoritical fundamentals and implementation of novel self-adaptive distance protection resistant to power swings, IEEE Trans. on Power Delivery, vol. 5, no. 3, 1, pp [7] Ziegler, G., Numerical Distance Protection - Principles and Applications, Siemens, Germany, 8, pp [8] Mohamad, N.Z., Abidin, A.F., Musirin, I., Intelligent power swing detection scheme to prevent false using S-Transform, International Journal of Emerging Electric Power Systems, vol. 15, no. 3, 14. pp [9] Mohamad, N.Z., Abidin, A.F., Musirin, I., Application of S-Transform for fault detection during power swing, International Review on Modelling and Simulations, vol. 6, no. 5, 13, pp ISBN: