Table 5 Comparison between alienation/correlation coefficients-based ADOCRs and form/ripple factors-based ADOCR.
From: Adaptive differential current relay based on form/ripple factors for busbar current signals
Item | Published ADOCRs based on the alienation/correlation coefficients12,13,14 | Proposed ADOCR based on the form/ripple factors |
|---|---|---|
1. Main concept | Adaptive differential relaying scheme based on the alienation12,13 and correlation14 coefficients estimated between the input and output current signals of the protected power system element | Adaptive differential relaying scheme based on the form and ripple factors computed for the measured current signals |
2. Operating characteristic type | It is described as a variable-bias digital differential relay for protecting a power system element. The amount of bias is varied linearly with the values of alienation12,13 and correlation14 coefficients calculated between the calculated input and output current signals of the power grid element The operating characteristic includes three zones as follows: blocking zone, adaptive zone, and tripping zone | It is described as a variable-bias digital differential relay for protecting power system elements. The amount of bias is varied linearly with the values of form and ripple factors calculated for the measured currents The operating characteristic includes three zones as follows: blocking zone, adaptive zone, and tripping zone |
3. Restraint factor (Characteristic slope) | It is based on a linear equation derived from the alienation12,13 and correlation14 coefficients calculated between the summation of input currents and the summation of output currents for the protected equipment | It is based on a linear mathematical formula derived from the form and ripple factors computed for the measured phase current signals |
4. Feeder selection of saturated CT | It has the ability to determine CT saturation condition and its assessment, but it fails to find which feeder CT is saturated | It is able to identify CT saturation condition, assess its level, and select which feeder CT is saturated |
5. Multi-functions | The alienation12,13 and correlation14 algorithms integrated with the differential current scheme can be used to carry out various protection functions, such as Current fault detector, Faulty phase selection, Fault classifier, Fault direction discrimination, CT saturation detector, CT saturation assessment, and Adaptive tripping characteristics during the time periods of CT saturation | The differential current scheme can be used to carry out various protection functions, including Current fault detector, Faulty phase selection, Fault classifier, and Fault direction discrimination, Whereas the form and ripple factors can be used for CT saturation and DC component detector, CT saturation and DC component assessment, and Adaptive tripping characteristics during the time periods of CT saturation and DC component current |
6. Data window size | The data window size can be modified and selected to be 1/8. 1/4, 1/2, 3/4, or one cycle | |
7. Relay stability | The relay is restrained from operation on CT saturation in the case of the external faults. The proposed relay is stable on those heavy through-faults on which a fixed-bias relay may operate The stability is characterized by the efficiency of the relay’s method of identifying the electrical system’s operating conditions | The relay is restrained from operation on CT saturation and DC component in the case of external faults. The proposed relay is stable on those heavy through-faults on which a fixed-bias relay may operate |
8. Relay reliability | It is characterized as high reliability because it is immune to fault time duration, fault inception angle, fault location, or fault type issues. Besides, it is able to detect all types of shunt faults The suggested protective relay satisfies the requirements of protection reliability (i.e., protection dependability and security) for operation. The reliability is determined primarily by the absence of failures in the operation of the protective relays. However, a compromise in the relay settings is still required to make coordination between protection stability and dependability, as well as between protection security and sensitivity | It is characterized as high reliability because it is immune to fault time duration, fault inception angle, fault location, or fault type issues. Besides, it is able to detect all types of shunt faults The suggested protective relay satisfies the requirements of reliability (i.e., dependability and security) for operation |
9. Data synchronization system | The proposed and existing protection schemes require no data synchronization system (it needs only fiber optics) | |
10. Digital low-pass filter | The selected data window size, used to calculate the alienation12,13 and correlation14 coefficients and differential and restraining currents, performs the functional role of the digital low-pass filter | The selected data window size, used to compute the form and ripple factors, and differential and restraining currents, behaves as the task of the digital low-pass filter |
11. Fields of relay applications | The proposed method can be advantageous with wide application scope, where it is useful in Smart Grids (SGs) and Substation Automation Systems (SAS). Moreover, it can be used for various equipment (including synchronous generators, power transformers, AC motors, underground cables, and short transmission lines) with different voltage levels | The proposed method can be advantageous with wide application scope, where it is useful in Smart Grids (SGs) and Substation Automation Systems (SAS). Moreover, it can be used for various equipment (including synchronous generators, power transformers, AC motors, underground cables, and short transmission lines) with different voltage levels |
