Bernhard Deck

Smart distribution protection using current-only directional overcurrent relay

Overcurrent relays are widely used for power systems protection. Transmission side uses more directional type relays, while distribution systems, e.g., radial and ring-main subtransmission systems use non-directional types. The fault direction may be forward (between relay and grid), or reverse (between relay and source), the normal power flow being from source to the grid. Traditional directional overcurrent relays utilize the reference voltage phasor for estimating the direction of the fault. This requires measurement of both current and voltage using respective sensors. This makes the directional overcurrent relays more costly than the non-directional type. In this paper, a novel current-only directional detection possibility is highlighted along with theoretical and test signal analysis. Possible utilization of the current-only directional relay for intelligent directional protection in the distribution systems are described. Directional protection for distribution systems is a key focus area for enabling the smart grid.

Current-Only Directional Overcurrent Protection for Distribution Automation: Challenges and Solutions

Overcurrent relays are widely used for power systems protection. Transmission side uses more directional type relays, while distribution systems, e.g., radial and ring-main subtransmission systems use nondirectional types. The fault direction may be forward (between relay and grid), or reverse (between relay and source), the normal power flow being from source to the grid. Traditional directional overcurrent relays utilize the reference voltage phasor for estimating the direction of the fault. This requires measurement of both current and voltage using respective sensors. This makes the directional overcurrent relays more costly than the nondirectional type. In this paper, a novel current-only directional detection possibility is highlighted along with theoretical, test signal analysis, challenges and associated solutions. Possible utilizations of the current-only directional relay in the distribution side protection are described, which is a key focus area for enabling the smart grid.

Current-Only Directional Overcurrent Relay

Overcurrent relays are widely used for protection of power systems, directional ones for transmission side, and nondirectional ones for distribution side. The fault direction may be forward (between relay and grid), or reverse (between relay and source), the normal power flow being from source to the grid. Known directional overcurrent relays rely on a reference voltage phasor for estimating the direction of the fault, requiring both current and voltage sensors. This increases the cost of the relays, prohibiting the utilization of such relays in the distribution side protection and automation, which is going to be a key part in the smart grid initiative. In this paper, a novel current-only directional detection possibility is highlighted.

Fast computation of arctangent functions for embedded applications: A comparative analysis

Inverse tangent or arctangent function has many applications, for example, in estimating the phase angle of complex number utilized in electrical ac circuit analysis, power systems analysis, etc. Therefore, fast and accurate computation of the arctangent function is of great importance. Implementation of the arctan or atan2 using series expansions is accurate when computational cost is not an issue. However, for embedded applications such implementations cannot be used. As alternative, different approximations are proposed. In this paper, we present an efficient implementation using look-up table with 101-points. The accuracy is then increased by linear interpolation. The arctangent computation is extended to four quadrant operation using particular properties of arctan. The proposed scheme is implemented in a 60MHz microcontroller platform, typical for embedded applications. Comparative evaluations show that the accuracy of the proposed method is better than the reported approximation techniques. The time consumption of the proposed method is significantly less than that of the library function of the same microcontroller platform.