Demystifying Busbar Protection – Self Adapting Algorithms

In the realm of power systems, busbar protection is a critical aspect that ensures the stability and reliability of electrical networks. Traditionally, busbar protection relied on differential protection schemes that utilized simple threshold-based tripping mechanisms. However, advancements in technology have introduced self-adapting algorithms that significantly enhance the protection mechanism by making it more responsive and adaptive to varying fault conditions.

Understanding the Basics

Busbar protection is essential to safeguard the nodes in a power system where multiple circuits are connected. Busbar differential protection operates on the principle of comparing the sum of currents entering and leaving the busbar. Under normal conditions, according to Kirchhoff's law, this sum should be zero. Any deviation indicates a fault. The differential current (Idiff) and the stabilizing current (Istab) are the two key components in this protection scheme.

Self-Adapting Algorithms: The Game Changer

Self-adapting algorithms are designed to adjust dynamically to different fault scenarios, thereby enhancing the reliability of the busbar protection. These algorithms use different criteria for selection based on the current magnitude, slope of the stabilizing current, and fault location. The key self-adapting algorithms include:

1.?????? 1-of-1 Algorithm: This algorithm is triggered by a sudden jump in stabilizing current (dIstab/dt). It is particularly useful for high fault current levels and ensures a very fast trip time of around 7 milliseconds in Siemens SIPROTEC relays. However, it blocks for external faults after two samples to maintain stability. It ensures immediate response to severe faults, taking advantage of the saturation-free period at the beginning of a short circuit.

2.?????? 2-of-2 Algorithm: For faults with moderate current levels, this algorithm requires the tripping condition to be met for two successive half cycles. It provides stability even under heavy saturation and transient DC conditions, making it suitable for evolving faults with small jumps in amplitude For Siemens SIPROTEC devices, the typical tripping time is about 17 milliseconds.

3.?????? Fourier Filter Algorithm: This algorithm is optimal for low fault current levels and the presence of DC components. It provides a more stable response in conditions where the other algorithms might struggle, with a typical tripping time of 27 milliseconds.

Measurement and Evaluation

The efficiency of these algorithms hinges on precise measurement and evaluation of current values. The following are key metrics:

• Differential Current: Sum of all incoming and outgoing currents. Any non-zero value indicates a fault.
• Stabilizing Current: Sum of absolute values of individual currents. It helps differentiate between load and fault conditions.

The algorithms adjust their response based on these values, ensuring both sensitivity to genuine faults and immunity to false trips due to external disturbances or CT errors.

Coordination of Algorithms

Effective busbar protection requires coordinated action among different algorithms, for specific nature of faults. The self-adapting nature ensures that:

• 1-of-1 Algorithm: Activates for immediate response but blocks if external fault conditions persist beyond 2 samples.
• 2-of-2 Algorithm: Provides a secondary check, ensuring stability under varying conditions.
• Fourier Filter Algorithm: Adds a tertiary layer of evaluation for low current faults with DC components.

Figure 1 explains this coordination in further detail.

This multi-layered approach ensures robust protection, minimizing the risk of false trips while guaranteeing swift action in actual fault scenarios.