Protection Relay Current Measurement Using Digital Integration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing protection relays face challenges in achieving accurate measurement of line current with fast response time, particularly in scenarios requiring immediate fault detection and response, as they often compromise between accuracy and response time due to the differentiated signal output from Rogowski coils, leading to increased complexity and cost with analog-hardware filtering.
Innovation Solution
A method involving a protection relay that digitizes the differentiated current signal from a Rogowski coil, iteratively computes integrated and compensated current data using specific digitized functions, and evaluates this data within the alternating current cycle to identify faults and generate trip signals, thereby achieving accurate and rapid current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cutoff frequency of an integrator is kept at a range to provide accurate measurement output, then measurement precision is improved, but response time is compromised
Solution Approach 1:
The patent replaces the traditional hardware-based integrator circuit with a software-based integration algorithm implemented in a microprocessor. This substitution allows flexible adjustment of integration parameters through software rather than being constrained by fixed hardware circuit characteristics, enabling optimization of both accuracy and response time through programmable control.
Solution Approach 2:
The patent implements a variable cutoff frequency mechanism where the integration parameters can be dynamically adjusted based on system conditions. The microprocessor can modify integration constants and time constants in real-time, allowing the system to adapt between prioritizing accuracy or response time depending on operational requirements, thus resolving the fixed trade-off between these parameters.
2Measurement precision
If additional analog-hardware filtering circuit is implemented for integration, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex analog filtering circuits with digital signal processing algorithms executed by a microprocessor. The software-based integration and filtering eliminate the need for additional analog components such as capacitors, resistors, and active filters, thereby reducing circuit complexity while maintaining or improving measurement accuracy through programmable processing.
Solution Approach 2:
The patent uses digital sampling and discrete-time integration algorithms to replicate the function of continuous analog integrators. By converting the analog current signal to digital samples and performing integration computationally, the system achieves the same mathematical operation without requiring physical analog integrating circuits, thus simplifying the hardware architecture.
3Measurement precision
If additional analog-hardware filtering circuit is implemented for integration, then measurement accuracy is improved, but reliability is reduced
Solution Approach 1:
The patent replaces analog filtering and integration circuits with software-based processing in a microprocessor. This substitution eliminates reliability issues associated with analog component drift, temperature sensitivity, and aging effects that plague hardware integrators. The software implementation provides consistent, repeatable performance without degradation over time, thereby improving system reliability while maintaining measurement accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise and speedy reconstruction of line current, allowing for immediate fault detection and response, improving measurement accuracy and response time while reducing complexity and cost by using software or firmware-based processing.
Implementation Method 1
A Rogowski coil sensor is commonly used for measurement of line current and the measured current is provided to the IED/protection relay for processing
Data Source
AI summary
The present disclosure relates to a method of integration and compensation in a protection relay. The method may include the protection relay: receiving a measured signal from a Rogowski coil and converting the measured signal to digitized samples, where the measured signal is a differentiated current signal over time; iteratively computing integrated current data from the digitized samples using a first digitized function to obtain integrated value; iteratively computing a compensated current data from the integrated current data using a second digitized function to remove a DC component in the integrated current data; evaluating the compensated current data to identify a fault condition; generating a trip signal on identification of a fault condition to operate a switch to electrically disconnect to protect the power equipment. The steps of integration and compensation may be performed in time window that is within the time period of the measured signal.