Op-Amp Voltage Sensing Circuit for Galvanic Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electrical metering systems require large and expensive instrument transformers for voltage sensing at higher voltages, which are cumbersome and inefficient, especially with the shift towards solid-state metering where burden is minimal.
Innovation Solution
A compact voltage sensing transformer operating in current mode, providing galvanic isolation and voltage input conditioning, which can be combined with a conventional control power transformer, allowing for smaller and less expensive designs suitable for electronic metering and protection devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional potential transformer is used for voltage sensing, then galvanic isolation is provided, but the transformer becomes very large and heavy
Solution Approach 1:
The patent replaces the conventional potential transformer with an operational amplifier-based voltage sensing circuit. The op-amp circuit uses high-impedance input buffering and voltage division to achieve voltage sensing without requiring a heavy transformer, thereby substituting a mechanical/electromagnetic system with an electronic system.
Solution Approach 2:
The patent introduces an operational amplifier as an intermediary component between the high-voltage line and the metering circuit. The op-amp provides high-impedance buffering and signal conditioning, enabling accurate voltage sensing while maintaining galvanic isolation through its input impedance characteristics rather than through transformer coupling.
2Measurement precision
If a potential transformer is oversized to maintain accuracy, then voltage measurement precision is improved, but device size and cost increase
Solution Approach 1:
The patent replaces the oversized potential transformer with a compact operational amplifier circuit that achieves accurate voltage measurement through high-impedance input buffering and precision voltage division. This electronic approach eliminates the need for large transformer cores and windings while maintaining measurement accuracy.
Solution Approach 2:
The patent changes the operating parameters by using high-impedance input buffering and precision voltage division ratios instead of transformer turns ratios. This allows accurate voltage sensing with minimal burden on the measurement circuit, eliminating the need for oversized transformers.
3Area of stationary object
If a voltage divider circuit is used directly from the line, then device size is reduced, but galvanic isolation is lost
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary between the voltage divider circuit and the metering input. The op-amp's high input impedance acts as a buffer that maintains galvanic isolation while allowing the compact voltage divider circuit to function accurately without directly loading the high-voltage line.
Solution Approach 2:
The patent substitutes the transformer-based isolation mechanism with an operational amplifier-based isolation approach. The op-amp provides electrical isolation through its high input impedance characteristics, enabling direct voltage division from the line while maintaining safety isolation.
4Measurement precision
If instrument transformers are used to step down high voltage, then voltage sensing accuracy is maintained, but cost and device size increase
Solution Approach 1:
The patent replaces expensive instrument transformers with operational amplifier-based voltage sensing circuits. The op-amp circuit uses standard electronic components and precision voltage division to achieve accurate voltage sensing at a fraction of the cost of conventional instrument transformers.
Solution Approach 2:
The patent uses inexpensive operational amplifiers and passive components to replace costly instrument transformers. The electronic circuit components are much cheaper than precision-wound transformers while providing equivalent or superior measurement accuracy for modern solid-state metering applications.
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 solution offers significant cost and space savings by eliminating the need for oversized transformers, enabling efficient voltage sensing and input conditioning in electronic metering and protection devices, suitable for applications like meters, monitors, and relays.
Implementation Method 1
a primary winding of a transformer T1 through a current limiting resistor R1... A transformer T1 provides galvanic isolation between circuits coupled to the primary and secondary windings
Data Source
AI summary
A voltage isolation circuit. The input voltage Vin is connected to a primary winding of a transformer T1 through a current limiting resistor R1. R1 is preferably sized such that the current flow in the primary at nominal input voltage is approximately 1 milliamp. Transformer T1 is wound as a current transformer with a fixed ratio between the primary and secondary windings. Thus, when 1 mA flows in the primary winding, 1 mA will also flow in the secondary winding. An inverting operational amplifier will continuously attempt to drive its inverting input to a zero potential through resistor R2. The voltage at Vout produced by the op-amp is a faithful replica of the voltage at Vin, but scaled according to the values selected for R1 and R2.