Tap Changer Contact Position Stability Calculation
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Solution Overview
Problem
On-load tap changers in power transformers face a risk of carbonization at specific contact points due to uneven current distribution, leading to potential overheating and damage when the contacts remain in the same position for extended periods.
Innovation Solution
A method to calculate the maximum time a tap changer can remain in the same position by measuring cooling media temperature, current load, and contact surface temperatures, using the Kohlrausch method to determine A-spot temperatures and ageing acceleration, and providing warnings and alarms based on predetermined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the tap changer contacts remain in the same position for extended periods, then the operational stability and reduced wear are improved, but the risk of carbonisation and overheating increases
Solution Approach 1:
The system performs preliminary calculations of A-spot temperature and ageing acceleration before carbonisation occurs. By continuously monitoring contact temperature and computing the maximum safe time period in advance, the system enables proactive tap position changes before damage happens, resolving the contradiction between maintaining position stability and preventing carbonisation.
Solution Approach 2:
The invention implements a feedback mechanism where the actual time period is continuously compared against the calculated maximum time period. When the actual time approaches or exceeds the maximum safe duration, warning and alarm messages are generated, providing real-time feedback that enables operational adjustments to prevent carbonisation while maximizing contact position stability.
2Reliability
If the contact temperature is continuously monitored and calculated, then the risk of carbonisation is reduced, but the system complexity and measurement requirements increase
Solution Approach 1:
The invention uses the cooling media temperature as an intermediary parameter to infer contact temperature. Instead of directly measuring complex contact surface temperatures, the system measures the more accessible cooling media temperature and uses it as a basis for calculating A-spot temperature through established thermal models, reducing measurement system complexity while maintaining reliability.
Solution Approach 2:
The system replaces direct physical temperature measurement at contact points with a computational approach. By using the Kohlrausch method and thermal ageing models, the invention substitutes complex hardware temperature sensing with mathematical calculations based on readily available electrical and thermal parameters, reducing device complexity.
3Measurement precision
If the maximum time period is calculated using detailed temperature and ageing acceleration data, then the precision of carbonisation risk assessment is improved, but the calculation complexity increases
Solution Approach 1:
The invention transforms the complex problem of contact temperature assessment by changing parameters to more manageable forms. It uses current load and cooling media temperature as input parameters and applies the Kohlrausch method with ageing acceleration factors to calculate A-spot temperature. This parameter transformation approach maintains high precision in carbonisation risk assessment while keeping the calculation system manageable through standardized thermal models.
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 method effectively reduces the risk of carbonization by determining a safe time limit for tap changer contact position stability, preventing overheating and extending the lifespan of transformer contacts.
Implementation Method 1
When current flows in a contact, the actual current flow path is not over the whole surface of the contacts... where the contact surfaces are in direct contact with each other. If the temperature in the A-spots is too high, the risk of carbonisation is increased.
Implementation Method 2
measuring the temperature of the cooling and isolating media surrounding said tap changer... From the measured values of the cooling and isolating media temperature and the current load, the contact temperature is calculated.
Implementation Method 3
From the calculated contact temperature and the measured current load, the temperature of the A-spots located in the contact surface is calculated. From said calculated temperature of the A-spots, the ageing acceleration is calculated.
Data Source
Figure 1
AI summary
The present invention relates to a method for calculating a time period, for which time period a tap changer in a transformer is placed in the same position. The method comprising the steps of measuring the temperature of the cooling and isolating media surrounding said tap changer and measuring the current load in the tap changer. Further, from the measured values of the cooling and isolating media temperature and the current load is the contact temperature calculated. The temperature of the A-spots located in the contact surface is then calculated from the calculated contact temperature and the measured current load. An ageing acceleration is calculated from the calculated temperature of the A-spots, and a maximum time period for the tap changer to be in the same position is calculated from the calculated temperatures and said ageing acceleration.