By sion932 
In the power system, current transformers (CTs) play a crucial role as they can proportionally reduce high voltage and high current, facilitating measurement and protection. The performance of CT is directly related to the stable operation of the entire power system. At this point, the CT volt ampere characteristic tester becomes the “little doctor” ensuring CT performance. This may sound like a somewhat professional technical device, but what exactly does it do? Why is it so important?
CT volt ampere characteristic tester: What is it?
Simply put, a CT volt ampere characteristic tester is an instrument specifically designed to measure the volt ampere characteristic curve of a current transformer (CT). The volt ampere characteristic curve, as the name suggests, is a curve that reflects the variation of current (A) of CT at different voltages (V). This curve can intuitively display the excitation characteristics of CT, that is, the relationship between the induced voltage and current on the secondary side of CT at different primary currents. A good CT should have good excitation characteristics during operation to ensure its accuracy.
The “things” that affect CT volt ampere characteristics
The volt ampere characteristics of CT are not constant and can be influenced by various factors
The manufacturing process and materials of CT, including the material of the iron core, the number of turns of the winding, and the insulation level, are all key factors affecting its performance.
Operating environment: Temperature, humidity, and even vibration may have a subtle impact on the electrical performance of CT.
Aging and loss: Over time, the insulation material of CT may age, and the iron core may also experience loss, thereby changing its characteristics.
Load variation: The load variation of the secondary circuit connected to CT can also affect its excitation state.
What can ‘it’ do for us?
The CT volt ampere characteristic tester can quickly and accurately measure key parameters such as the knee point voltage, inflection point voltage, and excitation current of CT by simulating various operating conditions of CT in actual operation. These parameters directly reflect the accuracy limit factor (ALF) and composite error of CT, and are important criteria for determining whether CT is qualified.
Knee Point Voltage: The turning point on the CT excitation characteristic curve where the rate of voltage change gradually decreases. Beyond this point, the error of CT will rapidly increase, and the accuracy of measurement and protection cannot be guaranteed.
Inflection Point Voltage: The point on the volt ampere characteristic curve where the slope changes the fastest.
Exciting Current: The current that flows through the secondary side of the CT when it reaches the knee point voltage.
By mastering these data, we can determine whether there is saturation phenomenon in CT and whether it can still meet the system’s requirements for measurement accuracy and protection response speed.
How can we do better?
To better utilize CT volt ampere characteristic testing, the following can be done:
Regular testing: According to regulatory requirements, conduct regular volt ampere characteristic tests on CT, establish CT operation records, and track its performance change trends.
Data analysis: Combining historical data to analyze the degree of CT degradation and predict potential failure risks.
Choosing the appropriate instrument: It is crucial to choose a CT volt ampere characteristic tester with stable performance, easy operation, and accurate data. For example, various power testing equipment produced by HVHIPOT enjoys a high reputation in the industry. They have a professional R&D team and advanced production processes, which can provide reliable testing solutions.
Other devices related to it
In addition to CT volt ampere characteristic testers, there are also some equipment closely related to CT testing and maintenance, such as:
Transformer secondary load measuring instrument
DC resistance tester
Insulation resistance tester
These devices together form a comprehensive evaluation system for CT, safeguarding the safe and stable operation of the power system.
Frequently Asked Questions:
Q1: What is the testing principle of CT volt ampere characteristic tester? A1: It mainly analyzes the excitation characteristics of CT by applying voltages of different amplitudes to the CT secondary winding, measuring the corresponding secondary current, and drawing the volt ampere characteristic curve.
Q2: Why is the volt ampere characteristic curve of CT important? A2: The volt ampere characteristic curve directly reflects the accuracy and overload capacity of CT, and is a key indicator for determining whether CT is qualified.
Q3: What problems will CT saturation bring? A3: CT saturation can lead to increased measurement errors, misoperation or refusal of protection devices, seriously affecting the safe and stable operation of the power system.
Q4: What should be noted when testing CT volt ampere characteristics? A4: Before testing, ensure that the CT secondary circuit is open and correctly connected to the testing instrument, and select the appropriate testing voltage range. The products provided by HVHIPOT will have detailed operation guidelines.
Q5: What factors affect the volt ampere characteristics of CT? A5: This mainly includes the manufacturing quality, operating years, working environment, and secondary load of CT.