What are Current Transformers?

Current transformers (CT) are devices that convert the existing electrical current into a reduced current that is safe for use with meters, relays, control equipment and other electrical devices. These devices are essential for the monitoring and protecting power systems.

Why is CT Testing Required?

There are several specific reasons to test current transformers.

• One significant reason for completing CT testing is to protect the delicate secondary device. At times, the ratio of current reduction that takes place can be as much as 30 times the normal current.
• Another equally important reason is to ensure the accuracy of your electrical billing. You should expect the reading to be accurate up to 0.1.
• As with any device, it is crucial to catch minor changes in the readings to avoid a major breakdown. Regular testing of these devices provides you with the health of your system.
• It is equally important to complete the CT testing before any new installation to verify that it is working correctly. With electrical current, safety is of primary concern. Typically, CTs are used for 30 years.

Types of Testing Procedures

CT testing is performed during development, production, installation and as a regular part of power maintenance. It is conducted in a variety of ways depending on the exact device. Among the procedures that you can do are ratio tests, polarity tests, excitation tests, insulation resistance tests, winding resistance test and burden tests.

• Ratio Test: This test compares the ratio of the primary current to the secondary current. The ratio should remain constant unless any factors change.
• Polarity Test: This test confirms that the direction of the secondary current is right, dependent on the direction of the primary current. It is based on the direction of the coil windings, either clockwise or counterclockwise.
• Excitation Test: In this circumstance the test consists of the injection of a specific voltage on the secondary side while taking a reading on the primary side. However, this type of testing has physical limitations and does not replicate all possible conditions from actual service. Other significant factors that cannot be tested by this method include transit diminishing, accuracy, safety, multiple errors, and consistency over time.
• Insulation Resistance Test: The insulation resistance test determines whether the resistance readings remain constant. If there is a significant drop, there is a problem.
• Winding Resistance Test: In this test, you divide the voltage drop across the winding by the DC current readings through the windings. A consistent figure indicates no issues.
• Burden Test: In this method, a high current is applied to the primary side, and the signal on the secondary side is read. In the testing procedure, a variety of current strengths is used to simulate different states of the primary side beyond normal operating conditions. This method is time-consuming and equipment intensive. At times it is not possible to test for very high current conditions.

The CT Analyzer Test Device

This device builds a model of the designated performance of your current transformer from manufacturers’ specifications. Once the data is entered, this test device can calculate different parameters such as standard performance, accuracy limiting factor, and safety factor. The software in the device can also simulate different burdens or various primary currents. Through the analysis of copper losses and iron losses, this device models the operation of the current transformer and then can calculate the current ratio error. Every international standard for current transformers can be obtained.

Also,  the device can be used in power system simulations for groups of CT testing. This ability gives your power system engineer better fault simulation which provides more accuracy overall.

The analyzer can also measure residual magnetism, providing your company with a new measurement option to detect faults.

The advantage of this small, lightweight device is that it is highly adaptable, fully automated, and provides the results promptly. The analyzer’s accuracy can be verified by metrological companies in Australia.

How to Find a Reputable Metrological Company

There are many critical indicators for reputable firms that perform calibration of instruments. The following criteria outline the essential points:

• Experience: Often, experience is a good indicator of competency. Somewhere on the company website there will be documentation of the company’s years in the field. Also, look for testimonials or case studies to determine the way clients are treated and the thoroughness with which they approach and conduct CT testing.
• Accreditation: Since you may be requiring certification for government compliance, make sure the firm you select can provide you with the proper documentation to perform this task.
• Company Values: Companies that post their values often are enterprises that understand how to treat their clients in a fair, respectful manner. Their dedication to displaying their core beliefs demonstrates that they have policies to support a positive business environment.
• Adaptability: You need an institute that is willing to work around your schedule to meet your business’s needs, even if it means working through traditional holiday time or requiring a quick turnaround. At times it may be beneficial to have the team come to your site to complete the calibration of your devices.

Does your company need to conduct CT testing or other specialist high- and low-voltage asset testing and commissioning services in project or maintenance environments? Contact us to learn more about our services.