A few instruments commonly used in the monitoring of electrical power systems are the current transformer, or CT, and the potential transformer, or PT. The PT is used to ensure correct the voltage in the power system such as the voltage in power lines– it is not unusual for a power line to be rated at 400,000 to 700,000 volts!
The CT is used to convert a primary current into a reduced secondary current to accurately measure the current of the power system the CT is attached to. This is important for many businesses, especially for electric companies, as it ensures the accuracy of electric billing statements. In order to maintain a CT and ensure it is measuring current accurately, current transformer testing must be performed regularly.
Here are several CT tests you perform using current transformer testing equipment to determine the effectiveness of your CT.
1. Ratio Test
This test is performed in order to determine the ratio of primary current input to secondary current output at full load. As the primary current changes, the secondary current changes at the same rate. For instance, if the primary current is decreased by half, then the secondary current decreases by half as well. This test is performed in order to prove the ratio of the CT is as specified by the manufacturer, and this test can be performed by most CT meters.
2. Polarity Test
The polarity of a CT is the direction in which current is flowing throughout the CT. Polarity indicates where the primary current is entering the primary terminal, and where the secondary current is exiting the secondary terminal. The CT polarity is considered correct when the directions for the primary and secondary current oppose each other. Observing that correct polarity is important when first installing a CT, and the polarity test is often done at the same time as the ratio test using most current transformer instruments.
3. Burden Test
Performing the burden test is important for verifying that a CT is supplying current to a circuit that does not exceed the manufacturer’s burden rating. If the burden is too high, then it could result in a decrease in the CT secondary current, and a decrease in the accuracy of the CT. Burden tests are often more time-consuming than other current transformer testing, but still essential to maintaining the current transformer.
Maintaining an accurate CT is important in monitoring the energy use of any business. Regularly testing your CT will make sure that your CT remains functioning, and will help reduce electrical costs due to inaccurate billing statements. For more information, give us a call at PowerMetrix today!