T&D World Magazine

Test Set Performs Current Transformer Saturation Test

The EZCT-S2 from Vanguard Instruments is a second-generation, microprocessor-based, current transformer set. The EZCT-S2 will perform the current transformer saturation test and the CT (current transformer) turns-ratio automatically. The saturation test voltage is automatically raised and lowered by the EZCT-S2. No operator intervention is required.

With up to 1500 VAC saturation test voltage available, the EZCT-S2 can easily perform saturation tests on very large CTs.

The CT saturation test is performed using the ANSI/IEEE C57.13.1 test method. The test voltage [50 Vac, 250 Vac, 500 Vac, to 1500 Vac] is selected by the user for the CT saturation test. The test voltage is raised and lowered automatically by the EZCT-S2. Test voltage and current data are collected and stored in the EZCT-S2 internal memory. Up to 10 CT saturation and turns-ratio tests can be stored in one test record. Once the test is completed, the user can print test results and plot excitation curves on the built-in 4.5-inch-wide thermal printer.

The EZCT-S2 determines the CT turns-ratio using the ANSI/IEEE C57.12.90 measurement method. A test voltage is applied on two CT secondary terminals (X1 to X5). The induced voltage is measured through the CT H1-H2 terminals. CT turns-ratio and polarity are displayed and stored in memory. The turns-ratio measuring range is from 0.8 to 5000. The CT winding polarity is displayed as a + sign (inphase) or a – sign (out-of-phase) and is printed with the phase in degrees.

The EZCT-S2 displays messages on a 4-line by 20-character, sunlight-viewable LCD. The LCD is also backlit for low-light viewing condition. An alphanumeric keypad allows the users to enter test information and control functions.

A built-in 4.5-inch-wide thermal printer prints the CT test results and saturation curves.

Test-record header information includes the company name, substation names, circuit ID, manufacturer, CT serial number, operator’s name, and test-record comments. In addition to the test-record header, the user can enter a 20-character test description for each test in the record (10 test descriptions per record). The test-record header and the 10 test descriptions are stored with each test record in Flash EEPROM.

The EZCT-S2 can store up to 140 test records in Flash EEPROM. Each test record may contain up to 10 saturation curves, turns-ratio readings, and winding polarity. Test records can be recalled and printed by the thermal printer.

The EZCT-S2 will store up to 128 CT test plans in Flash EEPROM. A test plan defines the saturation test voltage and current selection, CT name-plate ratio, and CT winding terminal connection instruction for each test. Up to 10 test definitions can be stored in each test plan. With the use of a test plan, CT testing is greatly simplified. The user needs only to follow the test plan connection instructions for the EZCT-S2 cables to the CT terminals (X1 to X5) and command the EZCT-S2 to perform the test. Test plans can be created from the EZCT-S2 front panel keyboard or on the PC and downloaded to the EZCT-S2 via the RS-232C or USB port. EZCTTM S2

The EZCT-S2 can be used as a stand-alone unit or in a computer-control mode. A Windows XP-based “Current Transformer Analysis” software program is provided with each EZCT-S2. In computer control mode, the user can retrieve test records from the EZCT-S2 memory, create test plans, download test plans to the EZCT-S2 or run a CT test from the PC. A built-in RS- 232C or USB port can be used for the computer interface. Tabulated test records can be exported to EXCEL.

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