Designed to measure the turns-ratio of power, instrument, and distribution transformers in a substation or manufacturing environment, AVO's Biddle three-phase automatic TTR weighs only 7,5 kg.
Spescom MeasureGraph, its distributor, points out that this is lighter than any other commercially available instrument. A rugged and robust design makes this TTR well suited for use in a variety of harsh environments. It is particularly well suited for testing in power transformer manufacturing environments where testing of complex, three-phase substation power transformers can be performed quickly while minimising the possibility of errors.
Able to measure the highest turns ratio range in the industry (10 000:1) - the instrument is also said to provide the highest accuracy (0:1%).
A useful feature of this new TTR is the ability to measure phase deviation (in minutes or centiradians) of the transformer primary versus secondary. This will quickly indicate problems in a transformer such as partial shorted turns and core faults. This measurement is also useful in verifying phase errors of all types or PTs and CTs.
It comes equipped with sufficient onboard memory to store up to 200 test results in the field for later retrieval at the office. Test results can be printed on an optional serial printer whenever a hard copy is desired, or the data can be downloaded to a PC. Identification of individual test readings is also easily done. The system software allows entry of the transformer alphanumeric serial number, transformer type and tap information for each test performed.
The TTR also comes with a unique optional, remote control software program. This Windows-based program permits control and operation from a PC keyboard, downloading of test data from the TTR to a PC, printing of test results reports and assists in the preparation of management and/or analysis reports using Excel, or Access.
Catering for the environments in which the TTR must operate, it features a high contrast LCD screen, which can be seen in bright, or dim, ambient lighting, and comes equipped with specially designed leads that provide the necessary flexibility needed in cold weather conditions.
Applications
The proper operation of a transformer relies almost entirely on the electrical properties of its windings. To ensure continued proper operation, transformers are tested to verify that their electrical properties have not changed from design specifications.
The instrument can locate several types of problems within a transformer. It is suitable for testing in meter shops for the upcoming inspection of CTs and PTs and also determines the need to further test faulty CTs and PTs.
The TTR applies voltage to the high voltage winding of a transformer and accurately measures the resulting voltage from the low voltage winding. In addition to turns-ratio, the unit measures excitation current, phase angle deviation between the high and low voltage windings and percent ratio error.
Transformer turns-ratio
Transformer turns ratio is the ratio of the number of turns in the high voltage winding to that in the low voltage winding. This TTR can directly measure the ratio of most types of transformers. Transformer ratio can change due to several factors, including physical damage from faults, deteriorated insulation, contamination and shipping damage. If a transformer ratio changes more than 0,5% from the rated voltage ratio, it may not operate reliably. To measure small ratio changes such as this, the accuracy of a Biddle TTR is needed.
Exciting current
The exciting current is the current that maintains the magnetic flux excitation in the core of a transformer.
A transformer turns ratio test set such as the Biddle three-phase automatic TTR is capable of measuring exciting current because it applies a voltage across one of the transformer's windings. An accurate measurement of exciting current can provide information about the condition of a transformer's core. Unwanted circulating currents or unintentional grounds can affect the exciting current and indicate a problem.
Phase angle deviation
The phase angle deviation is the relationship between the voltage signal applied to the high voltage winding and the voltage signal extracted from the low voltage winding. The phase deviation between the high and low side of a transformer is generally very small. If there is a deterioration or damage on the transformer core, however, the phase deviation can change significantly. The Biddle three-phase TTR can measure this phase relationship with the resolution necessary to detect a problem.
Spescom MeasureGraph, a subsidiary of JSE-listed Spescom, and a leading supplier of test and measurement equipment, is the sole local distributor of the Avo product range.
Kevin Preston, Spescom MeasureGraph
011 266 1500
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