Circuit Breaker Testing

WHAT IS CIRCUIT BREAKER & WHY SHOULD WE TEST IT? Circuit breakers allow the flow of energy to be controlled by safely switching current on and off at all voltage levels of the energy grid. In the opened position, they have to ensure isolation across the switching distance between phases and to ground, in the closed position, they have to allows the energy to flow with minimum losses. They need to be able to reliably interrupt short circuit currents without damaging themselves or adjacent equipment even after long idling times. Different circuit breaker technologies are in use depending on voltage level, application and the age of their design. […]

Vacuum Bottle Insulation Integrity Test

WHAT IS VACUUM BOTTLE INTERRUPTER? A vacuum circuit breaker is a kind of circuit breaker where the arc quenching takes place in vacuum medium. The operation of switching on and closing of current carrying contacts and interrelated arc interruption takes place in a vacuum chamber in the breaker which is called vacuum interrupter. In electrical engineering, a vacuum interrupter or Vacuum Bottle is the core component of medium-voltage circuit-breakers, generator circuit-breakers & high-voltage circuit-breakers. Separation of the electrical contacts results in a metal vapour arc, which is quickly extinguished. Vacuum interrupters are widely used in utility power transmission systems, power generation unit, power distribution systems for railway, arc furnace application and Industrial plants. Fig.1. Vacuum Interrupter WHY DO WE TEST VACUUM BOTTLE INTERRUPTER? Fast and reliable protection are the [...]

Phase-Shifting Transformer tests

A phase-shifting transformer is a specific form of electrical transformer used to manage the flow of active power on 3Ø electric transmission lines. It is often called a phase angle regulating (PAR) in the US and a quadrature booster in the UK. In this application note, we will use the phase-shifting (PST) term. Physically, phase-shifting transformers are static machines whose general construction characteristics are in some respects similar to conventional transformers with two separate transformers: A Shunt unit or Exciting unit (EU) and a series unit (SU). Due to their internal connections, they make it possible to obtain a phase shift between the input and output voltages. The phase shift between the input and output [...]

Temperature Rise (Heat Run) test

Heat run test or temperature rise test is one of the type tests on the power transformer. This test’s results are really important for the operational economy to show the performance of the transformer in the fields. The mean purpose of this test is to check whether the oil and winding temperatures of the transformer meet the values specified in the standard and technical projects. […]

Tests on the on-load tap changer (OLTC)

WHY DO WE PERFORM OLTC TEST? The on-load tap changer (OLTC) is the only moving part in a typical power transformer, it permits tap changing and regulating voltage without affecting the network operation. This frequently movements between transformer taps makes the OLTC components the most vulnerable, which implies regular testing and maintenance. On the other hand, by using a conventional static winding resistance measurement, it is hard to detect any anomalies during the switching process because of the fast movements of the OTLC’s switches (40-60 ms). Many mechanical parts are not easily accessible for inspection, and it is recommended to perform additional tests to establish the OLTC condition. Usually, winding resistance measurements are performed on offline power transformers. In [...]

Transformer Vector Group Detection

The three-phase transformer comprises three separate single-phase transformers with shared limbs, each representing a phase consists of primary and secondary windings. The primary or secondary windings are connected in one of several ways. The most common configurations are the star, delta, and Zigzag. The phase angle between the high voltage and the low voltage windings varies between 0o and 360 o. The vector group is the method of categorizing the high voltage HV windings and low voltage LV windings configurations of three phase transformers [1]. The vector group of a transformer is presented as follow: Fig.1. Vector Group Representation THE IMPORTANCE OF THE TRANSFORMERS VECTOR GROUP DETECTION. The transformers vector group identification (Y-Y, Delta-Y, Delta-Delta… etc.) is an essential [...]

Transformer Magnetic Balance Test

The magnetic balance test is a most commonly used proactive test is performed only on three-phase transformers to detect the faults in the core and to verify the imbalance in the magnetic circuit also to identify inter-turn faults in the transformer at the early stage of manufacturing work. HOW DO WE TEST TRANSFORMER MAGNETIC BALANCE? Transformer Magnetic Balance Test Procedures: 1. Keep the transformer Tap Changer in an ordinary position. 2. Apply a single-phase AC voltage on one of the terminals of the HV winding. 3. Measure the voltage between the two other HV terminals. 4. Repeat the test for each of the three phases. Left side phase Central phase  Right side phase AN BN CN Voltage applied at [...]

How Do We Measure Transformer Winding Resistance?

The rotating machine and Transformers are permanently prone to vibrations. Therefore, some problems or defects may occur due to poor design, assembly, overload, poor maintenance, even poor environment around the transformer during operation. Transformer resistance measurement is an image of the copper length of a given winding, and the quality of the contacts, present on the electrical circuit. On a three-phase transformer, the resistances between similar phases must be relatively identical. There is usually a tap changer built into the power transformers. These taps allow to increased or decreased the turns number in the main winding of the transformer. These taps changes will be also checked during the winding resistance test. Measurement of the transformer winding resistance is performed [...]

Why ratio measurements of transformers are important?

A transformer turns ratio test confirms the ratio accuracy of a transformer. The test ensures the correct ratio of both primary turns and secondary turns and guarantees the proper functioning of the power transformer. Furthermore, Turns Ratio test can help to identify issues related to tap-changer performance, incorrect and open winding connections. Due to the significant benefits, can be reaped by the Turns Ratio test, it is necessary to have your transformer tested frequently. Turns Ratio measurements of a transformer are extremely important for several reasons, such as Quality verification, Validation of design specifications, Assessment of possible damage, Establishment of transformer condition and condition trends. During the test, if the Turns Ratio results differ from the expected target [...]

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