Types of Transformer Field Tests and Diagnostics
The difference in voltage between the primary and the secondary windings is the turns ratio expresses a very different transformer relationship and output. A transformer is a static electrical device that transfers electrical energy between two or more circuits. A varying current in one coil of the transformer produces a varying magnetic . Joule losses due to resistance in the primary and secondary windings; Leakage flux that escapes from the core and passes through one winding. how to find primary and secondary winding of transformer?This video is about that topic A transformer is an electrical device that transfers.
Laminating the core greatly reduces eddy-current losses One common design of laminated core is made from interleaved stacks of E-shaped steel sheets capped with I-shaped pieces, leading to its name of 'E-I transformer'. The cut-core or C-core type is made by winding a steel strip around a rectangular form and then bonding the layers together. It is then cut in two, forming two C shapes, and the core assembled by binding the two C halves together with a steel strap.
A steel core's remanence means that it retains a static magnetic field when power is removed. When power is then reapplied, the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC waveform. On transformers connected to long, overhead power transmission lines, induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices.
The higher initial cost of the core material is offset over the life of the transformer by its lower losses at light load. These materials combine high magnetic permeability with high bulk electrical resistivity. For frequencies extending beyond the VHF bandcores made from non-conductive magnetic ceramic materials called ferrites are common.
Toroidal cores[ edit ] Small toroidal core transformer Toroidal transformers are built around a ring-shaped core, which, depending on operating frequency, is made from a long strip of silicon steel or permalloy wound into a coil, powdered iron, or ferrite. The closed ring shape eliminates air gaps inherent in the construction of an E-I core.
The primary and secondary coils are often wound concentrically to cover the entire surface of the core. This minimizes the length of wire needed and provides screening to minimize the core's magnetic field from generating electromagnetic interference.
RELATIONSHIP BETWEEN PRIMARY AND SECONDARY WINDINGS
Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I types, include smaller size about halflower weight about halfless mechanical hum making them superior in audio amplifierslower exterior magnetic field about one tenthlow off-load losses making them more efficient in standby circuitssingle-bolt mounting, and greater choice of shapes.
The main disadvantages are higher cost and limited power capacity see Classification parameters below. Because of the lack of a residual gap in the magnetic path, toroidal transformers also tend to exhibit higher inrush current, compared to laminated E-I types. Ferrite toroidal cores are used at higher frequencies, typically between a few tens of kilohertz to hundreds of megahertz, to reduce losses, physical size, and weight of inductive components.
A drawback of toroidal transformer construction is the higher labor cost of winding. This is because it is necessary to pass the entire length of a coil winding through the core aperture each time a single turn is added to the coil. As a consequence, toroidal transformers rated more than a few kVA are uncommon.
Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and secondary windings. The air which comprises the magnetic circuit is essentially lossless, and so an air-core transformer eliminates loss due to hysteresis in the core material. A large number of turns can be used to increase magnetizing inductance, but doing so increases winding resistance and leakage inductance.
Air-core transformers are unsuitable for use in power distribution. Conveniently, one can measure and compare heat readings for each part of the equipment without disrupting the transformer's operation.
Prevention, diagnosis, and repair benefits can be obtained for transformers by introducing Infrared thermography into your predictive maintenance plan. Insulation Resistance Test Insulation ages and deteriorates because of moisture, dust, and electrostatic stress.
Types of Transformer Field Tests and Diagnostics
Insulation should be monitored continually to avoid sudden failure of the equipment. An insulation resistance test detects insulation quality within the transformer.
The conductive impurities or mechanical flaws in the dielectric can be analysis based on this test. The instrument used to measure insulation resistance is known as the "megger.
Each winding should be short circuited at the bushing terminals. The resistance value should be measured between each winding and with respect to ground also. The winding should be discharged after the test is completed by connecting to the ground.
The insulation resistance value measured is usually in the order of mega-ohms. Generally the value should be greater than 1 megohm for every 1kV rating of the equipment. Insulation resistance values decrease with increase in the temperature. Therefore the values should be normalized for a standard temperature. It is necessary to have the insulation resistance as high as possible.
Transformer Turns Ratio Test Each winding of a transformer contains a certain number of turns of wire. The "transformer turns ratio" is the ratio of the number of turns in the high voltage winding to that in the low voltage winding.
The ratio is calculated under no-load conditions.
- Thermal Imaging (Thermography)
- Visual Inspection
- Contact Us
The transformer ratio can change due to several factors like physical damage because of faults, deteriorated insulation, contamination of oil etc. If a transformer ratio changes more than 0.