Transformer Interview Questions & Answers Part-1
What is BDV Test of transformer oil?
BDV test, or Breakdown Voltage test, measures the dielectric strength of transformer oil, crucial for its insulating and cooling properties in transformers. This test evaluates oil’s healthiness.
What is the meaning of Dyn11?
Dyn11 is a transformer vector group designation indicating delta connection on the primary side, star with neutral on the secondary side, and a 30-degree phase shift between primary and secondary voltages.
How many earthing are required for a distribution & power transformer?
Three earthings are required: Neutral Grounding, Body Earthing, and additional as per electricity laws.
What is the main reason for using NGR in a power transformer?
Neutral Grounding Resistor (NGR) limits fault current during unbalance or fault conditions, protecting the transformer from damage.
Why is a step down transformer used for welding purposes?
A step down transformer is used in welding to provide high current required for generating the necessary heat, as it reduces voltage while increasing current.
What is the difference between an on load tap changing transformer and off load tap changing transformer?
ON load tap changing transformers allow voltage regulation without interrupting the supply, whereas off load tap changers require the transformer to be de-energized.
Which type of transformer is used in mobile chargers?
Switched mode power supply transformers, operating at high frequencies, are used in mobile chargers for efficiency and size reduction.
Differences between Transmission Line and Distribution Lines
| Parameter | Transmission Line | Distribution Line |
|---|---|---|
| Description | Carries high voltage power over long distances from generating stations to substations. | Delivers electrical energy from substations to end consumers at lower voltages. |
| Voltage Level | Operates at higher voltages (e.g., 33kV, 66kV, 132kV, etc.) | Operates at lower voltages, typically less than 33kV |
| Current Capacity | Designed to carry large amounts of current | Carries lower current compared to transmission lines |
| Conductor Size | Uses larger diameter conductors | Uses relatively smaller diameter conductors |
| Electricity Flow | Can flow in bi-directions depending on the grid connection | Usually unidirectional, towards the load only |
| Line Length | Carries electricity over long distances | Covers shorter distances, such as within a city |
| Phases | Three-phase lines only | Can be three-phase or single-phase; depends on the power delivering capacity |
| Types of Line | Long, medium, and short transmission lines | Radial, ring, and interconnected distribution lines |
| Line Support | Uses large steel towers for support | Supports include wooden poles, rail poles, RCC poles, etc. |
| Wire System | Three-phase three-wire system | Both three-phase three-wire and three-phase four-wire systems |
| Ground Clearance | High ground clearance due to operation at very high voltages | Comparatively less ground clearance required |
Why voltage is stepped up and then stepped down?
Stepping up voltage for long-distance transmission reduces line losses, and stepping down at the receiving end makes it usable for equipment and consumer applications.