11 Questions
Why is it considered completely normal for transformers to heat up?
Because a non-heating transformer is not working properly
What can be expected regarding the surface temperature of a plastic enclosed safety transformer at rated load and 40°C ambient temperature?
70-80°C
Why is it difficult to touch a transformer's enclosure at a temperature of 70-80°C?
It is too hot to handle
In which scenario would a transformer's service life be considerably reduced?
When operating at high temperatures
Why is it important to determine the load by KVA when sizing a transformer?
To determine the appropriate size
What common standard KVA ratings are used for three Phase Delta-Wye transformers?
15 KVA, 30 KVA, 45 KVA, 75 KVA
What is the purpose of a single-phase transformer in non-urban areas?
To decrease home voltage
What are the standard KVA sizes for single-phase transformers?
1, 1.5, 2, 3, 5, 7.5...
What is a common application of encapsulated single-phase transformers?
Indoor and outdoor general loads
What distinguishes a ventilated single-phase transformer from other types?
Relatively high ratings
When are totally enclosed non-ventilated transformers ideal to use?
In high dirt and debris environments
Study Notes
Single-Phase Transformers
- Used in non-urban areas for power distribution due to lower demand and costs
- Step-down transformer to decrease home voltage to a suitable value without frequency change
- Standard KVA sizes: 1, 1.5, 2, 3, 5, 7.5, 10, 15, 25, 37.5, 50, 75, 100, 167, 200, 250, and 333
- Types:
- Encapsulated: for general loads, indoor and outdoor, with ratings from 50VA to 25 kVA
- Ventilated: for multiple single-phase indoor and outdoor loads, with ratings from 25 to 100 kVA
- Totally enclosed non-ventilated: for environments with high dirt and debris, with ratings from 25 to 500 kVA
Potential Transformers
- Used to step down voltage from a high level to a lower level with a small rating voltmeter
- Primary winding has a number of turns and is connected in parallel with the circuit
Distribution Transformers
- Also known as isolation transformers
- Function: alter high voltage to normal voltage (e.g., 240/120V) for electric power distribution
- Types:
- Single-Phase: used in non-urban areas where a three-phase supply is not required
- Three-Phase: used to hold electrical energy from the main distribution circuit to a minor distribution circuit
- Underground Residential Distribution (URD): a common power distribution system for modern cities
- Pad-Mounted: used in places where a fenced enclosure is not feasible
- Pole-Mounted: mounted on an electrical service pole to change high distribution voltage to low
Autotransformers
- A type of electrical transformer with only one winding
- Primary and secondary windings are linked together both electrically and magnetically
- Reduces cost over conventional transformers
Transformer Rating Plate
- Must include:
- Maker's name or initials
- Serial Number
- Current type (if DC)
- Phase (if single or three-phase)
- Rated Current
Test your knowledge about different types of transformers such as series transformer and potential transformer. Learn about their characteristics and applications in power systems.
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