Page 267 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Fig 7

Fig 8

Open delta - VV connection (Fig 9)

• Used when load is less or future expansion expected
• When a 1f transformer need repairs
• The total load that can be carried by a VV bank is not two-third of the capacity of a bank but it is only 57.7%
of it.
• one of the transformers of a 3f is removed and 3-phase supply is connected to the primaries
Instrument transformers
The transformer which is required to facilitate measurement of high voltage and current are known as instrument
transformers. They are of two types
1 Current transformer
2 Potential transformer
Current transformer (CT)
Used with low-range ammeters to measure currents in high-voltage alternating-current circuits, where it is not
practicable to connect instruments and meters directly to the lines. They step down the current in a known ratio.

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CITS : Power - Electrician & Wireman - Lesson 41-49