This document provides a summary of key aspects of transformer basics: - It describes the working principle of transformers using Faraday's law of electromagnetic induction and discusses the main parts of a transformer including its magnetic core and windings. - It lists different types of transformers classified by their use, construction, cooling method and other factors. Common types include distribution, power, control, and instrument transformers. - Key aspects of distribution transformers like primary and secondary voltages, capacities, construction types and impedance ranges are outlined. - Star and delta connections are explained along with diagrams and equations relating line and phase voltages. Advantages and disadvantages are also summarized. - Other transformer components like tap changers, bushings

1. Transformer Basic
-B. Prasad
Chartered
Engineer
amieclub@gmai
l.com

2. working principle
A transformer
works on the
Faraday,s
law
of
electromagne
tic induction.
A transformer
consists of a
laminated
magnetic

3. Transformerparts

4. Winding

5. Type of transformer
 Distribution
 Power.
 Control.
 Auto.
 Isolation.
 Instrument potential.
 Instrument current
 Indoor
 Outdoor
 Oil type
 Dry type
 Core type
 Shell type
 Natural cool
 Forced air/water
cool

6. Distribution transformer
Primary
voltage
Secondary
voltage
Capacity
(KVA)
Construction Impedance
range
3-11 380-440 25,40,63 Dry type 3-7%
100,150,250 Dry type
300,400,500 Oil/dry type
630,750,1000 Oil type
1250,1600 Oil type
2000,2500 Oil type

7. Star delta connection

8. Star delta diagram

9. Star delta voltage current
 Line voltage on Primary side = √3 X Phase voltage on
Primary side. So
 Phase voltage on Primary side = Line voltage on Primary
side / √3
 Transformation Ration (K) = Secondary Phase Voltage /
Primary Phase Voltage
 Secondary Phase Voltage = K X Primary Phase Voltage.
 As Secondary in delta connected:
 Line voltage on Secondary side = Phase voltage on
Secondary side.
 Secondary Phase Voltage = K X Primary Phase Voltage.
=K X (Line voltage on Primary side / √3)

10. Advantages of StarDelta Connection
 The Y-D connection has no problem with third
harmonic components
 fewer numbers of turns are required
 The neutral available on the primary can be
earthed to avoid distortion.
 Neutral point allows both types of loads
(single phase or three phases) to be met
 Large unbalanced loads can be handled
satisfactory

11. Disadvantages of star delta
 The secondary voltage is not in phase with the
primary
 If secondary of this transformer should be
paralleled with secondary of another transformer
without phase shift, there would be a problem
Application:
 commonly employed for power supply
transformers.
 Y connection on the HV side reduces insulation
costs the neutral point on the HV side can be
grounded.

12. Tap changer
It is a device fitted in
the transformer,
which is used to
vary the voltage
transformation
ratio.
 Off load tap
changer
 Onloadtap
changer(OLTC)

13. BUSHING
Transformer Bushings
are specially designed
electrical terminals for
taking out winding
ends (leads) through
the openings provided
on the top cover or
wall of the of
transformer tank and
connecting to the
incoming and
outgoing lines.

14. CT =CURRENT
TRANSFORMER
Typical specification fora 11
kV CT
 System voltage:11 KV
 Insulation level voltage (ILV) :
12/28/75 kV
 Ratio: 200/1 - 1 - 0.577 A
 Core 1: 1A, metering, 15
VA/class 1, ISF<10
 Core 2: 5A, protection, 15
VA/5P10
 Short time rating:20 kA for 1
second

15. PT=POTENTIAL
TRANSFORMER
Typical specification fora 11 kV VT
 System voltage: 11 KV
 Insulation level voltage (ILV) : 12 /
28/75 kV
 Number of phases: Three
 Vector Group: Star / Star
 Ratio: 11 kV/ 110 V
 Burden: 100 VA
 Accuracy: Class 0.5
 Voltage Factor: 1.2 continuous and
1.5 for 30 seconds With provision for
fuse

16. Condition ForParallel Operation Of
Transformers
 Same voltage and Turns Ratio (both primary and
secondary voltage rating is same)
 Same Percentage Impedance and X/R ratio
 Identical Position of Tap changer
 Same KVA ratings
 Same Phase angle shift (vector group are same)
 Same Frequency rating
 Same Polarity
 Same Phase sequence

17. TRANSFORMER OIL
FILTRATION

18. Impedance Levels
 Based kVA Minimum Impedance, %
0 – 150 Manufacturer’s standard
151 – 300 4
301 – 600 5
601 – 2,500 6
2,501 – 5,000 6.5
5,001 – 7,500 7.5
7,501 – 10,000 8.5
Above 10,000 9.5

19. Oil and winding temperature indication
Description Setting, degree C
Fan start 85
Fan stop 75
Pump start 90
Pump stop 80
Oil temperature alarm 85
Oil temperature trip 95
Winding temperature
alarm
100
Winding temperature trip 110

20. Transformer protection–
 Overcurrent & Short circuit (51):
The relay used is CDAG 51.
 Earth Fault (51N): The relay used is CAG 14.
 TransformerDifferential (87T): The relay used is
DTH 31, 11/6.6KV transformers.
 WTI (49WTX/49WAX): protected against increase
in winding temperature. The relay used is VAA 34.
 OTI (49TX/49AX): protected against increase in oil
temperature. The relay used is VAA 34.
 Buchholz (63TX/63AX): protected against internal.
The relay used is VAA 34.

21. ACT FAST AND INITIATE
FIRST
 बड़ा सोचो
 तेजी से सोचो व
 सबसे पहले सोचो
 िवचारो पर िकसी का
 एकािधकार नही होता.
---- धीरभाई अमबानी

22. THANK YOU