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
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