4. Type of construction and difference
Live Tank Design Dead Tank Design
Weight at Top Weight at bottom
Short Primary length Longer Primary length
Main Insulation at top Main insulation at bottom
Failure generally in top
chamber
Failure normally at bottom
Special precaution must be
taken to pass fault current
from top chamber to earth
Fault current passes through
the primary winding safely up
to the earthed bottom tank
Suitable for high currents
even above 2000 Amps
Suitable for currents up to
2000 Amps
5. Safety Point of view difference
Live Tank Design Dead Tank Design
Possibilities of fire and
blast is higher because
fault occurred at Live HV
Side Voltage level
Possibilities of fire is
less.
6. Dead tank CT Winding
Primary winding
Secondary WDG
13. Detail On Name Plate
Primary Terminal And CT Ratio
Nos. of Core used in CT
Rated Burden
Accuracy Class And ALF
Knee Point Voltage
Type of Cooling
Tan Delta Value
LOI / A-T No
YEAR OF MFG.
14. Use of CT
For Metering. : Measurement of Current –
Which is in put quantity to meters for
measurement and display
For Protection. : Measurement of Current –
Which is in put to relays like O/C, E/F,
Differential , Distance , Bus Bar protection
etc
15. Metering Core And Termination
Generally 1- St Core of CT is used for
Metering and hence having class of
accuracy 0.2 / 0.2 S / 0.5 / 1.0
1S1-1S2-1S3 are the terminal on CT
secondary Box
If we choose ratio: 1200 Amp then full
secondary winding comes in picture and
Terminals are 1S1- 1S3 Similarly For 600
Amp Terminals are 1S1-1S2
16. Back Up Protection Core
And Termination
This CT name plate details shows : Class of
accuracy is 5 P 10 And Burden is 15 VA
This core i.e. 2nd Core is for Back up
protection O/C And E/F relay function as in
put current.
We connect wires on 2S1- 2S2 For 600 Amp
And 2S1-2S3 For 1200 Amp.
17. Differential or Distance
Protection Core And Termination
Third core of This detailed CT with
Accuracy class PS:
Knee Point Voltage : 950 Volt @ 1200/ 1 A.
For 1200 /1 Amp : 3S1- 3S3
And 600 /1 Amp : 3S1- 3S2
Other Cores if available it is 4th and 5th. In CTs
of 132 KV And above class in GETCO For
Bus Bar protection Scheme all these core of
PS Cl.
19. Ferrules practice
D – FOR METERING
C – FOR BACK UP PROTECTION
A – FOR DIFFERENTIAL / DISTANCE
B – FOR BUS BAR PROTECTION
20. Metering CT
Metering CTs are having Secondary with
1 Amp or 5 Amp in GETCO
Why in 11 KV At 5A ?
66 KV And Above at 1 A ?
21. CT Ferrules at MK Box
A>> Metering Circuit :: -
R-Phase CT : R1S1- R1S2 (Metering)
Y-Phase CT : Y1S1-Y1S2 (Metering)
B-Phase CT : B1S1- B1S2 (Metering)
Pilot wire S1 And Star Point S2 Hence All
1S2 points are shorted and earthed at Yard
MK
22. For similar we can do for Back
up and Differential
• For Back UP Protection : “ C ” We Use
• R- Phase C 11
• Y-Phase C31
• B- Phase C51
• Star Point C71
• And For Differential / Distance : “A” We
use
• A11 , A31 , A51, A71
28. Maint. Check Point
For Current Transformer :
• Checking daily for any leakage of Oil or for
corona and for abnormal noise ,or any hot
glow etc.
• Periodic Checking of IR Value and Tan
Delta of CT & Condition of Oil and
nitrogen pressure if CT Without Bellow
• Checking of Knee Point voltage and ratio
test and Secondary Wdg. Resistance
measurement .
29. Reasons for failure of CTs.
> Low IR Value (Failure of insulation)
>High Tan Delta Value
>Opening of secondary Wdg.
>Primary winding joint opening during
fault.
>Loose / no proper earthing connection at
tan delta point
30. CVT : Capacitive Voltage Transformer
Generally provided for dual purpose of
communication and for monitor line voltage
and frequency
Where Two line parallel operation either of
Generation or of other grids then checking
of Voltage / Frequency /Phase sequence
condition is essential before make it
parallel
31. CVT Use:
>One Line having CVT and secondary side
There will be decided voltage 110 V A.C
>This voltage is used to compare with Bus PT
and Phase sequence through
Synchronization trolley.
33. General Ckt Dia. for CVT
V1
V2
C1
C2
Secondary
Voltage
Circuit Diagram of a C.V.T
Secondary
Voltage
V2
C1
C2
Equivalent Circuit
V1
___
V2
= 1+ ___
Notes:
______
Where K- Factordepending upon losses in
Capacitors and Electro-magnetic Portion
O - Phase error change in Minutes/Hz
Maximum Output from a C V T=K(C1+C2) V2
2
C 2
C 1
Protective Spark Gap
35. Maint. Care To be taken for CVT
Cleaning of porcelain insulators
Checking of secondary connections
Measurement of IR value and Tan Delta as
per OEM Recommendation
Never store in horizontal position.
