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Topic Title: CVT Replacement
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Created On: 07 April 2010 11:47 AM
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 07 April 2010 11:47 AM
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janaka077

Posts: 38
Joined: 25 July 2008

Background:
There are 3 CVTs in a tx Line at a grid sub (GS). They reach high gas pressure level. Therefore we have decided to replace them. Detail of a CVT is given bellow.
core 1: 132kV/√ 3 : 110/√ 3 class 1
core2: 132kV/√ 3 : 110/3 class 3p
Burden 100VA

ALSTHOM , TROPIC relays are use for DOC and DEF relays and it receives voltage signal from core2 of the CVT

We have got two new CVTs (CVT 1 , CVT 2)from stores and one used CVT (CVT 3) available with us.
Data CVT 1 and CVT 2 (from Kotugoda)
core 1: 132kV/√ 3 : 110/√ 3 class 1
core2: 132kV/√ 3 : 110/√ 3 class 3p
burden 50VA

Data CVT 3 (available with us)
core 1: 132kV/√ 3 : 110/√ 3 class 0.5/3p
core2: 132kV/√ 3 : 110/√ 3 class 0.5/3p
core3: 132kV/√ 3 : 110/ 3 class 1/3p
burden 200 VA

We are planning to replace existing 3 CVTs from these CVTs. If so we have to use 110/√ 3 core instead of 110/3 core. We would like to have your comment regarding this modification and see whether existing relays settings can be modified according to new CVT ratios.
 07 April 2010 08:30 PM
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dlane

Posts: 690
Joined: 28 September 2007

Hi,

Directional relays take the voltage signal in to check the phase angle of the current flowing so there probably won't be an actual voltage setting on the protection relay to adjust, although I am not familiar with the Tropic range of relays.

You need to know that the CVTs you are fitting are giving the same phase shift as the ones you are taking out. You also need to check what loading is on them. The 50VA of the 2 CVTs from your stores is lower than the 100VA CVTs you are replacing, the CVTs from the stores are not as powerful and may not be able to supply the load of whatever relays, transducers etc are connected to them.

Kind regards

Donald Lane
IET » Energy » CVT Replacement

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