HV TEST FOR 230 KV GIS 

High Voltage level of injection is below 

Highest voltage level 380 kv is calculated from 80% of factory Hi Voltage injection Level 

304 kV is 80% of 380kv 

170 kv is 1.2X Un/ rot 3

132 kv is  Un/ rot 3 

PD measurement curve at 132kv & 170 voltage level 

THE STORY OF TRANSFORMER STABILITY

The transformer stability test used to conform the CT connections for Differential and REF protection. This test also used as a primary injection test for HV & LV side BCT's.

Example   Transformer Data

Voltage Ratio :             230/ 34.5/13.8 kV

MVA Rating :              100/133 MVA                                                                                                                  

Vector Group:             YNyn0(d5)

% Impedence :             12.24 @ 100 MVA BASE.

CALCULATION TO FIND THE PRIMARY AND SECONDARY CURRENT


PRIMARY SIDE : -

HV side full load current  =  Power /  √3 x Voltage = 100×10^3            =  100000000 = 251 Amps

                                                                                √3 × 230× 1000        399050

HV side Impedence    =   HV side Voltage              =   230× 1000  = 916 Ohms
                                          HV side full load current       251

HV side Impedence/ Phase =  HV side Impedence X % Impedence = 916 X 12.24  =  112 Ohms
                                                                                                                          100

HV side current / Phase    =  Applied Voltage / HV side Impedence/ Phase

                                        = 380 / 112 =  3.38 Amps


 LV side SIDE : -

Transformer Ratio = 230/ 34.5 = 6.66

LV side current = 6.6666* 3.38 = 22.53 Amps
                                                                                                             

TEST -1 Three Phase Balanced Injection

Test connection: Three phase short circuit outside protected zone on 34.5kV side. Three phase voltage injected on HV side = 380V

The balanced current can measured in the relay as follows 

                                                            

Relay - Primary Current (A)
HV	LV
3.326<0°	22.201<181.141°
3.205<241.5°	22.935<59.28°
3.288<121.5°	23.573<299.34°

Note : -


1. LV current 180 dec phase sifted from HV current.

2. No return current in Neutral 

TEST -2 Three Phase Unbalanced condition

To make this condition open any one of CT FT fingers and short by insert the FT jack. 

The Unbalanced current can measured in the relay as follows 

Relay- Primary Current (A)
HV	LV
0.00	21.985
0.00	22.226
0.00	22.265

TEST -3 Three Phase REF balanced condition

Test connection: Three phase short circuit outside protected zone on LV side. Single Phase Injection was done one by one  on the primary to check the stability and sensitivity.

1. No return current in Neutral 

2. During single phase injection voltage will developed  in the one phase Tertiary winding. If winding is connected with ground  a circulating current will flow through ground during stability.

TEST -4 Three Phase REF Unbalanced condition

 Polarity of the neutral BCT was reversed at the protection panel to simulate the unstable condition.

TEST -5 BCT primary injection

PRIMARY INJECTION HV & LV  WINDING :

Test connection: Three phase short circuit outside protected zone on LV side. Three phase voltage injected on HV side = 380V 

PRIMARY INJECTION TERTIARY  WINDING :

Test connection : The shorting and grounding bar was removed from the Delta winding and current was injected with Severker Test Kit and secondary currents were measured in the Transformer LCP panel.

                                     

TIMINGS & TIME SETTINGS

ABTS LOGIC

ABTS logic truth table for two transformer arrangement
Closing Logic











Tripping Logic
















Note:-
ABTS Block
1. Transformer Timed Over current Trip ( This trip non directional some times happend for low side fault also. So its block the ABTS)
2. Lower side BB protection Operated in Unhealthy Bus
3. Over current operate in Lower side Bus Tie
4. FFR operated in Healthy Bus
ABTS Initiation
1. Low side Incomer Manual opens
2. High side instantaneous transformer protection trip
3. Transformer Mechanical protection trip
4. High side BB protection trip
General Conditions
1. All low side breakers should be in service conditions
2. One Bus should be unhealthy condition
3. One Bus should be healthy condition
4. ABTS in service position

INTER LOCK FOR TRANSFORMER HI & LOW SIDE INCOMER

LOW SIDE CB RACK IN BLOCK
1.Low Side Inter locks
1.1 CB Aux Contact - CB should be open Condition
1.2 Bus Earth & feeder line side switch should be Open condition
2 Hi Side Inter Locks
2.1 Transformer side ES should be open condition

LOW SIDE CB CLOSE BLOCK COIL
1. Transformer Protection all lockouts should be normal position
2. 34.5kv Bus earth switch should be open

LOW SIDE CB CLOSEING COIL
1.Hi side breaker should be in close condition
2.Transformer side Disconnector switch should be in closed condition.

LOW SIDE CB TRIPPING

1.All protection LOR

2.High side CB service condition and open

LOW SIDE INCOMER EARTH SWITCH
1.Hi side breaker should be in open condition
2.Transformer side Disconnector switch should be in open condition.

HI SIDE TRANSFORMER FEEDER DS INTERLOCK
1.Low side CB open
2.Low side ES open
HI SIDE TRANSFORMER FEEDER ES INTERLOCK
1. Low side CB open
2. Low side CB in test position