Capítulo 4. Resultados de la investigación
4. Resultados de la investigación
4.2. Contraste de hipótesis TAM
4.2.2. Contraste de hipótesis del TAM del objeto de aprendizaje de RA del
CT #1 : Incoming line CT (Tie Line) CT#2 : CT on Transformer I side CT#3 : Bus Coupler CT
CT#4 : Incoming line #2 CT (Jemina Line) CT#5 : CT on Transformer II Side
Aim : Knee Point Voltage Testing of Current Transformers.
Objective :
This test should confirm that at any case the saturation point shouldn’t lie before 100% of KPV. It may occur at 110% or higher, doesn’t matter but saturation point shouldn't occur before 100% of the KPV. If saturation point occurs before 100% of KPV then the relays will operate before reaching its set value (100%) which is not desirable.
To find the saturation point of CT i.e. at what point of voltage it get saturated.
Compare the obtained saturation point with that of the name plate rating.
Theory :
Knee point voltage is the point on the graph obtained between voltage and current beyond which the current rise is very sharp when voltage in increased slightly. When the applied voltage is increased in steps the current also rises in certain step. When the knee point voltage is reached then the current shoots up beyond its normal increasing step. Therefore in this test we see whether the KPV given on the name plate is correct or not. If the saturation point is reached before the actual KPV then the relays are going to trip before fault occurs. In fact the relays should trip upon reaching KPV or later. Therefore for proper coordination and tripping or relays KPV should be checked accurately. Since minimum KVP at lowest tap is provided for core 3 &4 of CT, so we test KPV for only these cores.
V
I KPV
0
KPV Test of Current Transformer
Instrument used:
Sl. no Description Specification Quantity Remarks 1 Auto Transformer 0-260V, 50Hz 1
2 Transformer 230V-3000V, 50Hz 1 3 Multimeter AC/DC, Analog, Multi-range 1 4 Clamp leaker DC-10A, Motwane 1 5 Connecting wires --- APR
6 1-Ф Supply 230V, 50Hz 1
Name plate rating
Procedure:
1. Set up the connection as shown below.
2. Apply certain percentage of Knee point Voltage to Core #3 and Core #4 and then note down the readings as shown by clamp leaker.
3. Repeat the same step for other two phases.
4. Compare the readings.
AVΩ Meter Test applied to/ experimental set up :
Figure 4 KPV Testing of Current Transformer 1‐Ф, 230V, 50Hz Supply
Junction box
Clamp leaker Current Transformer #1 Sl.No. 2373/1/5/08
Sl.No. 2373/1/12/08 Sl.No. 2373/1/10/08 Current Transformer #3 Sl.No. 2373/1/7/08
Sl.No. 2373/1/8/08 Sl.No. 2373/1/6/08
Variac 0-260V, 50Hz Transformer 230-3000V, 50Hz
KPV Test of Current Transformer
Primary
P1 P2
1S1 1S2 1S3 2S1 2S2 2S3 3S1 3S2 3S3 4S1 4S2 4S3 Lowest Tap
(325V) Full Tapping (650V)
Technical terms:
Name plate rating : Minimum Knee Point Voltage at lowest Tap = 325V
There are two tapping in each core of CT. Therefore in this case lowest tap refers to the tapping between one end and the middle point. So at full tapping the Knee Point Voltage will be the double of the KPV of lowest tap.
KPV for Core#3 and Core#4
Knee Point Voltage is available for only core #3 and core #4. This is because these cores are specifically designed for protection class core. For protection class core, saturation of current is very important and need to protect the equipment from over current. Whenever the current reaches its saturation point, relay should trip off. Therefore these cores have Knee point Voltage, before which saturation shouldn’t occur.
Accuracy rating for Core#1 and Core#2
However this is not the case with core#1 and core#2. These cores are specifically designed for metering purposes, where accuracy is of much importance. If saturation point exists for these cores then when the current increases beyond certain value, the meter will stop reading, in fact the meter should record whatever the amount of current drawn. Therefore these cores are rated at 0.2 class of accuracy.
For half the winding of each core, the rated KPV is 325V therefore for full winding the rated KPV is 650V. More the number of turns, greater will be the voltage and lesser will be the current, thereby the ratings 325V, 60mA and 650V, 30mA.
If the saturation point is reached, CT will make humming sound and must be avoided.
Results :
1. Incoming Tie line CT, CT#1
CT# 1, 3S1-3S2, 325V, 60mA at Vk/2 Date: 19/10/09, Monday, 3:30pm, Sunny.
R-Sl.no. OC 2373/1/5/08, Y-Sl.no. OC 2373/1/12/08, B-Sl.no. OC 2373/1/10/08
% of KPV Applied Voltage (V) R-phase (mA) Y-phase (mA) B-phase (mA)
25% 81.25 7.31 8.22 7.79
50% 162.50 10.99 12.43 12.08 75% 243.75 16.31 20.34 19.45
100% 325.00 29.98 40.00 36.70
110% 357.50 45.90 71.00 67.80
CT# 1, 3S1-3S3, 650V, 30mA at Vk/2
25% 162.50 3.65 3.97 3.76
50% 325.00 5.55 6.31 5.91
75% 487.50 7.46 9.69 8.88
100% 650.00 11.93 18.55 15.39
110% 715.00 15.79 25.77 23.10
CT#1, 4S1-4S2, 325V, 60mA at Vk/2
25% 81.25 7.54 8.25 8.34
50% 162.50 11.95 12.74 13.16 75% 243.75 17.14 19.55 20.42
100% 325.00 31.26 42.50 39.50
110% 357.50 53.90 70.30 72.60
For demonstration of saturation current, 400V was being applied to B-phase and the current was observed to be 215mA. See the graph.
CT#1, 4S1-4S3, 650V, 30mA at Vk/2
25% 162.50 3.79 4.06 4.33
50% 325.00 5.40 6.27 6.45
75% 487.50 8.00 8.83 8.70
100% 650.00 13.13 15.67 17.12
110% 715.00 18.33 24.03 24.59
KPV Test of Current Transformer
2. CT Transformer 1 side, CT #2
CT# 2, 3S1-3S2, 325V, 60mA at Vk/2 Date: 19/10/09, Monday, 4:20, Sunny.
R-Sl.no. OC 2373/1/15/08, Y-Sl.no. OC 2373/1/9/08, B-Sl.no. OC 2373/1/1/08
% of KPV Applied Voltage (V) R-phase (mA) Y-phase (mA) B-phase (mA)
25% 81.25 7.26 7.60 8.29
50% 162.50 11.36 12.43 13.22 75% 243.75 18.38 18.04 19.90
100% 325.00 35.00 31.84 35.5
110% 357.50 49.90 46.80 50.80
CT# 2, 3S1-3S3, 650V, 30mA at Vk/2
25% 162.50 3.73 3.91 3.89
50% 325.00 6.42 5.72 6.85
75% 487.50 8.73 8.40 8.72
100% 650.00 15.05 14.47 15.68
110% 715.00 22.05 20.11 22.23
CT#2, 4S1-4S2, 325V, 60mA at Vk/2
25% 81.25 7.43 7.38 8.41
50% 162.50 11.29 11.01 13.96 75% 243.75 17.65 16.43 21.43
100% 325.00 29.39 26.27 39.50
110% 357.50 55.8 49.40 63.30
CT#2, 4S1-4S3, 650V, 30mA at Vk/2
25% 162.50 3.85 3.77 4.20
50% 325.00 5.72 6.54 6.67
75% 487.50 8.88 8.31 10.35
100% 650.00 14.20 13.14 17.72
110% 715.00 20.06 19.46 22.87
3. CT on Bus Coupler, CT #3
CT# 3, 3S1-3S2, 325V, 60mA at Vk/2 Date: 19/10/09, Monday, 4:45pm, Sunset.
R-Sl.no. OC 2373/1/7/08, Y-Sl.no. OC 2373/1/8/08, B-Sl.no. OC 2373/1/6/08
% of KPV Applied Voltage (V) R-phase (mA) Y-phase (mA) B-phase (mA)
25% 81.25 7.29 7.09 7.24
50% 162.50 11.83 11.66 11.26 75% 243.75 17.84 17.21 17.14
100% 325.00 32.8 32.9 37.30
110% 357.50 46.2 58.6 54.30
CT# 3, 3S1-3S3, 650V, 30mA at Vk/2
25% 162.50 3.38 3.29 3.47
50% 325.00 5.53 5.37 5.36
75% 487.50 7.80 7.85 8.03
100% 650.00 13.65 13.53 14.42
110% 715.00 19.66 22.66 20.47
CT#3, 4S1-4S2, 325V, 60mA at Vk/2
25% 81.25 7.84 7.53 8.09
50% 162.50 12.66 11.82 13.23 75% 243.75 19.88 18.50 19.64
100% 325.00 37.50 40.4 36.80
110% 357.50 60.00 64.40 59.60
CT#3, 4S1-4S3, 650V, 30mA at Vk/2
25% 162.50 3.66 3.32 3.79
50% 325.00 5.82 5.44 6.10
75% 487.50 8.86 8.43 8.66
100% 650.00 16.11 15.76 16.73
110% 715.00 23.83 23.75 24.76
KPV Test of Current Transformer
4. CT on Jemina Line CT #4
CT# 4, 3S1-3S2, 325V, 60mA at Vk/2 Date: 22/10/09, Thursday, 10:20am, Sunny.
R-Sl.no. OC 2373/1/14/08, Y-Sl.no. OC 2373/1/2/08, B-Sl.no. OC 2373/1/16/08
% of KPV Applied Voltage (V) R-phase (mA) Y-phase (mA) B-phase (mA)
25% 81.25 7.53 7.61 7.66
50% 162.50 11.73 12.03 12.20 75% 243.75 17.89 17.89 18.57
100% 325.00 36.3 34.4 33.3
110% 357.50 69.2 55.1 52.0
CT# 4, 3S1-3S3, 650V, 30mA at Vk/2
25% 162.50 3.25 3.39 3.43
50% 325.00 5.38 5.50 5.51
75% 487.50 8.22 8.26 8.23
100% 650.00 15.33 14.27 14.64
110% 715.00 22.20 19.20 20.25
CT#4, 4S1-4S2, 325V, 60mA at Vk/2
25% 81.25 7.38 7.65 7.30
50% 162.50 11.65 11.88 11.17
75% 243.75 17.18 17.80 15.24
100% 325.00 35.7 37.60 28.35
110% 357.50 55.4 51.30 47.6
CT#4, 4S1-4S3, 650V, 30mA at Vk/2
25% 162.50 3.47 3.49 3.29
50% 325.00 5.33 5.48 5.18
75% 487.50 7.91 8.17 7.43
100% 650.00 14.23 14.81 12.34
110% 715.00 20.36 20.98 17.01
5. CT on Transformer#2 side, CT#5
CT# 5, 3S1-3S2, 325V, 60mA at Vk/2 Date: 22/10/09, Thursday, 10:50am, Sunny.
R-Sl.no. OC 2373/1/3/08, Y-Sl.no. OC 2373/1/18/08, B-Sl.no. OC 2373/1/4/08
% of KPV Applied Voltage (V) R-phase (mA) Y-phase (mA) B-phase (mA)
25% 81.25 6.90 7.76 7.84
50% 162.50 10.92 11.90 11.48 75% 243.75 16.12 18.35 15.54
100% 325.00 29.52 36.5 28.31
110% 357.50 45.2 67.6 40.6
CT# 5, 3S1-3S3, 650V, 30mA at Vk/2
25% 162.50 3.29 3.59 3.50
50% 325.00 5.36 5.78 5.24
75% 487.50 7.90 8.93 7.64
100% 650.00 13.66 16.17 12.44
110% 715.00 18.49 23.70 16.45
CT#5, 4S1-4S2, 325V, 60mA at Vk/2
25% 81.25 6.82 6.59 7.90
50% 162.50 10.70 10.39 11.55 75% 243.75 15.96 14.82 16.91
100% 325.00 28.41 25.06 31.20
110% 357.50 45.7 38.3 53.4
CT#5, 4S1-4S3, 650V, 30mA at Vk/2
25% 162.50 3.23 3.20 3.44
50% 325.00 5.12 5.06 5.43
75% 487.50 8.03 7.32 7.85
100% 650.00 13.36 11.55 13.62
110% 715.00 18.02 15.27 19.44
KPV Test of Current Transformer
Graphical Analysis for CT#1, 4S1-4S2, 325V, 60mA, B-phase
CT#4, 4S1-4S3, 650V, 30mA at Vk/2, R-Phase