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Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
KURSUS LATIHAN KEKOMPETENAN
Unit PerlindunganSeksyen Latihan Penghantaran
Institut Latihan Sultan Ahmad Shah (ILSAS)
PERLINDUNGAN PENGHANTARAN(SETAKAT 132kV)
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
SKIM PERLINDUNGAN ALATUBAH.
TRANSFORMER DIFFERENTIAL
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
Institut Latihan Sultan Ahmad Shah(ILSAS)
ObjektifPada akhir pengajaran, pelatih-pelatih akan dapat 1. Mengenal pasti dan melukis litar skimatik
perlindungan geganti Tx. Differential.2. Mengira tatahan perlindungan geganti Tx.
Differential 3. Mengaturkan prosidur pengujian skim perlindungan
geganti Tx. Differential.4. Melukis litar pengujian “secondary”, “primary” dan
“stability” skim perlindungan geganti Tx. Differential.dengan betul apabila skim perlindungan Tx. Differential
digunakan pada alatubah.
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION
1. Overall differential protection may be justify for large transformers (generally >5MVA)
2. This scheme provides fast operation.
3. Measuring principles
a. Based on the same circulating current principle as the restricted earth fault protection.
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION
b. However, it employs the biasing technique to maintain stability for heavy trough fault current.
- Biasing allows mismatch between CT outputs.
- It is essential for transformer with tap changing facility
- Another important requirement of transformer differential protection is immunity to magnetizing inrush current
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION
Correct application of differential protection requires CT ratio and wining connection to match those of Txmer
CT secondary circuit should be a replica of the primary system.
Consider
1. Difference in current magnitude
2. Phase shift
3. Zero sequence current.
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL CONNECTION
e.g.
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL CONNECTION
Use of Interposing CT
Provides
1. Ratio Correction
2. Vector Correction
3. Zero Seq. Compensation
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION (EXAMPLE)
A1
B1B2
C1C2
a1b1
c1
a2
b2
c2
Yd 190MVA 132/33kV
A2
Given above:
Need to consider –
1. Winding full load current
2. Vector correction
3. Effect of tap changer
4. CT polarities
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION (EXAMPLE)
A1
B1B2
C1C2
a1b1
c1
a2
b2
c2
Yd 190MVA 132/33kV
A2
First consider no tap changer or tap changer must at nominal ratio.Full load current at nominal voltage ratio:-
132kV = 393.65Aprimarychoose CT ratio = 400/1 -> secondary current = 0.984A
33kV = 1574.59primarychoose CT ratio = 1600/1 -> secondary current = 0.984A
Because of the vector transformation on primary LV side of transformer then compensation of vector group is required on the secondary circuit.
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION (EXAMPLE)
Vector group compensation on secondary circuit can be done using
i. Line/Phase CT (refer Fig. ii. Interposing CT
A1
B1B2
C1C2
A2 a1
b1
c1
a2
b2
c2
a1
b1
c1
Yd1
Our normal practice, vector group compensation is done using Interposing CTs which were arranged such as the replica of the Power Transformer. This will involve the Delta connection on the LV side of ICT
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION (EXAMPLE)
Thus, sec. current after vector correction = √3 * 0.984 = 1.704A. (For 1:1 winding ratio).There will mismatch current enter the Transformer Differential Relay
= 1.704 - 0.984= 0.72 this will cause relay to operate at normal rated load condition.
Suitable ratio should be selected to eliminate the mismatch current. For the above example
Let secondary current of ICT (delta side) ILine = 1 AIphase = 1/√3 = 0.5774So turn ratio required = 1 : 0.5774
Interposing CTA
CB
N,
Vphase = VLine
VLine = 3 Vphase
ILine = 3 Iphase
VLineVphase
Iphase = ILine
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION (EXAMPLE)
Interposing CTA
CB
N,
Vphase = VLine
VLine = 3 Vphase
ILine = 3 Iphase
VLineVphase
Iphase = ILine
YΔ interposing CT connected on HV side of Transformer Differential scheme will eliminate the effect of Zero Sequence / Earth Fault current on the primary network (out zone fault) which could cause instability of the scheme.
Elimination of zero seq. current on LV side. This can be achieved by using YΔY connection ICT.
Delta connection of YΔY LV ICT should be left open. Delta winding provide a path for the flow of zero sequence current to balance the LV current transformer under earth fault condition.
It is important to note that the star point of the relay must not connected to the star point of the LV ICT as this would create an alternative zero seq. path and current may flow through the relay under external fault condition.
Since effectively the relay is connected to the CT through YY then there will be no ratio different.
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION (EXAMPLE)
It is important to note that the star point of the relay must not connected to the star point of the LV ICT as this would create an alternative zero seq. path and current may flow through the relay under external fault condition.
Since effectively the relay is connected to the CT through YY then there will be no ratio different.
So turn ratio required for YΔY LV ICT normally 1: 1: 1.
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
400/1 A1
B1B2
C1C2
a1
b1
c1
a2
b2
c2
Yd190MVA 132/33kV
400/1
1600/1
1600/1
LV ICT1: 1: 1
HV ICT 1:0.5774
6464
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION
EFFECT OF TAP CHANGER
Example: Transformer tap changer with +5% and –15% of turn ratio / nominal voltage.
Effect of tap changer on voltageAt tap where –15% turn ratio = 112.2kV this mean that the LV terminal voltageLV = (33kV * 132kV) /112.2kV
= 38.8kV
Effect of tap changer on currentTurn ratio N1/N2 = 112.2/33Where transformation formula
N1/N2 = I2/I1At full load where LV current I2primary = 1574.6 A
I2sec. = 0.984A
Than I1primary = I2 * N2/N1= 463.12 A
I1sec. = 1.1578A
Mismatch current I1sec.- I2sec. = (1.1578A - 0.984A)= 0.1738 A
The operation current for most of differential relay is about 20% / 0.2A.With above condition relay might operate for external fault. Due to this effect then transformer differential is equipped with bias element for bias characteristic.
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION
BIAS DIFFERENTIAL SCHEME
I1 I2
Io = I1 -I2Operate
BiasBias
Assume that external fault current = 10 * Full load current. Io = I1 – I2
= (11.578A - 9.84A)= 1.738 A
IBias = (I1 + I2) / 2= (11.578A + 9.84A) / 2= 10.709 A
Io < IBias
Io < IBias cause relay to restrain.Io > IBias cause relay to operate
0.2 A
1.74A
10.76AIBias
Io
20%slope
80% slope
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION
EFFECT MAGNETISING INRUSH CURRENT
1. Appears on one side of transformer only2. Seen as fault by differential relay.3. Normal steady state magnetizing current is less than
relay setting4. Transient magnetizing inrush could cause relay to
operate
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION
EFFECT MAGNETISING INRUSH CURRENT
Solution 1: Time delay
•Allow magnetizing current to die away before relay can operate.
•Slow operation for genuine Txmer faults.
Solution 2: 2nd and 5th harmonic restrain
•Makes relay immune to magnetizing inrush.
•Slow operation may result for genuine Txmer faults if CT saturation occurs.
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION
EFFECT MAGNETISING INRUSH CURRENT
Solution 3: Gap measurement technique
•Inhibits relay operation during magnetizing inrush
•Use in Alstom relay (MBCH & KBCH)
•Operate speed for genuine transformer faults unaffected by significant CT saturation
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION
TRANSFORMER GUARD
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION
TRANSFORMER GUARD
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATIONEFFECT ON OVERLOADTRANSFORMER INSULATION LIFE
OVERHEATING PROTECTION
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
TRANSFORMER DIFFERENTIAL PROTECTION APPLICATION
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
STANDBY EARTH FAULTStandby Earth fault Relay
– CT located at Neutral Cable thus sensing any earth fault through the transformer
– Stage 1 trips the bus section and/or bus coupler– Stage 2 trips HV and LV transformer feeders– To act as backup to feeder earth fault relays by
sectionalising busbar
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
STANDBY EARTH FAULTStandby Earth fault Relay (Continued)
– To act as backup to feeder earth fault relays by sectionalising busbar
– To act as backup to transformer incomer feeder for busbar and downstream feeder fault
– Maximum delay time based on rating of NER– Relays usually located at bus section panel
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
earth
STAND BY EARTH FAULT
CT
SBEF OPERATIONAT TWO STAGESFOR ANY FAULTDOWNSTREAM
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
earth
STAND BY EARTH FAULT
CT
SBEF WILL NOTOPERATEFOR PH-PH FAULT
Institut Latihan TNB - ILSAS
Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak
THANK YOU