EEE 1106 017 Impact of Series Compensation MHO Distance Relay in Algerian PDF
EEE 1106 017 Impact of Series Compensation MHO Distance Relay in Algerian PDF
EEE 1106 017 Impact of Series Compensation MHO Distance Relay in Algerian PDF
6, June 2011
I. INTRODUCTION
This Increased transmittable power, improved system
stability, reduced transmission losses, improved voltage
profiles and more flexible power flow control are technoeconomical reasons behind installing Series Capacitors (SCs)
on long transmission lines [1], [2]. SCs and their over voltage
protection typically Metal Oxide Varistors (MOV), in spite of
their beneficial effects on the power system performance,
introduce additional problems and make operating conditions
unfavourable for the protective relays that uses conventional
techniques [3].
During a power system fault the nonlinear behaviour of
series capacitor arrangement, the rapidly changing
characteristic of circuit impedance, and the high frequency
noise generated from the nonlinear protective devices of the
compensation capacitors affects the voltage and current signals
and thus creates problems with relay functionality [4]-[6].
Following paragraph explains the problem in detail. Series
compensating capacitors were initially introduced in
transmission networks mainly to increase the power transfer
capacity of long transmission lines. These series compensating
capacitors bring with them significant protection challenges
for relay manufacturers, utility engineers and researchers.
181
(1)
PR = ER .I L cos(R ), QR = ER .I L sin(R )
(2)
RL
IL
jXL
- jXC
Load
ES
Therefore:
ER
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 6, June 2011
PR .RL + QR .( X L X C )
ER
V =
XS
(3)
XR
XL
~
A
ES
ER
P
(a)
XS
XL1
XC
XL2
XR
~
B
ES
ER
P
Voltage (kV)
(b)
No load
With SC
XC
Without SC
Lenght (km)
RL
XL
B. Power Transfer
SC transmission lines utilize series capacitors to reduce the
net series inductive reactance of the line in order to enhance
the power transfer capability of the line. The power transfer
along a transmission line is often explained in terms of the
simple two-source power system shown in figure.3.a without
series capacitor and figure.3.b with series capacitor. The active
power, P transferred by the uncompensated and compensated
transmission lines are computed using equations (4) and (5)
respectively:
P=
Es . Er
sin ( )
XT
Power (P)
With SC
Without SC
Po
(4)
o
Angle ()
(a)
P=
Es . Er
sin ( )
XT X C
(5)
182
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 6, June 2011
allows it to provide overvoltage protection across the capacitor
when connected in parallel with it. The MOV holds the voltage
across the capacitor within the permissible range of the
capacitor by allowing a self-regulating amount of current
through itself automatically. This non-linear relationship
between the voltage and current is shown in figure 5.
The MOV protective voltage is the instantaneous voltage
across the series capacitor at a specified current when the
MOV starts conducting. The protective voltage is typically
chosen above normal operating conditions, power system
swing, and overloads as illustrated in figure 5 [13], [15], [16].
V otage (V B )
W ithout SC
W ith SC
Po
Power (P)
(b)
Isc
SC
IL
Im ov
MOV
X
B y p a s s s w itc h
Fig. 6. Protection of the SC bank against overvoltages.
183
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 6, June 2011
capacitor as a function of normalized line current based on the
capacitors protective level current. The equivalent model is
depicted in figure 7.
Vsc
IL
IL
Isc
XMOV-SC
RMOV-SC
Bypass switch
Fig. 7. Equivalent model.
0,243.I pu
35.e
5.I pu
0,6e
1,4. I pu
Busbar
B
Line protected
) (6)
Adjacent line
0,8566. I pu
(7)
The trip delay is not possible for faults surely on the line. It
is the role of measurement in the first zone, set at 80% of the
reactance of the line. It triggers instantaneous. The trip must be
ordered online for failure is the role of other zone settled more
than 100% of the line, which then overflows to the first zone
line adjacent to the position facing. The outbreak, called 2nd
and 3rd stage, must be selectively controlled the 1st stage. The
trip time t1, t2 and t3 correspond to these four zones of
operation and interval of different selective t are indicated in
figure 10.
A. Measurement Principle
The numerical DR uses to locate a fault on a distance
measurement between the fault and the point where it is
installed. It is determined through a measurement of Xd which
ranges from 0,33 to 0,42 per kilometer depending on the
type of high-voltage line. This measure must be of a directed
character. By taking into account the reactive part of the
impedance Zd between the fault point and the relay, can
liberate the distance measurement from the RF. In the presence
of a fault as shown in figure 8.
Time (sec)
Z2
t2
t
t1
Z1
Distance (%)
Busbar A
Busbar B
Forward
IF
Fault
DP
Z3
t3
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 6, June 2011
Xi ()
Ri ()
Time (sec)
Z LV = ZHV .l = ( RHV + jX HV ) .l .
kVT
kCT
(8)
Without SC
TABLE I
THE RELAY SETTING WITHOUT SC
Parameter
1st zone
2nd zone
3rd zone
Percentage (%)
Xi ()
Ri ()
Time (sec)
80
0,8.XLV
0,8.RLV
0,00
120
1,2.XLV
1,2.RLV
0,30
140
1,4.XLV
1,4.RLV
1,50
E.2 With SC
To determine the optimum reach of first zone, the
decrease of the series reactance of the transmission line,
caused by the capacitors inclusion, should be considered:
Z L j. X C
(9)
Z LV = ZHV .l = [ RHV .l + jX HV .l jX c ] .
kVT
kCT
Percentage (%)
1st zone
2nd zone
3rd zone
80
120
140
1,2. XLV
1,2.RLV
0,30
1,4.XLV
1,4.RLV
1,50
(10)
TABLE II
THE RELAY SETTING WITH SC
Parameter
0,8.XLV
0,8.RLV
0,00
185
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 6, June 2011
figure 13. In each of the cases illustrated in figures 12 and 13,
the one line diagrams depict three-phase faults in system
without load flow. Three phase faults, zero load flow as well
as reactive impedances are assumed in these examples in order
to simplify the representation [18].
V
jX S
jXH
~
ES
Fault
V
= j.k.X H
I
(a)
jX S
- jXC
jX H
Fig. 11. The effect of RF and MOV and series capacitor on the
impedance seen by the relay.
ES
Fault
V
= j .(k .X H X C )
I
(b)
Fig. 12. Impedance measurement with bus side potential source,
a). Inductive system. b). Capacitive system.
jX S
- jX C V
jX H
~
ES
Fault
V
= j.k .X H
I
(a)
jX S
- jX C V
jX H
~
ES
Fault
V
= j.X C
I
(b)
Fig. 13. Impedance measurement with line side potential source.
a). Forward fault, b). Reverse fault.
V. CASE STUDY
The data for the 220 kV transmission line studied in this
case are summarized in the Annex. The following settings
programmed distance relay MHO:
186
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 6, June 2011
The proposed relay settings with SC are summarized in
table IV.
Busbar B
ZL = RL + jXL
CT
TABLE IV
THE RELAY SETTING WITH LINE END SC
ES
Fault
VT
Load
MHO
Relay
1st zone
2nd zone
3rd zone
Xi ()
Ri ()
Time (sec)
51,0873
13,2000
0,00
76,6309
19,8000
0,30
89,4027
23,1000
1,50
XC
CT
1st zone
2nd zone
3rd zone
Xi ()
Ri ()
Time (sec)
48,5418
13,2000
0,00
72,8127
19,8000
0,30
84,9482
23,1000
1,50
Busbar A
ZL / 2
CT
XC
Busbar B
ZL / 2
Parameter
ES
Fault
MOV
VT
Load
MHO
Relay
Busbar B
ZL
Fault
ES
MOV
VT
Load
MHO
Relay
Parameter
1st zone
2nd zone
3rd zone
Xi ()
Ri ()
Time (sec)
48,5418
13,2000
0,00
72,8127
19,8000
0,30
84,9482
23,1000
1,50
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 6, June 2011
the first zone.
[6]
VI. CONCLUSION
This paper presents firstly a detailed model of a series
capacitor used in power system. A calculation procedure of the
apparent impedance of the series capacitor is outlined and
explained. This article is addressing the change settings MHO
distance relay protection with different point location on
transmission 220 kV line high voltage such as sending end line
and mid-point line series compensation.
As can be seen the effect of series capacitors on distance
elements is more critical for capacitors located at the sending
end line than the mid-point. The degree of complexity depends
on the degree of compensation and the location of the series
capacitor. SC introduced additional challenges over well
known protection challenges on HV transmission networks.
These challenges must be considered carefully when setting
numerical distance protection relays.
[7]
[8]
[9]
[10]
[11]
[12]
[13]
APPENDIX
APPENDIX A: TRANSMISSION LINE STUDY
[14]
[15]
[16]
[17]
[18]
[19]
[20]
BIOGRAPHY
REFERENCES
[1]
[2]
[3]
[4]
[5]
188
Canadian Journal on Electrical and Electronics Engineering Vol. 2, No. 6, June 2011
power system protection, harmonics, and power quality. He has published
about 16 international conferences papers and about 21 international journal
papers.
189