fault location estimator in series compensator

Fault location estimator for
series compensated
transmission line under
power oscillation conditions

Contents
• Introduction
• Need of compensation
• Types of compensation
• Objectives
• Advantages/ Problems
• Principle of the new fault location algorithm
• conclusion

Introduction to Compensation
Compensation of transmission lines is meant the use of
electrical circuits to modify the electrical characteristics
of the lines within the prescribed limit.

Need of Compensation
The line requires the compensation of transmission lines
due to:
Reduction of power transfer capability of lines which
reduces the margin between the stable and unstable
operation of system.
Ferranti effect.
Sub-synchronous resonance.

Various Types of Compensation
Various types of compensation techniques are used for
compensating the EHV lines:
Series compensation
Shunt compensation-SVS (Synchronous voltage
Source)
Synchronous condenser

Objectives of Series and Shunt
Compensation
Main objective of series and shunt compensation of
EHV lines for transmitting bulk power over the long
distance may be stated as:
To improve transfer capability along with increased
steady state and transient stability limits.
To obtain flat voltage profile as possible along the
length of the EHV line while maintaining the equal
sending end and receiving end voltage.
To avoid degree of compensation leading to sub-
synchronous resonance.

SERIES COMPENSATION
The series capacitor offers an effective and economic
means for improving stability limits of long distance
transmission by reducing the net reactance of
transmission line.
In the present case of 400kv and 600km transmission
system, the maximum value of receiving end power,
compensation efficiency, optimum value of series
capacitive reactance are obtained using computer
program.

Series compensation is used in long lines to increase
transmission capacity, improvement of system stability
and to obtain correct load division between parallel
circuits.
Series capacitors are connected in series with the line to
reduce the net impedance of the transmission line. This
reduced impedance causes the reduced voltage drop
across the line.
Series capacitors are generally installed on special
platforms at one or both ends of the lines.

Installation of Series Capacitor
Series capacitors are generally installed on special
platforms at one or both ends of the lines.
Series Capacitor
Current Limiting
Reactor
Spark Gap
Bypass Switch
Metal Oxide Resistor

Bypass switch
the bypass switch must be able to carry the rated current and
the rated short-circuit current in the closed position, as well as
withstand the overvoltages specified across the open gap and
phase-to-earth.
METAL OXYDE VARISTORS (MOVs)
Metal oxide varistors, which are connected in parallel
with the capacitors , provide overvoltage protection of the
capacitors during and after power system faults and thus
are conducting a large part of the fault current. MOVs are
then protected by the spark gap activation against
excessive energy absorption

SPARK GAP
• In case of operation of the MOV protection relay, the spark gap is
force-triggered by the protection and control system.

Advantage of Series Compensation
There are various advantage of series compensation:
Increase in power transfer capability
Improvement of system stability
Load division among parallel lines
Control of voltage

Location of Series Capacitor
Location along the line.
Location at one or both ends of line section on the line
sides in the switching stations.
Location between Bus Bars and switching station.

Problems Associated with Series
Compensation
Sub – Synchronous Resonance
Sustain oscillation
Unreliable protection of transmission lines

Application of Series Compensation
They have been primarily used to improve system stability
and to obtain the desired load division among parallel lines.
High compensation levels also increase the complexity of
protective relaying and the probability of sub-synchronous
resonance.
A practical upper limit to the degree of series compensation
is about 80%.

Following are some of the key considerations in the
application of series capacitor banks:
Voltage rise due to reactive current: Voltage rise of on one
side of the capacitor may be excessive when the line
reactive-current flow is high, as might occur during heavy
power transfers.
Bypassing and reinsertion: provision is made for
bypassing the capacitor during faults and reinsertion after
fault clearing. Speed of reinsertion may be an important
factor in maintaining transient stability.
Present trend is to use nonlinear resistors of zinc oxide
which have the advantage that reinsertion is essentially
instantaneous

SHUNT COMPENSATION- SVS
Shunt compensation may consist of static (using
capacitor and reactor) or synchronous compensation to
avoid voltage stability.
Shunt capacitors supply reactive power and boost local
voltages. They are used throughout the system and are
applied in a wide range of sizes.
The principal advantages of shunt capacitors are their
low cost and their flexibility of installation and
operation.
The principal disadvantage of shunt capacitors is that
their reactive power output is proportional to the square
of the voltage.

Application of shunt compensation
Shunt capacitors are used to compensate for the XI2
losses in transmission system and to ensure satisfactory
voltage levels during heavy loading conditions.
Switching of capacitor banks provides a convenient
means of controlling transmission system voltages.

Types of SVS
Self Saturated Reactor (SR)
Thyristor Controlled Reactor (TCR)
Thyristor Switched Capacitor (TSC)
 Fixed Capacitor (FC), Thyristor Controlled Reactor
(TCR) scheme
Thyristor Switched Capacitor (TSC), Thyristor
Controlled Reactor(TCR) scheme

Advantages of SVS
Increased power transfer capability
 Enhancement of transient stability
The dynamic response of SVS is very fast
Steady –State and temporary overvoltage can be
controlled

SYNCHRONOUS CONDENSER
 A synchronous condenser is a synchronous machine running
without a prime mover or a mechanical load. By controlling
the field excitation, it can be made to either generate or
absorb reactive power. With a voltage regulator, it can
automatically adjust the reactive power output to maintain
constant terminal voltage.
Synchronous compensators contribute to system short-circuit
capacity. Their reactive power production is not affected by
the system voltage.

UB = UE − US
US = IS*1/(jw0CS)
IB = IE
Principle of the new fault location algorithm
Terms can be calculated

(1) Static-fault locator algorithm for transmission line
Based on the distributed parameter model of transmission line, it is easy
to obtain the voltage and current at a distance x from the terminal N
Where UBF and UNF are the voltage estimates at point F, respectively.
Since the UBF is equal to UNF, the fault location can be expressed as

(2.1) Dynamic fault locator for two-terminal
transmission Lines
Dynamic parameters estimator
From here we can calculate characteristics impedance (Zc) and
propagation constant (gamma)
Zc = sqrt (Z/Y)
gamma = sqrt (Z.Y)

(2.2)Analysis of the compensation capacity’s
influence
…….(a)
here US(x, t) = us (x, t) * exp(jw0t)

……..(b)
This is Equivalent admittance
…….(c)
uS(x, t) = Us (x, t) * exp(-jw0t) ……..(d)
From equation (b), (c), and (d)
Hence, a corrected voltage drop across the SC can be
obtained
Us = Is * (1/Ys)
Ys

2.3 Dynamic fault locator algorithm:
The fault section needs to be identified since the fault could be
occurred randomly in any side of the SC. A method is employed
to identify the fault section. The criterion is expressed as follows
fault located at the left-hand side of SC
fault located at the right-hand side of SC
where 1/C is an indicator of the fault location relative to SC,
(1/C)set is the setting, it can be set by (1/C)set = 0.5 × (1/Cs).

Fig. flowchart of the iteration
uS(x, t) = Us (x, t) * exp(-jw0t) ………..(21)
Ys ……(22)
Us = Is * (1/Ys) ……..(23)

fault location estimator in series compensator

………(22)
………(26)
Us = Is * (1/Ys) ……..(23)
UB = UE – US ……..(27)
UBF = (0.5*(UB–IB .ZBC))*exp(gammaB * ((1-k)*l - x)) + (
0.5*(UB+ IB .ZBC))*exp(gammaB*((1-k)*l – x)) ……(28)

Performance evaluation
Performance evaluation for 300km, 500kV line and

Conclusion
This paper proposes a novel fault location algorithm for SC
compensated transmission line under dynamic conditions by
using synchronised phasor measurements obtained by PMUs.
The influence on the SC caused by power oscillation has been
fully considered by DFLSC. The algorithm gives better fault
localisation estimate under power oscillation condition with
comparison to the fault location algorithms which did not
consider the dynamic characteristics of line or the SC.

fault location estimator in series compensator

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