Protection

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A New Adaptive High Speed Distance Protection Scheme for
Power Transmission Lines
M.M. Saha, T. Einarsson, S. Lidström
ABB AB, Substation Automation Products, Sweden
Direct application of the classic distance protection (designed
for traditional lines) to the series-compensated lines results in
considerable shortening of the first zone reach and also in poor
transient behavior [1]. In order to overcome these difficulties
the new distance protection principle for the first zone has been
developed [5].
Keywords: Adaptive distance protection, high speed tripping,
numerical simulations, RTDS testing.
Abstract
This paper describes a new, high-speed protection for
EHV transmission lines. The presented scheme also performs
well on series compensated lines. The High speed distance
protection (ZMFPDIS) function is a six zone full scheme
protection with three fault loops for phase-to-phase faults and
three fault loops for phase-to-earth faults for each of the
independent zones, which makes the function suitable in
applications with single-phase auto-reclosing. The zones can
operate independently of each other in directional (forward or
reverse) or non-directional mode. A new built-in adaptive load
compensation algorithm prevents overreaching of the distance
zones in the load exporting end during phase-to-earth faults on
heavily loaded power lines. It also reduces under-reach in the
importing end. The ZMFPDIS function-block itself
incorporates a phase-selection element and a directional
element, where these elements are represented with separate
function-blocks. Implementation of the new distance
protection with fast tripping algorithms has been made in a
modular line terminal platform. Comprehensive test results on
various test systems show the benefits of the scheme. The
results with a Real Time Digital Simulator (RTDS) are
presented in this paper. The scheme is now in operation under
trade name REL670 2.0.
A digital distance relaying algorithm based upon symmetrical
components was introduced few decades ago [6]. This
protection method utilizes certain relations between voltages
and currents in a three-phase post fault power system [6-7], the
phase voltages and currents are transformed into symmetrical
components by means of digital filtration. Ultra-high speed
impedance estimation, in turn, is natural in time domain
methods. This group of algorithms based on the resistiveinductive model of the fault loop circuit, usually neglecting
shunt capacitances, assumes the appropriate voltages and
currents as measured and solves the appropriate differential
equation with respect to resistance (R) and reactance (X) of
positive sequence. Various approaches to numerical
differentiation and solution of relevant equation originate a
number of different relaying methods of this kind [8-10].
It is therefore, not possible to use only one algorithm but rather
a hybrid solution with parallel and adaptive algorithms have
to be implemented. This paper explores such a hybrid solution
in order to achieve high speed of operation while maintaining
high dependability and security.
1 Introduction
Distance relay is one of the most important components of
protection systems available to protection engineers. Distance
relays can benefit from ideas in the newly developed field of
adaptive protection, and can offer an even more selective and
sensitive form of protection, under a variety of system
configurations.
The benefits of installing series capacitors in the power system
include increased power transfer capability, improved power
system stability, reduced system losses, improved voltage
regulation, and the possibility to regulate power flow.
Installation of series capacitors, however, introduces
challenges to protection systems with regards for both the
series compensated lines and the adjacent lines [1-3]. The
protection of systems with series compensated lines is
considered one of the most difficult tasks both for relay design
and utility engineers. The paper [4] explores such a hybrid
solution in order to achieve high speed of operation while
maintaining high dependability and security.
2 New Protection Scheme
2.1 Functionality
The ZMFPDIS is providing sub-cycle, down towards halfcycle, operate time for basic faults within 60% of the line
length and up to around SIR 5. This is a six zone full scheme
protection with three fault loops for phase-to-phase faults and
three fault loops for phase-to-earth faults for each of the
independent zones, which makes the function suitable in
applications with single-phase auto-reclosing. The zones can
operate independently of each other in directional (forward or
reverse) or non-directional mode. This makes them suitable,
together with a communication scheme, for protection of
power lines and cables in complex network configurations,
such as parallel lines, multi-terminal lines, and so on.
A new built-in adaptive load compensation algorithm [11]
prevents overreaching of the distance zones in the load
1
can be verified that within the accuracy no operation will occur
outside the characteristic. The different measuring criterion can
be identified in the characteristic and all of them have to be
fulfilled for operation. The characteristic is principally
identical for all type of faults. The reactive and resistive reach
settings are different for the phase to ground and the phase to
phase measuring loops.
exporting end during phase-to-earth faults on heavily loaded
power lines. It also reduces under-reach in the importing end.
The ZMFPDIS function-block itself incorporates a phaseselection element and a directional element .The operation of
the phase-selection element is primarily based on current
change criteria, essentially those of the High-Speed Distance
function as in [12]. The directional element utilizes a set of
well-established quantities to provide fast and correct
directional evaluation during various conditions, including
close-in three-phase faults, simultaneous faults and faults with
only zero-sequence in-feed.
2.2 Principles of Operation
Filtering
Practically all voltage, current and impedance quantities used
within ZMFPDIS are derived from fundamental frequency
phasors filtered by a half cycle filter. To improve the properties
of the filter, it is reset at fault inception. The reset means that
just after fault detection the filter size is reduced to sub quarter
cycle length and then increased one step for each new sample
until the half cycle length is reached. The aim is to only use
samples from the fault period in the filter and hereby estimating
the properties of the fault signal more quickly.
Main Distance Protection
The main protection function is a full scheme distance
protection with six impedance measuring zones, having a
quadrilateral characteristic [13], as shown in figure 1. The
setting for each zone are independent for: reactive and resistive
reach, resistive reach for single phase to ground and multiphase faults, zero sequence compensation factor and
directionally of all zones.
The phasor filter is frequency adaptive in the sense that its
coefficients are changed based on the estimated power system
frequency. By switching to filter coefficients which are more
closely related to the actual power system frequency, the
properties of attenuating harmonics are maintained also during
off-nominal frequency conditions.
This means that the total protection scheme can be seen as a
combination of three impedance elements: Phase to phase
measuring elements, phase to ground measuring elements and
fault detection/phase selection measuring elements for each
zone and three phases.
Distance Measuring Zones
Each quadrilateral distance measuring zone includes six
impedance measuring loops; three intended for phase-to-earth
faults, and three intended for phase-to-phase as well as threephase faults. It is well-known that transients from CVT’s may
have a significant impact on the transient overreach of a
distance protection. At the same time these transients can be
very diverse in nature from one type to the other.
There are basically two types of CVT’s from the point of view
of ZMFPDIS; the passive and active type, which refers to the
type of ferro-resonance suppression device that is employed.
The active type requires more rigorous filtering which will
inflict negative impact on operate times. However, this will be
evident primarily at higher source impedance ratios (SIR’s),
SIR 5 and above, or close to the reach limit.
Figure 1. Fault detection elements and adaptive expanding
characteristic.
A filter described in [13] gives initially an underestimation of
the current, which increases security of the scheme. The
comparison of the currents and voltages gives an impedance
circle and the operating time is shorter. The apparent characteristic will increase when the filter factors are adjusted towards
a narrower bandwidth and as the estimate of the fault current
grows.
Circular Characteristic
The primary instrument for avoiding overreach and at the same
time achieving fast operate times is a supplementary circular
characteristic that includes some alternative processing [12].
One such circular characteristic exists for every measuring
loop and quadrilateral characteristic. There are no specific
reach settings for this circular zone. It uses the normal
quadrilateral zone settings to determine a reach that will be
appropriate. This implies that the circular characteristic will
always have somewhat shorter reach than the quadrilateral
zone.
Basic Characteristic
The characteristic can be described by the figure 1. Due to the
transient character of the measuring principle static
measurement cannot verify the characteristic. Dynamically, it
2
ܷͳ௅ଵ௅ଶ
Phase-Selection Element
ܷͳ௅ଵ௅ଶெ
The operation of the phase-selection element is primarily based
on current change criteria [12]. The current change criteria
itself can however only be relied on for a short period following
the fault inception (during what this will call the current change
phase). Subsequent switching in the network may render the
change in current invalid. So, naturally, the phase-selection
element also operates on continuous criteria.
‫ܫ‬௅ଵ௅ଶ
k
2.3 Measuring Principles
The phase-selection element can, owing to the current change
criteria, distinguish faults with minimum influence from load
and fault impedance. In other words, it is not restricted by a
load encroachment characteristic during the current change
phase. This significantly improves performance for remote
phase-to-earth faults on heavily loaded lines. One exception
however is three-phase faults, for which the load encroachment
characteristic always has to be applied, in order to distinguish
fault from load.
Fault loop equations use the complex values of voltage,
current, and changes in the current. Apparent impedances are
calculated and compared with the set limits. The apparent
impedances at phase-to-phase faults as follows: (example for
a phase L1 to phase L2 fault)
ܼ௔௣௣ ൌ
The continuous criteria will in the vast majority of cases
operate in parallel and carry on the fault indication after the
current change phase has ended. Only in some particularly
difficult faults on heavily loaded lines the continuous criteria
might not be sufficient, e.g. when the estimated fault
impedance resides within the load area defined by the load
encroachment characteristic. In this case, the indication will be
restricted to a pulse lasting for one or two power system cycles.
ܼ௔௣௣ ൌ
Several criteria are employed when making the directional
decision. The basis is provided by comparing a sum of positive
sequence voltage and memory voltage with phase currents. For
extra security, especially in making a very fast decision, this
method is complemented with an equivalent comparison
where, instead of the phase current, the change in phase current
is used.
‫ܫ‬௅ଵ
ܷ௅ଵ
‫ܫ‬௅ଵ ൅ ‫ܫ‬ே ൈ ‫ܰܭ‬
ܷ௅ଵ, ‫ܫ‬௅ଵ and ‫ܫ‬ே are the phase voltage, phase current and
residual current present to the IED
‫ ܰܭ‬is defined as:
‫ ܰܭ‬ൌ
Where:
ܼͲ െ ܼͳ
͵ ൈ ܼͳ
ܼͲ ൌ ܴͲ ൅ ݆ܺͲ
ܼͳ ൌ ܴͳ ൅ ݆ܺͳ
R0 is setting of the resistive zero sequence reach
X0 is setting of the reactive zero sequence reach
R1 is setting of the resistive positive sequence reach
X1 is setting of the reactive positive sequence reach
ሺͳ െ ݇ሻ ή ܷͳ௅ଵ ൅ ݇ ή ܷͳ௅ଵெ
െͳͷι ൏ ܽ‫݃ݎ‬
൏ ͳʹͲι
‫ܫ‬௅ଵ
ܷͳ௅ଵெ
‫ܫ‬௅ଵ െ ‫ܫ‬௅ଶ
Where:
Moreover, a basic negative sequence directional evaluation is
taken into account as a reliable reference during high load
condition .Finally, zero sequence directional evaluation is used
whenever there is more or less exclusive zero sequence in-feed.
Nominally, the directional sectors that represent forward
direction, one per measuring loop, are defined by the following
equations.
Where,
ܷͳ௅ଵ
ܷ௅ଵ െ ܷ௅ଶ
Here U and I represent the corresponding voltage and current
phasors in the respective phase Ln (n = 1, 2, 3)
The earth return compensation applies in a conventional
manner to phase-to-earth faults (example for a phase L1 to
earth fault) as:
Directional Element
െͳͷι ൏ ܽ‫݃ݎ‬
Voltage different between phase L1 and
L2 (L2 lagging L1)
Memorized voltage difference between
phase L1 and L2 (L2 lagging L1)
Current difference between phase L1 and
L2 (L2 lagging L1)
Factor determining the amount of memory
voltage
ሺͳ െ ݇ሻ ή ܷͳ௅ଵ௅ଶ ൅ ݇ ή ܷͳ௅ଵ௅ଶெ
൏ ͳʹͲι
‫ܫ‬௅ଵ௅ଶ
Here ‫ܫ‬ே is a phasor of the residual current in IED point. This
results in the same reach along the line for all types of faults.
The apparent impedance is considered as an impedance loop
with resistance R and reactance X.
Positive sequence phase voltage in phase
L1
Positive sequence memorized phase
voltage in phase L1
Phase current in phase L1
Measuring elements receive current and voltage information
from the A/D converter. The check sums are calculated and
compared, and the information is distributed into memory
3
illustrated with the full loop reach while the phase-to-phase
characteristic presents the per-phase reach.
locations. For each of the six supervised fault loops, sampled
values of voltage (U), current (I), and changes in current
between samples (DI) are brought from the input memory and
fed to a recursive Fourier filter. The filter provides two
orthogonal values for each input. These values are related to
the loop impedance according to:
ܷ ൌܴൈ݅൅
ܺ ο݅
ൈ
߱଴ ο‫ݐ‬
in complex notation, or:
ܺ ܴ݁ሺο݅ሻ
ൈ
ο‫ݐ‬
߱଴
ܺ ‫݉ܫ‬ሺο݅ሻ
‫݉ܫ‬ሺܷሻ ൌ ܴ ൈ ‫݉ܫ‬ሺ݅ሻ ൅
ൈ
ο‫ݐ‬
߱଴
ܴ݁ሺܷሻ ൌ ܴ ൈ ܴ݁ሺ݅ሻ ൅
߱଴ ൌ ʹߨ݂଴
where:
Figure 2. Characteristic for phase-to-earth measuring,
ohm/loop domain.
Re designates the real component of current and voltage,
Im designates the imaginary component of current and voltage
and ݂଴ designates the rated system frequency.
The algorithm calculates ܴ௠ measured resistance from the
equation for the real value of the voltage and substitute it in the
equation for the imaginary part. The equation for the ܺ௠
measured reactance can then be solved. The final result is equal
to:
ܴ௠ ൌ
‫݉ܫ‬൫ܷ൯ ή ܴ݁൫ο݅൯ െ ܴ݁ሺܷሻ ή ‫݉ܫ‬ሺο݅ሻ
ܴ݁൫ο݅൯ ή ‫݉ܫ‬൫݅൯ െ ‫݉ܫ‬ሺο݅ሻ ή ܴ݁ሺ݅ሻ
ܺ௠ ൌ ߱଴ ή ο‫ ݐ‬ή
ܴ݁൫ܷ൯ ή ‫݉ܫ‬൫݅൯ െ ‫݉ܫ‬ሺܷሻ ή ܴ݁ሺ݅ሻ
ܴ݁൫ο݅൯ ή ‫݉ܫ‬൫݅൯ െ ‫݉ܫ‬ሺο݅ሻ ή ܴ݁ሺ݅ሻ
The calculated ܴ௠ and ܺ௠ values are updated each sample and
compared with the set zone reach. The adaptive tripping
counter counts the number of permissive tripping results. This
effectively removes any influence of errors introduced by the
capacitive voltage transformers or by other factors.
Figure 3. Characteristic for phase-to-phase measuring
The fault loop reach in relation to each fault type may also be
noted as in particular that the setting RFPP always represents
the total fault resistance of the loop, even while the fault
resistance (arc) may be divided into parts like for three-phase
or phase-to-phase faults. The R1 and jX1 represent the positive
sequence impedance from the measuring point to the fault
location.
The directional evaluations are performed simultaneously in
both forward and reverse directions, and in all six fault loops.
Positive sequence voltage and a phase locked positive
sequence memory voltage are used as a reference. This ensures
unlimited directional sensitivity for faults close to the IED
point.
3 Implementation
Implementation of the new distance protection with fast
adaptive features has been made in a modular line terminal
platform that is a part of an automated substation concept. The
transformer module, the A/D conversion module, the main
processing module, the power supply module, the binary I/O
module and the communication module are shown in Figure 4.
2.3 Measuring Zones Settings
All zones operate according to the non-directional impedance
characteristics presented in figure 2 (phase-to-earth) and figure
3 (phase-to-phase). The phase-to-earth characteristic is
4
The main processing module has CPU logics and a main logic
processor. A 1 ms sampling interval has been used.
4 Testing
Development and evaluation of the new protection schemes
has been done within an interactive software environment. The
software testing of the protection schemes is accomplished by
using EMTP-MATLAB software tools. EMTP/ATP files and
recorded data from a real time power system simulator (with a
connected disturbance recorder) have been used as input data.
To thoroughly evaluate operation of the proposed protection
schemes, several network configurations have been simulated.
Additional tests have been done using a RTDS real time power
system simulator. The simulator test was carried out in
accordance with IEC standard [14]. The responses of the
protection in terms of “operating times” for different types of
faults and SIR are shown in figure 5. The parameters for the
tests are shown in Table 1 in Appendix.
Figure 4. The protection platform
Figure 5. Operating times for different fault types and SIR
5
[6]
5 Conclusions
This paper describes a new, high speed protection for EHV
transmission lines. The presented scheme also performs well
on series compensated lines. The distance protection is
providing a fast operate time for basic faults within 60% of the
line length. The protection is as well designed for extra care
during difficult conditions in high voltage transmission
networks, like faults on long heavily loaded lines and faults
generating heavily distorted signals.
[7]
[8]
[9]
A new built-in adaptive load compensation algorithm prevents
overreaching of the distance zones in the load exporting end
during phase-to-earth faults on heavily loaded power lines. It
also reduces under-reach in the importing end.
[10]
[11]
Comprehensive test results on various test systems show the
benefits of the scheme. The results with a Real Time Digital
Simulator (RTDS) are presented in this paper. The scheme is
now in operation in several countries around the world under
trade name REL670 2.0.
[12]
[13]
Acknowledgements
[14]
The authors extend their grateful acknowledgement to the
colleagues at the Application Function Development
department of ABB AB, Substation Automation Products,
Sweden, for their substantial contributions during the basic
development of this concept, and colleagues at Application
department for the evaluation of the algorithms and testing at
RTDS.
Appendix
Tests and settings are for 50 Hz and 1 A.
References
[1]
[2]
[3]
[4]
[5]
A.G.Phadke, M.Ibrahim ,T.Hlibka, “ Fundamental basis
for distance relaying with symmetrical components,
IEEE Trans. Power Appar. Syst. PAS-96 (2) (1977)
D.I.Walkar, S.Elagovan,A.C.Liew, “ Fault impedance
estimation algorithm for digital distance relaying “,
IEEE Trans. Power Deliv., 9 (3) (1994)
B.Jeyasurya , W.J.Smolinski, “ Identification of a best
algorithm for digital distance protection of transmission
lines”, IEEE Trans. Power Appar. Syst. PAS-102 (10)
(1963)
A.M.Ranjbar, B.J.Cory, “An improved method for
digital protection of high voltage transmission lines”,
IEEE Trans. Power Appar. Syst. PAS-91 (2) (1975)
M.S.Sachdev, M.A.Baribeau, “A new algorithm for
digital impedance relays”, IEEE Trans. Power Appar.
Syst. PAS-98, (1979)
M.Akke, B.Westman,“ Load compensation in distance
protection of a three-phase power transmission line”,
European Patent Specification, EP2084798 B1,24
March, (2010).
M.M.Saha, K.Wikstrom, S.Lindhal, “ A new approach
to fast distance protection with adaptive features”,
IEE/DPSP, Nottingham, UK, 24-27 March, (1997).
A. Engqvist, L. Eriksson,”Numerical Distance
Protection for Sub-transmission lines”, Cigré, 34-04,
Aug./Sept., (1988).
IEC Final draft International Standard, “Measuring
relays and protection equipment-Part 121: Functional
requirements for distance protection”, IEC 60255121,Ed. 1.0,95/319/FDIS, January 3, (2014)
“Application guide on protection of complex
transmission network configurations”, CIGRE
materials, CIGRE SC–34 WG-04, August, (1990).
F. Andersson, W. Elmore, “Overview of SeriesCompensated Line Protection Philosophies”, Western
Relay Protective Conference, Washington State
University, Spokane, Washington, October, (1990).
J. Cheetham, A Newbould, G. Stranne, “SeriesCompensated Line Protection: System Modelling and
Test Results”, 15th Annual Western Relay Protective
Conference, Washington State University, Spokane,
Washington, October, (1988).
M.M.Saha , S.Ward , “Adaptive Distance Protection
For Series Compensated Transmission Lines”, 29th
Annual Western Protective Relay Conference
,Spokane,WA,October 22-24,(2002).
M.M. Saha, B. Kasztenny, E. Rosolowski, J.
Izykowski,”First zone algorithm for protection of series
compensated lines”, IEEE Trans. on Power Delivery,
Vol.16, NO.2, pp. 200–207, (2001).
RLdFw
ShortLine-20km
150.00
LongLine-100km
80.00
RLdRv
150.00
80.00
XLd
400.00
400.00
ArgLd
30.00
35.00
ZoneLinkStar
t
CVTtype
Phase Selection
Phase Selection
Passive type
Passive type
INReleasePE
400
400
X1
5.82
29.09
R1
0.51
2.55
X0
23.28
116.42
R0
2.04
10.19
RFPP
40.00
100.00
RFPE
60.00
150.00
Table 1: Test settings for RTDS real time power system
simulator.
6
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