the relay protection scheme for distribution network with distributed generations
TRANSCRIPT
The Relay Protection Scheme for Distribution Network with Distributed Generations
1aHe Shien ,2 b Dong Xinzhou ,3 c Z. Q. Bo and 1 d Suonan Jiale 1Dept. of Electrical Engineering, Xi’an Jiaotong University, Xi’an China
2Dept. of Electrical Engineering, Tsinghua University, Beijing, China, AREVA T&D Co. Stafford, UK
3Dept. of Electrical Engineering, Xi’an Jiaotong University, Xi’an China
[email protected], [email protected], [email protected],[email protected]
Keywords-non-communication protection; distributed generation; tapped-line; double-circuit
Abstract. Three-zone distance protection and four-zone zero sequence over-current protection are
traditional relay protection schemes used for tapped-lines that connect distributed photovoltaic,
wind, and small hydro power sources into a distribution network. These protection schemes cannot
quickly clear the faults that occur at the end of the protected line. A newly developed non-
communication protection scheme for tapped-line and double-circuit line tested at Gansu Power
Grid can significantly speed up fault clearing at the end of the lines, and achieve fast tripping for the
entire line section. This protection scheme also shows advantageous results for distribution grid
with distributed generation.
Introduction
A variety of power failures or abnormal operations caused by natural conditions (e.g. lightning),
maintenance, and etc. in an electric power system may result in shortened component life
expectancy, power quality disturbances, or even power outage. Protection relay is an automatic
device that responses to electrical component failure or abnormal operations by tripping the circuit
breakers. Protection should be selective, swift, sensitive and reliable to detect and isolate the faults
so as to maintain the system stability while reduce equipment failures and power line damages.
In China, there are many tapped-lines in the low-voltage transmission and distribution systems.
There are many 110kV lines in Gansu Power Grid and an 110kV line may have one or more tapped-
lines in a line section. Recent clean power development in the under-developed regions of Gansu
has seen photovoltaic, wind, and small hydro power plants increasingly connected to power grid
through tapped-lines. The main relaying protection for these lines are traditional three-zone distance
and four-zone zero sequence over-current protection. These protections cannot quickly clear the
faults occurring at the end of the protected lines.
When the three-zone distance and four-zone zero sequence over-current protection are employed,
the relay away from a fault point can only clear the fault line with the second zone time delay,
normally 0.3s-0.5s for a fault at the end of the line section. This does not meet the requirement of
fast fault clearing.
Non-communication protections have been installed on the 110 kV Yan-Da-Gu double-circuit
line with tapped lines connected to distributed power sources. The operational experience shows
that the non-communication protection [1-3] can significantly improve the fault clearing speed at
the line end and achieve fast fault tripping for the entire line without communication links. Its
setting is simple and it can effectively improve power system security and reliability.
The basic principles of non-communication protection
Non-communication protection is an auxiliary speed-up protection. It can work together with
distance protections for a whole line by using single-end measurement. Distance protection can only
fast clear the fault in distance zone 1. Other faults can be cleared in distance zone 2 or zone 3 based
Advanced Materials Research Vols. 433-440 (2012) pp 4046-4052Online available since 2012/Jan/03 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.433-440.4046
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on protection selectivity, which usually means there is a time delay of 0.3s or longer. In order to
shorten the time delay, non-communication protection bundled with distance protection can
improve the performance of traditional relays. For different applications based on system
configurations, two types of non-communication protections are used in Gansu Power Grid. 1. Tapped line non-communication protection [4, 6]; 2. Double-circuit non-communication protection [5]. See Table 1 for the characteristics of these two types.
The basic principles of non-communication protection for tapped-line. When an asymmetric
fault near remote end occurs on a power line with tapped lines, the circuit breaker at remote end of
faulted line will trip. This will change the configuration of the system and lead to increase or
decrease of the non-fault phase current. When this change takes place within the time window of
the non-communication protection at the line end, and the distance zone 2 maintains the pick-up
state, the non-communication protection ascertains that the fault occurred in its zone and will
accelerate the distance zone 2 to trip out.
The time period for line distance zone 1 trip plus the circuit breaker trip is normally fixed. When
the non-communication protection detects the current change point is within this time window, it
can distinguish the current change caused by the remote end circuit breaker tripping from other
disturbances. If an internal fault near remote end occurs on the line, the distance zone 2 remains at
pick-up state when the remote circuit breaker tripped out. Therefore the distance zone 2 acts as the
necessary condition for the non-communication protection picking-up. On the contrary, if the fault
occurs on an adjacent line, then the tripping of circuit breaker of that line must clear the fault and
the distance zone 2 of this line should be drop-off.
TABLE I. THE TWO TYPE OF NON-COMMUNICATION PROTECTIONS
Type Advantages Disadvantages
Tapped line non-
communication
protection
No need for communication with remote
protections;
Applicable to any line with or without tapped
line;
Applicable to single line or double-circuit
lines.
Can only be applied to asymmetric
fault;
Can only be applied to three-phase
trip system.
Double-circuit non-
communication
protection
No need for communication with remote
protections;
Suitable for all types of fault;
Setting is simple;
Can be applied to the three-phase trip or
single-phase trip system.
When the non-communication
protection system is installed at the
strong system side, the protection
may refuse to trip three phase fault;
Can only be applied to double-circuit
system.
The non-communication protection accelerates the distance zone 2 only for asymmetry fault. For
the three-phase fault there is no so-called non-fault phase, the criteria of the non-communication
protection cannot work properly.
The conclusion can be drawn. When asymmetric fault occurs on lines with tapped lines, if the
non-communication protection detects that the current ratio is greater than the ratio of setting within
the setting time window τ, and at the same time the current change is greater than that of the setting,
this is an internal fault and accelerated tripping decision is made. Otherwise, the protection will take
no action if the fault is outside. Figure 1 shows the logic of tapped line non-communication
protection.
Figure 1. Non-communication protection logic for tapped line
The setting menu for tapped line non-communication protection is shown in Table 2.
Advanced Materials Research Vols. 433-440 4047
The basic principles of non-communication protection for double-circuit Lines. The overall configuration of non-communication protection for double-circuit lines is shown in Figure 2.
TABLE II. TAPPED LINE NON-COMMUNICATION PROTECTION SETTINGS MENU
Setting Meaning Range Default
Delta Acc Status Enabled/Disabled Enabled/Disabled Disabled
Ratio Set Current unbalance ratio，
(I2+I0)/I1
0.05-2 0.1
Time Delay The middle point of time
window
50-200ms 100ms
Delta Time Half of time window 10-200ms 90ms
Current Set Low load 0.01-2A 0.05A
Delta Current Current change 0.01-2A 0.1A
In Figure 2 the distance relays RS1 and RS2 are installed on each line of the double-circuit lines.
Two double-circuit non-communication protection modules are incorporated into each distance
relay respectively. The double-circuit non-communication protection of the two lines are connected
through the cross-connected cables, which will be used to enable the mutual transfer permission /
latch-up signal to speed up the clearing of line end fault. The two modules together with the
communication link between them constitute the double-circuit non-communication protection
(RS12 in Figure 2).
Figure 2. Double-circuit non-communication protection
When a short circuit occurs on one line of the double-circuit and the remote end circuit breaker is
tripped out, the electrical symmetry of the two lines no longer exists. The detected fault directions
of the near end of the two lines should be opposite. The fault direction of the faulted-line is forward
and that of the healthy-line is backward. The double-circuit non-communication protection can
distinguish an internal fault from an external one based on this feature.
The permission signal is exchanged between the two double-circuit non-communication
protections. If one protection ascertains that fault direction is backward and the distance zone 2 does
not pick up, it transmits the permission signal to the same end protection at the other line. If zone 2
of the other distance protection pickups and the relay receives this permission signal, then the fault
is confirmed and a tripping-signal is activated. Otherwise, non-communication protection will be
blocked. In order to protect symmetry fault and asymmetry fault, the positive-sequence power
direction component and negative-sequence power direction component are adopted in fault
direction detection unit of the relay. The basic logic of non-communication protection is shown in
Figure 3.
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Figure 3. Double-circuit non-communication protection logic
As seen from Figure 3, the key component of the protection is fault direction detection. Negative
sequence component is fault super-imposed quantity, which is sensitive and used for asymmetry
fault. The positive sequence component is for symmetry fault.
The settings for double-circuit non-communication protection are shown in Table 3.
TABLE III. SETTINGS OF DOUBLE-CIRCUIT NON-COMMUNICATION PROTECTION
Settings Meaning Range Default
DL Acc Status Enabled/Disabled Enabled/Disabled Disabled
Angle1 Positive sequence direction angle 20-90° 70°
Angle2 Negative sequence direction angle 20-90° 90°
V1pol Set Positive sequence voltage threshold 0.5-25V 5V
V2pol Set Negative sequence voltage threshold 0.5-25V 5V
The fault direction detection unit is the key component of double-circuit non-communication
protection. It compares the angle between voltage phasor and current phasor to determine fault
direction. Angle 1 and angle 2 in the menu represent the angle between the real axis and the central
line in the operation characteristics diagram of positive sequence direction unit and negative
sequence direction unit respectively, as shown in Figure 4.
In general, Angle 1 is set as line positive sequence impedance angle, while Angle 2 is set as 90°
because the impedance of the negative sequence equivalent circuit of the system can be considered
as reactance. Since voltage should be used in the direction detection unit, and sometimes positive
sequence and negative sequence voltage may be too low to calculate accurately, positive sequence
voltage threshold V1pol Set and negative sequence voltage threshold V2pol Set should be set in the
menu. When measured voltage is less than the settings, the direction component will be blocked.
(a) Positive sequence direction
(b) Negative sequence direction
Figure 4. Direction component characteristic
110 kV Yan-Da-Gu double-circuit line protection configuration and operational problems
The topology of 110 kV Yan-Da-Gu double-circuit is shown in Figure 5. The protection of the
Yanguoxia is CSL-164B, and that of Guchen Substation is PSL-621C. These two kinds of
microprocessor based relays have three-zone phase to phase and phase to ground distance elements
as well as four-zone zero sequence over-current element and reclosing element.
Advanced Materials Research Vols. 433-440 4049
The settings of Yan-Da-Gu II Guchen side relay is as follows: positive sequence impedance
angle is 73°, the phase to phase impedance zone I, II, Ⅲ are 0.15Ω/Φ, 0s; 1.96Ω/Φ, 0.6s; 7.63Ω/
Φ, 5.2s respectively; the phase to ground impedance zone I, II, Ⅲ are 0.12Ω/Φ, 0 s; 1.78Ω/ Φ,
0.6s; 3.05Ω/Φ, 2.3s respectively; zero sequence current zone I, II, III, IV are 44.1A, 0 s; 4.05A,
0.6s; 0.98A, 4.4s; 0.98A, 4.4s respectively; reclosing time 2.6s.
Figure 5. 110 kV Yan-Da-Gu double-circuit with tapped lines.
As shown above, the time setting of zone II and III are long. And the power line supplies power
to loads in Linxia and Gannan districts, in which there are many small hydro power plants. So the
operation modes will be changed frequently. Sometimes the load is heavy. However, when a fault
occurs at the remote end of the protected line, the long time delay to clear the fault can still threaten
system safety.
Because the electrical distance from tapped line connection node to substation Guchen is less
than 20% of the whole line, and the length of tapped line to substation Dagou is very short, if only
distance protection is configured without non-communication protection in the substation, zone I
setting of distance protection at substation Guchen must be very small, and most of the protected
line can only be protected by zone II of distance protection, which can not meet the operational
requirements.
In upgrading and retrofitting of above protection system, three zones distance protection and
tapped line and double-circuit non-communication protection are adopted, which can trip a fault at
any point of the protected line with high speed based on single-terminal measurement. Two tapped
line non-communication protection relays have been installed at substation Guchen and hydro plant
Yanguoxia respectively and one double-circuit non-communication protection relay has been
installed at substation Guchen. They have been put into operation after commissioning test.
Non-communication protection operation in the field
The correctness and reliability of non-communication protection principle and scheme have been
validated by many simulation and tests. The protection relay has been implemented based on
AREVA relay platform and passed the tests. AREVA P540 series relay integrated with non-
communication protection module can trip a fault at any point of the protected line with high speed.
Although non-communication is based on distance protection, it will not affect distance protection.
Whether non-communication protection is activated or not, it will not block distance protection and
will not affect the operation characteristics of distance protection. If distance protection is blocked,
non-communication protection will be blocked too. But if non-communication protection is
blocked, distance protection will operate normally. Setting of tapped line non-communication protection. P543 protection relay integrated with tapped line non-communication protection has three zone distance protection and over-current protection.
The functions and logics of the relay based on P543 can be configured according to the field
requirements. The key setting of the scheme for tapped line non-communication protection is shown
in Table IV.
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TABLE IV. THE SETTING OF TAPPED LINE NON-COMMUNICATION PROTECTION
Settings Delta
Acc
Status
Ratio
Set
Time
Delay
Delta
Time
Current
Set
Delta
Current
Value Enabled 0.2 90ms 60ms 0.05A 0.5A
Wiring and setting of double-circuit non-communication protection. Unlike general single-terminal protection, the double-circuit non-communication protection need to exchange permission / block signal between two relays installed at the same terminal of the double-circuit, which is implemented by connecting the output of one protection relay to the input interface of the other protection relay. The connection is as shown in Figure 6.
Figure 6. Wiring of double-circuit protection relays
P543 has many output and input interfaces. Depending on the requirements, field applications
can be configured by setting PSL logics. In the application presented in the paper, the connections
are that 220VDC+ to F16 (opto input) of P543 relay at Gu side of line Yan-Da-Gu I, F15 of P543
relay to G11 of P543 relay at Gu side of line Yan-Da-Gu II, and G12 of P543 relay at Gu side of
line Yan-Da-Gu II to 220VDC-; 220VDC+ to F16 of P543 relay at Gu side of line Yan-Da-Gu II,
F15 of P543 relay to G11 of P543 relay at Gu side of line Yan-Da-Gu I, and G12 of P543 relay at
Gu side of line Yan-Da-Gu I to 220VDC-.
The settings of double-circuit non-communication protection are given in Table V.
TABLE V. SETTINGS OF DOUBLE-CIRCUIT NON-COMMUNICATION PROTECTION
Setting DL Acc
Status
Angle1 Angle2 V1pol Set V2pol Set
Value Enabled 70° 90° 5V 5V
Non-communication protection operation. The non-communication protection relay has
experienced three external faults, of which one is a close-to-busbar phase to ground fault, and one internal fault on the tapped line, the relays respond correctly for each fault since it has been put into operation [7].
Conclusions
Non-communication protection can trip a fault at any point of the protected line with high speed
without communication channels. It can reduce the protection coordination time, simplify the
settings, improve the sensitivity, and ease the installations. It helps to improve system operation
safety and reliability.
It is suitable for the smart distribution grid. With the rapid development of renewable energy, the
non-communication protection can be widely used in distribution networks with distributed power
sources such as photovoltaic, wind, and small hydro power as these distributed power sources are
tapped onto the distribution networks.
Advanced Materials Research Vols. 433-440 4051
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4052 Materials Science and Information Technology
Materials Science and Information Technology 10.4028/www.scientific.net/AMR.433-440 The Relay Protection Scheme for Distribution Network with Distributed Generations 10.4028/www.scientific.net/AMR.433-440.4046