U.S. patent application number 09/812560 was filed with the patent office on 2002-04-25 for interconnection protective device for generator set.
Invention is credited to Katoh, Toyokuni, Nomiya, Shigeo.
Application Number | 20020047699 09/812560 |
Document ID | / |
Family ID | 18599370 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020047699 |
Kind Code |
A1 |
Katoh, Toyokuni ; et
al. |
April 25, 2002 |
Interconnection protective device for generator set
Abstract
The present invention provides a system interconnection
protective device. A command for dropping a voltage is issued when
the frequency change rate of a private generator set is positive,
and a command for raising a voltage is issued when the frequency
change rate is negative. The output voltage of the private
generator set is varied by supplying an automatic voltage regulator
with the voltage variation reference obtained by assisting the
commands based on a rough tendency of frequency variations. Thus, a
sole operation of the private generator set, which interconnects
with a system, can reliably and easily be detected and protected on
the side of the private generator set by enlarging the frequency
variations without using any expensive transfer breaker.
Inventors: |
Katoh, Toyokuni;
(Funabashi-shi, JP) ; Nomiya, Shigeo;
(Funabashi-shi, JP) |
Correspondence
Address: |
Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
1300 I Street, N.W.
Washington
DC
20005-3315
US
|
Family ID: |
18599370 |
Appl. No.: |
09/812560 |
Filed: |
July 18, 2001 |
Current U.S.
Class: |
324/76.39 |
Current CPC
Class: |
H02J 3/388 20200101;
H02J 3/38 20130101; Y02E 20/14 20130101 |
Class at
Publication: |
324/76.39 |
International
Class: |
G01R 023/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2000 |
JP |
2000-082583 |
Claims
What is claimed is:
1. A system interconnection protective device for a private
generator set, which interconnects with a system power supply via a
circuit breaker, the device comprising: frequency detection means
for detecting a frequency from an output of the private generator
set; frequency change rate detection means for detecting a
frequency change rate of the frequency detected by the frequency
detection means; voltage variation reference determination means
for defining a relationship between the frequency change rate and
voltage variation reference by a function, the voltage variation
reference increasing a leading reactive power of the private
generator set when the frequency change rate detected by the
frequency change rate detection means is positive increasing a
lagging reactive power of the private generator set when the
frequency change rate is negative; frequency change rate
integration means for integrating the frequency change rate
detected by the frequency change rate detection means; frequency
variation tendency determination means for determining whether the
frequency rises or lowers, based on a frequency change rate
integration amount integrated by the frequency change rate
integration means; bias means for applying a bias to the voltage
variation reference output from the voltage variation reference
determination means to decrease the voltage variation reference
when the frequency variation tendency determination means
determines that the frequency rises and applying a bias to the
voltage variation reference output therefrom to increase the
voltage variation reference when the frequency variation tendency
determination means determines that the frequency lowers; and
protection means for detecting a frequency variation promoted due
to a voltage variation of the private generator set caused by
adding the voltage variation reference to which the bias is applied
by the bias means, to voltage reference of an automatic voltage
regulator of the private generator set, thereby opening the circuit
breaker and disconnecting the private generator set from a system
bus.
2. The system interconnection protective device according to claim
1, further comprising reset means for determining whether the
frequency change rate detected by the frequency change rate
detection means falls within a narrow range close to zero and
resetting the frequency change rate integration integrated by the
frequency change rate integration means to zero when the frequency
change rate falls within the small range.
3. The system interconnection protective device according to claim
1, wherein the protection means determines whether the private
generator set is to be disconnected from the system line on a first
condition that the frequency change rate detected by the frequency
change rate detection means exceeds a value, on a second condition
that the frequency change rate integration amount integrated by the
frequency change rate integration means exceeds a value, or by AND
of the first and second conditions.
4. The system interconnection protective device according to claim
2, wherein the protection means determines whether the private
generator set is to be disconnected from the system line on a first
condition that the frequency change rate detected by the frequency
change rate detection means exceeds a value, on a second condition
that the frequency change rate integration amount integrated by the
frequency change rate integration means exceeds a value, or by AND
of the first and second conditions.
5. A system interconnection protective device for a private
generator set, which interconnects with a system power supply via a
circuit breaker, the device comprising: frequency detection means
for detecting a frequency from an output of the private generator
set; frequency change rate detection means for detecting a
frequency change rate of the frequency detected by the frequency
detection means; voltage variation reference determination means
for defining a relationship between the frequency change rate and
voltage variation reference by a function, the voltage variation
reference increasing a leading reactive power of the private
generator set when the frequency change rate detected by the
frequency change rate detection means is positive increasing a
lagging reactive power of the private generator set when the
frequency change rate is negative, and for allowing a gain or a
shape of the function to be switched to a plurality of stages;
voltage variation reference selection means for setting a plurality
of threshold values to the frequency change rate detected by the
frequency change rate detection means and issuing a select command
for selecting the gain of the function or the shape thereof to the
voltage variation reference determination means whenever the
frequency change rate exceeds each of the threshold values;
frequency change rate integration means for integrating the
frequency change rate detected by the frequency change rate
detection means; frequency variation tendency determination means
for determining whether the frequency rises or lowers, based on a
frequency change rate integration amount integrated by the
frequency change rate integration means; bias means for applying a
bias to the voltage variation reference output from the voltage
variation reference determination means to decrease the voltage
variation reference when the frequency variation tendency
determination means determines that the frequency rises and
applying a bias to the voltage variation reference output therefrom
to increase the voltage variation reference when the frequency
variation tendency determination means determines that the
frequency lowers; switch means for determining whether the bias
means applies the bias to the voltage variation reference in
response to the select command output from the voltage variation
reference selection means; and protection means for detecting a
frequency variation promoted due to a voltage variation of the
private generator set caused by adding the voltage variation
reference to which the bias is applied by the bias means, to
voltage reference of an automatic voltage regulator of the private
generator set, thereby opening the circuit breaker and
disconnecting the private generator set from a system bus.
6. The system interconnection protective device according to claim
5, further comprising reset means for determining whether the
frequency change rate detected by the frequency change rate
detection means falls within a narrow range close to zero and
resetting the frequency change rate integration amount integrated
by the frequency change rate integration means to zero when the
frequency change rate falls within the small range.
7. The system interconnection protective device according to claim
5, wherein the protection means determines whether the private
generator set is to be disconnected from the system line on a first
condition that the frequency change rate detected by the frequency
change rate detection means exceeds a value, on a second condition
that the frequency change rate integration amount integrated by the
frequency change rate integration means exceeds a value, or by AND
of the first and second conditions.
8. The system interconnection protective device according to claim
6, wherein the protection means determines whether the private
generator set is to be disconnected from the system line on a first
condition that the frequency change rate detected by the frequency
change rate detection means exceeds a value, on a second condition
that the frequency change rate integration amount integrated by the
frequency change rate integration means exceeds a value, or by AND
of the first and second conditions.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 2000-82583,
filed Mar. 23, 2000, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a system interconnection
protective device for a private generator set such as an
urban-waste power generation system and a cogeneration system,
which interconnects with a system power supply via a circuit
breaker.
[0003] FIG. 1 shows a conventional system interconnection
protective device that has been used in order that a customer can
interconnect a system power supply with a private generator set
such as an urban-waste power generation system and a cogeneration
system.
[0004] As FIG. 1 illustrates, a host substation 4 drops a voltage
of a system power supply 1 via a transformer 2 and supplies power
to a customer 7 through a circuit breaker 3.
[0005] The customer 7 supplies the power to a load 6 through a
circuit breaker 5.
[0006] The private generator set 10 supplies an output voltage of
an alternating-current generator 12 to the system power supply 1
via a circuit breaker 11.
[0007] To control the output voltage of the alternating-current
generator 12, an automatic voltage regulator (AVR) 13 controls a
voltage of a field winding 14 of the generator 12.
[0008] To control the output frequency of the generator 12, a
governor 15 of an engine 16 for driving the generator 12 controls
power of the engine.
[0009] A generator fault detection circuit 22 is employed as a
failure detection means. The circuit 22 detects an abnormal current
based on a relationship between an output current of the generator
12 detected by a current transformer 21 and an output voltage of
the generator 12. The circuit 22 then supplies a detection signal
of the abnormal current to a trip circuit 23 to thereby open the
circuit breaker 11.
[0010] A current transformer 24 is provided as a protecting means
on the output side (the substation side) of the circuit breaker 11.
An overcurrent relay (OC) 25 receives an output of the current
transformer 24 to operate the trip circuit 23.
[0011] When the system power supply 1 malfunctions, especially when
the power supply 1 is broken or the circuit breaker 3 is opened,
various types of protective relays, such as an underfrequency relay
(UF) 26, an overfrequency relay (OF) 27, an overvoltage relay (OV)
28, and an undervoltage relay (UV) 29, detect that an abnormal
frequency or voltage is generated from an imbalance between an
output power of the generator 12 and a load power of the load
6.
[0012] In response to a detection signal output from the protective
relays, the trip circuit 23 gives a trip instruction to the circuit
breaker 11 to open the circuit breaker 11 and allow the circuit
breaker 3 to be reclosed.
[0013] The foregoing system interconnection protective device has
the following problems:
[0014] If the active and reactive components of the output power of
the alternating-current generator 12 and the required power of the
load 6 are almost equal to each other when the system power supply
1 malfunctions to open the circuit breaker 3, the frequency and the
voltage hardly vary. For this reason, none of the protective relays
25 to 29 operate, but the private generator set continues to
operate. A so-called sole-operation (islanding) phenomenon occurs
to prevent the circuit breaker 3 to be reclosed.
[0015] Some conventional devices adopt the following method in
order to prevent the above islanding-operation phenomenon:
[0016] In this method, a transfer breaker 8 is connected to a
private line extending from the substation 4. This device 8 causes
the circuit breaker 11 to break the transfer of power.
[0017] In other words, the transfer breaker 8 detects a signal
indicating that the circuit breaker 3 of the host substation 4 is
opened and transmits a break signal to the circuit breaker 11 to
open the breaker 11.
[0018] However, the cost of the transfer breaker 8 is very high for
the private generator set 10 having a small-to-medium power of
several hundreds of kilowatts. There is no practical merit in
providing the transfer breaker in the system interconnection
protective device.
BRIEF SUMMARY OF THE INVENTION
[0019] It is accordingly an object of the present invention to
provide a system interconnection protective device for a private
generator set, which is capable of reliably and easily detecting
and protecting a sole operation of the private generator set, which
interconnects with a system, without providing any expensive
transfer breaker.
[0020] According to a first aspect of the present invention, there
is provided a system interconnection protective device for a
private generator set, which interconnects with a system power
supply via a circuit breaker, the device comprising frequency
detection means for detecting a frequency from an output of the
private generator set, frequency change rate detection means for
detecting a frequency change rate of the frequency detected by the
frequency detection means, voltage variation reference
determination means for defining a relationship between the
frequency change rate and voltage variation reference by a
function, the voltage variation reference increasing a leading
reactive power of the private generator set when the frequency
change rate detected by the frequency change rate detection means
is positive increasing a lagging reactive power of the private
generator set when the frequency change rate is negative, frequency
change rate integration means for integrating the frequency change
rate detected by the frequency change rate detection means,
frequency variation tendency determination means for determining
whether the frequency rises or lowers, based on a frequency change
rate integration amount integrated by the frequency change rate
integration means, bias means for applying a bias to the voltage
variation reference output from the voltage variation reference
determination means to decrease the voltage variation reference
when the frequency variation tendency determination means
determines that the frequency rises and applying a bias to the
voltage variation reference output therefrom to increase the
voltage variation reference when the frequency variation tendency
determination means determines that the frequency lowers, and
protection means for detecting a frequency variation promoted due
to a voltage variation of the private generator set caused by
adding the voltage variation reference to which the bias is applied
by the bias means, to voltage reference of an automatic voltage
regulator of the private generator set, thereby opening the circuit
breaker and disconnecting the private generator set from a system
bus.
[0021] In addition to the above means, the system interconnection
protective device may further comprise reset means for determining
whether the frequency change rate detected by the frequency change
rate detection means falls within a narrow range close to zero and
resetting the frequency change rate integration amount integrated
by the frequency change rate integration means to zero when the
frequency change rate falls within the small range. The protection
means can determine whether the private generator set is to be
disconnected from the system line on a first condition that the
frequency change rate detected by the frequency change rate
detection means exceeds a value, on a second condition that the
frequency change rate integration amount integrated by the
frequency change rate integration means exceeds a value, or by AND
of the first and second conditions. The same is true of the reset
means and the protection means of the second aspect described
below.
[0022] According to the second aspect of the present invention,
there is provided a system interconnection protective device for a
private generator set, which interconnects with a system power
supply via a circuit breaker, the device comprising frequency
detection means for detecting a frequency from an output of the
private generator set, frequency change rate detection means for
detecting a frequency change rate of the frequency detected by the
frequency detection means, voltage variation reference
determination means for defining a relationship between the
frequency change rate and voltage variation reference by a
function, the voltage variation reference increasing a leading
reactive power of the private generator set when the frequency
change rate detected by the frequency change rate detection means
is positive increasing a lagging reactive power of the private
generator set when the frequency change rate is negative, and for
allowing a gain or a shape of the function to be switched to a
plurality of stages, voltage variation reference selection means
for setting a plurality of threshold values to the frequency change
rate detected by the frequency change rate detection means and
issuing a select command for selecting the gain of the function or
the shape thereof to the voltage variation reference determination
means whenever the frequency change rate exceeds each of the
threshold values, frequency change rate integration means for
integrating the frequency change rate detected by the frequency
change rate detection means, frequency variation tendency
determination means for determining whether the frequency rises or
lowers, based on a frequency change rate integration amount
integrated by the frequency change rate integration means, bias
means for applying a bias to the voltage variation reference output
from the voltage variation reference determination means to
decrease the voltage variation reference when the frequency
variation tendency determination means determines that the
frequency rises and applying a bias to the voltage variation
reference output therefrom to increase the voltage variation
reference when the frequency variation tendency determination means
determines that the frequency lowers, switch means for determining
whether the bias means applies the bias to the voltage variation
reference in response to the select command output from the voltage
variation reference selection means, and protection means for
detecting a frequency variation promoted due to a voltage variation
of the private generator set caused by adding the voltage variation
reference to which the bias is applied by the bias means, to
voltage reference of an automatic voltage regulator of the private
generator set, thereby opening the circuit breaker and
disconnecting the private generator set from a system bus.
[0023] According to the first aspect described above, a frequency
change rate of a private generator set is detected. A command for
dropping a voltage is issued when the detected frequency change
rate is positive, and a command for raising a voltage is issued
when the frequency change rate is negative. The output voltage of
the private generator set is varied by supplying an automatic
voltage regulator with the voltage variation reference obtained by
assisting the commands based on a rough tendency of frequency
variations.
[0024] Thus, a sole operation of the private generator set, which
interconnects with a system, can reliably and easily be detected
and protected on the side of the private generator set by enlarging
the frequency variations and without using any expensive transfer
breaker.
[0025] According to the second aspect described above, the
multi-step detection method reduces an influence upon a system with
which the private generator set is interconnecting and enlarges a
frequency variation in a sole operation of the private generator
set by assisting voltage variation reference, thus detecting a
frequency and an abnormal frequency change rate.
[0026] The sole operation of the private generator set that
interconnects with a system can be detected and protected more
reliably and easily on the side of the private generator set by
enlarging the frequency variation and without providing any
expensive transfer breaker.
[0027] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0028] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detailed description of the
preferred embodiments give below, serve to explain the principles
of the invention.
[0029] FIG. 1 is a block diagram showing an example of a prior art
system interconnection protective device for a generator set;
[0030] FIG. 2 is a block diagram of a system interconnection
protective device for a generator set according to a first
embodiment of the present invention;
[0031] FIGS. 3A and 3B are graphs each showing an example of the
shape of a function for determining voltage variation reference in
the system interconnection protective device according to the first
embodiment of the present invention;
[0032] FIG. 4 is a block diagram explaining an operation of the
system interconnection protective device according to the first
embodiment of the present invention;
[0033] FIG. 5 is a chart explaining an operation of the system
interconnection protective device according to the first embodiment
of the present invention;
[0034] FIG. 6 is another chart explaining an operation of the
system interconnection protective device according to the first
embodiment of the present invention;
[0035] FIG. 7 is a still another chart explaining an operation of
the system interconnection protective device according to the first
embodiment of the present invention;
[0036] FIG. 8 is a block diagram of a system interconnection
protective device for a generator set according to a second
embodiment of the present invention;
[0037] FIG. 9 is a graph showing an example of the shape of a
function for determining voltage variation reference by a
multi-step detection method in the system interconnection
protective device according to the second embodiment of the present
invention;
[0038] FIG. 10 is a block diagram illustrating a main part of a
system interconnection protective device for a generator set
according to a third embodiment of the present invention; and
[0039] FIGS. 11A and 11B are block diagrams each showing a main
part of a system interconnection protective device for a generator
set according to a fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Embodiments of the present invention will now be described
in detail with reference to the accompanying drawings.
[0041] FIG. 2 is a block diagram illustrating a system
interconnection protective device for a generator set according to
a first embodiment of the present invention.
[0042] In FIG. 2, the same constituting elements as those in FIG. 1
are indicated by the same reference numerals and their descriptions
are omitted. In other words, only different constituting elements
will be described hereinafter.
[0043] The system interconnection protective device of FIG. 2
differs from the prior art one of FIG. 1 in that it excludes the
above-described expensive transfer breaker 8 and substitutes the
following constitution therefor.
[0044] As FIG. 2 shows, a frequency (f) detector 31 detects a
frequency from an output voltage of an alternating-current
generator 12. A frequency change rate (df/dt) detector 32 detects a
frequency change rate V30 from the detected frequency.
[0045] An excessive frequency change rate (df/dt) detector 33
detects whether the frequency change rate V30 exceeds a set value.
If the rate V30 is not lower than the set value, the detector 33
outputs an abnormal output signal V31 and supplies it to a trip
circuit 23.
[0046] Upon receiving the abnormal output signal V31, the trip
circuit 23 supplies a trip signal to a circuit breaker 11 to open
an electric circuit.
[0047] A reactive power (Q) detector 35 receives an output current
of the alternating-current generator 12 detected by a current
transformer 21 and an output voltage of the generator 12 and
detects reactive power Q based on the output current and output
voltage.
[0048] An active power (P) detector 36 receives an output current
of the alternating-current generator 12 detected by the current
transformer 21 and an output voltage of the generator 12 and
detects active power P based on the output current and output
voltage.
[0049] An active power control circuit (APR) 38 compares active
power reference P from an active power reference (P*) setting
device 37 with the active power P from the active power detector
36. The circuit 38 supplies a difference between them to a governor
15 to control a motor of an engine 16.
[0050] A voltage variation reference determination means 40
receives a frequency change rate V30 from the frequency change rate
detector 32 and outputs voltage variation reference .DELTA.V*1.
[0051] The relationship between the frequency change rate V30 and
the voltage variation reference .DELTA.V*1 is defined as a function
as shown in FIG. 2 so as to
[0052] In order to output voltage variation reference .DELTA.V*1
that lowers an output voltage of the alternating-current generator
12 and raises the frequency when the frequency change rate V30 is
positive (while the frequency is increasing) and that raises an
output voltage of the generator 12 and lowers the frequency when
the frequency change rate V30 is negative (while the frequency is
decreasing), a relationship between the frequency change rate V30
and the voltage variation reference .DELTA.V*1 is defined by the
function as shown in FIG. 2.
[0053] FIGS. 3A and 3B each show an example of the above
function.
[0054] A frequency change rate integration means 41 integrates a
positive signal (indicating an increasing frequency) of the
frequency change rate V30 and a negative signal (indicating a
decreasing frequency) thereof.
[0055] A frequency variation tendency determination means 42
roughly determines a variation direction of the frequency based on
the amount of integration of frequency change rates obtained by the
frequency change rate integration means 41.
[0056] A bias means 43 outputs a bias signal .DELTA.V*2 in
accordance with the frequency variation direction determined by the
frequency variation tendency determination means 42.
[0057] If the frequency variation direction corresponds to a
direction in which the frequency increases, the bias means 43
outputs a bias signal .DELTA.V*2 that lowers the voltage variation
reference .DELTA.V*1. If the frequency variation direction
corresponds to a direction in which the frequency decreases, the
bias means 43 outputs a bias signal .DELTA.V*2 that raises the
voltage variation reference .DELTA.V*1.
[0058] A reactive power control circuit (AQR) 45 outputs voltage
reference .DELTA.VQ* such that reactive power reference Q* set by a
reactive power reference (Q*) setting device 44 and active power Q
detected by the reactive power detector 35 coincide with each
other.
[0059] An automatic voltage regulator (AVR) 13 regulates a field of
a field winding 14 so as to control an output voltage of the
alternating-current generator 12 on the basis of voltage reference
V* set by a voltage reference (V*) setting device (90R) 46, voltage
reference .DELTA.VQ* output from the reactive power control circuit
45, voltage variation reference .DELTA.V*1 output from the voltage
variation reference determination means 40, and bias signal
.DELTA.V*2 output from the bias means 43.
[0060] In the foregoing system interconnection protective device,
the active power reference (P*) setting device 37, the active power
control circuit 38, the governor 15, and the engine 16 constitute
an active power control loop.
[0061] The reactive power reference setting device 44, the reactive
power detector 35, and the reactive power control circuit 45
constitute a reactive power control loop.
[0062] The voltage reference (V*) setting device (90R) 46, the
voltage reference .DELTA.VQ* that is an output of the reactive
power control circuit 45, the voltage variation reference
.DELTA.V*1 determined by the voltage variation reference
determination means 40, the bias signal .DELTA.V*2 from the bias
means 43, and the automatic voltage regulator 13 constitute a
voltage control loop.
[0063] An operation of the system interconnection protective device
for a generator set according to the first embodiment described
above will now be described with reference to FIGS. 4 to 7.
[0064] Assuming in FIG. 4 that the active power of the
alternating-current generator 12 is P, the reactive power thereof
is Q, the active power of a load 6 is PL, and the reactive power
thereof is QL, the active power .DELTA.P and reactive power
.DELTA.Q flowing into a system power supply 1 are represented as
follows:
.DELTA.P=P-PL
.DELTA.Q=Q-QL
[0065] Assume that an inductance between the alternating-current
generator 12 and the system is 1, the voltage of the load 6 is V,
and the frequency thereof is f.
[0066] In the normal operation, the voltage V and frequency f of
the load 6 hardly vary even though a circuit breaker 3 opens when
.DELTA.P.apprxeq.0 and .DELTA.Q.apprxeq.0.
[0067] None of protective relays 25 to 29 can detect the voltage V
or frequency f of the load 6. The private generator set therefore
continues to perform its sole operation.
[0068] The phases of the system power supply 1 and the load 6 are
shifted slowly. The reclosing of the circuit breaker 3 will cause
an accident. Thus, the circuit breaker 3 cannot be reclosed to
prevent an accident, which decreases the stability of a
distribution system.
[0069] The voltage in the sole operation depends upon the following
equation: P=V.sup.2/R. On the other hand, the frequency f depends
upon the following equation:
Q=(V.sup.2.omega.C)-(V.sup.2/.omega.L).
[0070] When the reactive power supplied from the
alternating-current generator 12 is shifted in the leading
direction from the reactive power QL required by the load 6, the
frequency f rises, the current iC of a capacitor C increases, the
inductance current iL decreases, and the reactive power changes in
its balanced direction.
[0071] When the reactive power supplied from the
alternating-current generator 12 is shifted in the lagging
direction from the reactive power QL required by the load 6, the
frequency f lowers, the inductance current iL increases, the
capacitor current iC decreases, and the reactive power changes in
its balanced direction.
[0072] If the sole operation is performed when .DELTA.P.apprxeq.0
and .DELTA.Q.noteq.0, the frequency f varies and comes close to
stable points f1 and f2 after the system is broken (t0), as
illustrated in FIG. 5.
[0073] In FIG. 5, f1 indicates that .DELTA.Q slightly leads, and f2
represents that .DELTA.Q slightly lags.
[0074] In FIG. 5, +.DELTA.f and -.DELTA.f are levels at which a
sole operation can be detected by the protective relays 25 to
29.
[0075] FIG. 6 is a chart explaining an advantage of the second
embodiment shown in FIG. 2.
[0076] In FIG. 6, f represents a frequency detected by the
frequency detector 31, df/dt shows a frequency change rate of the
frequency detected by the frequency change rate detector 32, and
.DELTA.V*1 indicates an output of the voltage variation reference
determination means 40.
[0077] If the frequency f changes as shown in FIG. 6, the frequency
change rate df/dt exhibits a waveform the phase of which advances
90.degree..
[0078] When the frequency change rate df/dt is larger than 0, the
frequency f is increasing. During this period, the voltage
variation reference determination means 40 issues a voltage drop
command (leading reactive power command), and the frequency f
increases further.
[0079] When the rate df/dt is smaller than 0, the frequency f is
decreasing. During this period, the voltage variation reference
determination means 40 issues a voltage rise command (lagging
reactive power command), and the frequency f decreases further.
[0080] If, then, the polarity of df/dt varies to positive and
negative values at very small regular intervals after the system is
disconnected, a delay of an exciting system prevents the voltage
from being changed sufficiently based on the voltage variation
reference. It is thus thought that the frequency is difficult to
vary smoothly.
[0081] By integrating frequency change rates using the frequency
change rate integration means 41 and frequency variation tendency
determination means 42, a rough variation of the frequency f is
detected, and a bias signal .DELTA.V*2 is supplied to the voltage
variation reference .DELTA.V*1 in accordance with the frequency
variation direction. Thus, the voltage variation direction is held
on one of the rising and lowering directions to facilitate the
voltage variation.
[0082] The variation in frequency is increased by the positive
feedback due to the voltage variation, and the abnormal frequency
and the excessive frequency change rate are detected by the
excessive frequency change rate detector 33.
[0083] Consequently, the sole operation of the private generator
set 10 can reliably be detected without using any expensive
transfer breaker 8 that has been used conventionally.
[0084] The frequency variation in the islanding operation of the
private generator set 10, as shown in FIG. 5, is increased to that
as shown in FIG. 7, thereby detecting a frequency and an abnormal
rate of the frequency variation.
[0085] Consequently, the sole operation of the private generator
set 10 can be detected easily and reliably on the side of the
private generator set 10.
[0086] In the foregoing system interconnection protective device
according to the first embodiment, a voltage drop command is issued
when the frequency change rate df/dt of the alternating-current
generator 12 is larger than 0 and a voltage rise command is issued
when the frequency change rate df/dt is smaller than 0.
Furthermore, the output voltage of the alternating-current
generator 12 is varied by supplying the automatic voltage regulator
13 with voltage variation reference that is obtained by assisting
the voltage drop command or voltage rise command based on a rough
tendency of the frequency variation.
[0087] Consequently, the sole operation of the interconnected
private generator set 10 can reliably and easily be detected and
protected on the side of the private generator set by enlarging a
variation in frequency, without providing any expensive transfer
breaker 8 as described above.
[0088] FIG. 8 is a block diagram showing a system interconnection
protective device for a generator set according to a second
embodiment of the present invention.
[0089] In FIG. 8, the same constituting elements as those in FIG. 2
are indicated by the same reference numerals and their descriptions
are omitted. In other words, only different constituting elements
will be described hereinafter.
[0090] The interconnection protective device shown in FIG. 8
differs from the device shown in FIG. 2 in the following
points.
[0091] In the device illustrated in FIG. 8, the following functions
are added to the voltage variation reference determination means 40
shown in FIG. 2, and a voltage variation reference selection means
51 and a switch means 52 are newly added.
[0092] As described above, the voltage variation reference
determination means 40 defines a relationship between frequency
change rate V30 and voltage variation reference .DELTA.V*1 by a
function. The gain of the function or the shape of the function can
be switched to a plurality of stages.
[0093] The voltage variation reference selection means 51 sets a
plurality of threshold values to the frequency change rate detected
by the frequency change rate detector 32. The means 51 issues a
command for switching the gain or shape of the function to the
voltage variation reference determination means 40 whenever the
frequency change rate exceeds each of the threshold values.
[0094] The switch means 52 controls the bias means 43 to determine
whether the bias means 43 biases the voltage variation reference in
response to a selection command output from the voltage variation
reference selection means 51.
[0095] An operation of the above-described system interconnection
protective device according to the second embodiment of the present
invention will now be described with reference to FIG. 9.
[0096] In FIG. 8, the voltage variation reference determination
means 40 receives a frequency change rate V30 from the frequency
change rate detector 32 and outputs voltage variation reference
.DELTA.V*1.
[0097] As in the first embodiment described above, when the
frequency change rate is positive (while the frequency is
increasing), the output voltage of the alternating-current
generator 12 lowers to promote the increase of the frequency.
[0098] When the frequency change rate is negative (while the
frequency is decreasing), the voltage variation reference
.DELTA.V*1 is output so as to increase the output voltage of the
alternating-current generator 12 and thus promote the decrease of
the frequency.
[0099] The greater the voltage variation, the greater the frequency
variation. In order to determine whether the private generator set
10 is operating solely or interconnecting with a system, it is
favorable to vary a voltage that causes a frequency to vary
sufficiently when the private generator set operates solely. If,
however, a command for greatly varying a voltage is issued during
the interconnection with the system, it is likely that a
disturbance will be caused in the system.
[0100] At first, the voltage variation reference .DELTA.V*1 is set
at a small level that has no adverse influence on the system. When
the frequency change rate exceeds the first-set threshold value,
the voltage variation reference .DELTA.V*1 is set at a larger
level.
[0101] If the frequency change rate exceeds the next threshold
value, the voltage variation reference .DELTA.V*1 is set at a still
larger level.
[0102] The multi-step detection method is therefore achieved in
which the above operations are repeated some times to gradually
enlarge the action due to the voltage variation reference
.DELTA.V*1 while confirming that the private generator set seems to
operate solely.
[0103] The multi-step detection method is achieved by the voltage
variation reference selection means 51 having a plurality of
frequency change rate threshold values and issuing a voltage
variation reference selection command to the voltage variation
reference determination means 40.
[0104] The voltage variation reference determination means 40
allows the gain or the shape of a function for determining voltage
variation reference from the frequency change rate to be switched.
This switching is performed in response to a command from the
voltage variation reference selection means 51.
[0105] FIG. 9 is a graph showing an example of a function for
determining voltage variation reference. In this example, a
plurality of stages of functions are prepared, and a limit level
can be set.
[0106] The frequency change rate integration means 41, frequency
variation tendency determination means 42, and bias means 43
perform the same operations as those of the means of the first
embodiment.
[0107] If the frequency change rate enlarges to some extent, the
multi-step detection method produces a sufficient voltage variation
reference .DELTA.V*1 without a bias signal .DELTA.V*2.
[0108] The switch means 52 stops an assist of the bias signal
.DELTA.V*2 in accordance with the progress of the multi-step
detection.
[0109] The multi-step detection method reduces an influence upon a
system with which the private generator set is interconnecting.
[0110] In other words, when the private generator set 10 operates
solely, the voltage variation reference .DELTA.V*1 is assisted in
addition to the operation of enlarging a variation in frequency,
and the frequency variation in the sole operation of the private
generator set 10, as shown in FIG. 5, is increased to that as shown
in FIG. 7, thereby detecting a frequency and an abnormal frequency
change rate.
[0111] Thus, the sole operation of the private generator set 10 can
reliably and easily be detected on the automatic private set
side.
[0112] In the system interconnection protective device described
above, the multi-step detection method reduces an influence upon a
system with which the private generator set is interconnecting and,
when the private generator set operates solely, the voltage
variation reference is assisted in addition to the operation of
enlarging a variation in frequency, and the frequency variation in
the sole operation of the private generator set is increased,
thereby detecting a frequency and an abnormal rate of change of the
frequency.
[0113] Consequently, the frequency variation is enlarged, and a
sole operation of the private generator set 10, which interconnects
with a system, can reliably and easily detected and protected on
the private generator set 10 without providing any expensive
transfer breaker 8.
[0114] FIG. 10 is a block diagram showing a main part of a system
interconnection protective device for a generator set according to
a third embodiment of the present invention.
[0115] In FIG. 10, the same constituting elements as those in FIGS.
2 and 8 are indicated by the same reference numerals and their
descriptions are omitted. In other words, only different
constituting elements will be described hereinafter.
[0116] The system interconnection protective device shown in FIG.
10 differs from the devices shown in FIGS. 2 and 8 in the following
points.
[0117] The device illustrated in FIG. 10 is achieved by newly
adding a reset means 61 to the devices of the first and second
embodiments shown in FIGS. 2 and 8.
[0118] The reset means 61 determines whether the frequency change
rate detected by the frequency change rate detector 32 falls within
a narrow range close to zero. When it falls within the range, the
frequency change rate integration amount obtained by the frequency
change rate integration means 41 is reset to zero.
[0119] An operation of the above-described system interconnection
protective device according to the third embodiment will now be
described.
[0120] In FIG. 10, the reset means 61 determines whether the
frequency change rate falls within a small range close to zero. If
it falls within the narrow range, the reset means 61 issues a
command for resetting a frequency change rate integration amount to
the frequency change rate integration means 41.
[0121] It is thus possible to prevent the amount of integration of
frequency change rates from continuing to increase in accordance
with a slow change of the frequency of the private generator set
that is interconnecting with the system. It is also possible to
prevent a bias signal .DELTA.V*2 from issuing from the bias means
43 to the polarity other than the direction of frequency variation
when the private generator set shifts to its sole operation.
[0122] Moreover, the issuance of the bias signal .DELTA.V*2 from
the bias means 43 can suppress an increase in cross current of
reactive power and a change in voltage.
[0123] In the above-described system interconnection protective
device according to the third embodiment, the amount of integration
of frequency change rates is reset to zero when the frequency
change rate of the private generator set 10 falls within a narrow
range close to zero.
[0124] The amount of integration of frequency change rates can thus
be prevented from continuing to increase in accordance with a slow
change of the frequency of the private generator set that is
interconnecting with the system. Furthermore, the bias means 43 can
be prevented from applying a bias to the polarity other than the
direction of frequency variation when the private generator set
shifts to its sole operation.
[0125] Moreover, the application of the bias from the bias means 43
during the interconnection of the private generator set can
suppress an increase in cross current of reactive power and a
change in voltage.
[0126] FIG. 11A is a block diagram showing a main part of a system
interconnection protective device for a generator set according to
a fourth embodiment of the present invention.
[0127] In FIG. 11A, the same constituting elements as those in
FIGS. 2 and 8 are indicated by the same reference numerals and
their descriptions are omitted. In other words, only different
constituting elements will be described hereinafter.
[0128] The system interconnection protective device shown in FIG.
11A differs from the devices shown in FIGS. 2 and 8 in the
following points.
[0129] The device illustrated in FIG. 11A is achieved by newly
adding an excessive frequency change rate integration detector 62
and an OR circuit OR to the devices shown in FIGS. 2 and 8.
[0130] The detector 62 detects whether the frequency change rate
integration amount supplied from the frequency change rate
integration means 41 exceeds a set value. If the amount exceeds the
set value, the detector 62 outputs a signal indicative of the
excessive amount.
[0131] The OR circuit OR receives a detection signal from the
excessive frequency change rate detector 33 and a detection signal
from the excessive frequency change rate integration detector 62,
and supplies the trip circuit 23 with an OR signal of both the
detection signals as an abnormal output signal V31.
[0132] An operation of the above-described system interconnection
protective device according to the fourth embodiment of the present
invention will now be described.
[0133] In FIG. 11A, the excessive frequency change rate integration
detector 62 detects whether the frequency change rate or the
frequency change rate integration amount becomes excessive on the
basis of both the detection signals from the detectors 33 and 62.
When the detector 62 detects that the rate or amount becomes
excessive, it supplies an abnormal output signal V31 to the trip
circuit 23.
[0134] In the above-described system interconnection protective
device according to the fourth embodiment, the private generator
set 10 is disconnected from a system bus when the frequency change
rate or frequency change rate integration amount of the private
generator set 10 exceeds a certain value.
[0135] Consequently, the sole operation of the private generator
set 10 that is interconnecting with the system can be detected and
protected more reliably and easily on the side of the private
generator set 10.
[0136] (Modification)
[0137] FIG. 11B is a block diagram showing a main part of a system
interconnection protective device for a generator set according to
a modification to the present invention.
[0138] In FIG. 11B, the same constituting elements as those in
FIGS. 2 and 8 are indicated by the same reference numerals and
their descriptions are omitted. In other words, only different
constituting elements will be described hereinafter.
[0139] The system interconnection protective device shown in FIG.
11B differs from the devices shown in FIGS. 2 and 8 in the
following points.
[0140] The device illustrated in FIG. 11B is achieved by newly
adding an excessive frequency change rate integration detector 62
and an AND circuit to the devices shown in FIGS. 1 and 7.
[0141] The detector 62 detects whether the frequency change rate
integration amount supplied from the frequency change rate
integration means 41 exceeds a set value. If the amount exceeds the
set value, the detector 62 outputs a signal indicative of the
excessive amount.
[0142] The AND circuit AND receives a detection signal from the
excessive frequency change rate detector 33 and a detection signal
from the excessive frequency change rate integration detector 62,
and supplies the trip circuit 23 with an AND signal of both the
detection signals as an abnormal output signal V31.
[0143] An operation of the above-described system interconnection
protective device according to the modification to the present
invention will now be described.
[0144] In FIG. 11B, when the excessive frequency change rate
integration detector 62 detects that the frequency change rate and
the frequency change rate integration amount becomes excessive on
the basis of both the detection signals from the detectors 33 and
62, it supplies an abnormal output signal V31 to the trip circuit
23.
[0145] In the above-described system interconnection protective
device according to the modification, the private generator set 10
is disconnected from a system bus when the condition of AND that
the frequency change rate of the private generator set 10 and the
frequency change rate integration amount thereof exceeds a certain
value is satisfied.
[0146] Consequently, the sole operation of the private generator
set 10 that is interconnecting with the system can be detected and
protected more reliably and easily on the side of the private
generator set 10.
[0147] According to the system interconnection protective device
described above, the sole operation of a private generator set that
is interconnecting with a system can be detected and protected more
reliably and easily on the side of the private generator set
without providing any expensive transfer breaker.
[0148] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *