Electricity: single generator systems – Automatic control of generator or driving means – Antihunting or rate of change
Reexamination Certificate
2000-07-13
2002-01-08
Ramirez, Nestor (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Antihunting or rate of change
C322S006000, C322S020000
Reexamination Certificate
active
06337561
ABSTRACT:
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 10-005043, filed Jan. 13, 1998, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention generally relates to a generating system interconnected to a power system. More particularly, it relates to a stabilizing apparatus to be incorporated into the magnetic excitation control system of a rotating type generator such as an alternator and designed to attenuate power fluctuations and enhance the stability of the power system.
Magnetic excitation systems for exciting field circuits of generators such as alternators that are rotating type generators can be generally and roughly classified into AC excitation systems, DC excitation systems and static excitation systems. The AC excitation system uses an AC exciter. The DC excitation system uses a DC exciter. The static excitation system uses a semiconductor switching element such as a thyristor.
A thyristor excitation system, which is a typical static excitation system being popularly used at present as excitation system, will be described below. Also, a power stabilizing system (PSS) adapted to be used in a thyristor excitation system will be explained.
FIG. 1
is a block diagram of an excitation system using a conventional PSS that can effectively attenuate power fluctuations of generator mode (power fluctuations of a short cycle of about 1 to 2 seconds).
As shown in
FIG. 1
, the generator excitation control system receives an input an AVR reference voltage
2
(hereinafter referred to as “
90
OR”) and the output of transformer
3
(hereinafter referred to as “PT”) operating an instrument to an automatic voltage regulator
4
(hereinafter referred to as “AVR”) in order to maintain at a constant value the terminal voltage of generator
1
connected to a turbine T. The AVR reference voltage
2
serves to establish a generator voltage. The potential transformer
3
detects the generator voltage. The AVR
4
operates to control the generator voltage.
PSS
5
is provided to produce the generator
1
operate on a stable basis. The output signal of the PSS is input to the AVR
4
and used in the operation of controlling the generator voltage. The field voltage of the generator
1
is thereby regulated to control the transient active power of the generator
1
in order to suppress power fluctuations.
An excitation transformer
6
is arranged to get an excitation source out of the voltage of the generator
1
. The output voltage of the excitation transformer
6
is input to a thyristor bridge
7
. The field voltage of the generator
1
is modified to regulate the generator voltage according to the value set by said
90
R
2
by controlling the ignition angle of the thyrister bridge
7
.
The PSS
5
, which is currently commercially available, detects the active power P
8
of the generator
1
from the generator voltage detected by the PT
3
and the generator current detected by the CT. The PSS
5
then detects and calculates a change &Dgr;P in the active power P
8
, a change &Dgr;&ohgr; in the rotational speed &ohgr;
9
of the rotor of the generator
1
, or a change &Dgr;f in the generator voltage frequency corresponding to the change in the system side frequency (not shown). The PSS may use one of these signals or two or more of the signals (hereinafter referred to as “multivariable PSS”).
Of multi-variable PSSs, those of the type that use the change &Dgr;P in the active power of the generator
1
as input and have an appropriate stabilization function (hereinafter referred to as “&Dgr;P-PSS”) are most widely used at present.
The reason for this is that the change in the active power of the generator can be electrically detected and a stabilization function can be set into the PSS with ease because the PSS does not require phase compensation as much as a PSS (hereinafter referred to as “&Dgr;&ohgr;-PSS”) that uses the change &Dgr;&ohgr; in the rotational speed &ohgr;
9
of the rotor of the generator
1
as input, although the latter also has an appropriate stabilization function.
The multi-variable PSS
5
shown in
FIG. 1
is a typical PSS adapted to cover a broader frequency band subject to power fluctuations than a &Dgr;P-PSS and a &Dgr;&ohgr;-PSS as it comprises both a &Dgr;P-PSS and a &Dgr;&ohgr;-PSS that can effectively suppress power fluctuations. This is why such a multi-variable PSS (hereinafter referred to as “(&Dgr;P+&Dgr;&ohgr;)-PSS” is used for a thyristor excitation system.
There are PSSs of other types that may also be used for thyrsitor excitation systems, including one (hereinafter referred to as “&Dgr;f-PSS”) that uses a frequency signal representing either the voltage or the current of the generator
1
as input and also has an appropriate stabilization function) and one (hereinafter referred to as “(&Dgr;P+&Dgr;&ohgr;)-PSS”) that comprises both a &Dgr;P-PSS and a &Dgr;&ohgr;-PSS.
Various PSSs as described above may also be used for AC/DC excitation systems.
The excitation system further comprises an excessive-excitation limiting device for preventing excessive excitation of the generator
1
, an inadequate-excitation limiting device for limiting inadequate excitation of the generator
1
, a V/F controlling device for excessive excitation of the exciting transformer
6
or the armature winding of the generator
1
, and the like, where V represents the generator voltage and F represents the generator frequency.) However, these devices do not exert any direct influence on the operation of the PSS
5
and, therefore, only the AVR
4
and the PSS
5
are discussed here in detail.
Both analog hardware and digital hardware are commercially available. The AVR
4
and the multi-variable PSS
5
are applicable to hardware of either type in functional terms.
While various types of excitation systems are available as pointed out above, the one shown in
FIG. 1
is of the type that is mainly used at present. Therefore, the prior art technologies will be discussed below by way of this excitation system.
FIG. 2
is a block diagram of a conventional AVR
4
, illustrating its configuration. Referring to
FIG. 2
, PSS output signal
5
A of multi-variable PSS
5
is input to the AVR
4
. Adder A
1
adds the PSS output signal
5
A to the outcome of the computation for determining the deviation of the generator voltage Vg
3
A as detected by PT
3
from the
90
R
2
. The signal &Dgr;V
70
obtained as a result of the addition is input to a voltage control section
11
operating on the basis of a gain and an advance/delay to be used to stabilize the voltage control loop.
The output of the voltage control section
11
is equivalent to the field voltage Efd
12
of the generator
1
.
FIG. 3
is a schematic block diagram of a known multi-variable PSS
5
. As shown in
FIG. 3
, the change −&Dgr;P in the active power is made to pass through a stabilization function Gp(S)
13
, while the change Aco
9
A in the rotational speed &ohgr;
9
of the generator
1
is made to pass through a stabilization function Gw(S)
14
before they are added by adder A
2
. The sum of the addition is input from an output limiter
15
to the AVR
4
as PSS output signal
5
A. The stabilization functions Gp(S)
13
and G(w)
14
can remove noise from the input signal by passing the latter through a reset filter
16
, an advance/delay circuit
17
and a limiter
18
, as shown in FIG.
4
.
Due to the above described functional features, the multi-variable PSS
5
can eliminate any steady-state deviations for AVR control that arises when no power fluctuation occurs and correct the phase to output an appropriate voltage regulating signal.
Meanwhile, in recent years, the stability of power system is threatened than ever as the power system increases in scale. As a result, there occur not only local fluctuations that have been a main problem and are short-cycle fluctuations lasting for about 1 second but also inter-system fluctuations that are long-cycle fluctuations lasting for about 2 to
Andou Mikihito
Fukushima Nobuo
Hirayama Kaiichirou
Kawasaki Mamoru
Mitani Yoshinobu
Chubu Electric Power Co., Inc.
Gonzalez Ramirez Julio
Ramirez Nestor
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