Power plants – Combustion products used as motive fluid – Combined with regulation of power output feature
Reexamination Certificate
2002-02-05
2004-04-13
Koczo, Michael (Department: 3746)
Power plants
Combustion products used as motive fluid
Combined with regulation of power output feature
Reexamination Certificate
active
06718749
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a speed control apparatus of a combined cycle power generation plant.
2. Description of the Related Art
As a power generation system, a combined cycle power generation plant is known. The control of the combined cycle power generation plant is achieved by a gas turbine control system. A control logic circuit is incorporated in the gas turbine control system to output a gas turbine load instruction. Such a control logic circuit is shown in FIG.
1
. Referring to
FIG. 1
, the control logic is composed of a load limit control circuit
101
, a speed governor control circuit
102
, a temperature limit control circuit
103
and a fuel limit control circuit
104
. The load limit control circuit
101
outputs a load limit control signal (LDCSO)
105
. The speed governor control circuit
102
outputs a speed governor control signal (GVCSO)
106
. The temperature limit control circuit
103
outputs a temperature limit control signal (TCSO)
107
. The fuel limit control circuit
104
outputs a fuel limit control signal (FLCSO)
108
. Of the signal lines in the figure, the broken line shows a digital signal and the solid line shows an analog signal.
A minimum level selector
109
is supplied with the load limit control signal
105
, the speed governor control signal
106
, the temperature limit control signal
107
, and the fuel limit control signal
108
. The minimum level selector
109
selects a signal with a minimum level L< from among the above-mentioned four control signals
105
,
106
,
107
and
108
and outputs it as a final fuel control output signal (CSO control signal)
110
. The final fuel control output signal
110
is a control signal to control a fuel quantity supplied to the gas turbine
111
.
A house load operation signal
112
and an over-speed protection control (OPC) operation signal
113
which is sent from an over-speed protection control circuit are supplied to the load limit control circuit
101
. The house load operation signal
112
and the over-speed protection control signal
113
are supplied to a logical summation (OR) unit
114
. A one-shot timer
115
outputs a signal
116
for a predetermined time period in response to the signal outputted from the logical summation unit
114
. The control output signal (CSO)
117
is further supplied to the load limit control circuit
101
. The control output signal
117
is supplied to a function value unit
118
and an adder
119
. The function value unit
118
converts the control output signal
117
into a value signal. The adder
119
adds the control output signal
117
and the value signal from the function value unit
118
. A signal obtained by the addition in the adder
119
is supplied to a rate-added switching unit
120
in which a rate is switched at the same time as a switching operation, in addition to a constant time signal
116
. The switching unit
120
outputs not an addition value obtained by the addition in the adder
119
but a signal with a value set by a constant value unit
121
as the load limit control signal
105
in response to the signal
116
for the predetermined time period.
The house load operation signal
112
′, a variable value signal (SPSET)
122
which indicates the difference of a load set value and an actual load value, and an axis rotation frequency signal
123
are supplied to the speed governor control circuit
102
. The house load operation signal
112
′ and the variable value signal
122
are supplied to a proportional integrator
124
. The proportional integrator
124
integrates the variable value signal
122
proportionally to produce an integration value output signal
126
. Also, the proportional integrator
124
outputs a constant value signal of 0 which is set to a constant value unit
125
in response to the house load operation signal
112
′. A subtractor
127
subtracts the axis rotation frequency signal
123
from the integration value output signal
126
to produce a subtraction Resultant signal
128
. The subtraction resultant signal
128
is amplified by an amplifier
129
and is outputted as the above-mentioned speed governor control signal
106
.
FIG. 2
shows the control logic of the over-speed protection control (OPC) circuit. The rotation frequency signal
131
of the gas turbine
111
, an entrance pressure signal
132
in a middle-pressure turbine of the gas turbine
111
, a generator current signal
133
, and a generator output signal
134
are supplied to function value units
137
,
138
,
139
, and
140
to convert the physical quantities of them into percentage values, respectively. A generator breaker-on signal
135
is supplied to an inverter (NOT) unit
130
. A house load operation switching signal
136
is supplied to a one-shot timer
152
. The middle-pressure turbine entrance pressure signal
132
and the generator current signal
133
are supplied to a subtractor
142
through the function value units
138
and
139
. The subtraction value obtained by the subtractor
142
or, a load difference signal
143
is supplied to an adder
145
through the other function value unit
144
. The rotation frequency signal
131
is supplied to the adder
145
through the function value unit
137
. The addition value
146
obtained by the adder
145
is supplied to a monitor unit
147
which sends a digital signal based on an optional setting range. The generator output signal
134
is supplied to a logical product (AND) unit
149
through a function value unit
140
, a monitor
141
, and an off-delay timer
148
. The generator breaker-on signal
135
is supplied to the logical product unit
149
through the inverter unit
130
. A monitor signal
150
-
1
outputted from the monitor unit
147
, a signal
150
-
2
outputted from the logical product unit
149
and a signal
150
-
3
outputted from the one-shot timer
152
are supplied to a logical summation (OR) unit
151
. The output signal outputted from the logical summation unit
151
is the above-mentioned over-speed protection control signal (OPC signal)
113
shown in
FIG. 1
for the OPC operation.
The over-speed protection control (OPC) circuit has the control logic shown in
FIG. 2
, and is a protection unit of the gas turbine
111
from over-speed trip which occurs when the turbine
111
is accelerated rapidly in case of rapid load decrease due to load blocking-off and so on. The over-speed protection control (OPC) circuit monitors the speed increase rate as the output signal of the function value unit
137
and the load difference as subtraction value
143
. When the value obtained by adding a bias (preceding) signal based on the load difference to the turbine rotation speed increase rate is larger than a threshold value set in the monitor unit
147
, the over-speed control (OPC) operation is carried out to close a turbine governor rapidly.
In the above conventional apparatus, there is a case that the OPC operation is not carried out because the switching to a system isolated operation is carried out but a system load loss is small. In such a case, the final fuel control output signal (CSO control signal)
110
is limited based on the load limit control signal
105
which follows a change rate which is determined from the viewpoint of the gas turbine protection or the control signals such as the temperature limit control (TCSO) signal
107
. Also, the time period appears during which the axis rotation frequency control cannot be carried out based on the speed governor control (GVCSO) signal
106
. At that time, the phenomenon occurs where the rotation frequency decreases largely from a rating range of the rotation frequency, and the trip is caused. Also, when the variable value signal
122
is determined from the difference of a load set value and an actual load value after the switching to the system isolated operation, the variable value signal
122
and the integration value signal
126
change based on an erroneous load set value regardless that the load is not clear. Therefore, there is f
Nagata Shouichi
Saitoh Akihiko
Sonoda Takashi
Tateishi Teruo
Koczo Michael
Mitsubishi Heavy Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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