Energy and Power E ngineering, 2013, 5, 319-323
doi:10.4236/epe.2013.54B063 Published Online July 2013 (http://www.scirp .o rg/journal/epe)
Copyright © 2013 SciRes. EPE
Study on Valve Management of DEH for Steam Turbine*
Changjie Yin, Jizhen Liu
The State Key Lab of Alternate Electr ical Power System with Renewable Energy Sources,
North China Electric Power University , Beijing, China
Email: m
Received March, 2013
Valve management is one of the major functions of DEH for steam turbine. It has an important practical significance for
the security and economy of the steam turbine. This paper starts from the valve configuration figure of the domes-
tic-type 300 MW steam turb in e , a nd then makes a simple comparison between the two types of valve gove r ning mo des.
In order to realize the valve co ntrol, the structure of control system has been established, in which the roles of the ma-
thematical functions are discussed. On the basis of the experiment of valve flow characteristic, thi s article carries out a
quantitative study on the functions of the valve management and the parameter tuning method. Through a serious cor-
rections, the sequence valve flow characteristic curve is obtained, which can provide significant guidance on the re-
search of valve manageme nt o f the similar steam turbines.
Keywords: Valve Mana gement; Steam T urbine ; Digital Ele c tr o-Hydraulic Control System; Valve Flow Characteristic
1. Introd uction
As one of the three main units in thermal power plant,
steam turbine, whose rotor is in High-speed rotation
under high temperature and high pressure steam, com-
pletes the conversion of heat energy to mechanical en-
erg y, wh il e d r a ggi n g t he ge ne r at or so that the mechanical
energy into electricity. Electric power system raises two
basic requirements on steam turbines used for power
generation of electricity: one is guaranteed to meet the
electricity needs of users at any time; the other is to en-
able the roto r to maintain in a certain speed, to e ns ur e t he
stab ili t y o f freq uenc y o f power gri ds and the sa fe t y of t he
steam turbine it self [1].
For variable load of constant pressure operation unit,
the rotor speed and power regulation are achieved by
changing the flow of steam. Steam volume changes can
be adjusted by changing the number of opened valves
and controlling the inle t area of the valve s [2]. There are
two types of governing modes in steam turbine, single
valve (throttle governing) mode and sequential valve
(nozzle governing) mode. When the steam turbine oper-
ates in single valve mode, the regulation performance of
steam turbine is much better, but the throttle loss is seri-
ous; when in sequential valve mode, the valves can be
adjusted to reduce the throttle loss, to improve the
efficiency of the steam turbine, but the flexibility of reg-
ulation performance is reduced. The appropriate valve
controlling mode can improve the control quality and
regulation performance of the steam turbine, thereby
cutting down on coal consumption needed for power
gener ation [3].
The Digital Electro-Hydraulic Control System (DEH),
whic h is t he be st s yste m for valve mana ge ment, has b ee n
installed in almost all 300600 MW steam turbines of
Thermal Power Plants in China. DEH can switch be-
tween the two types of governing modes, whose essence
is to achieve undis tr ib uted shift between throttle regula-
tion and nozzle regulation, thus making steam turbine to
achieve i ts best running sta te. This article analyzed the
valve mana gement of DEH co ntrol system of the domes-
tic-type 300 MW steam turbine, describing the function,
principle and parameter tuning method of valve control.
2. The Overview of Valve Control
2.1. The Valve Configuration Structure
For one example generation unit, the domestic-type 300
MW steam turbine is a subcritical two-cylinder, two
exhausts reheat condensing steam turbine manufactured
by Dongfang Steam Turbine Company Limited. The
nozzle group layout of control stage of N300-16.7/
537/537 steam turbine is shown in Figure 1. It has two
high pressure main stop valves (MSV) and four high
pressure main steam regulating valves (GV). The nozzle
number of four nozzle groups is different, GV1 valve
controls the number of nozzles 32; GV2 valve controls
*This work was supported by the National Basic Research Pro
gram of
China (“973” Program) (Grant No. 2012CB215203) and the Na
Natural Science Foundati on of China (Grant No. 51036002 ).
C. J. YIN, J. Z. LIU
Copyright © 2013 SciRes. EPE
the number of nozzles 32; GV3 valve controls the num-
ber of nozzles 30; GV4 valve controls the number of
nozzles 27. Whe n the ste am t urb ine i s in a normal opera-
tion, the main st op val ves are fully opened and the steam
flow is controlled by the four contro l valves.
2.2. Comparison of the Single Valve Mode and
Sequence Va lve Mode
For the constant pressure operation of power generation
units, steam turbine regulation is mainly to regulate the
speed of rotor and the power of generator, which are
achieved by regulating the steam flow. The amount of
inlet flow is altered by changing the number of opened
valves and va l ve op e nin g, namel y c ha ngi n g the to ta l inl e t
area of steam turbine. Therefore, depending on how to
change the inlet area of valves, we can divide the control
mode into two types: single valve mode and sequential
valve mode, which have their own advantages and dis-
Single valve control means that all the control valves
accept a valve control signal to make the valves turn up
or down at the same time, which is characterized by the
throttle adjusting and full arc admission. The cylinder
rotor heat expansion is uniform and the metal tempera-
ture of different steam turbine parts is in a stable condi-
tion, making the unit withstand greater load change rate.
But because all of the adjustment valves are not in the
fully opened state, the valves have a great throttle loss,
reducing t he thermal efficiency of t he unit.
Sequence valve control means that the control valve
turns on o r off ind ividual ly along wit h the rotor speed or
turbine load changing, which is characterized by the
nozzle adj usting and partial arc admissio n. That is to say,
at any time only one steam valve is in a non-fully open
state while the o t her val ve s a r e in full y op e n state o r full y
closed state. This control mode reduces the throttling
losse s and ther eb y i mproves the the rmal e f ficie nc y of t he
stea m turb ine. B ut because the position of the stea m inlet
is asymmetric, the cylinder rotor heat expansion is un-
even and the metal temperature difference of different
steam turbine parts is rather large, and the unit ca nnot
withstand greater load change rate.
Figure 2 is the 300 MW units thermal efficiency
curve of si ngle valve control and sequence valve control.
When the load percentage is 60%, sequence valve mode
can improve thermal efficiency by about 3%.
3. The Principle of the Valve Control
The function of valve control is to transfer the required
flow into the degree of valve opening. In order to realize
the function, there are several mathematical functions
used to correct the flow and distributing it among the
four valves. For a valve, the valve control structure is
shown in Figure 3, in which the roles of functions are
explained as follows.
3.1. Flow Pressure Correc tion Fun ct ion f(x1) and
and 4
fx are correction functions
between the unit’s theoretical demand flow and the
actual demand flow. Under low load condition, actual
demand flo w is equal to the theoretical demand flo w. But
as the load increases, the pressure of steam turbine
governing stage rises and its actual amount of steam
decreases although under the same valve opening. That is
to say actual demand flow is higher than the theoretical
demand flow. Therefore, the functions are used for
amending the flow directive at different load levels, to
ensure the consistency of the theoretical flow and the
actual flow.
Main stream
Bottom part
Figure 1 . The nozzle gro up s s t ructure chart of control st age.
55 60 65 70 7580 85 9095100
Load perc ent age (%)
Thermal eff i ci ency (% )
Sequence valve mode
Si ngl e valve mode
Figure 2. Ther mal efficiency comparison chart.
valve mode
Single valve mode
Figure 3. Func tional s tructure of valve c ontrol system.
C. J. YIN, J. Z. LIU
Copyright © 2013 SciRes. EPE
3.2. Flow Proportion and Bias Factor K + B
When the steam turbine is under single valve control, all
the valves are directly controlled by the flo w instr uction,
so proportion and bias factor are not needed. When the
steam turbine is under sequen ce valve control, the valves
are opened one by one, so it need to give each valve the
proportion and bias factor, to ensure that the valve is
opened according to the designed order.
3.3. Valve Overlap Correction Function f(x2)
In the sequence valve control mode, the valves are se-
quentially opened. If a valve is opened after the full
opening of another, the relationship between the total
valve lift and flo w is squiggle according to a single val ve
characteristic [4]. In order to ma ke the c urve line ari sm, it
is needed to open the next valve in advance before the
previous valve being fully opened. How much the next
valve is opened is controlled by2
fx .
3.4. Valve Flow Characteristic Curve f(x3)
Valve flow characteristic curve, which convert the flow
instruction into the valve opening instr uction, is the one-
to-one correspondence between the valve opening and
steam flow through the valve. The curve is determined
by the physical characteristics of the valve, such as valv e
lift and valve area.
3.5. The Undisturbed Switch between Single and
Sequence Va lve Mode
During unit start-up and load changing, the valve man-
agement in the control system is set at single valve con-
trol mode to ensure full arc steam admission around the
nozzles to achieve uniform heating and reduce thermal
stress. Under stable load operation, the system is shifted
into sequence valve contro l mode to reduce the thro ttling
loss caused by full arc steam admission and improve the
thermal efficiency. In order not to affect the stability of
the unit output, the switching process must be smoothly
operated without any perturbations. One of the excellent
features of DEH is the undisturbed switch between the
two steam governing methods.
First l y, va l ve ma na ge me n t p r ogram calc ul ates the fi nal
flow for each valve under the two control modes at the
same ti me. Whe n the mod e is switc hed fro m sin gle va lve
mode to sequence valve mode, the final flow of each
valve calculated under single valve mode is changed to
the final flow calculated under sequence valve mode in a
certain rate, and as a result, the opening of each valve is
approaching to the position required by sequence valve
mode. The switching process is completed after all
valves reaching their required opening position. During
the conversion process, some valves must be opened in-
creasingly, while the others closed gradually. At any
moment throughout the process, increased flow and de-
creased flow should be equal, so that the total flow re-
mains unchanged. Thus, the load of power unit in the
conversion process will not be affected, but thermal
efficiency is higher than in the sequence valve control
mode, so electric power will increase after the switching.
When the sequence valve control is switched to single
valve control, the process is reversed though the princip le
is the same,
Figure 4 is the switching logic between sequence
valve mode and single valve mode.
The switching logic is expressed as follows
112 2
µµ µ
= ×+×
whe r e
is the final degree of valve opening, 1
the degree of sequence valve opening, 2
is the degree
of single valve opening,
is sequence valve coeffi-
cient and 2
is single valve coefficient.
The relationship between the two coefficients is de-
scribed as follows
The essence of the switching process from single valve
mode to sequence valve mode is that the coefficient
transforms from 0 to 1 according to a certain rate while
transforms from 1 to 0 according to Equation (2). The
coefficient 2
variation wit h time is shown Figure 5 [5].
The switching rate is decided by the Division of logic
circuits: 0.2/120.In Figure 5, the period of logic circuits
is 0.2 seconds, so after 12 seconds, coefficient
comes 0.9; after 120 seconds, coefficient
becomes 0.
In order to make the switching process much more stable,
the denominator can be modified to 180, and then the
conversion time is extended to 180 seconds.
Figure 4 . Switching log ic.
Time (s)
Figure 5 .Coefficient2
variation with time.
C. J. YIN, J. Z. LIU
Copyright © 2013 SciRes. EPE
4. Parameter Tuning of Valve Control
In Figur e 3,
, 3
fx and 4
fx are decided by
the attribute of the steam turbine, so generally, they are
provided by the steam turbine factory. Therefore, this
article only discusses sequence valve control parameter
In this mode, the given flow value of FDEM firstly is
amended by flow pressure correction function
flow proportion and bias factor
, valve overlap
correction function 2
fx , and then through valve flow
characteristic curve 3
fx , turned into the final valve
opening instruction. The experiment of valve flow cha-
racteristic was carried out in the 300MW capacity steam
turbine. Much more details about the tests can be found
in [6].The experimental data after processed is as shown
in Table 1.
4.1. Flow Pressu re Cor rec tion Fun ct ion f(x1)
, provided by the turbine manufacturer, is
set as shown in Table 2.
4.2. Flow Proportion and Bias Factor K + B
K and B are determined by the design flow rate and the
opening sequence of the valve. When the ste a m t urb ine is
in sequential valve operation, GV1 and GV2 are opened
at the same time while GV3 and GV4 opened in se-
quence order under the consideration of degree of over-
According to the design data, when FDEM is 0% (the
value is 0% af ter a mend ed by f unctio n 1
fx ), the flow
instructions of GV1 and GV2 are 0%; when FDEM is
78.7% (the value is 80.3% after amended by function
fx ), the flow instructions of GV1 and GV2 are 100%,
that is to sa y, the two valves are opened fully. So by the
following for mula:
100 80.3
= ×+
One can get the result:
1.239, 0KB= =
GV3 is opened after GV1 and GV2 fully opened. So
whe n FDEM is 7 6. 3% ( the va lue is 77.5% after amended
by function
), the flow instruction of GV3 is 0%;
when FDEM is 93.3% (the value is 107.1% after
amended by function 2
fx ), the flow instruction of
GV3 is 100%, that is to say, GV3 is opened fully. So by
the followin g formula:
0 77.5
100 107.1
Table 1. Valve flow characteristic test data u nder sequence valve mode.
Instructio n
(M W)
Main stream
Press ure af ter
regulating stage
The opening instruction
of GV1 and GV2
The opening
instruction of GV3
The opening
instruction of GV4
68.0 184.4 15. 411 7.450 39.2 0.1 -0.2
68.2 188.7 15. 354 7.674 40.3 0.6 -0.2
68.6 199.6 15. 504 8.252 42.8 1.8 -0.2
69.2 214.8 15. 617 8.851 45.8 3.3 -0.2
70.1 225.3 15. 630 9.311 51.0 6.0 -0.2
71.1 232.0 15. 379 9.478 56.5 8.5 -0.2
72.1 237.0 15. 421 9.686 62.1 11.0 -0.2
73.1 237.8 15. 379 9.762 67.2 11.4 0.0
75.1 241.9 15. 298 9.846 78.7 12.1 0.0
77.1 244.9 15. 454 9.990 88.7 12.8 0.0
79.1 247.3 15.548 10.080 98.0 13.7 0 .0
81.1 246.4 15. 561 10.084 98.0 15.6 0.0
83.1 247.3 15. 454 10.152 98.0 18.2 0.0
85.1 250.8 15. 292 10.292 98.0 20.5 0.0
87.1 257.7 15. 304 10.631 98.0 24.3 0.0
88.1 275.3 15. 461 11.319 98.0 32.6 9.9
88.5 280.4 15. 461 11.557 98.0 36.0 10.0
90.5 283.0 15. 398 11.720 98.0 56.3 11.0
92.5 284.6 15. 392 11.765 98.0 84.2 12.3
95.0 285.8 15. 411 11.844 98.0 98.0 16.1
97.0 287.2 15. 173 11.924 98.0 98.0 21.4
98.0 288.7 15. 066 12.016 98.0 98.0 25.9
99.0 290.0 14. 960 12.137 98.0 98.0 34.0
100.0 294.2 14.972 12.332 98.0 98.0 98.0
C. J. YIN, J. Z. LIU
Copyright © 2013 SciRes. EPE
Table 2. The functional settings of flow pressure correc-
Flow instruction (%) Flow instruction after amended (%)
0 0
60.011 60.011
71 71.428
74 74.732
79 80.686
86 90.928
100 122.025
020 40 60 80 100 120
Flow instr uc tion (%)
The degree of valve opening (%)
the c urve of GV1 and GV2
the c urve of GV3
the c urve of GV4
Figure 6 .Valve flow charact eristic cur ve.
One can get the result:
3.378, 261.8KB== −
GV4 is opened after GV1, GV2and GV3 fully opened.
So when FDEM is 91.6% (the value is 103.4% after
amended by function
), the flow instruction of
GV3 is 0%; when FDEM is 100% (the value is 122%
after amended by function 2
), the flow instruction
of GV3 is 100%, that is to say, GV4 is opened fully. So
by the following formula:
0 103.4
100 122
One can get the result:
5.376, 555.9KB== −
4.3. Valve Overlap Correction Function f(x2)
Generally speaking, when the ratio between the main
stream pressure and the stream pressure in the back of
the previous valve is 0.85~0.9, the next valve starts to
open. In this paper, based on observing the test data of
Table 1, the degree of valve overlap is obtained by the
graphing method [4].
Through the above corrections, the final valve flow
characteristic curve is shown in Figure 6.
5. Conclusions
Valve management is an important aspect of Digital
Electro-Hydraulic Control System, which is directly re-
lated to the security and economy of unit operation. This
article analyzed the DEH control system of the do mestic
type 300 MW steam turbine, described the function,
principle and parameter turn method of valve control,
and finall y obtained the valve flow characteristic curve in
sequence valve mode. The study in this paper can pro -
vide significant guidance on the research of valve man-
age ment of the similar steam turbine.
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