DEH Control Function

Control Principles And

Function Design

Shanghai CAC,2009
 A. Principle Of
Rotating Speed Control
1. Target, setting value, real value, speed rate

ws
Target：ws1, ws2
ws2 Setting value：ws0
ws0
Real value：ws
Speed rate：slope of the curve
ws1
where the setting value varies
from ws1 to ws2
t

Ws0 is the set point of speed at current time

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2. Loop of rotating speed control
Physical meaning of each point：
WS0：speed setting
WS0
WS： real speed
WSdev: deviation of speed
WS
△ Gref：reference of main steam flow
WSdev GVcmd：GV openness command
D
F1(X)：single valve characteristic of GV
K ∫ ─
Dt

Gref

F1(X)

GVcmd

Notes: This loop cannot be released by operator.

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B. Principle of Load Control
1. Target, setting value, real value, load rate

MW
Target：MW1, MW2
MW2
Setting value：MW0
Real value：MW
MW0 Load rate：slope of the curve
MW1 where the setting value varies
from MW1 to MW2
t

MW0 is the set point of speed at current time

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2. Loop of load control
MW00
（DEHor
CCS）
Physical meaning of each point：
F0
F0 Σ
MW01
MW0：load setting
F
△ F T
MW： real load
Sec freqFdev
△
Pri freq MWdev: deviation of load
Fdev
regulating loop
D
regulating loop MW
△ IMP0：impulse pressure setting
K ∫ ─
Dt F3(X)
MW loop MWdev IMP：real impulse pressure
DW2 DW1
K ∫
D
─
Dt
IMPdev: deviation of impulse pressure
Σ
IMP0
F0：rating grid frequency
IMP
△
F：real grid frequency
IMP loop
IMPdev Fdev：deviation of grid frequency
K ∫
D
─
F3(X)：primary frequency regulating
characteristic of the turbine
Dt

Gref
Gref：reference of main steam flow
F1,2(X) GV1 cmd
GV2cmd GVcmd：GV openness command
GV3cmd
GV4cmd F1,2(X)：single valve or sequence
∆N %
valve characteristic of GV
100

-150
∆n
150 rpm
0

-100
Notes: IMP loop, MW loop and Primary
frequency regulating loop can be taken or
released by operator. GE job title/7
3. Load and impulse pressure
characteristics of turbine
MW
• Turbine load characteristic curve
• Turbine impulse pressure
characteristic curve
• Features and usage

Proportional with the main steam
G flow

MW loop and IMP loop constitute a
IMP
serial regulating loop, improving
the quality of load control.

Load increment is also proportional
with the flow increment

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4. Primary frequency regulation
characteristics of turbine
Features and usages
∆N %

• Frequency deviation indicates the

100
unbalance degree of load-power in the
electrical grid. Turbine automatically
-150
150
∆n regulates its power output in order to
rpm
0 compensate such an unbalance. This is
-100
called as the frequency regulation.
• On one hand, DEH positions the valve
proportionally according to the unit droop;
while on the other hand, it has adjustable
∆n / n 0 frequency dead range and upper/lower
δ= × 100% load limit
∆N / N 0

3～7％ adjustable droop

Setting up upper/lower dead range

Continuous dead range
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5. Valve characteristics of the turbine
• Single valve characteristic of GV
• Sequence valve (multi-valve)
characteristic of GV
• Features and usages

Valve position is a function of
main steam flow

The function is nonlinear in the
whole area but linear in the
working area

Implying the condition that the
throttle pressure is rating value

Single valve and multivalve – two
operating mode
Notes: In order to ensure the load control stability, suitable superposition of valves
in multi-valve mode is needed. The superposition is flow but not valve position.
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6. Benefit Of Valve Management

When turbine is normal Operation

In partial load, multivalve has
lower heat rate or higher heat
efficient.

The lower is load, the bigger is
Heat Rate

the deviation between the two

mode.

For full load, the two mode has
same heat efficient.
When turbine is starting up

Single valve mode has lower
hot stress than multivalve.
Load Percent

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7. Open Loop Control Of Load
MW In many case , load control is located at
open loop status. Understanding some
features of such a control is important.
MW0 • Process: open the GV of turbine to the
related valve position V0 with MW0.
G • Phenomenon: load setting is different
with real load. Usually the deviation is
bigger.
• Reason: the throttle pressure is not
equal to the rating value. (The valve
V0 characteristic implies the condition
that the throttle pressure is rating)

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8. Secondary frequency regulation
The unit may be operated in isolated island or plant service (small scale grid). When
the grid frequency deviation exceeds the set value, DEH will automatically start
secondary frequency regulation, and increase the OPC protection setting from
103% to 107% upon synchronization.
n
%

107%
O P C acting area
105%

103%
Pri
Freq

IE P -M W
100%
30% 60% 100% dM W

P LU 、 107% acting area

Sec
103% acting area
Freq
Pri, Sec freq area
95%

SDP_T
SDP_S
Ref=3000 SDP_R
探头
-
WS1 + dn=0~1 1 107%
dn +
7% 0~1 1 OPC
IEP0 2/3
+ 1

P 1
P= IEP1 0~1 dMW PLU
P=
= + dMW dn
2/3
- 30% 60% OPC
107 动作
P
P= MW1 0~1 % 区域
UI=
=

100
MW0 % 30% 60% dMW
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C. Principle of Valve Position
1. VPC card principle

VPC DBG
DPU
DPU
调试软件

G V1 S P O R
G V1 S P O
VPC或BC
通讯断

手动钥匙
DPU
+ T 零
手动增 位
手动减 计数 和
输 输 满

G V1 S 1

G V1 S 2
入 出 度
偏 偏 调
LVDT1
偏置 比例 置 置 整 VPC _ TB
解调 P1

LVDT 2 +
解调 P2
智能 -
偏置 比例 选择
PID D/A
4-20mA P3
-

4- 20 mA P4 -100/+100
ASL 1
ASL 2 ASL
ASL 3 2/3 仿真
OPC OPC

伺服阀

阀门开度
D/A
4- 20mA

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 2. Control Loop Of Valve Position
GVcmd1
• This loop is realized in VPC
LVDT card
△
• Its role is to overcome the
GVdev inactivity of the oil driver.

D
• Meaning of s value
K ∫ ─
S value is a volt, standing for
Dt
the valve position regulating
GVcmd2 output.

volt ( S ) = current (regulating output ) ×

( solenoid resistence + line resistence)

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 D. Summary of Control Loops
From bottom to top, DEH has 6 loops:
•Control loop of valve position. Precisely control the GV position. It is the most
fundamental regulating loop and cannot be released, no matter whether DEH is
manual or automatic status.
•Control loop of rotating speed. Precisely control the rotating speed when turbine is
being impulsed to rotate. It is a fundamental regulating loop and can not be
released. It lose its role after turbine connects to grid.
•Control loop of impulse pressure. Coarsely regulate the load. It can play a role of
improving the load control precision when it is taken. It must be released if CCS is
taken.
•Control loop of load. Precisely load control. It must be released if CCS is taken.
•Primary frequency regulation. Compensate the unbalance between the power
and load of large scale grid, improving the quality of grid.
•Secondary frequency regulation. Compensate the unbalance between the power
and load of small scale grid, maintaining the stability of grid.
 E. Real Example
of
DEH Function Design
A. Speed Control
1. Auto. The DEH manual panel key is at Auto position. This means that the
FVcmd comes from DPU.
2. Latch. Close the resetting solenoid, resetting the turbine. Build up safe oil
pressure and open throttle valve to prepare for impulsing rotation- by
resetting emergency trip system
3. GV Control. Select the governing valve to control turbine.
4. Friction Check. During the startup of the turbine, it is required to check
turbine rotation and monitor metering system whether there are abnormal
conditions under low speed to ensure safe operation of the turbine. DEH is
designed with a friction check function, which will make DEH automatically
impulse the turbine to 500 ~ 600rpm via a button, and automatically close
the governing valve 2 ~ 5 minutes later, allowing the operator to check
operational conditions.
• Raising speed to 500 rpm
• Last 120 S, then automatically release or click button to release manually.

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A. Speed Control
5. Raising Speed and Pass Through the Critical Speed Area. DEH automatically checks if the
speed ranges within shaft critical speed, and will automatically disallow the turbine to keep
in this range and pass through it with the preset high speed rate to prevent the turbine from
excessive vibration to ensure the safety of the turbine once the critical speed is reached.
 Speed Rate Selection.
• Friction check, rate=100 rpm/min
• Operator normally set rate=0-500 rpm/min
• Over critical area, rate=500 rpm/min
• Approach to rating (Ws≥2950 rpm)，rate=50 rpm/min
 Critical Area
• First rank, 1200-1800 rpm
• Second rank, 1800-2300 rpm
• Third rank, 2300-2650 rpm
• Blade resonating speed, 3590-3600 rpm
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A. Speed Control
 Programming Start Up. Based on the HP inner cylinder up-wall
temperature, DEH automatically set speed target, speed rate, warming
time.
• Wall temperature < 150 ℃，COOL； Wall temperature 150-300 ℃，
WARM； Wall temperature 300-400 ℃，HOT； Wall temperature >
400 ℃，HOTTEST；
• First target 500 rpm；secondary target 1100 rpm；third target 3000
rpm；
• Speed rate and warming time. Taking different values according to
status and targets.
6. Automatically Synchronizing. In order to achieve connecting condition
(speed matches to grid frequency), DEH receives the increasing (or
decreasing) pulses from electrical synchronization device, plus (or
minus) 1 rpm per pulse.
ASPERM
D A 7. Pseudo Synchronization. Before
AS synchronization, shielding “sync” signal
E
AS + to make convenience for testing “sync”
H AS - S switches of electrical system. GE job title/21
B. Over Speed Test
1. Overspeed Protection Test. After synchronizing and warming up for a
period of time, turbine may step out to conduct overspeed protection test.
Under the control of DEH, 103%, 110% and mechanical emergency trip
overspeed test may be carried out.
 When DEH performs overspeed test, the target value and speed rate
are set by the operator
 Under normal speed control, DEH’s speed setting is up to 3050rpm.
This limit will automatically change when different overspeed test is
selected:
103% 3100
110% 3310
111% 3340
 When overspeed test is performed, DEH will automatically shield the
protection item of low setting, e.g., when 110% test is selected, 103%
protection will be automatically be shielded.
 When mechanical overspeed test is performed, DEH will
automatically trip if there is no operation after the speed reaches the
setting value.
2. Valve Rigorousness Test. Close GV or TV when performing test, check the
lazy time of the rotor.

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C. Load Control
1. At synchronizing moment, speed control switches to load control: open
loop and single valve mode.
2. Take initial load, to avoid the generator running at reverse power
condition.
3. Note the real load is not equal to the setting value when load control is
open loop.
4. Close loop load control. When real load > 10% rating, load loop and ImP
loop can be taken.
5. Primary frequency regulation.
6. Valve management - Single valve / sequence valve. Switching time is
120 S.
POZ POZ
7. Single valve characteristic.
8. Sequence valve characteristic.
GV1-4 GV1,2 GV3 GV4

FDEM FDEM
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C. Load Control
 Automatically taking initial load

After the turbine is in synchronization, DEH will correct target load value
according to current parameters of the unit, to take initial load automatically to
prevent reverse power operation.

 Automatically adjusting electric load

DEH may conduct open-loop and close-loop load control. When it is in open-loop
control, DEH only controls the valve position, with unit power being determined by
steam parameters. When it is in close-loop control, DEH may adjust unit power via
power control loop or impulse pressure loop. The impulse pressure loop is suitable
for the occasion where quick load response is required because the impulse pressure
has quicker response. The power control loop is slower, but it may conduct precise
power adjustment. Either or both of these two close loops may be put into operation.

Note: For the extractive steam turbine, the impulse pressure loop cannot be put into
operation if the extractive pressure loop is in operation.
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D. Other Functions
1. Valve Test.
• Role: Avoid GV or TV getting stuck. Doing the test at middle load.
• There two types: partial journey test or whole journey test. The selected valve
will close by 15% when partial journey or 100% when whole journey.
• When a valve is testing, other valves automatically compensate flow.
2. Extractive Steam Pressure Control.
• Role: There are another group of low pressure governing valves which will vary
their openness to keep the extractive steam pressure stable when load is
varying.
• Load vs extractive steam pressure uncoupled control
3. CCS Remote
• Role: when CCS is taking, the load control power is handed to CCS (desiring load
loop and IMP loop all released), DEH only controls the valve position.
• CCS sends the load setting to DEH, DEH return load reference to CCS (next page).

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D. Other Functions
DEH provides boiler-turbine control interface. The interface signals between DEH
and CCS are showed in the right figure:
CCS command interface signal may be pulse train or analog signal
DEH and DCS integrated project may be interfaced via network related points

ADSPERM
REFDMD
+
CCSREF + + + 负荷给定
+ +
FDEM ADS
+ -
PID
- +
D C
X1 X1
MW REFDMDMW 负荷参考 ADS +
E C
调频量 ADS -
X1
H S
dn ADS DEMAND
CCSDMD：CCS功率给定
REFDMD：DEH功率给定
REFDMDMW：DEH功率给定参考 频率给定 +
FDEM：DEH流量参考 3000
X1：一次调频量 - 探头
MW：实际电功率 n
n：机组转速

侧
CCS侧 侧
DEH侧

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D. Other Functions
4. TGRB. There are 3 designed RB items in DEH. They can be integrated into the RB
function of CCS, forming full RB designing strategy of unit.
• TGRB1，target 50% rating, rate 100MW/min。
• TGRB2，target 2.5% rating, rate 150MW/min。
• TGRB3，target 10% rating, rate 200MW/min。
• When TGRB, DEH is open loop, that is, load loop and IMP loop are released.
5. TPC. Throttle pressure protection, that is, closing GV if throttle pressure is less than
limit.
6. TCP. Throttle pressure control, that is, maintaining the throttle pressure at setting
value.
7. Load limit function
DEH is equipped with high & low load limiter, which limits DEH set values. The
system is defaulted with set values, which can be changed as required by the
operator
8. Low vacuum protection and limitation
Excessive low vacuum will damage the last stage blade of the LP cylinder of the
steam turbine. DEH will limit unit output to protect the last stage blade. GE job title/27
The End

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