EN 61362:1998

SLOVENSKI STANDARD
01-april-1999
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Guide to specification of hydraulic turbine control systems
Leitfaden zur Spezifikation der Regelungssysteme für hydraulische Turbinen
Guide pour la spécification des régulateurs des turbines hydrauliques
Ta slovenski standard je istoveten z: EN 61362:1998
ICS:
27.140 Vodna energija Hydraulic energy engineering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEI
NORME
IEC
INTERNATIONALE
INTERNATIONAL
Première édition
STANDARD
First edition
1998-03
Guide pour la spécification des régulateurs
des turbines hydrauliques
Guide to specification of hydraulic turbine
control systems
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For price, see current catalogue

61362 © IEC:1998 – 3 –
CONTENTS
Page
FOREWORD . 5
INTRODUCTION . 7
Clause
1 General. 11
1.1 Scope and object . 11
1.2 Normative references. 11
2 Terms, definitions, symbols and units . 13
2.1 General definitions . 13
2.2 List of terms, definitions, symbols and units. 13
2.3 Terms relating to the plant and the machines . 15
2.4 Terms relating to the control system. 17
3 Control system structure. 29
3.1 Main control functions . 29
3.2 Configurations of combined control systems . 31
3.3 Configurations of servo-positioners . 37
3.4 Multiple control. 37
4 Performance and components of the control systems . 39
4.1 Modeling and digital simulation. 39
4.2 Characteristic parameters for PID-controllers . 45
4.3 Other parameters of the control systems . 47
4.4 Functional relationship between servo-positioners . 51
4.5 Actual signal measurement . 53
4.6 Manual control . 57
4.7 Linearization . 57
4.8 Follow-up controls. 57
4.9 Optimization control . 59
4.10 Monitoring parallel positioning of amplifiers . 59
4.11 Provision of actuating energy . 59
4.12 Power supply for electronic control systems. 69
4.13 Operational transitions . 69
4.14 Safety devices/circuits. 73
4.15 Supplementary equipment . 75
4.16 Environmental suitability of governor components. 79
4.17 Electromagnetic compatibility . 79
5 How to apply the recommendations . 81
Data sheets 6.1a to 6.6d . 83 to 103
Annex A – Definitions . 105

61362 © IEC:1998 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_________
GUIDE TO SPECIFICATION OF HYDRAULIC TURBINE
CONTROL SYSTEMS
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters, express as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61362 has been prepared by IEC technical committee 4: Hydraulic
turbines.
The text of this standard is based on the following documents:
FDIS Report on voting
4/119/FDIS 4/142/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
Annex A forms an integral part of this standard.
The contents of the corrigendum of March 2000 have been included in this copy.

61362 © IEC:1998 – 7 –
INTRODUCTION
Recent developments have led to more stringent control system requirements with respect to
power frequency regulation and to isolated network operation. These requirements essentially
concern the primary control, which due to the use of modern, mostly electronic components,
can be tasked with some additional control functions. Also the primary control responds to a
superimposed large network control system (secondary control).
This guide mainly deals with primary control specifications; additional tasks are covered but the
guide does not elaborate on specific details.
Specifically the primary control can include some or all of the following functions:
– unit start-up and shut-down;
– idling before synchronizing and after separation from the network and synchronizing;
– isolated network operation;
– parallel operation on large networks in speed control and power output control mode;
– head water level and/or flow control;
– operating mode transitions;
– monitoring and safety functions.
The guide also deals with aspects of the actuating energy supply.
The controlled system in a hydroturbine control loop, i.e., the respective transfer function, is
characterized by:
– the unit(s), i.e. turbine(s) and generator(s);
– the water passage system;
– the network to which the unit(s) is (are) connected;
– the modes of operation as mentioned above.
The parameters of the primary control system (speed governor, power output governor, etc.)
are to be carefully matched to the prevailing system conditions in order to:
– achieve adequate stability;
– satisfy performance requirements with respect to damping, response and accuracy;
– provide safety with respect to limitations in hydraulic transients, etc.
To achieve the above, in many cases modeling and simulations are valuable. The guide refers
to some important aspects in this respect.
Since the governors have to be able to cope with a range of conditions, it is suitable practice to
specify that a certain range for the setting of parameters is available in the governors. The
guide follows this practice in the relevant part.

61362 © IEC:1998 – 9 –
Specifically, in this guide, the performance-relevant definitions refer to the PID-controller,
which can be implemented by analog or digital means. With appropriate microcomputer
technology, higher control algorithms also can be implemented. Although it is deemed difficult
to set up specific rules at the time of the issue of this guide, the general criteria for the
adequate performance of a control system are essentially independent of the control strategy
used. This means that they remain applicable as described in this guide and that the PID-
controller can be regarded and used as a reference governor to gauge the control performance
of a system.
The guide makes reference to IEC 60308 on hydraulic turbine control systems. It relies on it for
the methods of system identification and verification of performance, etc. It is the intention of
this guide to supplement IEC 60308 by recommending performance criteria and ranges for the
setting of parameters.
To facilitate the setting up of specifications, this guide also includes data sheets, which are to
be filled out by the customer and the vendor in the various stages of the project and the
contract.
61362 © IEC:1998 – 11 –
GUIDE TO SPECIFICATION OF HYDRAULIC TURBINE
CONTROL SYSTEMS
1 General
1.1 Scope and object
This guide includes relevant technical data necessary to describe hydraulic turbine control
systems and define their performance. It is aimed at unifying and thus facilitating the bidding
specifications and technical bids. It will also serve as a basis for setting up technical
guarantees.
In case of separate vendors for different segments of a system, the interface between them is
especially important.
The guide is not confined to the control loop functions proper but includes all important
functions of a control system, i.e., it also treats sequencing functions, etc. Hydraulic turbine
control is thus understood to include:
– speed, power, water level and discharge control for reaction and impulse-type turbines
including double regulated machines;
– means of providing actuating energy;
– safety devices for emergency shut-down, etc;
– environmental performance criteria.
The guide aids the selection of some important parameters to be specified and checked in
relation to the different types of installations.
Excluded topics are acceptance tests, specific test procedures and guarantees.
1.2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this International Standard. At the time of publication, the editions
indicated were valid. All normative documents are subject to revision, and parties to agreement
based on this International Standard are encouraged to investigate the possibility of applying
the most recent editions of the normative documents indicated below. Members of IEC and ISO
maintain registers of currently valid International Standards.
IEC 60068-2-6:1995, Environmental testing – Part 2: Tests – Test Fc: Vibration (sinusoidal)
IEC 60308:1970, International code for testing of speed governing systems for hydraulic
turbines
IEC 61000-3-2:1995, Electromagnetic compatibility (EMC) – Part 3: Limits – Section 2: Limits
for harmonic current emissions (equipment input current ≤16 A per phase)
IEC 61000-3-3:1994, Electromagnetic compatibility (EMC) – Part 3: Limits – Section 3:
Limitation of voltage fluctuations and flicker in low-voltage supply systems for equipment with
rated current ≤16 A
61362 © IEC:1998 – 13 –
IEC 61000-4-1:1992, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement
techniques – Section 1: Overview of immunity tests
CISPR 11:1990, Limits and methods of measurement of electromagnetic disturbance
characteristics of industrial, scientific and medical (ISM) radio-frequency equipment
ISO 3448:1992, Industrial liquid lubricants – ISO viscosity classification
2 Terms, definitions, symbols and units
2.1 General definitions
This guide uses as far as possible the terms and definitions of IEC 60308. For clarification, the
simplified differential equation of the idealized PID-governor as used in this guide in
comparison with that of an idealized PI-governor used in IEC 60308 is given in annex A.
For the purpose of this International Standard the following definitions, as well as the
definitions given in IEC 60308, apply.
2.1.1
differential equation
equation describing the dynamic system behavior in the time-domain, as shown in annex A.
2.1.2
transient response
system response (output) to a step change of the input.
2.1.3
frequency response
dynamic response of the linearized system to a sinusoidal change of the input signal derived
from the differential equation by applying the Fourier transformation.
2.1.4
transfer function
dynamic response of the linearized system to an arbitrary variation of the input signal derived
from the differential equation by applying the Laplace transformation.
2.2 List of terms, definitions, symbols and units
Sub- Term Definition Symbol Unit
clause
2.2.1 Rated Subscript indicating the rated operation point of the system. r –
2.2.2 Subscript indicating maximum or minimum values of any term. max. –
Maximum
Minimum min.
2.2.3 Deviation of any term from a steady-state value –
Deviation Δ
2.2.4 Guide vanes Subscript associating a quantity to wicket gate ga –
2.2.5 Subscript associating a quantity to runner ru –
Runner
2.2.6 Nozzle Subscript associating a quantity to nozzle nz –
2.2.7 Subscript associating a quantity to deflector de –
Deflector
61362 © IEC:1998 – 15 –
2.3 Terms relating to the plant and the machines
Sub-
Term Definition Symbol Unit
clause
–1
2.3.1 Specific energy Specific energy of hydraulic water available between the high- J ⋅ kg
E
and low-pressure side sections of the machine
of machine
2.3.2 Turbine head H =E/g definition of E, see 2.3.1 m
H
g = acceleration due to gravity.
–2
= 9,81 m⋅s (at sea level)
2.3.3 Discharge Volume of water per unit time flowing through any section in 3 –1
Q m ⋅ s
the system
2.3.4 Number of revolutions per unit time
Rotational –1
n t ⋅ min
speed
2.3.5 Cycles per second f Hz
Frequency
2.3.6 Generator Generator power measured at generator terminals P W
G
output
2.3.7 Moment of Moment of inertia for calculation of fly-wheel effect. 2
kg ⋅ m
I
2 2
I = M D /4 = MR
inertia of mass
(M = mass, D = diameter of gyration,
R = radius of gyration)
61362 © IEC:1998 – 17 –
2.4 Terms relating to the control system
Sub-
Term Definition Symbol Unit
clause
2.4.1 Controlled Variable which has to be controlled as speed n, output P ,
G
water level h:
variable
– absolute, dimensional value X var.
–
– relative deviation from a steady-state x
–
value, x = ΔX/X
r
x –
Rotational speed
n
x –
Output
p
x –
Water level
h
2.4.2 A signal which can be set by an external adjustment:
Command
signal
– absolute, dimensional value C var.
c –
– relative deviation from a steady-state value, c = ΔC/C
r
–
Rotational speed c
n
–
Output c
p
–
Water level c
h
2.4.3 Stroke of the main servomotor which moves the gate/runner
Servomotor
stroke blades/nozzles/deflectors
– absolute value Y m
y –
– relative deviation from a steady-state value, y = ΔY/Y
max
2.4.4 Controlled Adjusting range for the setting of the controlled variable with
an average setting of the permanent droop:
variable range
– maximum value of the controlled variable for Y/Y = 0 X –
max max
– minimum value of the controlled variable for Y/Y = 1,0 X –
min min
(see figure 1)
X
X
X
max
X
max
Y
Y
Y
Y max
max
1,0
X
min
X
min
IEC  320/98
Fig. 1
Figure 1 – Controlled variable range

61362 © IEC:1998 – 19 –
Sub-
Term Definition Symbol Unit
clause
2.4.5 Governor output Output signal at the governor = input signal of the following
servo-positioner
signal
Relative deviation from a steady-state value s –
2.4.6 Output signal of Output signal of a pilot servo-positioner = input signal of
the following main servo-positioner
a pilot servo-
positioner
Relative deviation from a steady-state value –
s
v
2.4.7 droop graph: A graph showing the relative controlled variable as a function of the
relative servomotor stroke/the relative output under steady-state conditions (see figure 2).
X
X
b
b s
b b
pp s
Y P
Y P
, ,
Y P
1,0 Ymax rP
max r
Fig. 2
IEC  321/98
Figure 2 – Permanent droop
Sub- Term Definition Symbol Unit
clause
2.4.8 Permanent Slope of the droop graph (see figure 2):
droop
– at a specific point of operation, %
b
p
– defined by the end values of the droop graph b %
s
2.4.9 Proportional Proportional amplification, defined by the step of the governor K –
p
1)
transient function with b = 0, p = 0, T = 0 and input signal x = 1
gain
p p v
(see figure 3)
1)
Reciprocal value of the temporary speed droop, b , as per 5.3.5 of IEC 60308.
t
61362 © IEC:1998 – 21 –
Y
Y
K
Kp
p
t
t
T
Ti
d
IEC  322/98
Fig. 3
Figure 3 – Integral time constant
Sub-
Term Definition Symbol Unit
clause
2.4.10 Integral action Time constant of the integral action of the governor, defined by T s
i
1)
time the slope of the governor step response curve with b = 0,
p
T = 0 and input signal x = 1 (see figure 3)
D
2)
2.4.11 Derivative Time constant of the derivative action of an idealized PID- T s
d
governor according to annex A. T can be realized
action time
v
approximately only by a derivative term multiplied by a first-
3)
order delay according to the transfer function of the
derivative part
k T p
D ⋅ 1d
1 + T p
1d
For small values of T p, then
1v
T = K ⋅ T
d D 1d
The step response of an idealized PID-governor according to
annex A, the proportional and integral term being zero, is
shown in figure 4.
1)
Damping time as per 5.3.4 of IEC 60308, T = K /K , K integral gain. T ⋅ T (IEC 60050-351).
d p I I
d i
2)
Realization also by second-order delay.
3)
T = K /K (IEC 60050-351) in parallel structured governors with gain adjustment, K = differential gain.
d D P D
In IEC 60308, no derivative action time is defined.

61362 © IEC:1998 – 23 –
Y
y
0,63 K
0,63 K pD K v
K
KD p K v
t
t
T
1d
T
1v
IEC  323/98
Fig. 4
Figure 4 – Derivative time constant
Sub-
Term Definition Symbol Unit
clause
2.4.12 Dead band The maximum band between two values inside of which the i –
x
variation of the controlled variable does not cause any
governing action (see figure 5).
X
X
i
x
i
x
Y
Y
YY
1,0 mamaxx
IEC  324/98
Fig. 5
Figure 5 – Dead band
Sub-
Term Definition Symbol Unit
clause
2.4.13 One-half of the dead band i /2 –
Insensitivity
x
2.4.14 Minimum servo- The opening/closing time for one full servo-motor stroke at T , T s
g f
maximum velocity cushioning times disregarded (see figure 6).
motor opening/
closing time
61362 © IEC:1998 – 25 –
Y
Y
Y
max
Y
max
1,0
t
t
TT
ff
T
Tg
a
IEC  325/98
Fig. 6
NOTE – In case of stepped opening/closing velocities a diagram may be provided.
Figure 6 – Minimum servomotor opening/closing time
Sub-
Term Definition Symbol Unit
clause
2.4.15 The reciprocal value of the slope of the curve showing the T s
Time constant
y
of the servo- servomotor velocity dy/dt as a function of the relative deviation
1)
of the position of the control valve, s, s , from the zero
positioner
v
position related to s, s = 1 (s, s = 1 theoretical relative spool
v v
stroke in the absence of feedback) (see figure 7)
1)
Servomotor response time as per 5.3.1 of IEC 60308.
ddy
y
ddt
t
T
y2
T 2
y
T
T T
g 1
g Ty
y1
1,0 s,s
v
s,s
v
T
fT
f
Fig. 7
IEC  326/98
Figure 7 – Time constant of the servo-positioner

61362 © IEC:1998 – 27 –
Sub-
Term Definition Symbol Unit
clause
2.4.16 Amplifier dead The maximum band between the main servo-positioner i –
a
defined positions which can occur for a constant input signal
band
(see figure 8)
Y
Y
Y
max
Y
max
1,0
ii
a
a
1,0 s,s
v
,
s s
v
Fig. 8 IEC  327/98
Figure 8 – Amplifier dead band
Sub-
Term Definition Symbol Unit
clause
2.4.17 Amplifier One-half of the dead band i /2 –
a
inaccuracy
2.4.18 Control system Time interval between a specified change in speed or T s
q
command signal and the first detectable movement of the
dead time
servomotor (see figure 9)
yy
10%
≥ 10 %
T
q
T
a
t
0 t
IEC  328/98
Fig. 9
Figure 9 – Control system dead time

61362 © IEC:1998 – 29 –
Sub-
Term Definition Symbol Unit
clause
2.4.19 Actuating energy Required energy for one servomotor stroke under the E N · m
R
minimum required pressure p = E /V
R R S
2.4.20 Servomotor Oil volume of the servomotors V m
S
volume
2.4.21 Tripping oil Oil volume of the pressure tank at the tripping point V m
T
volume (between p and p , see figure 20)
T R
2.4.22 Usable oil volume Usable oil volume between p and p V m
O min R u
(figure 20)
2.4.23 Residual (not Oil volume of the pressure tank after a full-load shut-down V m
res
usable) oil volume from the tripping point
(figure 20)
1)
2.4.24 Design oil Design pressure of the oil pressure tank p Pa
D
pressure
1)
2.4.25 Operating oil Operating oil pressure under normal operating condition p Pa
O
pressure
1)
2.4.26 Tripping oil When the tripping pressure p is reached after a full-load p Pa
T T
pressure emergency shut-down, it implies p < p < p < p
R T O D
1)
2.4.27 Minimum required Minimum required pressure in the oil servo system p Pa
R
pressure
1)
The unit bar is also used.
3 Control system structure
In the hydraulic turbine control, various tasks can be specified with varying priority. Realization
leads to certain typical control system structures and in turn to some basic rules to be adhered
to.
Such typical arrangements are compiled for clarification.
3.1 Main control functions
In hydraulic turbine control, these major control functions can be distinguished:
– speed control;
– power output control;
– level control;
– opening and flow control.
In some systems combinations of these control functions also occur.

61362 © IEC:1998 – 31 –
3.1.1 Speed control
The purpose of the speed control basically is to maintain constant frequency. In the various
modes of operation this means that:
– in the isolated network mode, the actual speed and therefore the frequency corresponds to
the command signal setting;
– in the operation on the grid, where the speed is determined by the network frequency, the
speed control contributes to the network frequency control through the permanent droop
and the dynamic characteristics of the controlled system;
– in the idling mode (before synchronization and after separation from the network), the
actual speed corresponds to the command signal or the existing network frequency with
some slip.
3.1.2 Power output control
The power output control with a separate power governor is applied with the unit connected to
the grid, its purpose is to control the power output of the unit according to a power command
signal irrespective of head variations. Any frequency variations influence the power level
additionally via the permanent droop.
It is noted that in the cases where head variations can be ignored, a closed loop power output
control, i.e., a power output governor, may not be necessary. In such a case, linearization
between command signal and power output may suffice (see 3.2.1). In this case also, any
frequency variations influence the power level additionally via the permanent speed droop.
3.1.3 Level/flow/opening control
The purpose of a level/flow/opening control is to keep the level, flow or opening constant or to
make it follow a command signal.
3.2 Configurations of combined control systems
In combined systems, each control function can be assigned to a separate controller. However,
the controllers all actuate the same main servo-positioner through the opening setpoint.
Thereby, a bump-free switch-over between modes requires attention. In case of separate
controllers, parameters shall be set according to the respective control loop. Level and power
output control, etc, are often incompatible with the maintenance of speed in an isolated
network. The speed governor always remains functional for safety reasons, e.g., to take over in
the case of a load rejection.
3.2.1 Parallel structure
Two governors are arranged in parallel and actuate one or several servo-positioners via a
selector or a summing point. If a selector is applied, it often includes a max./min. function for
the speed control loop to prevail in the case of a load rejection.

61362 © IEC:1998 – 33 –
If a summing point is applied, the switching of signals is avoided, but the power output
governor then influences speed control additionally and shall be set to ensure stability.
x
n
Speed governor
c
n
Selector or
y
summing
Servo-positioner
x
p
point
Power output governor
c
p
IEC  329/98
Figure 10 – Control system with speed and power output governor in parallel
The configuration according to figure 10 is often used in peak-load power stations.
x
n
Speed governor
c
n
Selector or
Servo-positioner y
summing Linearization
point
c
p
IEC  330/98
Figure 11 – Control system with speed governor and
power command signal in parallel
Figure 11 shows an arrangement with speed governor and power command signal in parallel
according to 3.1.2.
x
n
Speed governor
c
n
Selector or
y
summing
Servo-positioner
x
h
point
Water level controller
IEC  331/98
c
h
Figure 12 – Control system with speed governor and level controller in parallel

61362 © IEC:1998 – 35 –
3.2.2 Series structures
Power output governor or level controller precede the speed governor. They actuate the speed
signal setter of the speed governor (figure 13) or the opening limiter (figure 14).
c
n
c
p
Selector or
y
Power output governor
summing Speed governor Servo-positioner
x
p
point
x
n
IEC  332/98
Figure 13 – Governing system with power output and speed governor in series
The power output governor actuates the speed signal setter of the speed governor.
Opening limiter
x
h
Water level controller
c
h
x
n
Speed
y
Servo-positioner
governor
c
n
IEC  333/98
Figure 14 – Governing system with level controller and speed governor in series
The level controller actuates the opening limiter of the speed governor.
The configurations of figures 13 and 14 are typical examples. However, there are also
configurations with the power output controller acting on the opening limiter of the speed
governor or with the level controller acting on the speed signal setter. In the power output and
the level control mode, the speed governor acts essentially as a positioner.
The configuration as per figure 14 is often used in base-load power stations.
3.2.3 Other configurations
3.2.3.1 Power output control via the speed governor (power output introduced
as feedback signal)
c , c
n p
Speed
y
Servo-positioner
x governor
n Selector
IEC  334/98
x
p
Figure 15 – Power output control via the speed governor

61362 © IEC:1998 – 37 –
Changeover between control modes is by switching from actual speed signal to the actual
power output signal.
3.2.3.2 Level controller without speed governor
x
h
Water level controller
Servo-positioner y
Positioner
c
h
IEC  335/98
Figure 16 – Level controller without speed governor
In simple cases (for example in the case of induction units), its level controller acts on the
servo-positioner via a setter.
3.3 Configurations of servo-positioners
Depending on the actuating energy required, the main servomotor can be:
− directly actuated by an electro-hydraulic amplifier; the electronic feedback signal is fed back
to the governor;
− actuated via a pilot servomotor; it positions a closed-loop hydro-mechanical follow-up
system consisting of main control valve, servomotor and mechanical feedback;
− actuated via a piloted main control valve with parallel feedback signals from main control
valve and servomotor, etc.
The type of configuration has a bearing on positioning accuracy and manual control options.
3.4 Multiple control
In case of multiple control members (e.g. dual control of a turbine with controllable guide vanes
and runner blades),
− parallel and
− series
arrangements are distinguished. The functional relationship can be defined non-linearly
through a function generator. Frequently an additional parameter is superimposed (e.g. the
head can be made to influence the guide vane-blade angle relationship). In the case of more
than two positioners (e.g. individual servomotor control), only parallel control is applied.

61362 © IEC:1998 – 39 –
3.4.1 Parallel structure
s
y
Servo-positioner 1 1
y
c Servo-positioner 2
Functional relation 2
a
IEC  336/98
s is the output signal of governor
y is the output signal of servo-positioner 1
y is the output signal of servo-positioner 2
c is the signal to be superimposed on the input signal of servo-positioner 2
a
Figure 17 – Parallel structure with defined functional relation and
an additional parameter super-position
3.4.2 Series structure
Y
s 1
Servo-positioner 1
Functional
c
y
a
Servo-positioner 2 2
relation
IEC  337/98
Figure 18 – Series structure with defined functional relation and
additional parameter superimposition
4 Performance and components of the control systems
This clause is concerned with the overall performance criteria for a control system. As
performance of a governor will strongly depend on the characteristics of the individual
controlled system, some guidance is offered first as to its modelling and digital simulation.
Then recommendations are given for the ranges of parameter settings for a PID configuration
as the most common example of a governor. Other control strategies may be applied if suitable
or desirable for superior performance in relation to the PID-reference governor.
Servo-positioners, requirements for signal transmitters and the actuating energy supply are
also covered with the purpose of guiding the establishing relevant specifications.
4.1 Modeling and digital simulation
In the case of new hydropower schemes, a mathematical model of the total system is valuable
for an optimization of the control, unless the system is straightforward and/or similar to existing
plants. The same applies to the modernization of existing plants. The purpose of such compu-
tations can relate to three areas:

61362 © IEC:1998 – 41 –
− physical dimensioning of components of the plants;
− demonstrating the dynamic behavior of the system (resonance phenomena, etc.);
− control system analysis and optimization.
These computations shall be based on a representative model of the system components,
such as:
− the water passages;
− the turbine with its mechanism;
− the essential generator characteristics in the isolated network and the grid mode;
− the network characteristics;
− the control system.
All the mentioned areas of interest can in principle be served by the same models while the
mathematical approach can vary. Whilst physical dimensioning of components of the plant
shall be based on computations in the time domain, the dynamic behavior of the total system
can also be evaluated in the frequency domain. Control performance can be treated either
− in the frequency domain with respect to small deviations from the steady state, or
– in the time domain for large deviations where non-linearities are significant.
If mathematical investigations of the dynamic behavior in the frequency domain are applied, a
suitable variable such as the gate opening shall be subjected to sinusoidal variations
(frequency analysis). Thereby all frequency ranges shall be considered at which excitations,
e.g. suction tube vortices in Francis turbines and/or resonances such as with natural
frequencies of tunnel, penstock or the generator may occur. Thereby it should be noted that
calculated natural frequencies of the hydro system may be inaccurate because the wave travel
speed cannot be determined precisely.
For investigations with the aim of an optimization of the parameter setting of the controller,
calculations in the time domain offer the advantage of considering non-linearities. Usually an
integral criterion is applied, e.g.
∫ |
x - x |. dt = minimum
c
or
∫
t. |x - x |.dt = minimum
c
There are computer programs available which systematically vary the parameters and select a
set of optimal values. By applying this method to the complete operating range, the setting of
an adaptive governor may also be determined.
Optimization of the parameter setting of the controller in the frequency domain requires a
linearized model. The set of optimal controller parameters can, for example, be determined by
positioning the poles, i.e., the roots of the characteristic equation for optimal performance. This
requires some experience.
The degree of detail in the modeling of a plant depends on the requirements with respect to
controllability of the plant.
61362 © IEC:1998 – 43 –
The effort even for smaller systems may be considerable and costly. The following may help to
make a judgment as to how far the modeling should be carried in individual cases.
Water passages
− For the simulation of the water passages, the compressibility of the fluid and the elasticity
of the penstock material shall be taken into account. For dimensioning and resonance
studies, this should also be applied on tunnels and on galleries and shafts of surgetanks. If
in the time domain, the length of a water column changes, then water and walls of this part
are usually regarded as incompressible and un-elastic.
– A separate analysis of the tunnel-surgetank section and the penstock-machine section is
desirable to determine maximum excursion of the surgetank water level and maximum
machine transient variables such as speed and pressure rises, respectively. System
oscillations and control system behavior can only be reliably judged on the basis of the total
system description.
– In surgetank calculations, energy dissipators such as throttles and the fluid inertia shall be
taken into account.
– In low head plants, the inertia of water masses in the head and tailwater housings shall be
taken into account while the elasticity can be neglected. Also surge phenomena in
headwater canals can be relevant.
Turbine, generator, network
– The turbine characteristics should be defined in the investigation. The speed control of
Pelton turbines may pose difficulties due to the lack of a negative torque and the non-
linearities introduced by the deflector. For isolated network operation, controlled deflectors
are needed.
– For investigations on resonances and the behavior of the unit connected to the grid the
synchronization and damping factor of the generator shall be taken into account.
– The stability of frequency control in isolated networks depends on the type of load, such as
resistor, motor or combined loads. The resistor type load is the most stringent requirement.
Control concept
It is to be expected that in the future, PID-controllers will remain in use for many plants for
speed, power and head level control. Higher order algorithms, e.g., state control schemes will
be used for the more complex system requirements. These control schemes, while
necessitating more effort to implement, are justified where superior behavior with respect to the
magnitude of deviations from steady state and its return to steady state can be achieved.
It is to be noted that an electronic PID-controller´s behavior can also be enhanced considerably
by readily available special means, such as disturbance superposition and the feedback of
secondary variables.
This in turn justifies the intention of this guide to use the PID-governor as a basis and
reference for recommendations relating to system control. The recommended ranges in
parameter adjustment will suffice in all normal cases. Special conditions – extremely low

61362 © IEC:1998 – 45 –
inertias, extremely long penstocks – should in all cases be subjected to digital simulation and
may require an extension of the recommended parameter adjustment range.
4.2 Characteristic parameters for PID-controllers
These subclauses relate to the characteristic parameters of a PID-controller (analog or digital)
with permanent droop. It does not cover relevant parameters for other higher algorithms/control
strategies.
4.2.1 Permanent droop b
p
The permanent droop establishes a defined relationship between the controlled variable x, and
the relative servo-position or any other signal, in the steady-state condition, e.g.:
– speed control: between frequency and servo position;
– level control: between level and servo position;
– power control: between power and frequency.
Recommended minimum setting range of the permanent droop for speed control: 0 % to 10 %
Linearity (maximum allowable deviation of the permanent droop b ) for any value of y from the
p
maximum stroke permanent droop b : < ±5 %.
s
Example: b = 4,5 %, b = 4,4 %,
s p
linearity ((b – b )/b ) 100 = (0,1/10)100 = 1,0 %
s p pmax
4.2.2 Gain K , integral action time T , and derivative action time T
p d v
The parameters K , T and T establish the transient response of the governor. The desired
p d v
transient response can be achieved
− with parallel structure,
− with series structure, or
− with feedback structure of the elements.
The suitable adjustment of the parameters depends on the controlled system and shall be
selected so as to provide a satisfactory transient response. Depending on the mode of
operation, different adjustments may be necessary, e.g.
with speed control:
– in idling mode;
– in an isolated network mode (required only for part load in some cases);
– in operation on the grid (over the complete power range);
with combined power output and speed control figures 10, 11, 13 and 15:
− for speed control (with inoperative power output control);
− for speed governor acting as positioner (with operative power output control).

61362 © IEC:1998 – 47 –
Usually the same parameter selection can be applied for idling and operation on an isolated
network; it may differ considerably from the suitable adjustment for grid operation.
If necessary an automated changeover parameter adjustment is to be provided (e.g., through
generator breaker position, or by sensing the transition to isolated network operation via a
large frequency excursion or a power step).
a) Gain K (= reciprocal value of the temporary speed droop b )
p t
Recommended minimum adjusting range:
1)
– for speed governors, between 0.6 and 10 ;
– or power output governors, between 0,2 and 1.
b) Integral action time T
d
2)
Recommended minimum adjusting range: between 1 s and 20 s .
c) Derivative action time T
v
Recommended adjusting range: between 0 and 2 s.
where the relation T /T = 1/K is generally between 0,1 and 0,2.
1v v v
4.3 Other parameters of the control systems
4.3.1 Command signal adjustments for controlled variables (speed, power output, etc.)
and load limiter
a) Command signal ranges
Recommended adjusting range:
– for speed controls: +6 % to 10 % with b = 4 %.
p
b) Command signal setting times
The setting times (stroke times) shall be adjusted so as to exceed the shortest servomotor
stroke times as defined by the limiting orifices (see also 4.3.3). Setting times should usually
not be smaller than 20 s.
Recommended time setting range:
– speed setting: between 20 s and 100 s, normally between 30 s and 60 s;
– power output setting: between 20 s and 80 s for the full travel of the servomotor;
– limiter: between 20 s and 80 s for the full travel of the servomotor.
4.3.2 Control insensitivity i /2
x
Recommended limits:
–4
− speed control: i /2 < 2 · 10
x
–2
− power output control: i /2 < 1 · 10
x
− level/discharge control: i /2 < (X – X )/1 m;
x max. min.
–2
– discharge control: i /2 < 1 · 10 .
x
________
1)
k T
A range between 1,2 and 10 for and 1 s and 5 s for may be sufficient for many applications, e.g.
p d
rehabilitations without additional performance requirements.
2)
(Minimum required range between 0 s and 1,4 s.) 0 s means deactivation of derivative actions is possible.

61362 © IEC:1998 – 49 –
–2
In case of less stringent requirements relative to network frequency control, also i /2 < 2 · 10
x
is acceptable for the speed control function. This may, for example, apply for networks, in
which larger frequency variations occur frequently, and also in cases where stability is critical.
4.3.3 Parameters of servo-positioner
Input: electrical signal or position of the pilot servomotor.
Output: relative position Y/Y of the main servomotors.
max
For all servo-positioners, including those of double regulated turbines, the following applies.
a) Minimum servomotor opening/closing times T and T which are separately determined to
g f
satisfy waterhammer and overspeed limitations
NOTE – The limiting orifices or other suitable devices are dimensioned such that the actual stroke times in the
presence of the highest supply pressure and the lowest required regulating capacity will not be lower than the
allowable stroke time.
b) Time constant of the main servo-positioner T
y
This value is introduced in any digital simulation of the system.
Recommended values for T :
y
– gate/needle servo: between 0,1 s and 0,
...