FIELD OF INVENTION
The present invention relates to an electronic governing system through
speed control of Pelton turbine, using direct needle control method.
BACKGROUND & PRIOR ART OF THE INVENTION
The speed control of Pelton turbines is implemented in either of the two methods
1) Deflector control: Deflectors are used as primary control equipment whereas
needles are used as secondary control. The control loop makes adjustments in
the deflector position to regulate speed or load of the turbine. Needle move as
per the Needle-Deflector conjugation curve.
2) Needle control: Needles are used as primary control whereas deflectors are
used as secondary control. The control loop makes adjustments in the needle
position to regulate speed or load of the turbine. Deflectors move as per the
Needle-Deflector conjugation curve.
In either of the two methods the primary control software determines a
position reference for the primary control element (Deflector/needle).
A secondary position control loop receives the position reference and
then takes the control element to the desired position.

The problem with the existing speed is that the actual control element
is not directly controlled by variation in the reference (speed/load). The control blocks
uses more software blocks to calculate position reference for the primary control
element and some additional control blocks to position the control element as per the
calculated reference.
OBJECTS OF THE INVENTION
The object of the invention in to select needles as the primary control
element for smooth and faster speed control of Pelton turbine.
Further object of the invention is to reduce software control blocks for
speed/load control of turbine.
Another object of the invention is to use speed error to directly control
the needles instead of using position references.
The control of the speed is achieved by moving the primary control
element directly according to the variation in the reference and actual value (Speed
error) based on a parallel PID controller and for load control mode the controller will
calculate the position reference for the required load reference and then the controller
will position the needles to achieve the required Load.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
1) Fig. 1: Functional control diagram for speed control mode.
2) Fig.1(a) – 1(c): Block diagram of needle control at various stages of speed-error
calculations.
3) Fig. 2: Functional control diagram for load control mode.
4) Fig.2(a) – 2(c): Load control mode at various stages.
As depicted in Fig.1 the new needle control scheme can be divided into
two sections.
a) When the turbine speed is less than 80% of the rated speed:
When the turbine speed is less than 80% of the rated speed the needles
are open to a fixed opening as per parameter (2.5% in this case). The number of
needles that would act during the initial start-up of the turbine is also a parameter.
The fixed needle opening parameter is to be selected based on the no load opening
parameter provided by the turbine manufacturer for achieving rated speed at a
specified water head.

The fixed needle opening will cause the unit speed to increase gradually
and as soon as the speed reaches the threshold value of 80% the PID control takes
over.
Deflector opening is carried out in such way that deflector kept away
from water path. In this case this can be 30%
b) When the turbine speed is greater than 80% of the rated speed:
The control system accepts a speed reference from the operator
(individual) via Human machine interface (HMI). The controllable range for speed that
is available is 90% to 110%. The actual speed of the turbine is measured via speed
sensing device. The error of the speed signal is passed on to a PI controller with a
temporary droop (Td) stabilizing signal (based on needle opening feedback) to
enhance system stability. The overall output of the PI and Td is the actual control
signal for the needles. This actual control system is realized in the hardware to provide
an electrical control signal to the needle opening/closing device (the signal can be 4-
20mA, 0-10V DC, etc.).
The opening of the deflector is computed based on the actual needle
position through the needle/deflector conjugation curve.
As a safeguard, a limiter is also positioned to limit the opening of the
needles and deflectors beyond a limiting value. This limiting value of the limiters is

calculated by a function generator in the control software based on the design
parameters of the turbine at different heads.
As depicted in Fig. 2 after synchronization of the turbine with the grid
the control loop switches over to load control mode. In this mode the speed reference
raise/lower is replaced by power/Load reference raise/lower signal.
The Power reference is given by the operator. This power (Load)
reference can be a power set-point or a pulse signal to raise/lower the reference
value. Additional droop signal for frequency error in the grid is also added. This power
reference and droop signal is added to generate a final power reference. This power
reference is then calculated to compute needle position reference for a given power
reference at present head. The difference in the Load reference and actual load (MW
error) is further added to the reference for faster load taking/shedding by the
governor.
The number of needles that would work at a given power reference is
calculated as per the discharge and efficiency curve provided by the turbine
manufacturer to maximize the turbine efficiency at varying load conditions. The needle
combination for a 5 needle based Pelton turbine can be 2 needles, 3 needles or 5
needles at a time.
The control function has the following additional features
1) Selection of needle for starting and initial loading

2) Automatic Disabling of defective needle to allow part loading of the turbine to
reduce outage of the unit
3) Provision of determining failure of needle control actuators
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION
a) Fig. 1(a) illustrates the calculation of the speed error. Nref if the default speed
reference which is 100%. As soon as any of the inputs (Measurement Failure,
Generator Circuit Breaker Off, Governor stop or Field breaker trip) to the OR
block is HIGH, the speed reference is set to 100% irrespective of the original
value.
b) The speed reference block accepts a set point input (between 90% to 110%
of rated speed) and pulse input for incremental inputs by external or software
pulse inputs (viz. from Auto-synchronizer).
c) The speed error is the difference between the final speed reference and the
actual speed (measured by the speed sensors)

d) The speed error calculated above is passed to a parallel PI controller. To
stabilize the output of the PI controller and to reduce the oscillations a
temporary droop signal is added to the output of the PI controller. This
temporary droop signal is calculated based on the change in needle position.
e) The output of the PI controller and Temporary droop signal is then multiplied
by an overall NEEDLE GAIN.
f) As seen in Fig. 1(c) that an error of 2.5% (adjustable) is initially feed to the
needle control signal initially to enable the needles to open for turbine start-
up. The error signal to control the needle opening is limited by the MIN block
which allows the minimum value between the error signal and the NEEDLE
LIMIT. The needle limit is calculated by the limit imposed by the DEFL ELE
LIMIT parameter. This parameter is common for deflectors and needles. The
NEEDLE LMT CONJUGATION is a function generator which accepts DEFL ELE
LIMIT (0-100%) as input and calculated corresponding NEEDLE LIMIT. The
difference between the NEEDLE LIMIT and actual needle position is calculated
and multiplied by NEEDLE LIMIT GAIN to generate an error signal.
g) An AND block is used which accepts the following inputs

1) GCB Open (Turbine is not synchronized with grid)
2) SPD >80% (Turbine speed is greater than 80%)

3) SEL SPD CTRL (Turbine is in speed control mode)
The AND block is used to select between the fixed error of 2.5% and the error
signal calculated by the speed error controller (PI and TD controller)
h) The output of the MIN block is then fed by the hardware output modules to
the needle actuators (servo valves) to position the needles in order to run the
turbine at the speed reference set in the software via HMI.
As per Fig. 2(a) block diagram,
a) which accepts the power reference. Similar to the speed reference the power
reference block is present in the software which accepts both set-point and
pulse inputs.
b) As soon as the generator synchronizes with the grid, the power reference is
raised to an adjustable pre-set value to enable the turbine to achieve a non-
zero base load.
c) The speed error signal is used to generate a droop signal based on the
permanent droop setting parameter BP which is then added to the power
reference (Pref) so as to contribute in grid frequency stability.

d) Power reference (Pref) v/s needle position conjugation is made available by the
turbine manufacturers which lists out the relationship between the Needle
openings, which would be required for achieving a specified turbine output at
rated water head.
e) The Pref signal is input to the POW REF v/s NEEDLE POS. CONJUGATION
function block which will determine the position of the needle that would result
in achieving the required load.
f) Since the water HEAD is continuously varying, the output of the conjugation
function block will not hold true at a head other than the rated head hence a
HEAD CORRECTION factor is introduced.
g) There is an exponential relation between the HEAD and POWER output of a
turbine for a certain nozzle opening so that HEAD correction block accepts the
actual head and computes a correction factor so that a final control signal is
generated which would result in the needle opening and would make the
turbine to achieve required load, set by the power set point (Epos).
h) The MW ERROR signal is generated as per block diagram 2(b) by subtracting
the Power reference (Pref calculated earlier) and the actual output of the
turbine. The contribution of this error signal is limited to +/- 10% of the turbine

rated load. This MW ERROR is added to the signal Epos calculated in the
paragraph – (g) and a final position signal reference is generated.
i) The final position reference in - (h) and the actual needle position is subtracted
to generate an error signal. This error signal is fed to a parallel PID controller.
The output of the PID controller is fed to the needle actuator (servo valve)
through the hardware modules.
Invention is emphasized on system of controlling needle of the hydro
turbine as primary control. Accordingly Controller system function has been
developed.

WE CLAIM

1. A method of governing impulse turbine (vertical Pelton) of hydro power plant using
direct needle control as primary control element, wherein speed error sets the
needle positions instead of using position reference.
2. The method as claimed in claim 1, wherein, speed control of the turbine is achieved
by using speed error directly to position the needles, eliminating any control loop.
3. The method as claimed in claim 1, wherein in MW error is used over the position
reference of the needles in execution of loading of impulse turbine.