process controllers functions in hydro power plant

8/8/2019 Process Controllers Functions in Hydro Power Plant

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d

c Designed by B. Horvat KON^AR

b Checked by B. Premer POWER PLANT AND ELECTRIC

a . . Approved by T. Duzevic TRACTION ENGINEERING Co.

Rev Description Date Sign. Name Sign. ZAGREB, C R O A T I A

Project: TD No: 8345-62-98-000X BOOK: Title:

PROCESS CONTROLLERS’ FUNCTIONS

IN HYDRO POWER PLANT

Dep.No: Drawing No: KET-201

=

File: KET-201

PROCESS CONTROLLERS’ FUNCTIONS IN HYDRO POWER PLANT



KON^AR Project: KET-201 POWER PLANT AND ELECTRIC Title:

ZAGREB, C R O A T I A - PROCESS CONTROLLERS’ FUNCTIONS IN HYDRO

POWER PLANT Sheet 2 of 6

Format: A4 No. TD: 8345-62-98-000X Book:

File:KET-201

CONTENTS

1 Introduction2 Data acquisition3 Start/stop sequences4 Active and reactive power setpoint control5 Stator current limitation6 Thermal supervision7 Spillway gate position adjustment8 Auxiliary services power supply control9 Flow calculation10 Water level control11 Joint active power control

12 Joint reactive power control13 Reports







File:KET-201

1 INTRODUCTION

The purpose of the following description is to give to the reader a quick general insightinto the way Kon>ar uses DCS technology (ABB and Siemens) in hydro power plants control. Itdoesn't refer to control scheme in any specific hydro power plant.

Some typical functions realized in hydro power plant control system are given. The finalscope of these functions is in any particular case tailored according to customer needs asexpressed in tender documents and agreed upon during the project design phase.

2 DATA ACQUISITION

Digital data are red out either cyclically or by change of state, and time tagged for eventhandling in operator station (1 ms time resolution in controllers). Analog data reading takesplace only cyclically, with selectable scanning time. Analog signals are prefiltered, convertedfrom raw to engineering units, and checked against the limits. Passing of any of limit values (2low and 2 high limits) is treated as the event. For living zero signals additional validity check isdone, and the alarm is given in the case measured value is out of expected range. The alarmsignal is also given in the case of faulty channel on input module.

3 START/STOP SEQUENCES

Each start up / shut down sequence is divided into a number of steps. Start/stop orderscome either from the operator, via Operator Station, or in some cases from water level controlprogram. Before the commencement of the start sequence, fulfilment of start conditions ischecked; the same is case with each step of the sequence. The whole sequence and thesteps in it are time monitored and the fault signal is given with proper fault information in thecase of malfunctioning.

4 ACTIVE AND REACTIVE POWER SETPOINT CONTROL

Depending on the type of turbine governor (voltage regulator) setting device, setpoint is

simply transmitted in the form of BCD or mA signal, or adjusted by sending the train of raise/lower pulses of variable length. Controlled value is monitored during adjustement, andthe fault signal is given when it doesn't behave in accordance with the sent pulses.

Setpoints come from different places within control system: start/stop sequences, jointor water level control, limitation functions or directly from the operator. Selection of valid one isdone by program, depending on the control status of generating unit and the priority level of the function setting the request.







File:KET-201

5 STATOR CURRENT LIMITATION

When the unit is in automatic mode of operation, stator current is monitored, andcorrective action is taken when it exceeds the limit longer than allowed. Reactive power isreduced first, if necessary to zero. If this reduction doesn't bring stator current back into theallowed range, the active power is reduced.

Very often, the supplier of the excitation system realizes the same function within thisequipment. In this case these limit values should be co-ordinated. However, theimplementation of this function within the integrated plant control system has severaladvantages. The first of them is the ease of changing of limit value, via the keyboard and notwith a potentiometer, especially if it is to be done temporarily, e.g. due to some troubles in thecooling system.Also, the excitation system can act only on excitation current, which might be unsatisfying in

the cases, actually very seldom, of too low network voltage.Generally, supervision and limitation functions in such a system are more flexible incomparison with those realized with conventional circuitry. All measurements of interest areaccessible (active and reactive power, current, voltage, excitation current, guide vane opening,temperatures, vibrations intensity ...), limitations can be done on any one or combinations of them, obeying the priority, and by acting either on excitation system or turbine governor, or both, even in some cases on auxiliaries (cooling water system or fans).

6 THERMAL SUPERVISION

Temperatures of all points of interest are continuously measured and shown on processdisplays and trend curves. They can be also used for tripping of generating unit in case of hightemperature or for reduction of active or reactive power, rarely directly, but more often usingthe results of calculation of dependency between stator current and winding temperature for setting of stator current limit.By means of local display all temperatures can be selected and displayed. An alarm isactivated in the case of adjustable limit crossing of each and every measured chanel.

7 SPILLWAY GATE POSITION ADJUSTMENT

This adjustment takes place in form of continuous raise/lower orders. Measured value ismonitored during adjusting, and fault signal is given in the case of malfunctioning. A setpointcomes either from water level control program or is issued directly by the operator.

8 AUXILIARY SERVICES POWER SUPPLY CONTROL

Auxiliary services are usually supplied from two or more sources, e.g. auxiliary power transformers connected to transmission or distribution network and diesel-generator set, or other auxiliary generating unit. Sometimes the power of diesel-generator set is not enough for the supply of all auxiliaries and care must be taken of its load. As the philosophy of auxiliarypower supply varies from plant to plant, control program is adapted to each particular case.







File:KET-201

9 FLOW CALCULATION

Turbine flow is usually measured using flow transducers, but it can be also calculatedfrom the measured guide vane opening and the difference between head - and tailwater.Spillway gates flow is normally calculated on the basis of their openings and water level, usingspillway discharge curves. Measured and calculated flow values are shown on process andtrend displays, and are included in daily and monthly reports. Turbine flows can be used for unit efficiency calculations.

10 WATER LEVEL CONTROL

There exist in fact two water level control programs. First of them tries to keep water

level at a desired value adjusting the active power and therefore turbine flow. Here it should beemphasized that the water level control makes sense only in plants with rather smallreservoirs, i.e. where utilizable volume can be emptied in several hours.

The second program is protective one and it regulates the level in the reservoir byspillway gates, doing this of course only when generating units work at their maximum or theyare out of operation. These two programs are therefore coordinated by setting the levelreference value for turbines little below the setpoint for spillway gates. For rather short andnarrow reservoirs, a statism cm/MW is very often included in the calculation of error signal. Inaddition, these reservoirs have strong dynamics, and more sophisticated control methods (likefeed-forward, variable control parameters etc.) must be used.

The output from this controller is active power which is distributed among the generating

units taking into account their efficiency curves, limit values and possible forbidden operationareas, for instance due to oscillations, vibrations and cavitations.

The program takes care of the number of units in operation, with respect to efficiency.Besides, water level measurement, as the most critical one, is continuously checked, and if itfails the units are switched off from this control.

This program package can be simply adapted to the case when there exist more usersof water resources: irrigation, water supply of big cities etc.

11 JOINT ACTIVE POWER CONTROL

Active power is distributed among the generating units following the same rules as inwater level control. As the applied regulator is of PI-type, the statism of joint controller is validfor the behaviour of the plant active production in the cases of frequency disturbances and notthe statisms of individual governors. Of course, this is an important issue only in isolatednetworks.

12 JOINT REACTIVE POWER CONTROL

Total reactive production is also controlled in closed loop. Depending on the plant sizeand its importance in power system, busbar voltage deviation is included in error calculationwith greater or lower weighing coefficient. Required reactive power at the regulator output isdistributed among the generating units proportionally to their maximum reactive powers, takinginto account the limit values.







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13 REPORTS

Energy meter reports and flow reports are commonly used in hydro power plants.Energy counters are software realized if using ordinary digital inputs. Daily and monthly reportsare printed out automatically or upon operator's request. Reports can be also shown onprocess displays on VDUs and copied on hardcopy. Beside flow and energy, other reports arealso possible, including both measured and calculated values: electrical measurements,temperatures, levels, and so on.

process controllers functions in hydro power plant

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