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1、Electrical auxiliary supply systems for hydro-electric power plants J.A. Wade, B.Sc.(Eng.), C.Eng., M.I.E.E. Indexing terms: Natural resources, Power systems and plant Abstract: The paper examines the auxiliary equipment of hydro-electric generating stations and associated dams, spillways and other

2、works in respect of the essentiality of electrical auxiliary supply to these equipments. Various alternative sources of auxiliary electrical supply are considered, the advantages and disadvantages of these are compared and proposals are made for high voltage distribution systems around the hydro-ele

3、ctric plant and associated works. Arrangements for DC supply systems and uninterruptable power supply (UPS) systems are also discussed. 1 Introduction The safety and continuity of output of a generating plant largely depend on the reliability of the electrical supplies to the auxiliaries. Hence care

4、ful consideration should be given to the design of the electrical auxiliary distribution system. As a point of interest, the electrical load which is required for running the various items of auxiliary plant and services on a hydro-electric project, including those at the associated dam, spillway an

5、d other works, may amount to about j% of the maximum station capacity in the case of a normal hydro-electric station above ground. This may be up to 2 to 2| / of the station capacity in the case of a pumped storage generating station situated below ground. 2 General auxiliaries and their supply requ

6、irements In arriving at the arrangements required for an auxiliary electrical supply system, it is firstly pertinent to consider the auxiliaries for which electrical supplies have to be provided and the circumstances surrounding their use. From this one can then evaluate whether the auxiliary suppli

7、es which should be provided in each case need to be highly secure, whether a standby supply needs to be immediately available or can be less immediately available, and whether a standby supply is necessary under all operating conditions. 2. 7 Main auxiliary plant items The main items of auxiliary pl

8、ant which have to be provided for from the electrical auxiliary power supply system, whether AC or DC, and the considerations of security which are applicable in each case are generally as follows: 2.1.1 Turbine-generators: For turbine-generators the following unit auxiliary items will need to be co

9、nsidered: (a) Main inlet valves: The control system is by hydraulic opening of the valve with gravity closing. Other than the DC control system, no electrical auxiliary power requirements exist for this fairly important item of auxiliary equipment. It is an important item because main inlet valve cl

10、osure is usually a part of the turbine-generator set shut-down sequence. Its closure will obviate shaft rotation at low speeds which could be caused by guide vane Paper 4377C (P103 PI, P9), first received 19th September 1984 and in revised form 22nd November 1985 The author is with Kennedy & Donkin,

11、 Consulting Engineers, Westbrook Mills, Godaiming, Surrey GU7 2AZ, United Kingdom leakage and which could have an undesirable effect on bearing wear, a point which will be mentioned later. (b) Governor oil pumps and associated compressed air cushion for the guide vane control system: This system mus

12、t be brought up to and maintained at appropriate oil levels and air pressure before a start-up procedure can be commenced, and must be so maintained during operation. In the event of auxiliary supply failure, sufficient oil capacity for a number of operations is available. The system is therefore ad

13、equate to perform a shut-down procedure, and the shut-down process would not be adversely affected by the loss of AC supply. (c) Generator excitation: It is some years since amplidyne sets were common, these requiring main and standby driving motors. The usual current practice is to use excitation t

14、ransformers at the generator terminals, these being effectively unit transformers, energising the thyristor converter system. Start-up and run-down periods are adequately covered by the control of this system, as also is the effect of short-circuit on the generator terminals. A DC field flashing sup

15、ply is normally the only alternative supply required, this being necessary for a brief period at start-up. In the case of generator-motor units in pumped storage schemes a DC excitation supply may be required to maintain dynamic braking. (d) Bearing oil systems: Oil supply to thrust and guide bearin

16、gs during running conditions has been made by main AC and standby DC pumps. However, the use of self-lubricating bearings, in which the pumping action is inherent in the bearing design, has now become prevalent. Under the running condition with such bearings there is no need for a continuous oil fee

17、d from an external system. Such bearings may be suitable for use without hydrostatic lift. However, where starting is frequent (for example in pumped storage plants) and/or the bearing pressure is high, then a high pressure lifting or jacking oil pump is used to force oil between the sliding surface

18、s of the pads. In the case of generator-motor units in pumped storage schemes, this also reduces the stiction torque which is important in starting such sets in the pumping mode. This pump may also be used during the run-down period on a shut-down sequence where, if this is likely to be long, there

19、is perhaps a greater danger of bearing wipe than at startup. However, the availability of hydrostatic lift or jacking oil supply may not be essential to enable black start of a generator to be undertaken. Equally, during the stopping sequence the same would apply when the stopping time does not exce

20、ed about 15 minutes. (e) Mechanical brakes: Hydro-electric units have high inertia and can therefore have long run-down periods, 148 IEE PROCEEDINGS, Vol. 133, Pt. C, No. 3, APRIL 1986 sometimes more than three or four hours, depending upon the type of set and the operating mode (e.g. blown down or

21、churning water). Many smaller hydro-electric units, and even some larger ones, do not have brakes, particularly when they are fitted with hydrostatic lifting equipment. When mechanical brakes are fitted, they are intended to deal with the following problems associated with the rundown period of the

22、set: Under a normal shut-down operation, when brakes may be applied at about 25% speed for perhaps about one minute, it is the intention (i) to reduce the time at low speed where there is no hydrostatic lifting for the thrust bearing and thereby to reduce the risk of bearing wipe (it) to hold the ro

23、tor at standstill until the main inlet valve has closed in cases where guide vane tolerances, erosion or sticking allow a leakage torque to continue. Under emergency shut-down conditions, brakes would probably be applied at about 50% speed and, depending on the type of set, may be on from 5 to 15 mi

24、nutes. The virtues of the use of mechanical brakes under these conditions are arguable but, if used, the emergency operation would be initiated by: (i) vibration (ii) bearing temperature (iii) failure of oil circulation (if non self-lubricated bearings) (iv) fire Thus it follows that where mechanica

25、l brakes are used, a compressed air system is required to operate them which must be available under the shut-down procedure. This compressed air system would be maintained fully charged and have adequate capacity at the commencement of the shut-down procedure. Hence the loss of compressor AC suppli

26、es would not affect the conditions of shut-down adversely. (/) Generator cooling: Internal cooling air is normally by rotor fan circulation, except in the case of reversible generator-motor units when motor-driven ventilating fans are required. Cooling water for the heat exchangers may require main

27、and standby pump sets to establish water circulation before start-up and to maintain it during running. Failure of this circulation during a run-down would not be of consequence as load would then have been removed. (g) Generator-transformer cooling: The generator- transformers would probably have f

28、orced oil pumps and, depending on circumstances, either water circulation or air cooling. As in the case of the main generator cooling, the supply to these auxiliaries needs to be established at startup and maintained during running. Again, it would not be essential to maintain the electrical supply

29、 during the shutdown sequence because the load would first have been removed. 2.1.2 Station general services and head works services: For the station general services and head works services associated with the hydro-electric project, the following principal items require consideration: (a) Compress

30、ed air systems: These have been referred to above in so far as they are required for certain items of turbine-generator auxiliary equipment. In general, compressed air plant may be installed to fulfil any of the following functions: (i) turbine low load injection (ii) blow-down for condenser operati

31、on (iii) blow-down for spinning reserve mode for pumped storage plant. The last function requires a reasonable level of electrical supply security to the compressed air system in question to ensure availability of the generator-motor for the various modes of operation which are important to its role

32、 in the supply system. (b) Drainage and dewatering pumps: Drainage pumps must be maintained in operation, particularly in underground power plants, although a short period of interruption may be of no consequence. Dewatering pumps may present a larger load but as they are associated with an inspecti

33、on and maintenance service their use can be programmed appropriately so as not to coincide with electrical supply loss conditions. (c) Fire fighting systems of the water spray or deluge types: These may use a compressed air service which must be maintained charged at all times in order to ensure the

34、 required water pressure at the spray nozzles. The storage capacity will be sufficient to tolerate loss of auxiliary supply for a reasonable interval. If DC fire pumps are alternatively employed very considerable addition to battery capacity may be needed. (d) Spillway gates: On the hydraulic side a

35、n item which may require secure electrical auxiliary supplies is the spillway gate system. These are hydraulically actuated. The importance of maintaining control of these gates under flood conditions is often sufficient to justify provision of a local low voltage diesel generator set in addition to

36、 the provision of a reliable AC auxiliary supply. The diesel generator set, which may only be 100 or so kVA, can be a mobile unit. (e) Intake (penstock) gates: Gravity operation would usually be adopted if they are required to be shut under emergency conditions, although some types of gates may be h

37、ydraulically actuated in which case a compressed air system situated locally would need to be maintained charged. 2.2 Assessment of auxiliary plant electrical supply requirements The above review indicates that in hydro-electric plants one does not generally experience the high degree of essentialit

38、y of auxiliary plant supply that is needed in a thermal power plant, where, for instance, such items as boiler feed pumps and condensate extraction pumps are of critical importance. If one wishes to have a black start capability it will be necessary usually to have a diesel generator set or auxiliar

39、y hydro set sufficient in rating to start oil pumps and cooling water circulation and to charge compressed air systems and battery systems if the black out has been of long duration. In the running condition all auxiliaries are, of course, essential to the continuous operation of a turbine- generato

40、r set. However, a reasonable degree of tolerance can exist in changeover time to a standby supply. The total loss of electrical auxiliary supply is not likely to cause damage, even in the case of the bearings system, provided that a shut-down sequence is initiated in good time and that mechanical br

41、akes are applied when the circumstances warrant them. If mechanical brakes are not used, a DC hydrostatic lift pump may be necessary to maintain bearing oil films below about 20% speed. It will, of course, be appreciated that control, alarms, recording and signalling systems must be available withou

42、t failure under all conditions to enable the necessary IEE PROCEEDINGS, Vol. 133, Pt. C, No. 3, APRIL 1986 149 sequences to proceed. The power requirements for these are not large and are met by DC batteries and/or uninter- ruptable AC power supply systems under auxiliary supply failure conditions.

43、Lighting systems, similarly essential to the maintenance of control of the plant, must be supplied to the minimum levels necessary under supply failure conditions. 3 Consideration of sources of AC auxiliary supplies The primary source of auxiliary supply is a high voltage AC system, preferably to en

44、sure security at least two HV AC systems. However, apart from the system into which the hydro-electric plant is generating, alternative or secondary AC systems are often not available or are unreliable in the environments in which hydro-electric plants tend to be situated. Sometimes, however, a reas

45、onable high voltage (or extra high voltage) AC supply is installed at the construction stage and this may continue to be used after completion of construction as an alternative auxiliary electrical supply source. 3.1 Main electrical system sources If a hydro-electric plant has a fairly high merit po

46、sition in the system, such that maximum continuity of output from it is desirable, or its size is such that its loss will be serious, then it becomes preferable to obtain the auxiliary electrical supply source from as close to the generator terminals as possible. The following alternative methods pr

47、esent themselves, offering a descending order of security in the order as given: 3.1.3 Connection from the main high voltage or extra high voltage system, as from the power plant switchyard by station transformers: This approach means the additional expense of HV or EHV switchgear bays and transform

48、ers. 3.2 Auxiliary hydro-electric generating set sources As a further alternative, although one presenting some considerable additional civil, electrical and mechanical cost, may be mentioned the use of an auxiliary hydrogenerating set. This is plainly a reliable form of alternative electrical auxil

49、iary supply as it is independent of any electrical system and perhaps more reliable than a diesel unit. It may be used as a standby or start-up supply. However, if intended as a normal source of auxiliary supply, the auxiliary hydro-electric generator set should be designed appropriately for higher efficiency. 3.3 Local electrical system sources A further source of AC auxiliary supply is the possible use, if available, of a local high voltage (or even extra high voltage) system. As mentioned earlier, such a system may be the original construction supply or may be a local distr