CLP: The construction of Hok Un power station 1921, Part Four

Graham Wood has kindly sent a copy of the souvenir brochure issued at the official opening of the Hok Un power station in 1921.

HF: I have retyped the original PDF version of the brochure sent by Graham and as it is a fairly lengthy document this is the fourth in a series of articles. I will include all the images and script shown in the original brochure but am unable to reproduce its exact format. Unfortunately two pages from the original brochure sent to me by Graham were missing. However Leanne Molloy, who has recently been in touch with me about Hok Un power station, says that she has by coincidence a copy of the souvenir brochure and I have asked if she can send me the missing pages which I can then retype and add to the article below.

Thanks to SCT for proofreading the retyped copy.

ELECTRICAL POWER GENERATION

The new 12,500 kW. turbo-alternator set, manufactured by Metropolitan-Vickers Electrical Co., is of the single cylinder direct coupled impulse type running at 3,000 r.p.m. The photograph on page 34 [see next image] shows the characteristic robustness of this type in which relatively large running clearances at the blades are employed.

Designed for inlet conditions of 395 lb. sq. in. g. 625° F, the turbine contains 18 low velocity high efficiency stages preceded by a velocity compounded or two-row stage. All parts subject to high pressure and temperature are of cast steel, the steel portion of the casing extending over the first eight stages and incorporating in the top half the steam chest housing four nozzle control governor valves. The remainder of the casing is of cast iron, with the exception of the bottom half exhaust end, incorporating the inboard turbine and generator bearings and pedestal, and this is of robust welded steel construction.

The diaphragms of the first eight stages are made entirely of molybdenum steel; they are built up with plate centres to which are fitted and riveted machined nozzle blades. The remaining diaphragms are of cast iron with cast-in blades of stainless steel. The rotor contains 19 forged steel discs shrunk and keyed on to a mild steel shaft, the blading of the first 9 discs being of the T root type and the remainder of the straddle root type securely attached to the discs by rivets.

The axial thrust on the rotor, which with the impulse type of turbine is relatively small, is carried by a thrust bearing of the Michell type, the bearing also serving to locate the rotor in its proper axial position.

The spindle gland at the high pressure end is of the radial clearance labyrinth type. It consists of a number of steel rings each provided with a series of horizontal fins which register with running clearance against radial fins formed on a sleeve on the shaft. Each ring and also the housings in which they are carried, are backed by a series of flat springs in grooves so permitting radial movement of the entire gland in the event of accidental contact. At the exhaust end the gland is of the water seal type which consists of an impeller, secured to the shaft, rotating in a housing to which a constant head of water is applied. The rotation of the impeller forms a water seal around its periphery in the housing so preventing the ingress of air to the condenser. This gland is supplemented by a labyrinth gland to which steam is admitted for starting up purposes.

The main oil supply is provided by a gear wheel type oil pump coupled to the bottom end of the governor spindle. This pump delivers the whole supply at the governor relay pressure, the supply to the bearings  being reduced in pressure by means of a reducing valve. An oil cooler, of the tubular type and supplied with water from the circulating system, is interposed between the reducing valve and the supply to the various bearings.

For starting up, shutting down and emergency conditions a turbine driven auxiliary oil pump is provided. This pump is mounted on the oil tank, with pump submerged, and it is automatically brought into operation in the event of the oil pressure falling below a certain value.

The main governor is of a sensitive vertical type driven by worm gearing from the turbine spindle  and operates the steam governing valves through the medium of an oil relay system. Changes in load on the set with resulting changes in speed cause the governor weights to move the central control piston of a relay valve within a compensating sleeve containing oil ports. This movement causes oil to be admitted to or released from an oil operated power piston operating the steam valves until a steam valve setting appropriate to the load is reached, the movement of the power piston being automatically compensated by the movement of the compensating sleeve back to its original setting relative to the control piston, thus ensuring stability of governing.

For adjustment of running speed or load transference to other plant operating in parallel, both hand and electric motor speeder control are provided. In each case the adjustment is effected by raising or lowering the setting of the compensating sleeve.

Additional safeguard against overspeed is provided in the form of a bolt type emergency governor fitted at the end of the turbine spindle. It consists of a spring retained plunger which when moved out by excessive centrifugal force engages with a trip lever which actuates an oil valve instantly releasing the oil pressure in the relay system but without affecting the supply to the lubricating system. This action not only allows the governor valves to close under spring action but also releases a trip device on the emergency stop valve bolted to the steam chest, causing it to close instantly under spring action.

A selective device is incorporated in the mechanism operating the governor valves which enables the sequence of opening of the four governor valves to be changed at will by the operation of one or both of two small hand levers. By such means and by suitably proportioning the four nozzle groups controlled by the valves, it is possible to provide six loadings at which throttling losses are entirely avoided while at intermediate loads such losses are reduced to negligible values.

The condenser is of the Metropolitan-Vickers Central Flow type, and has a cooling surface of 16,000 square feet. It is normally supplied with 11,000 g.p.m. of cooling water at 85° F. The characteristic feature of this type of condenser is the access of exhaust steam to practically the whole periphery of the tube nest and the withdrawal of the air from the centre.

This design results in a number of important advantages. Firstly, the pressure drop on the steam side across the tube nest to the air suction is relatively small, and results in a high

rate of heat transmission. Secondly, the final temperature of the condensate leaving the condenser is high as the greater part of the condensed steam falls through a steam atmosphere before it is collected in the condenser base. Thirdly, the withdrawal of the air from the centre results  in the atmosphere at the base being principally water vapour without air concentration and the condensate withdrawal at the latter point results in the oxygen content being extremely low and thus rendering the employment if separate de-aerating plant quite unnecessary.

The condenser shell is of welded steel construction, and is bolted directly to the turbine exhaust flange. The tubes are of 1″ dia. Admiralty mixture.

The water flow is divided, with separate water box doors on each flow, enabling either half of the tube nest to be cleaned while the other is in operation.

The condensate is withdrawn from the condenser by motor driven extraction pumps installed in duplicate, while the air is dealt with by duplicate two-stage steam operated air ejectors.

The feed heating system consists of two low-pressure and one high-pressure feed heaters, each supplied with steam tapped from a point in the turbine expansion, together with a drain cooler, while the inter- and after-coolers of the air ejectors through which the feed passes also constitute a supplementary feed-heating stage. A simplified diagrammatic arrangement of the complete feed circuit is shown on page 37  [the last image above]. It will be noted that a connection is provided from the surge tank back to the condenser, through which a portion of the feed is continuously recirculated, and the feed in the tank is thus maintained in a de-aerated state.

The make-up supply to the closed feed circuit is provided by means of a Metropolitan-Vickers straight tube type evaporator incorporated in the feed heating system. The evaporator operating steam is diverted from the turbine with the supply to the second low pressure feed heater, after performing work in the turbine, while the evaporated make-up is condensed in the first low pressure heater from which it ultimately passes to the condenser.

The feed heating system provides for the final feed temperature leaving the high pressure heater of 275° F. at the maximum rating of 12,500 kW.

PAGES 39 + 40 ARE MISSING AND WILL HOPEFULLY BE ADDED AT A LATER TIME.

together with the generator-field instruments, frequency meter, emergency trip-switch, exciter-field switch, synchronising plugs, and engine-room telegraph-transmitter.

In all, six generator control desks and seven cubicle type control-panels have been supplied, together with ten control-panel cubicles to receive panels and equipment transferred from the existing flat-back control-board in the North Station. With the new arrangement, the whole of the control for the existing North Station and the new South Station is centralised in one control-room.

The multi-core control cables are of the cambric-insulated lead-sheathed type, asbestos braided and fireproof compounded, supplied by W.T. Henley’s Telegraph Works Co. Ltd., through Reyrolle.

(2) 350-volt Main Switchgear.

[please note, there is no subheading (1) in the original brochure]

This is a 16-panel 3-phase, 4-wire 350-volt horizontal drawout metalclad switchgear, mounted on a gallery above the turbine room, and consists of four 2,500 ampere type H1 and twelve 800 ampere type-D1 panels with manually-operated oil-immersed circuit breakers having a breaking capacity of 25,000 kVA.

The auxiliary-transformer panels are each equipped with an inter-tripping feature to ensure that the opening of the 6,600 volt oil-immersed circuit-breaker under short circuit conditions will trip the corresponding 350-volt oil-immersed circuit-breaker. No.2 panel controlling the lighting is arranged for remote tripping from the control room to enable the Station to be “blacked out” immediately in case of air raids. A special separate system of air raid lighting has been provided.

(3) 350-volt Distribution Switchgear.

This consists of 3-phase 4-wire 440-volt type-HH air insulated metal-clad switch-and-fuse gear with cartridge fuses and type-HH E5 oil-immersed circuit-breakers, suitable for use where the prospective short-circuit fault is of the order of 25,000 kVA. There are several switch boards, comprising varying arrangements of units of standards sizes ranging from 60 amperes to 1,000 amperes.

These switchboards are interconnected in such a way that an alternative supply may be obtained in an emergency.

(4) 350-volt Distribution Fuse Gear.

There are five Distribution fuse-boxes, fed from the 350-volt distribution switchgear, arranged for 3-phase 4-wire service and equipped with semi-enclosed fuses.

This article was first posted on 5th December 2021.

Related Indhhk articles:

1. CLP: The construction of Hok Un power station 1921, Part One
2. CLP: The construction of Hok Un power station 1921, Part Two
3. CLP: The construction of Hok Un power station 1921, Part Three
4. CLP – Hok Un (Yuen) Power Station 1921-1991 – updated
5. John M. Henderson, Engineering Company, Aberdeen, Scotland…link to Hok Un power station, Hong Kong
6. Andrew Wood biography – involvement in the repair of Hok Un power station at the end of the Japanese occupation of Hong Kong
7. Hok Un Power Station, post World War Two images
8. CLP’s Hok Un Power Station – immediately post World War Two
9. Preece, Cardew and Rider – Consulting Engineers for Hok Un power station
10. CLP’s Hok Un Power Station during the Japanese occupation
11. CLP- Lawrence Kadoorie speech 1977 – HK + Hok Un Power Station during WW2
12. Hok Un Power Station, a compilation of those who helped restore it at the end of World War Two
13. Robert Gordon Shewan – CLP, Green Island Cement and HK Rope Manufacturing