Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

A Constant Frequency System for Aircraft Electrical Supplies

A Constant Frequency System for Aircraft Electrical Supplies AUXILIARY POWER A Constant Frequency System angle is controlled by a governor driven from the for Aircraft Electrical Supplies output shaft. The governor consists of hydraulic valve, which supplies the cylinders which actuate the swash­ Details of the English Electric Sundstrand plate, and which is controlled by flyweights driven from the output shaft of the drive. The Hydro-Mechanical Constant Speed Drive thrust from the rotating flyweights is balanced by two springs, one pre-set, and the other connected to a plunger rod driven by a two-phase induction motor, giving frequency control. This motor is actuated by signals from a magnetic amplifier controlled by current transformers in each of the HE rapidly increasing electric power re­ bility. Air turbines are another possibility, but alternator circuits. A considerable measure of quirements of aircraft, together with their they make large demands on the main engine load sharing is thus achieved, as well as frequency Tmore arduous operating conditions, have compressor. Variable ratio friction drives may be constant to within one per cent. An overspeed accelerated the trend towards the adoption of useful, especially at high altitudes, but little work governor is also provided. 400 c.p.s. a.c. supplies as standard for general has been done on them. The most promising services. The point is being reached where a.c. system at present seems to be the hydraulic pump distribution and control systems based on ground and motor transmission, particularly if it is used Two Types power station practice are becoming applicable differentially, rather than carrying the full load The unit which is at present under development to aircraft. The main advantages of a.c. over the power. is known as the Package type, being a self-con­ corresponding d.c. systems are: tained assembly, shown in FIG. 2 coupled to a Easier commutation, particularly at high The Sundstrand Drive 40-kVA alternator. In this type, which will be altitude; the first to be produced in this country, the unit The English Electric Co. Ltd. have been Inverters are not needed and motors are has its own scavenge pump and charge oil pump, developing an aircraft system, using many of the lighter and simpler so the weight of the system the latter supplying the oil under pressure to the established principles of power station practice, is less; drive pump, which is not self-priming. The only and have adopted a constant speed drive of this The alternator, being essentially a constant external components needed are the oil reservoir, type, the Sundstrand drive, which they are to speed machine, can be designed for that filter and cooler. The system can be integrated manufacture under license from the American speed only, and so be lighter than a wide range with the engine lubrication system to make use of Sundstrand Machine Tool Corporation. machine; its corresponding components, possibly with a A schematic diagram of the drive is reproduced On a star-connected three-phase system the fuel-cooled oil system. This principle is extended in FIG. 1. The input from the engine is transmitted failure of one phase does not imply complete in the proposed Cartridge type installation, which through the gear wheel 13 to the pump and motor breakdown; would be completely integrated with the engine's cylinder assembly. The rotation of this relative Many of the loads require a.c. in any case; oil system, and so save weight. In this case the to the pump swashplate 4 causes reciprocation Circuit breakers are much smaller and lighter engine's pumping and scavenging system would of the pistons I, if the swashplate is inclined. The for a.c. be used as well as the cooler. displacement of fluid from the pump to the motor The coupling to the alternator is through a sets up a corresponding cyclic displacement of Possible Systems sprag clutch which prevents the alternator the motor pistons, and hence a rotation of the motoring the drive if, when paralleled, it tends to The main factor which has been limiting the fixed-angle swashplate 11 relative to the cylinder do so. development of a.c. systems has been the difficulty barrel. The output gear 12 is thus driven at a of running main-engine driven alternators at suf­ higher speed than the input gear 13. If the pump ficiently constant speed under varying conditions. swashplate is not inclined the pump and motor Test Rig assembly is locked solid hydraulically, and the At first sight the independent auxiliary power unit input and the output are at the same speed. If the Development work is being carried out on a is attractive, but the only suitable prime mover pump swashplate is inclined in the reverse direc­ test rig at the Acton works of D. Napier and Son from weight and space considerations is the small tion the pump allows a metered flow of fluid to Ltd. Two Rover Meteor petrol engines, of some gas turbine. Unfortunately, in such small sizes the gas turbine has a high fuel consumption, and return from the motor, and the motor swashplate 50 b.h.p., each drive one 40 kVA alternator this is felt still more if the load is to be divided is then driven so that the output r.p.m. of the through Sundstrand drives. Various electrical between two or more units for reasons of relia­ drive is lower than the input. The swashplate loads are provided, including a pulse load of 8 kW which is on for 40 milliseconds every half second, simulating a type of radar installation. On this rig, as the various loads are switched in and the input r.p.m. varied between 3,000 and 8,000 the drive can be seen to maintain the alter­ nator speed and frequency constant to within one per cent, even under rates of input acceleration or deceleration of 1,000 r.p.m./sec. The rig is fully instrumented for parallel operation, and the two alternators can be paralleled, for example, with one input speed at 4,000 and the other at 8,000 r.p.m. Aircraft Engineering http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

A Constant Frequency System for Aircraft Electrical Supplies

Aircraft Engineering and Aerospace Technology , Volume 27 (4): 1 – Apr 1, 1955
Download PDF
1 page

Loading next page...
 
/lp/emerald-publishing/a-constant-frequency-system-for-aircraft-electrical-supplies-UqXffm00qE

References

References for this paper are not available at this time. We will be adding them shortly, thank you for your patience.

Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0002-2667
DOI
10.1108/eb032547
Publisher site
See Article on Publisher Site

Abstract

AUXILIARY POWER A Constant Frequency System angle is controlled by a governor driven from the for Aircraft Electrical Supplies output shaft. The governor consists of hydraulic valve, which supplies the cylinders which actuate the swash­ Details of the English Electric Sundstrand plate, and which is controlled by flyweights driven from the output shaft of the drive. The Hydro-Mechanical Constant Speed Drive thrust from the rotating flyweights is balanced by two springs, one pre-set, and the other connected to a plunger rod driven by a two-phase induction motor, giving frequency control. This motor is actuated by signals from a magnetic amplifier controlled by current transformers in each of the HE rapidly increasing electric power re­ bility. Air turbines are another possibility, but alternator circuits. A considerable measure of quirements of aircraft, together with their they make large demands on the main engine load sharing is thus achieved, as well as frequency Tmore arduous operating conditions, have compressor. Variable ratio friction drives may be constant to within one per cent. An overspeed accelerated the trend towards the adoption of useful, especially at high altitudes, but little work governor is also provided. 400 c.p.s. a.c. supplies as standard for general has been done on them. The most promising services. The point is being reached where a.c. system at present seems to be the hydraulic pump distribution and control systems based on ground and motor transmission, particularly if it is used Two Types power station practice are becoming applicable differentially, rather than carrying the full load The unit which is at present under development to aircraft. The main advantages of a.c. over the power. is known as the Package type, being a self-con­ corresponding d.c. systems are: tained assembly, shown in FIG. 2 coupled to a Easier commutation, particularly at high The Sundstrand Drive 40-kVA alternator. In this type, which will be altitude; the first to be produced in this country, the unit The English Electric Co. Ltd. have been Inverters are not needed and motors are has its own scavenge pump and charge oil pump, developing an aircraft system, using many of the lighter and simpler so the weight of the system the latter supplying the oil under pressure to the established principles of power station practice, is less; drive pump, which is not self-priming. The only and have adopted a constant speed drive of this The alternator, being essentially a constant external components needed are the oil reservoir, type, the Sundstrand drive, which they are to speed machine, can be designed for that filter and cooler. The system can be integrated manufacture under license from the American speed only, and so be lighter than a wide range with the engine lubrication system to make use of Sundstrand Machine Tool Corporation. machine; its corresponding components, possibly with a A schematic diagram of the drive is reproduced On a star-connected three-phase system the fuel-cooled oil system. This principle is extended in FIG. 1. The input from the engine is transmitted failure of one phase does not imply complete in the proposed Cartridge type installation, which through the gear wheel 13 to the pump and motor breakdown; would be completely integrated with the engine's cylinder assembly. The rotation of this relative Many of the loads require a.c. in any case; oil system, and so save weight. In this case the to the pump swashplate 4 causes reciprocation Circuit breakers are much smaller and lighter engine's pumping and scavenging system would of the pistons I, if the swashplate is inclined. The for a.c. be used as well as the cooler. displacement of fluid from the pump to the motor The coupling to the alternator is through a sets up a corresponding cyclic displacement of Possible Systems sprag clutch which prevents the alternator the motor pistons, and hence a rotation of the motoring the drive if, when paralleled, it tends to The main factor which has been limiting the fixed-angle swashplate 11 relative to the cylinder do so. development of a.c. systems has been the difficulty barrel. The output gear 12 is thus driven at a of running main-engine driven alternators at suf­ higher speed than the input gear 13. If the pump ficiently constant speed under varying conditions. swashplate is not inclined the pump and motor Test Rig assembly is locked solid hydraulically, and the At first sight the independent auxiliary power unit input and the output are at the same speed. If the Development work is being carried out on a is attractive, but the only suitable prime mover pump swashplate is inclined in the reverse direc­ test rig at the Acton works of D. Napier and Son from weight and space considerations is the small tion the pump allows a metered flow of fluid to Ltd. Two Rover Meteor petrol engines, of some gas turbine. Unfortunately, in such small sizes the gas turbine has a high fuel consumption, and return from the motor, and the motor swashplate 50 b.h.p., each drive one 40 kVA alternator this is felt still more if the load is to be divided is then driven so that the output r.p.m. of the through Sundstrand drives. Various electrical between two or more units for reasons of relia­ drive is lower than the input. The swashplate loads are provided, including a pulse load of 8 kW which is on for 40 milliseconds every half second, simulating a type of radar installation. On this rig, as the various loads are switched in and the input r.p.m. varied between 3,000 and 8,000 the drive can be seen to maintain the alter­ nator speed and frequency constant to within one per cent, even under rates of input acceleration or deceleration of 1,000 r.p.m./sec. The rig is fully instrumented for parallel operation, and the two alternators can be paralleled, for example, with one input speed at 4,000 and the other at 8,000 r.p.m. Aircraft Engineering

Journal

Aircraft Engineering and Aerospace Technology – Emerald Publishing

Published: Apr 1, 1955

There are no references for this article.