GB2052881A - Dynamoelectric machines; emergency power supplies - Google Patents

Abstract

An apparatus for storing electrical energy comprises an electric motor (2) and spring means (16) arranged to be tensioned by the motor when electrical energy to be stored is applied to the motor; if the power supply to the motor fails the spring means drives the motor in reverse as a generator to produce in electrical form the energy stored in the spring means. In an emergency electrical power supply comprising apparatus as above arranged to be normally supplied with electric energy to be stored, disconnecting means (18, 22) disconnects the motor (2) from the normal supply (4) in the event of failure of the normal supply. The disconnecting means may be also arranged (as shown) to connect, in the event of failure of the normal supply, the motor to an emergency load (20) not connected to the normal supply or the emergency load and the motor may be connected in parallel with the normal supply (Fig. 2-not shown). <IMAGE>

Description

SPECIFICATION Energy storage This invention relates to apparatus for the storage of electrical energy. The invention has particular application to the storage of electrical energy to power an emergency lighting system.

A serious disadvantage of existing emergency lighting systems incorporating either primary or secondary batteries is the difficulty in ensuring that the batteries are always fully charged and in a condition for instant use.

Primary batteries require replacement at regular intervals of from one to two years and secondary batteries of the lead-acid type require their acid levels and specific gravity to be checked at intervals of from three to six months.

Sealed lead-acid or nickel-cadmium batteries on float charge require less attention, but still tend to deteriorate over periods from three to five years.

It is an object of this invention to provide an apparatus for storing electrical energy wherein the above mentioned disadvantages may be overcome.

According to a first aspect of the invention there is provided an apparatus for storing electrical energy comprising: an electric motor; and spring means arranged to be tensioned by the motor when electrical energy to be stored is applied thereto or to drive the motor to produce in electrical form the energy stored in the spring means.

Preferably the spring means is connected to the motor via gearing means.

Preferably the motor is arranged to stall when the spring means can be tensioned no further thereby to maintain the spring means fully tensioned.

Preferably the spring means comprises a plurality of spring elements in parallel acting on a main shaft. This minimises the loss of energy due to the failure of a spring element and also minimises any hazard associated with the storage of energy in a single large spring element.

Each spring element may be of the conventional single spiral type or of the constant torque type. The assembly of spring elements, together with the gearbox, may be immersed in oil.

Preferably the apparatus further comprises indicator means arranged to indicate the amount of energy stored in the spring means.

The apparatus may further comprise regulator means arranged to regulate the speed of the motor.

According to a second aspect of the invention there is provided an emergency electrical power supply comprising: an apparatus according to the first aspect of the invention arranged to be normally supplied with electrical energy to be stored; and disconnecting means arranged to disconnect the motor from the normal supply in the event of failure of the normal supply.

Preferably the disconnecting means comprises a voltage sensing relay.

Preferably the disconnecting means is also arranged to connect, in the event of failure of the normal supply, the motor to an emergency load not connected to the normal supply.

Alternatively, an emergency load and the motor may be connected in parallel with the normal supply, so that the emergency load may always be supplied either by the normal supply or by the motor driven by the spring means. This latter arrangement would provide a constant checking facility on the correct operation of the emergency load, which may be desirable where the emergency power supply might be expected to remain dormant for many years without maintenance or checking.

Although regulator means may be provided to regulate the speed of the motor, the motor will tend to regulate its speed according the emergency load.

Two emergency lighting systems incorporating emergency electrical power supplies in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows schematically a first emergency lighting system; and Figure 2 shows schematically a second emergency lighting system.

Referring firstly to Fig. 1 in the first emergency lighting system a D.C. electric motor 2 is arranged to be normally driven by a D.C.

supply derived from an A.C. mains supply 4 through a mains switch 6, transformer 8 and bridge rectifier 1 0. Relay switch contacts 22 are normally in the upper position. The motor 2 drives a main shaft 1 2 through a gearbox 1 4 to tension each of an assembly of single spiral springs 1 6 arranged in parallel acting on the shaft 12. The motor 2 is arranged to stall when the springs 1 6 can be tensioned no further, thereby maintaining the springs fully tensioned once that state has been reached after closure of the switch 6 and while the normal supply is maintained.

In the event of a failure in the normal supply to the motor 2, this failure is sensed by a voltage sensing relay 1 8 connected across the mains supply 4 through the switch 6. The relay 18, upon sensing a failure in the mains supply 4, disconnects the motor 2 from the supply and connects an emergency load in the form of lamps 20 across the motor 2 by changing the position of relay switch contacts 22 to the lower position as shown in Fig. 1.

With the motor 2 now no longer being driven from the bridge rectifier 10, the main shaft 1 2 is turned in the opposite sense to before and so drives, through the gearbox 14, the motor 2 as the springs 16 untension. The motor 2, since it is mechanically driven, now acts as a generator, generating in electrical form the energy stored in the springs 1 6. The electricity now generated by the motor 2 is used to power the lamps 20.

Referring now to Fig. 2, the second emergency lighting system comprises essentially the same components as the first emergency lighting system and so the same components are given the same reference numerals in Fig.

2 as in Fig. 1. The operation of the second emergency lighting system is similar to the already described first emergency lighting system and so will not be described in detail save to elucidate its differences from the first emergency lighting system.

In the second emergency lighting system, the lamps 20 are arranged to be always illuminated, either from the normal supply 4 (with the relay switch contacts 22 in the upper position) or from the motor 2, when acting as a generator, driven by the assembly of springs 1 6 (with the relay switch contacts 22 in the lower position as in Fig. 2). This arrangement provides a constant checking facility on the correct operation of the lamps 20, which may be desirable where the emergency power supply may be expected to remain dormant for many years without maintenance or checking. In the second emergency lighting system, the motor 2 is arranged to stall when the assembly of springs 1 6 cannot be tensioned further, as in the first system. In the second system, however, the stall current drawn by the motor 2 is limited by a resistance 24 connected in series with the motor.

The stall current limiting resistance 24 is arranged to be short circuited by a second set of relay switch contacts 26 which are normally in the upper position but are moved to the lower position (as shown in Fig. 2) by the voltage sensing relay 1 8 in the event of a failure of the supply 4.

It will be appreciated that although in the above described emergency lighting systems the electric motor is a D.C. motor normally driven from an A.C. supply through a bridge rectifier 10, the motor may alternatively be an A.C. motor normally driven directly from the A.C. supply and acting as an induction generator when driven by the springs 16.

Claims (12)

1. An apparatus for storing electrical energy comprising: an electric motor; and spring means arranged to be tensioned by the motor when electrical energy to be stored is applied thereto or to drive the motor to produce in electrical form the energy stored in the spring means.

2. An apparatus according to claim 1 wherein the spring means is connected to the motor via gearing means.

3. An apparatus according to claim 1 or 2 wherein the motor is arranged to stall when the spring means can be tensioned no further thereby to maintain the spring means fully tensioned.

4. An apparatus according to claim 1, 2 or 3 wherein the spring means comprises a plurality of spring elements in parallel acting on a main shaft.

5. An apparatus according to any one of claims 1 to 4 further comprising indicator means arranged to indicate the amount of energy stored in the spring means.

6. An apparatus according to any one of claims 1 to 5 further comprising regulator means arranged to regulate the speed of the motor.

7. An emergency electrical power supply comprising: an apparatus according to any one of claims 1 to 6 arranged to be normally supplied with electric energy to be stored; and disconnecting means arranged to disconnect the motor from the normal supply in the event of failure of the normal supply.

8. An emergency electrical power supply according to claim 7 wherein the disconnecting means comprises a voltage sensing relay.

9. An emergency electrical power supply according to claim 7 or 8 wherein the disconnecting means is also arranged to connect, in the event of failure of the normal supply, the motor to an emergency load not connected to the normal supply.

10. An emergency electrical power supply according to claim 7 or 8 wherein an emergency load and the motor are connected in parallel with the normal supply.

11. An apparatus for storing electrical energy substantially as hereinbefore described with reference to the accompanying drawings.

12. An emergency electrical power supply substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.