WO1979000187A1

WO1979000187A1 - Synchronous machines

Info

Publication number: WO1979000187A1
Application number: PCT/GB1978/000018
Authority: WO
Inventors: E Beedham
Original assignee: Ass Elect Ind; E Beedham
Priority date: 1977-10-06
Filing date: 1978-10-02
Publication date: 1979-04-19
Also published as: GB2021328A; NO783310L; SE7904782L; CA1108213A; GB2021328B; JPS54500001A

Abstract

Synchronous machines for which, for reason of size or physical arrangement, normal excitation arrangements are not practicable. The invention provides a synchronous machine having a brushless A.C. exciter whose armature comprises a series of separate segments (5, 7) arranged with substantial gaps therebetween. Each segment (5, 7) preferably comprises an independently wound and impregnated core section mounted on a frame. The invention may be used in a rim-type hydro-generator.

Description

Synchronous Machines .

This invention relates to synchronous machines.

Excitation for synchronous machines is normally provided either from static equipment through a set of sliprings or from an A.C. generator through a rotating rectifier. The arrangement is normally such that a set of one piece sliprings or a complete exciter armature assembly could be mounted conveniently on the shaft system of the main machine_*

This invention relates particularly to synchronous machines for which, by reason of size or physical arrangement, such normal excitation arrangements are not practicable. One example is the rim-type hydro-electric generator in which the rotor system is mounted round the periphery of a water turbine. In this case, any excitation equipment also has to be mounted round the turbine.

This precludes the use for such cases of small diameter exciters.

Furthermore, for such cases, static excitation would entail the use of sliprings built as a series or segments. Rings of this type would be difficult to assemble and keep in alignment; inevitably there would be high wear, producing large quantities of carbon dust and requiring frequent maintenance of brush-gear.

Hence the only remaining solution is to adopt a brushless excitation system.

For the normal construction of brushless A.C. exciter, the rotating armature has ring punchings or, in the case of larger diameters, a core built up of overlapping layers of punching segments clamped between endplates . This form of construction has several disadvantages for the application being considered. Firstly even when using the minimum practicable core length,the large diameter entails a quantity of material in the armature which is considerably more than that determined by the exciter rating; there is thus a significant waste of material. Secondly, the construction of the armature will be time consuming and expensive since it must be carried out at site. Thirdly, since the armature is wound on site without proper varnish or other treatment , the winding will be less reliable than normal. Lastly, in the event of an armature failure the outage would be expensive and time consuming simply because the correction work would have to be done largely in situ.

It is an object of the present invention to provide a synchronous machine wherein the above disadvantages are overcome.

According to the present invention there is provided a synchronous machine having a brushless A.C. exciter whose armature comprises a series of separate segments arranged with substantial gaps therebetween.

Preferably said armature is mounted on the machine rotor.

Preferably each said segment comprises an independently wound and impregnated core section mounted on a frame.

Each said segment may be single layer chain wound, in which case the wound peripheral length, L, of each said armature segment is preferably given by the formula

where t is the pole pitch, n is the number of phases of the machine and ns is an integer.

Alternatively each said armature segment may be double layer lap wound, in which case the wound peripheral length, L, of each said armature segment is preferably given by the formula

L = t (p_c + n_d) where t is the pole pitch, p_c is the ratio of coil pitch to pole pitch and n_d is an integer.

The output of each said armature segment may be separately rectified, in which case each said armature segment preferably incorporates an integral rectifier unit.

Alternatively the outputs of two or more of said armature segments may be combined before rectification, said two or more of said armature segments being so spaced as to have an armature segment pitch, t_a, given by the formula

where t is the pole pitch, n is the number of phases of the machine and n a is an integer.

The invention also provides an A.C. exciter for use in such a machine. The number and size of the armature segments is determined solely by the rating required for a particular application. The segments can be constructed at a factory and simply bolted in position at the site, thus minimising site work and ensuring a reliable winding system. If maintenance is required, a segment can easily be removed from the armature and replaced by a spare.

In order that the invention may be better understood, there will now be described, by way of example only, a rimtype hydro-generator; with reference to the accompanying drawings, in which:-

Figure 1 is a simplified sectional side view of the complete arrangement of the generator;

Figure 2 is an end view of part of the exciter;

Figure 3 shows an alternative arrangement of exciter;

Figure 4 shows an armature segment showing winding slots;

Figure 5 shows a single layer chain winding suitable for the segment in Figure 4; and

Figure 6 shows a double layer lap winding suitable for the segment in Figure 4.

In Figure 1, 1 represents the blades of a turbine runner which is supported on bearings (not shown) and is caused to rotate by the flow of water as indicated by the arrows. 2 indicates the boundary of the water ducting. Seals (not shown) between the ducting and the turbine runner prevent leakage of water from the duct. Mounted on the periphery of the turbine runner but outside the water ducting is the rotor, 3, of the main generator. This is surrounded by the main generator stator 4.

The machine includes a brushless A.C. exciter having a rotating armature and a stationary field pole system. In accordance with the invention the armature comprises a series of separate segments with substantial gaps therebetween mounted on a bracket system carried by the generator rotor. Surrounding these segments is the stationary pole system, 6, of the exciter. The peripheral distribution of the poles and armature segments can be seen in Figure 2. Rectifier units (not shown) are mounted either between adjacent armature segments, or other available space e.g. between the exciter armature and the main machine rotor. As further explained below the rectifier units may be integral with the armature segments.

In Figures 1 and 2 the exciter armature faces radially outwards and the pole system radially inwards. Other arrangements are possible; one variation is shown in Figure 3 where the exciter armature, 7, faces radially inwards and the pole system, 8, faces radially outwards.

To obtain a balanced winding, the wound peripheral length, L, of an armature segment must have one of a range of specific values. The values depend on the type of winding and are: for a single layer chain winding

and for a double layer lap winding

L = t (p_c + n_d)

Where t = pole pitch, n = number of phases,

P_c = coil pitch pole pitch and n_s, n_d, are integers.

For a single layer chain winding the quantity slots/ pole/phase is an integer and the mean value of p_c is fixed.

For double layer lap winding there is a choice of values of pc and slots/pole/phase need not be an integer provided the number of slots over the distance n_dt is divisible by the number of phases.

The number of phases is open to choice but a system would be typically based on three phase windings feeding into three phase bridge rectifier units. This is generally recognised to be the most effective rectification system.

The outputs of the armature segments may be combined in series/parallel arrangements to feed each rectifier unit and the D.C. outputs of the rectifier units combined to give a total output to suit the main machine field system. Each armature segment suitably incorporates an integral rectifier unit. However, separate rectifier units mounted either alongside the armature or in the space between the armature segments may alternatively be used. The arrangement chosen would depend on the particular application.

If the output of each armature segment is separately rectified, spacing of the segment is not critical. If the segment outputs are combined before rectification then the sets of outputs must be in phase. This requirement can be met by spacing the segments according to the following rule:

Where t_a = armature segment pitch t, n are as defined previously n_a is an integer

A typical armature segment is shown in Figure 4. It has 30 slots and spans five pole pitches. Alternative winding arrangements for this segment are shown in Figure 5 and 6.

Figure 5 shows a suitable three phase single layer chain winding. The winding has 2 slots/pole/phase and the mean value of p_c = 1. For the sake of clarity, typical coil connections are shown for one phase only. There are completely empty slots at or near each end of the segment. For this reason, the segment length could be reduced at one end by two slot pitches. This would give a length corresponding to the formula, putting n_s = 1.

Figure 6 shows a three phase double layer lap winding. The winding has two slots/pole/phase and p_c = 1. Typical coil connections are shown for one phase only. There are half empty slots at each end of the segment; the slots at one end contain top coil sides only and the slots at the other end contain bottom coil sides only. The segment length corresponds to the formula, putting n_d = 4. By using shorter pitch coils the segment length may be decreased. For example, by making p_c = ⅚ the length is reduced by one slot pitch and the number of half empty slots is reduced by two.

Claims

1. A synchronous machine having a brushless A.C. exciter whose armature comprises a series of separate segments arranged with substantial gaps therebetween.

2. A machine according to claim 1 wherein said armature is mounted on the machine rotor.

3. A machine according to claim 1 or 2 wherein each said segment comprises an independently wound and impregnated core section mounted on a frame.

4. A machine according to claim 1, 2 or 3 wherein each said segment is single layer chain wound.

5. A machine according to claim 4 wherein the wound peripheral length, L, of each said armature segment is given by the formula

where t is the pole pitch, n is the number of phases of the machine and n_s is an integer.

6. A machine according to claim 1, 2 or 3 wherein each said armature segment is double layer lap wound.

7. A machine according to claim 6 wherein the wound peripheral length L, of each said armature segment is given by the formula

L = t(p_c + n_d) where t is the pole pitch, p_c is the ratio of coil pitch to pole pitch and n_d is an integer.

8. A machine according to any preceding claim wherein the output of each said armature segment is separately rectified.

9. A machine according to claim 8 wherein each said armature segment incorporates an integral rectifier unit.

10. A machine according to any one of claims 1 to 7 wherein the outputs of two or more of said armature segments are combined before rectification, said two or more of said armature segments being so spaced as to have an armature segment pitch, t_a, given by the formula

where t is the pole pitch, n is the number of phases of the machine and n _a is an integer.

11. An A.C. exciter for use in a machine according to any preceding claim.