Manual For LC And LCS Range Alternators

‘FOSTER’ WIC Alternator LC AND LCS RANGE ALTERNATORS

MARKON alternators SELF EXCITING

SELF REGULATING

REVOLOVING ARMATURE GENERATORS

A.C.

Type LC & LCS 19-32

Operating and Maintenance Instructions

Ref. No. 93-022

LC AND LCS RANGE ALTERNATORS GENERAL DESCRIPTION The Markon LC and LCS 2 and 4 pole alternators are simple and reliable conventional rotating armature machines, incorporating a completely static, and self-regulating, self-exciting power factor compensating control unit All machines are of robust mechanical construction, with rolled steel magnet frame cast iron endbrackets high quality steel shaft and first grade fully sealed bearings. Sliprings are of the moulded construction with brushgear of generous proportions. All windings are wound with synthetic enamel or polyester covered wire and are insulted to E, B or F specifications. They are all impregnated suitable for tropical conditions Special attention has been given to the accessibility of control gear and brushgear which is readily obtained by removal of the inlet louver and enclosing hand They have been specially designed for operating high overloads experienced on motor starting together with normal lighting heating and other standard electrical loads Frame sizes 19,20,24,28 and 31 are available with electric starting and battery charging windings. They are designed LCS INSTALLATION The alternator has been specially tested and set up at our works. However, a preliminary check should be carried out to ensure that the machine has not suffered external damage during transmit and that the nameplate particulars are as specified (a) Install in a dry and well ventilated location (b) Remove the enclosing cover and check that brushes are making full contact with the sliprings. Ensure that the brushes on LCS machines are free to move in their holders and that the ac brush holder arms are free on their pivots (c) For direct drive a good quality flexible coupling should be utilized and the alignment very carefully checked

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(d) The external cabling should be of ample capacity to carry the rated load, and the cables kept as short as possible as this will help to reduce radio and television interference. All external circuits should be checked to ensure there are no loose connections which can give rise to false load conditions and increase radio interference (e) Direction of rotation is immaterial for LC type machines LCS is connected for anticlockwise direction of rotation looking at non-drive end unless otherwise ordered. Should it be required to reverse the direction of rotation it is necessary to change over the internal connections to the dc brush holders. In the case of 4 pole alternators the connections are changed over on the top two brush holders. If necessary adjust the brush rocker position to the point where to sparking of the brushes occurs (f) All machines are supplied as standard with 1’6 long flexible output leads through a grommeted hole at the top of the non-drive and bracket NOTE: Before flash testing refer to section (b) under maintenance

OPERATION There are three main electrical parts, namely the armature, field and control gear. In order to obtain the output voltage constant at all conditions of load the field winding must be supplied with the correct dc exciting current from the control gear. The control gear is split into two parts, one supplying the no load excitation and the other the additional excitation required under load conditions On no load the field excitation is obtained from the ac output voltage, which is fed through a linear reactor or in the case of certain single-phase alternators through capacitors and is rectified to dc. This current gives the open circuit voltage On applying load additional field excitation is obtained from the current transformer. The load current passing through the primary windings induces a current in the secondary windings, which is added vectorially to the current passing through the linear reactor or capacitors. This also is rectified and fed to the field and gives the required excitation to maintain the voltage on load. The machine voltage should be maintained within the order of + or -31% between 0.95 and 0.8 power factor lagging, at any load up to full load. Sight deterioration will occur at other power factors. On frame sizes LCS 19,20,24,28 and 31 series start and de armature windings are fitted, which when connected across a battery, provide the necessary torque for starting most petrol and diesel engines. A small charging current can be taken from the armature winding and should be limited by a charge resistor to 2 amp on LCS 19 & 20 and 3 amp on LCS 24,28 and 31 A reverse current diode should be prevent feedback from the battery

3

ADJUSTMENT All equipment is tested and adjusted during manufacture unless otherwise specified to suit a speed regulation in accordance with B.S 649 for diesel engine driven alternators. If however, different speed regulation conditions exist it may be found advantageous to readjust for optimum performance Whilst the voltage regulation of the Markon alternators can be adjusted for speed variations even outside the limits of B.S 649 it must be stressed that quick and accurate governing is essential and that the speed must be constant and stable for any given loading In order to carry out adjustments the inlet louver and enclosing band must be removed. This exposes the resistor and diodes on LC/S 19 & 20 and all of the control gear on LC/S 24 to 32 On frame sizes 19 & 20 resistor is filled in parallel with the field and adjustment will raise or lower the voltage over the complete band from no load to full load. Increasing the resistance in circuit will increase the voltage output of the alternator. On single-phase machines in the LC/S 24 to 32 ranges fitted with capacitors in the excitation circuit a resistor is connected in series with one capacitor. Adjustment of this resistor will adjust the no load voltage. Increasing the resistance in circuit will increase the voltage output of the alternator On all other machines voltage varying the size of the air gap in the linear reactor carries out adjustment. This component is mounted at the bottom of the control gear To alter the air gap length the clamping bolts must be loosened and the amount of the packing in the air gap altered as required. This packing consists of thin strips of non-magnetic material Increase of air gap length increases the output voltage On some LC/S 24 to 32 alternators additional resistors are fitted and connected across the input to the field. Adjustment of this resistor will vary the voltage over the complete band from no load. Increasing the resistance in circuit will increase the voltage output of the alternator It should be noted that in all machines each time they are run up to speed output voltage would not reach the normal operating voltage at no load until a large proportion of full load has been switched to the alternator. This should be taken into account when attempting to adjust the no load voltage The adjustments are not normally necessary and in any case should be made by competent engineer

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ALTERNATOR AND CONTROL GEAR CIRCUITRY Typical wiring diagrams are given at the end of this book but do not necessarily apply in all cases due to variations of customer’s requirements.

ELECTRICAL EXTRAS 1. Hand voltage trimmer – where a hand voltage trimmer is supplied this is connected in series with a ballast resistor across the input to the field. The variable resistor should be wired so that for increase in output voltage the value of resistance increases 2. Parallel Operation – for parallel operation LC/S alternators should have a drooping voltage/load characteristic – this will be allowed for in the design of the machine. Field linking must be employed by means of an auxiliary switch on the main switch or circuit breaker. This will equalize the fields of the alternators and will reduce the amount of circulating current to a minimum. Only machines with field voltage within 10% of each other can be paralleled by this method PARALLEL OPERATION OF LC TYPE ALTERNATORS For successful parallel operation of type LC alternator sets it is important that there is accurate and consistant governing of each engine with about 41% speed droop no load to full load and that the alternator voltage also has a regulation about 4% no load to full load at 0.8 p.f At O p.f lag the voltage regulation no load to full load should be in the order of 10% The drooping voltage characteristic is obtained by increasing the no load voltage by means of the linear reacter air gap. Increase the air gap to increase the no load voltage. It is probable then that the voltage will be too high and this can be reduced throughout the range by fitting a resistance in parallel with the field. The actual connections are made on the positive and negative rectifier heat sinks. The characteristics, which may be obtained, are shown below:

1) Level compounded for single running 2) Droop characteristic with linear reacher air gap increased 3) Reduced level by fitting resistance across field

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The importance of obtaining identical characteristics on each set cannot be over-emphasized. If the speed characteristics vary from set to set then proportional and sharing or KV Ar sharing is dependent on generated emf of the various machines. To assistant with current sharing the fields are linked via auxiliary contacts on the main switches or circuit breakers. In this way an increase in the field voltage on one machine causes a corresponding voltage increase on the fields of other machines tending to restore the balance of all the e.m.f.s. See diagram 12-057E GENERAL MAINTENANCE When regular inspection by a component service engineer is not practical, the following points will enable the user to carry out routine maintenance (a) LCS Range – The commutator sliprings and brushgear should be inspected at regular intervals. Worn brushes should be replaced by new ones of the correct grade and size. New brushes must be properly bedded and the de brushes must be quite free in their holders. Badly worn commuters and sliprings may requite skimming and if it is necessary the mica separators in the commuters must be slightly undercut after skimming LC Range – The sliprings and brushgear should be inspected by new ones of the correct grade and size. New brushes must be properly bedded to the sliprings. Badly worn sliprings should be skimmed (b) Insulation Resistance and Flash Testing – If the alternator has been stored for any length of time the insulation should be checked. When checking the winding resistance the earth terminal should be disconnected from the line terminals. In addition it is important that rectifiers containing silicon diodes should be short circuited If the tests show that insulation resistance is below 0.5 megohms the machine should be dried out until the value rises to 2 megohms Bearings are fully sealed and require no lubrication. (c) To Remove Armature 1. Removing enclosing band and inlet louver 2. Lift brushes 3. Remove the screws fixing D.E endbracket to frame and withdraw end bracket 4. Remove non drive end bearing clamping screws when fitted

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5. The armature can now be withdrawn towards the drive end taking care not to damage the brushgear (d) To Remove Control Gear 1. 2. 3. 4.

Remove enclosing band and inlet louver Disconnect leads from ac brushgear and field windings Disconnect external cabling Remove two control gear fixing nuts securing control gear in position, these are on the same studs which hold the inlet louver in position 5. The control gear can now be removed as a unit

FAULT CAUSE (a) Machine Fails 1. Loss to excite Residual Magnetism

TEST of Check voltage across slip rings this should be at least 1% of line voltage 2. Loose Examine all connections connections 3. Sticking Check for free Brushes movement of brushes 4. Faulty rectifier Remove and test with Avometer resistance

+ -

Repair where necessary Adjust or replace it necessary Replace.

- < 1000Ω + > 1000Ω

5. Incorrect Check whether running speed machine is running at correct 6. Open circuit in Isolate each winding windings. and check for continuity 7. Open circuit in Test with Megger. If condenser when faulty will show fitted in place of infinity. If OK will linear reactor. show zero rising to infinity. 8. Short circuit in Examine windings windings. for signs of burning (b)Machine 9. Incorrect gap on Test for movement excites but linear reactor of bottom limb. voltage incorrect. 7

REMEDY Flash field with 12 volt battery

Repair or rewind where necessary Repair and rewind where necessary. Replace

Rewind where necessary. Adjust to obtain correct N.L. voltage.

10. Faulty rectifier 11. Incorrect running speed

Voltage high when regulator is fitted ( c) Voltage falls 13. Incorrect or off as load is loose connections applied on C.T. 14. Rectifier failure 15. Open circuit on C.T. secondary winding

Check as in (4).

Replace

Check as in (5)

Adjust speed.

Check connections from C.T. Secondary Check as in (4) Check windings for continuity

Repair where necessary Replace. Repair or rewind where necessary

List of running Spares Description Brush ac Brush dc Bearing N.D.E. Bearing D.E. Rectifier Diode forward polarity 3ph. Rectifier Diode reverse polarity 3ph. Rectifier Diode forward polarity 1ph. Rectifier Diode reverse polarity 1ph.

FRAME19 Part QTY No.

FRAME 20 Part QTY No.

FRAME 24 Part QTY No.

010001

010001

010005

010018 014001 014003

4 or 8 2 1 1

010018 014001 014003

4 or 8 4 1 1

4,8 or 16

010006 014003 014007

2 1 1

002008

FRAME 28 Part QTY No. 4,8 010or 005 16 0104 006 014003 0141 004

FRAME 31 Part QTY No. 4,8 010or 005 16 0104 006

002008

002008

014009

1

FRAME 32 Part QTY No. 010005

4,8 or 16

-

-

014009

1

002031

6

002031

-

-

-

-

002009

3

002009

3

002009

3

002009

3

002031

4

002031

4

002006

2

002006

2

002006

2

002006

2

-

-

-

-

002007

2

002007

2

002007

2

002007

8

002008

9

10

11

12