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Leroy-Somer LSA 40 Alternator Technical Characteristics and Installation

Oct. 19, 2018

This article will guide you to learn Leroy-Somer LSA 40 series 4 pole low voltage alternator technical characteristics and installation. 

Technical Characteristics

2.1 - Electrical characteristics

This alternator is generator without slip rings and revolving field brushes, wound as “2/3 pitch”; 12-wire, with class H insulation and a field excitation system available in either SHUNT or AREP version.

excitation system

In order to conform to standard EN 61000-6-3, EN 61000-6-2, EN 55011, the R 791 interference suppression kit is needed.

alternator excitation system

Electrical options

- Stator temperature detection probes.

- Space heaters.

2.2 - Mechanical characteristics

- Steel frame

- End shields in cast iron

- Greasable ball bearings

- Mounting arrangement

MD 35: single bearing with standard feet and SAE flanges/coupling discs.

B 34: two-bearing with SAE flange and standard cylindrical shaft extension.

- Drip-proof machine, self-cooled

Mechanical options

- Direct power output by (non reconnectable) cables, regulator fitted outside the alternator.

- Protection against harsh environment.

- Air input filter, air output labyrinth cowling. Alternators fitted with air inlet filters should be derated by 5% (power).

To prevent excessive temperature rise caused by clogged filters, it is advisable to fit the stator winding with thermal sensors (PTC).


Personnel undertaking the various operations indicated in this section must wear personal protective equipment appropriate for mechanical and electrical hazards.

3.1 – Assembly

All mechanical handling operations must be undertaken using suitable equipment and the machine must be horizontal. Check how much the machine weighs (see 4.8) before choosing the lifting tool.

During this operation, do not allow anyone to stand under the load.


The generously-sized lifting rings are for handling the alternator alone. They must not be used to lift the genset. The choice of lifting hooks or handles should be determined by the shape of these rings. Choose a lifting system which respects the integrity and the environment of the machine.

During this operation, do not allow anyone to stand under the load.



After handling the machine using the lifting ring, snap on the plastic cover provided in the maintenance manual wallet.

Leroy-Somer part

Single-bearing coupling

Before coupling, check the compatibility between the alternator and the engine by performing:

- undertaking a torsional analysis of the transmission (alternators data are available on request),

- checking the dimensions of the flywheel and its housing, the flange, coupling discs and offset.


When coupling the alternator to the prime mover, do not use the fan to turn the alternator or rotor.

The holes of the coupling discs should be aligned with the flywheel holes by cranking the engine.

Make sure the machine is securely bedded in position during coupling. Check that there is lateral play on the crankshaft.

Double-bearing coupling

- Semi-flexible coupling

Careful alignment of the machines is recommended, checking that the lack of concentricity and parallelism of both parts of the coupling do not exceed 0.1 mm.

This alternator has been balanced with a 1/2 key.


The room where the alternator is placed must be ventilated to ensure that the ambient temperature cannot exceed the data on the nameplate.

3.2 - Checks prior to first use

• Electrical checks

Under no circumstances should an alternator, new or otherwise, be operated if the insulation is less than 1 megohm for the stator and 100,000 ohms for the other windings.

There are 2 possible methods for restoring the above minimum values.

a) Dry out the machine for 24 hours in a drying oven at a temperature of 110 °C (without the regulator).

b) Blow hot air into the air intake, having made sure that the machine is rotating with the exciter field disconnected.

Note : Prolonged standstill

In order to avoid these problems, we recommend the use of space heaters, as well as turning over the machine from time to time. Space heaters are only really effective if they are working continuously while the machine is stopped.

Ensure that the alternator has the degree of protection matching the defined environmental conditions.

When the alternator’s power output is ensured directly through cables, these must be connected before start-up.

Mechanical checks

Before starting the machine for the first time, check that:

- all fixing screws are tight,

- the length of screw and the tightening torque are correct,

- the cooling air is drawn in freely,

- the protective grilles and housing are correctly in place,

- the standard direction of rotation is clock-wise as seen from the shaft end (phase rotation in order 1 - 2 - 3).

For anti-clockwise rotation, swap 2 and 3.

- the winding connection corresponds to the site operating voltage (see section 3.3).

3.3 - Terminal connection diagrams

To modify the connection, change the position of the stator cables on the terminals. The winding code is specified on the nameplate.

Any intervention on the alternator terminals during reconnection or checks should be performed with the machine stopped.

In no case should the internal connections in the terminal box be subjected to stresses due to cables connected by the user.

Electrical installations must comply with the current legislation in force in the country of use.

Check that:

- The residual circuit-breaker conforms to legislation on protection of personnel, in force in the country of use, and has been correctly installed on the alternator power output as close as possible to the alternator. (In this case, disconnect the wire of the interference suppression module linking the neutral).

- Any protection devices in place have not been tripped.

- If there is an external AVR, the connections between the alternator and the cabinet are made in accordance with the connection diagram.

- There is no short-circuit phase-phase or phase-neutral between the alternator output terminals and the generator set control cabinet (part of the circuit not protected by circuit breakers or relays in the cabinet).

- The machine should be connected with the busbar separating the terminals as shown in the terminal connection diagram.

- The alternator earth terminal inside the terminal box is connected to the electrical earth circuit.

- The earth terminal is connected to the frame.

The connections inside the terminal box must never be subjected to stress due to cables connected by the user.

terminal box

3.4 – Commissioning

The machine can only be started up and used if the installation is in accordance with the regulations and instructions defined in this manual.

The machine is tested and set up at the factory. When first used with no load, make sure that the drive speed is correct and stable (see the nameplate). With the regreasable bearing option, we recommend greasing the bearings at the time of commissioning (see section 4.3).

On application of the load, the machine should achieve its rated speed and voltage; however, in the event of abnormal operation, the machine setting can be altered (follow the adjustment procedure in section 3.5). If the machine still operates incorrectly, the cause of the malfunction must be located (see section 4.5).

3.5 - Setting up

The various adjustments during tests must be made by a qualified engineer. Ensure that the drive speed specified on the nameplate is reached before commencing adjustment.

After operational testing, replace all access panels or covers.

The AVR is used to make any adjustments to the machine.

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