LEROY SOMER R220 Analogue AVR - Analogue Automatic Voltage Regulator for LEROY SOMER Alternators | OEM Replacement

What the R220 is. A Analogue Automatic Voltage Regulator built by LEROY SOMER for brushless excitation systems. On paper the specification is a list; in service it is a set of limits. The current the board will hold indefinitely is 2-4 A class depending on variant; the field resistance window it will drive without exceeding its output voltage is Matched to the exciter field; the tightest voltage band it can maintain is +/-1.0 per cent; and the ambient range in which all of that remains true is -40 to +70 degC.

Excitation architecture. Self-excited, shunt or AREP fed. That single sentence decides most of the regulator's behaviour in a fault: whether the field survives a close-up short circuit, whether the machine builds up from residual voltage on its own, and how much the terminal voltage dips when a large motor starts on the same bus. If two identical sets behave differently on the same load, swap the regulators before swapping anything else. The result tells you which side of the machine the fault is on.

Sensing. Single-phase sensing with 0-110 / 0-220 / 0-380 V taps. The sensing circuit is the regulator's only view of the outside world, so its wiring matters as much as its specification. A voltage error introduced by a loose terminal or a long run of untwisted cable is indistinguishable, from the regulator's point of view, from a genuine voltage error on the alternator. A regulator is a closed loop with a slow plant attached, and the plant is a large inductance. That is why the stability adjustment exists and why it is set after, not before, the voltage is correct.

Power stage and field drive. Power input From the main stator, 50 / 60 Hz, output Up to 90 Vdc. Field current rating 2-4 A class depending on variant, forcing capability Short-term forcing current available for load steps, field resistance window Matched to the exciter field. These are not independent numbers: the output voltage ceiling and the field resistance together set the maximum current the board can actually deliver, and the continuous rating is only reachable at the low end of the resistance window. A regulator rated for a minimum field resistance of a few ohms will not drive a high resistance field to full current, however good its specification looks on paper.

Accuracy and response. +/-1.0 per cent steady-state accuracy, Standard analogue response, thermal drift Low thermal drift. In practice the accuracy figure is the least interesting of the three. What an operator notices is recovery after a load step, which is governed by response and by available forcing current, and what a maintenance engineer notices after two years is drift, which is governed by the reference circuit and the ambient temperature inside the terminal box. A regulator is a closed loop with a slow plant attached, and the plant is a large inductance. That is why the stability adjustment exists and why it is set after, not before, the voltage is correct.

Frequency behaviour. Rated for 50 / 60 Hz, with Frequency-sensitive roll-off on most variants. The frequency-sensitive function exists to protect the prime mover, not the alternator: as engine speed falls the regulator reduces excitation so the alternator stops demanding torque the engine cannot supply. Without it, an overloaded engine is dragged down until it stalls, and the alternator is blamed for a fault that belongs to the fuel or governor system. The trim potentiometer is not a calibration device. If rated voltage is not reachable near the middle of its range, the sensing tap is wrong.

Paralleling. Reactive droop via CT. On a single set this circuit does nothing. On two or more sets it is the only thing that stops the machines from exchanging reactive power in a slow oscillation, and it is the first place to look when a parallel installation shows a circulating current that nobody can explain. An alternator that has been rewound needs its field resistance re-measured, because a rewind commonly moves it by ten to twenty per cent in either direction.

Protection built into the regulator. Over-excitation protection, fuse. These functions protect the alternator and the regulator, not the installation. Downstream protection, loss of mains and reverse power all belong to the controller, and a site that relies on the AVR for them is a site that will eventually trip in a way nobody can explain. The most common cause of intermittent excitation loss is a crimp terminal that was never properly made. Wiggle the harness with the machine running before replacing anything.

What it fits. Leroy Somer LSA 35-44 alternators. Lifecycle status: Legacy, replaced by R438 and R449 on new build. Both halves of that sentence matter at order time. A board that fits perfectly but has been discontinued is a different commercial decision from one that fits and is in current production, and the price difference rarely reflects the difference in risk. Take a photograph of the terminal block before removing anything. Wiring drawings for older machines are frequently wrong, and the photograph is the only reliable record.

Field notes on this model. The R2xx range is the older generation of Leroy Somer analogue regulators and it is still the most common AVR on LSA alternators built before the AREP era. The last two digits tell you the build: the sensing tap set, the field current class and whether a frequency roll-off is fitted all change across the range, so the model number has to be matched exactly when ordering a spare.

Matching the board to the duty, not to the label. Two LEROY SOMER alternators of the same kVA can need different regulators if one is specified for motor starting and the other for a resistive load. The R220 is specified at +/-1.0 per cent regulation accuracy, which is the number that matters when the load is a mix of drives and lighting. For a purely resistive load even a looser board is invisible to the customer, and paying for accuracy that nobody measures is the most common way money is wasted on a rebuild.

Earthing and shielding. The regulator reference is the machine frame. Bond the AVR mounting plate to the frame with a dedicated conductor rather than relying on the mounting screws, and earth the sensing cable shield at one end only. When a set shows a voltage that wanders slowly with no load change, the cause is usually a circulating current in the shield rather than a failing board.

Commissioning sequence. Start with the machine at rated speed, no load, and the field disconnected. Confirm the sensing voltage at the AVR terminals is inside the window the board expects, then connect the field with the voltage trim at minimum. Bring the trim up slowly and watch the field current, not the terminal voltage, because the terminal voltage will look correct long before the field current has stabilised on a cold winding.

Temperature drift of the field. Copper rises about 0.4 per cent in resistance per degC, so a field that measures 12 ohm cold will measure around 15 ohm at a 70 degC winding temperature. A regulator set up on a cold machine and never re-checked will therefore be running at a different operating point every time the season changes, and the symptom is a voltage that is correct in winter and low in summer.

Voltage drifts with ambient temperature. If the voltage is correct cold and low hot, the thermal drift of the regulator and the temperature coefficient of the field are adding up in the same direction. The R220 is specified at +/-1.0 per cent; a drift of a couple of per cent over a fifty degree swing is normal for an analogue board and is not a fault.

Part numbers are not interchangeable across suffixes. On this family the suffix carries the field current class, the sensing arrangement or the frequency band, and two boards that look identical in a photograph can be a hundred per cent different in rating. Quote the full model number including the suffix, and where the suffix is unclear send a photograph of the original board with the terminal markings visible.

Standby versus prime power. A standby set runs a few hundred hours a year and its regulator spends most of its life cold; a prime power set runs continuously and its regulator spends its life at operating temperature. The R220 is rated for -40 to +70 degC, which is fine in both cases provided the terminal box has any ventilation at all. What changes between the two duties is the capacitor ageing inside the board, not the semiconductor, so a prime power machine should have the regulator inspected on a schedule rather than on failure.

Field cable sizing. The field circuit carries DC at low voltage and high current, so volt drop matters more than ampacity. Size the cable so that the drop at 2-4 A class depending on variant stays under about one volt, and torque the terminals to the manufacturer figure. A field circuit that loses half a volt in the cable is a regulator that cannot reach full forcing when the load steps.