AVR Before or After the Generator? The Right Answer for Kenyan Sites

The question that gets asked every week

You have a generator that takes over when Kenya Power drops out. You are about to buy an AVR for the supply. The electrician asks where to wire it: between the meter and the changeover, between the changeover and the load, or on the generator side?

The answer matters more than most installers realise. Wiring it wrong burns out the AVR servo within months and gives you neither the protection nor the regulation you paid for. Wiring it correctly means the AVR sees only the supply it is built to handle, and your equipment sees clean voltage regardless of which source is feeding it.

The short answer

For almost every Kenyan commercial site, the AVR sits after the changeover switch and before the main distribution board. That way it regulates whatever source is feeding the load, whether that is Kenya Power or the generator.

Kenya Power ─┐
             ├─→ Changeover Switch ─→ AVR ─→ Main Distribution Board ─→ Equipment
Generator ───┘

The AVR does not care which source is upstream. It just sees an input voltage and produces a regulated output. As long as the source is within its working band (170 V to 280 V single-phase, equivalent on three-phase), the AVR delivers a steady 230 V to your equipment.

Why not before the changeover?

Some installers want to put the AVR upstream of the changeover, so it only sees Kenya Power. Their logic: "the generator is already regulated, the AVR only needs to fix Kenya Power." This is wrong on two counts.

First, generators are not as well regulated as people assume. A diesel generator's automatic voltage regulator (built into the alternator) holds output within roughly ±5% under steady load. The moment a big load switches on or off, voltage swings by 10% to 15% for several seconds while the AVR catches up. On a Kenyan site with mixed motor and electronic loads, that swing is often enough to crash the sensitive equipment the AVR was meant to protect.

Second, putting the AVR upstream of the changeover means you have to size it for full site load even though it only ever sees Kenya Power. That is wasted capital. Worse, when the generator runs, your equipment sees the raw generator output, which is exactly when sensitive loads need help most.

Why not after the main distribution board?

Less common, but we have seen it: an AVR wired in to feed only one circuit, with the rest of the load going around it. People do this when they think only one piece of equipment (a CNC, a server rack, a medical device) needs voltage regulation.

The mistake is that the AVR is then the only protection for that circuit, and any voltage event on the rest of the site bleeds back through the shared supply and the protective ground. You end up paying for an AVR that protects one machine while every other machine on the site sees the same poor supply.

If you genuinely only need to protect one circuit, fine, but the right placement is still upstream of the panel that feeds it, not downstream of the rest of the site.

The two specific cases where it sits elsewhere

There are two situations where the standard placement does not apply.

1. Very large generator-only installations (no Kenya Power feed)

Some factories run entirely off generator with no grid connection at all (typical for sites in remote industrial areas, or where the cost of a Kenya Power connection is prohibitive). In that case the AVR goes between the generator and the load, sized for full plant load, and protects against the slower regulation and load-step swings of the generator.

2. Soft-start or motor-only loads where the AVR would compete with a VFD

If the entire load downstream is motors on variable-frequency drives, the VFDs do their own voltage and frequency regulation, and an upstream AVR can interact badly with the VFD's input filter under certain conditions. This is rare in Kenya outside of pure manufacturing lines, but it is a case for an engineer to specify, not a generalist installer.

What goes wrong when the AVR sees the generator directly

This is the failure mode worth understanding because it is common and expensive.

Generators on a Kenyan industrial site typically run for a few minutes to a few hours at a time. When they start, output voltage takes 10 to 30 seconds to stabilise. When a heavy load switches on, output sags 10% to 15% for several seconds before the generator's AVR recovers. When the load switches off, output overshoots by similar amounts.

A servo AVR downstream of that supply tries to regulate against these swings continuously. The servo motor moves the carbon brush across the variable transformer to compensate, then has to reverse when the swing reverses. Over hundreds of hours of generator runtime per year, the servo wears out years early. We have seen carbon brushes that should last fifteen years burn through in three.

The fix is not to take the AVR off the generator side. It is to size and specify the AVR for genset-fed operation: heavier-duty servo motor, wider input band, and ideally an instruction to the generator's automatic mains failure (AMF) panel to delay closing the load contactor for 5 to 10 seconds after the generator starts, so the genset stabilises before the AVR has to deal with it.

The standard installation diagram

For 95% of Kenyan commercial and industrial sites:

Kenya Power ──┐
              ├─ ATS (Automatic Transfer Switch) ──→ Vener 7 AVR ──→ MDB ──→ Loads
Generator ────┘                                                            │
                                                                           ├─ UPS ──→ Critical IT
                                                                           │
                                                                           └─ Direct ──→ Motors, lighting, etc.

This gives you:

• AVR regulation regardless of source (Kenya Power or generator)
• A single AVR sized for total site load
• UPS protection for the small slice of equipment that cannot tolerate any outage
• Clean handover when Kenya Power returns and the generator stops

The settings that matter

When commissioning the AVR on a generator-fed installation, three things need attention:

1. Input band. Most Vener 7 AVRs are spec'd for ±15% to ±30% input. On generator-only operation, set or specify a wider band so the AVR does not trip during start-up swings.
2. AMF delay. On the changeover panel, build in a 5 to 10 second delay between generator start and load transfer. The generator stabilises, then the AVR sees a steady supply.
3. Bypass switch. Always specify a manual bypass on the AVR. If the AVR ever needs service, the bypass lets you keep the site running on raw supply (or generator) until it is back online.

So, where does it go?

After the changeover, before the main distribution board, sized for total site load, with manual bypass and input band set for the worst of either source. That is the answer for every Kenyan site we have commissioned in the last five years that has both Kenya Power and a generator.

If you want a sense check on your own installation, book a site visit and we will walk the panel with your electrician. For a fresh installation, the sizing tool gets you to a kVA figure and we take it from there.