Michel Goffin writes that the music roll in his Welte Mignon piano is
driven by a modern electric dc (direct current) motor which has failed.
He notes that the mains voltage is uneven in Jakarta, but I think the more
likely cause of failure is the voltage surge when the mains of a neighbor-
hood (e.g., one square kilometer) is abruptly disconnected from the
regional mains system during a storm.

Jakarta experiences violent lightning storms just like our American
Southeast states have.  When a fuse atop a power pole suddenly disconnects
the neighborhood load from the regional supply, the energy stored in the
big motors of the neighborhood (e.g., air-conditioners & refrigeration) is
"dumped" into the neighborhood electric lines.  Surges of more than 600
volts, lasting tens of milliseconds, are observed on American 120-volt
mains.

The available current during this short period is monstrous: it's
equivalent to the transformed current at the power-pole fuse before the
disconnect event.  Electric motors designed for 120- or 240-volt mains
easily withstand the voltage surge; the mass of the windings absorbs the
jolt of energy without damage.  But inexpensive consumer electronics,
including many computers, aren't designed to withstand these high-voltage
surges.

The simple and ubiquitous "computer surge protector" in the home and
office wilts instantly and provides no protection.  It tries to limit the
voltage surge but the input current is so large it overpowers the small
varistors.  Circuit breakers which protect the branch circuit wiring
react far too slowly, and even most small fuses cannot rupture fast enough
to limit the current.

The best protection methods employ a device which limits the fault current
sent to the load, like the computer or electronic player piano.  An
example is the old-fashioned "line conditioner" unit, made by Sola and
General Electric and others, which provides very good protection against
mains surges.  This device resembles a big electric transformer (which it
is) with a large capacitor built-in.  A loosely-coupled resonant "tank"
circuit is thus created, and, much like a flywheel on a rotary machine,
blocks the surges from appearing at the output.

Ten years ago a Sola 2- or 3-kva ferro-resonant line conditioner for
60 Hz cost about $2000; it will run indefinately with no maintenance,
and protect all the computers and consumer electronics found in a home.
I think it's very well-suited for places like Florida and Jakarta!

Robbie Rhodes