A severe gale took the wind generator out of control at 2.28pm on 12 September.
During the overspeed condition, the disc brake failed, possibly due to
inadequate brake pad material, but certainly a consequence of the severe
weather. The wind was estimated at  80-90 km/hr. Interestingly, the wind
generator has stayed online during stronger gusts than this in the past
without being damaged. The critical factor seems to be the duration of the
gust: the microprocessor only disconnects the generator if a set speed is
exceeded for a certain time (probably 10-15 seconds). Westwind advise that
low volts may have aggravated the situation. Barwon Water's data records
indicate normal voltages at the time of the overspeed.

Two of the three air brakes deployed. This is quite a dramatic sight and
sound. The rotor overspeed appeared to reach the resonant frequency of
the tower briefly. This is 1.33 Hz or 80 rpm equivalent. At this speed the
air brakes are moving at over 250 km/hr. and although weighing only 25 kg,
are exerting a 2 tonne pull on the tip of each rotor blade (80 G). Not
surprisingly one of the air brakes appears to have sustained a little
damage, and has not been successfully reset.

Definitive overhaul and repair of the air brakes is scheduled for Sunday
20 October. Attempts will also be made at that time to repair cracks in the
leading edges of 2 blades and one air brake. The machine will be offline for
3-4 days while epoxy resin cures. It is possible all three air brakes will
have to be taken off site for repair and modification.

In the meantime, the wind generator returned to operation at 5.50pm on
Sunday 29 September, some 17 days after the brake failure. Windspeed during
this interval has been measured at 6.6 m/sec, and calculated lost production
is 7940 kWh: average power would have been 17.2 kilowatts

This return to operation with faulty air brakes has only been possible
because of  the implementation of the following measures:

	1. A high performance woven brake pad material has been substituted
in the brake caliper. The disc has also been cleaned, ground with an oilstone
and degreased. Stopping time 6 seconds (from 750 rpm only)

	2. A secondary windvane has been fabricated, installed and wired into
the existing slew motor control circuitry. Every time the brake solenoid is
de-energised, the windgen. now slews left 90 degrees and continues to "track"
the wind in that position (i.e. keeping the rotor out of the wind). A
3 phase switch has been hard wired into the tower and no longer relies on
the microprocessor to prevent over twisting of the cables.

	3. Wind gusts are monitored by the data logger every 15 seconds. If a
gust is recorded over 20 metres/sec (72 km/hr), the data logger now operates
the wind generator's "stop" button via a miniature relay.  Braking and slewing
out of the wind then commence immediately. Restarts are currently manual only,
although the logger could easily be programmed to perform a restart when
the average windspeed falls below 15 metres/sec.

The Alternative Technology Association's Breamlea Operations Group members
have performed all the work mentioned above. Much time has been spent on
the telephone, and helpful advice has been obtained from Westwind, Esperance
Power Station, Barwon Water (Blackrock), Ian Dorward (now in New Zealand),
Fitzgerald Racing Services, Northern Brake & Clutch, and Ciba-Geigy Polymers.