Helicopter Starting Rectifier

The Transformer Rectifier Unit 3RC15KB is intended for
shipboard Helicopter Start applications. There are three
basic modes of operation
i) Powering the starter motor of a helicopter
ii) Providing a 28VDC supply to aircraft on-board equipment
iii) Providing an 18.2V DC supply for turning the helicopter
turbo shaft engine at reduced speed for compressor
washing.
The 3RC10KB provides a high quality 28V regulated output
with a two stage current limit protection circuit that allows for
a short time rating of 3000A and a continuous rating of 540A.
The Transformer Rectifier Unit is built into a custom built
steel enclosure, which is designed for deck mounting. The
enclosure may be direct mounted for shock levels up to 30g,
above this suitable shock mounts may be used. Protection
level is to IP23.
Access for maintenance and repair is from the front via a
0
hinged door that opens to the left, it will open to 180 with a
0
minimum maintenance-opening requirement of 90 . The
door contains indicating lamps for supply available, anti
condensation heater on, and output on, together with the
ON/OFF switch.

3RC15KB

Louvres pressed inwards on the front and sides of the
assembly and also a shielded vent on the top of the unit
provide for fan assisted cooling during normal operation.
The Transformer Rectifier Unit is cooled by natural
convection when the Anti Condensation Heaters are
operating.
A soft start system is employed such that the input inrush
current is less than the full load current.
The TRU has an input isolation transformer and a 12 pulse
thyristor rectifier configured as two fully controlled bridges
combined in parallel by an interphase transformer. This
produces a very smooth DC output and eliminates all
harmonics below the 11th from the input current waveform.
The input current to the equipment is close to sinusoidal with
a “traditional” lagging power factor dependent on loading and
mains voltage.
Electrical connections to and from the Transformer Rectifier
Unit for supply, heater, remote and sense connections are
made on rail-mounted terminals. Provision for the output is
by means of M12 bolt connections. The terminals are
situated inside the cubicle and access is via a cable gland
plate that is situated on the bottom of the enclosure. An
M10 (x 1.5) external earth stud is provided adjacent to the
gland plate, on the bottom of the enclosure.