liquid resistance starter

Topics: Electric motor, Electrolyte, Electrical engineering Pages: 5 (1488 words) Published: November 3, 2014
EPMA Liquid Resistance
Starters for Slip-ring
motors. 200 to 20 000 kW.

The EPMA starter has been specifically designed
by AOIP for controlled starting and speed control
of large slip ring motors in arduous applications
such as:
Crushing
Milling
Conveyors
Pumps
Ventilation
In a variety of industries such as mines, quarries,
cement plants, water treatment and associated
Industries.
CSE-Uniserve Pty Limited has adapted this basic
design under license to AOIP to suit the harsh
conditions
typical
of
Australian
mining
installations. The starter tanks are manufactured
here in Australia from stainless steel to AS 1554,
and customized to suit outdoor installation, with
minimal maintenance requirements.

All Unistarter units are manufactured in Australia
and in conformance with Australian Standards.

The EPMA rotor starter is used to
control the starting of a slip ring
(wound rotor induction) motor. The
starting current is generally limited to
a maximum of 250% Full Load
Current. Optimal starting torque for
each application is selected by the
choice of the initial value of
resistance. The principle of the liquid
starter is that of a secondary
resistance starter, where by the rotor
resistance is reduced to a minimum
during the starting period.

This type of starter is designed to
provide the optimum starting
characteristic, which results in
smooth progressive acceleration
to full load speed. It can also be
used for speed variation and
torque control. Plug braking can
also be implemented with this
system. The variation in the
resistance is achieved by
displacement of the electrodes in
the electrolyte. At the end of the
acceleration, the electrodes are
shorted out.

Electrical Engineering Excellence

Description

Electrode control system.........

EPMA DUO starter...............

EPMA starter

The
moving
electrodes
travel
vertically inside the insulating
container, guided by a nylon rod.
Two solid brass rods, fixed to a
transversal carrier, support the
assembly. This carrier is common to
all three electrodes and constitutes
the neutral point (start point).

For starting machines of large
powers, or to reduce mechanical
stress, it may some-times be
preferable to use two motors which
total the rated power rather than a
single one. (Such as a dual drive
mill) A dual EPMA starter is then
used, to ensure synchronized
acceleration of both motors.

Displacement of the electrodes is
effect-ed by a motor driven worm
screw assembly. This is normally
controlled by either an electrode
drive motor, which is operated by a
VVVF. A hand wheel is also provided
for emergency manual operation.
Starting times are adjustable from 8
to 150 seconds.

The EPMA DUO comprises two
electrolyte tanks. The resistance
values are equalized between the
two tanks as they use common
electrolyte, which is circulated
between each tank. The electrode
drive assemblies are mechanically
coupled via a cardin shaft, so as to
ensure complete synchronization of
the movement of the two electrode
assemblies.

An EPMA unit comprises:
The electrolytic resistance contained
within a tank complete with electrodes
of a size rated for the specific kW
rating. A separate H.V enclosure
houses the Shorting contactor, and a n
L.V enclosure contains the control
system (control panel).

Tank......................................
The tank is manufactured with 304L
stainless steel from 2 to 5 mm. The
tanks include lifting points suitable for
hoist to facilitate loading, unloading
and positioning. Tank capacity and
dimensions are deter-mined by the
motor rating. (See characteristics). The
tank is filled through a access point in
the side cover, and emptied through
valves situated at the base of the unit.
The tanks Ingress Protection rating is
IP 54

Electrolyte.............................
Various concentrations of sodium
carbon-ate are normally employed. A...
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