Technical Description
MOBILE WORKSTATION WM-DP1
31
Chapter 10 Technical Description
The block diagram shown in Figure 10.1 shows the different sub-units within the Separation
Transformer.
The mains cable connects to the transformer through a high current IEC-320 style connector,
allowing it to be easily replaced if it becomes damaged during use. It is secured to the transformer
by a pair of clamps, to prevent accidental disconnection during use. The protective earth terminal
connects to the metal enclosure of the unit and the output socket earthing system; the line and
neutral conductors connect to the primary side of the transformer via two thermal circuit breakers
and an inrush limiting circuit.
As with any transformer, the primary circuit will draw an inrush current surge when it is connected
to the mains supply, which can sometimes be very large, depending on the magnetic state of its
core at the instant it is powered. The inrush limiting circuit inserts a high power thermistor in series
with the primary winding to limit the initial surge, dissipating it as heat. After approximately 0.5
seconds a relay closes (producing an audible ‘click’) to by-pass the thermistor, both to avoid any
steady-state losses that would adversely affect the load regulation and to allow it to cool in
readiness for the next switch-on.
The transformer is wound with a nominal input-to-output ratio of 1:1, with concentric primary and
secondary windings. An additional low voltage secondary winding powers the circuit for the remote
switch. Electrical separation between windings is maintained by overlapping layers of “Nomex” and
“Melinex” tapes.
The secondary winding supplies power to the separated output sockets via a fuse to protect the
unit against short-circuit faults in the external equipment. An additional socket enables a remote
switch to be connected if required, operating a relay to control the power to the output sockets.
This provides a convenient way of turning the entire system (apart from the transformer itself) on or
off from a central point on the mobile workstation. When the remote switch is not connected, the
outputs default to the permanently energised state. To isolate the unit from the mains supply, set
the remote switch to its stand-by’ position, then disconnect the mains connector from the wall
outlet socket.
Potential equalisation terminals are provided adjacent to the input cable and either side of the top
cover, for use where local regulations require the enclosures of each part of the system be
connected to a common earth point, independently of the mains supply cables.
