Page 130 - Offshore Electrical Engineering Manual

Solid-State Controllers 117

room. Failure of the battery charger to limit charge voltage would lead to a short-
lived evolution of hydrogen, and the room ventilation would need to cater for this.
A dedicated room also prevents the access of unauthorised personnel who may not
be aware of the dangers associated with stored electrochemical energy; tools or other
metal objects inadvertently placed across battery terminals will cause heavy short-
circuit currents to flow.

SOLID-STATE CONTROLLERS

BURST-FIRED (INTEGRAL CYCLE FIRED) PROCESS HEATER
CONTROLLERS
Burst firing consists of supplying a series of whole mains cycles to the load. This
method of control is used for controlling heaters, but not motors, for obvious rea-
sons. It has the benefit of avoiding the production of nonsinusoidal waveforms (Fig.
2.11.1). Unfortunately, it can produce flicker in lighting if the heater it is controlling
is large (Fig. 2.11.2).

FIGURE 2.11.1
Waveforms of a burst-fired controller. T F , firing time; T M , modulation time; T NF , nonfiring time.