Honeywell ACS-8, Руководство по установке

Страница: 12 / 142

12 Installation Instructions / ACS-8
4. Protective measures
Defence against electrostatic discharge
Modern semiconductor devices are susceptible to electrostatic charges. The higher the integration density,
the finer the structures on the chip and the greater the danger of electrostatic damage.
With some semiconductor devices, damage may be caused by less than 20V. This is a very low value when
values of greater than 1000v can be generated by walking across a carpet.
Damage caused by electrostatic discharge rarely leads to instant failure. More commonly, semiconductor
structures receiving damage from electrostatic discharges have a residual burning trace which initiates a
chemical process on the chip, causing it to degrade over a period of days, weeks, months or even years.
Partial operation can be difficult to detect until eventual failure occurs.
Protection against electrostatic charge
As electrostatic charges cannot be avoided, the electronics must be protected from dangerous voltage
levels.
- Wear an ESD wriststrap connected to the earth connection of the controller.
- Use only soldering irons that are galvanically separated from the power supply and equipped with
an electronic temperature control.
Protective measures against over-voltage transients
Protective shielding and grounding must be provided to avoid malfunctions and damage to system
components due to over-voltage. This may occur due to switching of supplies or heavy machinery on the
supply line or from direct or indirect effects of thunderstorms. (See DIN VDE 0845 part 1, Protection of
telecommunication systems against lightning strokes, static charges and over-voltages caused by power
installations – measures against over-voltages.)
Protection according to the VdS requirements is built into the products.
Protection against damage caused by lighting strokes and over-voltages can be assured by implementing
appropriate measures for internal and external lightning (medium and coarse) protection. Additional
requirements will depend on the installation location and the nature of other equipment connected to the
system.
Over-voltage caused by switching actions causes a very steep rate of change of voltage. This means that
the voltage can reach values of several kV within a few microseconds. Such voltage pulses (transients)
cause the destruction of electronic components.
Adequate over-voltage protection, will absorb these transients.
Causes of transient interference voltages
Transient voltages are often caused by atmospheric discharge, i.e. lightning stroke. A lightning discharge
may release currents reaching values over100kA with very short rise times. This current causes a high
voltage drop in the earth resistance of a building and the high rate of change of current induces high
voltages in conductive loops. The energy resulting causes the damage to unprotected devices.
Switching actions in electrical systems also cause over-voltage transients.
High-voltage power supply networks are fitted with high-frequency compensation systems and are coupled
to low-voltage parts of the network. Over-voltages and high-frequency power transients in low-voltage
installations can also be caused by sharp drops in voltage, phase control, etc. In these instances, the rate
of change of current can reach higher values than a lightning stroke.