PGA-016A Littelfuse Inc, PGA-016A Datasheet - Page 44

• Manufacturer Part Number: PGA-016A
• Description: BULK / WATERTIGHT COVER FOR PGR-6200 / PGR-7200
• Manufacturer: Littelfuse Inc

Specifications of PGA-016A

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

P
www.littelfuse.com/ProtectionRelays
Outputs
The relay has several ways of communicating that a decision
has been made. Typically the relay will operate a switch (relay
contact) to indicate that an input has surpassed a setting,
or the relay can provide notification through visual feedback
such as a meter or LED. One advantage of electronic or
microprocessor relays is an ability to communicate with a
network or a PLC.
As an example, a thermostat can be evaluated using
the diagram in Figure 1. The input that is measured is
temperature and the protection relay input device is the
temperature sensor. The user sets the desired temperature
setting (pick-up level). The relay measures the existing air
temperature and compares it to the setting. The outputs
can be used to provide controls (turning an air conditioner
or furnace on or off) and visual indication on the thermostat
display.
How Do Protection Relays Solve
Electrical Problems?
Similar to how the thermostat solves the problem of
automating the control of the air conditioner or furnace in a
home, protection relays can solve electrical problems.
The purpose of the protection relay is to detect a problem,
ideally during its initial stage, and to either eliminate or
significantly reduce damage to personnel and/or equipment.
The following stages illustrate how an electrical problem
develops:
Stage 1: When conductors with good insulation are exposed
to fault initiators such as moisture, dust, chemicals,
persistent overloading, vibration or just normal deterioration,
the insulation will start to slowly deteriorate. Such small
changes will not be immediately obvious until the damage is
severe enough to cause an electrical fault. Relays can detect
that a problem is developing by identifying slight deviations
in current, voltage, resistance, or temperature. Due to the
small magnitude in change, only a sophisticated device such
as a sensitive protection relay or a monitor can detect these
conditions and indicate that a problem may be developing,
before any further damage has occurred.
Stage 2: As the problem becomes more severe, further
changes take place such as insulation breakdown,
overheating, or overvoltage. Since the change from
normal to abnormal is great, traditional devices can be
used to interrupt power. Protection relays can also be
used to provide additional protection by detecting the fault
contributors (overheating, overvoltage, etc.) not possible
with fuses and circuit breakers.
POWR-GARD
Ground Fault Protection
42
Stage 3: At this point, the problem has occurred and caused
damage. Different types of protective relays and monitors
can reduce or eliminate damage because they detect
problems in advance of traditional devices.
As an example, if a facility is continually resetting circuit
breakers, replacing fuses, or repairing equipment and cannot
locate the problem, they may be experiencing overcurrents.
If this is the case, the user can install a protection relay that
has an overcurrent feature. The relay measures the current
(input) and allows the user to program limits (settings) into
the relay. The settings typically are more sensitive than the
fuses or circuit breakers. Once these limits are exceeded,
the relay will operate an internal switch (relay contacts).
The user has the option to use the switch to turn on a light
(alarm indication) or remove power (shunt-trip) before greater
problems occur. The user can use the alarm indication to
help identify the faulty equipment prior to the traditional
device clearing the fault.
II. RELAy APPLICATION
Ground-Fault Protection
The primary purpose of grounding electrical systems is to
provide protection against electrical faults. However, this was
not realized until the 1970’s. Until then, most commercial and
industrial systems were ungrounded. Although ungrounded
systems do not cause significant damage during the first
ground fault, the numerous disadvantages associated
with ground faults resulted in a change to the grounding
philosophy. There are other advantages for a grounded
system, such as reduction of shock hazards and protection
against lightning.
Electrical faults can be broken down into two categories:
phase-to-phase faults and ground faults. Studies have
shown that 98% of all electrical faults are ground faults
(Source: Woodham, Jack, P .E. “ The Basics of Grounding
Systems” May 1, 2003 <http://www.ecmweb.com/mag/
electric_basics_grounding_systems_2/index.html>). Where
fuses can protect against phase-to-phase faults, additional
protection, such as protection relays, are typically required to
protect against ground faults.
Definition of Ground Fault
A ground fault is an inadvertent contact between an energized
conductor and ground or equipment frame. The return
path of the fault current is through the grounding system
and any personnel or equipment that becomes part of that
system. Ground faults are frequently the result of insulation
breakdown. It’s important to note that damp, wet, and
dusty environments require extra diligence in design and
maintenance. Since water is conductive it exposes degradation
of insulation and increases the potential for hazards to develop.
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