PGA-016A Littelfuse Inc, PGA-016A Datasheet - Page 49

• 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

© 2009 Littelfuse
POWR-GARD
Motor Protection
Solutions: A multifunction motor protection relay has
multiple trip and alarm settings for current protection.
Overcurrent protection is typically set above locked rotor
current and has a minimal delay time. Overcurrent protection
may be used to trip a breaker instead of a starter due to the
high fault levels. Jam protection is set below overcurrent
and has a slightly longer delay time. Jam protection prevents
motor heating that would otherwise lead to an overload trip.
Jam protection is enabled after the motor is running to avoid
tripping on starting current. Undercurrent is set below full-
load current to detect loss of load.
Under and Overvoltage
Overvoltages cause insulation stress and premature
breakdown. Undervoltages, such as those caused by
brownouts, can lead to increased motor heating. Torque
developed by an electric motor changes as the square of the
applied voltage. A 10% reduction in voltage results in a 19%
reduction in torque. If the motor load is not reduced, the
motor will be overloaded.
Solution: Under and overvoltage protection are features
found in a higher-end motor-protection relays. Voltage
protection can be used proactively to inhibit a start.
Ground Faults
Ground faults are the most common fault and can lead to more
serious problems. Ground-fault protection, described elsewhere
in this text, is an important consideration in motor loads.
100 000
50 000
10 000
5000
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100
50
10
5
1
•
POWR-GARD
CLASS F
®
HOTTEST TEMPERATURE (°C)
Protection Relay Catalog
®
Protection Relays
FIGURE 11
10
7
5
1
5
2
1
20
10
5
3
2
1
47
Solution: The motor protection relay should be able to
detect low-level ground-fault current when used on a
resistance-grounded system.
High Resistance Winding Faults
Winding-to-winding and winding-to-ground failures inside the
motor are difficult to detect using the phase and ground-fault
CTs due to low magnitudes of current.
Solution: Differential protection in high-end motor
protection relays use multiple CTs to compare the current
entering and leaving the winding. If there is a difference in
currents then leakage is occurring. This sensitive protection
is used on very large motors.
Current and Voltage Unbalance, Phase Loss,
Phase Reverse
Older motor protection did not consider current unbalance and
today it is often overlooked. Unbalance increases negative-
sequence current which causes additional rotor heating.
Phase loss is also referred to as single phasing. When a
phase loss occurs, negative-sequence current is equal to the
positive-sequence current and unbalance is 100%. In this
condition, one motor winding attempts to do the work of
three, inevitably leading to overheating.
Phase reversal causes the negative-sequence current and
voltage to be greater than the positive-sequence current
and voltage. Voltage-based protection is advantageous
to prevent a start with incorrect sequence. In some
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0 8
0 6
0 5
0 4
0 3
0 2
0 1
80
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10
8
6
5
4
3
2
1
0
100
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SERVICE FACTOR 1 00 TO 1 25
SHOWN AT 1 15
300
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500
MOTOR CURRENT (%FLA)
TIME TO TRIP DECREASES
AS USED I t INCREASES
600
FIGURE 12
700
2
800
0% USED I t (cold)
25% USED I t
900
www.littelfuse.com/ProtectionRelays
2
50% USED I t
1000
2
1100
2
75% USED I t
1200
2
1300
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1500
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