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ELECTRICALS & ELECTRONICS |
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CT4 Electronic Control and Protection System |
For ultimate motor
protection and increased
productivity |
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The Sprecher + Schuh CET4
Electronic Motor Protection
Unit is a unique digital microprocessor
controlled system that
creates an exact thermal image
of the motor. This technology
permits motors to run at their
full capacity while providing
maximum overload protection.
Options are available that
provide additional protection
functions including short
circuit, phase reversal, underload
protection, ground fault,
and much more.
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| Use Overload Relay Family… |
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CEP7 |
CT7 |
CT7K |
CT4 |
CEF1 |
CET4 |
| CA7 |
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| CA6 |
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| CA5 |
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| CA4 |
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| Make full use of equipment |
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The CET4 provides extremely accurate
thermal imaging of the motor.
This means that equipment can be
safely run at maximum output even
with fluctuating loads, brief overloads,
phase unbalance, and other conditions.
The precise thermal imaging takes into
account the temperature rise of the
stator winding and the iron mass of
the motor. This two-body simulation
provides accuracy during all conditions
of starting, running, and stopping
motors. Simple adjustments provide
accurate thermal simulation for all
types of motors. |
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| Use with all types of motors |
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Adjustments can be made for different
motor cooling constants, such as those
found on separately ventilated or
liquid cooled motors. Also, the degree
of inertia setting can be changed to
adapt to motors with differing locked
rotor time ratings. This makes the
CET4 adaptable to protecting all
motors under maximum loading
conditions in both high and low
inertia applications.
The CET4 is not directly connected to
the motor voltage. Because of this
feature, and the fact that it is so
flexible, it can be effectively used on
medium voltage motors. For these
applications, the user must supply appropriate current transformers. |
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| Avoid unplanned downtime,
diagnose problems quickly |
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The various protective and control
functions can be easily programmed to
trip the main (tripping) relay, a
separate alarm relay, or any of five
auxiliary relays. This means that a
warning can be given rather than
tripping the motor off line, allowing
the unit to be repaired during a
planned shutdown.
In addition to causing output relays to
trip, all parameters can be displayed on
the LCD panel located on the front of
the CET4. |
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| Monitor thermal usage |
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For increased safety and productivity,
an optional 4-20 milliamp analog
output is available that allows monitoring
of thermal usage of the motor.
When used for load control, such as a
feeder conveyor on a rock crusher, the
loading can be continually matched to
the motor’s maximum temperature.
This permits optimum utilization of
the motor with full thermal overload
protection. |
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| Wide array of standard
features |
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• Thermal overload
• Single-phase protection
• Phase unbalance protection
• Ground fault protection
• Stall protection
• Underload protection
• Starting time monitor
• Limited starts per hour
• Warm start limit
• Emergency override
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| Available options |
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• Short circuit
• Ground fault leakage
• Stall during start
• Multiple RTD temperature sensor inputs
• PTC thermistor input
• Phase sequence monitor
• Analog output of thermal
utilization (4-20mA)
• Wye-Delta starting
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| Standard protection
functions |
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Thermal Overload - Under many
conditions it is only necessary to set
the full load amps of the motor. The
time/current trip characteristics are
factory set for most motors - six times
FLA for 10 seconds. In addition to
setting the full load amps, five other
parameters can be set. This means
accurate protection for all types of
motors |
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Phase Unbalance and Single-phase
Protection - When phase voltages are
unbalanced, the resulting current
unbalance in the motor can be six to
ten times the voltage asymmetry.
These currents can quickly cause
damage to the motor. The CET4 can
provide warning and trip functions for
current imbalances of 5 to 80%, with
tripping delay adjustable from one to
five seconds. |
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High Overload and Stall Protection -
When motor driven machinery
becomes blocked or jammed, unnecessary
motor temperature rise and
mechanical damage can result. The
CET4 can provide tripping or alarm
signals under these conditions. The
stall current is adjustable from one to
six times full load amps and the trip
delay can be set from 0.1 to 5 seconds.
Since the motor has not experienced a
significant temperature rise, it can be
restarted immediately after the blockage
has been removed. |
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Underload Protection - Pump motors
that are cooled by the medium they
are pumping can be overheated in
spite of underloading. Also, pumps
can be damaged by cavitation or noloadpumping. On other equipment,
broken shafts, belts etc., can cause
severe damage quickly. Very often,
these motors are only accessible with
difficulty, so any damage would cause
long and costly repairs. The CET4 can
detect underload conditions and
provide warning or trip. The response
level is adjustable from 0% to 100% of FLA. The time delay is adjustable
from 1 to 60 seconds after the motor
current has fallen below the set
response level. |
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Ground Fault Protection - Most
insulation faults in motors result in
small ground currents which can
rapidly rise to a very high value
causing motor failure. The CET4 can
be set to trip or provide warning of
ground currents of 10-100% of FLA,
with a time delay of 0.1 to 5 seconds.
For even greater protection, the CST4
option is available which can utilize a
100/1 ratio core balance current
transformer to detect ground currents
as small as 0.5 - 10 amps. This can
provide early warning to protect
against motor damage from ground
faults. |
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| Other important functions
Limited starts per hour - Total number
of starts per hour can be limited from
1 to 10. |
| Monitor starting time - Maximum
starting time of the motor can be set
from 1 to 240 seconds. |
| Warm start - If desired, tripping time
for a warm start can be extended to
50-100% of the cold start setting. The
number of warm starts per hour can be
set from 1 to 15. |
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