Specifications

A2
GE Limitamp
®
Medium Voltage Motor Control
General
A
Comparison of Controller Types
Full Voltage Non-Reversing
The Limitamp control across-the-line (FVNR) controller is the
most popular type of controller. In general, high-voltage sys-
tems have fewer power restrictions than low-voltage systems;
therefore, full-voltage controllers may be applied to a greater
number of applications. Full-voltage controllers provide
lowest cost, simplicity, minimum maintenance and highest
starting torque.
Reduced Voltage
Primary reactor (closed-transition) Limitamp controllers (RVPR)
are the most popular of the reduced-voltage type starters
because they provide a simple, low-cost means of obtaining
reduced-voltage starts. The starting time is easily adjustable in
the field.
Limitamp closed-transition auto-transformer controllers (RVAT)
provide higher starting torque efficiency and a more favorable
power factor during starting than a primary reactor starter.
The transition time can be easily adjusted in the field. NEMA
medium-duty reactors and autotransformers with 50-, 65-
and 80-percent taps are provided as standard.
Limitamp solid state controllers (RVSS) are available for
applications requiring very tightly controlled motor torque
and acceleration times and where avoidance of sudden
switch-on of inrush current is desired. RVSS controllers offer
several advantages over FVNR controllers:
• RVSS reduces mechanical stress on driven equipment and
motor linkage while maximizing torque capability of the motor
• RVSS provides for special stopping requirements of motor/
pumps (soft stop/eliminating water hammer effect, etc.)
• RVSS minimizes voltage fluctuations on weak power distri-
bution systems, reducing undervoltage supply to critical
loads or causing light flicker
• RVSS may reduce utility demand penalties
GE’s RVSS controllers can be programmed for a variety of
soft start/soft stop parameters; upon reaching normal run
conditions, the controller automatically transfers the load to
a fully rated NEMA bypass contactor. They also provide
state-of-the-art, built-in motor protection, including:
• Electronic overload
• Ground fault
• Phase loss, phase unbalance, and phase reversal
• Over/under current (including loss of load)
• Over/under voltage
• Optional RTD Input
Among the metering values provided by GE’s RVSS are:
• Percentage full load amperage (FLA)
• Phase current
• KVAR
• KVA
• KW
• Ground fault current
• Thermal capacity to start
• Remaining thermal register
• Frequency
Reduced Inrush
Reduced voltage controllers provide a means of reducing
the starting inrush where the starting duty is not limited by
the controller. This type of controller can be used where
extremely long acceleration times are required.
Table A.3 Comparison of Starting Characteristics
À Autotransformer magnetizing current is not included in listed values.
Magnetizing current is usually less than 25 percent motor full-load current.
Á X = % of rated RVSS output volts, Y = (X/10)
2
Transformer Feeders
Limitamp controllers are generally considered motor starting
equipment; however, they are not strictly limited to motors and
can provide very good protection for loads such as transformers.
Transformers that can be controlled by Limitamp controllers
must have a primary rated in the 2400- to 7200-volt range.
To adequately protect a transformer, it is necessary to define
specific protection requirements. The following areas will be
considered:
1. Transformer winding fault (primary and secondary)
2. Single-phasing, resulting in a phenomenon known as
“ferroresonance”
Starter Starting Characteristics Expressed in Percent Rated Value
Type
Voltage
on Motor
Motor
Current
Line
Current
Torque
Torque
Efficiency
Full Voltage 100 100 100 100 100
RVSS (Solid State Starter with infinitely variable volts)
80 percent volts 80 80 80 64 80
65 percent volts 65 65 65 42 65
50 percent volts 50 50 50 25 50
“X” percent voltsÁ
X X X Y X
Autotransformer (RVAT)
80 percent tap 80 80
64À
64 100
65 percent tap 65 65
42À
42 100
50 percent tap 50 50
25À
25 100
Primary-Reactor (RVPR)
80 percent tap 80 80 80 64 80
65 percent tap 65 65 65 42 65
50 percent tap 50 50 50 25 50