Trane Starters Engineering Bulletin page 80

Glossary
Shunt trip
A tripping coil added to a circuit breaker or non-fused
disconnect to provide a means of tripping the circuit
breaker with an external signal. See "Ground fault
protection–low voltage" , p.
Silicone controlled rectifier (SCR)
A solid state signal controlled, one-way power switching
device commonly used in solid-state starters and variable-
frequency drives.
Single phase (single phasing)
See "Phase failure" , p. 78.
Solid-state starter
A starter that starts and accelerates a motor at a preset
acceleration rate and current limit. A solid state starter
performs this function by modulating the current/voltage
wave form delivered to the motor with silicon controlled
rectifiers (SCRs). For more information on this starter
type, refer to CTV-SLB017-EN (Solid-State Starters for
Trane Chillers ).
Starter
A device consisting of both a contactor and an overload
protection system or device whose purpose is to start and
stop a motor and protect the motor from overcurrent.
Variable-frequency drives are also classified as starters.
Stress cone (stress relief cone)
Cables carrying above 2000 volts must have a metallic
shield unless the cable is specifically listed or approved for
non-shielded use. Shielding is necessary because of the
danger of corona or ionization. The purpose of shielding a
cable is to confine its dielectric field to the inside of the
cable or conductor insulation. The shielding must be
grounded at one end.
Stress cones are used to reduce and control longitudinal
and radial electrical stresses at the cable end to values
within safe working limits for the material used to make-
up the termination. An oversized junction box at the motor
may be required to accommodate stress cones.
Surge capacitor
A device that protects electrical equipment from high
voltage spikes by absorbing the peak energy of the spike
and then releasing it into the tail of the spike.
Although surge capacitors may be used alone, they are
usually used in conjunction with lightning arresters. See
"Lightning arrester" , p. 77.
Surge capacitors are a starter option.
80
76.
Switchgear
A switchgear type starter is an across-the-line low-voltage
starter that uses a circuit breaker to connect and
disconnect the compressor motor to and from the line.
Usually a separate power source (i.e., 125 Vdc from a
battery bank) is used to open and close the circuit breaker
on demand.
Switchgear starters should be used with caution. Some
switchgear starters contain a relay that will trip the circuit
breaker if auxiliary power is lost. Others do not contain
this auxiliary power monitoring relay. It may then be
impossible to automatically disconnect the compressor
motor from the line in case of a compressor, chiller or
starter fault, if auxiliary power is lost while the compressor
is running.
T
Top hat
A supplementary sheet-metal enclosure provided with
unit-mounted medium-voltage starters and SMP cabinets
to help accommodate the space requirements of stress
cones.
Transducer
A device that converts a control signal from one form to
another. For example, conversion of a 0–20 psig
pneumatic control signal to a 4–20 milliampere electrical
control signal.
Transition
Transition is the action taken by a starter when changing
from one configuration to another, such as changing
(transitioning) from the wye/star configuration to the delta
configuration.
Open transition ... a term indicating that the motor is
disconnected from the line, transition is performed and
then the motor is reconnected to the line.
Closed transition ... a term indicating that the motor
remains connected to the line during transition.
All CenTraVac starters are closed transition. All SBO
starters must be closed transition. Open transition
starters cause stresses in the motor windings that
shorten motor life.
Inrush current is nearly constant during acceleration and
then drops quickly to less than RLA when the motor
reaches full speed. Starters using the Trane
microprocessor controller monitor motor current
continuously and initiate transition when the motor
current drops below 85 percent of RLA.
®
CTV-PRB004-EN