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2.3 Voltage Balance
The voltages between compressor terminals should be balanced. When the line voltages applied to a three-
phase compressor are not equal, unbalanced current in the stator windings will result. A small percentage
voltage unbalance will result in a much larger percentage current unbalance. Consequently, the temperature
rise of the motor windings is unbalanced and the overheated motor will cause the compressor failure.
The temperature rise can be estimated using the formulation as follows:
Percent Voltage Unbalance
=
100 X Max. Volt. Deviation from Avg.Volt./ Average Volt.
Temperature Rise= [Percent Voltage Unbalance]
2
X 2
To well protect the motor, The voltage unbalance(%) should be lower than 2%.
2.4 Deep vacuum Operation
Scroll compressors should never be used to evacuate an air-conditioning or refrigeration system. As a high
volumetric efficiency machine, compressor will achieve extremely low vacuums when the suction side is
restricted, this may cause internal arcing at the electric terminal and the damage of compressor.
2.5 Brief Power Interruptions
The brief power interruptions can cause powered reverse rotation on single phase compressors. When power
is reapplied, the compressor may continue to run in the reverse direction for several minutes, until the internal
linebreak cycles the compressor off. After tripping the linebreak, the compressor will operate in the correct
direction when power is restored. During powered reverse rotation, the compressor will sound much louder
than during normal operation.
To prevent this situation, an anti-short cycle timer of 3 minutes off / 7 minutes on duration is recommended.
This will allow the compressor to be de-energized for at least 3 minutes after each power interruption.
2.6 Protection Devices
2.6.1 Internal Motor Protector
Panasonic scroll compressors are protected by internal linebreaks on the motor windings for single phase
and three phase models. Internal linebreaks respond to over-current, high temperature and a combination of
both.
The protector is the automatic reset device containing a snap action bimetal switch. In three phase
compressors they protect against secondary single phasing. The motor protector is designed to protect
against variety fault conditions such as failure to start, running overload and fan failure, locked rotor, abnormal
operation of contactor. The test is necessary to be sure that the motor protector will not trip under the overload
conditions.
For B3 models (for Japan market, 3PH-50Hz-200V/3PH-60Hz-200~220V), the motor is protected by internal
thermostats with external breakers. The internal thermostats respond only to high temperature, so an outside
overload relay is required to protect compressor against over-current conditions.
