Emerson ZB Copeland Scroll Service Manual download pdf (Page 14)

ZB Series

Installation and piping arrangement

Electrical connection

Power supply voltage and connecting terminals

Please note the direction of the connecting terminals in the

connecting box (single-phase power: R, S, C; three-phase power: T1;

T2; T3). To ensure normal start and operation of the compressor, the

power supply voltage should not drop more than 10% below the rated

voltage for the compressor.

Starting characteristics of the single-phase compressor

The single-phase scroll compressor is equipped with a permanent

fractional capacitor motor (PSC). Auxiliary starting equipment is

unnecessary for most applications. But auxiliary starting equipment is

necessary for some applications (for example, if the starting voltage

is lower). In the latter case, a starting capacitor and a secondary relay

may be used at start-up.

Rotation direction of three-phase compressor

The compression process of the scroll compressor occurs only in one

direction. The single-phase compressor starts and operates based on a

correct direction of rotation (except under such conditions where the

power supply is abruptly cut off). The direction of the rotation for the

three-phase compressor depends on the phase sequence of the power

supply. Hence, the compressor has a 50% chance of "reverse-rotation".

When the installation operation is carried out at-site, the correct

direction of the rotation can be judged by discharge pressure increase

and suction pressure decrease. However, if the compressor is running

in reverse direction, the compressor will give out an abnormal noise

and the current draw will clearly be lower than the rated value as well.

A brief reverse-rotation is harmless to the compressor. But a reverse-

rotation for long periods can damage the compressor. Equipment

manufacturers can place a phase sequence protection module in the

control circuit to ensure that the machine will not operate in case of

incorrect phase sequence. Since there is a 50-50 chance of connecting

power in such a way as to cause rotation in the reverse direction, it is

important to include notices and instructions in appropriate locations

on the equipment to ensure proper rotation direction is achieved

when the system is installed and operated.

Instantaneous Power Shut-Off

Instantaneous shut-off (power-off time is below 0.5 sec.) can lead to

change in the direction of rotation of the single-phase compressor.

After shut-off, the compressor operation will last several minutes

in the reverse direction until the internal motor protector of the

compressor is triggered. The compressor will not be affected in

this process. After the motor protector resets, the compressor

will re-start and operate in the correct direction of rotation.

Copeland recommends using a relay that can respond to this

instantaneous shut-off. The relay helps to re-start the compressor

automatically after a time-delay of two minutes. Three-phase

compressors do not need a relay.

High-voltage test

The motor of the refrigerating scroll compressor is in a casing. After

charging refrigerant into the system, the motor could be immersed

into the liquid refrigerant. When the liquid level in the casing is

higher, the result of the high-voltage test could indicate a higher

current value, because the conductivity of the liquid refrigerant is

higher than that of the gas or the lubricating oil. This phenomenon

will only happen when the compressor motor is entirely immersed

in the liquid refrigerant, but there is no safety issue.

Evacuation (drying)

The system must be evacuated after current leakage test. A

vacuum pump must be used to evacuate. The compressor

should never be used for self-evacuation. To evacuate, it is

suggested that the vacuum pump be connected to the high and

low-side evacuation valves with copper tube or high-vacuum

hoses (with internal diameter of at least 8mm). The sum of the

sectional areas of all connecting pipes should not be below the

sectional area of the inlet pipe for the vacuum pump.

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Emerson ZB Copeland Scroll Service Manual Page 14

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