Emerson VSG & VSSG Troubleshooting Guide download pdf (Page 34)

VSG/VSSG • Compact Logix PLC Manual •Vilter/Emerson • 35391CL

· Minimum Run Capacity – The Minimum Run

Capacity is the minimum capacity the com-

pressor will be allowed to run at. When the

compressor is started, it will be loaded to the

Minimum Run Capacity control setpoint minus

5%. This is done to prevent the capacity control

from hunting if the load is not great enough to

keep the compressor capacity at the Minimum

Run Capacity setpoint. On a call for unloading,

the compressor will unload until it reaches the

Minimum Run Capacity control setpoint. It will

remain there until the suction pressure reduces

and the compressor cycles off on the Suction

Pressure On/Off control setpoint.

· Volume Slide Adjustment Factor – This value is

normally zero (0) and will not require changing.

However, if the system operating conditions

show the volume ratio is not at the optimum

value for the system, this value can be adjusted

up or down to permit the most efficient position-

ing of the volume slide valves. To determine the

value to enter, first ensure that the system is in

a steady operating state and place the volume

side in manual. NOTE: The volume position set-

ting and increase the volume side position slowly

until the lowest amperage level is achieved. If the

amperage level rises instead of falls, decrease the

volume slide position until the lowest amperage

is achieved.

Record the differential from the original position.

This will then be adjustment factor to enter for

our system. NOTE: Negative numbers can be

used for this setting. This setpoint is active on a

drop in capacity below the Capacity Slide Adjust-

ment Range cut-in (ON) setting. The adjustment

is disabled when capacity rises above the Adjust-

ment Range OFF setting. Normally, the “ON-Off”

set points should both be set at 100%, so the

volume side adjustment factor will be applied

over the full range of 0 to 100%

· Current Transformer Ratio – The value entered

must agree with the Current Transformer Ratio

on the current transformer being used. The

current transformer is mounted in the compres-

sor motor conduit box. The ratio is stated as

the ratio of measured current to a nominal full

scale current in the secondary of 5 amps; only

the first of these is entered. For example, if the

ratio reads 250/5, enter 250.

· Low Suction Pressure Load Limit – Active in

Discharge Pressure Capacity Control mode only.

These setpoints limit the compressor from load-

ing at low suction pressure conditions. They

override the discharge pressure capacity control

setpoints. When the OFF setpoint is reached

(at or below setpoint), the compressor will not

be allowed to load any further. If the suction

pressure continues to fall, the capacity of the

compressor will decrease when the suction

pressure is at or below the ON set point. It will

stop decreasing when the suction pressure rises

to a point that is just below the ON set point.

· Forced Unload – Capacity Decrease (%/sec) –

This is the rate at which the Main Motor VFD will

drop when there is a Forced Unload condition

present in the Compressor.

· Forced Unload – VFD Transition Point to Capacity

Decrease (%/sec) – This is VFD speed at which

the physical capacity slide will begin to decrease

while there is a Forced Unload condition present

in the Compressor.

Additional Compressor Controls

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Emerson VSG & VSSG Troubleshooting Guide Page 34

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