York MILLENNIUM YCAS 250 Manual Download

Page: 154 / 196

154

YORK INTERNATIONAL

Low Motor Current Cutout / Motor Protector (Hi
Motor Winding Temp Cutout) / Mechanical High
Pressure Cutout / External Motor Overload:

The Low Motor Current Safety prevents a compres-
sor motor running with less current than would nor-
mally be expected. This may result from loss of refrig-
erant, contactor, or power problems as well as from a
compressor that is not pumping due to a mechanical
malfunction. Motor current is monitored using 3 Cur-
rent Transformers (CTs) per motor, one on each phase.

Average motor current is monitored after 3 seconds of
compressor operation. From this time the system will
be shut down if average motor current is less than 10%
of FLA.

Compressor Motor Protection Modules, External
Motor Overloads and Mechanical High Pressure
Cutouts are fitted to each system. All these devices
stop the compressor by removing power from its motor
contactor coils. This causes the CTs to obviously sense
a zero current draw by the compressor motor and causes
a Low Motor Current Fault to be displayed. These de-
vices operate as follows:

The Motor Protection Module protects against exces-
sive motor winding temperature by monitoring 3 or 6
sensors built into the motor windings. If the tempera-
ture becomes excessive, the module will cause power
to be removed from the compressor contactors shutting
down the compressor. Auto restart will not occur since
manual reset is required. A fault lockout will automati-
cally occur after the micro attempts 2 more starts with

S Y S

L O W

C U R R / M P / H P

S Y S

L O W

C U R R / M P / H P

to loading or fan cycling from causing shutdown. If
suction pressure drops below the cutout point after 225
seconds of operation, the transient timer is activated.
While the transient timer is active, suction pressure must
not drop below 10% of the cut-out initially programmed
and must be greater than:

C.O. = Programmed C.O. X ( Time + .1 )

33.3

This transient cutout value increases with time until
after 30 seconds it equals the programmed cutout value.
If the suction pressure falls below the value as calcu-
lated by the formula relative to time, the system will
shut down on a low suction pressure fault. If the suc-
tion pressure rises above the programmed cutout value,
the 30 second timer will be reset.

If the Dip Switch on the microprocessor board is set
for “Water Cooling” (see page 158), the cutout is pro-
grammable between 44 - 70 PSIG (3-5 bar) for both R-
22 and R407c models. In this mode, settings of 44 PSIG
(3 bar) for R22 and R407c are recommended. If the
Switch is set for “Brine Cooling” (glycol) the cutout is
programmable between 5 - 70 PSIG (0.3 - 5 bar) for R-
22 and R407c models. In this mode, the cutout should
typically be set to the saturated refrigerant pressure
equivalent to 18°F (10°C) below the temperature of the
chilled liquid. NOTE: The sludge point of the glycol
MUST be at least 20°F (11°C) below the equivalent
cutout temperature. This programmable value is pass-
word protected.

High Compressor Motor Current Cutout:

The High Motor Current Safety protects against exces-
sively high motor current and shuts a system down and
locks it out after only a single occurrence of a rise in
average motor current above the cutout point. Motor
current is monitored using 3 Current Transformers
(CTs) per motor, one on each phase.

Average motor current is monitored after 7 seconds of
compressor operation. The system will be shut down if
average motor current exceeds 115% FLA.

S Y S

H I G H

M T R

C U R R

S Y S

H I G H

M T R

C U R R

FLA (full load amps) is approximately
1.2 x RLA (rated load amps). RLA is
specified on the motor / chiller name-
plate and is typical current demand un-
der rated operating conditions in a
fully loaded system. When a system is
fully loaded, typical motor currents
may be at 60 - 85% FLA depending on
operating conditions.

MicroPanel Contents