GENER
AL INFORMA
TION
SY
STEM DESIGN
INTEGR
ATION INT
O SY
STEM
ORDERING INFORMA
TION
PR
ODUC
T INFORMA
TION
The MCC is the current at which the motor
protection trips under maximum load and
low voltage conditions. This MCC value is the
maximum at which the compressor can be
operated in transient conditions and out of
the application envelope. Above this value, the
internal motor protection or external electronic
module will cut-out the compressor to protect
the motor.
Locked Rotor Amp value is the higher average
current as measured on mechanically blocked
compressors tested under nominal voltage. The
LRA value can be used as a rough estimation for
the starting current. However, in most cases, the
real starting current will be lower. A soft starter
can be applied to reduce starting current (see
section
“
soft start
“
).
MCC (Maximum Continuous
Current)
LRA (Locked Rotor Amp)
Motor protection
DSH090 to DSH184
Compressor models DSH 090 to 184 are
provided with internal overload motor
protection to prevent against excessive current
and temperature caused by overloading, low
refrigerant flow or phase loss. The cutout current
is the MCC value listed in table “Three phase
electrical characteristics”.
The protector is located in star point of motor
and, should it be activated, will cut out all three
phases. It will be reset automatically.
While not compulsory, an additional thermal
magnetic motor circuit breaker is still advisable
for either alarm or manual reset.
Then it must be set below MCC value (at max
operating current):
• When the motor temperature is too high, then
the internal protector will trip.
• When the current is too high the thermal
magnetic motor circuit breaker will trip before
the internal protection therefore offering
possibility of manual reset.
Electrical data, connections and wiring
Winding resistance is the resistance between
phases at 25°C (77°F) (resistance value +/- 7%).
Winding resistance is generally low and it
requires adapted tools for precise measurement.
Use a digital ohm-meter, a “4 wires” method and
measure under stabilised ambient temperature.
Winding resistance varies strongly with winding
temperature. If the compressor is stabilised at a
different value than 25°C (77°F), the measured
resistance must be corrected using the following
formula:
a + t
amb
R
tamb
= R
25°C (77°F)
_______
a + t
25°C (77°F)
t
25°C
: reference temperature = 25°C (77°F)
t
amb
: temperature during measurement °C (°F)
R
25°C (77°F)
: winding resistance at 25°C (77°F)
R
amb
: winding resistance at tamb
Coefficient a = 234.5
The MOC is the current when the compressors
operate at maximum load conditions and 10%
below nominal voltage (max. evaporating
temperature and max. condensing temperature).
MOC can be used to select cables and contactors.
In normal operation, the compressor current
consumption is always less than the MOC value.
Winding resistance
MOC (Maximum Operating
Current)
Compressor models DSH240-295-381-485 are
delivered with a pre-installed motor protection
module inside the terminal box. This device
provides efficient and reliable protection against
overheating and overloading as well as phase
loss/reversal.
The motor protector comprises a control module
and PTC sensors embedded in the motor
winding.
The motor temperature is being constantly
measured by a PTC thermistor loop connected
on S1-S2 . If any thermistor exceeds its response
temperature, its resistance increases above the
trip level (4.500 Ω) and the output relay then
trips – i.e. contacts M1-M2 are open. After cooling
to below the response temperature (resistance <
2.750 Ω), a 5-minute time delay is activated.
After this delay has elapsed, the relay is once
again pulled in – i.e. contacts M1-M2 are closed.
The time delay may be cancelled by means
DSH240 to DSH485
18
FRCC.PC.045.A7.02
Содержание DSH Series
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