Electrical Components - Midea LSBLG MCF Series Technical & Service Manual

MCAC-CTSM-2018-1 Flooded type water cooled screw chiller (MIC)
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Electrical components

1) Power protector
This module detects power supply and protects if phase loss, phase sequence, and under voltage of
incoming line power, occurs. It prevents damage to the compressor or other components if there is a
power failure. Some models also provide protection for overvoltage and three phase imbalance.
2) Time Relay and Intermediate Relay
The time relay is an automatic switch device that performs delayed control based on electromagnetic or
mechanical principles. It controls the star delta switching time for the compressor contactor. The preset
time is the start operation time (6s). The coil voltage is AC 220V. The rated contact current is usually low
and is only used for controlling the loop.
The intermediate relay delivers intermediate signals among control circuits to increase the number and
capacity of contacts. Normally, the main control board output controls starting and stopping of loads such
as motor and water pump by using the intermediate relay to drive the contactor coil. The coil power
supply can be DC or AC. Our standard screw compressor model uses the AC220V coil.
3) Compressor thermal overload relay
The thermal overload relay works are based on heating effect of electric current. With inverse time limit
action feature which is similar to the permissible overload feature of the motor, it provides overcurrent
protection for the compressor and fan. For compressor overload protection, the major loop current of the
motor is converted to an AC 0-5 A current signal by the current mutual inductor. Then the thermal
overload relay performs overload protection. For fan overload protection, the thermal overload relay is
connected in series with the major loop.
4) Current transformer and Transducer
The current transformer transforms primary current with a larger value to secondary current with a
smaller value for protection or measurement. A current transformer with transformation ratio of 400/5 can
transform 400A current to 5A.
A transducer transduces the measured current to DC voltage or DC current. After the current transformer
transforms the current to AC 0-5 A current signals, the transducer outputs 4-20 mA analog signasl based
on the linear scale to the main control board.
5) Electronic Expansion Valve
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