Flooded type water cooled screw chiller (PCB Control)
60
2.
Electrical components introduction
1) Power protector
This module is used to detect power supply and provide protection in case of phase loss, phase
sequence, and under voltage of incoming line power, so as to prevent damage to the compressor or
other components caused by 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 which performs delayed control based the electromagnetic
or mechanical principles. It controls the star delta switching time for the compressor contactor. The
preset time is star operation time (6s). The coil voltage is AC 220V. The rated contact current is usually
low and is used for controlling the loop only.
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 based on the principle of heating effect of electric current. With inverse
time limit action feature which is similar to the permissible overload feature of the motor, it is used to
provide 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 the purpose of 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 signal based
on the linear scale to the main control board.
