When it comes to refrigeration compressors, the term HST holds significance. HST, which stands for High Starting Torque, refers to a specific characteristic of the compressor’s motor.
In simpler terms, an HST compressor possesses a motor designed to deliver a powerful starting torque. This trait holds crucial importance for the compressor’s functionality.
HST compressors are unique in that they can effectively accommodate both capillary tubes and thermostatic expansion valves as expansion elements. Unlike some other compressors, HST units display a remarkable ability to achieve equilibrium between low and high pressures promptly once the equipment is deactivated, in the case of capillary tube systems.
In contrast, systems utilizing a thermostatic expansion valve exhibit a slower pressure balance restoration after shutdown. This can present a challenge during the subsequent startup of the compressor’s motor.
Illustrated in the accompanying graph are the distinctive performance curves of a High Starting Torque (HST) compressor, providing a clear comparison against compressors with lower starting torque. The tabulated data reveals that HST compressors require a start capacitor for proper operation.
HST compressors are associated with two types of motors: C S R and C S R I. These motors are equipped with an induction design and incorporate a start capacitor. Notably, the C S R motor includes a relay to govern the actions of the start capacitor.
The functionality of the relay is crucial in HST compressors, particularly those employing a voltmeter relay with normally closed contacts. The relay coil operates in parallel with the compressor’s start coil. As the motor-compressor’s speed increases, the voltage in the start coil rises until it reaches a specific threshold. At this point, the relay’s armature is engaged, leading to the disconnection of the start capacitor from the circuit. This action ensures the continued operation of the compressor without interference.
It’s worth noting that the HST compressor’s motor configuration extends to the C S I R type motor as well. While similar to the C S R motor, the C S I R motor lacks a run capacitor, providing a streamlined design.
In summary, the HST compressor’s unique motor design and high starting torque capability make it a versatile and essential component in refrigeration systems. Whether paired with a capillary tube or a thermostatic expansion valve, the HST compressor ensures efficient performance and reliable startup, bolstered by its intricate motor configuration.