Chiller controls

In combination:

• a chiller system for providing cooling to a medium to be cooled, said chiller system including an AC electric motor for driving a compressor;
• controlled conduction solid state switch means having a line side and a load side;
• means for coupling said line side of said solid state switch means to a source of AC electric power;
• means for coupling said load side of said solid state switch means to said AC electric motor;
• and
• means for accelerating said AC electric motor to running speed comprising means for controllably applying trigger signals to said solid state switch means such that the firing angle at which said solid state switch means is fired in relation to the voltage phase angle of the source of AC electric power is progressively increased from a minimum firing angle to a maximum firing angle to thereby start and accelerate the motor to running speed;
• said electric motor being of the polyphase type;
• said solid state switch means comprising a solid state switch in each of said phases;
• and voltage safety means for protecting said motor against a fault in the voltage actually applied to the motor;
• said voltage safety means comprising a transformer for each of said phases;
• each of said transformers having a respective primary and a secondary winding;
• each of said transformers having a primary winding connected between a line side of said switch associated with a respective phase and a load side of said switch associated with another phase;
• monitoring circuit means connected across the respective secondary windings of each of said transformers for monitoring a parameter of the voltage waveform of each of said phases, and for generating a signal when the monitored parameter exceeds a preselected value;
• and disconnect means responsive to said monitoring circuit means signal for disconnecting said motor from the source of AC electric power.