🔍 Key Concepts

• Centrifugal compressor load at start-up and how flow affects required horsepower • Function of variable inlet guide vanes in controlling refrigerant flow and compressor head • Relationship between motor current draw and the load placed on the compressor during acceleration

💭 Think About

• At start-up, do we want the compressor to move a lot of refrigerant or very little if we are trying to protect the motor from overload? Think about how that affects torque and current. • How do inlet guide vanes change the amount of gas entering the impeller, and what does that do to the work the motor has to do? • When the motor is first connected at full voltage, is the current naturally high or low, and does the control strategy try to add load before or after that current stabilizes below full-load current?

✅ Before You Answer

• Decide whether open or closed vanes produce higher mass flow and higher load on the motor at start-up. • Make sure the choice you pick explicitly keeps motor current below full-load current during the acceleration period. • Verify that the timing in the option you choose matches a protect-the-motor-first, then take on load strategy.