Single-Phase AC Motor Auxiliary Circuit to Reduce Relay Arcing
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Solution Overview
Problem
Existing single-phase AC compressor motors face issues with reliability due to excessive arching and wear of relay contacts, particularly when using current relays, and suffer from inefficient starting performance and torque fluctuations under voltage deviations.
Innovation Solution
The motor incorporates a dual-section auxiliary circuit with a Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC) components, combined with a current relay, to manage current levels and reduce arching, while utilizing split relay coils and overload protection structures to enhance starting performance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a current relay is used instead of a voltage relay, then the relay cost is reduced, but the relay contacts experience excessive arching and wear
Solution Approach 1:
The PTC component performs preliminary action by conducting current immediately upon motor startup, before the relay contacts close. This pre-charges the start capacitor and reduces the potential difference that would otherwise cause arching when the contacts close, thereby protecting the relay contacts from excessive wear while using the cheaper current relay
Solution Approach 2:
The PTC acts as an intermediary element between the power supply and the relay contacts. By being in parallel with the relay contacts and conducting current initially, it mediates the harmful potential difference and discharge effects, allowing the current relay to be used without suffering from contact arching problems
2Speed
If the relay contacts close quickly after motor startup, then the starting response is faster, but arching across the contacts increases
Solution Approach 1:
The PTC performs preliminary action by conducting current and charging the start capacitor before the relay contacts close. This eliminates the potential difference that would cause arching, allowing the relay to close quickly without suffering from contact damage due to discharge arcing
3Power
If the NTC resistance is low to allow high starting current, then starting torque is improved, but current surge increases
Solution Approach 1:
The patent merges the PTC and NTC components in a parallel configuration within the auxiliary circuit. The PTC provides immediate current conduction to establish starting torque, while the NTC limits current surge by presenting high resistance initially and gradually decreasing it as it heats up, thereby combining the benefits of both temperature coefficient components to achieve high starting torque with controlled current surge
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces relay contact arching, improves starting performance, and ensures stable torque delivery by dampening current surges, thereby enhancing motor reliability and efficiency.
Implementation Method 1
a current in the second section is limited by a positive temperature coefficient component (PTC)
Implementation Method 2
a current in the first section is limited by a negative temperature coefficient component (NTC)
Implementation Method 3
a current relay arranged to activate and deactivate current in the first section of the auxiliary circuit based on a current level in the main circuit
Data Source
AI summary
A motor is connectable to a single-phase AC power supply and forms a hermetic compressor. The motor includes a main circuit connected in parallel with the auxiliary circuit, and a winding structure having a main winding arranged as part of the main circuit and an auxiliary winding arranged as part of the auxiliary circuit. The motor includes a rotor arranged to be rotated by a current in the winding structure. To provide a motor durable and cheap to manufacture and to ensure a suitable response to overload situations, the auxiliary circuit has a first section and a second section extending in parallel where an NTC is inserted in the first section. A PTC is inserted in the second section, and a relay is arranged to activate and deactivate current in the first section of the auxiliary circuit based on a current level in the main circuit.