Understanding OLP Connection in Refrigerator Circuits

The question asks about how the Overload Protector (OLP) is connected within the refrigeration circuit of a refrigerator. While the term "refrigeration circuit" usually refers to the path of the refrigerant, in the context of electrical connections like the OLP, it implicitly refers to the electrical circuit controlling the compressor, which is the heart of the refrigeration system.

What is an OLP (Overload Protector)?

An OLP is a crucial safety device used in refrigerator compressors. Its main purpose is to protect the compressor motor from damage caused by excessive current draw or overheating. If the motor pulls too much current (e.g., due to a locked rotor, low voltage, or issues with windings) or gets too hot, the OLP trips, interrupting the power supply and preventing the motor from burning out.

Compressor Motor Windings

A typical single-phase compressor motor in a refrigerator has three terminals corresponding to its electrical windings:

• Common (C): This is the terminal where both the running and starting windings are connected internally. It's the main power input point for the motor.
• Running (R): This winding is used for continuous operation of the motor. It has lower resistance compared to the starting winding.
• Starting (S): This winding provides the necessary initial torque to start the motor. It has higher resistance than the running winding and is typically disconnected from the circuit by a starting relay once the motor reaches operating speed.

Connecting the OLP for Motor Protection

For the OLP to effectively protect the entire motor under all operating conditions (starting and running), it must be placed in a position where it senses the total current flowing into the motor. The current flows from the power source, through any control devices (thermostat, etc.), through the OLP, and then into the motor windings.

Considering the motor structure with a Common terminal where both windings are connected, placing the OLP in series with the Common terminal ensures that all current entering the motor must first pass through the OLP. This allows the OLP to monitor the total current draw, whether it's the higher current during startup (running + starting winding current) or the normal current during steady-state running (running winding current).

If the total current exceeds the OLP's rating due to any fault condition, the OLP will heat up and trip, breaking the electrical connection to the Common terminal and shutting off the compressor. This interrupts the power supply to both the running and starting windings simultaneously, providing comprehensive motor protection.

Analyzing the Options

Let's look at the given options:

• Option 1: Parallel with Running & Starting - Connecting a safety switch in parallel wouldn't effectively interrupt the circuit when tripped. It would simply provide an alternative path for current, which defeats the purpose of an overload protector.
• Option 2: Series with Common winding - As explained above, this is the standard and most effective way to connect an OLP. It is in series with the main power input terminal (Common), ensuring it monitors and can interrupt the total motor current.
• Option 3: Series with Running winding - If the OLP were only in series with the Running winding, it might not adequately sense the high starting current (which flows through both windings before the starting relay opens). Also, some faults related to the starting circuit might not be detected efficiently.
• Option 4: Series with Starting winding - The Starting winding is only active during the brief startup period. Placing the OLP solely in series with this winding would offer no protection once the motor is running normally.

Therefore, connecting the OLP in series with the Common winding is the correct method for effective overload protection of the refrigerator compressor motor.

Conclusion on OLP Connection

The Overload Protector (OLP) is connected in series with the Common winding terminal of the compressor motor in a refrigerator's electrical circuit to monitor the total current and protect the motor from overloads and overheating.

Revision Table: Refrigerator Electrical Components

Additional Information on Refrigerator Motor Protection

Beyond the OLP, refrigerator compressor circuits often include a starting relay and sometimes other protective or starting components like capacitors.

• Starting Relay: Essential for single-phase induction motors. It provides power to the starting winding only during the brief period needed to get the motor up to speed. Once running, the relay opens, disconnecting the starting winding. Common types include current relays and potential relays.
• Capacitors: Some refrigerator motors, particularly larger ones, may use a start capacitor (connected with the starting winding and relay) to provide extra torque during startup. Some might also use a run capacitor (connected in series or parallel with the running winding) for improved efficiency and power factor during continuous operation. These are also protected by the OLP being in series with the common terminal.
• Thermal Protection: While external OLPs are common, some compressors have internal thermal protection embedded within the motor windings, which senses winding temperature directly. However, external OLPs are also widely used.

Understanding the roles and connections of these components is vital for diagnosing and repairing refrigerator electrical systems. The series connection of the OLP with the Common terminal is a fundamental safety principle in these circuits.