LDMUI-001 61320946C voltage transient during load disconnection

To protect the contacts of relay outputs, especially when dealing with inductive loads such as relays, contactors, and motors, it’s essential to mitigate voltage transients that occur when these loads are switched off. Here are some LDMUI-001 61320946C recommended practices:

1. Noise Attenuating Circuits: Equip inductive loads with noise attenuating circuits such as varistors, RC filters (for AC), or diodes (for DC). These components help minimize electromagnetic compatibility (EMC) emissions during switch-off. Installing these components close to the inductive load is crucial to effectively suppress voltage transients.
2. Location of Protective Components: Install protective components (varistors, diodes, RC filters) as close to the inductive load as possible. Avoid installing them at the I/O terminal block to ensure optimal protection.

LDMUI-001 61320946C Below is an illustration depicting the placement of protective components for different types of loads:

• For 24 V DC loads: Use diodes as protective components.
• For 230 V AC loads: Utilize varistors or RC filters as protective components.

LDMUI-001 61320946C Planning the Electrical Installation:

• The chapter emphasizes the importance of checking the insulation of the assembly and ensuring compatibility with IT (ungrounded) and corner-grounded TN systems.
• Only qualified electricians should perform the work described in this chapter to prevent injury or death.
• Before installation, ensure that the drive is disconnected from the input power. If already connected, wait for 5 minutes after disconnecting the input power.

LDMUI-001 61320946C Checking Insulation:

• Avoid voltage tolerance or insulation resistance tests (e.g., hi-pot or megger) on any part of the drive, as it may damage the drive. The drive undergoes insulation testing at the factory, and there are voltage-limiting circuits inside to protect against excessive testing voltage.
• Inspect the insulation of the input power cable according to local regulations before connecting it to the drive.
• When checking the insulation of the motor and motor cable, ensure the motor cable is disconnected from the drive output terminals U2, V2, and W2. Measure the insulation resistance between each phase conductor and the Protective Earth conductor using a measuring voltage of 500 V DC. The insulation resistance of an ABB motor should exceed 100 Mohm, while for other motors, refer to the manufacturer’s instructions. If moisture is suspected inside the motor casing, dry the motor and repeat the measurement.

By following these guidelines, you can effectively protect relay contacts from voltage transients and ensure the safety and reliability of the electrical installation.