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Guidelines for contactor inspection and maintenance

Guidelines for contactor inspection and maintenance
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Guidelines for contactor inspection and maintenance - 1

Manual Guidelines for Contactor inspection and maintenance ABB A/AF-line and EH/EK series Contactors

Guidelines for contactor inspection and maintenance - 2

The purpose of this manual is to provide guidance for correct selection and maintenance of contactors in industrial installations to ensure a trouble free operation. This without increasing the overall cost.

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Guidelines for contactor inspection and maintenance - 4

1. Choose correctly • Nature of the duty • Positioning of the contactor • Voltage and frequency • Frequency of operation • Safety regulations • Electrical and mechanical stresses 2. Mounting/installation • The instructions supplied with every contactor should be followed. • In case of drilling in the panel make sure to protect the contactor from falling metal shavings that otherwise could lead to excessive hum or flashovers. 3. Storage and climate Consider the immediate environment (variable temperatures, humidity, storage conditions etc). 4. Connections Make sure the recommended torque...

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Guidelines for contactor inspection and maintenance - 5

The number of mechanical operations has a low impact on the life of the main contacts and their overall electrical life. However general information concerning mechanical wear could be of interest. AC-Hum Pollution of the magnet pole surfaces will create a slight hum coming from the contactor in the closed position. When cleaning, use a soft and dry piece of cloth. Hum can also occur if the pole surfaces are deformed. A louder hum will occur if the shading coil (does not apply to AF) is broken because the magnet will cause the contactor to chatter. If so the complete contactor needs to be...

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Guidelines for contactor inspection and maintenance - 6

A contact is not necessarily damaged or worn out, just because the surface is rough and discolored. The contacts in the figure below may look like bad contacts but the fact is that they are better than a new set of contacts. This is because they are ”electrically seated” and make good contact over a larger surface. Based on this it would be completely wrong to change a contact only by judging from the appearance of the surface. Also it is quite normal that the contacts in the three phases are not evenly worn and because of this all contacts both fixed and movable need to be changed. At the...

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Guidelines for contactor inspection and maintenance - 7

Interpreting levels of electrical contact wear General Depending on the severity of the application contact inspection may be required. A typical severe application would involve frequent making and breaking of high currents, reversing and inching (AC4). Premature service on contactors will increase the overall cost while delayed service could cause costly interruptions or breakdowns. Service at the right time will avoid these kind of problems. The following main utilization categories are the most common ones. AC-1. (General purpose) Non-inductive or slightly inductive loads, resistance...

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Guidelines for contactor inspection and maintenance - 8

AC-3. Cage motors. Starting, switching off running motors. Closing of the main contacts with approximately 6 to 8 times (or higher with today´s high efficiency motors) the rated motor current, depending on motor characteristics and type of load. Breaking is easier, as the current equals the rated motor current, and voltage is reduced to 17 % of the rated voltage. Typical electrical wear comes from the contact making operation. Visual inspection of an AC-3 application normally shows none or very little material from the contact tips thrown out into the arc chutes. 1. Early stage of fixed and...

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Guidelines for contactor inspection and maintenance - 9

AC 4. Cage motors. Starting, plugging, inching. Making and breaking the motor starting current approximately 6 to 8 times (or higher with today´s high efficiency motors) the rated motor current. Voltage is not reduced and equals the rated voltage of the motor. Both making and breaking are contributing to the contact wear. The arc chutes have an important role in extinguishing the arc. Therefore material from the contact tips is in most cases thrown out in the packages. See picture B below. 1. Early stage of fixed and movable contacts, 5000 operations 2. Mid-life stage of fixed (above) and...

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Guidelines for contactor inspection and maintenance - 10

Changing main contacts, arc chutes and coils For information on how to take the contactors apart see the instruction that comes with the contactors or go to www.abb.com/lowvoltage if instruction is not available. Before any dismantling of the contactor: Make dead by, turning off the contactor. Opening the main circuit by turning off the main switch, if any, or by removing the main fuses in all three phases. To protect against making attempt, open also the control circuit. When changing the AF coil with its PCB (printed circuit board) care must be taken to avoid ESD damage.

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Guidelines for contactor inspection and maintenance - 11

Voltage drop during start up of the motor Voltage drop to less than 85 % of nominal voltage for 5 to 10 ms can be enough for the contactor to start opening. Also, other disturbances in the control voltage such as poor relay contacts or too small control transformer/power supply could be responsible for this problem. The result of these voltage problems can be increased contact wear and also lead to welding of main contacts. With the AF technology these problems are avoided. Poor voltage to coil Control voltage less than 85% during pick up may not be enough to safely close the contactor and...

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Guidelines for contactor inspection and maintenance - 12

Restarting with motor idling - Attempting to restart the motor before it has come to a full stop will cause a current peak that theoretically can reach twice the current compared to starting the motor from a standstill. This can result in welded contacts. Star delta (wye-delta) starters Change over time between star and delta - Setting the change over time between star and delta too short will not allow the motor to reach 80-90% of its nominal speed. This will cause the star contactor to break a higher current than expected. If the starter stays in the star position for too long of a...

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Guidelines for contactor inspection and maintenance - 13

PLC control of AF400 and above Make sure the dip switch is in the correct position for proper operation See picture below. Position A when using PLC control and position B for conventional operation (default). High temperature readings When concern of high temperatures on and around the contactor please check the following (also see picture below for max permitted temperatures). • Make sure the connections are properly torqued. • Make sure the cable size is what is recommended in our catalogs. • Make sure the correct coil is selected for the applications. Measurement of the resistance of...

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