The cooling units normally require little maintenance but it is advisable to regularly check their condition in order to ensure trouble-free operation.
***Following chapter for cooling type: Open air
7.8.1 Maintenance instructions for machines with open air cooling
The cooling air is normally circulated by a fan and/or by the rotor. The fan may be mounted on the shaft or driven by a separate motor. A connection to external air pressure is also possible. Depending on the machine design, the circulation may be axially symmetrical or asymmetrical. The cooling air should be as clean as possible, because any dirt, which drifts into the machine, causes contamination and reduces the efficiency of the cooling.
The upper covers of the standard weather protected machines are delivered with or without filters according to the specification. By special order, the upper cover is equipped with a differential pressure switch for monitoring the condition of the filters.
If the winding or cooling air temperature detectors show an abnormal temperature, a check of the cooling system has to be made. The two maintenance issues are to check the condition of air filters and to ensure good air circulation inside the machine. The machine interior should be cleaned and checked during overhauls or if problems arise.
Other possible causes for poor cooling system performance might include elevated ambient temperature or high intake air temperature. In addition, lubrication or bearing malfunction might lead to high bearing temperature.
A seemingly high temperature might also be caused by a problem in the temperature measurement system Chapter 8.3.2 Pt-100 resistance temperature detectors.
7.8.1.1 Cleaning of filters
The filters should be cleaned regularly. The cleaning interval depends on the cleanliness of the air in the surrounding environment. The filters have to be cleaned when the temperature detectors in the winding show abnormal temperature or approach the alarm level.
If a filter differential pressure monitoring system is being used, the filters should be changed immediately after a pressure alarm. The alarm level is such that 50% of the air filter surface is obstructed. The operating personnel should also manually inspect the filters frequently.
Remove the air filters for cleaning. If the surrounding air is sufficiently clean, the filters can be changed during operation. They should regularly be cleaned by vacuuming first from the upstream side, then on the discharge side. Periodically, a thorough wash with clean water is recommended to release any dirt not removed by vacuuming. When heavy grease
concentrations are encountered, the filters should be washed with a detergent solution. This solution should be rinsed thoroughly before returning the filter to service. Be careful to install the air filters in the correct direction, i.e. the arrows on the air filter frame indicate the direction of airflow. Some filters can be installed in either direction. Refer also to the air filter
Maintenance - 95
3BFP 000 050 R0101 REV D
3BFP 000 059 R0101 REV D
***Following chapters for cooling type: Air-to-water
7.8.2 Maintenance instructions for air-to-water heat exchangers
If the temperature detectors show normal operating temperature, and the leakage detectors indicate no leaks, usually no additional supervision is required for the cooling system.
***Following chapters for cooling type: Air-to-air
7.8.3 Maintenance instructions for air-to-air heat exchangers
The cooling unit is installed on the machine. The air tubes in the heat exchanger are normally made of Aluminium.
7.8.3.1 Air circulation
The inner air is normally circulated by a fan and/or by the rotor. The fan may be mounted on the shaft or driven by a separate motor. Depending on the machine design, the circulation may be axially symmetrical or asymmetrical.
The outer air flow is normally created by a fan, mounted on the shaft or driven by a separate motor. Connection to external air pressure is also possible.
Figure 7-11 Cooling air flow (typical asymmetric construction)
The machine can be equipped with temperature detector(s) for monitoring the internal cooling air. If the temperature detectors show normal temperature, no additional maintenance to the supervision inspection is usually required for the cooling system.
If the temperature detectors show abnormal temperature or close to the alarm level in winding or in cooling air, the cooling system has to be checked. If the coolers have to be cleaned, see the instructions below.
96 - Maintenance 3BFP 000 050 R0101 REV E
3BFP 000 059 R0101 REV E
7.8.3.2 Cleaning
Some fouling of the cooling surface and the tube wall will eventually occur. This fouling reduces the cooling capacity. The heat exchanger should therefore be cleaned at regular intervals, to be determined from case to case, depending of the properties of the cooling air. During the initial period of operation, the heat exchanger should be inspected frequently. Blow the heat exchanger clean with compressed air or clean it with a suitable brush. Do not use a steel brush in aluminium tubes as it can damage the tubes; a soft round brass wire brush can be used instead.
7.8.4 Maintenance of external blower motors
The external blower motors are maintenance free units, e.g. the bearings of external blower motors are greased for life. A spare external blower motor is recommended. The maintenance of the blower motor is performed according to the motor's manual.